JPH01238325A - Method and apparatus for eliminating inter-code interference by decision feedback - Google Patents

Abstract

PURPOSE:To guarantee the constitution, to simplify the control without requiring any complicated control and to reduce the scale of hardware by taking the sum or difference between the present value and a value by several preceding data, revising the coefficient while selecting the sum or difference signal corresponding to the sampling phase thereby controlling the adaptive filter. CONSTITUTION:A sample for each Tsec is stored in a memory corresponding to the symbol waveform of the said sample and added to the sample when a waveform of opposite polarity is received to cancel the reception signal. Since the selector 11 selects the symbol waveform discriminated by a discriminator 3 with the data from the memory corresponding to the symbol waveform of the opposite polarity, then the reception signal is cancelled by an adder 12 thereby extracting the residual inter-code interference accurately. Thus, the residual inter-code interference component obtained as the output of a polarity detection circuit 13 is used to revise the tap coefficient of an adaptive filter 25. Since the reception signal giving disturbance to the adaptive operation of the filter 25 is cancelled, the adaptive operation of the filter 25 is guaranteed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intersymbol interference removal method and apparatus using decision feedback for removing intersymbol interference that occurs during waveform transmission.

[Conventional technology]

A decision feedback equalizer is known as a known technique for removing intersymbol interference that occurs during waveform transmission (IEgET AN8 ACTIONS ON COMMUNI-C).
ATIONS: Volume 32, No. 3, 1984, 258-26
(See page 6).

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

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

In the subtracter 2, the difference signal obtained by subtracting the pseudo intersymbol interference signal generated by the 7-adaptive filter 5 from the received signal supplied to the input terminal l (=received signal containing residual intersymbol interference components, [residual intersymbol interference component] = [intersymbol interference component] −
[pseudo intersymbol interference signal]) is obtained.

Judgment device 3. It is supplied to a subtracter 6. The determiner 3 determines the received signal data from the output of the subtracter 2, and supplies the determination result to an output terminal 4, an automatic gain controller (AGC) 7, and an adaptive 11 filter 5. The pseudo intersymbol interference signal adaptively generated by the adaptive filter 5 is supplied as one input of the subtracter 2. The output signal of the determiner 3 supplied to the AGC 7 is multiplied by 1 and input to the subtracter 6. Here, γ 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.

The AGC 7 uses the signal fed back from the subtracter 6 to adjust γ so that the output of the subtracter 6 is equal to the residual intersymbol interference component.
Correct. That is, the closed loop circuit consisting of the subtracter 6 and the AGC 7 operates to extract only the residual intersymbol interference component in the difference signal that is the output of the subtracter 2. This is AG
This is achieved by adaptively determining the gain of the output signal of 8007 by correlating the output signal of the subtracter 6 and the output signal of the determiner 3 in C7. The residual intersymbol interference component, which is the output of the subtracter 6, is also supplied to the adaptive filter 5 and used for coefficient updating. Subtractor 21 Determiner 3
．． The closed loop circuit consisting of the adaptive filter 5 is
It operates to remove intersymbol interference experienced by the received signal supplied to input terminal 1.

[The problem to be resolved by the invention] In order for the adaptive filter 5 to perform an adaptive operation, it is necessary that the residual intersymbol interference component be correctly supplied to the adaptive Φ filter 5. However, the difference signal that is the output signal of the subtracter 2 also contains signals other than the residual intersymbol interference component.

Assuming that the output signal of the subtractor 2 was directly supplied to the adaptive filter 5, the adaptive filter 5 would lose its adaptive ability. Therefore, conventionally, as shown in FIG. 8, a subtracter 6. A method has been used in which the adaptive operation of the adaptive filter 5 is guaranteed by extracting the residual intersymbol interference component using the AGC 7. However, in such a control method, the AGC 7 is required, and in order to obtain a sufficient degree of intersymbol interference suppression, the subtracter 6 needs to adjust the received signal, which is not affected by intersymbol interference, supplied from the AGC 7 to a desired level. However, it requires control to maintain the current level, which has the disadvantage of increasing the hardware scale. Further, although the conventional decision feedback equalizer can remove inter-symbol interference caused by a sequence of past transmitted symbol waveforms, it has been impossible to remove interference within symbol waveforms.

An object of the present invention is to provide a method and apparatus for removing intersymbol interference using decision feedback that is simple and has a small hardware scale. Another object of the present invention is an intersymbol interference cancellation method using decision feedback, which is capable of canceling not only intersymbol interference caused by a sequence of past transmitted symbol waveforms, but also interference within a symbol waveform. The goal is to provide that device.

