JPS6249732A - Decision feedback type equalizing system - Google Patents

Abstract

PURPOSE:To obtain a controlling method which is simple and requires a small scale of hardware, by obtaining a difference signal by subtracting inter-dummy code interference from a receiving signal containing inter-code interference, then, finding inter-remaining code interference by adding or subtracting a delaying signal which the difference signal to or from the difference signal. CONSTITUTION:A receiving signal inputted to an input terminal 1 is supplied to a subtractor 2. A difference signal (= a receiving signal containing inter- remaining code interference) obtained by subtracting the inter-dummy code interference produced by an adaptive filter 5 at the subtractor 2 is supplied to a discriminator 3, delay element 8, and subtractor 9. The output of the discriminator 3 is supplied to an output terminal 4, pattern checking circuit 11, and the adaptive filter 5. The pattern checking circuit 11 controls the said loop circuit so that coefficient updating can be performed selectively. A selector 13 selects the outputs of another selector 10 and the subtractor 2 in accordance with the signal of the discriminator 3 and supplies the selected result to a switch 14. The switch 14 selects the output of the selector 10, output of the subtractor 2, or output of the selector 13 in accordance with a sample phase and supplies the selected one to the adaptive filter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control method for a decision feedback type equalizer used to eliminate intersymbol interference that occurs during waveform transmission.

(Prior Art) A decision feedback type isolator is known as a known technique for removing intersymbol interference that occurs during waveform transmission. (Ieeeeee Transactions, on.

Communications (IEEE TRANSACTI)
ONS ONCOMMUNICATIONS) Volume 32 3
No. 1984, pages 258-266. ) The decision feedback equalizer generates pseudo intersymbol interference corresponding to the received data sequence using an adaptive filter with tap coefficients of a length that is affected by intersymbol interference.
It operates to suppress intersymbol interference received while the waveform is being transmitted through the transmission path. At this time, each coefficient of the adaptive filter is successively modified by correlating the residual intersymbol interference with the determination result of the received signal.

When modifying coefficients in a decision feedback equalizer, if the residual intersymbol interference contained in the difference signal obtained by subtracting the pseudo intersymbol interference from the received signal containing intersymbol interference cannot be detected correctly, the adaptive operation will fail. The problem arises that it becomes impossible. For example, when a binary code such as a biphase code is used as a transmission line code, due to the nature of the binary code, there is no section where the received signal level is zero, and it is not possible to extract only the intersymbol interference independently. This will not be possible and the above problem will occur. Therefore, a conventional technique for solving this problem will be described next.

FIG. 8 shows a conventional example of a decision feedback type equalizer. Here, the circuit shown in FIG. 8 is connected to the transmitting side via a transmission path. Here, for simplicity, explanation will be given assuming baseband transmission.

In FIG. 8, a received signal containing intersymbol interference is supplied from a transmission path to an input terminal 1, and is input to a subtracter 2.

Subtractor 2 obtains a difference signal by subtracting pseudo intersymbol interference from the received signal supplied to input terminal 1 (=received signal including residual intersymbol interference, residual intersymbol interference = intersymbol interference - pseudo intersymbol interference). and is supplied to the determiner 3 and the subtractor 6. The result determined by the determiner 3 becomes a binary data series, which is supplied to the output terminal 4, the AGC 7, and the adaptive filter 5. The output of the adaptive filter 5 is supplied to a subtracter 2. The closed loop circuit consisting of the subtracter 6 and the AGC 7 operates to accurately extract only the residual intersymbol interference in the difference signal input to the subtracter 6. This is achieved by the AGC 7 multiplying the signal supplied from the determiner 3 by a certain constant to generate a received signal that does not contain residual intersymbol interference. The received signal generated by the AGC 7 is subtracted from the difference signal, which is the output of the subtracter 2, in a subtracter 6.

The output of the subtracter 6 is supplied to the adaptive filter 5 and used for updating coefficients. A closed loop circuit consisting of a subtracter 2, a determiner 3, and an adaptive filter 5 operates to remove intersymbol interference in the received signal supplied to the input terminal 1. This is achieved by the adaptive filter 5 generating pseudo intersymbol interference. Therefore, the adaptive filter 5 will be explained in detail.

FIG. 9 shows a detailed block diagram of the adaptive filter 5 of FIG. 8. Input signals 106 and i07 in FIG. 9 correspond to the binary data series that is the output signal of the determiner 3 and the output signal of the subtracter 6 in FIG. 8, respectively. In addition, the output signal 10 in FIG.
8 corresponds to the output number of the adaptive filter 5 in FIG. The input signal 106 includes a delay element 1001, multipliers 101o, 1011, . . . , 101R-1, and coefficient generators 102o, 1021, . . . , 102
It is supplied to R-1. Delay element 10 providing a delay of T seconds
01.1002, · Song, 100N/R-1 are connected in this order, and each can be realized by a flip-flop. Here, X and R are positive integers, and R is a divisor of N. Further, the data period of the input signal 106 is T seconds. Delay element 1001 (i=1, 2...
, N/R-1) are output from the dew generator 101j, respectively.
101j+l,...+101j+R-1 and coefficient generator 102j.

