Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
sP~CIEICATIQ~
This application is a Continuation-in-Part of
Application Serial No. 685,831, filed April 16, 1991.
Backround of the Inve~tion
This invention relates in general to a
communications interface device whereby a facsimile
transceiver is enabled to send and receive copies of
documents over a two-way voice radio transceiver; and more
particularly to a communications interface device which
lo contains electrical interface means which, when connec~ed to
a standard facsimile transceiver, simulate a two-wire public
switched telephone line; which contains facsimile data
modulator and demodulator means for converting facsimile
image data into audible tones, and audi~le tone~ into
facsimile image data; which contains destination addres ing
means to allow a user to selectively transmit a facsimile
message to any one of multiple compatible devices on the
same channel; which provides error detection and correction
means which assure error-free communications over the radio
channel; which contains radio interface means which,
connected to a voice radio, simulate an external microphone,
talk switch, and spea~er, and wherein the data transmlssion
speed is automatically optlmized ~or existing radio channel
conditions.
Facsimile transceivers have commonly been used to
send and receive copies o~ written documents over two-wire
voice telephone lines. Suc:h a facsimile transceiver
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contains station selection (dialing) means to place calls
over the public switched voice telephone network; answering
means to detect ringing signals from the telephone central
office; and electrical coupling means to send and receive
analog electrical signals in the voice frequency range, at
signal levels and frequencies compatible with the voice
telephone network. Such a facsimile transceiver also
contains optoelectronic document scanning means, which, for
each horizontal scan line of a pr~determ~ned height across
the document to be copied, produce a string of digital data,
where, for example, a binary one digit represents a black
picture element of a predetermined size, and a binary zero
digit represents a white picture element. Such a
transceiver also contains modulation means which, for
transmission, convert digital ~mage data into ~ones in the
voice frequency range, as well as demodulation means which,
for reception, convert audio tones into binary image data.
Such a facsimile transceiver also contains hard-copy
printing means, such as a thermal print mechanism which -
20 ~ makes images by selectively heatinq elements on a thermal
print head in contact with thermally-sensitive paper, or a
laser print mechanism which produces images on bond paper
using a xerographic process, or similar print mechanism;
such printing means converting the received digital image
data into a printed document, and reproducing a copy of the
transmitted document. Such facsimile transceiver also
includes a timing and control means which control and
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coordinate the above elements in accordance with procedures
and protocols established by telephone authorities and by
international telecommun~cations standards bodies~
There are many applications where it is desirable
to send and recelve documents using such a facsimile
transceiver, but where telephone lines are not available.
Examples include mobile vehicles, temporary work locations,
and remote and undeveloped areas. one such radio data
system is the facsimile-radiQ communication sy~tem described
lo in related U.S. Patent Application No. 685,R31, ~iled Apr~l
16, 1991. As set forth in detail in this patent
application, the facsimile radio communication~ interface
device enables a facsimile transceiver to send and receive
copies of documents over a two-way voice radio transceiver,
and includes electrical interface means which, when
connected to a standard facsimile transceiver, simulate a
two-wire public switched telephone line; facsimile data
modulator and demodulator means for converting facsimile
image data into audible tones, and audible tones into
facsimile image data; destination addressing means to allow
a user to selectively transmit a facsimile message to any
one of multiple ~ompati~le devices on the same radio
channel; error detection and correction means which assure
error-free communications over ths radio channel; and radio
inter~ace means which, connected to a voice radio, simulate
an external microphone, talk switch, and speaker.
High data transmission speeds are desirable in any
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system where digital in~ormation is transmitted over radio.
High transmission speeds are especially desirable when large
amounts of data must be communicated, as in facsimile-radio
communication systems. Facsimile images are data-intensive,
typically requiring as many as 262,000 bits (binary digits)
or more to be transmitted to reproduce each 8-l/2 by 11 inch
page.
It would be ideal for a radio data system to be
able to transmit all data at tha ~astest availablQ speed,
for example, 9600 bps (bits per second). Unfortunately, in
practice higher data speeds may be real~zable only when
radio propagation conditions are very good. When th~
received radio signal strength is weak, or when the radio
channel is noisy, it may be necessary to us~ a lower ~peed.
, It is known to those familiar with the art of
digital data communications that the BER (bi~ error rate),
or the probability that a given binary digit will be
received in error, tends to increase as the noise level on
the communications channel increases relative to the
strength of the signal. For example, one common method of
sending digital data by radio is to encode binary digits in
the form of audible tones in the voice frequency spectrum of
from 300 to 3400 Hz (Hertz, or cycles per second), and then
to transmit these tones over the radio channel. Encoding
schemes for sending digital data may include, for example,
FSK (frequency shift keying~, whereby binary ls and Os are
sent as audio tones with two distinct frequencies; MSK
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(minimum shift keylng), a variation of FS~ in which the
frequency shift is minimized to reduce RF channel bandwldth;
PSK (phase shift keying), whereby binary dlgits are encoded
as changes in the phase of an audio frequency tone; or QAM
(quadrature amplitude modulation); whereby binary dig~ts are
encoded using both the phase and the amplitude of an audio
frequency tone; and other encoding techniques may also be
employed.
The relationship of BER to communications channel
noise level may be understood by the example of one
commercially available modem integrated circuit, which
supports data speeds of 9600, 7200, 4800, 2400, and 300 bps,
as follows. For example, assume a desired 3ER of 10-4 ~.
(i/lO,ooO), or an error rate wh2reby a single bit error is
probable for every 10,000 bits. To achieve a BER of 10-4 at
9600 bps for this modem circuit, the SNR tsignal to noise
ratio, the quotient of thP power of the received audio
signal toncs, representing the transmitted binary digits,
divided by the power of the noise component of the received
audio signal, caused primarily by no~se on the :~
communications channel~ must be 21 dB (decibels). By
reducing the data speed from 9600 bps, this modem device can
maintain the same desired 10-4 BER level in the presence of
increasingly unfavorable communications conditions :
~decreasing SNR), as follows:
* At 9600 bps, reguires 21 dB SNR, or noise -
voltage of up to 9% of signal voltage.
* At 7200 bps, requires 17 dB SNR, or noise
voltage o~ up to 14% of signal voltaqe.
* At 4~00 bps, requir~s 15 dB SNX, or noise
voltage of up to 18% of signal voltage.
* At 2400 bps, requires 8 dB SNR, or noise
voltage of up to 40% of signal voltage.
