JPH0541679A - Method for measuring bulk delay for echo canceller for modem - Google Patents

Abstract

PURPOSE:To easily set the accurate bulk delay even when the line state is not good. CONSTITUTION:A dial-tone modem transmits a first tone signal from a tone signal generator 16 to a response modem. The response modem receives a first tone signal, and transmits a second signal with different frequency to the dial-tone modem. The dial-tone modem stops the transmission of the first tone signal from the tone signal generator 16 when a tone signal detection device 17 detects the second tone signal. Thus, the dial-tone modem can find the bulk delay based on the time from the transmission of the first tone signal to the reception of the second tone signal and the response modem can know it based on the time from the reception and the end of the reception of the first tone signal.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of training to determine the amount of bulk delay associated with the far end echo canceller of a two wire full duplex modem.

[0002]

2. Description of the Related Art In a two-wire full-duplex modem, a transmission signal is circulated by a two-wire four-wire conversion hybrid in a self-modem and a two-wire four-wire conversion hybrid in a station accommodating a partner modem. Since the received signal transmitted from the other party is distorted due to the echo and the far-end echo, it is necessary to provide a near-end echo canceller and a far-end echo canceller to cancel these echoes.

A conventional technique for echo cancellation will be described below with reference to FIGS. 2, 3 and 5. Here, FIG. 2 shows a communication conceptual diagram of a two-wire full-duplex modem. Also, FIG.
(A) is V.I. 32 (CCITT RECOMMENDATIONS Recommendation V.3
2) Modem startup procedure, FIG. 3 (b) is a training method for determining the amount of bulk delay therein, FIG.
(C) shows the signal constellation of the modem. FIG. 5 shows an example of the impulse response of the echo path seen from the own modem.

In FIG. 2, the transmission signal is a self-modem 20.
2 in order to cancel the near-end echo shown in FIG. 5 that wraps around by the 2-line to 4-line conversion hybrid 4 and the hybrid 5A of the own exchange, the near-end echo canceller 6 shown in FIG.
Is provided.

Further, the transmission signal is delayed by the two-wire / four-wire conversion hybrid 5B in the station accommodating the partner modem 40 and the two-wire / four-wire conversion hybrid 4 of the partner modem 40, which is delayed in time as shown in FIG. A far-end echo canceller 7 shown in FIG. 2 is provided to cancel the far-end echo. The near-end echo canceller 6 and the far-end echo canceller 7 are composed of an adaptive digital filter (hereinafter referred to as ADF) that uses the modem transmission data as a reference signal, and a near-end echo canceling signal and a far-end echo canceling signal are output to adders. A / D converter 9 with 10 and 11
The near-end echo and the far-end echo input from are subtracted from each other to erase the echo.

However, the bulk delay amount (round-trip round-trip time) shown in FIG. 5 until the far-end echo appears is 6 when the satellite line is included in the public line.
Since it may exceed 00 ms, the far-end echo canceller 7
Since it is wasteful in terms of hardware to have a corresponding number of ADF taps, the bulk delay 8 absorbs this portion.

The operation of the two-wire full-duplex modem shown in FIG. 2 will be described in detail below.

The digital data signal input from the transmission data terminal 1 of the self-modem 20 is modulated in the modem transmission section 2 and converted into an analog signal (transmission signal) in the D / A converter 3 to be converted into 2-wire 4-wire in the modem. Public line 30 through hybrid (hereinafter referred to as hybrid) 4
Sent to. At this time, near-end echo occurs mainly in the hybrid 4 and the hybrid 5A of the converter of the local station mainly due to impedance mismatch of the hybrid. Further, this transmission signal is transmitted through the public line to the hybrid 5B in the station accommodating the partner modem 40 and the partner modem 40.
And the far-end echo shown in FIG. 5 is generated. As described above, these echoes return to the own modem 20 and are converted into digital signals by the A / D converter 9, and the echoes from the near-end echo canceller 6 and the far-end echo canceller 7 are added at the adders 10 and 11, respectively. The near-end echo and the far-end echo are canceled by subtracting the cancellation signal. As a result, only the signal from the partner modem 40 is sent to the modem reception unit 13 after the full-duplex communication state is reached, and the demodulated reception data reaches the reception data terminal 14.

If the impulse response of the echo path is not sufficiently estimated before entering the full-duplex communication state, the signal from the other party cannot be correctly received when the full-duplex communication is established, so that the initial training is generally performed. As an example, V.I. The startup procedure of 32 will be described below with reference to FIG. Figure 3
(A) is V.I. 32 is a schematic diagram of 32 startup procedures. FIG. Sequence 1 for bulk delay measurement is performed at the beginning of the start-up procedure of the call modem and answer modem in the figure. Sequence 2
Items 4 to 4 will not be described here except for the description shown in the drawing.

FIG. 3B shows the details of the sequence 1.
FIG. 3C shows the signal constellation of the modem used for the training performed in sequence 1.