LO2j+1. . . . is supplied to 102j+R-1. However, =iXR. In the multiplier 101, 10
1 +R,・'.

For LO1 and +NR (k=o, 1..., R-1), the coefficient generator 102 and 102 +Rt...
..., 102 is multiplied by each coefficient that is the output of +N-H and the input data, and then all the multiplication results are sent to the adder 103k.
are input and added. R additions 5103Q, 10
31. --..., the output of 103R-1 is switch 10
4 input contact. The switch 104 is a multi-point switch with a period of T seconds, and has R adders 1o3o, 1o
31. (2) The output of LO3R-1 is selected and outputted in this order every T/R seconds, resulting in the output signal 108. Output signal 10
8 is pseudo intersymbol interference, and pseudo intersymbol interference is generated every T/R seconds. R is the interpolation constant (interpolation
tR is an integer of 2 or more in order to eliminate intersymbol interference within a required signal band. on the other hand,
A switch 105 that operates in synchronization with the switch 104 has an input/output reversed to that of the switch 104 . That is, the switch 105 functions to sequentially distribute the input signal 107 to R contacts every T/R seconds. Each contact output of the switch 105 is supplied to a coefficient generator present in a signal path input to the contact corresponding to the switch 104 operating synchronously. Next, the coefficient generation circuit will be explained in detail.

FIG. 10 shows the coefficient generator 1021 (l=0.1·
. . , N-1). The input signal 200 in FIG. 10 is the input signal 10 in FIG.
6 or delay elements 1001, 1002, ..., 10
It corresponds to the output signal of 0N/R-1. Also, the 10th
The input signal 201 in the figure is connected to the switch 105 in FIG.
Compatible with contact output. Furthermore, output signal 203 in FIG. 10 corresponds to the output of coefficient generator 102 in FIG. In FIG. 10, input signals 200 and 2
01 is supplied to the multiplier 204, and the multiplication result becomes one input of the adder 205. The output of the adder 205 is fed back through a delay element 206 of T seconds, and the coefficients are updated every T seconds by updating the correlation value of the input signals 200 and 201 supplied to the multiplier 204 by one sample. This is realized by adding it to the coefficient value of . Output signal 203 is the coefficient.

(Problems to be Solved by the Invention) As described above with reference to FIGS. 9 and 10, the pseudo intersymbol interference generated by the adaptive filter 5 in FIG. Become. The subtracter 2 generates a difference signal obtained by subtracting the pseudo intersymbol interference from the received signal supplied from the input terminal 1 (=received signal including residual intersymbol interference, where [residual intersymbol interference] = [intersymbol interference] - [Pseudo intersymbol interference]) is obtained and supplied to the determiner 3 and subtraction S6. On the other hand, the closed loop circuit consisting of the AGC 7 and the subtracter 6 operates to accurately extract only the residual intersymbol interference in the difference signal supplied to the subtracter 6. The output signal of the determiner 3 supplied to the AGC 7 is multiplied by r and input to the subtracter 6. Here, r is a positive number. The signal supplied from the AGC 7 to the subtracter 6 is subtracted from the difference signal supplied to the subtracter 6, and is fed back to the AGC 7 as a control signal. AGC7
Now, using the signal fed back from the subtracter 6, r is corrected so that the output of the subtracter 6 is equal to the residual intersymbol interference. That is, the AGC 7 pseudo-generates a signal other than the residual intersymbol interference included in the difference signal. The output of the subtracter 6 is supplied as an error to the adaptive filter 5,
Used for updating coefficients. Here, in order for the adaptive filter 5 to perform an adaptive operation, the residual intersymbol interference must be correctly supplied to the adaptive filter 5. However, since the difference signal that is the output signal of subtractor 2 also contains signals other than residual intersymbol interference, subtracter 2
If it is assumed that the output signal of is directly supplied to the adaptive filter 5, the residual intersymbol interference cannot be accurately obtained. Therefore, the adaptive ability of the adaptive filter 5 will be lost. Therefore, conventionally, as shown in FIG. 8, by adding a subtracter 6 and an AGC 7 and subtracting signals other than the pseudo residual intersymbol interference from the difference signal that is the output signal of the subtracter 2, adaptive, Methods have been used to ensure adaptive operation of the filter 5. In this method, a received signal containing no intersymbol interference is generated by an AGC 7 using a binary data sequence that is a determination result of a received signal, and a subtracter 6 subtracts it from the difference signal. AG
C7 and the subtractor 6 obtain the residual intersymbol interference component,
Adaptive operation of the adaptive filter 5 will be guaranteed. However, in the conventional control method, the AGC 7 is required, and in order to obtain a sufficient degree of intersymbol interference suppression, it is necessary to maintain the received signal, which does not include intersymbol interference, supplied from the AGC 7 to the subtracter 6 at a desired level. This method has the drawback of requiring complicated control and increasing the hardware scale. In addition, conventional decision feedback type equalizers do not have a function to match the zero crossing point of the received signal with the sample point, and the phase of the zero crossing point changes depending on the transmission distance. There was a problem that the maximum eye opening could not be obtained and the device was susceptible to clock jitter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a decision feedback type isolator that is simple, has a small domain size, and allows the zero crossing point of an equalized waveform to coincide with a sample point.