A difference signal is obtained by subtracting the pseudo intersymbol interference signal from the interfered received signal, and the demodulated data sequence obtained by demodulating the difference signal is used to generate already stored data corresponding to the symbol waveform of the received signal. *, calculate or subtract the slJ difference signal to obtain the residual intersymbol interference signal, store the difference signal in a memory corresponding to the symbol waveform of the received signal, and apply it to the first adaptive filter. Which of the residual intersymbol interference signal and the difference signal is selected based on the sampling phase and the demodulated data sequence and receives the error No. 16 and the demodulated data sequence to update the coefficients, and An adaptive number filter receives the polarity of the difference signal and the demodulated data series, and updates coefficients only when the demodulated data series reaches a specific value, and a third adaptive filter completely receives the symbol waveform of the difference signal. Before the completion of demodulation, the coefficients are updated by receiving the temporary demodulated data series obtained by demodulating and the difference signal, and the coefficients are updated.
．． The configuration is such that the pseudo intersymbol interference signal is generated by adding the outputs of the second and third adaptive fist filters.

An intersymbol interference removal device using decision feedback according to the present invention is as follows.

a subtractor for obtaining a difference between the received signal and the pseudo intersymbol interference signal;
a first receiving the output of the subtracter and generating a demodulated data sequence;
a first adaptive filter that receives the demodulated data series and the first error signal supplied from the first determiner; a delay element that delays the output of the subtracter; a first switch that distributes the output of the delay element based on the demodulated data series; a plurality of memories that hold the output of the first switch; and a first switch that selects the output of the memory based on the demodulated data series. 1 selector, an arithmetic unit that obtains the sum or difference between the output of the slow search element and the output of the first selector, and a second selector that distributes the output of the subtracter based on the phase of the received signal. a second adaptive filter that receives one contact output of the second switch and a second error signal; a second selector that selects based on;
a third selector that selects either the output of the arithmetic unit or one contact output of the second switch based on the demodulated data series; one contact output of the second switch and the arithmetic unit; and a third switch that selects either the output of the input signal or the output of the third selector based on the phase of the received signal.

a second determiner that receives the output of the subtracter and generates a temporary demodulated data sequence before completely receiving the output symbol waveform of the subtracter; and an output of the second determiner and a third error signal. a third adaptive filter receiving said first . an adder that adds the outputs of the second and third adaptive filters to generate the pseudo intersymbol interference signal.

The output of the third switch is fed back to the first adaptive filter as the first error signal, and
Said selector output! 2 as the error signal of the second
, and one contact output of the second switch is fed back to the third adaptive filter as the error signal of g3.

[Effect]

The present invention differs from the conventional method in which the output of the 1 determiner is multiplied by a constant to generate a received signal that does not contain residual intersymbol interference components, and the received signal is subtracted from the difference signal. The system was designed to accurately extract residual intersymbol interference components by focusing on the characteristics of the eye pattern of the signal. That is, according to the characteristics of the received signal eye pattern of a transmission line code including a binary code system, if intersymbol interference can be ignored, the current sample value and JT seconds (J is a positive integer).

T is the data period) The previous sample value is almost the same value, or
The minimum probability that the absolute values of the polarities are almost the same in opposite polarities is a certain positive value that is not zero. Therefore, by calculating the sum or difference between the current temple value and the sample value JT seconds ago for the received signal (in which the difference signal contains a residual intersymbol interference component), the residual intersymbol interference can be calculated with a certain positive a rate that is not zero. Only interference components can be extracted. Therefore, if the sum or difference is used as an error signal, the adaptive operation of the adaptive filter is guaranteed. In addition, 1) the present invention has two types of 1-tap 7-adaptive filters for eliminating interference within the symbol waveform, and 2 is configured to be able to eliminate interference within the symbol waveform, which was impossible with conventional methods. In addition, the resistance to black and ringing jitter is higher than in the past,9 and performance can be improved.

〔Example〕

Next, the present invention will be described in detail with reference to FIG. 1.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the same figure, a received signal subjected to intersymbol interference is supplied from a transmission path to an input terminal 1, and is supplied to a subtracter 2. In FIG. First, transmission line codes will be explained.

