JPH01233839A - Method and device for eliminating inter-code interference by decision feedback - Google Patents

Abstract

PURPOSE:To eliminate interference in a symbol waveform by using 1st-3rd adaptive filters so as to revise the coefficient, adding outputs of the adaptive filters so as to generate a pseudo inter-code interference signal. CONSTITUTION:The 1st adaptive filter 19 receives an error signal and a demodulated data series so as to revise the coefficient and the 2nd adaptive filter 25 receives the polarity of the 1st half of the succeeding symbol waveform predicted from the polarity of a difference signal and the demodulated series to revise the coefficient only when the demodulated data series takes a specific value, and the 3rd adaptive filter 21 receives the inverted demodulated data series and the difference signal obtained through the demodulation before the symbol waveform of the difference signal is finished for the reception completely to revise the coefficient and outputs of the 1st-3rd adaptive filters 19, 25, 21 are added to generate the pseudo inter-code interference signal. Thus, the interference in the symbol waveform is eliminated.

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 completely removing intersymbol interference generated during waveform transmission.

(Prior Art) Decision feedback type is known as a known technique for removing intersymbol interference that occurs during waveform transmission (IEEE T
几ANSACTfONS ON GUM AllianceNfCATI
-ONS; Vol. 32, No. 3, 1984, pp. 258-266).

FIG. 8 shows an example of a decision feedback 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 l, and is input to a subtracter 2.

The subtracter 2 produces a difference signal obtained by subtracting the pseudo intersymbol interference signal generated by the 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, and the determiner 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 filter 5. The pseudo intersymbol interference signal adaptively generated by the adaptive filter 5 is supplied as an input to the subtracter 2. The output signal of the determiner 3 supplied to the AGC 7 is multiplied by 7 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 80C7 as a control signal.

The AGC 7 uses the signal fed back from the subtracter 6 to adjust r 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
By correlating the output signal of the subtracter 6 and the output signal of the determiner 3 in C7, fi is realized by adaptively determining the gain of the output signal of the AGC 7. 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. A closed loop circuit consisting of an adaptive filter 5 operates to remove intersymbol interference experienced by the received signal applied to the input terminal 1.

(Problem to be Solved by the Invention) In order for the adaptive filter 5 to perform an adaptive operation, the residual intersymbol interference component must be correctly supplied to the adaptive filter 5. However, since the difference signal that is the output signal of the subtracter 2 includes signals other than the residual intersymbol interference component, assuming that the output signal of the subtracter 2 is directly supplied to the adaptive filter 5, the adaptive filter 5 The adaptive ability of the filter 5 will be lost. Therefore, conventionally, as shown in FIG. 8, a subtracter 6. A.G.O.
By extracting the residual intersymbol interference component by 7,
A method has been used to ensure adaptive operation of the adaptive filter 5. However, in such a control method, the AGC 7 is required, and in order to obtain sufficient intersymbol interference suppression, it is necessary to adjust the received signal that is not affected by intersymbol interference supplied from the AGC 7 to the subtracter 6 at 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 an intersymbol interference removal method and apparatus using decision feedback that is simple and has a small hard 9-air scale. Another object of the present invention is to provide an intersymbol interference cancellation method using decision feedback that can not only cancel intersymbol interference caused by a sequence of past exit symbol waveforms, but also interference within a symbol waveform. The goal is to provide equipment.

