United States Patent
`4,606,044
`Kudo
`Date of Patent:
`[45]
`Aug. 12, 1986
`
`[111
`
`Patent Number:
`
`[19]
`
`[54] ADJUSTING DATA TRANSMISSION RATE
`BASED ON RECEIVEDSIGNAL QUALITY
`
`Inventor:
`
`Shozo Kudo, Yokohama, Japan
`
`Primary Examiner—Benedict V. Safourek
`Assistant Examiner—Raymond C. Glenny
`Attorney, Agent, or Fz'rm—David G. Alexander
`
`Assignee:
`
`Ricoh Company, Ltd., Tokyo, Japan
`
`[57]
`
`ABSTRACI‘
`
`[75]
`
`[73]
`
`[21]
`
`App1.No.: 586,509
`
`[22] Filed:
`
`Mar. 5, 1984
`
`Foreign Application Priority Data
`[30]
`Mar. 9, 1983 [JP]
`Japan .................................. 58-37274
`
`Int. c1.-1 .............................................. .. 1104.1 3/22
`[51]
`[52] US. Cl. ...................................... .. 375/13; 375/58;
`370/84
`Field of Search ................. .. 375/13, 58, 109, 121;
`371/5; 370/79, 34; 178/69 A, 69 M
`References Cited
`
`[53]
`
`I56]
`
`U.S. PATENT DOCUMENTS
`
`3,536,840 10/1970 Sullivan ................................ 375/58
`3,988,539 10/1976 Motley et al.
`.
`375/39
`
`4,153,916
`5/1979 Miwa et a1. ......................... 358/288
`
`FOREIGN PATENT DOCUMENTS
`
`A data transmission control system for allowing remote
`transceiver stations to transmit data via a telephone line
`or like analog transmission line through modems. When
`transmit and receive stations have been interconnected
`by a call, a training sequence for the modem is executed
`and, also, a test signal transmission sequence is effected
`to set up a data transmission rate before delivery of
`information. When the receive station has received test
`training data inclusive of a plurality of transmission
`rates from the transmit station,
`the function of the
`modem at the receive station is checked with respect to
`each of the transmission rates on a signal space diagram,
`thereby determining whether the receive station is ca-
`pable of normally receiving data at the transmission
`rate. Training on the transmission rates which a modem
`can use is executed satisfying a predetermined protocol
`and without increasing the protocol time.
`
`0039191 11/1981 European Pat. Off.
`
`................ 371/5
`
`9 Claims, 11 Drawing Figures
`
`SEI'wlD TEST
`TRAINING
`
`
`
`
`
`DATA 7
`
`
`
`
`TRAINING, MEASURE
`DEVIATION FROM
`IDEAL POINTS
`
`
`
`
`
`DETERMINE
`TRANSMISSION
`RATE
`RETURN ANSWER
`S I GNAL
`
`
`
`
`
`708
`
`SEND DATA AT NOTIFIED
`TRANSMISSION RATE
`
`
`
`RPX Exhibit 1140
` RPX Exhibit 1140
`RPX v. DAE
`RPX V. DAE
`
`

`
`U.S. Patent Aug,12, 1986
`
`Sheet1of4
`
`4,606,044
`
`TRANSMIT
`STATION
`
`STATION
`
`RECEIVE‘
`
`100
`
`300
`
`2OO
`
`

`
`4cm2w..n..S
`
`4,606,044
`
`ms
`
`6004
`
` 9EM,.mg:48IEJvowooq.we4AO
`tmat
`
`
`
`mm.Pam
`
` -
`
`.
`
`
`

`
`U.S. Patent Aug. 12,1986
`
`Sheet3 of4
`
`4,606,044
`
`

`
`U.S. Patent Aug. 12,1986
`
`Sheet4of4
`
`4,606,044
`
`Fig. 6A 4-2
`200
`—
`
`400
`12
`
`.t,
`
`404
`
`402
`
`400
`
`404
`
`Fig. 53 :33
`
`N
`
`.
`
`402
`
`
`TIME
`
`TIME
`
`Fig. 7
`100|2_00§.
`
` TRAINING, MEASURE
`
`DEVIATION FROM
`‘IDEAL POINTS
`
`702
`
`DETERMINE
`TRANSMISSION
`RATE
`4
`
`
`
`
`
`7C)4_
`
`
`
`RETURN ANSWER
`
`SIGNAL
`
`.