Figure 2 shows symbol waveforms and state transitions of an MSK (minimum shift-key ink) code as an example of a transmission line code.As shown in Figure 2, four types of symbol waveforms are prepared for the %M8 code. . For the data of ζ101 and 11, prepare two types of waveforms, "0' mode and 11@ mode, respectively, with reversed polarity. These four types of state transitions are indicated by arrows in Fig. 2, and the current state is The mode of is determined by the mode of the previous symbol.This MSK code has the property that the polarity always inverts at the boundary of the symbol waveform.The transmission line code shown in Figure 2 The subtracter 2 subtracts the pseudo intersymbol interference signal, which is the output of the adder 23, and the difference signal (= The received signal (including the residual intersymbol interference component) is supplied to a determiner 3, a delay element 8 that provides a delay of MT seconds, a polarity determination circuit 16, and a determiner 20.The determiner 3 determines the received symbol waveform. The corresponding data and mode are determined every t-1 seconds, and the output thereof is supplied to the output terminal 4, the switch 9, the selectors 11, 15 and 18, and the adaptive filter 25.Adaptive filter 25.Adder 22,
23. Subtractor 2, delay element 8. Switch 9. memory 10
t*10z*...10m, selector 11. Adder 12. Polarity detection circuit 13. A closed loop circuit consisting of switch 14 implements the adaptive operation of adaptive filter 25. Switch 9. Memory 10t*10*
t...10. o, the selector 11 removes the received signal component included in the output of the subtracter 2; The switch 14 selects the output of the polarity detection circuit 13, the output of the selector 15, or the output of the switch 17 based on the sampling phase, and supplies the selected output to the adaptive filter 25.

Next, the relationship between the output of the adder 12 and the residual intersymbol interference component in the difference signal that is the output of the subtracter 2 will be explained in detail. FIG. 3 shows an example of a received signal eye ringing pattern when the transmission line code shown in FIG. 2 is adopted. As shown in the figure, the received signal eye pattern has high frequency components removed and becomes rounded. Originally, the received signal eye pattern contains intersymbol interference components, but for the sake of simplicity, the eye pattern shown in the figure is based on the intersymbol interference components when waveform equalization is ideally performed. shall not be included. According to the characteristics of the received signal eye pattern shown in Figure 3, the probability that the current sample value and the sample value JT seconds ago (J is a positive integer) have opposite polarities and almost the same absolute value is zero. It takes a positive value. Therefore, the received signal can be canceled by storing the sample value every T seconds in the memory corresponding to the symbol waveform to which this sample value belongs, and adding it to the sample value when the waveform of the opposite polarity is received. Can be done.

Next, a note on Figure 1! J101*102*...
...The operation of the switch 9 and selector 11 that control the 10m Ota force signal will be explained. The switch 9 connects a memory 101 to a memory 101 to store the sample value corresponding to the symbol waveform of the received sample value. ,...
..., since the eye pattern of the 0M5K code selected from 10+m is a combination of four types of waveforms, as shown in Figure 3, m = 4, for example, if the memory is 101m.
1 Ox elos *l Os is “O-0” respectively
, 'Of', '10', and '11'.

Here, l o 11 represents a symbol waveform defined by the data signal 10 l and the mode signal 111. The switch 9 uses the data signal and mode signal supplied from the determiner 3 to determine whether the combination is #001#@01M
, 1 t o @ , l 111, the signals supplied from the slow g chord 8 are stored in the memories 101 and 102, respectively.
Switch the circuit so that it is stored at 103 and 104. In addition, in FIG. 1, 1 determiner 3 and switch 9.
The path connecting the selectors 11, 15, 18 and the adaptive filter 25 is shown as one line, but if a code is used for M8, two MNI't- lines corresponding to the data signal and mode signal are shown. represent.

Since the determiner 3 cannot determine the received symbol waveform until it has finished receiving the symbol waveform, and the data signal and mode signal are not determined, the signal supplied to the switch 9 is delayed by fiT seconds by the delay element 8. . That is, M
In the SK code, M=1. At the same time, the difference signal supplied to the adder 12 is also delayed by the delay element 8 by T seconds. In the embodiment shown in FIG. 1, assuming that the number of rings R for an l symbol waveform is R=4, there are sample values at four phases of one symbol waveform.

Therefore, the memory 101 e 10 z # 10 s
Each of the e 104 consists of four Buf' memories, each corresponding to one symbol waveform at one sample phase. Conversely, since there is only one memory that corresponds to one symbol waveform in one sample phase, the sample values corresponding to the same symbol waveform in the same sample phase are always updated, and the latest values are stored in the memory. This also applies to the case of 几〆4.