(Means for Solving the Problems) The intersymbol interference removal method using decision feedback of the present invention subtracts a pseudo intersymbol interference signal from a received signal subjected to intersymbol interference to obtain a difference signal, and demodulates the difference signal. Using the demodulated data series obtained from the demodulation data series, extract the already stored data corresponding to the symbol waveform of the received signal, add or subtract it from the difference signal to obtain a residual intersymbol interference signal, and calculate the difference signal. A first adaptive filter selects one of the residual intersymbol interference signal and the difference signal based on the prefuge phase and the demodulated data sequence. update the coefficients in response to the obtained error signal and the demodulated data series;
A second adaptive filter receives the polarity of the difference signal and the polarity of the first half of the next symbol waveform predicted from the demodulated data sequence, and updates all coefficients only when the demodulated data sequence reaches a specific value. The first, second and third coefficients are updated in response to the provisional demodulation data series obtained by performing demodulation before the symbol waveform of the difference signal is completely received by the adaptive filter of the adaptive filter, and the difference signal is received. The configuration is such that the pseudo intersymbol interference signal is generated by adding the outputs of the adaptive filters.

The intersymbol interference canceling device using decision feedback of the present invention includes a subtracter that obtains the difference between a received signal and a pseudo intersymbol interference/1M code, and a first decision that receives the output of the subtracter and creates a demodulated data sequence. a first adaptive filter that receives the demodulated data series and a first error signal supplied from the first determiner, a delay element that delays the output of the subtracter, and the demodulated data series. a first switch that distributes the output of the delay element based on the output of the delay element, a plurality of memories that hold the output of the first switch, and a first selector that selects the output of the memory based on the demodulated data series. an arithmetic unit that obtains the sum or difference between the output of the delay element and the output of the first selector; a second switch that distributes the output of the subtracter based on the phase of the received signal; a polarity prediction circuit that receives a data sequence and predicts the polarity of the first half of the next symbol waveform; a second adaptive filter that receives a prediction signal and a second error signal supplied from the polarity prediction circuit; a second selector that selects either one contact output of the switch or zero based on the demodulated data series; and a second selector that selects either the output of the arithmetic unit or the one contact output of the second switch. a third selector that selects based on the demodulated data series;
a third switch that selects one of the contact output of the second switch, the output of the arithmetic unit, and the output of the third selector based on the phase of the received signal; and the output of the subtracter. a second determiner that generates a temporary demodulated data sequence before completely receiving the symbol waveform of the output of the subtracter; a third adaptive filter receiving the fourth adaptive filter; adding the outputs of the second and third adaptive filters to generate the pseudo intersymbol interference 1g signal;
and 'Ik, 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 first adaptive filter as the second error signal. 2 adaptive filter, and the contact output of one of the 242 switches is fed back to the third adaptive filter as the third error signal.

(Function) The present invention differs from 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 components and subtracting it from the difference signal. We focused on the characteristics and designed it so that the residual intersymbol interference component can be extracted accurately. That is, according to the characteristics of the received signal eye pattern of the transmission path code including the binary code system, if intersymbol interference can be avoided, 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 taking the sum or difference between the current sample value and the sample value JT seconds ago for the difference signal (=received signal containing residual intersymbol interference components), it is possible to obtain a residual code with a certain positive probability that is not zero. Only the interfering 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. Another aspect of the present invention is to bias two types of one-tap adaptive filters to remove interference within a symbol waveform.

It is constructed to be able to eliminate interference within symbol waveforms, which was impossible with conventional methods, and has increased tolerance to clock jitter compared to conventional methods.

Performance can be improved.

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

FIG. 1 is a diagram 411g showing an embodiment of the present invention. In the same figure, a receiving 1 & signal which has received intersymbol interference from a transmission path is supplied to an input terminal 1, and is supplied to a subtracter 2. First, transmission line codes will be explained.

FIG. 2 shows symbol waveforms and state transitions of an M8K (minimum shift keying) code as an example of a transmission line code. As shown in FIG. 2, all four types of symbol waveforms are prepared in the MSK code. That is.

For the @0'' and @l 1 # data, two types of waveforms, 9''0'' mode and 11'' mode, are prepared with the & character inverted, respectively. These four types of state transitions are indicated by arrows in FIG. 2, and the current mode is determined by the previous mode. The M8 code has the property that the polarity always inverts at the symbol waveform boundary.