`
`7C)8
`
`
`
` SEND DATA AT NOTIFIED
`TRANSMISSION RATE
`
`

`
`1
`
`4,606,044
`
`ADJUSTING DATA TRANSMISSION RATE BASED
`ON RECEIVED SIGNAL QUALITY
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a data transmission
`control system and, more particularly, to a data trans-
`mission control system which allows remote transceiver
`stations to exchange images, digital data and like signals
`over an analog transmission line using modems.
`In data transmission using an analog transmission line
`such as a telephone line, it is a common practice to
`execute a training sequence for a modem when connec-
`tion has been set up between remote transceiver stations
`by a call. As soon as various parameters are converged
`by the training, a test signal transmission sequence is
`performed before the transmission of information in
`order to predetermine a data transmission rate. For
`example, in accordance with the facsimile transmission
`control procedure presented by the Consultive Com-
`mittee of
`International Telegraph and Telephone
`(CCITI), Recommendation T.30, training for a modem
`of the group 3 (G3) is confirmed and, then, a training
`check field (TCF) is defined as a test signal for setting
`up a data transmission rate. The TCF consists of a signal
`in which ZEROs sequentially appear for the duration of
`1.5 seconds. The receiving station, receiving the TCF
`and when found many transmission errors, requests the
`transmitting station to shift down the data transmission
`rate.
`
`As stated in the Recommendation T.30, if a modem at
`the receiving station fails to adapt itself to test data
`which is delivered thereto from the transmitting station
`for 1.5 seconds at the transmission rate of 9,600 bits per
`second (bps), for example, the receiving station notifies
`it to the transmitting station while the transmitting sta-
`tion responds to the notification by shifting down the
`transmission rate to 7,200 bps and then repeating the
`same test sequence. If the modem at the receiving sta-
`tion is failed to such a degree as to require further shift-
`down from 4,800 bps to 2,400 bps, 6 seconds will be
`consumed in total for the delivery of test data alone.
`The resulting increase in the total protocol time is unde-
`sirable because it lowers the data transmission efficiency
`of the whole system.
`system is
`Meanwhile, a communication control
`known in which test data is sequentially delivered from
`a transmitting station to a receiving station at all the
`transmission rates which a modem can accommodate,
`the delivery being repeated until the receiving station
`completes equalization (Japanese Patent Laid-Open
`Publication Nos. 52-947l5/ 1977 and 52-94716/1977).
`Such a system is not fully acceptable, however, consid-
`ering a possible occurrence that, even after equalization
`has been completed at a given transmission rate, test
`data of lower transmission rates are sent out, increasing
`the total protocol time.
`
`SUMMARY OF THE INVENTION
`
`It is therefore an object of the present invention to
`provide a data transmission control system which elimi-
`nates the drawbacks inherent in the prior art systems as
`described above and executes a training with transmis-
`sion rates which a modem can utilize, without prolong-
`ing the protocol time.
`It is another object of the present invention to pro-
`vide a data transmission control system which satisfies a
`predetermined protocol and, without
`increasing the
`
`2
`time, executes a training with transmission
`protocol
`rates which a modem can accommodate.
`
`It is another object of the present invention to pro-
`vide a generally improved data transmission control
`system.
`
`5
`
`l0
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`A data transmission control system for allowing re-
`mote transceiver stations to transmit data via an analog
`transmission line through modems which selectively
`use a plurality of transmission rates of the present inven-
`tion comprises the steps of transmitting test training
`data inclusive of a plurality of transmission rate data
`from a transmit station to a receive station, training a
`modem of said receive station when said test training
`data are received by the receive station, selecting a
`transmission rate adequate for communication between
`the transmit and receive stations by measuring deviation
`of the test training data received by the receive station
`from ideal data points on a signal space diagram, notify-
`ing said selected transmission rate from the receive
`station to the transmit station, and transmitting data
`from the transmit station at said notified transmission
`rate.
`
`The term “data” used in the instant specification
`should be understood to include not only the digital
`data used for digital computers but also the signals pre-
`pared by coding audio signals, video signals and like
`analog signals.
