Note: Descriptions are shown in the official language in which they were submitted.
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t 5 IN THE UNITED STATES PATENT AND TRADEMARK QFFICE
TITLE: SPREAD SPECTRUM TRANSCEIVER MODULE
UTILIZING MULTIPLE MODE TRANSMISSION
BACKGROUND
1. Technical Field:
The present invention relates generally to communication networks lltili7.ing spread
15 spectrum radio transceivers, and, more specifically, to multi-hop RF networks wherein
participating devices utilize spread spectrum transceivers that are capable of operating in any of
a variety of spread spectrum modes. The spread spectrum modes include, for example, direct
sequence tr~n.~mi.~ion across a spreading bandwidth or channelized across the spreading
bandwidth, frequency hopping tr~n~mis~ion across all or a part of the spreading bandwidth, a
20 hybrid combination of direct sequence tr~n~mi~ions and frequency hopping tr~n~mi~sions, and
tr~n~mi~ions on a portion of the spreading bandwidth. The selection of a spread spectrum
mode of operation depends upon signal conditions and characteristics of members capable of
communication within the RF communication network.
25 2. Description of Related Art:
Communication devices within a wireless local area network employ wireless
communication links to transfer data and comm~n-lc within the local area network. Typical
units within a wireless local area network include stationary wireless access devices, mobile
radio units, mobile image capture units, printing units, and other units operative with the data
30 and comm~n(lc These units often link to a wired local area network through a wireless access
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device to transfer data and commands to devices located on the wired network. The wireless
local area networks typically employ cellular communication techniques to provide the
wireless communication links within the local are network.
One common installation of a wireless local area network serves factory automation
5 functions. Because hard-wiring a local area network within a large, dynamic facility is both
expensive and difficult, the wireless local are network provides traditional network functions as
well as additional functions germane to the wireless attributes of the network. However, due to
difficult tr~nsmi.scion and interference conditions within a factory, establishing and m~int~ining
sufficient wireless communication ties oftentimes proves difficult. .Attenl-~tion of transmitted
10 signals, multi-path fading, ambient noise, and intelrel~llce by adjacent cells often disrupts
communication within the wireless local area network.
Spread spectrum tr~3n.smi.c.cions are often used in attempts to overcome communication
problems. With spread spectrum tran.cmis.cions, the bandwidth over which information is
broadcast is deliberately made wide relative to the information bandwidth of the source
15 information. Spread spectrum tr~ncmis.cion techniques include direct sequence tr~n.cmission,
frequency hopping trzln.cmis.cion, a combination of direct sequence tr~n.cmi.c.cion and frequency
hopping trzln.smission, and may include other techniques that deliberately transmit over a wide
spectrum.
Direct sequence spread spectrum transmitters typically spread by first moc~ tin,~ a
20 data signal with a pseudo random chipping sequence at a multiple of the source data clocking
rate. Once constructed, the composite modulation is coupled to a carrier via modulation
techniques and then transmitted. Phase modulation is typically employed, but frequency
modulation or other types of modulation may also be used. Circuitry in a receiving units
receives the signal, decodes the signal at the multiple of the source data clocking rate using a
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particular chipping sequence, and produces received data. In a typical direct sequence system,
the pseudo random chipping sequence applied by the receiving unit corresponds to all, or
respective portions, of the transmitted signal. In this fashion, the receiving unit receives only
intended data and avoids receiving data from adjacent cells operating on the sarne frequency.
5 Direct sequence spread spectrum modes also provide significant noise rejection characteristics
since each component of the source data is essentially transmitted multiple times. The received
signal is therefore a composite that may be averaged or weighted to avoid receiving h,l~lol)er
data or falsing based upon noise.
A frequency hopping system commonly uses conventional narrowband modulation but
10 varies the modulation frequency over time in accordance with a known pattern or algorithm,
effectively moving the modulated signal over the intencled spreading bandwidth. The spread
spectrum signal is only discernible to a receiver that has prior knowledge of the spreading
function employed and which has obtained synchronization with the spreading operation at the
transmitter. By spreading tr~n.~mi~ions over the spreading bandwidth, particular portions of
15 the spreading bandwidth within which tr~n~mi~ion is difficult may be substantially avoided.
In the United States and many other countries, spread spectrum communications is used
commercially within designated Industrial, Scientific and Medical (ISM) bands. These bands
are structured as multi-use bands cont~ining non-communications equipment such as industrial
and commercial microwave ovens as well as low power consumer grade transmitters, vehicle
20 location and telemetry systems and other spread spectrum devices of differing characteristics.
Operation in ISM bands is unlicensed and uncoor~lin~ted, so equipment O~ dLillg in these
bands must be designed to operate successfully without knowledge of the types of devices that
may be used in close proximity. The spread spectrum system design must also take into
consideration the occupants of the spectrum adjacent to the ISM bands which may be both
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potential sources of interference to, and susceptible to interference from, various types of
spread spectrum products.
Various forms of modulation across the spreading band may be utilized in commercial
spread spectrum packet data communication systems. Full band direct sequence systems
S occupy the entire width of an ISM band. The spreading ratio, the ratio of the bandwidth of the
spread spectrum modulated signal to the information bandwidth of the source modulation,
determines the process gain of the system. Regulations within the United States m~n-lAt.o a
minimllm process gain of 10 dB, which is determined from ten times the logarithm of the
spreading ratio. Process gain is a measure of the ability of a spread spectrum system to resist
10 interference. The larger the spreading ratio, the more resistant the system is to interference
within the receiver bandwidth. Wide bandwidth modulation is reasonably resistant to low or
moderate levels of interference, but even systems with relatively high process gains experience
difficulties when subject to strong interference.
When system throughout requirements dictate high data rates, the minimum process
15 gain requirements in the regulations necessitate using wide bandwidth trAn.cmi.ccions. For
example, a well-known system NCR Wavelan uses Quadrature PSK modulation at lmillion
symbols per second to achieve 2 megabits per second (MBPS) data rates with a source
information bandwidth available in the US ISM band at 902 MHz band. In practice,
implementation constraints dictate that this system uses the full 26 MHz band. Systems
20 operating at other data rates, including the original Norand system, utilize the full bandwidth at
lower source data rates, e.g., 200 kilobits per second (KBPS). Utilization of a wider spreading
bandwidth in this case provides greater rejection of multipath fading typical of the indoor RF
signal propagation environment.
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When it is anticipated the direct sequence systems may be used in environments with
strong in-band interference, a design choice is to employ channelization to reject interference.
~ In the case of channelized direct sequence (DS) modulation, the spreading bandwidth is
reduced to a fraction of the total available bandwidth, and a frequency-agile frequency
5 generation systems is employed. By selecting the carrier frequency of operation,
communications can be established in a portion of the band where interference is not present.
This technique requires the use of selective filters in the receiver intermediate frequency (IF)
section to provide the necessary interference rejection. These channelized DS systems utilize
interference avoidance rather than relying on process gain to reject interference.
10Utilization of frequency hopping spread spectrum systems is appropriate in
environments where interference within the band of operation is not confined to particular
portions of the band, but may periodically arise in various parts of the entire band. Frequently
hopping is also useful as a multiple access technique. Use of multiple hopping sequences
concurrently within a given location allows many simultaneous communication sessions to be
15 supported. Occasionally, devices operating on different hopping sequences will
simultaneously occupy the same channel within the band for short periods of time. For
moderate numbers of simultaneous hopping sequences, this occurs infrequently.
Frequency hopping also provides similar multipath rejection capabilities to wideband
direct sequence modulation. If a particular channel of operation is in a fade temporarily
20 preventing communication, a jump to a frequency sufficiently removed from the faded
frequency will often allow communications to resume.
Frequency hopping systems require more protocol overhead to aid in establishing and
m~int~ining synchronization between units sharing a given hopping sequence. Additionally,
the initial acquisition of the hopping sequence may require that an unsynchronized device scan
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the band for a period equivalent to may hop times. The overhead for direct sequence systems
is lower, with several bit-times usually allocated to receiver acquisition at the beginning of
each tr~n~mi~sion.
Spread spectrum communications may not be appropriate for some applications. For
5 example, short hop communications such as communications between a portable hand-held
terminal and a peripheral device such as a scanner or printer over a short distance is a very cost
sensitive application. Spread spectrum operation requires more circuit complexity and power
consumption than is tolerable for this application. Simpler FM or AM techniques such as ON-
OFF-Keying (OOK) may be desirable.
Conventionally, the particular spread spectrum modulation technique is chosen
according to the particular applications in which the data transceiver is to be utilized. For
example, in a small warehouse having few RF barriers, minim~l interference from cellular and
wireless phones, and minim~l amounts of cornmunication traffic, radio transceivers used
therein might only employ direct sequence spread spectrum tr~n~mi.~sion techniques. Thus,
15 conventionally, such transceivers would be specifically designed, constructed and installed.
However, after inct~ tion, if communication traffic or local noise increases, the
communication might fail to function as required. Likewise, after installation, if RF barriers
are installed or if the network is moved to an urban environment with a great deal of noise from
neighboring in.ct~ tions, cellular and mobile phones, etc., the network may fail to meet the
20 needs of the customer.
Similarly, a design might be based on a customer's needs for a small store in a
downtown urban area. Because of the greater likelihood of a great amount of radio frequency
traffic in the vicinity, the customer requires a radio which is free from interference from nearby
radio tr~n.~micsions with little concern for operating range. Consequently, a different specific
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type of radio would be designed to meet the needs of the corporation based upon the operating
conditions in which the radio is to be used, for example using frequency hopping modulation.
In the exemplary installations mentioned above, each of the radios would be optimized
to meet the needs of the customer. However, a customer's needs continll~lly change, and, if
5 the particular application or environment were to change justifying a different spread spectrum
modulation technique, the customer is either forced to change all of their radio transceivers or
live with the under-performance they currently receive.
Moreover, in a typical network in~t~ tion, a client may have diverse operational
requirements. For example, the particular applications of the radio unit may change several
10 times within the same day. The site may also have areas which are relatively noise and barrier
free and those which encounter heavy noise and barriers. Some areas may have high traffic
volume, while others experience only occasional traffic. In such networks, a single radio
transceiver design can never provide optimal performance in all areas. Sacrifices are made in
the design characteristics of the transceivers in an attempt to provide best performance overall.
Similarly, in mobile contexts, a worker may require mobile communications to a
vehicle based information system or forwarding to a central communication facility through a
vehicle based radio WAN transceiver. The characteristics of the communications medium for
this class of operation vary greatly. Interference will vary from location to location.
Additionally, it is necessary to allow operation if the worker moves away from the vehicle or
20 inside a building structure. Because each wireless local area network may have been ~lçsi~n~cl
for a particular set of criteria with particular spread spectrum operational abilities, mobile units
may be non-functional within particular wireless local area networks.
Thus, there is a need in the art for a communication network that operates dynamically
to optimize communication l~tili7in~ various spread spectrum tr~n~mi~.~ion techniques,
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considering the characteristics of RF noise, neighboring interference, RF barriers, participating
transceiver unit capabilities and applications to be performed in such dynamic optimization.
It is another object of the present invention to provide a spread spectrum RF transceiver
module, for use in wireless network devices, which utilizes multiple spread spectrum
5 modulation techniques providing multiple configurable modes of data tr~n.~mi~sion, whereby
modes may be selected to attain optimal tr~n~mission performance.
A further object of the present invention is to provide an RF data transceiver module
which combines frequency hopping and direct sequence tr~nsmi.c~ion techniques within a
single design.
It is an object of the present invention to provide a spread spectrum R~ transceiver
module which utilizes common media access protocols and interfaces for multiple nominal
carrier frequencies and modulation parameters.
It is a further object of the present invention to provide a spread spectrum RF
transceiver utili7ing 900 MHz tr~n~mi.~ion and having a standard interface with cornmon 2.4
15 GHz tr~n~micsion.
It is a further object of the invention to provide a spread spectrum RF transceiver which
may be utilized in several different types of multi-layered data communications networks.
Another object of the present invention is to produce a wireless local area network and
packet wireless data communication system that is flexible to operate reliably in varied and
20 unpredictable RF propagation and interference environments.
A further object of the present invention is to provide a wireless RF transceiver module
capable of utili7in~ a variety of operational modes thereby allowing large business operation to
purchase a single product meeting a multiple usage needs ma~cimi7ing operational flexibility
and minimi7in~ sparing and service concerns.
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It is another object of the present invention to provide a modular wireless LAN modem
capable of supporting multiple modes of operation under a single media access protocol with
a standardized interface to a hand-held portable data terminal such that the wireless LAN
modem may dynamically change modes of operation transparently to the host device, not
5 requiring that the host device be aware of changes in the modes of operation, or that operation
of higher protocol layers be impacted.
Yet another object of the present invention is to produce a modular wireless LAN
modem that may be utilized for both in-premise and worker to vehicle application. and for
short range communications to peripheral devices.
These and other objects of the invention will be ~al~-lt from e~min~ion of the
drawings and rem~incler of the specification which follows.
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SUMMARY OF THE INVENTION
The system and radio of the present invention to overcome the limitations of the prior
devices as well as other limitations therefore may operate in any of a plurality of spread
spectrum modes. A selected spread spectrum mode, or set of spread spectrum modes, is based
5 upon system characteristics as well as tr~n~mi~ion characteristics within an operating
environment.
One particular operating environment relates to multi-hop wireless networks that are
subject to in-band interference and multi-path fading. However, in these systems, members
(hereinafter '~transceiver devices") of the network may have different operating capabilities.
10 Therefore, the system and radio of the present invention provide a mech~ni~m for selecting
spread spectrum modes of operation to satisfy network member limitations, data tr~n~mi~.~ion
throughput requirements, neighboring system non-interference requirements, as well as noise
tolerance requirements.
By providing a dynamic mech~ni~m for selecting spread spectrum modes of operation,
15 the present invention provides many import objects and advantages that will become ~ nt
with reference to the entire specification and drawings. In particular, in one embodiment, a
communication network for collecting and communicating data is disclosed. The network
comprises a wireless access device and at least one mobile terminal. The wireless access
device comprises a control circuit and a first RF transceiver that selectively operates in one of a
20 plurality of spread spectrum modes. The at least one mobile terminal comprises a second RF
transceiver that operates in at least one of a plurality of spread spectrum modes. The control
circuit responds to tr~n~mic~ions received from the first RF transceiver to evaluate
communication performance and dynamically selects one of the plurality of spread spectrum
,
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modes of the first RF transceiver. Such selection also takes into consideration the at least one
of the plurality of spread spectrum modes of the second RF transceiver.
Further, the plurality of spread spectrum modes of the first RF transceiver may
comprise direct sequence tr~ncmi~.~ion, frequency hopping, channelized direct sequence and/or
5 hybrid frequency hopping(direct sequence) modes. The control circuitry may evaluate
communication performance through reference to received signal strength indications,
tr~nsmi~sion success rate and neighboring cell operating characteristics.
Other aspects may be found in a communication system for collecting and
communicating data using wireless data signal tr~n~mi~ion. Therein a wireless access device
10 capable of communicating with a plurality of radios comprises a radio capable of operating in a
plurality of spread spectrum modes. The wireless access device also comprises a spread
spectrum mode controller responsive to tr~n.~mi~ions and data received for evaluating the data
communication system and for controlling the radio to selectively operate in a spread spectrum
mode among a plurality of spread spectrum modes.