The transmission line code shown in Figure 2 is transmitted along the transmission line,
The signal is input to the input terminal l in FIG. 1 after receiving intersymbol interference.

The difference signal obtained by subtracting the pseudo intersymbol interference signal which is the output of the power zero adder 23 in the subtracter 2 (=received signal containing the residual intersymbol interference component) is delayed by the determiner 3° MT seconds. delay element 8. Polarity judgment circuit 16 and judgment 'a
20. The determiner 3 adds the data corresponding to the received 7/pol waveform every second, and outputs the output from the output terminal 4, the switch 9, the selectors 11, 15 and 18, and the polarity prediction circuit [24 and 7 adaptive].・Filter 25
is supplied to Adaptive filter 25, edge counter 22, 23, subtractor 2, delay element 8. Switch 9, memo +7101, 10s...10□, selector 1
A closed loop circuit consisting of a 1° adder 12, a polarity detection circuit 13, and a switch 14 realizes the adaptive operation of the adaptive filter 25. Switch 9, memory 10t
* 10g,...10m, selector 1
1 removes all received signal components included in the output of the attenuator 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 phase/prefuge phase, and the adaptive filter 2
Supply to 5.

Next, the relationship between the output of adder 12 and the residual intersymbol interference component in the difference signal output from subtracter 2 will be explained in detail. Figure 3 shows the received signal eye pattern (turn side) when the transmission line code shown in Figure 2 is adopted. f, it will be tinged.Originally, the received one word i・)
The eye pattern shown at the beginning to simplify the explanation is the eye pattern that does not contain intersymbol interference components when waveform equalization is ideally performed. shall be. 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 IT seconds (J is a positive integer) ago have opposite polarities and almost the same absolute value is zero. takes some positive value. Therefore, it is possible to cancel the received signal 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.

Next, a note on Figure 1! jlO,,10,.

. . . The operation of the switch 9 and selector 11 that control the input/output signals of lQm will be explained. switch 9
memory 101slO1 is used to store all sample values corresponding to the symbol waveform to which the received/pull] belongs.
*..., Select from lOm.

The eye pattern of the MSN code is 4 as shown in Figure 3:
Since the waveform of type f1 is distorted, m =
4 and 6D, for example memory 10. , 10. , 10s.

10, respectively “oo”, @01”, “10”,”
It can be considered that the symbol waveform corresponds to the symbol waveform represented by ``11''.Here, ``01'' represents the symbol waveform defined by the data signal @0'' and the mode signal @1''.

The switch 9 uses the data signal and mode signal supplied from the determiner 3, and the combination of these is @OO''.

16 supplied from the delay element 8 at the time of ``01'', @10''', and @11''' are respectively stored in the memory IQl@
Change the circuit so that it is stored in iol#10s*104.

In addition, in FIG. 1, the determiner 3, the switch 9° selector II, 15.18. The path connecting the polarity prediction circuit 24 and the adaptive filter 25 is shown as one line, but when the MSK code is adopted, two paths corresponding to the data signal and the mode signal are shown. 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 cannot be determined, the signal supplied to the switch 9 is passed through the delay element 8 Name the second delay. That is, M=l in the MSK code. At the same time, Ka3! The difference signal supplied to the circuit 12 is also delayed by the delay element 8 by T seconds. In the embodiment shown in FIG. 1, assuming that the number of sampling R, '1R==4 for the %1 Kunpol waveform, there are sample values at the phase of JIWh for one symbol waveform. For this reason, note! J 1 oi, 10. .

10,. 104 each consists of four sub-memories, each sub-memory 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 R←4. The selector 11 selects a memory I01@10! from which data is extracted corresponding to the symbol waveform to which the received sample value belongs. *・・・・・・
・, 10Xn. In the case of MSK code, the data signal and mode signal supplied from the determiner 3 are used to determine whether these are 100", @01", 1"10", or "11".
”, the memory is 101 and lOt*1, respectively.
04, the circuit is switched to select the data stored in 10m and supply it to the adder 12. In this way, the selector 11 selects the 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 by the adder 12, and the residual intersymbol interference is accurately eliminated. can be extracted. Therefore, if the output of the adder 12 is used to control the adaptive filter 25t.

