JPH01233837A - Method and device for eliminating inter-code interference by decision feedback - Google Patents

Abstract

PURPOSE:To guarantee adaptive operation and to simplify the control by receiving an error signal and a data series by a 1st adaptive filter to revise the coefficient, receiving the polarity of a difference signal and a demodulation data series by a 2nd adaptive filter, revising the coefficient only when the demodulation data series takes a specific value and adding outputs of the 1st and 2nd adaptive filters. CONSTITUTION:The 1st adaptive filter 19 receives an error signal and a demodulated data series obtained by selecting any of the inter residual code interference signal and the difference signal based on the sampling phase and the demodulated data series to revise the coefficient, and the 2nd adaptive filter 25 receives the polarity of the difference signal and the demodulated data series to revise the coefficient only when the demodulated series takes a specific value and outputs of the 1st and 2nd adaptive filters 19, 25 are added to produce a pseudo inter-code interference signal. Thus, the interference in a symbol waveform is eliminated and the performance is improved.

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 occurring during waveform transmission.

[Conventional technology]

A decision feedback equalizer is known as a known technique for removing intersymbol interference that occurs during waveform transmission (IEEE T
RANSACTIONS ON COMMUNICAT
IONS; Vol. 32, No. 3, 1984, 258-26
(See page 6).

FIG. 7 shows a conventional example of a decision feedback type equalizer. The circuit shown in FIG. 7 is connected to the transmitting side via a transmission line. Here, for simplicity, explanation will be given assuming baseband transmission.

In FIG. 7, a received signal subjected to intersymbol interference is supplied from a transmission path to an input terminal IK, and is input to a subtracter 2.

The subtracter 2 subtracts the pseudo intersymbol interference signal generated by the adaptive filter 5 from the received signal supplied to the input terminal 1, resulting in a difference signal (=received signal including the residual intersymbol interference component, [residual intersymbol interference component ]; [Intersymbol interference component] − [
A pseudo intersymbol interference signal]) is obtained and supplied to a determiner 3 and 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 one input of the subtracter 2. 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. The AGC 7 uses the signal fed back from the subtracter 6 to correct r so that the output of the subtracter 6 is equal to the residual intersymbol interference component.

In other words, 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 output from the subtracter 2. This is achieved by correlating the output signal of the subtracter 6 and the output signal of the determiner 3 in the AGC 7, and by adaptively determining the gain of the output signal of the AGC 7. The residual intersymbol interference component that is the output of the subtracter 6 is also supplied to the adaptive filter 5,
Used for coefficient update. A closed loop circuit consisting of a subtracter 2, a determiner 3, and an adaptive field filter 5 has an input terminal 1.
The receiver operates to remove intersymbol interference experienced by the received signal supplied to the receiver.

[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 also contains 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. 7, a method has been used in which the adaptive operation of the adaptive filter 5 is guaranteed by extracting the residual intersymbol interference components using the subtracter 6 and 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, it is desirable to receive a received signal that is not subjected to intersymbol interference and is supplied from the AGC 7 to the subtracter 6. This method requires control to maintain the same level, and has the disadvantage of increasing the scale of hard fair. Further, although the conventional decision feedback type equalization amount 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, which is simple and requires small hardware. Another object of the present invention is to provide a method and method for intersymbol interference cancellation using decision feedback, which is capable of removing 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 equipment.

[Means to solve the problem]

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 a demodulated data sequence obtained. Extracting already stored data corresponding to the symbol waveform of the received signal, adding or subtracting it to the difference signal to obtain a residual intersymbol interference signal, and adding the difference signal to the symbol waveform of the received signal. an error signal and the demodulated data sequence that are stored in a memory and obtained by selecting either the residual intersymbol interference signal or the difference signal with a first adaptive filter based on the sampling phase and the demodulated data sequence; Update the coefficients based on
A second adaptive filter receives the polarity of the difference signal and the demodulated data series, updates the coefficients only when the demodulated data series reaches a specific value, and updates the outputs of the first and second adaptive filters. The configuration is such that the pseudo intersymbol interference signal is generated by adding the signals.

