JPS593046B2 - Data transmission automatic equalization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic data transmission equalization method that automatically equalizes the frequency characteristics of a transmission path in a baseband pulse transmission method.

Conventionally, a sloped AGC method has been used as one of the automatic equalization methods used for baseband pulse transmission.

Figure 1 shows an example of a receiving section of a baseband pulse transmission system using this slope AGC system.The received wave from the transmission line is applied to the signal input terminal 1, and the slope AGC circuit 2 sends a signal to the transmission line. After the frequency characteristics are compensated and the signal is shaped into a Nyquist waveform by the waveform shaping circuit 3, the signal level is identified by the identification circuit 4 and outputted to the output terminal 5. On the other hand, the output 6 of the waveform shaping circuit 3 is applied to a peak detection circuit T, and the peak value of the signal is detected. This peak detection circuit T outputs a signal corresponding to the detected peak value, thereby controlling the characteristics of the slope AGC circuit 2. Further, the output of the waveform shaping circuit 3 is also applied to a timing generation circuit 8, and timing pulses necessary for identification are generated and applied to the identification circuit 4. By the way, in baseband pulse transmission using a cable, it is known that the peak value of a waveform-shaped signal is proportional to the cable loss at a frequency that is 1/2 of the transmission speed.

It is also known that the typical loss characteristics of cables can be approximated by a simple low-pass filter, and the above-mentioned conventional example was constructed based on this fact. That is,
The slope AGC circuit 2 is a simple high-pass type circuit that approximates the inverse characteristics of the transmission line within the signal band, and its characteristics are controlled and determined by a control signal so that the peak value of the signal becomes a constant value. By adjusting the characteristics of the slope AGC circuit 2, the frequency characteristics of the transmission path are compensated. In this method of compensating for the cable loss characteristics using the signal peak value, it is necessary that a simple relationship be established between the cable loss characteristics and the signal peak value, as described above.

- In general, the loss characteristics of cables have the form shown in Figure 2. Here, the loss where the loss is flat in the low frequency range will be referred to as the peace zone loss, and the slope of the loss characteristic in the high frequency range will be referred to as the loss deviation. The peak value of this signal is a function of the finger loss and the loss deviation, whereas the intersymbol interference, which actually becomes a transmission characteristic problem, is a function of the loss deviation. Furthermore, although the q relationship between flat part loss and loss deviation differs depending on the type of cable, the above method estimates and equalizes the frequency characteristics of the transmission line from the signal peak value, which is a function of flat part loss and loss deviation. The purpose of this is to reduce intersymbol interference, which is a function of loss deviation. Therefore, in this type of system, there are fewer types of cables used as transmission lines,
It is good if the relationship between flat part loss and loss deviation is simple, but
For example, in a transmission line where there are many types of cables, such as in a city section, and cables with different core diameters are connected in cascade, it becomes difficult to estimate the loss deviation from the signal peak value alone. The drawback was that intersymbol interference inevitably increased. In order to solve the drawbacks of the conventional example, the present invention provides an automatic data transmission equalization method that can achieve higher quality equalization by controlling a variable equalizer using intersymbol interference. It is.

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which 9 is a received signal terminal, 10 is an automatic gain control circuit, 11 is a variable equalizer, 12 is a waveform shaping circuit, 13 is an identification circuit, 14 is an identification result output terminal, 15 is a waveform shaping circuit output terminal, 16 is a timing generation circuit, 17 is a control circuit for a variable equalizer,
18 is an error extraction circuit. FIG. 4 shows a circuit example of the control circuit 17, in which 19 is a manual terminal that receives the waveform shaping circuit output, 20 is a manual terminal that receives timing pulses, 21 is a sampling circuit, and 22 is a manual terminal that receives a timing pulse.
23 is a multiplication circuit; 24 is a manual terminal that can receive an error signal; 25 is a sampling circuit; 26 is an averaging circuit; and 27 is a control signal output terminal. Next, the operation of this embodiment will be explained with reference to FIGS. 3 and 4.

