Note: Descriptions are shown in the official language in which they were submitted.
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Use of energy bursts for wireless networks
Background of the invention
1. Field of the Invention
This invention generally relates to communication networks and protocols, with
particular relevance to wireless networks, or other networks requiring minimal
turnaround
signaling time.
2. Discussion of the Related Art
Currently, communication networks are formed by interconnecting devices by
wire or cable, and having each device conform to a protocol for sending
messages along
these wires and cables. In some instances, a portion of such a network may be
implemented
as a wireless connection, employing radio or infrared frequency signals
between nodes. Such
wireless connections are point-to-point, having a single communications device
at each end,
each tuned to each other at a frequency different from other devices in the
same geographic
area.
A wireless network, on the other hand, is formed without physical connections
among the devices, employing, for example, radio frequency signals. Each
device on the
network is tuned to the same frequency, and each device conforms to a protocol
for sending
messages at this common frequency. The protocol may allow communication among
all the
devices in the network or the protocol may constrain each device to only
communicate with a
master device. Wireless networks offer a significant logistical advantage over
wired
networks, by obviating the need to run wires or cables to each device.
With increased availability of multimedia technologies, and the increased
demand for information access, the market potential for residence or business
based Local
Area Networks (LANs) is growing. The ease of installation and expansion of a
wireless
network is certain to create a large demand for wireless LANs. For example, a
central base
station may provide wireless services, including voice, video, and data, to
all the
communications devices in one's home, or a wireless base station may provide
for the
communication among ail the portable computers in an office, or all the
computers on a
campus. To be successful, however, the techniques and protocols employed in
these wireless
networks must not be significantly inferior to their wired network
equivalents.
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During the past decades, protocols have been developed for effectively and
efficiently managing the transfer of information within networks of
communicating
equipment. An underlying premise in the development of these network protocols
has been
that of a wired network infrastructure. In a wireless network, the assumptions
upon which
the wired network protocols were developed may no longer be valid. Although
most of the
existing protocols are functionally extensible to wireless networks, their
effectiveness and
efficiency may be adversely affected by the lack of a direct connection among
devices.
A common protocol employed for data communications in a wired network is a
bus structure with a "broadcast" protocol. Devices on the bus monitor the bus,
wait for a
quiet period, then transmit. Collisions occur when a second device, having
also waited for
the quiet period, simultaneously begins to transmit. The broadcast protocol
typically calls for
the devices to cease transmission in the event of a collision, and try again
at the next quiet
period. Repeated collisions are avoided by having the devices each randomly
change their
time of response from the start of the quiet period, so that they will no
longer respond
simultaneously. This broadcast protocol, as the name implies, has its roots in
radio
transmission, and is still widely used for voice wireless networks, such as CB
radios.
The broadcast protocol, however, is unsuitable for high speed data
communications on a wireless network because collision detection on a wireless
network is
time-consuming. On a wired network, the protocol typically calls for an active
assertion of
one logic level, but the passive assertion (i.e. a non-assertion of the active
level) of the other
level. Collisions are detectable at the transmitter by monitoring the bus
during the
transmission of a passive level. If an active level is detected during this
transmitter's
transmission of a passive level, it necessarily implies a collision. The wired
transmitter can
automatically retransmit the message at the next quiet period. A device
transmitting on a
wireless network, however, is unable to detect whether another device is
transmitting at the
same time. The device transmitting, if it monitors the transmission frequency,
will only
detect its own ta-ansmission, because its power level will be significantly
higher than that of a
remote transmitter. The intended receiver, however, being remote from both
transmitters,
typically receives a garbled message caused by the simultaneous transmission
by two
transmitters on the same frequency. Because collisions are likely to occur,
and the transmitter
has no means to detect these collisions, the wireless broadcast protocol
typically requires the
intended receiver to acknowledge (ACK) the receipt of each message. If it
doesn't receive
the message, or receives a garbled message, it doesn't transmit the
acknowledgement, or
transmits a Not-acknowledged (NAK) signal. If the transmitter fails to receive
an
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acknowledgement, it retransmits the prior message. The requirement for an
acknowledgement
from the receiver for each message in a wireless network has a compounding
adverse effect,
because the transmission of each acknowledgement can also cause collisions. As
traffic
density increases, the likelihood of collision increases exponentially because
of the increased
acknowledgement traffic, as well as the repeated transmissions with each
collision.