15The wireless access device may further comprise circuitry for evaluating the plurality of
spread spectrum modes to select a spread spectrum mode of operation. Such selection may
take involve the identification of a common spread spectrum mode.
Yet other aspects can be found in a data communication system having spread spectrum
capability for collecting and communicating data using wireless data signal tr~n~mi.~.cion.
20 Therein, an RF transceiver comprises an modulator having a spreader, a demodulator having a
~ despreader, a controllable oscillator attached to the modulator and demodulator, and control
cilcuiLly that both selectively enables the spreader and despreader and selectively controls the
controllable oscillator to cause operation in one of a plurality of modes of spread spectrum
operation.
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The data communication system may further comprising a host controller that directs
the control circuitry in the selection of the one of the plurality of modes of spread spectrum
operation. The host controller may comprise wireless access device control circuitry. In
addition, the control circuitry may wirelessly receive instruction regarding selection of the one
5 of the plurality of modes of spread spectrum operation. Many other aspects of the present
invention will be appreciated with full reference to the specification, drawings and claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. lA is a perspective view of a wireless communication network built in accordance
with the present invention which incorporates dynamically adapting spread spectrum
transceivers and supporting communication protocols;
FIG. lB is a flow diagram illustrating the operation of a wireless access device in
accordance with present invention whereby multiple wireless devices having potentially
different transceiver capabilities are supported;
FIG.lC is a block diagram illustrating a radio transceiver built in accordance with the
present invention to provide multiple modes of operation;
FIG. lD is a block diagram illustrating the operation of the wireless access device
having the multi-mode transceiver of FIG.lC installed therein.
FIG. 2A is a front elevation view of one embodiment of a hand-held portable dataterrnin~l having a transceiver module built in accordance with the present invention;
FIG. 2B is a side elevation view of the hand-held portable data terminal of FIG. 2A
15 showing a module of the present invention;
FIG. 3 is a side evaluation view of the hand-held portable data terminal of FIG. 2A
showing a module of the present invention;
FIG. 4 is a side elevation view of the hand -held portable data terminal of FIG. 2A
showing a removably insertible module of the present invention;
FIGS. 4A, 4B and 4C illustrate in detail the cooperation between a radio module and
the hand-held portable data terminal shown in FIG.3.
FIG. 5 is a perspective view of another hand-held portable data terminal which may
incorporate the present invention,
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FIG. 6 is a side elevation view of the data terminal of FIG.5 showing an extendibly
retractable rotating carriage housing for receiving a module incorporating the present
mventlon;
FIG.7is an exploded view of a radio module incorporating the present invention;
FIG. 8 is an exploded view of a radio module of the present invention further
cont~inlng a scanner;
FIG.9is an exploded view of a radio module of the present invention contained within
a PCMCIA type housing;
FIG. 10 is a functional block diagram of the architecture of the radio modules of the
present invention;
FIG. 11 is a conceptual block diagram of the operation of the transmitter of FIG. 10
when operating in a direct sequence spread spectrum tr~n.cmiccion mode;
FIG. 12 shows a conceptual diagram of the operation of the receiver utilized in
conjunction with the transmitter of FIG.ll;
FIG.13is a block diagram of an embodiment of a receiver of the present invention;
FIG. 14A is a diagram of the pseudo-random number generator shown in FIG.10;
FIG.I 4B is a schematic block diagram illustrating the interaction of the pseudo-random
number generator of FIG. 14Awith traverse filtering and formatter circuitry of FIG.10;
FIG. 15 is a block diagram illustrating the frequency generator circuitry as shown in
FIG.10;
FIG.16is a block diagram illustrating the transmitter circuitry as shown in FIG.10;
FIG. 17 illustrates the circuitry for selecting between the modes of modulation of the
present invention.
FIG. 18 is a block diagram of the MAC circuitry as shown in FIG.10;
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FIG.19is a block diagram illustrating the host interface circuitry as shown in FIG.10
for the radio module of FIG.7 and for the radio/scanner module of FIG.8; and
FIG.20is a block diagram illustrating the host interface circuitry as shown in FIG.10
for the radio module of FIG.9.
FIG. 21 is a diagram illustrating an ~lt~rn~te configuration of portable data tt?rmins
according to the present invention.
FIG. 22A illustrates one embodiment of the data collection termin~l of the present
invention, having both wired and wireless com~nunication capability.
FIG.22B is a ~ gr~m illustrating a specific implçment~tion of the portable t~rmin~l of
FIG.22A a single PCMCIA card contains not only a multi-mode wireless transceiver, but also a
wired modem transceiver.
FIG. 23 is a rli~rAm illustrating the use of portable termin~l~ according to the present
invention lltili7ing both wired and wireless communication in a network configuration.
FIG. 24 is a diagram illustrating the use of portable data t~rmin~l~ according to the
present invention lltili7ing both wired and wireless communication to access separate
subnetworks in an overall communication network.
FIG. 25a is a block diagram illll~1r~ting an embodiment of the present invention wherein a
wireless access device uses a dedicated control / busy channel to manage a plurality of modes of
communication with roaming termin~l~
FIG. 25b is a drawing illustrating advantageous operation of the wireless access device of
FIG. 25a when two roaming terminals encounter hidden termin~l conditions.
FIG. 25c is a flow diagram illustrating the functionality of the wireless access device of
FIGS. 25a-b in m~n~ging communication using a control / busy channel.
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FIG. 26a is a block diagram illustrating an alternate embodiment of that shown in FIG.
25a wherein a wireless access device uses a separate tr~n~mitt~?r for the dedicated control / busy
channel and a roaming tl~rmin~l uses either a shared multimode transmitter or a multimode
transmitter and a separate busy / control channel receiver.
FIG. 26b is a drawing illustrating advantageous operation of the wireless access device of
FIG. 26a when the two roaming terminals encounter hidden terminal conditions.
FIG. 26c is a flow diagrarn illustrating the functionality of the wireless access device of
FIGS. 26a-b in m~n~ging communication using a control / busy channel.
FIG. 27 is a block diagram illustrating a further embodiment of the present invention
wherein channel selection and operating parameters are delivered by a wireless access device on a
dedicated busy / control channel with or without multimode transceiver capabilities.
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DETAILED DESCRIPTION QF THE INVENTION
FIG. lA illustrates a communication network 1 incorporating the teachings of the
present invention. The system comprises wireless access devices 2A, 2B and 2C, portable
transceiver units 4A, 4B and 4C, a wireless code reader S and a peripheral device 6. The
5 wireless access devices 2A and 2B communicate directly on a wired network 3 to each other
and to other wired network devices (not shown). The wireless access device 2C comrnunicates
with the wired network 3 and the wireless access device 2A via wireless tr~n~mi~ions through
the wireless access device 2B.
The wireless access 2A-C may comprise wireless access points or wireless access
10 servers to provide an interface among the portable transceiver units 4A-C, the code reader 5,
the peripheral device 6 and devices on the wired network. Each of these wireless access
devices 2A-C has associated with it a range or cell of communication. For example, the
portable transceiver units 4A-C may wander in and out of range of the wireless access device
2A. Similarly, they may wander in and out of range of the wireless access devices 2B-C, i.e.,
15 they may wander from cell to cell. Each access device 2A-C, and many more as may prove
necessary, are located to provide coverage of a customer's premises. Cell areas typically
overlap somewhat to support ubiquitous coverage.
Because cells typically overlap slightly with one another, at any time, a hand-held radio
unit may communicate with at least two wireless access devices. To avoid conflicts with
20 tr~n~mi~ions in such overlap areas, it is desirable to configure neighboring cells operate with
different spreading codes, different hopping sequences or different modes, for example.
However, when the portable transceiver unit 4B for example passes from one cell to another, it
cannot communicate with a neighboring wireless access device without ch~ngin~ its operating
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characteristics. Thus, the present invention provides several techniques for accommodating
devices wishing to communicate in a new cell.
Moreover, the wireless access devices 2A-C, peripheral device 6 and code reader 5 may
be capable of only some modes of wireless operation. Thus, the present invention provides a
5 mechanism for each of the wireless access devices 2A-C to dynamically attempt to select a
common mode of appropriation for each participating device within its cell. Moreover, if a
given mode of operation proves ~ s~ticf~tory, a wireless access device may dynamically
switch modes to attempt to achieve superior performance.
In particular, data throughput concerns and requirements, ambient noise, power
10 consumption of portable units, previously recorded success rates, received signal strength
indications, neighboring cell operating modes and success rates, and mode capabilities of
participating devices are all considered in det~rmining the mode in which to operate. Each
wireless access device engages in such consideration when initially establishing
communication in its cell, when attaching or detaching a participating device and as channel
15 conditions are evaluated. In other embo-liment~, less than all of such considerations need be
made. For example, where all transceivers are known to operate in all available modes,
consideration of this factor is not necessary. Similarly, if only one cell exists or if problems in
overlap regions prove minim~l, consideration of neighboring cell operation need not be
engaged. Likewise, received signal strength alone may be used as a mode performance
20 indication.
Using lower power trz~n~mi.~cions, a benefit to battery powered portable transceiver
units, requires the use of more wireless access devices to cover a premises. Lower power
tr~n~mi.~.~ions might also or alternately require a mode having a wider spreading bandwidth or
slower data transfer rate to overcome the lower received signal strength. In other cells that
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have minim~l battery power concerns and little or no noise, a spread spectrum mode may be
chosen that provides higher data tr~n~mic~ion rates. In yet other cells experiencing significant
background noise, a direct sequence spreading mode may be employed that provides greater
noise tolerance.
In addition to ch~ngin~ modes, the wireless access devices 2A-.C also support changes
to various mode parameters such as data segment sizes, chipping rates, spreading code lengths,
etc. By supporting dynamic changes in operating modes and mode parameters, the
communication network 1 attempts to accommodate any transceiving device that enters any
cell. This flexibility allows for expansion without replacing existing equipment. An older
radio transceiver may be able to participate with newer transceivers that may support newer
modes of operation. The network 1 would attempt to accommodate such communication in a
common, older mode of operation.
RF signals are inherently subject to what is termed "multipath fading". A signalreceived by a receiver is a composite of all signals that have reached that receiver by taking all
available paths from the transmitter. The received signal is therefore often referred to as a
"composite signal" which has a power envelope equal to the vector sum of the individual
components of the multipath signals received. If the signals making up the composite signal
are of amplitudes that add ~'out of phase" the desired data signal decreases in amplitude. If
the signal amplitudes are approximately equal, an effective null (no detectable signal at the
receiver) results. This condition is termed "fading".
Normally changes in the propagation environment occur relatively slowly, i.e., over
periods of time ranging from several tenths (1/lO's) of seconds to several seconds. However,
in a mobile RF environment, receivers (or the corresponding transmitters) often travel over
some distance in the course of receiving a message. Because the signal energy at each receiver
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is determined by the paths that the signal components take to reach that receiver, the relative
motion between the receiver and the transmitter causes the receiver to experience rapid
fluctuations in signal energy. Such rapid fluctuations can result in the loss of data if the
amplitude of the received signal falls below the sensitivity of the receiver.
Over small distances, the signal components that determine the composite signal are
well correlated, i.e., there is a small probability that a significant change in the signal power
envelope will occur over the distance. If a tr~n~mi~ion of a data packet can be initiated and
completed before the relative movement between the receiver and transmitter exceeds the
"small distance" data loss to fading is unlikely to occur. The maximum "small distance"
wherein a high degree of correlation exists is referred to hereafter as the "correlation distance".
As expressed in wavelengths of the carrier frequency, the correlation distance is on half
(1/2) of the wavelength, while a more conservative value is one quarter (1/4) of the
wavelength. Taking this correlation distance into consideration, the size of the data packet for
segmentation purposes can be calculated. For example, at 915 MHz (a l~lcrcllcd RF
tr:~n~mi~sion frequency), a quarter wavelength is about 8.2 centimeters. A mobile radio
moving a ten (10) miles per hour, or 447 centimeters per second, travels the quarter
wavelength in about 18.3 milliseconds. In such an environment, as long as the segment packet
size remains well under 18.3 milliseconds, significant signal fluctuations during the duration of
a packet tr~n~mi.~ion is unlikely. In such an pl~er~lled embodiment, five (5) milli~econd data
packet segments are chosen which provides a quasi-static multipath communicationenvironment.
The faster the relative movement between a transmitter and a receiver the greater the
effect of fading. Similarly, if the relative movement is slower, fading is less pronounced. In
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many cornrnunication environments, the degree of fading effects varies drarnatically both from
time to time and from installation to installation.
One example of a receiver making such a measurement of fading can be found in the
abandoned patent application of Ronald L. Mahany, U.S. Ser. No. 07/485.313, filed Feb. 26,
1990, which is incorporated herein by reference. Specifically. in that reference, a received
signal strength indicator (RSSI) circuit is found in the receiver. The RSSI circuit sample the
signal strength of a tr~n.smi~.cion. If the signal strength samples are evaluated in sequence and
the trend analyzed, the degree of fading can be measured. If the signal strength samples
decrease in value, it is likely that fading is present in the network.
A transceiver using direct-sequence spread spectrum tr~n.~mi~ion uses a spreading-
code of a higher frequency than that of the data rate to encode the data to be sent. This higher
frequency is achieved by increasing the chip clock rate (wherein each chip constitutes an
element of the spreading-code). Using the same spreading code, the receiver decodes the
received signal while ignoring minor faults which occurred in tr~n~mi.~.~ion, providing noise
immunity and multi-path signal rejection. The frequency and length of the spreading-code can
be varied to offer more or less multi-path signal rejection or noise immunity. Although it may
result in improved communication, increasing the frequency or length of the spreading-code
requires additional overhead which may not be justifiable unless necessary.
Frequency-hopping is the switching of tr~n~mission frequencies according to a
sequence that is fixed or pseudo-random and that is available to both the transmitter and
receiver. Adaptation to the communication environment via an exchange in frequency-hopping
operating parameters is possible, for example, via selective control of the hopping rate or
through the use of coding or mterleaving. The greater the degree of frequency selectivity of the
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fading envelope (i.e., when fading is significant only over a portion of the spectrum of hopping
frequencies), the greater the benefit of such adaptation.
Particularly, a pararneter indicating the hopping rate can be varied to minimi7~ the
probability that the channel characteristics will detrimentally change during the course of a
5 communication exchange. To vary the hopping rate is to vary the length of a hopping frame.
Although multiple data (or message) exchanges per hopping frame is contemplated, the
preferred hopping frame consists of a single exchange of data, For example, in a polling
environment, the hopping frame might consist of: 1) a base station transmitting a polling
packet to a roaming terminal; 2) the roaming terminal transmitting data in response; and 3) the
10 base station responding in turn by transmitting an acknowledge packet. Each hopping frame
exchange occurs at a different pseudo-randomly chosen frequency.
For optimization, the hop frame length is adjusted to be as long as possible, while
rem~ining shorter than the coherence time of the channel by some safety margin. Although
such adjustment does not elimin~te the effects of fading, it increases the probability that the
15 characteristics of the channel will remain consistent during each hopping frame. Thus, in the
preferred embodiment, if the polling packet tr~nsmi.ssion is successfully received, the
probability of successful receipt of the data (or message) and acknowledge is high.