The selector 11 selects a memory 101*10 from which data is extracted corresponding to the symbol waveform to which the received sample value belongs.
1s...Select from 10 motions. In the case of MSK code, the data signal and mode signal supplied from the 1 determiner 3 are used to determine whether these are '00', '01', '10'.
, 1111, the memories 102 and 10t*1 respectively
The circuit is switched so that the data stored in 04sl Os is selected and supplied to the adder 12. In this way, the selector 11 selects data from the memory corresponding to the symbol waveform of opposite polarity to the symbol waveform determined by the determiner 3, so the received signal is canceled out by the adder 12.
Residual intersymbol interference can be extracted accurately. Therefore, if the adaptive filter 25 is controlled using the output of the adder 12, the received signal that interferes with the adaptive operation of the adaptive filter 25 is canceled out, so that the adaptive operation of the adaptive filter 25 is guaranteed. It turns out.

The difference signal that is the output of the subtracter 2 is also supplied to the polarity determination circuit 16, and after the polarity of the difference signal is detected, it becomes an input to the switch 170. The switch 17 has 4 output contacts, T/second (assuming it is an even number and 几=4)
At each time, the output is switched from the first output contact to the fourth output contact in the direction of the arrow in FIG. 1. From the left in the figure, the output contacts are set to 1, 2, 43, and 5144, and this operation is repeated 9 times for T seconds. The humpling phase of operation of switch 17 is shown in Figure 3, where 'Os'1
st1s'3 corresponds to the sampling phase of the 1°420 m3.44 output contact of switch 17 in FIG. 1, respectively. The third contact output of switch 17 is selector 1
Supplied as one of 50 manpower.

Further, the output of the polarity detection circuit 13 is supplied as the other manual power of the selector 15. On the other hand, the data signal which is the judgment result of the eleventh regulator 30 is manually inputted to the selector 15 as the control number -1d, and when the data number 1 is Jl, the third contact output of the switch 17 is selected. When the data signal is 10 m, the output of the polarity detection circuit 13 is selected and output. In other words, as is clear from FIG. 3, when the data signal is 111, the zero crossing point is waited for at the center of the symbol, so the output of the contacts 5!43 of switch 17 shown in FIG. 1 becomes the residual intersymbol interference component. For t! When the data number 1g is 101, there is no zero crossing point at the center of the symbol, so the output of the polarity detection circuit 13 becomes a residual intersymbol interference component. Therefore, the output of the selector 15 is supplied to the third manual contact of the switch 14 as the residual intersymbol interference component of the humpling phase t2. The switch 14 is a switch having four input contacts).

T/second in synchronization with switch 17 (however, here, 1
(assuming 4=4), the human power is switched in order from the first human power contact to the fourth human power contact in the direction of the arrow in FIG. From the left in the figure, the first, second, third, and so on. This operation is repeated every 1 second using the fourth manual contact.The "O*"La"2m"3 shown in FIG. 3 is the first, second, and The first contact output of the switch 17 corresponds to the sampling phase of the human power contacts g3 and d4.
'fIfI2 and the fourth manual contact have a polarity detection circuit 13.
The output of the selector 15 is supplied to the third manual contact f:L, respectively. As shown in FIG. 3, since a zero crossing point does not occur in the hump ring phases tl and t3, the residual intersymbol interference component obtained as the output of the polarity detection circuit 13 in FIG. Update the tap coefficients. At sampling position 11Lt*, data signals 10' and 1
The residual intersymbol interference component corresponding to 11 is obtained at the output of the selector 15 and is supplied to the third manual contact of the switch 14. Therefore, as the output of the switch 14, the residual intersymbol interference component necessary for updating the tap coefficients is obtained at each sampling phase and is supplied to the adaptive filter 25. In the above explanation, 1iR=4, but it is clear that R may be any even number.

Next, the adaptive fill 25 will be explained in detail. FIG. 4 shows a detailed configuration of the adaptive filter 25 of FIG. 1. The data signal 106' constituting the output signal of the determiner 3 in FIG. 1 and the output signal 107 of the mote 16 and the switch 14 are input to this filter. Mode 1g No. 106 is a delay cable 100t*
Multiplier 101o.

1011 # “”” # l 0111-1 and coefficient generator 1020 #1021, ..., 102m-
5. Still, the data signal 106' is passed through the delay element 1001' and the coefficient generator 1026m 1021m.
..., 102 is supplied with -1.

Delay elements 1001°100 each giving a delay of T seconds
1#..., 100 N/, -, and 1001
', 100. '.

°°゛°°°・100 N/, -, / are connected in this order.

Each can be realized by flip-flop and flip-flop.