Polling network protocols, wherein a master device polls each of the other
devices for messages, are applicable to wireless networks. Such protocols,
however, are
inherently inefficient for networks with uneven traffic patterns. During the
polling process,
each device on the network is queried, and the polling of inactive devices
consumes time.
i0 Most polling protocols allow for the suspension of the polling of a device
after some period
of inactivity, to save time, but such protocols must also include a means for
the unpolled
device to notify the master device when it becomes active again. Often this
reactivation
notification is accomplished by providing an auxiliary connection to the
master device, for
example an interrupt Line common to all devices. The equivalent of an
additional auxiliary
IS connection in a wired network is an additional auxiliary frequency in a
wireless network.
Alternatively, a period of time can be set aside in each message period for a
notification
signal. The occurrence of a reactivation notification on this common line, or
during the
notification period, causes the master device to repoll all the devices on the
network to
determine which device is now active.
20 Thus, it is seen that the transformation of a wired network protocol to a
wireless network protocol typically requires additional time, or frequency, or
both. This
added demand of time or frequency is for the transfer of control information
for the
management of the wireless network. It is the purpose of this invention to
minimize the time
required to communicate such control information within a network. Although
the invention
25 presented is particularly applicable to wireless networks, the principles
embodied are equally
applicable to minimize the time required to transfer control information on a
wired network
as well.
Summary of the invention
30 Essentially, the invention describes a method for transmitting control
information in short energy bursts within a wireless network protocol.
The invention is best appreciated by noting that control information on a
network typically comprises short messages with minimal, albeit important,
information.
That is, control information is typically that which, on a wired network,
might be
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implemented on a single wire having one of two states. For
example, a "Request to Send" line might be provided on a
wired network for a device to notify the master device that
it has information to send. A "Clear to Send" line might be
provided to notify the device that transmission can begin,
or, the same "Request to Send" line could be employed by the
master to signal this "Clear to Send" message at a
subsequent time period. Similarly, an "Acknowledge" line
might also be provided. In each case, the information
content comprises a single bit of information: either the
device has, or has not, something to send; either the
message was received, or it was not received; etc. Contrary
to this single bit control information content, the data
content communicated in a wireless network is expected to
contain significantly more information. Employing the same
protocol for both data and control is inefficient in one or
the other protocols, or both.
This invention provides for a very efficient and
effective means for communicating single bit control
information messages within a wireless network without
necessarily limiting or affecting the protocol employed for
effective data transfer.
This efficient and effective communications means
is effected by synchronizing all devices to a master device,
and allocating a small unit of time, relative to the
synchronous period, to each device. The presence, or
absence, of energy at the network frequency during each
device's allocated time will signify the state of the one
bit of control information for that device. Depending on
the function of the control bit, the presence of energy in
the allocated time slot can be asserted by either the master
device or each of the other devices. As an extension of
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this basic design, multiple control bits can be accommodated
by multiple allocations of time, as required.
According to one aspect the present invention
provides a method for communicating a set of control signals
among communication devices operating in a network, wherein
each of said control signals within said set is associated
with each of said communication devices, said control
signals each only having a first and second state, said
method comprising: allocating, relative to a time reference,
intervals of time associated with each of said communication
devices; transmitting, via a first of said communication
devices, a synchronizing signal to all other communication
devices on said network; receiving, by each of said other
communication devices on said network, said synchronizing
signal from said first communication device; determining in
dependence upon said transmission and reception of said
synchronizing signal, said time reference; and,
transmitting, by any of said communication devices, a burst
of energy during the time period associated with each of
said devices, if said control signal associated with said
each device is a particular one of said first and second
state.
According to another aspect the present invention
provides a method for communicating a set of control signals
among communication devices operating in a network, wherein
each of said control signals within said set is associated
with each of said communication devices, said control
signals each having a first and second state, said method
comprising: allocating, relative to a time reference,
intervals of time associated with each of said communication
devices; transmitting, via a first of said communication
devices, a synchronizing signal to all other communication
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devices on said network; receiving, by each of said other
communication devices on said network, said synchronizing
signal from said first communication device; determining in
dependence upon said transmission and reception of said
synchronizing signal, said time reference; transmitting, by
any of said communication devices, a burst of energy during
the time period associated with each of said devices in
dependence upon if said control signal associated with said
each device is in one of said first and second state; and
transmitting a message from the communications device
associated with the time interval within which said energy
burst was transmitted.
