JPH0124378B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a training method for a data modem, and more particularly to a training method for speeding up the setting of a modem receiver. In modems for high-speed data transmission, before transmitting data from a terminal device, the modem receiver includes a It is necessary to set up the various functional blocks that will be implemented. This setup procedure is called a turn-on sequence or a training sequence, and the CCITT (Consultative Committee for International Telegraph and Telephone) also recommends it according to the communication speed.
V27ter and V29 are recommended. In this training sequence, (1) establishing the operation of the automatic gain control circuit (AGC), (2) creating a synchronized clock, (3) converging the automatic equalizer and correcting the carrier phase, and (4) synchronizing the data are mainly performed. , for example the aforementioned CCIT
T. Recommendation specifies the sequence of line signal formats as shown in Table 1 below.

[Table] As can be seen from Table 1, the time required to execute the training sequence is 265 ms or 923 ms with segments and 923 ms on V27ter, and 50 ms without segments.
milliseconds or 708 milliseconds. Also, in V29 it is 253
It takes milliseconds. Therefore, for example, when performing multipoint operation by connecting three terminal stations with V29 interface circuits to one transmission line, the time required to execute the training sequence is at most 253.
×It takes 31 seconds. In such multipoint operations, the efficiency of using the transmission path is an important factor in terms of system cost and performance, and therefore it is desirable that the execution time of the training sequence be as short as possible. Conventionally, measures have been taken to speed up the convergence of the automatic equalizer, which is particularly important in the training sequence, for example, as shown in (1) to (3) below. (1) Send a pseudo-random signal sequence with a period equal to the tap length. In reception, after inputting one cycle, these signal sequences are used for cycling,
Convergence of the automatic equalizer is achieved through high-speed calculation. (2) A signal sequence on which the automatic equalizer can easily converge (a sequence with small variations in the eigenvalues of the autocorrelation matrix between signals)
, and thereby the automatic equalizer converges. (3) Regenerate impulses from pseudo-random sequences or modulated impulses, measure the frequency characteristics of the transmission path using Fourier transform, give inverse characteristics, and set the tap coefficients of the automatic equalizer using inverse Fourier transform. . However, when using the pseudorandom sequence in (3) above for convergence of an automatic equalizer in the so-called MS method, a considerably long trial time is required, and a large amount of correlation calculation is required to reproduce and use the impulse. Ru. That is, the frequency characteristics of the transmission path are investigated by sending out impulses and pseudo-random sequences as described above. This is because these signals contain components over the entire frequency band, so they can be estimated by looking at how they change. However, when transmitting a random sequence, a sufficiently long sequence is required to transmit components over the entire frequency band, which takes time. On the other hand, impulses cannot instantaneously send out large-level signals. Therefore, by using special training for modems,
By including impulses, it is possible to avoid the drawbacks of both. It is an object of the present invention to provide two signals necessary for setting an automatic equalizer as initial training signals for a data modem.
Based on the concept of using a modulated signal containing impulses with the same symbol interval data, the purpose is to shorten the execution time of the training sequence required to set up various functional blocks included in the modem receiver. In the present invention, an effective impulse sequence is provided for an equalization algorithm that actively uses impulses, and it is also useful for setting several functions other than automatic equalizers, such as automatic gain adjustment circuits and timing pull-in circuits. A data modem training scheme is provided that provides useful information. Hereinafter, embodiments of a data modem training method according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an example of a data transmission system to which the present invention is applied. In FIG. 1, after a transmission request is sent from the transmitting terminal device 1 to the modem receiving section 3 of the terminal station via the modem transmitting section 2, the data is reliably sent to the modem receiving section via the distorted line 4. A training signal is sent from the terminal device 1 so as to be received. The modem receiving section 3 receives this training signal and transmits the training signal to the modem receiving section 3.