The intersymbol interference canceling device using decision feedback according to the present invention includes a subtracter that obtains the difference between a received signal and a pseudo intersymbol interference signal, and a first determiner that receives the output of the subtracter and creates a demodulated data sequence. , a first 7-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 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 sequence; 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 second 7-adaptive filter that receives one contact output of the switch and a second error signal; and a second filter that selects either the one contact output of the second switch or zero based on the demodulated data sequence. a third selector that selects either the output of the arithmetic unit or the one contact output of the second switch based on the demodulated data series; and one contact of the second switch. a third switch that selects one of the output, 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 first and second adaptive filters. an adder that generates the pseudo intersymbol interference signal, and feeds back the output of the third switch as the first error signal to the first adaptive filter;
The configuration is such that the output of the second selector is fed back to the second adaptive φ filter as the second error signal.

[Effect]

Unlike the conventional method of multiplying the determiner output by a constant to generate a received signal that does not contain residual intersymbol interference components and subtracting it from the difference signal, the present invention focuses on the characteristics of the eye pattern of the received signal and generates a received signal that does not contain residual intersymbol interference components. The system was designed to accurately extract interfering components. 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
(data period) The minimum probability that the previous sample values are approximately the same value or that their absolute values are approximately the same value with opposite polarity takes 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) K, the residual code can be obtained 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 the winning difference signal, the adaptive operation of the adaptive filter is guaranteed. Furthermore, by providing a one-tap adaptive filter for eliminating interference within the symbol waveform, the present invention is configured to be able to eliminate interference within the symbol waveform, which was impossible with conventional methods.
, the resistance to clockwise jitter is higher than in the past, and performance can be improved.

〔Example〕

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

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

In the 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. First, transmission line codes will be explained.

FIG. 2 shows symbol waveforms and state transitions of an MSK (minimum shift keying) code as an example of a transmission line code. As shown in FIG. 2, 48 types of symbol waveforms are prepared in the MSK code. That is, for data “0” and 61’, @0’ mode and 11
Prepare two types of waveforms for one mode. These four types of state transitions are indicated by arrows in FIG. 2, and the current mode is determined by the mode one symbol before. This M
The SK code has the property that the polarity always inverts at the symbol waveform boundary. The transmission path code shown in FIG. 2 is transmitted through the transmission path, receives intersymbol interference, and is input to the input terminal IK shown in FIG.

The difference signal obtained by subtracting the pseudo intersymbol interference signal which is the output of the adder 22 in the subtracter 2 (=received signal containing the residual intersymbol interference component) is sent to the determiner 3, which gives a delay of MT seconds. The signal is supplied to the delay element 8 and the polarity determination circuit 16.

The determiner 3 determines the data and mode corresponding to the received symbol waveform every T seconds, and its output is supplied to the output terminal 4, the switch 9, the selectors (SEL) 11, 15, 18, and the adaptive filter 25. be done. Adaptive filter 25. Adder 22, subtracter 2, delay element 8
, switch 9, memory 10! #...10m1 The closed loop circuit consisting of the selector 11, adder 12, polarity detection circuit 13, and switch 14 is the adaptive filter 2
This realizes the adaptive operation of No. 5. Switch 9, menu 10. , 10. , . . . 10m1 Selector 11 removes the received signal component included in the output of 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 adder 12 and the residual intersymbol interference component in the difference signal, which is the output of subtracter 2, will be explained in detail. FIG. 3 shows an example of a received signal eye 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 number pattern contains inter-symbol interference components, but the eye-number pattern shown in the figure to simplify the explanation is the inter-symbol interference component when waveform equalization is ideally performed. shall not contain any ingredients. 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. takes some 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, the memory 10*elOt*"" in FIG.
The operation of the switch 9 and selector 11 that control the input/output signals of ELOM will be explained. The switch 9 connects a memory 10 to a memory for storing the sample value corresponding to the symbol waveform to which the received sample value belongs. , IQ, ,...-
・.

Select from lOm. The eye pattern of an MSK code is a superimposition of four types of waveforms as shown in Figure 3.
Therefore, m = 4, and for example, the memory 10 s e
10z e 10g + 104 are each 'oo'
, "Of', @10".