According to yet another aspect the present
invention provides a method for communicating a set of
control signals among communication devices operating in a
network, wherein each of said control signals within said
set is associated with each of said communication devices,
said control signals each having a first and second state,
said method comprising: allocating, relative to a time
reference, intervals of time associated with each of said
communication devices; transmitting, via a first of said
communication devices, a synchronizing signal to all other
communication devices on said network; receiving, by each of
said other communication devices on said network, said
synchronizing signal from said first communication device;
determining in dependence upon said transmission and
reception of said synchronizing signal, said time reference;
transmitting, by any of said communication devices, a burst
of energy during the time period associated with each of
said devices in dependence upon if said control signal
associated with said each device is in one of said first and
second state; and transmitting a message to the
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communications device associated with the time interval
within which said energy burst was transmitted.
According to still another aspect the present
invention provides a base station for communicating a set of
control signals to communication devices operating in a
network, wherein each of said control signals within said
set is associated with each of said communication devices,
said control signals each only having one of a first and
second state, said base station comprising: means for
transmitting a synchronizing signal to all of said
communication devices on said network, said synchronizing
signal establishing a time reference common to all
communication devices on said network, means for
delineating, relative to said time reference, intervals of
time associated with each of said communication devices,
means for transmitting a burst of energy during the time
interval associated with each of said communication devices
in dependence upon whether said control signal associated
with said each communication device is in a particular one
of said first and second state.
According to yet another aspect the present
invention provides a base station for communicating a set of
control signals to communication devices operating in a
network, wherein each of said control signals within said
set is associated with each of said communication devices,
said control signals each having a first and second state,
said base station comprising: means for transmitting a
synchronizing signal to all of said communication devices on
said network, said synchronizing signal establishing a time
reference common to all communication devices on said
network, means for delineating, relative to said time
reference, intervals of time associated with each of said
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communication devices, means for transmitting a burst of
energy during the time interval associated with each of said
communication devices in dependence upon if said control
signal associated with said each communication device is in
one of said first and second state, and means for
transmitting messages to each communication device in
dependence on said transmission of said energy burst.
According to still another aspect the present
invention provides a base station for communicating a set of
control signals to communication devices operating in a
network, wherein each of said control signals within said
set is associated with each of said communication devices,
said control signals each having a first and second state,
said base station comprising: means for transmitting a
synchronizing signal to all of said communication devices on
said network, said synchronizing signal establishing a time
reference common to all communication devices on said
network, means for delineating, relative to said time
reference, intervals of time associated with each of said
communication devices, means for transmitting a burst of
energy during the time interval associated with each of said
communication devices in dependence upon if said control
signal associated with said each communication device is in
one of said first and second state, and means for detecting
a second burst of energy from each of said communication
devices.
According to yet another aspect the present
invention provides a remote station for receiving a control
signal from a base station operating in a network, wherein
said control signal is associated with said remote station
and said control signal only having one of a first and
second state, said remote station comprising: means for
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receiving a synchronizing signal from said base station,
means for delineating, relative to a synchronizing signal,
an interval of time allocated to said remote station for
reception of said control signal, means for detecting a
burst of energy during said allocated time interval, and
means for determining if said control signal is in a
particular one of said first and second state if said burst
of energy was detected.
According to still another aspect the present
invention provides a remote station for receiving a control
signal from a base station operating in a network, wherein
said control signal is associated with said remote station,
said control signal having one of a first and second state,
said remote station comprising: means for receiving a
synchronizing signal from said base station, means for
delineating, relative to a synchronizing signal, an interval
of time allocated to said remote station for reception of
said control signal, means for detecting a burst of energy
during said allocated time interval, means for determining
if said control signal is in one of said first and second
state if said burst of energy was detected, and means to
receive messages from said base station, in dependence upon
the detection of said burst of energy.