Set up the automatic equalizer, automatic gain adjustment circuit, timing pull-in circuit, etc. included in the system. When this setup is completed, the modem transmitter 2 returns a send enable signal CS to the terminal device 1. The terminal device 1 transmits data only after receiving the send clear signal CS. The object of the present invention is to shorten the setup time of various functional blocks using this training signal. In Figure 1, line 4
shows the case where a single terminal station is tangential, but
When a plurality of terminal stations are connected, it is even more desirable to shorten the setup time from the viewpoint of cost performance. FIG. 2 is a signal constellation diagram showing the format of a training signal according to one embodiment of the present invention. As shown in FIG. 2, the training sequence is performed by sequentially delivering training signals from the segments. Only carrier signals are sent in the segment. Since the carrier signal has little level fluctuation due to differences in lines, it is useful for speeding up the setup of automatic gain adjustment circuits and carrier detection circuits. In the training signal segment, a signal that alternately repeats the zero phase and π phase on the phase plane is transmitted, and by transmitting the Nyquist component, it is easy to extract the timing component, and the timing of various functional blocks of the modem receiver is transmitted. Establishment is faster. In the segment of the training signal, according to the invention, the modulated signal shown in FIG. 3a containing an impulse is transmitted. That is, the segment is 3
It is divided into two subsegments -1, -2 and -3, and subsegments -1 and -3.
In this case, the same zero-phase and π-phase repetitive signals as in the segment are sent, but in the subsegment
In step 2, the data of two consecutive symbol intervals are made the same and transmitted. That is, the repetition of zero phase and π phase is interrupted by one symbol interval and then transmitted. The modem receiving section that receives the signal shown in FIG. 3a in the segment transmits the signal shown in FIG.
By obtaining the signal shown in FIG. 3b and calculating the sum of the signals in FIG. 3a and b, the impulse train shown in FIG. 3c can be easily reproduced. In this way, by sending out a signal including the impulse shown in FIG. 3a in the segment, the automatic gain adjustment circuit,
In addition to stabilizing the operations of the carrier detection circuit and timing detection circuit, the impulse train necessary for convergence of the automatic equalizer, which is the original purpose, can be obtained in the modem receiving section. In the training signal segment, a binary random signal sequence (PN pattern) or zero phase and π
A signal is sent out with alternating phases, thereby
The automatic equalizer converged by the impulses reproduced in the segment is further converged finally,
Also, synchronization of the descrambler in the binary code conversion section of the modem reception section is established. By using the training signals explained above, the execution time of the training sequence is approximately 20
Reduced to milliseconds. FIG. 4 is a block diagram showing a training signal generation circuit explained in connection with FIGS. 2 and 3. In FIG. 4, in an initial state such as when the power is turned on, the symbol counter 41 is set to the segment counter 4.
Loads the contents of the symbol read-only memory (ROM) 43 indicated by all 0's output from step 2.
The output of the ROM 43 indicates the number of symbols in each segment of the training signal, and the symbol counter 41 uses the loaded value as an initial value and counts each symbol by the symbol clock SC. Carry output of symbol counter 41
CR means the end of the segment, and this serves as a clock for the segment counter 42 and increments the counter 42 by one. That is, the counter 42 indicates the number of segments. One of the outputs of segment counter 42 addresses ROM 43 to give the number of symbols in the next segment;
The other output addresses the training signal ROM 44 to generate the training signal.
A training signal according to the present invention is stored in the ROM 44, and the symbol clock is divided into two by a frequency divider 4.
5 and the output of the segment counter 42. ROM
The output of 44 is latched into latch circuit 46 by symbol clock SC, and the desired training signal is available at its output. Detector 47 is used to generate impulses. That is, when a signal indicating that subsegment-2 within the segment has been addressed is given to the detector 47 from the ROMs 43 and 44, the detector 47
8 to stop the operation of the frequency divider 45.