It can be considered that it corresponds to the symbol waveform represented by @11#. ζHere, the symbol waveform defined by @01# and the mode signal @1# is represented.The switch 9 uses the data signal and mode signal supplied from the determiner 3 to determine the combination of these. @00”@101
Write down the signals supplied from the delay element 8 when Zl is "10" and "11" respectively.
0! Switch the circuit so that it is stored in #104.

In FIG. 1, the path connecting the determiner 3 and the switch 9, the selectors 11, 15.18, and the adaptive filter 25 is shown as a single line, but when the MSN code is adopted, the data 2 corresponding to the signal and mode signal
Represents the route of the book. Since the determiner 3 cannot determine the received symbol waveform until it finishes receiving the symbol waveform, and the data signal and mode signal are not determined, the signal supplied to the switch 9 is passed through the delay element 8 for fiT seconds. delay.

That is, M=1 in the MSK code. 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 samplings R for one symbol waveform is R=4, there are sample values at four different phases for one symbol waveform. Therefore, memory 101 +10z*10s*10
4 is each composed of four sub-memories, and each sub-memory corresponds to one symbol waveform in 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 is R
) The same applies to case 4. The selector 11 selects a memory from which data is to be extracted from the memories 10t+10zs, -, +10m corresponding to the symbol waveform to which the received sample value belongs. In the case of MSK code, the data signal and mode signal supplied from the determiner 3 are used to determine if these are '00'.
, @01″.

When @10” and @11”, memory 1 (h, 1
0ts1()a*10sK The circuit is switched so that the stored data is selected and supplied 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 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. TotoK becomes.

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 four output contacts, and the arrow in FIG. Switch to the desired direction and output. This operation is repeated every 7 seconds using the first, second, third, and fourth output contacts in order from the left in the figure. The spring/spring phase of the operation of the switch 17 is shown in FIG.
This corresponds to the sampling phase of the third and fourth output contacts. The third contact output of switch 17 is provided as one of the selector 150 inputs.

Further, as the other input of the selector 15, the output of the polarity detection circuit 13 is supplied. On the other hand, the data signal which is the judgment result of the judge 30 is inputted to the selector 15 as a control signal, and when the data signal is 1'', the third contact output of the switch 17 is selected and output, and the data signal is When is "O", the output of the polarity detection circuit 13 is selected and output.In other words, as is clear from FIG. to the third switch 17 shown in FIG.
The contact output of t becomes the residual intersymbol interference component, whereas t,
When the data signal is IIO'' in , there is no zero crossing point at the center of the symbol, so the polarity detection circuit 1
The output of No. 3 becomes the residual intersymbol interference component. Therefore, the output of the selector 15 is supplied to the third input contact of the switch 14 as the residual intersymbol interference component of the Templing phase "1." T/R seconds in synchronization with (however,
Here, it is assumed that R=4), and the input is sequentially switched in the direction of the arrow in FIG. 1 from the first input contact to the fourth input contact. From the left in the figure, the first, second, third, and fourth
as the input contact, and repeat this operation every second. josll, j2. shown in FIG. f3 corresponds to the sampling phase of the first, second, third, and fourth input contacts by the switches 14 and 17 in FIG. 1, respectively. switch 14
The first input contact of the switch 17 receives the first contact output of the switch 17, the second and fourth input contacts receive the output of the polarity detection circuit 13, and the third input contact receives the output of the selector 15 as described above. Outputs are provided respectively. As shown in Figure 3,
Sampling phase 1. and ts, no zero or difference point occurs, so the tap coefficients of the adaptive filter 25 are updated using the residual intersymbol interference component obtained as the output of the polarity detection circuit 13 in FIG. At the sampling phase t, the residual intersymbol interference components corresponding to the data signals @0" and "1# are obtained at the output of the selector 15 and supplied to the third input contact of the switch 14. Therefore, as the output of switch 14, at each sampling phase:
The residual intersymbol interference components necessary for updating the tap coefficients are obtained and supplied to the adaptive filter 25I/c. In the above description, R=4, but it is clear that R may be any even number.