* At 300 ~ps, requires 5 dB S~R, or noise
voltage of up to 56% of signal voltage.
While these specific figures on noise sensitivity
would not apply exactly to other specific modem device~, it
is generally the case that by decreasing data ~peed (ln
bps~, a greater effective immunity to nolse ~an b~ achleved.
Requiring users to select a s~ngle high fixed
speed (such as 9600 bps) might limit transmissions to only
those situations where very good reception Gan be expected.
On the other hand, requiring users to select a single,
relatively lower fixed speed (such as 2400 bps) might
needlessly slow down transmission speeds when higher speeds
are often possible.
To provide the greatest flexibility, it is
desirable to allow devices to communicate at multiple
speeds-- for example; at 9600l 7200S 4800, 2400, and 300
bps-- on an adaptive basis. The devices should
automatically use the highest speed that produces acceptable
error ratesO For example, the criterion might be
established that the link should provide a specified modem
BER, for example, 10-4. Two units close together with good
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radio propagation might be able to communicate at 9600 bps.
Two more distant stations may have to use a lower speed, for
example, to 2400 bps.
To avoid channel congestion and assure reasonable
network message throughput in a multi-user radio data
network, it is desirable to design the communication system
such that packets are received free of errors most of the
time. Otherwise, an excessive proportion of the
transmission time available on the network will be d~dicated
10 to parket retransmissions, using an er~or d~tectlon and
correction scheme such as that described for facsimile-radio
communication systems in related Patent Applicatlon 685,831.
For example, assume that the BER experienced under
prevailing radio propagation characteristics is 10-4 (1 in
15 10,000), and that information i~ transmitted in packets
containing 1,024 bits. Thls BER coul~ be expected to result
in a faulty packet about once every 10 packets (10,240
bits). Approximately 10% of the packets would have to be
retransmittedO A 10% packet retransmission rate is
20 tolerable, but if pac~et retransmission increases
significantly beyond that ratio, channel throughput would be
degraded to the point that users could not expect prompt and
reliable communications.
When communicating over the telephone networ~,
25 facsimile transceivers automatically change their data speed
to adapt to noise levels on the telephone lines. They
implement a standard procedure according to a protocol
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established by international communications standards. The
facsimile connecti~n starts at the relatively low speed of
300 bps, during which the sending and receiving transceivers
exchange data concerning their respective capab~lities,
including the maximum data speed at which each is capable of
communicating. Assu~ing that both fac~imile transceivers
have signaled that they can communicate at a 9600 bps rate,
the originating party then sends a trainlng sequence ta
predetermined data pattern) at 9600 bps; then drops back to
300 bps and listens. The answering party sends back a 300
bps message which either positively acknowledgas rsception
of the training se~uence at 9600 bps -- in wh~ ch case both
facsimile transceiver~ switch to 9600 ~ps and data
communications starts -- or else negatively acknowledges
training -- in which case the originator selects the next
lower available speed (typically 7200 bps), and sends a
training sequence at this lower speed -- repeating until
training is successful. If training is unsuccessful at all
available data speeds, the call cannot be completed.
In a voice telephone system, the switched
telephone network provides a separate circuit path for each
voi e connection, 50 that simultaneous conversations do not
mutually interfere. However, in a radio environment,
multiple devices share-the same radio channel, to allow
connectivity among many users, and to optimize usage of
radio frequency spectrum. Because more than two data modem
devices may often be activls at the same time, thus
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interspersing packets, the use of multiple data speeds may
give rise to transmission errors.
It is desirable in any network of communications
devices for each device to continually monitor the
communications channel, so as provide orderly access to the
channel, and provide suitable responses to all signals sent
to that device. In a network of multiple radio data units
where transmissions may occur at varying data speeds,
traffic on the radio channel may be unintelligible as among
units which have selected varying data speeds. Owing to the
complexity of the data demodulation processes involved,
practical data demodulator circuitq can success~ully receive
only one data speed at a time. ~he unit must be set to any
one of (for example) 300, 2400, 4800, 7200, or 9600 bp~, and
thereafter can decode only that data speed, until reset.
Suppose a network of three radio data communications units:
#1, #2, and #3. Units #1 and #2 are "connected" at 4800
bps; that is, a previous exchange of packets between units
#1 and #2 has been made, resulting in a virtual "connection"
over the radio, at 4800 bps. While this connection is in
place, unit #3 attempts to "connect" to unit #2 by sending a
9600 bps connection request packet, inserted into a time gap
in packets exchanged between units #1 and #2. ~n this
event, unit #2 should detect the connection request packet
from unit #3, and return a busy packet to unit ~3 to
indicate that it cannot currently make a connection. If no
provision were made to accommGdate the differing data
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speeds, then the g600 bps connection request packet could
not readily be detected; no busy packet would be returned;
and the operator of unit #3 would have no way to distinguish
whether the intended recipient of his message is busy, or
the equipment is out of order. q'his would be undesirable,
since any communications network should provide users with
indications as to message status to provide confidence in
the integrity of the system.
Further, when set to one specific data speed, a
lo demodulator device may not be able to distinguish between
valid data at a different speed, and noise on the radio
channel, and might therefore attempt to transmit a packet
while another unit is transmitting at an incompatibls speed,
thereby causing packet collisions, and adversely affect~ng
channel throughput.
Despite the desirability of multi-speed data
operation for the aforesaid reasons, multiple data speeds
have in the past been impractical in radio data networks,
since, owing to the practical limitations of modem devices,
packets sent at different data speeds would be mutually
unintelligible. This would violate the requirement for
continual communications status monitoring by all modem
devices, and in some cases lead to unnecessary packet
collisionsO These problems have in the past restricted
practical multi-user radio data modem networks to operation
at a single fixed speed.
It is therefore a primary object of the present
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invention to provide a radio data communication system which
permits multiple radio data communication devices to operate
at differing data speeds over the same radio channel,
optimizing data throughput by transmitting at higher speeds
when radio propagation conditions permit, and at lower
speeds when necessary to overcome poor signal conditions.
A more specific object of the present invention is
to provide a means of determining the optimum information
packet speed for a pair of radio data communication devices,
based on prevailing radio propagation condltions, by causing
each transmitting station to send a predetermlned data
sequence to the receiver, and the recelving stat~on to
return a packet indicating whether the data seguence was
received with an error rate no greater than a predetermined
level; if success~ul, by establishin~ that data speed as the
information packet speed to be used in subsequent
transmissions of information packets, but if the error rate
was exceeded, by causing the transmitting station to reduce
its speed to the next lower available speed, and to generate -
a new data sequence-- repeating such procedure until the
desired error rate i~ achieved, whereupon this lower data
speed i5 adopted as the information packet speed.