According to yet another aspect the present
invention provides a communications device for communicating
with one or more communication stations comprising: means to
delineate a set of time intervals following a known time
reference, each of said time intervals within said set being
associated with each of said communication stations, means
for receiving a synchronizing signal from a first
communication device, means for determining, by said
reception of said synchronizing signal, said time reference,
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and, means for transmitting a burst of energy during the
time interval associated with a target communication
station.
According to still another aspect the present
invention provides a communications device for communicating
messages with one or more communication stations comprising:
means to delineate a first set of time intervals following a
known time reference, each of said time intervals within
said first set being associated with each of said
communication stations, means to delineate a second set of
time intervals following said known time reference, each of
said time intervals within said second set being associated
with each of said communication stations, means to transmit
a first burst of energy during the time interval of the
first set associated with a target communication station in
dependence upon whether a first message is to be sent to
said target communication station, means to transmit said
first message to said target communication station, means to
detect a second burst of energy from a source communication
station during the time interval of the second set which is
associated with said source communication station, means to
receive said second message from said source communication
station in dependence upon whether said second burst of
energy was detected.
Brief description of the drawings
FIG. 1 shows a network of wireless devices,
FIG. 2 shows a timing diagram for receiving or
transmitting control bits in accordance with this invention.
FIG. 3 shows a circuit diagram for receiving and
transmitting control bits in accordance with this invention.
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FIG. 4 shows a timing diagram for receiving and
transmitting control bits and messages on the same
frequency, or wire, in accordance with this invention.
FIG. 5 shows a timing diagram for communicating
multiple messages on the same frequency, or wire, in
accordance with this invention.
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Detailed description of the preferred embodiments of the invention
Figure 1 shows a wireless network, comprised of mobile stations I01 through
105, and a base station 110. For ease of understanding, one frequency for
sending
information to the base station, F1, and one frequency for receiving
information from the
base station, F2, is shown, although alternative embodiments will be further
disclose the use
of the same frequency for both transmission and reception. The mobile station
equipment can
either be discrete, or incorporated directly into the destination device, such
as a telephone.
Each mobile station on this network is assigned an address. For simplicity,
address I is
assigned to mobile station 101, address 2 to station 102, etc. The assignment
of addresses
can be established either by setting switches on each device, or by
communicating messages
which instruct the device to change its internal address. Also, additional
devices can be
added to the network, or existing devices deleted, through the use of these
address assigning
and changing messages. Techniques are commonly known for such address
initialization and
are not presented herein.
Because each mobile station will be transmitting on the same frequency to the
base station, a protocol must be established to manage communications on this
network.
Figure 2 shows a protocol for transmitting to a base station in a wireless
network in accordance with this invention. At the first period of time 250,
the base station
I 10 will transmit a synchronizing pattern, which will be used by each station
to establish a
common time reference 200. The second period of time 260 is subdivided into
sub time
intervals 201 through 205. These time intervals are assigned to each mobile
station 101
through 105, corresponding to their addresses 1 through 5. These time
intervals are, for
efficiency, of very short duration, and each has a fixed relationship to the
time 200
established by the master station. If a mobile station has a message to
transmit to the base
station, it will transmit a burst of energy at the network frequency during
its assigned time
slot. That is, if mobile station 103 has information to transmit, it will
transmit a burst of
energy during time interval 203, informing the base station that the mobile
station with
address 3 has information to send. During time period 270, data transfer can
be
accomplished, using the protocol established for such data transfer,
independent of this
energy burst signalling protocol.
This particular embodiment is particularly well suited to a network with a
relative ranking of mobile stations, wherein messages from address 1 have
priority over
messages from address 2, address 2 messages have priority over address 3
messages, etc. In
such a network, the protocol could require that a mobile station not transmit
an energy burst
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if an energy burst is detected preceding its assigned time slot. That is, if
address 2 sends an
energy burst, addresses 3 through 5 would not be allowed to send an energy
burst. In so
doing, the possibility of collision is eliminated, and the station which sent
the energy burst
would be free to send its data in the immediately following time period 270.
The receiving
base station would know that the data came from the address corresponding to
the time
interval of the detected energy burst.