Another parameter for ch~nging frequency-hopping performance is that of coding.
Coding on the channel for error correction purposes can be selectively used whenever the
20 probability of data or message loss due to fading is high. In particular, coding methods which
provide burst error correction, e.g., Reed-Solomon coding, can be applied if the hop length is
likely to exceed the coherence time of the channel. Such coding methods allow some portion
of the data to be lost and reconstructed at the expense of a 30-50% reduction in throughput.
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The operating parameter for coding indicates whether coding should be used and, if so, the
type of coding to be used.
An operating parameter indicating whether interleaving should be used also help to
optimize the communication channel. Interleaving involves breaking down the data into
S segments which are re~ nc~ntly transmitted in different hopping frames. For example" in a
three segment exchange, the first and second segments are sequentially combined and sent
during a first hopping frame. In a subsequent hopping frame, the second and third segments
are sequentially combined and transmitted in a third hopping frame. The receiving transceiver
compares each segment received with the redlln-l~ntly received segment to verify that the
10 tr~n.~mi~ion was s~lçce~ful. I errors are detected, further tr~n.~mi.~sions must be made until
verification is achieved. Once achieved, the transceiver reconstructs the data from the
segments.
Other methods of interleaving are also contemplated. For example, a simpler form of
interleaving would be to sequentially send the data twice without segm~nt~tion on two
15 different frequencies (i.e., on two successive hops).
As can be appreciated, interleaving provides for a re~llln~ ncy check but at the expense
of data or message throughput. The interleaving parameter determines whether interleaving is
to be used and, if so, the specific method of interleaving.
In addition, any combination of the above frequency-hopping parameters might interact
20 to define an overall operating configuration, different from what might be expected from the
sum of the individual operating parameters. For example, selecting interleaving and coding,
through their respective parameters, might result in a more complex combination scheme
which combines segmentation and error correction in some alternate fashion.
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In the United States. data communication equipment operating in the ultra-high
frequency (UHF) range under conditions of frequency modulation (FM) is subject to the
following limitations.
1) The occupied band width is sixteen kilohertz maximum with five kilohertz maximum
frequency deviation.
2) The channel spacing is 25 kilohertz. This requires the use of highly selected filtering in
the receiver to reduce the potential for interference from nearby radio equipment
operating on adjacent channels.
3) The maximum output power is generally in the range of ten to three hundred watts. For
localized operation is a fixed location, however, transmitter power output may be
limited to two watts, maximum, and limitations may be placed on antenna height as
well. These restrictions are intended to limit system range so as to allow efficient re-
use of frequencies.
For non-return to zero (NRZ) data modulation, the highest modulating frequency is
equal to one half the data rate in a baud. Maximum deviation of five kilohertz may be utilized
for a highest modulation frequency which is less than three kilohertz, but lower deviations are
generally required for higher modulation frequencies. Thus, at a rate of ten thousand baud, and
an occupied bandwidth of sixteen kilohertz, the peak FM deviation which can be utilized for
NRZ data may be three kilohertz or less.
Considerations of cost versus performance tradeoffs are the major reason for theselection of the frequency modulation approach used in the system. The approach utilizes
shaped non-return-to-zero (NRZ) data for bandwidth efficiency and non-coherent
demodulation using a limited-discriminator detector for reasonable performance at weak RF
signal levels. However, the channel bandwidth constraints limit the maximum data "high" data
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rate that can be utilized for transmitting NRZ coded data. Significant improvements in system
throughput potential can be realized within the allotted bandwidth by extending the concept of
adaptively selecting data rate to include switching between source encoding methods. The
preferred approach is to continue to use NRZ coding for the lower system data rate and
5 substitute partial response (PR) encoding for the higher rate. The throughput improvements of
NRZ/PR scheme over an HRZ/NRZ implementation are obtained at the expense of additional
complexity in the baseband processing circuitry. An example of a transceiver using such an
approach can be found in the previously incorporated patent application of Ronald L. Mahany,
U.S. Ser. No. 07/485,313, filed Feb. 26, 1990.
Partial response encoding methods are line coding techniques which allow a potential
doubling of the data rate over NRZ encoding using the same baseband bandwidth. Examples
of PR encoding methods include duobinary and modified duobinary encoding. Bandwidth
efficiency is improved by converting binary data into three level, or pseudo-ternary signals.
Because the receiver decision circuitry must distinguish between three instead of two levels,
there is a slgnal to noise (range) penalty for using PR encoding. In an adaptive baud rate
switching system, the effects of this degradation are elimin~te~l by a~lo~liate selection of the
baud rate switching threshold.
Since PR encoding offers a doubling of the data rate of NRZ encoded data in the same
bandwidth, one possible implementation of a NRZ/PR baud rate switching system would be a
4800/9600 bit/sec system in which the low-pass filter bandwidth is not switched. This might
~ be desirable for example if complex low-pass filters constructed of discrete components had to
be used. Use of a single filter could reduce circuit costs and printed circuit board area
requirements. This approach might also be desirable if the channel bandwidth were reduced
below what is currently available.
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The implementation with bandwidth available is to use PR encoding to increase the
high data rate well beyond the 9600 bit/sec implementation previously described. An approach
using 4800 bit/sec NRZ encoded data for the low rate thereby providing high reliability and
backward compatibility with existing products, and 16K bit/sec PR encoded tr7ln.cmiccion for
5 the high rate may be utilized. The PR encoding techniques is a hybrid form similar to
duobinary and several of its variants which has been devised to aid.decoding, minimi~ the
increase in hardware complexity, and provide similar performance characteristics to that of the
previously described 4800/9600 bit/sec implementation. While PR encoding couid potentially
provide a high data rate of up to 20K bit/sec in the available channel bandwidth, 16K bit/sec is
10 preferable because of the practical constraints imposed by oscillator temperature stability and
the distortion characteristics of IF bandpass filters.
All of the above referenced parameters must be m~int~ined in local memory at both the
transmitter and the receiver so that successful communication can occur. To change the
communication environment by ch~n~ing an operating parameter requires both
15 synchronization between the transceivers and a method for recovering in case synchronization
fails.
In one embodiment, if a transceiver receiving a tr~ncmi.ccion (hereinafter referred to as
the "(icstin~tion~) determines that an operating parameter needs to be changed, it must transmit
a request for change to the transceiver sending the tr~ncmi.ccion (hereinafter the "source"). If
20 received, the source may send an first acknowledge to the destination based on the current
operating parameter. Thereafter, the source modifies its currently stored operating pararneter,
stores the modification, and awaits a tr~ncmi.ccion from the destination based on the newly
stored operating parameter. The source may also send a "no acknowledge" message, rejecting
the requested modification.
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If the first acknowledge message is received, the destination modifies its currently
stored operating parameter, stores the modification, sends a verification message based on the
newly stored operating parameter, and awaits a second acknowledge message from the source.
If the destination does not receive the first acknowledge is not received~ the destination
5 modifies the currently stored parameter, stores the modification as the new operating
parameter, and, based on the new parameter, transmits a request for acknowledge. If the source
has already made the operating parameter modification (i.e., the destination did not properly
receive the first acknowledge message), the destination receives the request based on the new
parameters and response with a second acknowledge. After the-second acknowledge is
10 received, communication between the source and destination based on the newly stored
operating parameter begins.
If the destination does not receive either the first or the second acknowledge messages
from the source after repeated requests, the destination replaces the current operating parameter
with a factory preset system-default (which is also loaded upon power-up). Thereafter, using
15 the system-default, the dçstin~tion transmits repeated requests for acknowledge until receiving
a response from the source. The system-default parameters preferably define the most robust
configuration for communication.
If after a time-out period the second request for acknowledge based on the newly stored
operating parameters is not received, the source restores the previously modified operating
20 parameters and listens for a request for acknowledge. If after a further time-out period a
request for acknowledge is not received, the source replaces the current operating parameter
with the factory preset system-default (which is the same as that stored in the destin~tion, and
which is also loaded upon power-up). Thereafter, using the common system-default, the
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source listens for an acknowledge request from the destination. Once received,
communication is re-established.
Other synchronization and recovery methods are also contemplated. For example,
instead of acknowledge requests origin~ting solely from the destination, the source might also
participate in such requests. Similarly~ although a polling protocol is used to carry out the
communication exchanges described above, carrier-sense multiple-access (CSMA) or busy
tone protocols might alternately be used.
In the embodiment illustrated in FIG. lA, various modes of operation are dynamically
controlled by the wireless access devices 2A-C. Such control involves the consideration by
each wireless access device of many factors such as: 1) received signal strength; 2) success /
fail rates; 3) mode capabilities of participating devices; 3) neighboring access device operation
and performance; 4) application support required; and 5) power concerns. In addition to
modifying the parameters of a particular mode (as previously mentioned), the wireless access
devices may also select from a plurality of modes (as described in more detail below in
reference to FIG. 10).
FIG. lB is a flow diagram illustrating the operation of a wireless access device in
accordance with present invention whereby multiple wireless devices having potentially
different transceiver capabilities are supported. In particular, a wireless access device manages
ongoing communication within its cell with a previously selected mode and mode parameters
at a block 401. At a block 403, the wireless access device identifies an attach request from a
wireless transceiver (hereinafter the ''requesting transceiver") that may have wandered into the
cell. The access device 403 responds at a block 405 by identifying the available modes of
operation of the requesting transceiver. At a block 407, the modes are added to a mode table,
which stores the available modes of all the participating devices. Note that a requesting
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transceiver only communicates the availability of those modes which are both possible
(determined by the transceiver's design) and useful (determined by a current application).
If the requesting device is capable of operating in the currently selected mode, as
determined at a block 409, the wireless access device communicates mode information and
parameters to the requesting transceiver at a block 413. Thereafter, the wireless access device
returns to the block 401 and services all participating devices including the requesting device in
the current mode with current parameters.
Alternatively, if the requesting device has a limited number of operating modes, at the
block 409 the current mode may not be a possibility. If the requesting device is not capable of
operating in the current mode, the wireless access device attempts to select a new mode at a
block 411. If at least one common mode can be found, e.g., if all the participating devices and
the requesting device have at least one common mode, the wireless access device chooses the
common mode that it believes will offer optimal performance. Thereafter, at a block 413, the
wireless access device communicates the selected mode and parameter information to the
requesting transceiver at the block 413 and returns to the block 401. At the block 401, because
a new mode has been selected, the wireless access device vectors to service the event at a block
419. At a block 421, the wireless access device bro~-lc~t~ the mode and parameter
information, and, at a block 423, changes its own mode. Thereafter, the wireless access device
returns to service ongoing communication in that mode at the block 401.
If however a common mode cannot be found for a requesting transceiver at the block
411, the requesting transceiver is rejected from participating. In such a case, the customer must
identify the radios causing -the limitations and upgrade them. In another embodiment, the
wireless access device operates in a time shared configurations, switching between two or more
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modes in a sequential fashion. In this embodiment~ however, the overall delays in the system
may still justify upgrading the radio transceiver(s) causing the limitations.
During the course of ongoing operation at the block 401, the wireless access device
monitors channel performance (a variety of factors described in more detail above), and
5 compares such performance to available other common modes of operation and considers
potential parameter modifications. In particular, as represented by the block 429, if channel
conditions degrade below a predefined threshold, the wireless access device vectors to consider
ch~nging modes. At a block 431, the wireless access device consults the mode table. If a new
mode is available and warranted, per a determination at a block 433, the wireless access device
10 responds by selecting an alternate common mode at the block 435, resets the conditions that
caused the vectoring and returns to the block 401 to complete the mode change via the blocks
419, 421 and 423. Similarly, each time a participating transceiver detaches from the cell
(through either active detachment or aging) as represented by an event block 445, the wireless
access device removes that transceiving device's mode information from active status in the
mode table and attempts to choose a better common mode via the blocks 431, 433, 435 and
437. Although not shown, the wireless access device might also periodically attempt to choose
a better common mode, without requiring channel conditions to change or degrade or
participants to detach.
FIG. lC is a block diagram illustrating a radio transceiver used in wireless access
20 devices and any transceiving device, such as a printer, code reader, hand-held terminal, etc.,
and built in accordance with the present invention tO support multiple modes of operation. The
transceiver module 501 comprises control circuitry 503, a modulator 505, a demodulator 507,
and oscillator 509 and a switch circuit S l l . The control module may have either an intern~l or
external antenna attached thereto, i.e., an antenna 513.
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The control circuitry 503 manages the operation of the other components of the
transceiver module 501. The control circuitry 503 receives instructions and data to be
- transmitted from a host unit (not shown) via a wired communication link 515. The control
circuitry 503 deliver such data to the modulator 505 for modulation (and possibly spreading).
Thereafter, the data is delivered to the antenn~ 513 via the switch 511. Data and control
signals received by the ~ntenn~ 513 passes through the switch 511 to the demodulator 507 for
demodulation (and possibly despreading). The control circuitry 503 receives the demodulated
data or control signals for processing and/or delivery to the host unit through the link 515.
The control circuitry 503 causes the selection of operating parameters and modes as
described previously and in reference to FIG. lB. Specifically, the control circuitry 503 sets
the configuration of the modulator 505, demodulator 507 and oscillator 509. For example, to
operate in a direct sequence spread spectrum mode, the control circuitry 503: 1) sets the base
frequency of the oscillator 509; 2) sets related mode parameters such as the chipping rate; and
3) delivers enable signals and a spreading code to a spreader circuit 515 and despreader circuit
517 of the modulator 505 and demodulator 507, respectively. To operate in a frequency
hopping mode, the control circuitry 503: 1) establishes related parameter set~in~.c; 2) disables
the spreading and despreading circuits 515 and 517; 3) selects a hopping sequence of
frequencies; and 4) directs the oscillator 509 through the sequence. To operate in a hybrid,
direct sequence, frequency hopping mode, the control circuitry 515: 1) establishes related
parameter settings; 2) delivers enable signals and a spreading code to a spreader circuit 515 and
despreader circuit 517; 3) selects a hopping sequence of frequencies; and 4) directs the
oscillator 509 through the sequence. Similarly, the control circuitry 503 may select any modes,
e.g., the modes identified in reference to FIG. 10 below, and set all parameters related thereto.
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FIG. lD is a block diagram illustrating the operation of the wireless access device
having the multi-mode transceiver of FIG. IC installed therein. In particular, a transceiver
module 501 (as described in relation to FIG. IC) is installed within a wireless access device
503. The wireless access device 503 contains control circuitry 505 and interface circuitry 507
5 for communicating with a wired network 509. In addition to providing typical access device
service, the control circuitry 505 of the wireless access device 503 manages all mode and
parameter changes for the transceiver module 501. The control circuitry 505 monitors, among
other factors, the historical performance characteristics of each mode, neighboring access
device modes, parameters and performance and current mode performance (via received signal
10 strength indications and success / failure rates). The control circuitry 505 also m~intzlin~ and
updates the mode table, attachment and detachment of participants, as described above in
reference to FIG. lB for example. The control circuitry 505 performs such functionality via
control signals delivered to the control circuitry of the transceiver module 503.
When installed in a portable / mobile or stationary transceiver unit (e.g., peripheral
15 device, code reader, hand-held terminal, etc.), a transceiver module responds to communication
control through comm~n-ls received from the wireless access device while attempting to attach.