(Means for Solving the Problems) According to the present invention, there is provided a decision feedback equalization method that removes intersymbol interference occurring during waveform transmission using pseudo intersymbol interference generated by an adaptive filter. , obtain a difference signal by subtracting the pseudo intersymbol interference from the received signal containing intersymbol interference, and then add or subtract the difference signal and a delayed signal obtained by delaying the difference signal to obtain residual intersymbol interference. ,
An error signal obtained by selecting one of the residual intersymbol interference and the difference signal based on a sample phase and a demodulated data sequence obtained by demodulating the difference signal is used to update the coefficients of the adaptive filter. , when the residual intersymbol interference is selected, a decision feedback equalization method is obtained in which the coefficients are updated only when a specific pattern of the demodulated data sequence is detected.

(Operation) Unlike the conventional method of multiplying the output of the determiner by a constant to generate a received signal that does not include residual intersymbol interference and subtracting it from the difference signal, the present invention focuses on the characteristics of the eye pattern of the received signal. The system is configured so that residual intersymbol interference can be extracted accurately with a certain probability. That is, according to the characteristics of the eye pattern of the received signal of the transmission line code including the binary code system, the current sample value and the sample value iT seconds (i is a positive integer) ago are almost the same value or have opposite polarity. The minimum probability that the respective absolute values are approximately the same value takes a certain positive value that is not zero. Therefore,
By calculating the difference or sum of the current sample value and the sample value iT seconds ago for the difference signal (=received signal containing residual intersymbol interference), with a certain positive probability that is not zero, when there is no intersymbol interference, The difference or sum becomes zero, and anything else becomes residual intersymbol interference itself. Therefore, since the residual intersymbol interference can be detected with a certain positive probability that it is not zero, if the difference or sum is used as an error signal, the adaptive operation of the adaptive filter is guaranteed. The sample phases at which the received signal that does not contain intersymbol interference crosses zero are at the center and ends of the symbol waveform, and at this time, the received signal that does not contain intersymbol interference is zero, so the residual intersymbol interference can be extracted by the above operation. becomes unnecessary. In other words, if we focus on a certain sample point and update the coefficients of the adaptive filter using the difference signal instead of the residual intersymbol interference, the received signal will cross zero at that sample point. . Therefore, depending on the sample phase, whether or not to perform the above operation is selected and output, and the output is supplied to an adaptive filter to ensure adaptive operation and sample the zero crossing of the equalized waveform. The function of the present invention is to match the points.

(Example) Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, functional blocks given the same reference numbers as in FIG. 8 have the same functions as in FIG. 8. The difference between FIG. 1 and FIG. 8 is that a delay element 8 providing a delay of iT seconds;
Subtractor 9, selector 10, pattern check circuit 11
, a selector 13, and a switch 14, and the other configurations are exactly the same as in FIG. Before explaining this circuit, the overall configuration will be briefly described. A received signal input to input terminal 1 is supplied to subtracter 2 . The difference signal (=
The received signal (including residual intersymbol interference) is supplied to a determiner 3 , a delay element 8 , and a subtracter 9 . The output of the determiner 3 is supplied to an output terminal 4, a pattern check circuit 11, and an adaptive filter 5. Adaptive filter 5
, subtracter 2, delay element 8, subtracter 9, selector 10, pattern check circuit 11, selector 13, switch 1
A closed loop circuit consisting of 4 realizes the adaptive operation of the adaptive filter 5, and a pattern check circuit 11 controls the closed loop circuit to selectively update coefficients. The selector 13 selects the output of the selector 10 and the output of the subtracter 2 based on the signal from the determiner 3 and supplies the selected output to the switch 14 . The switch 14 selects the output of the selector 10, the output of the subtracter 2, or the output of the selector 13 based on the sample phase, and supplies the selected output to the adaptive filter 5. Adaptive filter 5
The configuration of 9 is similar to that explained in 8.
The circuit configuration may be the same as that shown in FIGS. 1 and 10. Next, the relationship between the output of the subtracter 9 and the residual intersymbol interference in the difference signal that is the output of the subtracter 2 will be explained in detail, but before that, the transmission path codes will be described.