A further object of the presPnt invention is to
regulate channel access by radio data communications units
which may have adopted varying data speeds, and to avoid
collisions that might otherwise be caused due to the mutual
unintelliqibility of packets sent at varying speeds, by
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e~tablishing a network packet speed, typically the lowest
available data speed; by causing all network control packets
to be transmitted at this network packet speed; by causing a
transmitting unit to generate a channel reservation packet,
at network packet speed, reserving the channel for a
specified number of seconds, prior to sending an information
packet at a higher information packet speed; by causing a
receiving unit to generate a reservation acceptance packet,
at network packet speed, to signal its recognition of the
upcoming information packet; and by causing all units in the
respective vicinities of the transmitter and the recelver to
take notice of such reservation pa~kets, so that they will
not attempt to gain channel access during the spealfied
channel reservation period, thereby avoiding p~cket
collisions.
Various means have been developed to send and
receive digital data over wireless radio links. A radio
modem, for example, may be connected between a computer or
data terminal and a radio transceiver. The means for data
transfer between the computer or data terminal and the radio
modem comprise a direct electrical connection of two
closely-located data devices, for example, an RS-232 serial
data interface ~Electrical Industries Association Standard
RS-232). The radio modem contains means for converting
digital data received from the computer or data terminal
into electrical signals which modulate the carrier of the
connected transceiver. Conversely, the radio modem
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demodulates signals received from the radio so as to
regenerate digital data, and passes the data to the
connected computer or data terminal.
Summary of the Invent1on
The invention is directed to a digital facsimile
radio communication system wherein network packet speed $s
established by pre-agreement between all users on a radio
channel. The network pacXet speed is chosen to provlde
reasonably assured transmission under typical expected radio
propagation conditions, such that the probablllty 18 low
that packet retransmissions will be rRquirQd. Thi~ speed
mi~ht typically be 300 bps, ln the case wh~re speeds of 300,
2400, 4800, 7200, and 9600 bps are provided, and would
typically be the lowest data speed in the case where a
different range of data speeds were provided. ~ll data
packets intended for establishing link connections,
acknowledging previously received data packets, and all
other data link and network control functions -- but not
containing actual message information -- are defined as
network control data pac~ets and are sent at the network
packet speed exclusively. After a connection has been
initially established between two parties, the parties
determine whether it is possible to communicate reliably at
any higher speed than the network packet speed, through a
negotiation proced~re consistiny of a series of training
sequences. The highest resulting speed is designated the
information packet speed for this connection between these
two parties. The information packet speed may vary as among
different parties on the same network; may vary as between
the same parties at different times, depending on the
current radio propagation characteristics; and may be
renegotiated during a link connection, for example, when
either party detects that the BER or packet retransmiQsion
rate has increased, in response to an appropriate control
data packet sent from one connected party to the other.
The invention is further directe~ to a digital
lo facsimi]Le communication system wherein packets which contain
user message data or information to be delivered to the
remote destination are sent within a special multi-packet
sequence, each sequence normally containing these four
packets:
1. Channel reservation packet. Sent at network
packet speed from the message originator to
the message receiver. Includes the address
of the sending unit, the address of the
receiving unit, and a proposed time period
(in seconds) for which the channel is to be
reserved. This reservation timP is
calculated by the transmitting device to
allow ~ufficient time for transmission of ~he
data packet it is prepared to send, plus time ~ -
for the othex networX packets included in
this data packet sequence.
2. Reservation ~cceptance packet. Sent at
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netwoxk packet speed from th~ mes~age
receiver, back to the message originator.
Includes the addresses of both units, and the
time period (in seconds) for which the
channel will be reserved.
3. Information data packet. sent at data packet
speed from the message originator to the
message receiver.
4. Information acknowled~ment data packet. Sent
at network packet speed from the message
receiver, back to the message originator.
When sent, positively acknowl~d~es receipt of
the information data packet ~ust tran~mitted.
Each unit ordinarily set~ lts internAl demodulator
device to the network packet speed. It changes its
demodulator to a higher information packet speed only after
it has received a channel reservation data packet addressed
to this unit, and ha~ returned a reservat~on acceptance data
packet to the originating unit. After receiving the
information data packet -- or upon expiration of the
specified channel reservat~on time-- the unit resets its
demodulator back to the network packet speed.
The invention is fur~her directed to a digital
radio facsimile communication system wherein each unit
within radio reception range sf the message originator
monitors the channel reservation data packet at the
beqinning of an informatiorl data packet sequence. When the
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data packet is not addressed to that unit, the
facsimile-radio communication devi~e sets an internal timer
to the designated reservation time. During that time, this
unit does not attempt to transmit on the radio channel.
This assures that this unit will not interfere with the
information data packet sequence ln progress, even though it
may not be able to monitor the data packet being transmitted
at a ~ifferent speed. Each unit within radio reception
range of the message receiver monitors the channel
acceptance data packet. Each unit ~other than the
originator) sets its internal timer to tha designated
reservation time, ~nd, during this tlm~, will not ~tt3mpt to
transmit on the radio channel. It will be s~en that th~
originator's channel reservation data packet wlll tend to
eliminate interfering data packets generated by units in the
vicinity of the originator, while the receiver's channel
acceptance data packet will tend to eliminate interfering
data packets generated by units in the vicinity of the
message receiver.
The invention is further directed to a digital
radio facsimile communication system wherein information
data packets, which tend to be ~ar longer than network
control data packets, and for which high speed is therefore
the most important, are sent at the highest practical speed.
Furthermore, each pair o~ stations on the radio channel may
operate at differing data speeds, as may be appropriate to
the radio propagation conditions applying to that pair of
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stations. Network control data packets are not necessarily
sent at the highest possible data speed, leading to some
loss of the theoretically realizable network throughput.
However, these network control data packets are usually
quite short, contain~ng only address and control data but no
user information, leading tG minimal throughput loss; but
more importantly, any throughput loss is repaid by allowing
all units on the network to interoperate no matter which
higher data speed may be in effect ~or eac~ pair of
lo connected stations.