Such commzlndc direct the mode and parameters of operation of the transceiver module in the
transceiver unit. In addition, the control circuitry of the transceiver module 501 directs entry
of a default mode and default parameters prior to receiving direction from a wireless access
20 device. Although the transceiver module 501 may receive additional mode and parameter
commands from the host controller within the transceiver unit, in need not do so. Such local
control by a transceiver unit, however, may prove advantageous in other wireless network
embodiments or in specific applications. For example, other network embodiments might
involve only two transceiver units without a wireless access device. As such, the kansceiver
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units may negotiate a mode and related parameters amongst themselves, controlling such
changes via host processors within the transceiver units. Negotiation of mode and pararneter
changes might also involve channel condition monitoring or other factors currently assigned to
the wireless access device.
FIG. 2A illustrates a hand-held portable data terminal which incorporates the present
invention, designated generally by the numeral 10. The data terminal 10 may be one of several
data terminals in a local area network which utilizes radio frequency (RF) communications for
data transfer. The data terminal 10 illustrated is a mobile data unit that includes a radio
transceiver unit incorporating the present invention. Of course, as has been previously
described, the present invention may be incorporated into stationary units as well as mobile
units. Further, the stationary units may comprise wireless access points, other function
performing devices such as printers, stationary scanners, or other devices. Moreover, mobile
units incorporating the present invention need not comprise the hand-held radio format
illustrated in FIG. 2A. The mobile units could be installed in vehicles, worn by a user, or
installed in any other fashion that causes the device to be mobile.
The data terminal 10 includes an ~ntenn~ 12 is disposed at the top end 14 of the data
terminal for radio frequency tran~mi.~ion and reception. The data terminal may include a
display screen 16 for displaying program information and for interfacing the operator with the
data terminal 10. The display screen 16 may be a reflective super-twist liquid crystal display
(LCD), for example. The data termin~l 10 may include a keypad 18 having a plurality of keys
~ for entering data into the data terminal 10 and for control of the data terminal 10 by the
operator.
FIG. 2B shows the data terminal 10 of FIG. 2A which includes a module in which
circuitry for accomplishing the present invention is disposed. The data termin~l 10 has a
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modularly attached radio module 20 which also contains sc:~nning circuitry in addition to radio
circuitry. The antenna 12 of FIG. 2A is affixed to the radio/scanner module 20 and may be a
type suitable for portable battery powered electronic devices. The radio/scanner module 20 has
an extended outer shell 24 in order to contain both the radio and the scanner circuitry. A
5 button 26 may be disposed on either or both sides of the radio/scanner module 20 to activate
the sc~nning circuitry and scan encoded data, such as that contained in a bar code or two
dimensional image. The module 20 could, in another embodiment~ include a digital camera or
other functional equipment. As illustrated, the radio/scanner module 20 is constructed to be
modularly received by a recession 28 in the data terminal such that a continuous unit is formed
10 by attaching the module 20 to the data terminal.
FIG.3 shows a side view of another embodiment of a data terrnin~l 10 with an alternate
modular radio module attached thereto. The module 30 includes a radio incorporating the
teachings of the present invention but does not include the image capture electronics of the
radio/scanner module 20 of FIG. 2B. Because the module 30 is more compact than radio
scanner module 20 of FIG.2B, the body of radio module 30 is generally flush with the body of
the data terminal 10 when attached thereto.
FIG. 4 shows a data terminal 10 that is removably zltt~ch~ble to the radio/scanner
module 20 of FIG. 2B. The motion required for attachment of the module 20 to the data
terminal 10 generally follows the direction of line 32. The module 20 is positioned toward the
20 terminal 10 and then locked into place by a downward movement. L-shaped latches 34 may be
used to removably secure the module 20 to the terminal 10.
FIGS. 4A, 4B and 4C illustrate in detail the cooperation between a radio module and
the hand-held portable data terminal shown in FIG.3. The radio module 30 houses a radio unit
340. An antenna connector 342 connects to antenn~ connector pins 344 at an end of the radio
-
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unit 340 to provide electrical connection to an antenna which may be internally or externally
mounted on the module 30. An array of connecting pins 346 preferably connect the radio
unit340 to the data terminal which may have a receptacle for receiving the connecting pins 346.
The radio module 30 may include a hand strap 348, one end of which being connected to the
5 module 30 and the other end being connected to the terminal 10, to facilitate manipulation of
the terminal 10 in one hand and to prevent accidental dropping, for example.
FIG. S depicts another type of hand-held portable data terminal 36 that incorporates the
present invention and that is designed to receive standard PCMCIA computer feature card
modules. The terminal 36 may have a module carriage housing 38 which may receive various
types of PCMCIA cards 40: Type I (3.3 mm in thickness), Type II (5.0 mm in thickness) or
Type III (10.5 mm in thickness) PCMCIA sized modules for example.
FIG. 6 shows the data terminal of 36 of FIG. 5 having a rotatably extendible and
retractable carriage housing 38. The carriage housing 38 is shown in the extended position
holding a Type III PCMCIA module 42 which may, for example, contain the radio circuitry of
15 the present invention.
FIG. 7 is an exploded view of the internal components of a radio module 30 of the
present invention such as the module 30 of FIG. 3. The circuitry of radio module 30 of the
present invention such as the module 30 is preferably mounted on a circuit card assembly
(CCA) board 44 cont~ining, for example, the transmitter and receiver electronic components
20 (not shown). The radio CCA 44 may have metallic coverings, or cans (not shown), soldered to
the board over critical rad~o components to provide two-way electromagnetic shielding to
reduce or elimin~te radio frequency interference.
In embodiment of FIG. 7, the radio module CCA 44 is contained within a metallic radio
cover 46 to provide electromagnetic shielding of the radio CCA 44. The radio CCA 44 and
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radio cover 46 may be attached to a mounting frame 48 which provides supporting structure for
the internal components of the radio module 30. Radio cover 46 and mounting frame 48 may
be fabricated of ABS type plastic or of a conductive metal to provide electromagnetic
shielding. The radio CCA 44 and the radio cover 36 may be attached to the mounting frame 48
5 by a plurality of fasteners 50 which may be four #2 screws in a preferred embodiment.
An internal antenna 52 may be connected to the radio circuitry of the radio CÇA 44 in
lieu of the external linear antenna 12 shown in FIG. 2A and completely contained within the
radio module 30. The radio module 30 may utilize the antenna means of U. S. Patent No. 5,
322, 991 issued June 21, 1994 and assigned to NORAND Corporation of Cedar Rapids, Iowa,
the assignee of the present application, Said U. S. Patent No. 5, 322,991 is hereby incorporated
by reference in its entirety. The antenna 53 may comprise a quarter-wavelength single loop of
wire of approximately 83 mm for tr~n.~mi~ions near 900 MHz. When the loop ~nte~nn~ 52 is
driven by the output of the radio module 44, a uniform circulatory current flowing through the
antenna 52 results in a radiation pattern similar to that of a magnetic dipole. The ~ntenn~ 52
preferably has a nominal impedance of 50S.
An internal shield 56 may be utilized and inserted between the radio circuit card
assembly (CCA) 44 and the radio interface card (RIC) 58 which contains the electronic
circuitry necessary6 to interface the electronics of the radio CCA 44 with the electronics of the
data terrninal 10 of FIG. 2A. The radio interface card 58 may be a type used for a 2.4 GHz
radio since the interface to the radio CCA 44 is baseband. The 900 MHz radio 44 of the
present invention may be designed to appear as a 2.4 GHz radio accepting the same frequency
control inputs and employing the same media access control protocols as a 2.4 GHz radio.
Electrical connectors 60 may be mounted at an end of the radio interface card 58 for
providing electrical connection to the CPU board (not shown) of the portable data terrnin~l
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with which the radio module 30 is ~ltili7~A, such as terminal 10 of FIG. 2A. A mounting
- fastener 62, which may be a screw, fastens the radio interface card to the radio module
assembly 30. An acoustic-electric transducer such as buzzer 64 may be included with the radio
module 30 and electronically connected to the radio CCA 44 5to provide the operator with
5 audio information and cues, for example a beep or buzz when the radio module 30 is powered
on. Frame mounting screws 66 may be utilized to fasten the assembly to the outer shell 68 via
mounting frame 48. The entire module assembly may be wrapped in a metallic foil to provide
electromagnetic shielding to the radio module 30. The outer shell 68 is preferably a type of
ABS plastic and is formed to modularly and contiguously fit the recession 28 of the data
10 terminal 10 as shown in FIG. 2B.
FIG. 8 is an exploded view of the radio/scanner module 20 illustrated in FIGS. 2B and
4. The components and assembly thereof of the radio/scanner module 20 are substantially
similar, with some slight modifications thereof where necessary, to that of the radio module 30
of FIG. 7, the principle difference being the addition of scanner circuitry in the radio/scanner
15 module 20 for reading optically readable data files such as standard bar codes. The
radio/scanner module 20 includes radio interface card 58 with electrical connectors 60,
mounting frame 48, internal shield 56, radio CCA 44, ~n~nn~ 52, radio cover 46, and buzzer
64 as shown in FIG. 7 (and as described in the discussion of FIG. 7).
In addition to the above components, the radio/scanner module 20 includes a scanner
20 printed circuit board 70 on which the scanner electronic circuitry are mounted. A flex circuit
~ connection assembly 72 may be utilized to interconnect the electronic circuitry, such as the
circuitry of scanner card 70 and interface card 58. The outer shell 74 of the radio scanner
module is substantially similar to the outer shell 68 of radio module 30 as shown in FIG. 7,
modified to accommodate the additional components of the radio/scanner module 20.
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A rubber nose end cap 76 may be attached to the forward end of the outer shell 74 for
providing impact shock absorption and protection. A seal label 78 may be used to provide an
adhesive seal between rubber nose end cap 76 and outer shell 74. A lens 80 mounted with a
lens seal support 82 may be disposed in the rubber end cap 76 to provide a sealed light
S aperture for the scanner circuitry. Sc~nning of an optically readable data file may be controlled
with a scam button 86 which covers am input keyboard and elastomer 84 and is supported by
a scan button bezel 88 mounted in a button aperture 90 on a side of the outer shell 74. The
radio/scanner may have a plurality of scan or input buttons 86. For example~ an additional
button may be provided on the side of the outer shell 74 opposite the button 86 shown in FIG.
10 8.
Frame mounting screws 92 are provided to mount the mounting frame 48 Cont~inin~
the module assembly to the outer shell 74. The outer shell 74 and radio/scanner module are
formed to modularly and contiguously attach to the data terminal 10 as illustrated in FIGS. 2B
and 4 in a manner substantially similar the attachrnent of radio module 30 to data terminal 10.
15 The entire module assembly 20 may be wrapped in a metallic foil to provide electromagnetic
shielding to the radio module 20.
FIG. 9 is an exploded view of the PCMCIA Type III radio module 42 of FIG. 6. The
PCMCIA radio module 42 may also be constructed within a smaller sized PCMCIA module
such as Type II or Type I enclosure by combining the circuitry of the radio interface card 58
20 and the radio circuit card assembly 44 on a single printed circuit board, for example. The
PCMCIA radio module 44 may contain the radio circuit card assembly 44 and the radio
interface card 58 of FIGS. 7 and 8. The radio interface card 58 is preferably adapted to
conform to PCMCIA device interface standards for utilization in PCMCIA radio module 42.
The circuitry of the radio CCA 44 and the radio interface card 68 may be interconnected by a
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board to board connector 94. Alternatively, all of the circuitry of the RIC 58 and the CCA 44
may be combined on a single printed circuit board for smaller sized radio modules (20, 30 or
42).
Standoffs 96 may be soldered directly to the radio interface card 58 and are provided to
5 separate the radio CCA 44 from the radio interface card 58 and to provide attachment thereto
with fasteners 98 (preferably #2-56 screws). The screws 98 preferably attach the radio CCA 44
to a custom PCMCIA Type III frame 100 which provides structural support and protection of
the circuit boards 44 and 58. A PCMCIA electrical receptacle 102 may be provided to
electrically connect the radio module to standard PCMCIA connectors in the electronic
equipment in which the module 42 is to be ntili7~1, such as the data terminal 36 of FIGS. 5 and
6.
An antenna connector 104 may be mounted on the radio CCA 44 for connection of the
module to an ~nt~nn~ which may be, for example, the antenna 12 of FIG. 2A, the ~ntt?nnzl 52 of
FIGS. 6 and 7 of the antenna means of U.S. Patent No. 5,322,991 issued June 21, 1994
incorporated herein. Alternate ~ntçnn~ clips 106 may be utilized for adapting the radio module
42 to various ~ntçnn~ connection configurations.
The PCMCIA radio module 42 may be contained within top and bottom covers 108 and
110 respectively which are preferably comprised of tin plated cold rolled steel. The module
covers 108 and 110 may provide two way electromagnetic shielding of the radio frequency
circuitry. When the radio module 42 is assembled and contained within top cover 108 and
~ bottom cover 110 the module preferably conforms to PCMCIA Type III dimensions. The
module 42 may also be adapted to conforrn to PCMCIA Type II or Type I dimensions as well.
The transceiver module as shown in FIG. 9 may be utilized in a standard desktop or
portable computer such as a iaptop computer which is designed to utilize standard PCMCIA
-
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computer modules. The portable computer may be implemented as part of a multilayered
communication network such as a communications node to communicate, for example, with
several data terminal in a connected wired network, as well as with nodes in the wireless
network. In this fashion, the computer could serve as a wireless access point, a wireless access
5 server, or another type of wireless device providing access to the wireless network. A
preferred embodiment of the present invention implements Layer I (the physical layer) and the
medium access control (MAC) sub-layer of Layer 2 (the data link layer) of the International
Standards Org~ni7~tion Reference Model (ISORM) operating under an ODI or NDIS driver. A
driver interface to the MAC sub-layer allows the utilization of industry standard multi-layer
10 communications protocol above the MAC sub-layer.
FIG. 10 is a functional block diagram of an embodiment of the radio modules 20, 30
and 42 of the present invention. The components of FIG. 10 implement the t~ching.~ of the
present invention by causing the radio module to be operable in any of a plurality of spread
spectrum modes depending upon system and tr~n.~mi.~ion conditions. The components
15 illustrated could be found in a mobile unit or a stationary unit to provide equivalent
functionality in the units. In one embodiment, at least one stationary unit and a plurality of
mobile units in a wireless local area network are capable of operating in a plurality of spread
spectrum modes such as direct sequence, channelized direct sequence, frequency hopping,
channelized frequency hopping, or hybrid modes. The components illustrated in FIG. 10 allow
20 the radio modules to operate in such a fashion.
The antenna section includes an antenna 112 for transmitting and receiving radio
frequency energy. The antenna 112 may be one of the antennas described in the discussion of
FIGS. 7, 8 and 9. The radio clrcuitry corresponds to the radio circuitry of the radio CCA 44 of
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FIGS. 7, 8 and 9 and contains the receiver circuitry 114, the transmitter circuitry 118 and the
frequency generator ("FREQ. GENERATOR") 1 16.