As shown in FIG. 3, the received signal applied to input terminal 9 is
The automatic gain control circuit 10 automatically adjusts the gain to a specified level within the device. Information used for this adjustment is supplied from the terminal 15 of the waveform shaping circuit 12, and is adjusted by a known automatic gain control method so that the peak value or average power of the signal appearing at the terminal 15 is at a specified level. Further, the received signal adjusted to a specified level by the automatic gain control circuit 10 is compensated for the frequency characteristics of the transmission path by the variable equalizer 11, and is shaped into a specified waveform, for example, a Nyquist waveform by the waveform shaping circuit 12. , the signal level is identified by the identification circuit 13 and outputted to the identification result output terminal 14. The combination of the automatic gain control circuit 10 and the variable equalizer 11 corresponds to a slope AGC equalizer consisting of a conventional equalizer and a control signal extraction circuit. Also, terminal 1
The signal appearing at 5 is applied to a timing generation circuit 16, which generates timing pulses necessary for identification and timing pulses necessary for controlling the variable equalizer 11, which are then sent to the identification circuit 13 or the control circuit 17 for the variable equalizer, respectively. supplied to The error extraction circuit 18 is a subtraction circuit, which subtracts the output of the discrimination circuit 13 from the output of the waveform shaping circuit Ftl2 to extract an error signal at the discrimination time point and supplies it to the control circuit 17. This control circuit 17 uses the signal appearing at the terminal 15 and the output of the error extraction circuit 18 to estimate the amount of intersymbol interference after one Nyquist interval from the main response of the pulse response appearing at the terminal 15, and performs variable equalization. A control signal used by the equalizer 11 is generated and supplied to the variable equalizer 11. Further, in accordance with the configuration shown in FIG. 4, the output of the waveform shaping circuit 12 applied to the terminal 19 is sampled by the sampling circuit 21 in accordance with the timing pulse applied to the terminal 20 indicating the point 1Vf of the signal.

The sample value of this sampling circuit 21 is transmitted to the delay circuit 22.
The signal is delayed by one Nyquist interval and passed to the multiplication circuit 23. On the other hand, the error signal applied to the terminal 24 is sampled by the sampling circuit 25 according to the timing pulse from the terminal 20, and then passed to the multiplication circuit 23. This multiplier circuit 23 multiplies the signals from the delay circuit 22 and the sampling circuit 25, and the result is averaged by an averaging circuit 26 and output to a terminal 27. This output is a value proportional to the intersymbol interference that appears one Nyquist interval after the main response of the impulse response of the system, as shown below. Now, let g(0) be the impulse response of the entire transmission system including the waveform shaping circuit 12 of the receiving section, {An} be the transmission code sequence, and r(t) be the output of the waveform shaping circuit 12.
If 1 Nyquist interval is T, then

Here, g(t) is the Nyquist waveform, ideally g{
. )=1, g(IT)=0 (i is an integer excluding 0). To avoid complications, if r(KT) is expressed as Rk, then equation (1) for t=KT can be expressed as follows. The first term on the right side of equation (2) is the necessary information for t=KTltc, and the second term is the intersymbol interference that occurs when g(1) deviates from the ideal response. If the estimated value of the transmission code at t=KTVc is , then the output of the error extraction circuit 18 (e(1
) at t=KT is as follows.

This is because if the estimation is performed correctly, Ik=Ak.

On the other hand, the output of the delay circuit 22 at this point is Ak-,
Therefore, the output of the averaging circuit 26 is as follows.
However, it is assumed that E(x) indicates the average value of the random variable X. Here, assuming that there is no phase difference in the transmission code sequence, equation (5) becomes.