Since the received signal that interferes with the adaptive operation of the adaptive filter 25 is canceled out, the adaptive filter 25
5 adaptive behavior is guaranteed.

The difference signal that is the output of the subtracter 2 is also supplied to a polarity determining circuit 16, and after the polarity of the difference signal is detected, it becomes an input to the switch 17. The switch 17 has four output contacts.5. T/R seconds (assuming 几 is an even number and 几=4)
At each time, output is sequentially switched in the direction of the arrow in FIG. 1 from the first output contact to the fourth output contact. From the left in the figure, the first. 2nd, 3rd. This operation is repeated every %T seconds using the fourth output contact. The sampling phase of the operation of switch 17 is shown in FIG.

Fs t, respectively, are the 1st degree, the 2nd* degree, and the 3rd degree of the switch 17 in FIG. This corresponds to the spring/spring phase of the fourth output contact. The third contact output of switch 17 is selector 1
5 inputs.

Further, as the other input of the selector 15, the output of the polarity detection circuit 13 is supplied. - 10,000, the data signal which is the determination result of the determiner 3 is inputted to the selector 15 as a control signal, and when the data signal is 11'',
The third contact output of the switch 17 is selected and output, and when the data signal is @O'', the output of the polarity detection circuit 13 is selected and output. That is, as is clear from FIG. When the signal is 11'', there is a zero crossing point at the center of the symbol, so the third contact output of the switch 17 shown in FIG. 1 becomes a residual intersymbol interference component.
When the data signal is 10", there is no zero crossing point at the center of the symbol, so the output of the polarity detection circuit 13 becomes the residual intersymbol interference component. Therefore, the output of the selector 15 is the residual intersymbol interference component of the sampling phase t3. is supplied to the third input contact of the switch 14.The switch 14 is a switch having four input contacts, and is synchronized with the switch 17 and is supplied to the third input contact of the switch 14. ), the input is switched in order from the first input contact to the fourth input contact in the direction of the arrow in Fig. ,
This operation is repeated every T seconds. "6m" shown in Figure 3
Is Fs F are the switches 14 and 17 in Figure 1, respectively.
According to 1st. 2nd゜3rd. This corresponds to the spring/spring phase of the fourth input contact. The first contact output of the switch 17 is connected to the first input contact of the switch 14, the output of the polarity detection circuit 13 is connected to the second and fourth input contacts, and the selector is connected to the third input contact as described above. 15 deba.

Each is supplied. As shown in FIG. 3, the sampling phase ti and 1. In this case, since no zero crossing point occurs, the residual intersymbol interference component obtained as the output of the polarity detection circuit 13 shown in FIG.
The tap coefficients of are updated. Sampling phase 1. Then, the residual intersymbol interference components corresponding to the data signals ``0'' and ``1'' are obtained at the output of the selector 15, and the switch 1
4 to the third input contact. Therefore, switch 1
4, residual intersymbol interference components necessary for updating the tap coefficients are obtained in the valley/glyph phase and are supplied to the adaptive filter 25.

In the above explanation, L=4, but it is clear that L=4 may be any even number.

Next, the adaptive filter 25 will be explained in detail. FIG. 4 shows a detailed configuration of the adaptive filter 25 of FIG. 1. This filter has a first
Data signal 106' that constitutes the output signal of the determiner 3 shown in the figure.
, the mode signal 106 and the output signal 107 of the switch 14 are input.

The mode signal 106 is a delay element 100s1 a multiplier 101°.

101te..., 101 and coefficient generator 1
02.

1021, . . . , 102. Further, the data signal 106' is sent to the delay element 1001' and the coefficient generator 102.