As a result, the output of the halving cycle 45 has two identical states during the symbol interval of sub-segment-2, allowing impulse information to be included in the training signal. Note that the frequency divider by two is initialized by the clear signal C in the initial state. As explained with reference to FIG. 3, a modulated signal containing impulses can be obtained by inserting the same data into the zero-phase and π-phase repetitive signals at consecutive two-symbol intervals. is not limited to this. For example, as shown in Figure 5, a zero-phase carrier is sent out in a segment, and a π
The step signal in Fig. 5a obtained at the modem receiving section by sending out the phase carrier is delayed by one symbol interval to obtain the step signal in Fig. 5b, and the difference between the step signals in Fig. 5a and b is calculated. The impulse train shown in FIG. 5c may be reproduced by taking the following steps. In addition, as shown in FIG. 6a, the segment repeatedly sends out zero-phase and π-phase signals every 2 symbol intervals, the segment sends out the same phase signal over 3 symbol intervals, and the segment again sends out the same repeated signal as the segment. You may send it. The signal shown in Figure 6a itself is useful for stabilizing the operation of the automatic gain adjustment circuit and the carrier detection circuit, and the signal shown in Figure 6a is useful for stabilizing the operation of the automatic gain adjustment circuit and carrier detection circuit. The signal for timing extraction shown in Figure c is obtained. By taking the sum of the signal in FIG. 6 d and the signal in FIG. 6 a obtained by delaying the signal in FIG. 6 a by two symbol intervals, the signal in FIG.
The impulse train shown in figure e is still obtained. In addition, various methods of making the impulse train latent in the modulated signal can be considered, but as long as the impulse train is obtained by taking the sum or difference between the transmission signal and its delayed signal, they belong to the scope of the present invention. As is clear from the above description, according to the present invention, the modem receiver can be trained using a modulated signal containing an impulse train, so that the execution time of the training sequence can be significantly shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one example of a data transmission system applied to the present invention, and FIG.
A signal arrangement diagram showing the format of a training signal according to an embodiment, FIG. 3 is a waveform diagram of a modulation signal including an impulse train according to an embodiment of the present invention, and FIG. 4 is a training diagram explaining the format of FIGS. 2 and 3. A block diagram showing a signal generation circuit, and FIGS. 5 and 6 are waveform diagrams of modulated signals containing impulse trains according to other embodiments of the present invention, respectively. 1...Terminal device (transmission), 2...Modem transmission section,
3...Modem receiving unit, 4...Line, 5...Terminal device (receiving), 41...Symbol counter, 42...
...Segment counter, 43...Read-only memory for symbols, 44...Read-only memory for training signals, 45...2 frequency divider, 46...Latch circuit, 47...Detector, 48...Gate, T... …1
symbol interval.

Claims (1)

[Scope of Claims] 1. Equipped with an automatic gain adjustment circuit, a timing detection circuit, a carrier detection circuit, and an automatic equalizer, the zero-phase and m-symbol interval (m is a positive integer) sent from a transmitting terminal In a training method for a modem receiver that initially stabilizes the operation of the automatic gain adjustment circuit, timing detection circuit, and carrier detection circuit using a training signal that repeats a π phase of m symbol intervals, An impulse train connotative signal in which n symbol intervals (n is a positive integer greater than m) are data of the same phase, and the signal of the n symbol interval and the signal of the interval immediately before the n symbol interval are of opposite phase. The automatic equalization is performed by calculating the difference or sum between the impulse train inclusive signal and a signal obtained by delaying the impulse train inclusive signal by k symbol intervals (k is a positive integer smaller than n). A data modem training method characterized by obtaining an impulse train necessary for convergence of a data modem. 2. The training signal is a signal that alternately repeats a zero phase of one symbol interval and a π phase of one symbol interval, and the impulse train connotative signal is a signal that repeats a continuous two-phase signal in the middle of the training signal.
Claim 1, wherein the symbol interval is data of the same phase, and the signal of the two symbol intervals and the signal of the interval immediately before the two symbol intervals are of opposite phase. training method. 3. The training signal is a signal that alternately repeats a zero phase with a 2-symbol interval and a π-phase with a 2-symbol interval.
Claim 1, wherein the symbol interval is data of the same phase, and the signal of the 3 symbol interval and the signal of the interval immediately before the 3 symbol interval are of opposite phase. Data modem training method. 4 Equipped with an automatic gain adjustment circuit, a timing detection circuit, a carrier detection circuit, and an automatic equalizer, the automatic gain adjustment circuit and timing detection are performed using a step signal consisting of zero phase and π phase sent from a transmitting terminal. In a modem receiver training method that initially stabilizes the operation of the circuit and carrier detection circuit, the difference between the step signal and a signal obtained by delaying the step signal by k symbol intervals (k is a positive integer) is calculated. A training method for a data modem, characterized in that an impulse train necessary for convergence of the automatic equalizer is obtained by