Here, the number of taps N must be a positive integer, and R is a divisor of NO. Further, the data period of the data signal 106' and the mode signal 106 is T seconds. Delay element 100+(i=1.
2. . . . , N/几−1) are outputted to the multipliers 101 , , 101j+, , , , , , , , respectively.

1014-1-+a-8 and coefficient generator 102. ．． 10
2. +,.

. . . is supplied to 102□+s−t. Also,
100. '(i=1.2......, N/R-t)
The outputs of are respectively coefficient generators 1021-102j+x
a..., 102j10R-t. However, j=ixR. To the multiplier 101, + to 101
ua......+N-1% to #"01 (k:Q.

l, . . . , 1(-1), the coefficient generator 102 . #102k+, ,...#102h
After each coefficient which is the output of +s-n is multiplied by the input mode signal (+1 or -1), each multiplication result is all added to adder 1.
It is input to 03k and added. 8 adders 103g
, 103te, . Switch 101: A multi-contact switch with a period of tT seconds, 8 adders 10
The outputs of 3oa 103t *..., 103m-t are selected and output in this order every T/R, seconds, and the pseudo intersymbol interference signal 108 caused by the past transmission data series is transmitted to T/R.
Occurs every /R seconds. On the other hand, a switch 105 that operates in synchronization with the switch 104 has an input/output direction opposite to that of the switch 104 . That is, switch 105 receives input signal 1
07 to 8 contacts in turn 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 which operates synchronously.

Next, the coefficient generator will be explained in detail. FIG. 5 shows the coefficient generator 102j()=0. l.

. . . , shows the detailed configuration of N-1).

The mode signal 200 in FIG. 5 is the mode signal 106 in FIG.
Or delay element 1001* 100 z #...
, 100. It corresponds to the mode signal output from -1. Similarly, the data signal 200' of FIG. 5 is the data signal 106' of FIG. 4 or the delay element 1001'* l 00
x' x..., 100. It corresponds to the data signal output from -4'. Furthermore, the input signal 201 in FIG. 5 corresponds to the contact output of the switch 105 in the fourth factor. Further, the output signal 209H in Fig. 1g5 corresponds to the output of the coefficient generator 1021 in Fig. 4. In FIG. 5, a data signal 20 indicating '01 or 111
0' is supplied as a control signal to each of selectors 204, 205 and 208. Further, a mode signal 200 that takes 001 or "11" corresponding to the data signal 200' is supplied as one of the inputs of the multiplier 202. On the other hand, as the other input of the 1 multiplier 202, C is input from the residual intersymbol interference component. The multiplier 202 multiplies the mode signal 200 and the error signal 201, and then
The multiplication result is supplied to one side of the adder 203. Here, the delay elements 206 and 207 which provide a delay of T seconds are coefficient memories corresponding to @O1 and Ilg of the data signal 200', respectively.
Supplied as 08 manpower. On the other hand, the data signal 200' is input as a control signal to the selector 208, and when the data signal 200' is lol, the delay element 200'
6 is selected and outputted, and when the data signal 200' is 111, the delay element 20
The coefficient corresponding to 111, which is the output of 7, is selected and output, and in either case, an output signal 209 representing the coefficient is obtained.

Further, the output signal 209 is fed back to the adder 203, added to the output signal of the multiplier 202, and then inputted to the selectors 204 and 205. In addition, the delay element 206
The outputs of 207 and 207 are also supplied to selectors 204 and 205, respectively, as manual power. Furthermore, the outputs of selectors 204 and 205 are supplied to delay elements 206 and 207, respectively.

Next, the operations of selectors 204, 205, and 208 will be explained. If the data signal ZOO' is 10'',
The selector 208 selects the output of the delay element 206 corresponding to the data signal Mo1 and outputs it as an output signal 209. At this time, the output signal 209 is input to the adder 203 and then fed back to the delay element 206 via the selector 204, and the coefficient corresponding to the data 101 is updated.

On the other hand, since the selector 205 selects the output of the delay element 207 and supplies it again to the delay element 207, the coefficient corresponding to the data 111 is not updated.

Contrary to this case, when the data signal ZOO' is 111, the selector 208 selects the output of the delay element 207, which is a coefficient corresponding to the data 111, and outputs it as the output signal 209. is adder 203
After being manually input to the delay element 20 via the selector 205
7, and the coefficient corresponding to data 11' is updated. On the other hand, in the selector 204, the delay element 2
Since the output of 06 is selected and supplied to the delay element 206 again, the coefficient corresponding to the data 101 is not updated. According to the principle explained above, the data signal 200'
In addition to selecting the coefficients to be used in the adaptive filter operation corresponding to the value 101 or 111, the coefficients that have been used are updated, and the coefficients that were not used are restored to their original values. The holding operation adaptively obtains the coefficients of the adaptive filter. The pseudo intersymbol interference signal caused by the past data sequence generated by the adaptive filter 25 is as follows.