1021, . . . 102. Delay elements 1001e and 100 (h e·
・－・〜・・.

100N/R1 and 100 breath 'eioo*'...'
*10ON/R' can be connected in this order and each can be realized with a clip and 70 tubes. Here, the number of taps N is a positive integer υ, and R is a divisor of N. Further, the data period of the data signal 106' and the mode signal 106 is T seconds. Delay element 1001 (i=1.2...
.

101j+1. ..., 1o1j+&-1 and coefficient generator 102j.

102...-02j, supplied to a1. In addition, the outputs of J+1°100·' (1=1.2..., N/R-1) are respectively reduced coefficient generators 102, 102..., 1
02j+, -0js J”s. However, 5j=ix 几.N multiplier 101
, 101 +B, ...* 10 "ic+N
-R (K:Os l@”..., 几-1), to the related d fluorogen 102 and 102, respectively.

......, after 102 is multiplied by the valley coefficient which is the output of +NR and the input mode 1 (+1 or -1),
All of the multiplication results are input to an adder 103k and summed. 1 (one adder 103, 10311...
. . , the output of 103B-8 becomes a contact input of switch 104. The switch 104 is a multi-contact switch with a period of T gold dust, and has i(number of adders 103, 5103s*',
..., 103. The output sound of -0 is selected in T/R seconds and is output, and a pseudo intersymbol interference signal caused by the past transmission data sequence is generated at 108tl-'l'/R seconds. - The switch 105, which operates in synchronization with the sui-nochi 104, has an input/output direction opposite to that of the switch 104. The switch 105 is the input number 107eT/R.
It performs the function of sequentially distributing to nine contacts every second.

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.

The fifth factor is the coefficient generator 1021 (l=0.1.・
..., N-1: This shows the detailed configuration.

The mode signal 200 in FIG. 5 is the mode signal 106 in FIG.
or delay element 100. , 100. ,・・・・・・,1
00. It corresponds to the mode signal output from -1.

Similarly, the data signal 200' of FIG. 5 is connected to the data signal 106' of FIG.
'＋・〜・．

It corresponds to the data signal output from 100R-□'. Ninth, the input signal 201 of No. 56A corresponds to the contact output of the switch 105 in FIG.

Furthermore, output signal 209 in FIG. 5 corresponds to the output of coefficient generator 102 in FIG. In the fifth factor, a data signal 200' indicating %@On or @l'' is supplied as a control signal to each of the selectors 204, 205 and 20B.
The mode signal 200 that takes `` or @l'' is sent to the multiplier 202
is supplied as one of the inputs. The other input of the multiplier 202 is supplied with an error signal 201 consisting of a J134 inter-code interference component. After the mode signal 200 and the error signal 201 are multiplied by the multiplier 202, the multiplication result is supplied as one input of the adder 203. Here, delay elements 206 and 207 that provide a delay t of T seconds are @0'' and @1'' of data signal 200', respectively.
Coefficient memory corresponding to

Both outputs are provided as inputs to selector 208. - 10,000, the data signal 200' is input as a control signal to the selector 208, and the data signal 200' is @0.
'', the coefficient corresponding to @O'', which is the output of the delay element 206, is selected and output, and the data signal 200' becomes @1.
'', the output of the delay element 207 is ``1''''.
The coefficient corresponding to is selected and output, and in either case, an output signal 209 representing the coefficient is obtained. Furthermore, the output signal 20
9 is fed back to adder 203 and added to the output signal of multiplier 202, and then input to selectors 204 and 205. Further, the outputs of delay elements 206 and 207 are also supplied as inputs to selectors 204 and 205, respectively. 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 200' is 10'',
The selector 208 selects the output of the delay element 206 corresponding to the data signal 10'' and outputs it as an output signal 209. At this time, the output signal 209 is input to the adder 203 and then sent to the delay element 206 via the selector 204. The output of the delay element 207 is selected by the selector 205 and supplied to the delay element 207 again, so that the coefficient corresponding to the data "'O" is updated. ” is not updated.