Here, gl is the intersymbol interference that appears one Nyquist interval after the main impulse response of the system, so
It can be seen that the output of the averaging circuit 26 has a value proportional to this intersymbol interference. Figure 5 shows an example of the attenuation characteristics of a city cable transmission line, and the value when a paper insulated cable with a core diameter of 0.5 rrm is terminated with a pure resistance of 1100 is as follows.
The length of the cable is expressed as a parameter. 6th
The figure shows this transmission line with 64 kb/s and a duty of 50 yen (
Therefore, a rectangular pulse with a pulse width of 1/1.28 x 103 [seconds] is sent out, and the attenuation characteristics of the transmission path are adjusted to a certain equalization residual (
The cable characteristics of TOm in cable transmission are t+A
The output rectangular pulse is equalized by 100 (F6 squared cosine roll-off waveform). From the main response g (.) of the impulse response g (0 (t is time [seconds]) after passing through a waveform shaping circuit that shapes it into 1 Nyquist interval T [seconds] (1/64 × 104 [seconds]) The intersymbol interference amount g{r) that appears later is scaled by the value of the main response, and the value g(r)/g(.) is expressed in correspondence with the magnitude of the equalization residual.Cable transmission Since the path generally has low-pass characteristics, when equalization is insufficient (that is, when the equalization residual is negative), the response becomes slow, and as is clear from FIG. 6, g(. 》〉For O, g(r〆g(.)〉0. Conversely, when the equalization is excessive (that is, when the equalization residual is positive), it becomes a high-pass type, so the response is fast. If the equalization residual is below a certain level, then g(r〆g(.)〈O for g(0〉0). Therefore, by using this property, the entire system is automatically Thus, the automatic equalization method of the present invention is performed by controlling the frequency characteristics of the variable equalizer 11 so that the amount of intersymbol interference becomes zero. In other words, yo(
When r)/g(.)>0, the relative gain of the circuit 11 in the high frequency band relative to the low frequency band is made larger, and g(RY/g(.
), conversely, control is performed to make the relative gain in the high frequency range smaller than that in the low frequency range. In this example, an automatic gain control circuit is used as a circuit for adjusting the reception level to a specified level within the device, but this can also be configured with a manual variable amplifier or a variable attenuator. Further, although this embodiment is shown using an analog circuit, it may be constructed using a digital circuit having an equivalent algorithm.

Furthermore, in this embodiment, for estimating the amount of intersymbol interference g(r),
Although the method used in the method generally known as the MS method is shown, it is also possible to use a method used in the generally known ZF method, MZF method, or HYB method instead. As explained above, according to the present invention, the amount of intersymbol interference that appears after one Nyquist interval is estimated from the main response of the impulse response of the system, and the amount is
Since the variable equalizer 11 is controlled so that the flat section loss is There is an advantage that the attenuation characteristics of the transmission line, which has an uneven relationship with the Loss arrow deviation, can be automatically equalized using a relatively simple circuit. Brief explanation of the drawings Fig. 1 is a circuit diagram of an example of a baseband pulse transmission system receiving section using Jumei's sloped AGC system, and Fig. 2 is a diagram showing the loss frequency characteristics of the cable. , FIG. 3 is a circuit diagram of one embodiment of the present invention, and FIG. 4 is a circuit diagram of the third embodiment of the present invention.
FIG. 5 is a diagram showing an example of the attenuation characteristics of a local cable transmission line, and FIG. 6 is a diagram showing the relationship between the equalization residual and the amount of intersymbol interference. It is a figure showing an example.

1... Signal manual terminal, 2... Inclined AG
C circuit, 3... waveform shaping circuit, 4... identification circuit, 5... output terminal, 6... waveform shaping circuit output terminal, 7... ...Peak detection circuit, 8
..... Timing creation circuit, 9 .... Received signal manual terminal, 10 .... Force gain control circuit, 11
...Variable equalizer, 12...Waveform shaping circuit, 13...Identification circuit, 14...Separate result output terminal, 15...・Waveform shaping circuit output terminal,
16... Timing creation circuit, 17...
・Control circuit, 18...Error extraction circuit, 19...
...Human power terminal, 20...Timing pulse input terminal, 21...Sampling circuit, 22...
... Delay circuit, 23 ... Multiplication circuit, 24
......Human power terminal, 25...Sampling circuit, 26...Averaging circuit, 27...Control signal output terminal.

Claims (1)

[Claims] 1 In the receiving section of the baseband pulse transmission method, there is an automatic gain control circuit that adjusts the received signal level to a specified level within the device, a variable equalizer that compensates for the frequency characteristics of the transmission path, and a noise outside the signal band. a filter for removing the filter, an identification circuit for identifying the transmission code sequence from the output of the filter, and an error extraction circuit for extracting an error component in the received signal from the identification result of the reception signal and the transmission code sequence; A control circuit that estimates the amount of intersymbol interference in the impulse response of the transmission system from the received signal and the identification result and generates a control signal for controlling the variable equalizer from the estimation result, and a timing pulse necessary for device operation. 1. A data transmission automatic equalization system, comprising: a timing creation circuit for creating a signal, and controlling said variable equalizer using intersymbol interference to automatically equalize frequency characteristics of a transmission path.