Figure 2 shows a typical example of a binary code.
2A shows a biphase code, and FIG. 1B shows a pulse waveform of an MSK (minimum shift keying) code. As shown in FIG. 2(a), in the biphase code, pulse waveforms with inverted polarities are assigned to +Tol+ and 11111 data. Both pulses are 1
The polarity is reversed at the center of the bit width T seconds, and the polarity is balanced within one bit. On the other hand, as shown in FIG. 2(b), four types of pulse waveforms are prepared in the MSK code. That is, the polarity of data "'0" and 11111 is reversed!
Two types of pulse waveforms are prepared: 1011 mode and ``1'' mode. These two types of mote transitions are illustrated in Figure 2 (b
), and the current mode is determined by the mode one symbol before. This MSK code has a property that the polarity always inverts at the boundary of the transmitted symbol waveform. Note that in the MSK code, the positive and negative values are balanced within one symbol for IT, but 0'
′, the positive and negative values are not balanced. However, as is clear from the direction of the thick arrow indicating the mode transition in Figure 2(b), if there is an even number of 11011s in the continuous data series, the positive and negative values are balanced, and the DC component can be almost ignored. . The transmission path code shown in FIG. 2(a) is transmitted through the transmission path, receives intersymbol interference, and is input to the input terminal 1 in FIG.

FIG. 3 shows an example of a received signal eye pattern when the transmission line code shown in FIG. 2 is adopted. Figure 3 (a) and (b)
) are the biphase code and M, respectively, corresponding to FIG.
This is an eye pattern of the SK code. As shown in the figure,
The received signal eye pattern has high frequency components removed and becomes rounded. Originally, a received signal eye pattern includes intersymbol interference components, but for the sake of simplicity, the eye pattern shown is ideal and does not include intersymbol interference.

Now, the received signal eye of the MSK code shown in Fig. 3(b) is
Pay attention to patterns. According to the characteristics of the received signal eye pattern, if the current sample value and the sample value iT seconds (i is a positive integer) ago are almost the same value, or have opposite polarities and their respective absolute values are almost the same value. , iT seconds ago (i is a positive integer), the received signal can be canceled by delaying the sample value by iT seconds and then subtracting or adding it to the current sample value. FIG. 4 shows how received signals are canceled in the case of i=2, and the three waveforms are, from the right, the symbol waveforms of the current, T seconds ago, and 2T seconds ago.

In the case of the continuous waveform pattern shown in Fig. 4(a),
When the current symbol waveform and the symbol waveform 2T seconds ago are the same and have the continuous pattern of waveforms shown in FIG. 4(b), the waveforms have opposite polarities and have the same absolute value. In addition, except for the continuous waveform pattern shown in FIG. 4 or the waveform pattern with the same absolute value and opposite polarity as the combination shown in FIG. 4, the current symbol waveform and the symbol waveform 2T seconds ago are the same or It is also clear that the absolute values of each cannot be the same with opposite polarities. In the case of the waveform pattern shown in FIG. 4, it is easy to see that the current sample value and the sample value 2T seconds ago are the same value, or have opposite polarities and have the same absolute value. Therefore, by subtracting or adding the sample value delayed by 2T seconds from the non-delayed sample value, the received signal components are canceled and the output becomes zero. For the moment, we will only discuss the case where a sample value delayed by 2T seconds is subtracted from the undelayed sample value, and we will discuss the case where a sample value delayed by 2T seconds is added to the undelayed sample value. will be mentioned later. Now, considering a non-ideal case, the received signal includes residual intersymbol interference components. Considering the residual intersymbol interference component, the current residual intersymbol interference value and the residual intersymbol interference value 2T seconds ago are uncorrelated, so the residual intersymbol interference value 2T seconds ago is random noise. It can be considered. The amplitude distribution of the value of the residual intersymbol interference 2T seconds ago is symmetrical in positive and negative, and the probability that the amplitude d is also δ (however, O×δ) is not zero but takes a certain positive value. Therefore, subtractor 9
It can be seen that the probability that accurate residual intersymbol interference is included in the output signal of is a non-zero positive value. Furthermore, the magnitude of residual intersymbol interference is generally sufficiently small relative to the received signal. Therefore, the waveform shown in FIG. 4 can be regarded as the received signal waveform, even if it is not ideal. In addition, 2
Subtracting the sample-delayed sample value from the undelayed sample value will accurately extract only the residual intersymbol interference only when the received signal matches the pattern shown in Figure 4(a). , in other cases, it is not possible to accurately extract only the residual intersymbol interference, and therefore the adaptive filter 5 shown in FIG. 1 cannot be controlled correctly. Therefore, the adaptive filter 5
In order to control correctly, it is necessary to check the continuous pattern of the received signal waveform according to FIG. 4, and to stop updating the coefficients of the adaptive filter 5 when it does not match the pattern shown in FIG. Referring to FIG. 2(b), the continuous pattern of waveforms shown in FIG.
oo" or "111", the pattern check detects a continuous pattern of "ooo" and "111'" in the data signal. In addition, in Fig. 4, 2T is detected from the current sample value. seconds (data period is T seconds).