Contrary to this case, when the data signal 200' is 11'', the selector 208 selects the output of the delay element 207, which is a coefficient corresponding to the data @l'', and outputs it as the output signal 209. At this time, the output signal 209 is output from the adder 20
After the signal is input to the selector 205' and fed back to the delay element 207, the coefficient corresponding to the data "'1" is updated. On the other hand, in the selector 204,
The output of delay element 206 is selected and output to delay element 206 again.
Therefore, the coefficient corresponding to the data @O''' is not updated. Based on the principle explained above.

In addition to selecting the coefficients to be used in the adaptive filter operation corresponding to the value ``O'' or @l of the data signal 200', the coefficients that were used are updated, and the coefficients that were not used are updated. By maintaining the original values of the coefficients, the coefficients of the adaptive filter can be obtained adaptively.

The pseudo intersymbol interference signal caused by the past Dale sequence generated by the adaptive filter 25 is supplied to the subtractor 2 via the adder 22 and the adder 23t, and the intersymbol interference signal is supplied from the input terminal l. It can be subtracted from the received signal.

Next, interference cancellation within a symbol waveform will be explained. Demodulated data, which is the output of the @determiner 3, is input to the adaptive converter 19 via the polarity prediction circuit 24. In FIG. 1, there is only one line connected to the polarity prediction circuit 24. In the case of MSK code, there are two lines for supplying data signals and mode signals. The polarity prediction circuit 24 is composed of one exclusive NOR circuit, takes the exclusive NOR of these signals, and supplies the result to the adaptive filter 19. Since the MSK code always inverts the polarity at the boundary of the waveform, by using the mode signal which is the output of the legator 3 which is the judgment result of the received signal waveform T seconds ago, the received signal waveform at the boundary can be detected. You can know the mode signal. For example, when the data signal is @O'' and the mode signal is 11'', and when the data signal is ``1'' and the mode signal is @0@, the polarity of the first half of the next symbol waveform is positive, If this is defined as @0'', it matches the mode signal obtained as an exclusive NOR. This is also clear from FIG. 2. The output signal of the polarity prediction circuit 24 is represented by the symbol Adaptive data is used as judgment data for the first half of the waveform.
Used in filter 19.

-10,000, the polarity of the difference signal which is the output of the subtracter 2 is input to the selector 18 via the % polarity gain circuit 16 and the switch 17.
It is input at the prefuge phase tl. Further, zero is also input to the selector 18, and using the demodulated data output from the foot device 3, when the data signal is "O", it is zero t-, and when it is "1", the third signal of the switch 17 is input. The residual intersymbol interference component appearing at the output terminal is selected and output, and is supplied to the adaptive filter 19. The selector 18 distinguishes that at the sampling phase is, the symbol waveform represented by data @0111 does not have a zero difference point, but always has data "1". The selector 18 supplies the polarity of the residual intersymbol interference component when the data of the output signal of the si discriminator 3 is l'', and the polarity of the residual intersymbol interference component when the data is @O@ is supplied to the adaptive filter 19, so that the data is
Coefficients are selectively updated only when the flag is "1". vinegar/
Bling phase 1. The component caused by interference within the symbol waveform among the displacements from zero in It is removed by subtracting it from the received signal.