Brief Descrlption of the_Drawlngs
The features of the present invention which are
believed to be novel are set forth with particularity in the
appended claims. The invention, together with the further
objects and advantages thereof, may best be understood by
reference to the following description taken in conjunction -
with the accompanying drawings, in the several figures of
which like reference numerals identify like elements, and in
which:
Figure 1 shows two radio-facsimile communications
systems comprising two stations, each consisting of a
facsimile transceiver, a radio-facsimile interface device,
and a two way voice radio, ~oge~her with interconnecting
cables, illustrating a typical application of the invention.
Figure 2 is a simplified block diagram
illustrating that, with respect to the two-way voice radio,
the radio-facsimile interface device effectively simulates a
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microphone and a speaker; and, with respect to the fac~imile
transceivsr, ~he radio-facsimile interface device
effectively simulates the voice telephone network.
Figure 3 is a simplified functional block diagram
o~ the radio-facsimile interface device illustrating the
station addressing, error detection and correction, speed
control and channel reservation functions of the device.
Figure 4 illustrates the structure of a typical
data packet, and the derivation of the cyclical redundancy
check (CRC~ value thereof.
Description of the Preferred Embodiment
Referring to Figure 1, a radio-facsimile
communications station 11 is seen to comprise a facsimile
transceiver 12, connected via a cable 13 to a radio-
lS facsimile interface device 14. Radio-facsimile interface
device 13 is connected via a cable 15 to a two-way voice
radio 16.
A second identical radio-facsimile communications
station 17 comprises a two-way voice radio 18, a cable 19, a
radio-facsimile interfa~e device 20r a cable 21, and a
facsimile transceiver 22. This second station 17 is
typically located remotely from the first station 11, at a
maximum distance determined by the range of the radio
equipment employed.
In accordance with the invention, a user is
enabled to send a facsimile copy of a written message from
one station to another in substan~ially the same manner as
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though operating on the voice telephone network. For
example, the user places the original written document to be
transmitted in the facsimile transceiver 12, and, using the
ordinary facsimile calling procedure, dials the "telephone
number" of the station to which he de~ires to send the
message (each such station having been, by common agreement,
assigned a unique number whic~ is programmed into its
respective radio facsimile interface device by a suitable
programming facility). The radio-facsimile interface device
14 provides all required voice telephone network signalling
to the connected facsimile transceiver 12. It recognlze~
dual-tone multi-frequency (DTMF) and/or pulse dialing
signals, generated by the facsimile transce~ver 12, thereby
decoding the "telephone number" of the statlon to which the
user wishes to send a facsimile message.
When the user has finished "dialing", radio-
facsimile interface device 14 sends audible tones, encoded
as electrical signals, to two-way voice radio 16, which are ;
transmitt~d to two-way voice radio 18 and decoded by the
other radio-facsimile interface device 20. Radio-facsimile
interface device 20 accordinqly generates a telephone line
ringing signal over cable 21 to its connected facsimile
transceiver 22, preparing the device to accept a message, -~
and also sends an answering response over two-way voice
radio lB back to the originating station 11, to signal that
this station 17 is ready to receive the facsimile message.
Radio-facsimile interface device 14 now sends
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audible tones to originating facsimile transceiver 12
signifying that a "connection" has been made. Facsimile
transceiver 12 proceeds to send the facsimile call set-up
tones prescribed by applicable telecommunications standards,
which are responded to by radio-facsimile interface device
14. Facsimile transceiver 12 now proceeds with its normal
transmission mode: it scans the o:riginal document
optoelectronically; converts black and white images into
digital data; converts digital image data into audible
tones; and transmits these tones over cable 13 to th~ radio-
facsimile interface device 14.
Radio-facsimile interface device 14 convert the
tones received from originating facsimlle transceiver 12
back into the form of digital data. As will be subseguently
described in more complete detail, radio-facsimile interface
device 14 combines the original facslmile image data with
station addressing information as well as error detection
and correction information. It then re-encodes this
combined information data into audible tones, and passes
these tones over cable 15 to two-way voice radio 16.
Receiving two-way voice radio 18 passes received
audible tones over cable 19 to radio-facsimile interface
device 20, which demodulates these tones and converts them
to digital data. Provided that the information has been
received without error (as will be subsequently described),
radio-facsimile interface device 20 re-encodes the digital
image data into audible torles, and sends these tones over
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cable 21 to the receiving facsimile transceiver 22.
From the preceding description it will be seen
that radio-facsimile interface deYices 14 and 20, through
their respective connections to two-way voice radios 16 and
18, automatically deliver a facsimile message from one
radio-facsimile communications station 11 to the other
station 17 without manual control of the communications link
by the operator. In a like manner, the operator at radio-
facsimile communications station 17 can send a facsimile
lo message to station 11; the same procedure takes place, in
the reverse direction.
Figure 2 is a block diagram illustrating the
radio-facsimile interface device simulating a m~crophone and
a speaker (to the two-way voice radio) and the voice
telephone network (to the facsimile transceiver).
Referring to Figure 2, two-way voice radio 16
comprises a receiver stage 24 and a tran~mittsr stage 25,
either of which can be connected through an antenna switch
26 to a radio antenna 27. In its standby condition, the
radio is ~n receive mode; the antenna 27 i6 connected
through antenna switch 26 to receiver stage 24. In a
typical voice-mode radio connection, receiver stage 24 is
connected to a speaker 29~ and a microphone 30 connected to
transmitter stage 25. When a user wishes to speak, he
depresses a push-to-talk switch 31 on the microphone
activating a push-to-talk stage i8 within the radio, which
in turn conditions the antenna switch 26 into its transmit
mode, connecting the antenna 27 to transmitter stage 25.
When the radio/facsimile interface devlce 14 is
connected to the two-way voice radio 1~, the radio receiver
stage 24 is connected to a demodulator 33 which converts
audible tones to digital data. Demodulator 33 accepts
audible signals that would be connected to speaker 29 in a
voice-mode system. The radio transmitter stags 25 is driven
by a modulator 34 which converts digital data within the
radio-facsimile interface device 14 ts audible tones.
Modulator 34 provides audible signal~ that would be
generated by microphone 30 in a voice-mode system. The
radio PTT stage 2~ is controlled by transmit-receive control
device 35. The transmit-receive control device 35 places
the radio in transmit mode in the ~ame manner as the push-
to-talk switch 31 in a voice system.