) has been targeted at the value obtained by subtracting the previous sample value, but
Detects predetermined waveform patterns and performs adaptive
It is easy to see that if the coefficient update of filter 5 is controlled, the value obtained by subtracting the sample value iT seconds (i is a positive integer) ago from the current sample value will also accurately represent only the residual intersymbol interference with a certain probability. . Next, the meaning of accurate extraction of residual intersymbol interference in the adaptive operation of the decision feedback equalizer will be explained with reference to FIG.

In the embodiment shown in FIG. 1, reference numeral 8 is a delay element providing a delay of iT seconds, reference numeral 9 is a subtractor, reference numeral 1
0 is a selector and reference numeral 11 is a pattern check circuit. Here, in order for the adaptive filter 5 to perform an adaptive operation, the residual intersymbol interference component (=[symbol inter-symbol interference] - [pseudo inter-symbol interference])
It has already been mentioned that it is necessary to supply the adaptive filter 5 accurately.

In Fig. 1, delay element 8 and subtracter 9 are added to satisfy this condition, and the output of subtracter 9 is the value obtained by subtracting the sample value T seconds ago from the current sample value. It is about to appear. As mentioned in the explanation of FIG. 4, the residual intersymbol interference component in the difference signal that is the output of the subtracter 2 is It is clear that the output of the device 9 is accurately extracted with a certain probability. On the other hand, if we consider the residual intersymbol interference component included in the output of the compositor 9 (taking i=2 as an example), we can compare the current residual intersymbol interference value with 2
Since there is no correlation with the value of residual intersymbol interference T seconds ago, 2
The residual intersymbol interference value T seconds ago can be considered as random noise. The amplitude distribution of the value of the residual intersymbol interference 2T seconds ago is symmetrical in sign and negative, and the probability that the amplitude d satisfies ldl < δ (however, O > δ) is not zero but takes a certain positive value. Therefore, it can be seen that the probability that the output signal of the subtractor 9 contains accurate residual intersymbol interference takes a certain positive value that is not zero. Therefore, if the adaptive filter 5 is controlled using the output of the subtracter 9, the adaptive operation of the adaptive filter 5 is guaranteed. Up to now, we have explained the case where the delay element 8 in FIG. 1 provides a delay of 2T seconds, but as mentioned in the explanation of FIG.
A similar effect can be obtained by setting the time to T seconds (i is a positive integer). Next, the operation of the pattern check circuit that controls the output signal of the subtracter 9 and the selector 10 will be explained.

The pattern check circuit is for detecting the appearance of the waveform pattern of the received signal shown in FIG. 4(a), and otherwise stopping updating the coefficients of the adaptive filter 5. This can be achieved with the circuit shown. The input signal 51 in FIG. 5 is equal to the data signal of the determiner 3 in FIG. 1, and the input signal 52 is equal to the mode signal. In Fig. 1, the paths connecting the judge 3 and the pattern check circuit 11, the judge 3 and the adaptive filter 5, and the judge G3 and the selector 13 are shown as one line, but the MSK
When a symbol is used, it represents two paths corresponding to the data signal and the mode signal.

A delay element 53 providing a delay of iT seconds and an exclusive-OR circuit (XNOR) 55 check whether the current signal and the data signal of the signal iT seconds ago match. This connects the input signal 51 and the input signal 51 to the delay element 53.
, XN0R5 is the negative exclusive OR of the values delayed by iT.
This is achieved by taking 5.

The output of the XN0R55 becomes one input of an AND circuit (AND) 59. Similarly, input signal 52 and delay element 56
The negative exclusive OR of the values delayed by iT seconds is performed, and the output is used as the other input of AND59. The AND 59 performs a logical product of the coincidence output of the data signal and the coincidence output of the mode signal, and outputs the result as an output signal 60. Output signal 60 is equal to the signal provided to selector 10 from pattern check circuit 11 of FIG.

The selector 10 receives a control signal from the pattern check circuit 11, selects the output of the subtracter 9 or zero according to the control signal, and supplies the selected output to the adaptive filter 5.

The selector 10 adapts the output signal of the subtracter 9.