This same protocol could be employed by the base station for transmitting
information to the mobile stations. The base station 110 will transmit a
synchronization
pattern to the mobile stations, on the frequency assigned for receiving
information from the
base station, during time period 250. During time period 260, the base station
will transmit
an energy burst during the time interval assigned to the station intended to
receive the
message. The mobile station which corresponds to the time interval in which
the energy burst
occurred would thus be alerted to receive the subsequent data, transmitted by
the base station
during time period 270. Note also that this protocol is particularly well
suited for messages
intended for more than one mobile station. An energy burst for each of the
intended stations
can be transmitted during period 260, so that each are alerted to receive the
subsequent data
transmitted during period 270.
This protocol is similar in concept to protocols which include the source
and/or
destination addresses within the message data, but offers significant
advantages through the
use of energy bursts, as herein described. An energy burst, as the name
implies, is a short
burst of energy transmitted at the assigned radio frequency. Contrary to a
data signal, this
energy burst has a very easy to satisfy criteria. Existing digital devices are
very well suited
for precise time measurements, particularly with reference to a periodically
asserted
synchronization pattern. Thus, specifying time as the relevant criteria,
rather than content,
allows for a very cost effective solution. Rather than specifying content-
related criteria, as
must be done for data signals, the critical specification is merely when the
signal occurs, and
not its content.
Figure 3 shows a device for the reception or transmission of control
information
through the use of energy bursts at specified times, in accordance with this
invention. In
figure 3a, the energy pulse detector 302 is shown separate from the data
demodulator 301,
exemplifying the fact that energy burst detection does not require the signal
processing
typically applied for data reception. The receiver 300 receives a signal from,
for example, a
base station 110. A timing generator 303 provides a means for detecting the
sync signal 250
and establishing the time reference 200 of figure 2. The timing generator 303
produces a
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pulse at time 200 on Ref 350. This ref signal resets the RS latch 3I3, and is
also input to
delay elements 310 and 311. The delay element 3I0 produces a pulse 380 after a
predetermined time from receipt of the pulse on Ref 350. The predetermined
time is
determined by the address assigned to each device, so as to correspond, in
time, with one of
the time intervals 20I through 205 shown in figure 2. This pulse 380 is input
to the And gate
312. Also input to tile And gate 312 is the output of the detector 302. If an
energy pulse is
detected during the period assigned to this device, as signalled by pulse 380,
the output of
the And gate 312 sefs the RS Latch 313. Through the establishment of specific
time intervals
for each addressed device, the output of the RS Latch 3I3, therefore
corresponds to the
detection of a control signal from the base station intended for this device.
In this example embodiment, the detection of this control signal informs the
device that the subsequent message from the base station 100 is intended for
this device. The
delay element 311 generates a signal 381 after a predetermined time from
receipt of the pulse
on Ref 350. This signal 381 is asserted for the duration of message time
period 270. The
And gate 3 i4 thus enables the gate 315 during the message time period 270 if
and only if the
RS Latch had been set, as described above, by the receipt of an energy burst
during the
assigned time period.
Figure 3b shows a control device for generating an energy burst from a remote
transmitter in accordance with this invention. Items having the same function
as described in
figure 3a have the same reference numerals. As presented above, the reference
signal 350
will contain a pulse at a time reference 200 established by the base station's
transmission of a
sync signal 250. The RS Latch 313 will be reset by the occurrence of the pulse
on reference
signal 350. The delay element 310 will produce a pulse during the device's
assigned time
interval, one of 201 through 205. Figure 3b contains an additional latch 330.
This latch 330
is used to signal the occurrence of an energy burst prior to the time
allocated for this device.
The latch 330 is set by the reference signal 350. If an energy pulse is
detected by detector
302, the latch 330 is reset. Thus, at the time of the pulse 380, the output of
the latch 330
will be asserted if and only if no energy bursts have been detected since the
latch was set by
the reference pulse. The time interval pulse 380, the output of latch 330, and
a control signal
382 are input to And gate 312. The And gate 312 will set the latch 313 during
the time
period 380 only if the latch 330 is set, signalling that no other transmitter
sent an energy
burst before time 380, and control signal 382 is asserted. The output of And
gate 312 is also
provided to the transmitter 337 as signal 385. Upon receipt of an asserted
signal 385, the
transmitter 337 will be enabled, thereby sending an energy burst. The detector
302 will
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subsequently detect this burst, which will cause latch 330 to reset, which
will cause the And
gate to deassert signal 385, thereby terminating the transmission of the
energy burst.