The radio frequency (RF) transceiver 298 of the present invention comprises a receiver
114 and a transmitter 118. The transmitter 118 preferably comprises a data formatter and
spreader ("BASE BAND FORMATTER/SPREADER") 124, a selectable transversal filter 150
comprising programmable transversal filters ("PROGRAMMABLE TRANSVERSAL
FILTER") 146 and 148 (See FIG. 11), a binary phase shift keying (BPSK) modulator ("BPSK
MODULATOR") 130, and a transmitter up converter and linear transmit power amplifier ("TX
UP CONVERTER & AMP") 314. The receiver 114 preferably comprises a receiver down
convertor304, a selectable bandwidth intermediate frequency (IF) stage ("SELECTIBLE BW
IF") at a fixed IF center frequency, a non coherent I/Q base band converter ("BASEBAND
CONVERTOR"), and a demodulator/despreader ("DEMOD. DESPREAD.").
A common radio frequency b~nclp~ filter ("BPF") 399 iS shared by both the
transmitter 1 14 and the receiver 1 18. The transceiver 298 iS coupled to an antenna 1 12 through
an antenna switch circuit 302. A frequency generator 116 iS common to both the receiver 114
and the tr~n~mitter 118, producing a frequency agile main VCO output ("MAIN VCO") 332,
and an auxiliary output ("AUX VCO") 334 at twice the IF frequency. A divide by 2 circuit
(316 and 318) in the transmit path of the auxiliary VCO signal 334 iS activated when the
transceiver 298 iS switch to the transmit mode.
The transmit operation the media access control (MAC) microprocessor ("MAC ,uP")128 enables the various transmit circuits through the control bus (see CONTROL of FIG. 18).
In particular, however, the MAC ,uP 128 controls the various components illustrated in FIG. 10
as illustrated. However, in other embodiments of the present invention, the MAC ,uP 128 may
control only a portion of the components or even more of the components. To implement the
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teachings ofthe present invention, the MAC ~lP 128 controls the various elements illustrated in
FIG. 10 so as to perform transmission and reception in any of the various spread spectrum
modes. In order to accomplish such various modes, the MAC ~LP 128 must control the
frequency generator 116 to cause modulation over all of a spreading bandwidth via variations
S in the MAIN VCO frequency. In addition, the MAC IlP 128 provides control to the modulator
130, RECEIVER DOWN CONVERTER 304, TX UP CONVERTER & AMP 314, the
SELECTABLE BW IF 322, the MODULATOR 130, the SELECTABLE TRANSVERSAL
FILTER 150, the DEMODULATOR DESPREADER 184, and the
FORMATTER/SPREADER 124 in order to cause the circuitry to perform in the various spread
10 spectrum modes.
As is known, each of the various spread spectrum modes requires p~ck~gin~,
modulating, transmitting, and receiving data in particular formats and frequencies. Thus, the
MAC ~P 128 provides control over the elements illustrated in FIG. 10 in a fashion so as to
enable each of the various spread spectrum modes. Techniques known in the art may be
15 employed to cause the components illustrated in FIG. 10 to perform in particular spread
spectrum modes.
The functions of the baseband formatter/spreader 124 may be contained in a digital
application-specific integrated circuit, or ASIC, (not shown) with circuitry configurable to the
desired tr~n~mi~ion mode by the control microprocessor 128. The ASIC preferably produces
20 a clock at the correct data rate for the selected mode which is used to time serial transfer of a
data frame from the transmit data output of the MAC ~lP 128 (see TXD of FIG. 18).
In the direct sequence (DS) modes, the data is mapped into I/Q symbols for either
BPSK or QPSK modulation. The ASIC generates a synchronous chip clock at a multiple of the
symbol rate that is applied to the pseudo-random number (PN) generator of FIG. 14A to
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produce a chipping sequence at the selected spreading ratio. The exact chipping sequence is
selected by programming the feedback select of FIG. 14A. The chipping sequence is
multiplied with the I/Q data symbols by use of exclusive OR gates. The selected data rate and
spreading ratio determine the main lobe bandwidth of the transmitted signal. The bandwidth of
the main lobe and side lobes are reduced by applying the transversal filters (146 and 148 of
FIG. 148), which comprise circuitry of the transversal filter 150 of FIG. 10 with the shift
registers operating at the chipping rate rather than the symbol rate. The main lobe bandwidth is
limited to approximately 1.6 times the chip clock frequency.
The remainder of the Transmitter 118 is a standard I/Q modem. The I/Q waveforms are
applied to a quadrature PSK modulator operating at l/2 the Auxiliary VCO frequency. The
modulated signal is filtered to reduce harmonic content, then undergoes a second conversion
with the Main VCO output 332 to produce a final output frequency. This signal is filtered to
reduce the image of the mix product from this second conversion, and then amplified by the
antenna 112 through the antenna switch 302 and RF b~n~lpa~s filter 300.
In the receive mode, the receiver circuitry 118 is switched on and the transmitter
circuitry switched off through the control interface. Incoming signals present at the antenna are
amplified and converted to the IF frequency by mixing with the main VCO output 332. The
output of the receiver down converter 304 is applied to the selectable bandwidth IF filter 322,
which is programmed to the correct bandwidth for the selected mode of operation by the MAC
,uP 128. The filters 174, 176 and 178 provide rejection of out of band signals for the selected
~ signal bandwidth.
The filtered output is applied to a limiting amplifier, then to the I/Q baseband converter
312. The limiter 182 produces a received signal strength indication that is proportional to log
of the signal energy in the IF. This is applied to an A/D converter 126 then to the control ~uP
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128. This function is useful for detecting proximity to the transmitting unit, or to an interferor,
and is also useful as an OOK detector.
The baseband converter 312 contains an internal divide-by-two circuit which produces
a carrier at 1/2 the Auxiliary VCO frequency which is also at the nominal IF frequency. This is
5 mixed with the limited IF signal to produce baseband I/Q waveforms. These in turn are
applied to comparators that serve as hard decision circuits, then to the correlator 330 (see FIG.
17) within the ASIC.
The frequency generation system 1 16 must be programmed to produce the Main VCO
output. A serial interface within the control bus provides this capability. In the DS modes the
10 Main VCO is programmed to the correct channel frequency and remains there until a mode
change or the need to avoid interference is detected. For wideband DS operation, The Main
VCO is programmed to the center of the frequency range.
For FH or hybrid operation, i.e., frequency hopping combined with direct sequence
operation, the Main VCO is periodically reprogrammed to provide the hopping function. The
15 MAC ~P 128 m~int~in.~ a timer, and table of channels representing the hop sequence. When
the timer expires, the MAC ,uP initiates the hop to the next frequency in the sequence. Frames
passed between the various devices within the WLAN establish shared timing references so
that all units hop in synchronism.
The MAC ~lP 128 provides mode control, host interface, transmit frame generation,
20 channel access control, receive frame proces~ing, retries of erred packets, power management
of radio circuitry, and frequency hopping control. The frequency hopping control is a superset
of the rçm~inin~ functions, allowing common progr~mming of the rem~ining functions for
both DS and FH.
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The host interface for the PCMCIA version is compliant with the PCMCIA physical
interface. The software interface is structured to comply with the factory industry standards
NDIS and ODI formats.
Data to be transmitted is sent via a bus 131 to the MAC circuitry 128 from a host unit.
5 The data to be transmitted is be modulated by the modulator 130 and frequency controlled by
the spreader 124 according to the particular spread spectrum tr~ncmiccion mode to be ntili7P~l
The spreader 124 receives a chipping clock input that is at a frequency multiple of the source
data frequency. The output of the spreader 124 is sent to the transmitter up converter and
amplifier 314 to transmit the RF data signal through the antenna 1 12.
The radio modules of the present invention may utilize several modes of spread
spectrum RF data tr~ncmiCcion. In one embodiment of the present invention, the various
modes can be user selectable depending upon the particular application in which the radio
modules are to be lltili7P~ In another embodiment, the modes of operation are be
automatically and dynamically selected, e.g., by the MAC ,uP 128 based upon criteria
15 previously described. Such selection might also be performed by or with the ~cci.ct~nce of the
terminal unit or a digital signal processor provided for such task.
In a particular example, a microprocessor in the host terminal may retrieve stored
modes of operation utilized on the previous day to which a higher logical multiplier is used to
determine which tr~ncmic.cion mode or modes are to be selected for that day's data
20 tr~ncmiccions. Additionally, data such as the average signal strength, most frequently utilizes
~ tr~ncmi.c.cion mode, the average level of interference and noise for a particular mode or
tr~ncmicsion success rate (e.g. percentages of trancmi.ccions) may be saved in nonvolatile
memory and factored into the mode selection routine.
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A deseription of particular spread spectrum modes follows in Table 1. The modulation
techniques as described in Table I may be direct sequencing (DS), frequency hopping (FH) or
on-off-keying (OOK) or a combination thereof. The rate at whieh data may be transmitted is
given is kilobits per second (kb/s) and the ehannel bandwidth is given for each mode for the
operational frequeney range of 902 to 928 MHz. The full bandwidth of an embodiment of the
radio is 26 MHz Table 1.
Table 1: Spread Spectrum Transmission l\Iodes
MODEMODULATION DATA BANDWIDTH
TECHNIQUE RATE
DS 250 kb/s full band
2CHANNFT T7F.n DS 250 kb/s 5 ehannel
5 MHz
3 DS 500 kb/s full band
4 FH 250 kb/s 50 ehannels
500 kHz
FH/DS 10 kb/s 50 ehannels
500 kHz
6 OOK 19.2 kb/s50 channels
500 kHz
7 DS 10 kb/s 50 ehannels
500 kHz
The various spread spectrum modes are utilized to obtain optimum performance forparticular modes of operation of the data terminal. The radio of the present invention preferably
has a tr~n~mi~.~ion range of up to 300 feet for closely spaeed interior surfaees and up to 1300
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feet in open spaces resulting in an operational coverage area from 280.000 to 5,300,000 square
- feet.
Utilization of the various tr~ncmi~cions modes results in variable immunity of the data
signals from RF interference. The data terminal in which the radio is utilized thereby has the
5 ability to extract the best system performance in every application regardless of multipath
signal levels, interference levels and the sources thereof. The data terminal also thereby has the
ability to dynamically trade data rate in return for coverage range (coverage range being a
function of process gain) without the need to change radio hardware. Although not shown,
capable of operating in the 2.4 GHz circuitry of FIG. 10 or other frequency ranges. Multiple
10 intermediate frequency filter topology may be implemented to achieve interference rejection
via varying filter selectivity.
MODES 1 and 3 are full band direct sequence and provide no inband interference
protection other than high process gains of 18.7 dB and 15.7 dB respectively. Out-of-band
protection from cellular tr~n~mi~.~ions operating in the vicinity is provided. MODE 1 provides
15 good coverage area and rejection of multipath signal. MODE 3 provides shorter coverage are
in return for a high speed data rate.
MODE 2 is a channelized direct sequence mode having a process gain of 17 dB. A
single direct sequence cordless telephone operating in the vicinity will not degrade
performance on at least four of the channels. MODE 2 provides a reasonable coverage area
20 and jammer avoidance with channelization.
~ MODE 4 utilizes full band frequency hopping having a process gain of 17.1 dB. A
single direct sequence cordlcss telephone will not degrade average throughput by more than 10
percent. MODE 4 provides moderate coverage area and high system capacity with dynamic
jammer immllnity with frequency hoping.
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MODE 5 is a direct sequence mode which is frequency hopped having a process gain of
37dB. A single direct sequence cordless telephone operating in the vicinity will not degrade
average throughput by more than 10 percent. MODE 5 provides a long and high coverage area
and dynamic jammer immunity with frequency hopping in return for a low data rate.
MODE 6 is an on-off-keying (OOK) modulation mode having a process gain of 0 dB.
MODE 6 may be utilized as a low speed, low power link to a nearby scanner or printer for
example.
MODE 6 the transceiver module is intended to communicator with peripheral devices
contslining simple AM transceivers. The Main VCO is set to the center frequency of the
peripheral AM receiver. For OOK tr~n~mi.~ion, the data formatter is configured to produce a
CW output signal. OOK signaling is providing by strobing the enable line on the transmitter,
shown in figure 16.
For OOK reception, the Main VCO is set to receive at the AM tran~mitter center
frequency. The RSSI output from the limiting amplifier is used for AM detection. The
signaling rate is limited by the speed at which the A/D can quantize the RSSI (preferably
sampling several times per symbol), and at which the MAC ~LP128 can process the sampled
data to extract the modulation.
MODE 7 is a channelized direct sequence mode having a process gain of 20 dB. A
single cordless telephone operating in the vicinity will not degrade performance on more than
nine of the channels.
Other modes may also be included other than those listed above. Other possibly
included modes may be variations or new combinations of the above modes or modes l~tili~in~
different modulation techniques and frequencies such as other standard RF tr~n~mi~ion
techniques which may be contemplated by the present invention. For example, an additional
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mode in an alternative embodiment may include voice communications transmissions utili7inp
standard audio modulation techniques achieved by switching channels or tr~n~mi~ions modes.
Using voice communications the transceiver module may allow data terrninal operators of a
multi-level radio-frequency communications network to verbally communicate with one
5 another or their supervisors throughout the entire network. Voice and data communications
may be utilized with a single portable battery powered electronic device rather than having a
data terminal for data communications and a separate mobile radio for voice communications,
for example. Similarly, the process gains. sampling rates, etc., are exemplary value which may
be modified as proves desirable.
FIG. 11 is a conceptual block diagram of the operation of the transmitter of FIG. 10
when operating in a direct sequence spread spectrum tr~n.~mi~ion mode. As illustrated, in the
operation, data is received by the BASE BAND FORMATTER/SPREADER which, based
upon the CONTROL SPREADER signal received from the MAC ,uP 128, spreads the code
based upon a particular code spreading sequence or pattern. The BASE BAND
FORMATTER/SPREADER provides data on two output paths so that the data may be
modulated according to the BPSK modulation scheme. The spread code is then processed by a
programmable transversal filter 150 having two separate filters, 146 and 148, one for each data
path. Once filtered, the data is modulated by the components 136, 138, 140, 320, and 142 of
the BPSK modulator. From the BPSK modulator, the data proceeds until it is transmitted.
FIG. 12 shows a conceptual diagram of the operation of the receiver utilized in
conjunction with the transmitter of FIG. 11. In the embodiment, data received by the antenna
112 passes through a zero-degree phase shift block 152. From the block, one path goes directly
to one input of a multiplier 158 while the second path passes through an RF DELAY block 154
and then passes to a second input of the multiplier 158. DELAY CONTROL is supplied to the
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RF DELAY block 154 by the MAC ,uP 128 dependent upon the frequency of the received
signal to cause a desired phase shift. From the multiplier 158 the signal passes through a
baseband data filter 160 then through X~ block 162 prior to its furthered processing.
FIG. 13 is a block diagram of the receiver 114 of the present invention. The receiver
114 may be located on the radio card CCA 44 of FIGS. 7, 8 and 9. Wideband filter 170
provides additional interference protection in the narrow band modes. A preselector filter 164
receives an RF data tr~n~mi~.~ion signal from the antenna 112 (not shown). The preselector
filter 164 may be a two pole bfln~lp~c.~ filter (BPF) designed to have a wide bandwidth to keep
the insertion loss low. In an exemplary embodiment filter 164 has a center frequency of 915
MHz, a bandwidth of 26 MHz and an insertion loss of 3.5 dB. However, the filter 164 could
be controllable as well based upon desired filtering characteristics.