As already explained, the fourth filter is supplied to the filter 5.
The waveform pattern of the received signal shown in figure (a) is
This is when the check circuit detects it. Only when the residual inter-symbol interference is accurately detected by the selector 10 and the pattern check circuit 1, the residual inter-symbol interference is obtained at the output of the selector 10; otherwise, zero is obtained at the output of the selector 10.

The output of selector 10 is then supplied to switch 14.

In addition to the output of the selector 10, the output of the subtracter 2 and the output of the selector 13 are supplied to the switch 14.

The selector 13 switches between the output of the selector 10 and the output of the subtracter 2 according to the output of the determiner 3, and the determiner 3
1, the output of selector 10 is +1111
, the output of the subtracter 2 is selected and supplied to the switch 14. Therefore, when the output of the selector 13 corresponds to 11011, the residual intersymbol interference extracted by the delay element 8 and the subtractor 9 is output as 11111.
When it corresponds to , it becomes the output of the subtracter 2, that is, the difference signal. On the other hand, in FIG. 1, switch 14 operates at a rate of T/R seconds. However, R is an interpolation constant, and FIG. 1 shows the case where R=4. Received signal eye in Figure 3
As is clear from the example pattern, by selecting the sample phase, the zero crossing point of the received signal can be made to coincide with the sample point. This shows that it is possible to operate the decision feedback type isolator so that a certain sample point becomes the zero crossing point of the received signal. At the sample point that coincides with the zero crossing point, the difference signal that is the output of the subtracter 2 becomes the residual intersymbol interference itself, and there is no need to extract the residual intersymbol interference using the delay element 8 and the subtractor 9. In other words, if we focus on a certain sample point and update the coefficients of the adaptive filter using the difference signal instead of the residual intersymbol interference, the received signal will cross zero at that sample point. . Therefore, the signals to be supplied to the adaptive filter 5 are distinguished according to the sample phase. As shown in FIG. 3, the sample points separated by T/4 seconds are to, tl, t2 . Assuming ta, the sample point that coincides with the zero crossing exists twice within T seconds, t Generate an intersection. If the leftmost terminal of the input contacts of the switch 14 is selected by t□, the input terminals of the switch 14 will be to, to,
tt, t2. It is selected corresponding to ta. That is, the input contacts of the switch 14 are connected to the outputs of the subtraction S2, the selector 10, the selector 13, and the selector 1o in the order of tO-ta, and this is repeated sequentially thereafter. The operation of switch 14 means the following. That is, as is clear from FIG. 3, at tl and ta, the received signal is not a zero crossing, so the output of the selector 10 is used; at t□, it is a zero crossing, so the output of the subtracter 2 is used; and at t2, the output of the subtracter 2 is used; The coefficients of the adaptive filter 5 are updated using the output of the selector 13 which switches the outputs of the selector 10 and the subtracter 2 according to the output of the subtracter 3. In the above description, R=4, but it is clear that R may be any integer greater than or equal to 2.

The pseudo intersymbol interference generated by the adaptive filter 5 of FIG. Subtractor 2 generates a difference signal obtained by subtracting pseudo intersymbol interference from the received signal that is the input signal of input terminal 1 (=received signal including residual intersymbol interference, residual intersymbol interference = intersymbol interference - pseudo intersymbol interference)
is obtained and supplied to the determiner 3, selector 13, switch 14, delay element 8, and subtracter 9. The selector 10 selects the output of the subtracter 9 or zero according to the output of the pattern check circuit 11 and supplies it to the switch 14. On the other hand, in the selector 13, the selector 1
Either the output of 0 or the output of the subtracter 2 is selected and supplied to the switch 14 together with the output of the subtracter 2. The switch 14 selects one of the output of the selector 10, the output of the subtracter 2, and the output of the selector 13 according to the sample phase, and supplies the selected output to the adaptive filter 5. The result determined by the determiner 3 is supplied to the adaptive filter 5 and appears at the output terminal 4 at the same time. Adaptive filter 5 uses the output signal of switch 14 to update coefficients.

Furthermore, the adaptive operation of the adaptive filter 5 can be performed even if polarity detectors are provided at two locations, between the subtracter 9 and the selector 10 and between the subtracter 2 and the selector 13 and switch 14. At this time, the input to the selector 10 is the polarity of the residual intersymbol interference, from the subtracter 2 to the selector 13 and the switch 14.
The signal supplied to has the polarity of the difference signal.

FIG. 6 is a block diagram showing another embodiment of the present invention.