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 polarity prediction circuit 24 shown in the figure, that is, the polarity of the difference signal when the sampling phase is set to the input signal 301, is the output of the selector 18, that is, the sampling phase t1.
The polarity of the residual intersymbol interference component in , or the error signal that becomes zero, corresponds to this. 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 304, which provides a delay of T seconds, is a coefficient memory whose output is fed to multiplier 305 to generate a pseudo intersymbol interference signal 306. The output of the delay element 304 is also a force zero calculator 303'lf
- The output of the multiplier 302 that multiplies the polarity 300 of the difference signal and the error signal is the lJD multiplier 30.
3. When the error No. 1a 301 is zero, the output of the 1 multiplier 302 is zero, so the coefficient does not change,
Selective coefficient updates are performed. In this way, the value of pseudo intersymbol interference No. 18 at the zero difference at the center of the symbol waveform appears at the output of the adaptive filter 19,
After being added to the pseudo intersymbol interference signal generated by the adaptive filter 25 in the adder 22, the signal is added to the pseudo intersymbol interference signal generated by the adaptive filter 25.
The signal is supplied to the subtracter 2 via the 3-metal wire.

The adaptive filter 21 has the role of removing 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 power output J162, and determines the data and mode at the sampling phase ts for the waveform within the first half of 3T/4 seconds of the 7/pol waveform with a period of T seconds. The determination is made, and the obtained temporary demodulated data is supplied to the adaptive filter 21.

In addition, the adaptive filter 21 includes a polarity gain circuit 16.
A first contact output of the switch 17 is supplied via the switch 17. Therefore, at the sampling phase to, the subtracter 2
The polarity of the difference signal that is the output of the adaptive filter 2
1 and used as an error signal to update coefficients.

As shown in Fig. 3, in an ideal case without intersymbol interference, the sampling phase t, which is the end of the symbol waveform, is a zero crossing point, but in the near future, intersymbol interference occurs, so the sampling phase t
The width at ・does not 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 tap and one phase of the adaptive filter 25 shown in FIG. Therefore, the operating principle of coefficient updating is exactly the same as that shown in FIG. 7th
In the figure, components and signals indicated 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 are
It corresponds to an output of 0. Also, the error signal 21 in FIG.
3 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 and the output signal 209 of the selector 208 are multiplied in the multiplier 210.
't-This is the point at which the output is being made. Further, the error signal 201 in FIG. 5 takes three values, +1 and O, while 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 1OtelOss...
...1Orn, selector 11. Although the residual intersymbol interference component is extracted by the adder 12,
As is clear from the pattern, the same effect can be obtained by replacing the adder 12 with a subtracter and configuring the system to subtract sample values of the same polarity and the same absolute value from the current sample value. At this time, to avoid subtracting the current sample 1 shift, i.e., Sereno Ri 11
The configuration is such that the value supplied from the switch 9 is written into the memory after the memory is read out. 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 to multiply by -l and by +1 when it is 10''. That is, memory allocation is performed based only on symbol waveforms regardless of polarity, and even waveforms with the same polarity but different polarities are 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 -l, and supplies +1 or -1 to the multiplier. Note that 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 non-edge shape of the received signal cannot be obtained.

Furthermore, the polarity detection circuit 16 can also be removed. At this time, the adaptive filter 19°21.25 is L
It works with MS algorithm.

All nine effects mentioned so far are effective.

Up to now, the present invention has been described in detail using the M8 code as an example, but for example, a biphase code tone can be used as the transmission line code. When a biphase code is used, the received signal eye pattern '1T7 shown in Fig.
Although it differs from the MSN code in that the received signal is a waveform shifted by 2 seconds, 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, while The received signal components are canceled by adding or subtracting from the current sample value a memory value corresponding to a symbol waveform having the same absolute value as the symbol waveform to which the current sample value belongs. However, in the case of a biphase code, the input signals to the switch 9 and selector 11 are only data signals. Also, since it is impossible to know in advance the symbol waveform 9T seconds after the current time, wait until the symbol waveform 91 seconds after the current time is determined.
Update the coefficients. Therefore, for biphase codes 1
If M=2, the delay multiplier 8 must provide 2T seconds. In the case of a biphase code, the selector 15
The control signal of the MSK code is different from that of the MSK code. That is, 1. in FIG. The selector 15 selects the output signal depending on whether the received signal takes a value of zero at the sample point of
For biphase codes, t! 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,
Allocate memories 10111011...110,n based on the received signal eye pattern corresponding to FIG. 3,
It is clear that residual intersymbol interference can be extracted accurately if the coefficients of the adaptive filter 25 are updated after canceling the received signal.