The output of the preselector filter 164 is fed into two low noise RF amplifiers (LNA)
166 and 168 each of which preferably has a gain of 10 and a noise figure of 2.2 dB. The gain
of the RF amplifies 166 and 168 is sufficient to overcome any noise which may be present on
the input RF data signal. The amplified signal may be sent to a bandpass filter (BPF) 170 for
additional preselection filtering. R~n~1p~ filter 170 is preferably designed to have four poles
to provide high stop band rejection of possible signal images present in the data signal, having
design values of 915 MHz center frequency, bandwidth of 26 MHz and an insertion loss of 3.5
dB. Bandpass filter 170 could also be controlled to provide desired filtering characteristics.
The output of filter 170 is sent to the input of a mixer ("MIXER") 170 which mixes the
data signal with the output 332 from the main voltage controlled oscillator of the frequency
generator circuitry 116 of FIG. 10 which preferably has an output frequency of 844 MHz. The
output of the mixer 172 is passed through an additional b~n~lr~ filter 174 having a center
frequency of 71 MHz, a 26 MHz bandwidth and insertion loss of 2Ø
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The data signal is passed through an intermediate frequency selectable bandwidth filter
322 comprising filters 174, 176 and 178 for signal path 180, which varies the filtering of the
data signal according to the various modes of operation. B~n~lp~s filter 176 is utilized for
MODE 2 operation and has a bandwidth of 5 MHz and an insertion loss of 8 dB. MODES 1
and 3 utilize a direct signal path 180 with an overall bandwidth of 26MHz from the output of
filter 174. MODES 4, 5, 6 and 7 utilize bandpass filter 178 which has a bandwidth of 500kHz
and an insertion loss of 8 dB. Multiple intermediate frequency filter topologies may be
implemented to achieve interference rejection via varying filter selectivity.
The data signal is fed into an intermediate frequency arnplifier (IF) 182 to overcome the
losses from the filters. The IF amplifier 182 is a high gain amplifier having a gain and a noise
factor of 7 dB. The output of the IF amplifier 182 drives the demodulator 181 which also
receives the output from the auxiliary voltage controlled oscillator of the frequency generator
circuitry 116 of FIG. 10 which may operate at a frequency of 142 MHz. The demodulator 184
may have data signal products I and Q which are fed into the inputs of the despreader cil~;uill y
120 of FIG. 10. The receiver 114 may have a noise figure of less than 7 dB, an image rejection
figure of 60 dB and adjacent channel rejection of 40 dB.
FIGS. 14A and 14B are diagrams illustrating the operation of the pseudo-random
number generator circuitry ("PN GENERATOR") 122 of the traverse filter 150 of FIG. 10.
The pseudo-random number generator circuitry 122 is preferably located on the radio interface
card 58 of FIGS. 7, 8 and 9. The pseudo-random number generator 122 produces a pseudo-
random binary output which is mixed with the data signal code in order to minimi7~o the rate
distortion for a given number of bits used to represent the data signal. The PN generatorl22
may be comprising an 8-bit shift register ("8-BIT SHIFT REGISTER'~) 186 utili7ing a feed
back selector control ("FEEDBACK SELECT") 188 which provides programmable fee-lb~rk
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A restart control device (~'RESTART CONTROL~ ) 190 may be utilized to provide a
programmable restart interval and a programmable restart vector. The PN generator 122 is
preferably controlled by a control input (~'CONTROL") from the MAC circuitry 128 of FIG.
10 and produces a PN code output signal ("PN CODE").
In the frequency hop (FH) mode, data is converted to an I/Q format for minimum shift
keying (MSK) modulation. Narrowband modulation is preferably employed so the spreader
function may disabled. The power spectral density of MSK modulation exhibits a main lobe
bandwidth of approximately 1.5 times the symbol rate, but also contains substantial energy in
the side lobes. This energy might create interference to other in-band or out of band systems
and may also degrade operation if several frequency hopping sequences are used for increased
throughput or multiple access. To reduce side lobe energy, transversal filtering is employed in
the I/Q modulation paths. These consist of shift registers clocked at the symbol rate or a
multiple thereof. The digital outputs from the shift registers are summed using a weighted
resistor ladder (350 and 352) is external to the ~SIC and constitutes the interface between
digital and analog proces~ing.
In the direct sequence (DS) modes, the data is mapped into I/Q symbols for either
BPSK or QPSK modulation. The ASIC generates a synchronous chip clock at a multiple of the
symbol rate that is applied to the pseudo-random number generator 122 to produce a chipping
sequence at the selected spreading ratio. The exact chipping sequence is selected by
progr~mming the feec~b~cl~ select 188. The chipping sequence is multiplied with the I/Q data
symbols by use of exclusive OR gates (324 and 326). The selected data rate and spreading
ration determine the main iobe bandwidth of the transmitted signal. The bandwidths of the
main lobe and side lobes are reduced by applying the transversal filters (146 and 148) with the
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shift registers operating at the chipping rate rather than the symbol rate. The main lobe
bandwidth is preferably limited to approximately 1.6 times the chip clock frequency.
FIG. 15 is a block diagram illustrating the frequency generator circuitry 116 of FIG. 10.
The frequency generators 116 are preferably located on the radio card CCA 44 of FIGS. 7, 8
and 9. The radio interface card 58 of FIGS. 7, 8 and 9 may provide data signals ("DATA",
"CLOCK", ~STROBE" and "LOCK DET") 190 and a clock signal ("CLOCK") 192 2hich is
preferably a 30 MHz clock to the fractional number frequency agile synthesizer
("FRACTIONAL N SYNTHESIZER") 194. The 30 MHz clock signal may be divided to
produce frequencies of which 30 MHz is a multiple. The synthesizer 194 may also receive
frequency input signals from a main voltage-control oscillator (MAIN VCO) 196 and from an
auxiliary-voltage controlled oscillator (AUXILLARY VCO) 198. The synthesi7~r 194preferably switches between tr~n~mi~ion and receiving modes in 200 :s or less.
The main VCO 196 preferably operates at a nominal frequency of 844 MHz while theauxiliary VCO 198 preferably operates at a nominal frequency of 142 MHz. The synthesizer
194 has loop filter feedback paths 200 and 202 to oscillators 198 and 196 respectively for
control of the frequency of the outputs of the oscillators 196 and 198. The main VCO 196
supplies a signal to the down converter mixer 172 of the receiver 114 of FIG. 13 and provide a
signal to the modulator 206 of the transmitter 118 of FIG. 11 after being fed through a divide
by 2 circuit ("DIVIDE BY 2") 204.
FIG. 16 is block diagram illustrating the functionality of the transmitter circuitry 118 of
FIG. 10. The transmitter 118 is located on the radio card CCA 44 of FIGS. 7, 8 and 9. The
transmitter 118 receives data signal input products I and Q from the modulator and spreader
circuitry 124 and 130 of FIG. 10. The transmitter input data signal I and Q are mixed with the
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output of the auxiliary VCO 198 of FIG. 15 which are then combined and mixed with output of
the main VCO 196 of FIG. 15 using an up converter mixer in the transmitter modulator 206.
The output of the transmitter modulator 206 is preferably fed into a high pass filter
(HPF) 208 having the data signal below the nominal carrier frequency of 900 MHz for single
5 side band (SSB) tr~n~mission. The output of the high pass filter (BPF) 210 which preferably
has a counter frequency of 915 MHz and a band width of 26 MHz. The output of bandpass
filter 219 is fed into two amplifier (AMP) 214 preferably having a gain of 20 and a second
amplifier (AMP) 214 preferably having a gain 30 to provide the necessary tr~n.~mi~.sion output
power. The power of the data signal at the output of amplifier 214 is nominally at least l watt
which is fed through a lowpass filter (LPF) 216 and a bandpass filter (BPF) 218. Because of
the insertion losses of the filters 216 and 218 of 0.7 dB and 3.3 dB respectively, the transmitter
118 has a nominal output power of at least 250 mW which is transmitted via ~ntenn~ 112 of
FIG. 10.
FIG. 17 illustrates the circuitry for selecting between the modes of modulation of the
present invention. In frequency hopping mode the correlator ("CORRELATOR") 330 us
bypassed and the decision and timing recovery block ("DECISION TIMING RECOVERY")
332 performs MSK detection. An alternative approach would be to use an FM discriminator, a
function that is commonly available in limiting amplifier IC's. This is possible because MSK
signal are known to be capable of demodulation as either FM or PSK signals.
In DS modes the correlator 330 preferably extracts the data symbols from the chipping
sequence. The decision and timing recovery block 332 outputs send the recovered data
("DATA") and a clock signal ("CLOCK") to the MAC ~P 128 for frame processing.
FIG. 18 is a block diagram of the MAC circuitry 128 of FIG. 10. The MAC circuitry
128 is preferably located on the radio interface card 58 of FIGS. 7, 8 and 9. The medium
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access control circuitry 128 may be utilized in the protocol of communications media used in a
partieular communications network. The media access circuitry 128 may also utilize the 2.4
GHz MAC protocols to provide operation on both 9000 MHz and 2.4 GHz networks.
The media access protocol may be controlled by a MAC microprocessor ("MAC ~lP")
224 which receives a timing control signal from a crystal oscillator ("XTAL") 246. The MAC
microprocessor 224 may communicate with the electronic device in which the radio of the
present invention is to be utilized via a host communications bus ("HOST"). The MAC
microprocessor 224 may further have input and output signals 248 from an analog-to-digital
converter ("A/D"), digital-to-analog converter ("D/A")~ an electrically erasable read only
memory (E2ROM") or a reset control circuit ("RESET") for example. The MAC
microprocessor 224 may utilize random access memory ("RAM") 250 whieh may be either
volatile or nonvolatile memory. The MAC microprocessor 244 may also receive an input from
OTP 252. A control bus ("CONTROL") is utilized to control the circuitry of the radio card 44
of FIGS. 7, 8 and 9.
The MAC microprocessor 244 may have registers to read the status of and control the
functions of the radio interface card 58. Registers may also be provided to control the
tr~n~mission power state of the radio of the present invention. The MAC microprocessor 244
may provide a parallel-to serial converter for eontrol and progr~mming of the synth~ci7Pr 194
of FIG. 15. Additionally, the MAC microprocessor 224 may provide a programmable periodic
timer, clock control of the CPU of the data terminal 10 and PCMCIA programmable clock
generation.
FIG. 19 is a block diagram illustrating the host interface circuitry 132 of FIG. 10 for
radio module 30 of FIG. 7 and for radio/scanner module 20 of FIG. 8. The host interface
eireuitry 132 is preferably loeated on the radio interfaee eard 58 of ~IGS. 7 and 8. A regulator
_
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("REGULATOR") 254 functions as the power supply 134 of FIG. 10 and provides a regulated
voltage signal to the radio interface card 58 which is connected to the MAC circuitry 128 via a
host to MAC communications bus ("TO MAC") which connects to the electronic device in
which the radio of the present invention is utilized through connectors ("CONNECTORS") 60
5 on the radio interface card 58 of FIGS. 7 and 8. Further connection is made to a buzzer
("BUZZER") circuit 256 which may be the buzzer 64 of FIGS. 7 and 8. A bus connection to
the radio/scanner module 20 of FIG. 8 is provided for control of the scanner 258 which may be
a laser scan engine ("LASER SCAN ENGINE").
FIG. 20 is a block diagram illustrating the host interface circuitry 132 of FIG. 10 for
PCMCIA radio module 42 of FIG. 9. The PCMCIA radio module host interface circuitry 132
is preferably located on the radio interface card 58 of FIG. 9. A FET switched power supply
("POWER SUPPLY FET SWITCH") 260 functions as the power supply 134 of FIG. 10 and
provides a supply voltage output ("TO RIC") to the radio interface card 58 of FIG. 9. A
microcontroller ("~C") 262 provides interfacing signals ("TO MAC and PCMCIA
CONNECTOR") between the MAC circuitry 128 of FIG. 2B and the electronic device in
which the radio of the present invention is to be utilized through PCMCIA connectors 102 of
FIG. 9.
FIG. 21 is a diagram illustrating an alternate configuration of portable data terminals
according to the present invention. Specifically, a communication network 1450 provides an
overall network environment for portable data collection terminals 1454. A host computer 1451
is connected to access points 1452 via a wired connection 1453. The access points 1452 are in
turn communicatively coupled to portable data collection terminals 1454 via wireless links 1455.
The wireless links 1455 may be one or more of a plurality of wireless communications
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technologies, including narrowband radio frequency, spread spectrum radio frequency, infrared.
- and others.
A dock 1456 and a portable data terminal 1458 according to the present invention may be
connected to the wired backbone 1453, and may serve a function similar to an access point 1452.
S The dock 1456 may provide power to the t~rrnin~l 1458, or alternatively the dock may be absent
and the terminal 1458 may run for a limited time under the power of its battery. The terrninal
1458 connects directly to the wired backbone 1453, and also communicates with another terrninal
1454 through a wireless link 1455. The terminal 1458 may, for example, be equipped with
protocol converter circuitry to convert communication on the wire backbone 1453 into wireless
communication on the link 1455, and also to convert wireless comrnunication on the link 1455 to
a format for communication on the wire backbone 1453. The communication module associated
with terrnin~l 1458 thus improves the versatility ofthe tPrrnin~l 1458.
FIG. 22A ilhlstrates one embodiment of the data collection terrnin~l of the present
invention, having both wired and wireless communication capability. A data terminal 1500 is
shown having a communication module 1502 and a base module 1504. The communication
module 1502 contains a wired transceiver 1506, a wireless transceiver 1508, and proces~ing and
interface circuitry 1510. The base module 1504 contains a control processor and interface 1512,
an application processor 1514, and terrninal circuitry 1516 cont~ining data input and display
portions and other circuitry well known in the art. The blocks shown in comrnunication module
1502 and base module 1504 are simplified for exemplary purposes, and it will be understood by
one skilled in the art that a data terminal 1500 according to the present invention is not limited to
the block circuitry shown in FIG. 22A. In another embodiment, the communication module 1502
may contain additional transceivers for communicating on other mediums and in other net~,vorks.
The processing and interf:~ce circuitry 1510 of the communication module 1502 isolates the
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circuitry of the base module 1504 from the differing operating characteristics of the kansceivers,
so that communication by any of the transceivers can be accommodated by the circuitry and
software routines of the base module 1504.
In operation, the processing and interface circuiky 1510 of the communication module
5 1502 is programmed with the network configuration to route communication through either the
wired transceiver 1506 or the wireless transceiver 1508. An incoming message on the wired
transceiver 1506 may be routed and processed to a terminal display portion, or may be routed to a
host computer, a dock, or another portable data terminal 1500 through the wired kansceiver 1506
or through the wireless transceiver 1508, whichever is ~n)~l;ate. Similarly, an incoming
10 message on the wireless kansceiver 1508 may be routed to display or through the wireless
transceiver 1508 or through the wired kansceiver 1506, whichever is a~l~ iate for the
destination. By provided for the routing functions to be done in the communication module
1502, the power used in the base module 1504 can be minimi7~1 Specifically, the interface with
the control processor 1512 and the application processor 1514 need not be used, which allows the
15 main termin~l in the base module 1504 to remain dormant while communications are routed in
the comml-nication module 1502.