Because the radis-facsimile interface device 14 in
effect emulates the operation of a speaker 29 and microphone
30, it can be connected to a wide variety of two-way voice
radios without modification to those radios, except that
differing cable connections may be required for different
radios.
Figure 2 also ~hows facsimile transceiver 12 in
simplified form. It includes an image scanner 48, which
optoelectronically converts the image of an original
document into digital data. This information is converted
by a modulator 49 into audible tones. These tones are
routed to a telephone line interface 50.
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Telephone line interface 50 also connects to a
demodulator 52, converting received audible tones into
digital data. This information is sent to a thermal printer
53, which reproduces the image of the original document
. transmitted from a compatible facsimile transceiver.
In a telephone line application, facsimile
transceiver 12 is connected through a telephone cable 51 to
a telephone jack 46, which is a terminal on a switched voice
telephone network 42. The local telephone exchange 43
lo provides a gateway into the telephone network, and makes
connections to other exchange 54 and 55 in re~ponse to the
number dialed by the originating party.
When facsimile transce~ver 12 is connected to
radio/facsimile interface device 14, telephon~ line cable 51
connects to telephone receptacle 41. The radio-fac imile
interface device 14 contains a telephone line simulator 36,
which simulates the operation of the switched telephone
network 42. This telephone line simulator 36 furnishes
telephone line loop current; recognizes when the facsimile
transceiver goes off-hook, preparatory to dialing; generates
an audible "dial tone" compatible with the telephone network
standards; recognizes dual-tone multi-freq~ency IDTMF)
and/or pulse dialing s~gnals, generated by the facsimile
transceiver 12; and can generate a telephone line ringing
signal.
Audible tones received by radio-facsimile
interface devi~e 14 via its telephone line simulator 36 from
7 ~
the attached facsimile transceiver 12 are converted by
demodulator 38 into digital data. This informatio~ is
stored by a digital image data control and storage section
40 for subsequent transmission to the distant receiver over
the attached two-way voice radio 16.
Facsimile image data received by radio-facsimile
interface device 14 from the attached two-way voice radio 16
is routed via a demodulator 33 to the digital image data
control and storage section 40. Error-free image
information is converted into audible tones by a modulator
37, and converted by telephone line simulator 36 into
electrical signals appropriate to drive ~ac~mile
transceiver 12. A l~ne control circuit 39 provlda~ control
o~ the telephone line simulation acsompl~hed by telephone
line simulator 36.
It should be noted that radio-facsimile interface
device 14 does not simply change electrical levels in such a
way as to route modulated audio tones directly and in real-
time between two-way voice radio 16 and facsimile
transceiver ~2. Rather, radio-facsimile interface device 14
contains an independent modulator 34 and demodulator 33 for
interface to two way voice radio 16; an independent
modulator 37 and demodulator 38 for interface to facsimile
transceiver 12; and a d$gital image data control and storage
section 40 for providing separate and independent control of
data flow to and from two-way voice radio 16 and facsimile
transceiver 12. These provisions are utilized to provide
~4 .
S' ~..J l 7 ~
station addressing and error control.
Fi~ure 3 provides an expanded view of the internal
functions of the radio-facsimile interface device,
particularly, with respect to the station addressing, error
control, speed control and channel functions.
Referring to Figure 3, facsimile transceiver 12
connects view telephone jack 41 to tPlephone line interface
56. Telephone line interface 56 provides telephone line
"battery" voltage to attached facsimile transce~ver 12.
Assume that the operator of facsimile transceiver 12 w~she~
to originate a call. Facsimile transceiv~r ~2 goe~ "off-
hook" by closing an internal switch or relay contact,
drawing loop current from the voltage provided by telephone
line interface current 56. This loop current is detected by
off-hook detector circuit 57, which provides a signal to
facsimile interface mode control circuit 58, which in turn
causes selector switch 59 to connect tel~phone line
interface 56 to dial siqnal detect circuit 60. Dial signal
detect circuit 60 receives DTMF tones or dial pulses from
attached facsimile transceiver 12. Upon completion of
dialinq -- either upon reception of a predetermined number
of digits, or upon reception of a predetermined terminating
digit or symbol (such as the 11#11 symbol) -- dial signal :
detect circuit 60 transmits the station number dialed to
destination address encoding circuit 61.
Data packet assembler 62 assembles an initial data
packet whlch includes the d~_stination station address
. . . .
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received from destination address encoding circuit 61 in
binary digital form. Data packet assembler 62 also includes
the address of this radio-facsimile communications station,
as programmed by the installer and contained in a home
station address register 63. Since no image data has as yet
been accumulated from the transmitting facsimile transceiver
12 by image data demodulator circuit 64 and image data
buffer 65, this data packet does not contain image data.
Data packet assembler 62 instead inserts a digital code
indicating that this data packet is a channel reservation
data packet, rather than an information transfer data
packet. Data packet assembler 62 next inserts a digital
value indicating the amount of time in seconds for which the
channel is to be reserved. If no image data is as yet
available for transmission, a minimum reservatlon time is
specified, for example, five seconds, 50 as to reserve the
channel until the distant radio-facsimile communication
station has time to respond. Data packet assembler 62 also
inserts a digital code reflecting the radio data speed to be
used, as received from radio data speed control 101. For
example, "96" to denote 9600 bps~ "48" for 4800 bps, etc.
Data packet assembler 62 forwards the data packet
to data check value calculator 66l which appends a cyclical
redundancy check (CRC) value to th~ data packet (to be
explained in further detail below), and forwards the
modified data packet to tra,nsmit data packet register 67.
Transmit data packet regist:er 67 generates a signal to data
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packet transmitter control ~8 indicating that a data packet
is ready to transmit. Provided that the radio channel i8
not already busy, data packet transmit control 6~ energizes
push-to-talk signal circuit 69, which is connected through a
radio connector 70 to radio transceiver 16, causing the
transceiver to switch from receive to transmit. Data packet
transmit control 68 also signals a rad$o data modulator
circuit 72 to begin generating audible tones, which are
amplified by a radio output amplifier 73 to a suitable
electrical level, then connected via radio interface
connector 70 to radio transce~ver 16. After suitable
delays, both to allow radio transceiver 16 to switch to its
transmit mode, and to allow radio modulator circuit 72 to
complete its pre-data signal sequence, data packet transmit
control 68 signals transmit data packet register 67 to
transmit the stored data packet to radio data modulator
circuit 72. Radio data modulator circuit 72 converts the
digital data to audible tones, which are amplified by radio
output amplifier 73 to a suitable electrical level, then
connected ~ia radio interface connector 70 to radio
transceiver 16. At this phase, radio data modulator 72
operates at its lowest modulation rate, the network packet
speed, and continues to do so until commanded to a higher
data packet speed by radio data speed control 101.