The call modem waits for a response (ANS) from the answer modem, and points A of the constellation of modem signals in FIG.
The signal corresponding to the state is repeatedly sent to the answer modem by an even multiple of the symbol time T. In response to this, the answer modem alternately outputs signals corresponding to the states of points A and C in the constellation of the modem signal of FIG. After a certain period of time, the answer modem then alternately transmits a signal corresponding to the state of the points C and A of the modem signal constellation to the call modem at an even multiple of the symbol time T after t = t1. The call modem grasps this change and after 64T ± 2T time, at t = t2, sends a signal corresponding to the point C state of the modem signal constellation repeatedly to the answer modem at an even multiple of the symbol time T. When the answer modem receives and detects this change point, it
After T ± 2T time, at t = t3, this time again, the signals corresponding to the states of the points A and C of the modem signal constellation are alternately transmitted to the call modem by an even multiple of the symbol time T. The call modem detects this at time t = t4 and stops signal transmission. Similarly, the answer modem also stops signal transmission after confirming that the call modem signal transmission is stopped. As a result, the bulk delays of the call modem and answer modem are t4-t2- (64T ± 2T) and t3-t1-.
It is calculated as (64T ± 2T). ± 2 is decided by the modem. Control and calculation of these processes are performed by the control unit 1 of FIG.
2 takes place. In this way, bulk delay 8
Is set to the required value.

[0012]

However, the above-mentioned method for determining the bulk delay is as described in the previous section.
Since the inversion of the phase signal is used, the echo component of the self-transmitted signal is superposed, and when the line condition (S / N, distortion) is very bad, the line automatic equalizer of the receiving unit trains. Since it was before the operation, the receiving side sometimes made a mistake and sometimes the correct bulk delay could not be set. There is also a problem that the control method is complicated because the method for determining the bulk delay is relatively complicated.

The present invention eliminates the above-mentioned problems,
It is an object of the present invention to provide a bulk delay measurement method for an echo canceller for a modem, which is simple and can set a correct bulk delay even if the line condition is bad.

[0014]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a method of measuring the bulk delay of a far-end echo canceller in a two-wire full-duplex modem, in which a calling modem sends a first tone signal as a response modem. When the second tone signal from the answer modem is received and the answer modem receives the second tone signal from the answer modem, and when the answer modem receives the first tone signal, the answer modem has a frequency different from that of the first tone signal. 2 tones, the calling modem transmits the first tone signal and then receives the second tone signal, the response modem receives the first tone signal from the first tone signal to the second tone signal. The bulk delay is determined depending on the time until the reception ends.

[0015]

Since the frequency of the first tone signal transmitted by the calling modem and the frequency of the second tone signal transmitted by the response modem are set to be different during the bulk delay measurement, the tone transmitted by itself is set. Even if the echo component of the signal is superimposed, the tone signal from the other party can be accurately detected. Also, by detecting the level of the tone signal, it is possible to determine when the tone signal is received or when the reception is completed.
The bulk delay can be accurately measured even when the line condition is very poor.

[0016]

FIG. 1 is a block diagram showing the embodiment of the present invention.

The same parts as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 1, reference numeral 16 is a tone signal generator, 17 is a tone signal detector, and 15 has a function of controlling the tone signal generator 16 and the tone signal detector 17 in addition to the function equivalent to that of the control unit 12 shown in FIG. It is a control unit that has. FIG. 4 shows an embodiment of sequence 1 according to the present invention, which is similar to FIG. 3 (b).

The call modem shown in FIG. 1 waits for a response from an answer modem (not shown), and the switch sw1 shown in FIG.
To the frequency b from the tone signal generator 16
_Send a ₀ signal to the other answer modem. This time is t = t5. The answer modem detects this tone signal with a tone signal detector (similar to tone signal detector 17) for a tone signal of frequency f ₀ , and time t =
The process returns to t7 and the tone signal generator (similar to the tone signal generator 16) sends the tone signal of frequency f ₁ to the call modem. Call modem frequency f ₁ the tone signal of the frequency f ₁ tone signal detector 17
Detect with. This time is t = t6. After the detection, the transmission of the signal of frequency f ₀ is stopped. On the other hand, the answer modem detects this signal stop at time t = t8 and detects the frequency f ₁
Stop sending the tone signal.

The tone signal generator 16 can be executed by storing it in a ROM or the like and calling it. The tone signal detector can be realized by using methods such as filtering, zero-crossing detection, and tone signal prediction in addition to level detection.

The detection time until the tone signal is detected is A / D
If the sampling time of the converter 9 is high, it is possible to detect the signal within the symbol time T by using the level detection together. As a result, with the involvement of the control unit 15, the bulk delay 8 of the call modem and answer modem is obtained and set as follows.

Call modem side t6-t5- (T + T) Answer modem side t8-t7- (T + T) Here, the bulk delay 8 is to determine the number of stages of the shift register. After that, sw1 is tilted to the a side and the sequence 2 and subsequent steps are executed. Further, if this sequence is repeated and executed again, the bulk delay can be set more accurately.

[0022]

As described in detail above, according to the present invention, since the training sequence is simple and easy, the bulk delay can be set in a short time. In addition, since it is not necessary to determine the phase, the bulk delay can be set using simple tone detection even when the echo component of the self-transmitted signal is superposed or the line condition (S / N, distortion) is very bad. it can.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a communication conceptual diagram of a two-wire full-duplex modem.

FIG. It is explanatory drawing of the startup procedure of 32.

FIG. 4 is a diagram showing an example of sequence 1;

FIG. 5 is a diagram showing an impulse response example of an echo path.

[Explanation of symbols]

 16 tone signal generator 17 tone signal detector sw1 switch

Claims (1)

[Claims] 1. A method of bulk delay measurement of a far-end echo canceller in a two-wire full-duplex modem, wherein a calling modem sends a first tone signal to an answering modem and a second tone signal from the answering modem. When the answering modem receives the first tone signal, the answering modem transmits the second tone signal having a frequency different from that of the first tone signal, and the calling modem receives the first tone signal. 2nd after transmitting 1 tone signal
Of the echo canceller for a modem, wherein the response modem determines the bulk delay depending on the time from the reception of the first tone signal to the end of the reception. Bulk delay measurement method.