Alternatively, if the receiver 300 is disabled during transmission, the signal
385 will be
deasserted at the end of timing interval pulse 380.
In this example embodiment, the control signal 382 is asserted whenever the
device has a message to transmit, and the transmission of this message is
effected after
sending the above described energy burst. Messages are queued in transmit
buffer 335. Upon
receipt of a message, buffer 335 asserts the control signal 382. This control
signal 382
causes the generation of an energy burst during the time period assigned to
this device, as
described above. The enabling of the transmission of the energy burst also
sets latch 3I3, the
output of which is input to And gate 3I4. The delay element 3I1 asserts a
signal 381 during
the message period 270. If latch 3I3 is set during this period, the And gate
3I4 asserts an
enabling signal to the gate 336, which effects the transmission of the
contents of the transmit
buffer 335. If there are no additional messages queued, the transmit buffer
335 deasserts the
control signal 382, thereby inhibiting the subsequent transmission of an
energy burst.
The example embodiments in figure 3 demonstrate the use of energy bursts for
receiving and transmitting control signals which subsequently control the
reception and
transmission of messages. The same, or similar, logic could be employed to
receive or
transmit energy bursts at the appropriate time intervals corresponding to
other control signals
as well. Also, the common elements of figures 3a and 3b can be combined, and
the
embodiment shown could be implemented and executed by a software program, or a
combination of hardware and software, as would be evident to one skilled in
the art.
Note that the energy burst transmission and reception can be accomplished
without the data equalization techniques normally employed for reliable, error
free, data
transmission. The automatic gain control, signal pre- and post- conditioning,
error
correction, and other techniques required to reliably determine which of two
or more values
have been received during data transmission, are not required to determine
whether or not a
burst of energy occurred at a particular time.
The embodiment presented thus far required a separate transmit and receive
frequency relative to the base station, as well as the generation of a
synchronizing pattern by
the base station, and synchronization at the mobile stations, at each of these
frequencies.
Figure 4 shows a protocol which eliminates this redundant process. As shown,
at time period
450, the base station transmits a synchronizing pattern, on the one frequency
used for both
transmission and reception. This synchronizing pattern establishes a time
reference 400.
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Time period 460 contains time intervals 461 through 465, corresponding to
mobile station
addresses 1 through 5. During time period 460, the base station transmits one
or more
energy bursts during the time interval corresponding to the intended receiving
mobile
station(s). The receipt of an energy burst during the assigned time interval
alerts the
corresponding mobile station to receive the subsequent data, transmitted by
the base station
during time period 470. Time period 480 is also partitioned into time periods
481 through
485, corresponding to mobile station addresses 1 through 5. If a mobile
station has data to
transmit, it transmits an energy burst during its assigned time interval,
relative to time
reference 400. As previously described, the protocol for transmitting to the
base station
would dictate that a mobile station not transmit an energy burst if it detects
an energy burst
in time intervals prior to its assigned interval. The mobile station which
transmits the energy
burst would then subsequently transmits its data during time period 490.
The prior embodiments demonstrate the use of energy burst transmissions for
predominantly single addressee communications. That is, within the time frames
previously
described, one remote station transmits data to the base station, and, except
in the case of
multiple addressees for the same message, the base station transmits data to
one remote
station. In such protocols, there is one energy burst period per message, and,
in a network
with heavy traffic, such a protocol may be inefficient.
Figure 5 shows an embodiment of the subject invention, particularly well
suited
for networks with continually heavy traffic patterns. In this embodiment, the
periods 570 and
590 following the energy burst periods 560 and 580 contain a variable number
of message
transfer periods. For example, if the base station has messages for three
remote stations,
three message transfer periods would follow the base stations energy burst
period. The base
station would assert an energy burst at the time periods assigned to each of
the remote
stations, and transmit the messages in the same order as the asserted energy
bursts. Figure 5
shows, for example, that remote stations 2, 3, and 5 have messages being sent
from the base
station, as signalled by energy bursts at time periods 502, 503, and 505.