Since different models of radio transceiver 16 may
xe~uire differing signal strengths to provlde effective
operation' a user-adjustable output control 74 allows the
equipment installer to program a æpeci~ic output level.
Af~er the initlal data packet i~ transmitted, data
packet transmit control 68 reconditions push-to-talk signal
circuit 69 to its receive status, and radio transceiver 16
returns to its receive mode.
If the distant radio-facsimile communications
station receives the data packet just transmitted, it
returns an acknowledging data packet to this radio facsimile
communications station. The received audio signal from
radio transceiver 16 is coupled through radio interface
connector 70 to an automatic gain control circuit 75, which
automatically adjusts for variations in radio receive levels
and passes audio tones to a radio data demodulator circuit
76. ::
Automatic gain control circuit 75 also pas~es
audio tones to a radio channel carrier detect circuit 77,
which develops a signal indicating the presence of a data
carrier signal on the radio channel. This signal is
connected to radio demodulator circuit 76, helping to
prevent radio demodulator circuit 76 from ~alsely
interpreting radio noise as data. The signal developed by
radio channel carrier detect circuit 77 is also connected to
data packet transmit control circuit 68 inhibiting the
station from attempting to transmit when another signal is
already present on this radio channel.
At this time, radio data demodulator circuit 76 is
set to demodulate signals at its lowest modulation rate, the
28
network packet speed, and continues in this setting until
commanded to a higher data packet ~peed by a received data
packet interpreter 80.
~adio demodulator circuit 76 converts recPived
audible tones into digital data, passing the information to
a data check decoding logic circuit 78. Data check decoding
logic circuit 78 removes the CRC embedded ~n the received
data packet, then independently calculates a CRC check on
the remainder of the received data packet. If the CRC check
so calculated does not agree wlth the CRC included in the
received data packet, data check decoding logic circuit 78
discards this data pac~et. I~ the CRC aqr~e , ~t passas the
data packet to a station address decoding loglc circuit 79.
Station address decoding logic circuit 79 examines
the address to which the packet was addre~sed, comparing
this address to the address of this radio facsimile
communications station, as contained in home station address
register 630 If these addresses do not compare, the data
packet is intended for another radio-facsimile
communications station. If the address contained in the
received data packet matches, then the data packet is
intended for this radio-facsimile communications station.
In either case, station address decoding logic circuit 79
passes the data packet to the received data packet
interpreter circuit 80, along with a si~nal indicating the
results of the destination address comparison.
If received data packet interpreter 80 determines
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that this packet is a channel reservation packet addressed
to another radio-facsimile communications station, it
extracts the channel reservation time period encoded in the
packet and passes that value to channel reservation timer
102. Channel reservation timer 102 loads this value and
starts a count-down to zero. So long as channel reservation
timer 102 holds a non-zero timer value, it produces an
inhibit signal to data packet assembler 62, effectively
preventing this radio-facsimile communication station from
transmitting, and allowing the distant radio-facsimile
communication station to reserve the channel.
continuing however with the case just described,
received data packet interpreter 80 finds within the data
packet a control code showing that this is a reservation
acceptance packet, which indicates that the distant radio-
facsimile communications station is ready to accept a
connection, in response to the channel reservation data
packet just sent. Received data packet interpreter 8C now
sends a signal to facsimile interface control circuit 58,
indicating that the system is ready to receive a facsimile
message from connected facsimile transceiver 12. Facsimile
interface mode control circuit 58 switches selector switch
59 to connect telephone line interface circuit 56 to
facsimile data modulator circuit ~2. Facsimile interface
mode control 58 then causes facsimile data modulator circuit
82 to send facsimile connect signals via telephone line
interface circuit 56 to the! connected facsimile transceiver
/ 7
12, commanding the facsimile transcelver to start
transmitting image data. After these connection signal~ are
sent, facsimile interface mode control circult 58 causes
selector switch 5g to connect telephone line interface 56 to
image data demodulator circuit 64.
At this point the connected facsimile transceiver
12 starts sending image data, encoded in the form of audio
tones, in a continuous ~low, one page at a time, according
to the facsimile data communication~ protocol e~tablished by
lo international standards.
Image data demodulator circuit 64 convert~ these
audible tones into digital image data which are stored in
image data buffer 65. Periodically data packet assembler 62
accepts a packet of image data and a~semble~ an information
data packet for transmission. Because the effective speed
at which data packet assembler 52 can assemble and dispatch
information data packets varies depending on the effective
through-put of the data link over the radio, image data
buf~er 65 provides sufficient data buffer capacity to store
a ~ubstantial amount of facsimile image data.
As previously described, information data packets
are normally transmitted at a higher information packet
speed, requiring a shift in data rate before transmitting
each packet. Upon decoding a valid reservation acceptance
packet addressed to this unit, received data pack~t
interpreter 80 sends a sign,a~ to radio data speed control
lO1 indicating that an information data packet is ready to
:31
r, ~)
be sent. Radio data speed control 101 then sends a signal
to radio data modulator 72 to change its modulation speed to
the information packet speed. Provided that the
communications session is just beginning, the information
packet speed is the highest available, for example, 9600 bps
in a system providing data speeds of 300, 2400, 4800, 7200
and 9600 bps.
Data packet assembler circuit 62 now creates
information packets which each include the following: the
destination station address, as determined by destination
address encoding circuit 61; the home station addre~s, from
home station address register 63; a control code indicat~ng
that the data packet contains facsimile image data; a
sequence number generated by a sequ~nce number generator
circuit 83; and the facsimile image data. Th~ sequence
number generated by sequence number generator 83 is an
arbitrary packet serial number which is incremented each
time a packet is successfully transmitted. Each such data
packet is passed to data check value calculator 66, which
appends a CRC to the data packet, and forwards the modified
data packet to transmit data packet register 67 as
previously described.
The distant radio-facsimile communications station
acknowledges each correctly received data packet by sending
back an information acknowledgement data packet. Assuming
that this information acknowledgement packet is received
without error, it finds its way (via the stages previously
~J~ v7 7
described) to received data packet interpreter circuit 80.