(Effects of the Invention) As described in detail above, according to the present invention, the difference signal is received by calculating the sum or difference between the current value and the value JT seconds ago. The residual intersymbol interference component is extracted accurately with a probability of a certain positive value that is not zero. Therefore, using the above sum or difference, select the sum or difference and the difference signal ′ corresponding to the sum/glyph phase. The present invention provides an intersymbol interference cancellation method and device using decision feedback that guarantees adaptive operation by controlling the adaptive filter by updating all coefficients while updating the coefficients, and does not require complicated control, is simple, and has small hardware scale. Can be provided.

Further, according to the present invention, it is possible to make the received signal coincide with the pull point of the received signal, and at the same time eliminate not only intersymbol interference caused by a sequence of past symbol waveforms but also interference within the symbol waveform. Because you can.

It has the advantage of being able to maintain the optimum timing phase at all times regardless of the transmission distance and being resistant to clock jitter.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figure 2 is an M8
Figure 3 shows the symbol waveform and state transition of the 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 figure is a block diagram of the coefficient generator in Figure 4, Figure 6 is a block diagram of the adaptive filter 19 in Figure 1, and Figure 7 is a diagram of the coefficient generator in Figure 1.
The configuration diagram of the adaptive filter 21 in the figure, and FIG. 8 is a configuration diagram showing a conventional example of a decision feedback type equalizer. l...Input terminal, 2...Subtractor, 3.
20...Legacy device%4...Output terminal, 1
9,21.25...Adaptive filter%
8...Delay element%9゜14.17...
Switch, 101, 10. ~10m...Memory% 11,15.18...Selector, 12゜2
2.23... Adder, 13.16...
Polarity detection circuit, 24...Polarity prediction circuit. Agent Patent Attorney Susumu Uchihara 2nd Division 5 Zuko 5 Prisoner J Negative Otsu Dd $7 rgJ

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. In response to the polarity of the first half of the next symbol waveform predicted from the demodulated data series, the coefficients are updated only when the demodulated data series reaches a specific value, and a third adaptive filter changes the symbol waveform of the difference signal. The coefficients are updated by receiving the temporary demodulated data sequence obtained by demodulating before the complete reception and the difference signal, and the coefficients are updated.
and a third adaptive filter to generate the pseudo intersymbol interference signal. (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 adaptive filter that distributes the output of the delay element based on the demodulated data series. a switch, 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, and a plurality of memories that hold the output of the delay element and the first selector. an arithmetic unit that obtains the sum or difference with the output, and a second switch that distributes the output of the subtracter based on the phase of the received signal;
a polarity prediction circuit that receives the demodulated data series and predicts the polarity of the first half of the next symbol waveform; a second adaptive filter that receives a prediction signal and a second error signal supplied from the polarity prediction circuit; a second selector that selects either one contact output of the second switch or zero based on the demodulated data series; and one of the output of the arithmetic unit and one contact output of the second switch; a third selector that selects one of the outputs of the received signal based on the demodulated data series, one contact output of the second switch, the output of the arithmetic unit, and the output of the third selector; a third switch that selects based on the phase; 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; A third adaptive filter receives the output of the second determiner and the third error signal, and adds the outputs of the first, second, and third adaptive filters to obtain the pseudo intersymbol interference signal. an adder that generates the output, and feeds back the output of the third switch as the first error signal to the first adaptive filter;
The output of the second selector is fed back to the second adaptive filter as the second error signal, and
An intersymbol interference removal device using decision feedback, characterized in that a contact output of one of the switches is fed back to the third adaptive filter as the third error signal.