The choice of which transceiver to use in routing comrnunication is based on a "least
cost" analysis, considering factors such as the power required to send the message through a
particular transceiver, the speed at which the message will be received from a particular
20 kansceiver, the possibility of error associated with each transceiver, etc. A wired connection is
usually selected when available, but routing decisions may vary with the different characteristics
of each message and the mobility of the terminal. The processing and interface circuitry 1510 in
the communication module 1502 is preferably capable of performing the least cost routing
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analysis for all communication messages, without activating any processing power from the base
module 1504.
FIG. 22B is a diagram illustrating a specific implementation of the portable terminal of
FIG. 22A a single PCMCIA card contains not only a multi-mode wireless transceiver, but also a
wired modem transceiver. In particular, a portable terminal 1520 contains termin~l circuitry 1522
comprising processing circuitry 1526, conventional tPrmin~l circuitry 1528 and interface circuitry
1530. The interface circuitry 1530 provides a PCMCIA interface for receiving PCMCIA cards of
various functionality. The terminal circuitry 1522 is well known and can be found in
conventional portable or hand held computing devices.
Via the interface circuitry 1530, the portable termin~l 1520 accepts PCMCIA cards. As
illustrated, the PCMCIA card inserted constitutes a communication module 1524 which provides
both wired and wireless access. Specifically, the cnmmllnication module 1524 comprises
proces~sing circuitry 1532, a multi-mode wireless transceiver 1534 (such as set forth previously),
a wired modem transceiver 1536 and interface circuitry 1544. When in use, the wired modem
transceiver 1536 interf~es via a jack 1540 to a telephone line (not shown). Similarly, the
wireless multi-mode transceiver 1534 communicates via an ~ntenn~ 1538.
Whether the modem transceiver 1536 or multi-mode transceiver 1534 is being used, the
processing circuitry 1526 always delivers and receives data and messages via the interface
circuitry 1530 in the same manner and forrnat, i.e., the interface circuitry 1530 supports a
common communication interface and protocol. The processing circuitry 1532 of the
communication module 1524 receives data and messages via the interface circuitry 1544. If the
modem transceiver 1536 is being used, the processing circuitry 1532 ~plu~liately (de)segment.s
and (de)compresses the data/messages l]tili7ing a digital signal processor (DSP) 1542.
Otherwise, the processing circuitry 1532, including the DSP 1542, participate to assist in wireless
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communication via the multi-mode transceiver 1534. Thus, the module 1524 not only saves on
PCMCIA slots (as required when a conventional radio card and a conventional modem card are
both being used), but also saves costs and increases reliability by sharing common circuitry
resources. In particular, the modem and multi-mode transceivers 1536 and 1534 share the
interface circuitry 1544 and processing circuitry 1532 which includes the DSP 1542.
FIG. 23 is a diagram illustrating the use of portable t~ nninzll~ according to the present
invention ~Itili7inp; both wired and wireless communication in a network configuration.
Specifically, a server 1515 is shown connected to mobile computing devices (MCDs) 1554 via a
wired communication link 1552. The communication link 1552 may alternatively be an infrared
link, or another communication technology. MCDs 1554 are connected to each other and to the
server via the link 1552. MCDs 1554 are also communicatively coupled to each other via
wireless links 1556.
The network involving the server 1550, the communication link 1552, and the MCDs1554 represents a primary communication network, that is preferable to use when there are no
interference or disconnection problems in the network. The network between MCDs 1554
involving wireless links 1556 represents an auxiliary or backup network, which is used where
there are problems with the primary network, or to run diagnostics on the primary network. The
MCDs 1554 are equipped to automatically switch from the primary network to the auxiliary
network when a problem arises on the primary network. This network re~ n-l~ncy allows the
MCDs 1554 to remain in constant communication with each other and with server 1550.
For example, a wired network on a communication link 1552 does not recognize
connection well, and may not immediately detect a loss of connectivity. MCDs 1554 utilize
wireless links 1556 to diagnose a lack of connection on the wired network 1552. For exarnple, an
MCD 1554 may activate its radio to send a test message to another component of the network,
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either another MCD 1554 or the server 1550, to test communication on the wired link 1552 by
sending a reply test message back to the inquiring MCD 1554. The test routine is preferably
implemented and controlled by the processing/interface circuitry 1510 in the communication
module 1502 (see FIG. 49) of the MCD 1554. If the reply communication test is not received,
the MCD 1554 will know that there is a problem on the primary network, and will inform other
MCDs 1554 to switch to the auxiliary network. The MCDs 1554 can continue to check the
primary network via wireless links 1556 until the primary network is back in service.
Some MCDs 1554 may be out of range to effect wireless cornmunication with server
1550 by a wireless link 1556. An out-of-range condition is determined according to the particular
10 communication and connection protocol implementP~l by MCDs 1554 and other network
components such as server 1550. In this situation, the out-of-range MCD 1554 sends its message,
along with an out-of-range condition indicator, to another MCD 1554 that is in cornmunication
with the server 1550, and the in-range MCD 1554 forwards the message on to the server.
Similarly, the server 1550 sends its messages inten~ed for the out-of-range MCD 1554 to an in-
range MCD 1554 to be forwarded over a wireless link 1556. The MCDs 1554 are capable of
automatically switching from the wired network to the wireless network and vice versa for each
communication attempt.
FIG. 24 is a diagram illustrating the use of portable data terminals according to thepresent invention lltili7ing both wired and wireless communication to access separate
20 subnetworks in an overall communication network. Specifically, a wired network includes wired
server 1600 and mobile computing devices (MCDs) 1606 connected by a wired communication
link 1604. MCDs 1606 are also part of a wireless network with wireless server 1602, and are
communicatively coupled to each other and the wireless server 1602 via wireless communication
links 1608. Wireless links l 608 may be radio frequency communication links, such as
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narrowband, direct sequence spread spectrum~ frequency hopping spread spectrum or other radio
technologies. Alternatively, wireless links 1608 may be infrared communication links, or other
wireless technologie$. In another embodiment, the wired server 1600 and the wired
communication links 1604 may utilize infrared communication technology, with the wireless
communication links 1608 being radio frequency links. The present invention contemplates
various combinations of communication technologies, all accommodated by communication
modules of MCDs 1606. The communication modules of MCDs 1606 include any number of
transceivers operable on any number of communication mediums, since the differences in their
O~ldLillg characteristics are isolated from the base module of the MCDs 1606 by a
communication processor. The MCDs 1606 are preferably able to automatically switch between
the wired and wireless networks, controlled primarily by a communication processor in their
communication modules.
Some MCDs 1606 may be out of range to effect wireless communication with wireless
server 1602 by a wireless link 1608. An out-of-range condition is determined according to the
particular communication and connection protocol implemented by MCDs 1606 and other
network components such as wireless server 1602. In this situation, the out-of-range MCD 1606
sends its message, along with an out-of-range condition indicator, to another MCD 1606 that is in
communication with the wireless server 1602, either over a wireless link 1608 or alternatively
over a wired link 1604 if both MCDs 1606 are constituents of a wired network. The in-range
MCD 1606 then forwards the message on to the wireless server 1602 over wireless link 1608.
Similarly, the wireless server 1602 sends its messages int~?n~ i for the out-of-range MCD 1606
to an in-range MCD 1606 to be forwarded over a wireless link 1608 or a wired link 1604, if both
MCDs are constituents of a wired network.
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FIG. 25a is a block diagram illustrating an embodiment of the present invention wherein a
wireless access device uses a dedicated control / busy channel to manage a plurality of modes of
communication with roaming termin~l~. Specifically, a wireless access device 1701 manages
communication in a cell of network with a plurality of wireless terminals, such as a wireless
5 ttorrnin~l 1703. The network may contain a plurality of other cells each managed by an associated
wireless access device to provide site or premises wide ubiquitous wireless coverage for the
plurality of stationary and roaming wireless terminals. As illustrated, for example, the network
may also contain wired communication links therein as provided, for example, by a wired
Ethernet backbone LAN 1705.
The wireless access device 1701 comprises control circuitry 1711, a m~ imnde
transceiver 1713, an Ethernet transceiver 1715 and an antenna 1717. The Ethernet transceiver
1715 supports communication between the backbone LAN 1705 and the control circuitry 1711.
Similarly, the multimode transceiver 1713 supports communication into a wireless network cell
to wireless devices within range such as the wireless termin~l 1703 via the ~nt~nn~ 1717. The
multimode transceiver 1713 is more fully described below in reference, for example, to FIG. 1 C.
A wireless t~rmin~l 1703 also comprises a multimode transceiver, a multimode
transceiver 1721, as well as an associated ~ntenn~ 1723 and conventional termin:~l circuitry 1725.
Using the multimode transceiver 1721 and associated ~ntenn~ 1723, the wireless termin~l 1703
comrnunicates with the wireless access device 1701 when it is within tr~n~mi~sion/reception
20 range.
The wireless access device 1701 selects (and may periodically reselect) one of a plurality
of communication modes and associated parameters of operation based on a variety of factors
mentioned previously such as recent success rate, RSSI, neighboring cell operation, etc.
However, when the wireless terminal 1723 roams within range of the wireless access device
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1701, the roaming terminal must identify the currently selected mode and associated parameters
being used by the wireless access device 1701 to m~int~in the cell's communication. Although
the wireless terminal 1703 could be configured to scan each available mode to identify the
currently selected mode and parameters, such efforts often prove time consuming.S Tn~te~l, the wireless terminal 1703 and wireless access device 1701 are preconfigured
with mode and parameter information that defines a default, busy / control channel. ~hus, upon
roaming into range ofthe wireless access device 1701, the wireless tcrmin~l 1703 first switches to
the busy / control channel by Opt;ld~ g the multimode transceiver 1721 according to the
preconfigured mode and parameters, and then begins li~t~ning Within a predefined maximum
time period thereafter, the wireless terminal 1703 will receive tr~n~mi.~ions from the wireless
access device 1701 identifying the currently selected communication channel mode and
associated parameters. The wireless access device 1701 periodically broadcasts such information
on the busy / control channel to capture terminç~l that happens to need communication channel
definitions (e.g., selected mode and parameters) to participate. The wireless terminal 1703
utilizes identified mode and associated parameter information to switch the multimode
transceiver 1721 over to the selected communication channel and begins participation thereon.
FIG. 25b is a drawing illustrating advantageous operation of the wireless access device of
FIG. 25a when configured to handle hidden terrnin~l conditions. In particular, each of wireless
terminals 1751 and 1753 is configured to only switch from the busy / control channel (having
predefined mode and associated parameters) to the communication channel (selected by a
wireless access device 1755) when there is a need for access to the communication channel and
the communication channei is clear (available). In this configuration, when no desire to
communicate is present, the terrnin~l~ 1751 and 1753 need only occasionally check the busy /
control channel to identify any out~t~n~ling messages or communication requests as tr~n~mitte-l
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by the wireless access device 1755. If either terminal 1751 or 1753 desires to participate on the
communication channel (to initiate cornmunication or to respond to awaiting messages or
- communication requests), that terminal need only monitor the busy / control channel long enough
to identify a clear communication channel before switching over to the cornmunication channel to
5 participate. As before, the wireless access device 1755 also periodically identifies the
communication channel mode and associated parameters as selected and reselected by the
wireless access device 1755.
To fully appreciate this process, first assume that the wireless te~nin~l~ 1751 and 1753
are not within range of the wireless access device 1755. Upon wandering within range of the
wireless access device 1755, the wireless termin~l 1751 lltili7itlg the predefined mode and
parameters begins li~tPning for tr~n~miscions on a busy / control channel. Within some time
period thereafter, the wireless access device 1755 participates on the busy / control channel to
transmit: 1) the currently selected communication channel definition (i.e., mode and parameters);
2) pending message and communication request indicators; and 3) current channel conditions.
After identifying a need to participate, the wireless termin~l 1751 awaits a tr~n~mi~ion from
wireless access device 1755 (on the busy / control channel) that the selected communication
channel is clear (not in use). When the channel is clear, the wireless terminal 1751 adopts the
selected communication channel definition and begins participating thereon.
Second, assume that, while the wireless termin~l 1751 is engaged in ongoing
communication with a computing device 1761 on a backbone LAN 1763 via the wireless access
device 1755, the wireless terminal 1753 comes within range of the wireless access device 1755
and desires to participate on the currently selected communication channel. The wireless t~rmin~l
1753 adapts itself to participates on the busy / control channel and identifies, in periodic
tr~n~mi~ions from the wireless access device 1755, that the communication channel is busy.
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Thus, the wireless terminal 1753 must monitor the busy / control channel to identify when the
communication channel is clear before adapting to the cornrnunication channel to participate.
This operation works whether or not the terminals 1751 and 1753 are within range of each
other. In particular, the terminal 1751, terminal 1753 and access device 1755 have tr~nsmis~ion
S ranges illustrated by dashed circles 1771, 1773 and 1755, respectively. Although both t~?rmin~ls
1751 and 1753 are within range of the access device 1755, neither are in range of each other and,
thus, are referred to as "hidden" from each other. The access device 1755 is within range of both
of the terminals 1751 and 1753. If the wireless termin~l 1753 attempted to transmit on the
communication channel while the terminal 1751 was transmitting, a collision would occur at the
wireless access device 1755. However, this is not the case because both of the terminals 1751
and 1753 must receive a communication channel clear indication on the busy / control channel
from the wireless access device 1755 that is in range of both, avoiding the hidden terminal
problem. When participation is completed on the communication channel, the terminals 1751
and 1753 readopt the busy / control channel definition (i.e., mode and associated parameters).
Participation by the wireless access device 1755 on the busy / control channel need only
be by transmitting, although receiving might also be employed in case the busy / control channel
is to be shared. Similarly, participation by the wireless termin~l.s 1751 and 1753 need only be by
receiving tr~n~missions, although tr~nsmitting might also be employed. In particular,
tr~nsmission might be employed by a wireless terminal on the busy / control channel if the
wireless t~rmin~l does not support the currently selected communication channel, i.e., does not
support the mode and associated parameters.
In addition, should the two terminals 1751 and 1753 be within range of each other and
desire to intercommunicate, the wireless access device 1755 will allocate an unused, non-
competing mode in which the two terminals can exchange inforrnation or data. In particular, one
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ofthe wireless termin~l.c 1751 and 1753 first attempts to establish an exchange by gaining access
to the communication channel (via busy / control channel monitoring). Once access has been
established, the wireless terminal, e.g., the t~rmin~l 1751 delivers a request for poll message
(RFP) to the wireless access device 1755 which identifies the amount of data or inforrnation to be
5 exchanged if known, the recipient or target (e.g., the terrninal 1753), and characteristics of the
data or information such as whether real time dedicated bandwidth is not needed, desired or
required. If the arnount of data or inforrnation to be exchanged is minim~l and requires no
dedicated bandwidth, the wireless access device 1755 will not bother ~L~ g to dedicate a
mode to the transceivers 1751 and 1753. Tn~te~, the wireless access device 1755 will merely
relay the inforrnation or data received from the terminal 1751 to the terminal 1753 and vice versa.