`The above and other objects, features and advantages
`of the present invention will become more apparent
`from the following detailed description taken with the
`accompanying drawing.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`FIG. 1 is a block diagram of a communication system
`to which a data transmission control system of the pres-
`ent invention is applicable;
`FIG. 2 is a functional block diagram of a transmit
`station or a receive station implementing the data trans-
`mission control system of the present invention;
`FIGS. 3 and 4 are flowcharts representing a transmis-
`sion control flow in accordance with the present inven-
`tion;
`FIGS. 5A—5D are exemplary signal space diagrams
`indicative of data signals which are provided by 8-phase
`modulation;
`FIGS. 6A and 6B are flowcharts demonstrating a
`modification to the transmission control flow in accor-
`dance with the present invention; and
`FIG. 7 is a flowchart showing control flows per-
`formed at transmit and receive stations.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`While the data transmission control system of the
`present invention is susceptible of numerous physical
`embodiments, depending upon the environment and
`requirements of use, a substantial number of the herein
`shown and described embodiment have been made,
`tested and used, and all have performed in an eminently
`satisfactory manner.
`Referring to FIGS. 1 and 2, a transmitting transceiver
`station 100 and a receiving transceiver station 200 are
`interconnected by a transmission line 300. The transmit
`station 100 or receive station 200 includes a facsimile or
`like terminal 20. Coded data is applied from the terminal
`20 to an input/output (I/O) port 10 and vice versa. A
`system control processor (CPU) 12 supervises transmis-
`
`

`
`4
`thereby determining whether or not normal receipt is
`possible at the transmission rate (FIG. 7, step 702).
`In detail, the DSP 16 at the receive station 200 mea-
`sures signal space vectors of the test training data 400
`and, in response to the result of the measurement, noti-
`fies the transmit station an adequate transmission rate
`(FIG. 7, steps 704 and 706).
`Concerning an 8-phase phase modulation system, for
`example, the signal space diagram of a signal sent out
`from the transmit station 100 to the transmission line 300
`comprises eight points (ideal points) 600 as shown in
`FIG. 5A, which are identical in phase difference (‘IT/4)
`- and spaced equal distances from the origin 0 of a real
`axis (I) and an imaginary axis (Q).
`While propagating through the transmission line 300
`toward the receive station 200, the signal is subjected to
`various kinds of phase delay and attenuation. As shown
`in FIG. 5B or SC, so long as data points 604 of signal
`space vectors are distributed relatively adjacent to the
`ideal points 600 of the transmitted signal vectors in a
`signal space, information symbols contained in the re-
`ceived signal will be identified with ease. However,
`where the data point distribution extends over a sub-
`stantial range beyond the ideal points 600 as show in
`FIG. 5D, for example, accurate identification of the
`information symbols will fail. The critical condition for
`accurate identification is, as shown in FIG. 5C, one in
`which the data points 604 of the received signal vectors
`lie within eight circles 602'which respectively are con-
`centric with the eight ideal points 600 and in contact
`with each other.
`Once the critical condition such as shown in FIG. 5C
`is reached wherein the border between adjacent data
`points is identifiable to a certain extent, various parame-
`ters of the modem at the receive station 200 progres-
`sively converge with the lapse of time due to the auto-
`matic adaptive equalization function. This often results
`in the condition shown in FIG. 5B, in which data will
`be successfully received.
`At the receiver 200, the DSP 16 manages such space
`signal vectors of the received signal to see deviations, or
`displacements, of the data points 604 from the ideal
`points 600. That is, the DSP 16 measures the distances
`between the respective data points 604 of the received
`test training data 400 and the ideal signal points 600 on
`the signal space diagram, thereby determining whether
`the received signal was in a bad condition (FIG. SD) or
`in a critical condition. Such discrimination between the
`good condition (FIG. SB), the critical condition and the
`bad condition is effected at the DSP 16 by calculating
`by digital signal processings the distances of the data
`points 604 of the received signal input from the AIF 18
`from the ideal points 600 on the signal space diagram,
`and then comparing the largest distance with the dis-
`tance between adjacent ideal points 600. That is, if the
`deviation from the ideal point 600 is not larger than one
`half the distance between adjacent ideal points 600,
`signals will be normally received at the then existing
`transmission rate.
`
`4,606,044
`
`3
`sion controls and communication controls over the
`entire transceiver station inclusive of the terminal 20.