In this figure, functional blocks given the same reference numbers as in FIG. 1 have the same functions as in FIG. 1. The difference between FIG. 6 and FIG. 1 is that the subtracter 9 in FIG. 1 is replaced with an adder 12, and the other parts are completely the same. Therefore, in FIG. 6, regarding the difference signal that is the output of the subtracter 2, the sum of the current difference signal value and the difference signal value iT seconds ago appears at the output of the adder, and the value of this sum is added to the selector 13. This will be used as an input to the switch 14. 1
To explain the case where ==2 as an example, the waveform pattern shown in FIG. 4(b), that is, the data signal is ``010''.
101'', the residual intersymbol interference component in the difference signal that is the output of the subtracter 2 is accurately expressed at the output of the adder 12 for the same reason as explained in FIG. 4(a). Therefore, if the output of the adder 12 and the output of the subtracter 2 are selected by the selector 13 and the switch 14 and the adaptive filter 5 is controlled, the adaptive operation of the adaptive filter 5 can be performed. It will be guaranteed.

The waveform pattern shown in FIG. 4(a) can be detected by the pattern check circuit shown in FIG. 5, but in order to detect the waveform pattern shown in FIG. 4(b), the circuit shown in FIG. In place of the XN0R58 that detects coincidence of mode signals, an exclusive OR circuit may be used to detect mismatch of mode signals. In addition, although the case where the delay element 8 of FIG. 6 gives a delay of 2T seconds was explained as an example, as mentioned in the explanation of FIG. 4, the delay amount can also be iT seconds (i is a positive integer) A similar effect can be obtained.

Further, as in the explanation of FIG. 1, the adaptive filter 5 can be operated adaptively using the polarity of the residual intersymbol interference and the polarity of the difference signal using the polarity detector.

However, the insertion position of the polarity detector is between the adder 12 and the selector 10, between the subtracter 2, the selector 13, and the switch 14.
It will be between.

The present invention has been described above in detail based on examples, but M
When the SK code is adopted, it is adaptive for two reasons: the pulse waveforms for +1011 and ``1pa are different, and each has a 0 mode and a 1 mode.

The configuration of the filter 5 is slightly different from that shown in FIG. That is,
``It is necessary to prepare two types of tap coefficients corresponding to the different pulse waveforms of ``θ'' and +1111 and update them separately, and if the positive and negative balance of the sent pulse waveform is incomplete, the judgment It is necessary to distinguish the coefficients according to the mode signal received from the device 3. Furthermore, in the explanation so far, it has been assumed that the delay amount of the delay element 8 is 2T seconds or iT seconds (i is a positive integer), but it goes without saying that for practical purposes, it is sufficient if it is around iT seconds. .

Up to now, the present invention has been explained in detail using an MSK code as an example.
The pi-phase code shown in can be used. What differs when using a bi-phase code from when using an MSK code is the received signal eye pattern. Therefore, the pattern check method is also unique to biphase codes. Referring to FIG. 3(a), the received signal eye pattern of the biphase code takes two values, zero and non-zero, at the point where the symbol waveform changes. Therefore, it is necessary to check a pattern different from the received signal eye pattern of the MSK code, which always takes the value O at the point where the symbol waveform changes. FIG. 7 shows a pattern check waveform corresponding to a biphase code. The same figure (a
) is when the adaptive filter 5 is controlled by the value obtained by subtracting the sample value 2T seconds ago from the current sample value, and (b) in the same figure is controlled by the value obtained by adding the sample value 2T seconds ago to the current sample value. , corresponds to the case of controlling the adaptive filter 5. Figure 7 (a), (b)
, the five consecutive waveforms are sequentially T from the right.
These are symbol waveforms after seconds, now, T seconds ago, 2T seconds ago, and 3T seconds ago. Since it is impossible to know in advance the symbol waveform T seconds from now, the coefficients are updated after waiting until the symbol waveform T seconds from now is determined. In the case of a bi-phase code, the symbol waveform of interest is different depending on the symbol waveforms before and after, so the value obtained by subtracting the sample value 2T seconds ago from the current sample value, or the value obtained by subtracting the sample value 2T seconds ago from the current sample value. When controlling the adaptive filter 5 by the value obtained by adding 5
Two symbol waveforms, 2 symbols before and after the current symbol waveform, and 2 symbols before and after the symbol waveform 2T seconds ago, for a total of 6 symbols.However, if a symbol 2T ago is used, one symbol before the current symbol waveform and 2T seconds ago. Since the last symbol of the previous symbol waveform is common, it is necessary to check the continuous pattern of the received signal waveform over a total of five symbols. In Fig. 7(a), “10101”
The continuous pattern of "01100" and "11001" is shown in FIG. 3(b). For biphase codes, the pattern
The check circuit detects the five continuous waveforms shown in Figure 7, and if it is configured as a logic circuit that outputs +1111 only when these waveforms are detected, it can be used as the pattern check circuit for the MSK code shown in Figure 5. Can be used equally. However, in the case of a biphase code, the input signal to the pattern check circuit is only a data signal.