Otherwise, the wireless access device 1755 will examine its lookup table to see if the t~rmin~l
1753 ~ ,nlly participates within the network cell (i.e., within range) of the wireless access
device 1755. If the termin~l 1753 doesn't participate, the wireless access device 1755 will inforrn
the t~rmin~l 1751 and only proceed with relaying functionality (or sp~nning tree wireless routing,
for example) per confirm~ti~n by the tPrmin~l 1751. However, if the terminal 1753 does
participate, the wireless access device 1755 concludes that there is a good chance that the
termin~l~ 1751 and 1753 are within range of each other. Thus, the wireless access device 1755
attempts to identify an available and ~plopliate mode and associated parameters that may be
temporarily assigned to the terminals 1751 and 1753 for their communication exchange. The
20 wireless access device 1755 attempts to communicate such channel information to both of the
terrnin~l~ 1751 and 1753. Thereafter, as soon as either of the terrnin 1l ~ 1751 and 1753 receive the
information, the terrnin~l will immediately set their multimode radio to the ~le~ t~ci mode and
parameters, listen for polling messages from the other tPrminz~l, and, if no poll messages are
~let~ct~l, begin transmitting polling messages to the other tern in~l If a polling message is
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received, the communication exchange, such as dedicated voice bandwidth, will take place.
Afterwards, the terminals 1751 and 1753 inform the wireless access device 1755 that the
allocated channel is no longer needed and may be reallocated. Similarly, if a terminal polls for
the other for a predefined period of time on the allocated channel without receiving any response,
5 that terminal will inform the wireless access device 1755 of the failure, and the wireless access
device will free the allocated mode for reallocation or communication channel use.
FIG. 25c is a flow diagram illustrating the functionality of one embodiment of the
wireless access device of FIG. 25b in m~n~ging a communication channel using a second
channel, i.e., the busy / control channel. The wireless access device m~int~in~ ongoing
10 communication or otherwise waits in an idle state at a block 1781. If a predetermined time out
period (e.g., a B/C service time period) lapses while the access device is in an idle state as
indicated at a block 1782, the access device switches to the predefined mode and associated
parameters of the busy / control channel at a block 1783. At a block 1784, on the busy / control
channel, the access device transmits: 1) the currently selected communication channel definition
15 (mode and parameters); 2) channel status indications; and 3) pending message / communication
request indications. Thereafter, at a block 1785, the access device switches back to the selected
commnnic~fion channel mode and parameters, resets the B/C service time period (at a block
1786) and returns to the block 1781 to participate on the communication channel.
If, while participating on the selected communication channel at the block 1781, a request
20 for poll (RFP) tr~n~mi~ion is received from a wireless terminal as indicated at an event block
1787, the wireless access device responds by switching to the busy / control channel at a block
1788 to deliver cornmunication channel definition, channel "busy" indications and any pending
message / communication request indications at a block 1789. Although the busy indication may
only indicate that the selected communication channel is not available, it also indicates an
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estimated amount of time during which the channel will be busy. The wireless aecess deviee
derives this estimate from the overall data size to be transferred as determined from the data itself
~ or from a field in the RFP tr~n~mi~.cion, if known. This way, a waiting wireless transceiver may
go to sleep while an ongoing exchange is taking place and wake up when the exchange is
scheduled to have finished.
Thereafter, at a block 1790, the wireless access device switches back to the selected
communication channel mode and parameters, resets the B/C service time period (at a block
1791), transmits a Poll or Data message (whichever is ~lol-l;ate under the circllnn.ct~n~es) on
the communication channel at a block 1792, and returns to the block 1781 to await a Data or Ack
(acknowledge) message from a participating wireless transceiver. In particular, in response to an
RFP from a participating wireless deviee that has Data to deliver via the wireless access device,
the wireless aceess device delivers a Poll message at the block 1792 to the partieipant, p~ g
for the Data. Otherwise, if the RE~P indicates a desire by the participating wireless termin~l to
reeeive Data, the wireless aeeess deviee sends the Data at the bloek 1792. The Data sent at the
bloek 1792 may be of any length including dedicated bandwidth for an unknown duration. Thus,
if a wireless terminal listens for a period of time greater than the B/C service time period and
deteets no tr~n~mi~sion from the aecess device on the busy / eontrol ehannel, the wireless
tçrmin~l eoncludes that the selected communication channel is busy.
Alternately, data may be segmentec~ into Data paekets for tr~n.~mi~ion one paeket at a
time via the blocks 1781 and 1787-92. In this way, a li~t~ ning wireless Termin~l will can be sure
that it will receive a communieation ehannel broadcast via the blocks 1782-86 between eaeh Data
packet tr~n~mi~ion. Upon reeeipt, wireless termin~l~ may plaee their transeeivers in a sleep
mode until eaeh of the Data paekets of the data have been exehanged, and the eommunication
ehannel is elear.
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Upon receiving the data (or Data packet) or an acknowledge (ACK) message indicating
successful receipt of data (or a Data packet) as indicated at an event block 1793, the wireless
access device bro~clc~ctc a Poll, Ack or Clear message or sends data (or packets thereof) as proves
al.p~ol,liate at a block 1798. The access device then switches to the busy / channel at a block
5 1794 to transmit the currently selected communication channel definition, busy or clear
indications and pending messages / requests at a block 1794. Afterwards, the wireless access
device switches back to the communication channel at a block 1796, resets the B/C service time
period at a block 1797 and returns to the block 1781 to continue communication exchanges or
enter an idle state if the exchange is complete.
FIG. 26a is a block diagram illustrating an ~ltern~te embodiment of that shown in FIG.
25a wherein a wireless access device uses a separate transmitter for the dedicated control / busy
channel and a roaming terminal uses either a shared multimode transmitter or a multimode
transmitter and a separate busy / control channel receiver. In the previous emboriim~nt~ of FIGS.
25a-c, the wireless access device and wireless transceivers each used a multimode transceiver to
15 support participation on two wireless channels: the selected communication channel and the busy
/ control channel. As illustrated, this need not be the case. Instead, a wireless access device 1801
participates using two radios when communicating with a wireless transceiver 1803 (having only
a single multimode radio) and a wireless transceiver 1805 (having two radios). With a dual radio
configuration, participation on both channels may occur at the same time, increasing overall
20 perforrnance in many circl-m~t~nces.
In particular, a wireless access device 1801 comprises control circuitry 1811, an Ethernet
transceiver 1813, a busy / control transmitter 1815 and corresponding antenna 1817, and a
multimode transceiver 1819 and corresponding antenna 1821. Having separate radio units and
~nt~nn~, the wireless access device 1801 participates on: 1) a selected communication channel
=
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defined by mode and parameter information, servicing data exehanges in the communication
network cell; and 2) the busy / control channel defined by predetermined mode and parameter
information known to all wireless transmitters, controlling access to the seleeted eommunieation
ehannel. Sueh partieipation is often simultaneous, preventing a wireless terminal from having to
5 wait long on the busy / eontrol ehannel for a tr~n~mi~ion.
In one configuration, where hidden tPrmin~l~ prove to be of little concern, the wireless
t~rrnin~l~ 1803 and 1805 are only forced to wait on the busy / control channel until they receive
the selected communication channel definition. In another configuration, as better exemplified in
FIG. 26b which follows, all wireless termin~lc partieipate on the busy / eontrol ehannel exeept
10 when they have a need and gain aeeess to the seleeted eommunieation ehannel. In this latter
eonfiguration, when the wireless aeeess deviee 1801 is partieipating on the selected
eommunication channel with the wireless tPrmin~l 1805, for example, the wireless access device
1801 concurrently delivers communication channel definition, busy / clear status and message /
request indications on the busy / control channel. Such information can be repeatedly transmitted
15 at any time interval desired or may be tr~n~mittPd continuously.
Similarly, although a wireless transceiver may operate with a single multimode radio as
deseribed previously, it may also take advantage of multiple radios. Speeifieally, the wireless
transceiver 1803 eomprises tPrmin~l circuitry 1831 and only one radio, a multimode transceiver
1833. Thus, the ~,vireless transceiver 1803 is forced to time share participation on the busy /
20 control channel and the selected comrnunication channel - often all that is needed. However, the
wireless termin~l 1805 comprises terminal circuitry 1845 and two radios, a busy / control channel
receiver 1847 and a multimode transceiver 1849. As such, the wireless tPrmin~l 1805 may place
the multimode transeeiver 1849 in a low power state, and only powering up its busy / eontrol
-
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channel receiver 1847 to check in. Characteristics of the busy / control channel may be chosen to
permit significant overall power savings and simplicity in the design of the receiver 1847.
FIG. 26b is a drawing illustrating advantageous operation of the wireless access device of
FIG. 26a when configured to overcome the hidden terminal conditions. As with FIG. 25b7 the
range of a wireless access device 191 1 is defined by a dashed circle 1913. Similarly, the wireless
terminals 1915 and 1919 have ranges defined by dashed circles 1917 and 1921, respectively. The
wireless terminals 1915 and 1919 are out of range of each other. The wireless access device 191 1
is within range of each of the wireless terminals 1915 and 1919.
Unlike the wireless access device 1755 (of FIG. 25b), the wireless access device 1911
participates on both a busy / control channel and a selected communication channel
simultaneously. The wireless access device 1 9 11 delivers all communication channel
information either continuously or periodically on the busy / control channel, while idle or
servicing any wireless terminal on the communication channel. By doing so, the wireless access
device 1911 is free to set any length data segm~nt~ or none at all on a selected communication
channel, while delivering communication channel information as often as desired on the busy /
control channel. Thus, the busy / control channel and communication channel can be designed
for optimized performance without having to consider time sharing of a single channel or time
sharing a transceiver.
Thus, the busy / control channel can be designed to minimi7~ the lict~ning time of the
wireless terminals 1915 and 1919 to gain status information. Sleep periods of the wireless (and
often hand-held and portable) terminals 1915 and 1919 increased saving critical battery power.
Similarly, data segmentation can be set based solely on the conditions of the selected
communication channel, and not merely to guarantee the wireless access device 1911 a maximum
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interleaving time period during which the wireless access device 1911 will participate on the busy
- / control channel.
FIG. 26c is a flow diagram illustrating the functionality of one embodiment of the
wireless access device of FIG. 26b in m:~n~ging a communication channel using a control / busy
5 channel with dual radios. Specifically, a wireless access device waits in an idle state or is
engaged in ongoing communication on the selected communication channel at a block 1951. As
soon as a B/C time period lapses as indicated by an event block 1953, the wireless access device
branches to a block 1955 to transmit mode, parameter and status information regarding the
currently selected communication channel along with indicators of pending messages and
10 communication requests. Afterwards, the wireless access device resets the B/C time period at a
block 1957 and branches back to the block 1951 to continue servicing the selected
communication charmel or reenter an idle state. Thus, a preset (B/C time period) intervals, the
wireless access device delivers the selected communication channel information on the busy /
control channel. The B/C time period may be configured to either minimi7to tr~n.cmi.csit n
15 overhead or minimi7~? wireless termin~l lict~ning times. The B/C time peliod might also be set to
zero, causing the wireless access device to continuously transmit the selected control channel
inforrnation (i.e., the selected mode and parameters, busy or clear status, predicted duration of a
current exchange, and pending messages and communication requests). The B/C period is thus a
synchronous period. Thus, a maximum value of the B/C period (or an other comrnonly known
20 value) provides a wireless terminal with a guaranteed maximum listening time.
~ Although the B/C time interval may prove sufficient to communicate updates to the
selected communication charmel information, the wireless access device is also configured to
immediately identify any mode or parameter changes of the selected communication channel. In
particular, at a block 1961, if for any of a variety of reasons the wireless access device decides to
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switch the mode and/or pararneters of the cornmunication channel, the wireless access device
vectors to immediately deliver such information on the busy / control channel via the blocks 1955
and 1957. Similarly, the wireless access device may also be configured (as indicated by the
dashed lines) to respond to immediately report status changes such as whether a message or a
5 request for dedicated bandwidth has been received as indicated at a block 1963 and the blocks
1955 and 1957. Other immediate event servicing may also be added and similarly serviced.
Unlike the single radio (shared) embodiments previously mentioned, the wireless access
device services the block 1955 and 1957 no matter what the wireless access device is currently
engaged in on the selected communication channel.
FIG. 27 is a block diagram illustrating further embodiments of the present invention
wherein channel selection and operating parameters are delivered by a wireless access device on a
dedicated busy / control channel with or without multimode transceiver capabilities. In
particular, supporting a plurality of wireless termin~l~ such as a t~ n~l 2013, a wireless access
device 2011 , . ,~ i "~ two channels: a communication charmel and a busy / control channel as
previously described. To carry out such functionality, the wireless access device 2011 may
comprise control circuitry 2021, an Ethernet transceiver 2023 and either a single, configurable
transceiver 2025 (for operating on both the communication and busy / control channels) or a
single transceiver 2025 (for the communication channel which may have only limited if any
configuration capability) and a single tr~n~milter 2027 (for operating on the control channel).
With the single, configurable transceiver 2025, the wireless access device may operate
identically to that described in reference to FIGS. 25A-C. However, the configurable transceiver
2025 may not provide multimode operation, but only support multiple charmels operating in a
single mode. For example, the transceiver 2025 may only support the mode of channeli~d direct
sequence. Although only a single mode is available, the parameters such as (and defining)
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spreading codes, spreading code lengths, channel center frequency and channel bandwidth, for
example, alone, and without mode change, provide the wireless access device 2011 with the
ability to support a dedicated busy / control channel and provide a plurality of other channels for
m~ .g the cornmunication charmel.
.AIten~tively, the wireless access device 2011 may also comprise a dedicated busy /
control tr~n~mitter 2027. If it does, the wireless access device 2011 with a m~ imt~de transceiver
2025 would operate as detailed in reference to FIGS. 26A-C. If configured with a single mode
transceiver 2025 supporting only one channel, the wireless access device 2011 would still
",z~ t~ the communication and busy / control channels buy need only identify parameter and
pending messages and communication requests on the busy / control channel. Of course the busy
/ control channel would still solve the hidden t~rmin~l problems and provide the associated
benefits described above. Finally, with the tr~n~mitt~r 2027 supporting the busy / control
channel, the transceiver 2025 might support multiple con~ ication channels without
supporting multiple modes of operation. In such configurations, the wireless access device 2011
need not report mode change information on the busy / control channel. Reporting all other
information and aforementioned control would still take place.
The wireless tr~n~mitt~r 2013 could accommodate the same wireless configuration as
described in reference to the wireless access device 2011. Along with conventional termin~l
circuitry 2029, it may have a multimode or non-multimode, configurable or non-configurable
transceiver 2031. The transceiver 2031 might operate independently or utilize a supporting busy /
control receiver 2033. Lastly, although not necessary, the tr~n~milt~r 2027 and receiver 2033
might each constitute transceivers.
~ As is evident from the description that is provided above, the implementation of the present
invention can vary greatly depending upon the desired goal of the user. However, the
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scope of the present invention is intended to cover all variations and substitutions which are
and which may become apparent from the illustrative embodiment of the present invention
that is provided above, and the scope of the invention should be extended to the claimed
invention and its equivalents. It is to be understood that many variations and modifications
S may be effected without departing from the scope of the present disclosure.