`Preferably, the system control processor 12 comprises a
`digital processor.
`The transmission line 300 is such an analog transmis-
`sion line as a telephone line and may be in any desired
`configuration such as a public network, a private net-
`work, a switching network or a leased circuit.
`Essential portions of the transceiver station 100 or
`200 are shown in FIG. 2. As shown, the station 100 or
`200 includes a bus 14 to which are connected the CPU
`12, I/O port 10, a digital signal processor (DSP) 16, and
`an analog interface circuit (AIF) 18. The analog inter-
`face circuit 18 accommodates the transmission line 300
`to serve as an interface between the station 100 or 200
`and the line 300, while performing conversion between
`an analog signal on the line 300 and a digital signal in the
`station 100 or 200.
`
`Constituting a central device of the illustrated system,
`the digital signal processor 16 is a processing device
`which implements, by means of digital signal process-
`ings, various functions necessary for a modem which
`include carrier detection, timing extraction, automatic
`gain control and automatic adaptive equalization.
`Where the terminal 20 comprises a facsimile trans-
`ceiver, for example, the CPU 12in accordance with this
`embodiment performs a transmission control
`in the
`non-standard mode which is defined in the CCITT
`Recommendation T.30.
`
`Referring to FIG. 3, connection is set up between the
`transmit station 100 and the receive station 200 by a call,
`for example. In the case of non-standard facilities, when
`an NSF (non-standard facility) signal is returned from
`the receive station 200 to the transmit station 100, the
`CPU 12 at the transmit station 100 sends out test train-
`ing data 400 to the receive station 200 after an NSC
`(non-standard facility command) signal by means of the
`DSP 16 (FIG. 7, step 700).
`As shown in FIG. 4,
`the test training data in the
`illustrative embodiment is transmitted at four different
`transmission rates, 14.4 Kbps, 9.6 Kbps, 7.2 Kbps, 4.8
`Kbps and 2.4 Kbps. Shifting down the transmission rate
`in this manner is desirable from the efficiency stand-
`point.
`Concerning the transmission rate of 9.6 Kbps, for
`example, the symbols of segments 2, 3 and 4 prescibed
`by the CCITT Recommendation V.29 will be sent out,
`total tansmission time amounting to 233 milliseconds
`(ms). The same applies to the transmission rate of 7.2
`Kbps and, in this particular embodiment, also applies to
`the transmission rate of 14.4 Kbps although no such
`recommendation is present for the latter transmission
`rate. As for the transmission rates of 4.8 Kbps and 2.4
`Kbps, the symbols of segments 3, 4 and 5 prescribed by
`the CCITT Recommendation V.27 will be sent out and
`the total times consumed thereby are 708 ms and 943 ms
`respectivley. In the illustrative embodiment, the carrier
`is interrupted for a given period of time, e.g. on the
`order of 20 ms, between adjacent test data representa-
`tive of different transmission rates in order to show a
`change in the transmission rate. In total, therefore, the
`test training data 400 are transmitted over a period of
`2,430 ms.
`At the receive station 200, the DSP 16 causes various
`functions, as those of a modem, to converge using the
`test training data 400. At this instant, the DSP 16 checks
`the functioning state, as that of a modem, for each of the
`transmission rates by use of a signal space diagram,
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`The CPU 12 at the receive station 200, when identi- ,
`fied the normally receivable transmission rate (FIG. 7,
`step 704), returns an answer signal 402 to the transmit
`station 100 via the DSP 16 (step 706). The answer signal
`402 may be sent out at the transmission rate of 300 bps
`as advised by the Recommendation T.3O and includes a
`command indicative of the transmission rate decided by
`the DSP 16 of the receive station 200. At the transmit
`station 100 received the answer signal 402, the CPU 12
`
`

`
`4,606,044
`
`6
`log transmission line through modems which selec-
`tively use a plurality of transmission rates, said method
`comprising the steps of:
`(a) transmitting test training data comprised of data
`bursts in phase modulated form including a plural-
`ity of vectors transmitted at a plurality of data rates
`from a transmit station to a receive station;
`(b) training a modem of said receive station in re-
`sponse to said test training data;
`(c) selecting a transmission rate adequate for commu-
`nication between the transmit and receive stations
`by measuring deviation of the vectors of the test
`training data received by the receive station from
`ideal predetermined values, said measuring having
`a degree of accuracy which is sufficient to discrimi-
`nate among the deviations of test training data
`vectors which are all closer to the same ideal pre-
`determined value than to any other ideal predeter-
`mined value;
`(d) notifying said selected transmission rate from the
`receive station to the transmit station; and
`(e) transmitting data from the transmit station at said
`notified transmission rate.