Received data packet interpreter ~o recognizes that this is
an information acknowledgement packet, and signals data
packet assembler 62 to assemblP the next block of image data
in image data buffer 65 for transmission. Upon decoding an
information acknowledgement packet, received data packet
interpreter circuit 80 also send a signal to sequence
num~er generator 83, which accordingly increments ~o the
next sequence number, which will be embedded within the next
succeeding information data packet. ~eceived data packet
interpreter circuit 80 also sends this packet
acknowledgement signal to an acknowledgemsnt ~imer circuit
84.
Each time that data packet transmit control 68
causes a data packet to be transmitted, it starts
acknowledgement timer 84. The period of this timer is set
to a time period long enough for the distant radio-facsimile
communications station to receive the data packet, and to
acknowledge it. If such acknowledgement is timely received,
then the acknowledgement signal from received data packet
interpreter 80 resets the acknowledgement timer 84 be~ore
the timer expires. However, if acknowledgement timer 84
times out without having received such acknowledgement
signal, it sends a signal to data packet transmit control
circuit 68 causing data packet transmit control circuit 6B
to repeat transmission of the same packet. The purpose of
acknowledgement timer circui.t 84 is thus to prevent failure
~ 3 ~
of the communications link in the event that an earlier
packet transmission was not properly received and
acknowledged.
It will sometimes happen that a transmitted data
packet is correctly received by the distant radio~facsimlle
communications station, which sends back a suitable
acknowledgement packet -- but the acknowledgement packe~
encounters interference which causes its b~ts to be garbled.
Such an acknowledgement packet will be rejected by data
check decoding logic circuit 78, and will be discarded.
After a time, acknowledgement timer circuit 84 will cause
the same packet to be retransmitted. The distant recelving
station may well then receive the same packet correctly for
a second time. Herein lies the purpose of the sequence
number generator circuit 81; the sequence number will not
have incremented, so the receiving station will decode a
duplicate sequence number. It reacknowledges the packet,
but does not pass the duplicated data on the attached
facsimile transceiver.
Each time that received data packet interpreter 80
detects a valid information acknowledgement packet, it sends
a signal to success rate register 103, which increments a
success event counter. Each time that acknowledgement timer
84 times out, indicating that a valid information
acknowledgement packet has not been timely recsived, it
sends a signal to success rate register 103, which
increments a failure event counter. When the ratio of the
314
2 7 7
failure event count to the success event count exc~eds a
preset level, for example, 1/10, then success rate regls~er
103 sends a speed downshift signal to radio data speed
control 101. Radio data speed control 101 then causes the
next information data packet to be transmitted at the next
lower available data speed. If radio data speed control 101
is already set to the lowest available data speed, it sends
a disconnect signal to facsimile interface mode control 58,
which disconnects the connect facsimile transceiver and
terminates the message.
If the first information data packet to be
transmitted on a new message sesslon fails to be
acknowledged, the failure to success ratio is 1/0, that is
infinite, forcing an immediate downshift.
If, on the other hand, the failure to success
ratio falls below a preset level, for example, 1/25, then
success rate register 103 sends a speed upshift signal to
radio data speed control 101. Radio data speed control 101
will then cause the next information data packet to be
transmitted at the next higher data speed. If radio data
speed control 101 is already set to the highest available
data speed it will simply continue to operate at that speed.
When the originating facsimils transceiver 12
finishes sending a page, it drops its carrier (stops sending
audible tones) and awaits a response. This loss of carrier
is sensed by facsim~le data demodulator circuit 64, which
sends an appropriate signal to facsimile interface mode
_- ~'Jr ~ f I
control circuit 58. Facsimile inter~ace mode control
circuit 58 switches selector 59 to connect telephone line
interface 56 to facsimile data modulator circuit 82 and
sends a response back to facsimile transceiver 12 indicating
that it is ready to receive additional data. Facsimile
interface mode control circuit 58 then switches selector 59
back to connect telephone line interface 56 to facsimile
data demodulator circuit 64 to recelve either the next page
of facsimile images -- in which case the above sequence
lo continues; or a disconnect signal. Upon receipt of a
disconnect signal, facsimile data demodulator circuit 64
sends a signal to facsimile interface mode control circuit
58, which in turn signals telephone line interface circuit
56 to disconnect from facsimile transceiver 12. ~:
Even after originating facsimile transceiver 12
disconnects, image data will often remain as yet
untransmitted with image data buffer 65. This data will .
continue being transmitted, packet by packet, until image
data buffer 65 is empty. At that point, data packet
assembler circuit 62 generat~s a message complete packet to
the distant radio-facsimile communicatisns station.
Assuming that the radio-facsimile communications
station is idle, and that the operator of a distant radio-
~acsimile communications station wishes to send a facsimile
message to this station, radio transceiver 16 receives a
signal which results in digital data being detected by radio
data demodulator circuit 76. Provided that data check
36
rv ~. . ~ . L . ~ 7
decoding logic circuit 78 finds no data errors, station
address decoding logic circuit 79 attempts to match the
address in the packet received, with its own addre~s
contained in home station address register 63. Provided a
match is found, received data packet interpreter circuit 80
detects a reservation request packet. If the unit is not
already occupied, and channel reservation timer 102 is not
counting down from any as yet unexpired channel reservation,
received data packet interpreter 80 sends a signal to data
10 packet assembler 62 instructing it to return a connect
acknowledge packet to the originator. This packet ls
transmitted as previously described for other forms of data
packet.
Received data packet interpreter 80 also decodes
15 the information packet speed specified in the channel
reservation packet, and sends a speed select signal to radio
data demodulator circuit 76, preparing it to receive the
information packet. Once radio data demodulator circuit 76
starts receiving an information packet, indicated by a
20 carrier detect signal from radio channel carrier detect 77,
and subsequently detects loss of the carrier detect signal
from radio channel carrier detect 77, it reverts to its
lowest demodulator speed, that is, the network packet spead.