Remote station 2's
message will be transmitted first, at message transfer period 571; next,
remote station 3's
message, at message transfer period 572, followed by remote station 5's
message, at period
573. Each remote station will note whether its assigned time period contains
an energy burst,
and also how many energy bursts, for other remote stations, have preceded its
burst. In the
example given, station 2 will note that it received the first burst, and will
therefore know that
its message will be the first message from the base station. Similarly,
station 3 would note
that it received the second burst, and hence its message is the second
message. Station 5
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would similarly determine that its message is the third message. All stations
in this
embodiment will note how many messages are being transmitted, by noting how
many
energy burst are transmitted in period 560. Thus, the stations will know when
the time
period 580 begins, relative to the time reference 500. In this embodiment, the
remote stations
S are not prohibited from asserting an energy burst when another remote
station has also
asserted an energy burst. If two remote stations have messages to send to the
base station,
two message transfer periods will follow the remote station energy burst
period. Each remote
station which has a message to send asserts an energy burst during its
assigned time slot in
period 580. Each remote station also notes how many other remote stations have
transmitted
IO an energy burst before them. If a particular remote station is the first
station to transmit an
energy burst, it sends its message in the first message slot 29I of period
290. If another
remote station notes that one energy burst has preceded its energy burst, it
sends its message
in the second message slot 292.
Shown in figure 5, stations I and 3 have asserted energy bursts in time slots
15 581 and 583. Station 1 transmits its message in the first message time slot
591. Station 3,
having noted that one energy burst 581 has preceded its energy burst 583,
transmits its
message in the second message time slot 592. The base station, knowing that
only two
remote stations had messages to send, can immediately recommence the process
by
transmitting the synchronizing sequence for the next set of messages. Note
that if there are
20 no messages from the remote stations, the energy burst time period 580 will
not contain any
energy bursts and the synchronizing sequence 550 can commence immediately
after the
energy burst period 580. Similarly, if the base station has no messages to
send, energy burst
period 580 can begin immediately after energy burst period 560.
It is apparent in these embodiments that the format of the message transfer
25 protocol is independent of the energy burst timing protocol. This invention
is not limited to
the transfer protocols presented herein. For added reliability, for example,
explicit addressing
could be included within each message. The use of energy bursts in this
protocol would serve
the purpose of collision avoidance, by allocating the message transfer time in
accordance
with the occurrence of energy bursts, but would not be exclusively relied upon
to determine
30 the addressees. In a similar manner, the energy burst timing protocol could
be employed in a
network without an explicit base station. Each station could listen to all
transmitted
messages, and select those messages which contained its assigned address,
either as an
explicit address, or as determined by the energy burst time interval. The
energy burst timing
protocol would be established by having one station transmit the timing
signal, as in a
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11
distributed synchronization network, wherein the synchronizing signal is
transmitted by any
station which initiates the communication.
It is apparent that the use of the energy burst timing protocol disclosed is
not
limited to its use as a "request to send" signal as presented above. The
energy burst timing
protocol could be employed to signal other events as well. For example, an
intervening
period could be inserted between the aforementioned "request to send" energy
burst period
and the message transfer period. In this intervening period, the intended
recipients could
utilize energy bursts to signal a corresponding "clear to send" signal.
It is also apparent that the use of an energy burst timing protocol as
disclosed
herein is not limited to networks, nor to wireless networks in particular. In
a point to point
communications systems, wherein the possibility of collision does not exist,
energy bursts
may be used exclusively for acknowledgements. In a wired network, energy burst
periods
could be employed to eliminate signalling wires, by adding one or more burst
periods to the
message transferring wire.
IS Although the primary application of the energy burst timing protocol in
accordance with this invention is for single bit information, such as yes/no
signals, mufti-bit
information can be accommodated as well. The protocol may call for a priority
signal,
wherein the transmitter assigns a priority, for example from 1 to 3, for each
message. Two
time periods per remote station could be allocated in the energy burst period,
and two bits
could be transmitted as follows: 00 for no message, O1 for a Priority I
message, IO for a
Priority 2 message, 11 for a Priority 3 message.
The foregoing merely illustrates the principles of the invention. It will thus
be
appreciated that those skilled in the art will be able to devise various
arrangements which,
although not explicitly described or shown herein, embody the principles of
the invention and
are thus within its spirit and scope.