`2. A data transmission control method as claimed in
`claim 1, in which the transmission of the test training
`data at step (a) is stopped immediately after the notifica-
`tion at step (d).
`3. A data transmission control method as claimed in
`claim 1, in which the transmission of the test training
`data at step (a) is continued even during the notification.
`4. A data transmission control method as claimed in
`claim 1, in which a transmission rate set up when the
`deviation at step (c) is not larger than one half a distance
`between adjacent ideal data points is determined as the
`adequate transmission rate.
`5. A data transmission control method as claimed in
`claim 1, in which the notification at step (d) is effected
`by use of a backward channel.
`6. A data transmission control method as claimed in
`claim 1, in which the notification at step (d) is effected
`by use of a tonal signal.
`7. A data transmission control method as claimed in
`claim 1, in which the analog transmission line is a tele-
`phone line.
`8. A data transmission control method as claimed in
`claim 1, in which the test training data include transmis-
`sion rate data representative of 14.4 Kbps, 9.6 Kbps, 7.2
`Kbps, 4.8 Kbps and 2.4 Kbps.
`9. A data transmission control method as claimed in
`claim 8, in which the test training data further include
`non-transmission periods between the data bursts to
`separate the data bursts from each other, said non-trans-
`rnission periods having a predetermined duration.
`It
`¥
`Ill
`#
`ii
`
`5
`begins a usual sequence for transmitting facsimile data
`404 from the facsimile terminal 20 at the commanded
`trransmission rate (FIG. 7, step 708).
`The delivery of the answer signal from the receive
`station 200 to the transmit station 100 may be effected
`using a backward channel or a tonal signal. In such a
`case, it is preferable to use a frequency band other than
`the occupied bandwidth modems. Then, as shown in
`FIG. 6A, when the modem at the receive station 200
`has been found well conditioned at a time t1, for exam-
`ple, the identified transmission rate is commanded to the
`transmit station 100 by the receive station 200. In re-
`sponse to this command, the CPU 12 at the transmit
`station 100 may immediately stop transmitting the test
`training data 400 and start transmitting facsimile data at
`the commanded transmission rate. Such a construction
`serves to shorten the necessary training time.
`Another possible arrangement in accordance with the
`present invention is such that, as shown in FIG. 6B,
`when the modem at the receive station 200 has been
`found to be in a good condition at a time t1, for example,
`and the identified transmission rate is notified from the
`receive station 200 to the transmit station 100, the CPU
`12 at the transmit station 100 continues to send out the
`remaining part of' the test training data 400 while the
`DSP 16 at the receive station 200, in response to that
`part of the test training data 400, causes the various
`modem parameters to converge so as to further reduce
`the deviation from the ideal signal points, thereby refm-
`ing the receipt preparation.
`In summary, it will be seen that the present invention
`provides a data transmission control system which is
`capable of performing, on transmission rates which a
`modem may utilize, a training sequence within a test
`time which reconciles itself to a usual test sequence.
`Therefore, training can be excecuted for the transmis-
`sion rates usable for a modem which satisfies a predeter-
`mined protocol and, yet, entails no increase in the pro-
`tocol time.
`Especially, where the line condition involves fre-
`quent shift-downs in transmission rate where use is
`made of high-speed modems and, therefore, shift-downs
`are apt to occur, the present invention is successful to
`effectively shorten the protocol time. In practice, the
`effect of the present invention will become more promi-
`nent with an increase in transmission rate and it is feasi-
`ble for facsimile communications which uses 14.4 Kbps
`modems, for example.
`Various modifications will become possible for those
`skilled in the art after receiving the teachings of the
`present disclosure without departing from the scope
`thereof.
`What is claimed is:
`
`10
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`1. A data transmission control method for allowing
`remote transceiver stations to transmit data via an ana-
`
`55
`
`60
`
`65