Received data packet interpreter 80 also sends a
~5 connect signal to facsimile interface mode control circuit
58. Facsimile interface mode control circuit 58 in turn
causes selector switch 59 to connect tPlephone line
~- ~ r~ ~ ~ 3
interface circuit 56 to a ring signal generator 85,
generating a ringing signal to connected facsimile receiver
12. When facsimile transceiver 12 answers, it goes off
hook, drawing loop current through telephone line interface
56, which is detected by off hook detect circuit 57, which
in turn sends a signal to facsimile interface mode control
circuit 58. Facsimile interface mode control 58 switche
selector switcb 59 to connect telephone line interface 56 to
~acsimile data modulator circuit 82; facsimile interface
mode control 58 then causes facsimile data modulator circuit
82 to send facsimile connection signals via telephona l~ne
interface 56 to the connected facsimile transceiver 12, ln
effect commanding the facsimile transceiver to receive imag~
data. After these connection signals are sent, ~acsimile
interface mode control circuit 58 causes selector swltah 59
to connect telephone line interface circuit 56 to image data
demodulator circuit 64, which receives connection signals
from facsimile transceiver 12. Upon conclusion of these
signals, demodulator circuit 64 sends suitable connection
signals to facsimile inter~ace mode control circuit 58,
which switches selector switch 59 to connect telephone line
interface circuit 56 to facsimile data modulator circuit 82
ones again.
The distant originating radio-facsimile
communications station commences to send image data packets.
As received data packet interpreter circuit 80 decodes each
new image data packet, it sends a signal to data packet
~8 ..
assembler 62 to return an acknowledgement packet to the
originating station. Received data packet interpreter 80
also decodes the sequence number which is embedded within
each image data packet, as previously described. It
compares the received sequence number with the value
previously stored in a receive seguence number register 86.
If the sequence number is the same, then this is a duplicate
image data packet (as described above), and it is discarded.
If the sequence number received is different from the
previously stored sequence number, then recelved data packet
interpreter 80 stores this new sequence numbar in reseivo
sequence number register 86, and then forwards ths image
data contained in this new pac~et to a receive image data
storage circuit 81.
Whenever image data is available in image data
storage 81, it is sent to facsimile data modulator circuit
82 for transmission through telephone line interface circuit
56 to connected facsimile transceiver 12. -
When image data is not immediately available,
receive image data storage circuit 81 sends a signal to a
fill data timer circuit 87, which sends a signal to
facsimile data modulator circuit 82 causing it to interpose
fill bits in the data sent to facsimile transceiver 12. If
t~e buffer empty signal from rec~i~e image data storage 81
pexsists for a predetermined period, fill data timer 87
sends a signal to data modulator circuit 8~ causing it to
transmit the si~nal for a si.ngle blank scan line on the
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39 ,.
~J ~ 7 ~
print-out of facsimile transceiver 12; this signal is
necessary to prevent facsimile transcelver 12 from
disconnecting from the telephone line interface clrcuit 56
according to the inactivity time-out provisions embodied in
the facsimile communications protocol.
At the end of the facsimile message, after
sending the last imag~ data pack~t, the originating radio-
facsimile communications station generates a disconnect
packet, as previously described. Upon receipt of a
10 correctly formatted disconnect packet, received data packet
interpreter 80 monitors the hu~fer empty signal generated by
receive image data storag~ 81 until all previou~ly r~ceive
image information has been sent to facsimile data modulator
circuit 82, at which time received data parket interpreter
15 80 sends a disconnect signal to facsimlle interface mode
control 58. Facsimile interface mode control 58 proceeds to
generate a disconnect sequence to attached facsimile
transceiver 12 as previously described.
Figure 4 shows the structure of a typical data
20 packet 88. Each of the small data blocks within the data
packet 88 represents a conventional eight-bit binary number
(or octet) which can take on values fro~ 0 to 255. An
address section 89 contains a destination statlon address
90, followed by a source station address 91. Figure 4 shows
25 each address having four digits, but the actual sizes of
these address fields can vary, depending on the addressing
schemes chosen by the users of the system.
~0 ..
A control section 92 contains a coded data value
indicating the type of packet. ~or example, possible packet
types include 1) channel reservation request; 2) channel
acknowledgement; 3) information packet; 4) information
acknowledge; and 5) message complete. Obviously, other
packet types could be provided to achi~ve additional link
control functions with the scope of the invention.
A send sequence number 93 is present only when the
packet is conveying or acknowledging data, notably for an
information data transfer or information acknowledge packet.
It is an arbitrary number, 0 to 255, which is incremented
each time a packet is transmitted ~nd acknowledged. A
channel reservation time value 104 and an information packet
speed 105 are present only when the packet is requesting or
acknowledging a channel reservation, notably for a channel
reservation packet or reservation acceptance packet.
An information section 94 is present only when the
packet is conveying data, notably ~or an information data
packet. It may contain anywhere from a single eight-bit
octet to over a thousand octets. These octets represent
encoded facsimile images~
A data check sectivn 95 contains a 16-bit cyclical
redundancy check ~CRC), genPrated at the transmitter. The
16 bit CRC is initialized to all binary ~L's. Then the
multi-bit binary number which represents the address sPction
~9, control section 92, send sequence number 93 (if
present), channel reservatio;n timP value 104, and
~L , '
~J,~ 7 7
information section 94 (if present), all combined, is
divided by the binary polynomial X~6 + X12 +5 ~ 1. The one~s
complement of the 16-bit remainder after the aforesaid
division is transmitted as the CRC.
At the receiver, the 16-bit CRC is initialized to
all binary l~s. The multi-but binary number (as defined
above) actually received is first multiplied by xl6, then
divided by the binary polynomial xl6 ~ xl2 ~ xS + 1. The 16-
bit binary remainder resulting will be "0001 1101 0000 1111"
10 (x~S through x) in the absence of communicatlons errors.
Thus a communicatlons system is descrlbsd whlch
through use of a duplex packet transmission format, enable~
conventional facsimile apparatus to reliably communicate
over a conventional two-way voice radio communication ~y~tem
15 without modification to either th~ facs~mile apparatu~ or
the transceiver apparatus of the radio communication system.
In one preferred form, the system utilizes a novel packet
protocol including data check and system control features
which maximizes transmission accuracy and system efficiency,
20 even under adverse conditions. The system uses adaptive
speed control to permit transmission at optimum data speeds
over the radio channel, and a channel reservation scheme to
allow communications at differing speeds to take place in an
orderly, non-interfering manner.
While a partlcular embodiment of the invention has
been shown and described, it will be obvious to those
skilled in the art that changes and modifications may be
4~
~ ~ ! 3 ~ ~ 7
made therein without departing from the invention in its
broader aspects, and, therefore, the aim in the appended
claims is to cover all such changes and modifications as
fall within the true spirit and scope of the invention.
43
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