Adder 22. is supplied to the subtracter 2 via the adder 23,
It is subtracted from the received signal supplied from input terminal 1 and subjected to intersymbol interference.

Next, interference cancellation within a symbol waveform will be explained. The polarity of the difference signal, which is the output of the subtracter 2, is sent to the adaptive filter 19 via the polarity determination circuit 16 and the second output terminal of the switch 17. Manually operated. The polarity of the difference signal of the hump ring phase t1 is used in the adaptive filter 19 as judgment data for the first half of the symbol waveform shown in FIG. On the other hand, the polarity of the difference signal, which is the output of the subtracter 2, is sent to the selector 18 via the polarity determination circuit 16 and the switch 17 so that the polarity of the difference signal, which is the output of the subtracter 2, is determined to be at the Templing phase t! Manually operated. Also.

The selector 18 is also manually inputted with the demodulated data output from the determiner 3, and when the data signal is 101, it is set to zero, and when the data signal is 11'', the residual symbol interval that appears at the third output terminal of the switch 17 is The interference component is selected and output, and supplied to the adaptive filter 19.The selector 18 distinguishes that at the sampling phase t2, the symbol waveform representing data l01 does not have a zero crossing point, but data 11'' always does. . The selector 18 supplies the polarity of the residual intersymbol interference component when the data of the output signal of the output signal from the discriminator 3 is 111, and the polarity of the residual intersymbol interference component is supplied to the adaptive filter 19 when the data is 00'', so that the data is 1.
Coefficients are selectively updated only when 11. Of the displacement from zero at the sampling phase t2, the component caused by interference within the symbol waveform is added to the pseudo intersymbol interference signal generated by the adaptive stage filter 19 to the adder 2.
2.23 to the subtracter 2, and is removed by subtracting it from the received signal subjected to intersymbol interference.

Next, the adaptive filter 19 will be explained in detail. Figure 6 shows the adaptive filter 1 shown in Figure 1.
9 shows the detailed configuration of No. 9. The input signal 300 in FIG.
The output signal of the second output contact of switch 17 in the figure, that is, the polarity of the difference signal at sampling phase 11, is input to the input signal 301, that is, the polarity or zero of the residual intersymbol interference component at sampling phase t2. The corresponding error signal is Further, the output signal 306 in FIG. 6 corresponds to the output signal of the adaptive filter 19 in FIG. 1, and is a pseudo intersymbol interference signal caused by interference within the symbol waveform.

In FIG. 6, the polarity of the difference signal 300 is provided to multipliers 302 and 305. Delay element 3 giving a delay of T seconds
04 is a coefficient memory, the output of which is supplied to a multiplier 305 to generate a similar intersymbol interference signal 306. Delay element 3
The output of 04 is also fed back via the adder 303, and the output of the multiplier 302, which multiplies the polarity 300 of the difference signal and the error signal, is supplied to the adder 303. When the error signal g301 is zero, the output of the 1 multiplier 302 is zero, so the coefficients do not change, and selective coefficient updating is performed. In this way, the value of the pseudo intersymbol interference signal at the zero crossing at the center of the symbol waveform appears at the output of the adaptive filter 19, and is added to the pseudo intersymbol interference signal generated by the adaptive filter 25 in the adder 22. After that, it is supplied to the subtracter 2 via the adder 23.

The adaptive filter 21 serves to remove intersymbol interference components occurring at zero crossing points at the ends of the same symbol waveform depending on the waveform within the symbol. The determiner 20 receives the difference signal that is the output of the subtracter 2, and determines the sampling phase t for the waveform within 3T/4 seconds in the first half of the symbol waveform with a period of T seconds.
3, the data and mode are determined, and the obtained temporary demodulation data is supplied to the adaptive filter 21. The adaptive filter 21 is also supplied with the first contact output of the switch 17 via the polarity determination circuit 16, therefore, in the humpling phase 1G.

The polarity of the difference signal output from the subtracter 2 is input to the adaptive filter 21 and used as an error signal for updating coefficients. As shown in Figure 3, in an ideal case without intersymbol interference, the humpling phase to, which is the end of the symbol waveform, is a zero crossing point, but in reality, intersymbol interference occurs, so the amplitude at to It doesn't become zero. This difference is the intersymbol interference component, and the signal supplied from the output contact of the switch 17 matches the polarity of the intersymbol interference component.