The above explanation is about the case where the adaptive filter 5 is controlled by the value obtained by subtracting the sample value 2T seconds ago from the current sample value, or by the value obtained by adding the sample value 2T seconds ago to the current sample value. However, when using the sum or difference between the current sample value and the sample value iTT seconds ago, the check circuit calculates a total of 6 symbol waveforms, 1 symbol waveform before and after the two symbol waveforms of interest. The pattern is detected to control the adaptive operation of the adaptive filter 5. In the case of a bi-phase code, the control signal of the selector 13 is further different from that of the MSK code. That is, the selector 13 selects the output signal depending on whether the received signal takes a value of zero at the sample point t2 in FIG.
Since this is the boundary of the symbol waveform, it is necessary to use a circuit for controlling the selector 13 in response to two consecutive symbol waveforms. Considering transmission path codes other than these codes in the same way, if we detect the received signal pattern corresponding to Fig. 4 and control the update of the coefficients of the adaptive filter 5, we can accurately eliminate residual intersymbol interference with a certain probability. It is clear that it can be taken out.

(Effects of the Invention) As described in detail above, according to the present invention, the difference or sum of the current value and the value iT seconds (where i is a positive integer and T is the data period) before is calculated for the difference signal. By doing so, the residual intersymbol interference component contained in the received signal can be accurately extracted with a probability of a certain positive value other than zero. Therefore, by using the above difference or sum and further detecting a continuous pattern of the received signal waveform such that the residual intersymbol interference component can be accurately extracted, the sum or difference and the difference signal are extracted in accordance with the sample phase. By selectively updating the coefficients to control the adaptive filter, adaptive operation is ensured. Furthermore, according to the present invention, the above-mentioned adaptive operation can be guaranteed by combining a delay element that provides a delay of iT seconds and a subtracter or an adder. A method for controlling a small decision feedback equalizer can be provided. Further, according to the present invention, since the zero crossing point of the received signal can be made to coincide with the sample point, the determination timing phase can always be optimally maintained regardless of the transmission distance, and has the advantage of being resistant to clock jitter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2(a) and (b) are diagrams explaining transmission path codes, and FIG.
). (b) is a diagram showing the eye pattern corresponding to the transmission line code in Figure 2, Figures 4 (a) and (b) are diagrams showing the received signal waveform pattern for the MSK code, and Figure 5 is a diagram for the MSK code. Block diagram showing pattern check circuit, No. 6
The figure is a block diagram showing another embodiment of the present invention, FIG.
). (b) is a diagram showing a received signal waveform pattern for a biphase code, FIG. 8 is a block diagram showing a conventional example of a decision feedback type equalizer, FIG. 9 is a block diagram showing an example of the configuration of an adaptive filter, FIG. 10 is a block diagram showing details of the coefficient generation circuit. In the figure, 1...input terminal, 2...
Subtractor, 3... Determiner, 4.
...Output terminal, 5...Adaptive filter, 8...Delay element, 9...Subtractor, 10...Selector, 11...
. . . pattern check circuit, 13. song selector, 14 . . . switch. In addition, in Fig. 6, 1...input terminal, 2...
Subtractor, 3... Determiner, 4.
...Output terminal, 5...Adaptive filter, 8...Delay element, 10...Selector, 11...Pattern check circuit, 12. Song Adder, 13...Selector, 14
...Represents each switch. Representative Patent Attorney Uchihara 1゛・,-',,-';Ir'2 Figure Pa○''r Ll, II(a) (b) ';73 Figure ■ (a) (b) /1 '4 Figure (a) (b) O 7 Figure 1 1 14-T-111 (a) + 1 )-T-1-111 (b) 71-10 Figure

Claims (1)

[Claims] 1) Adaptive method for intersymbol interference occurring during waveform transmission.
This is a decision feedback equalization method that uses pseudo intersymbol interference generated by a filter to remove it. A residual inter-symbol interference is obtained by adding or subtracting a delayed signal obtained by delaying the signal and the difference signal, and one of the residual inter-symbol interference and the difference signal is obtained by demodulating the sample phase and the difference signal. An error signal selected based on the demodulated data series that is selected is used to update the coefficients of the adaptive filter, and when the residual intersymbol interference is selected, only when a specific pattern of the demodulated data series is detected; A decision feedback equalization method characterized by updating coefficients. 2) Adaptive method to reduce intersymbol interference that occurs during waveform transmission.
This is a decision feedback equalization method that uses pseudo intersymbol interference generated by a filter to remove it. The residual inter-symbol interference is obtained by adding or subtracting a delayed signal obtained by delaying the signal and the difference signal, and one of the polarity of the residual inter-symbol interference and the polarity of the difference signal is set as the sampling phase and the difference signal. An error signal selected based on the demodulated data sequence obtained by demodulation is used to update the coefficients of the adaptive filter, and when the polarity of the residual intersymbol interference is selected, a specific pattern of the demodulated data sequence is used. A decision feedback equalization method characterized by updating the coefficients only when .