FIG. 7 shows a detailed configuration of the adaptive filter 21 shown in FIG. 1. The basic configuration corresponds to one phase of the adaptive filter 25 shown in FIG. Therefore, the operating principle of coefficient updating Fi is exactly the same as that shown in FIG. In FIG. 7, components and signals designated by the same reference numerals as in FIG. 5 are the same. However, in the case of FIG. 7, the data signal 212' and mode signal 212 correspond to the output of the determiner 20 of FIG. 1. Also, the error signal 2 in Fig. 7
13 corresponds to the output signal of the first output contact of switch 17 in FIG. The difference between FIG. 7 and FIG. 5 is that the mode signal 212 is multiplied by the output signal 209 of the selector 208 in a multiplier 210, and a similar intersymbol interference signal 211 is output. Further, the error signal 201 in FIG. 5 takes three values, +1 and O, but the error signal 213 in FIG. 7 takes two values, +1. The pseudo intersymbol interference signal which is the output of the adaptive filter 21 constituted by the circuit shown in FIG.

In FIG. 1, switch 9. Memory 101, 102°...
...10m, selector 11. Only the residual intersymbol interference component is extracted by the adder 12, but as is clear from the eye pattern in Fig. 3, the adder 12 is replaced with a subtracter, and the sample values with the same polarity and the same absolute value are currently extracted. A similar effect can be obtained by configuring the subtraction from the sample value of . At this time, in order to avoid subtracting the current sample value, that is, itself, the selector 11 is configured to write the value supplied from the switch 9 into the memory after outputting 4Lυ values from the memory. When using a subtracter, sample values of the same polarity and equal absolute value are subtracted from the current sample value, so special operations can be performed even when the amplitudes of positive and negative pulses differ due to nonlinearity of the received signal. The same effect can be expected without doing so.

Further, an absolute value circuit is arranged on the path from the delay element 8 to the switch 9, and a multiplier is arranged on the path from the selector 11 to the adder 12. It can also be configured such that when 1 is 101, it is multiplied by +1. That is, memory allocation is performed based only on symbol waveforms, regardless of polarity.

Waveforms with the same waveform but different polarities are also stored in the same memory. Therefore, the number of memories is halved.

The mode signal obtained by the determiner 3 is used to control a new selector supplied with +1 and -1, and supplies +1 or -1 to the multiplier. In this case, since waveforms with different polarities are stored in the same memory, even if the adder 12 is replaced with a subtracter, the above-mentioned effect on the nonlinearity of the received signal cannot be obtained.

Furthermore, polarity detection circuits 13 and 16 are removed, switch 1
It is also possible to arrange a new polarity detection circuit in the path from 7 to the adaptive filter 19. At this time, the adaptive filters 19, 21 and 25 operate according to the LMS algorithm, and all the effects described above are effective.

Up to now, the present invention has been described in detail using the M8 code as an example, but a bi-phase code, for example, can be used as the transmission line code. When a biphase code is used, the received signal eye pattern shown in Figure 3 is T/2.
The waveform shifted by seconds becomes the received signal, which is different from the sign in M8, but the sample value every T seconds is stored in the memory corresponding to the symbol waveform and sample phase to which this sample value belongs. The received signal components are canceled by adding or subtracting from the current sample value a value in the memory corresponding to a symbol waveform having the same absolute value as the Mt-t symbol waveform of the current sample value. However, in the case of a biphase code, the input signals to the switch 9 and selector 11 are only data signals. Furthermore, since it is currently impossible to know in advance the symbol waveform 9T seconds later, the coefficients are updated after waiting until the symbol waveform 9T seconds later is determined. Therefore, for a pi-phase code, 1M
=2, and the delay element 8Fi2T seconds must be provided. In the case of a pi-phase code, the selector 150 control signal is also different from the M 8 K code. That is, the selector 15 selects the output signal depending on whether the received signal takes a value of zero at the 12 sample points of the third factor, but in the case of a pi-phase code, 1. Since this is the boundary between the symbol waveforms, it is necessary to use a circuit for switching the selector 15 in response to two consecutive symbol waveforms. Considering transmission line codes other than these codes in the same way, the memories 101 e 10Ss..., 1 are stored based on the received signal eye pattern corresponding to FIG.
It is clear that if 0.11 is assigned and used to update the coefficients of the adaptive filter 25 after canceling the received signal, the residual intersymbol interference can be extracted accurately.

〔Effect of the invention〕

As described in detail above, according to the present invention, the residual intersymbol interference component contained in the received signal is not zero by calculating the sum or difference between the current value and the value JT seconds ago for the difference signal. Extracted accurately with probability of positive value. Therefore, by using the above sum or difference and controlling the adaptive filter by updating the coefficients while selecting the above sum or difference and the difference signal t corresponding to the sampling phase, adaptive operation is guaranteed, and complex Therefore, it is possible to provide an intersymbol interference removal method and apparatus using decision feedback that is simple, does not require extensive control, and has small hardware scale.

Furthermore, according to the present invention, it is possible to match the zero crossing points of the received signal with the sample points and at the same time eliminate not only intersymbol interference caused by past symbol waveform sequences but also interference within symbol waveforms. , it has the advantage of being able to always maintain an optimal determination timing phase regardless of the transmission distance, and being resistant to blacks, rips, rips, and rips.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figure 2 is an MS
Figure 3 shows the symbol waveform and state transition of the K code.
8 shows the eye pattern corresponding to the code, FIG. 4 is a configuration diagram of the adaptive filter 25 in FIG. 1, and FIG.
The configuration diagram of the coefficient generator in Figure t1144, Figure 6 is the first
FIG. 7 is a schematic diagram of the adaptive fist filter 19 in the figure, FIG. 7 is a configuration diagram of the adaptive filter 21 in FIG.
The figure is a block diagram showing a conventional example of a decision feedback type equalizer. 1...Input terminal, 2...Subtractor, 3,
20...Judgment device %4...Output terminal, 1
9.21.25°°°°...Adaptive filter,
8...Delay element, 9゜14.17...
Switch % 10.10s~10-...Memory, 11,15,18...Selector, 12゜22
．． 23... Adder, 13.16... Polarity detection circuit. Agent Patent Attorney Uchihara J, $ 2 Kunicha 3 Figure Lo Otsu / Z2 Otsu 3 No. 55! i

Claims (2)

[Claims] (1) A difference signal is obtained by subtracting a pseudo intersymbol interference signal from a received signal that has undergone intersymbol interference, and a demodulated data sequence obtained by demodulating the difference signal is used to generate an image corresponding to the symbol waveform of the received signal. Retrieve the stored data,
A residual inter-symbol interference signal is obtained by addition or subtraction with the difference signal, the difference signal is stored in a memory corresponding to the symbol waveform of the received signal, and a first adaptive filter combines the residual inter-symbol interference signal with the The coefficients are updated by receiving the error signal obtained by selecting one of the difference signals based on the sampling phase and the demodulated data series and the demodulated data series, and the polarity of the difference signal is updated by a second adaptive filter. and the demodulated data series, the coefficients are updated only when the demodulated data series becomes a specific value, and demodulation is performed before the symbol waveform of the difference signal is completely received by the third adaptive filter. The pseudo intersymbol interference signal is generated by updating the coefficients in response to the temporary demodulated data series and the difference signal, and adding the outputs of the first, second, and third adaptive filters. Intersymbol interference cancellation method using decision feedback. (2) a subtracter that obtains the difference between the received signal and the pseudo intersymbol interference signal; a first determiner that receives the output of the subtracter and generates a demodulated data sequence; a first adaptive filter that receives a demodulated data series and a first error signal; a delay element that delays the output of the subtracter; and a first switch that distributes the output of the delay element based on the demodulated data series. a plurality of memories that hold the output of the first switch; a first selector that selects the output of the memory based on the demodulated data series; an output of the delay element; and an output of the first selector. a second switch that distributes the output of the subtracter based on the phase of the received signal; a contact output of one of the second switches and a second error signal; a second adaptive filter that receives the signal, a second selector that selects either one contact output of the second switch or zero based on the demodulated data series, and a a third selector that selects one contact output of the switch based on the demodulated data series; one contact output of the second switch, the output of the arithmetic unit, and the third selector; a third output that selects one of the outputs based on the phase of the received signal;
a second determiner that receives the output of the subtracter and generates a temporary demodulated data sequence before completely receiving the symbol waveform of the output of the subtracter; and an output of the second determiner. a third adaptive filter that receives a third error signal; and an adder that adds the outputs of the first, second, and third adaptive filters to generate the pseudo intersymbol interference signal; The output of the third switch is fed back to the first adaptive filter as the first error signal, and the output of the second selector is fed back to the second adaptive filter.
The decision feedback is characterized in that one contact output of the second switch is fed back to the third adaptive filter as the third error signal. intersymbol interference canceller.