Next, the adaptive filter 25 will be explained in detail. Figure 4 shows the adaptive clarity filter 25 in Figure 1.
This figure shows the detailed configuration of . This filter includes a data signal 106 that constitutes the output signal of the determiner 3 in FIG.
', mode signal 106 and output signal 107 of switch 14
is input. The mode signal 106 is a delay element 1001,
Multiplier 101°.

101xe-・”+101i-t and coefficient generator 1
020 * 1021 +..., 102R-1
is supplied to Also, the data signal 106' is transmitted to the delay element 1
00. ', and the coefficient generator 102o +102i·°゛°°゛, is supplied to the coefficient generator 102B-1. Delay elements 100x, 10(h, . . . each giving a delay of T seconds)
, 100N/R-1 and 1001' + 100 t'
+..., 100N/R-1' are connected in this order, and each can be realized by a clip-flop. Here, the tap coefficient N is a positive integer, and R is a divisor of N. Also, the data signal 106',
The data period of mode signal 106 is T seconds. Delay string 1001 (i=1, 2, . . .

The outputs of N/R-1) are sent to multipliers 101j and 101, respectively.
j+x.

......, 101j+i- and coefficient generator 10
2J, 102J+1. ...-, 102J+R-1. Also, 100i' (i=1゜2,...
..., N/R-1) are respectively output from coefficient generator 1.
02j, 102''+t,..., 102j+a
-xK supplied. However, j=iXR. Multiplier 101h+101h+ny..."-"+1011+N-
In R('=Oe 1 *..., R-1), +ie... is applied to the coefficient generator 102+c+102, respectively.
..., 102 is multiplied by each coefficient that is +N-i and the input mode signal (+1 or -1), and then all the multiplication results are input to an adder 103k and added. R adders 103os103s*..., 103B-
The output of , becomes the contact input of the switch 104. The switch 104 is a multi-contact switch with a cycle of T seconds, and R adders 103o-103ts...

The output of 103R-1 is selected and output in this order every T/R seconds, and a pseudo intersymbol interference signal 108 caused by the past transmission data sequence is generated every T/R seconds. - side, switch 1
105 switches operating in synchronization with 04
4 and the direction of input and output is reversed. That is, switch 10
5 performs the function of sequentially distributing the input signal 107 to the VCR 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 which operates synchronously.

Next, the coefficient generator will be explained in detail. FIG. 5 shows the coefficient generator 102t in FIG. 4 (t=0, 1, . . . ).

This figure shows the detailed configuration of N-1). The mode signal 200 in FIG. 5 corresponds to the mode signal 106 in FIG. 4 or the mode signal output from the delay elements 1001*100ze...-, 100R-1. Similarly, the data signal 222' in FIG. 5 is the data signal 106' in FIG.
It corresponds to the data signal output from 100R-1'. Furthermore, the input signal 201 in FIG. 5 corresponds to the contact output of the switch 105 in FIG. Further, the output signal 209 in FIG. 5 is output from the coefficient generator 10 in FIG.
Compatible with 2L output. In FIG. 5, a data signal 200' indicating "0#" or "1#" is input to a selector 204,
It is supplied as a control signal to each of 205' and 208. Also, @0# or @ which supports data signal 200'4C
A mode signal 200 taking 1" is supplied as one of the inputs of a multiplier 202. On the other hand, the other input of the multiplier 202 is an error signal 201 consisting of a residual intersymbol interference component.
is supplied. In the multiplier 202, the mode signal 200
After being multiplied by the error signal 201, the multiplication result is supplied as one input of the adder 203. Here, the delay elements 206' and 207 that provide a delay of T seconds are coefficient memories corresponding to @0'' and 11'' of the data signal 200', respectively, and their outputs are both supplied as inputs to the selector 208. On the other hand, the data signal 200' is inputted to the selector 208 as a control signal.
When ' is 10'', the output of the delay element 206 @
The coefficient corresponding to 0# is selected and output, and the data signal 20
When 0' is @1'', the coefficient corresponding to 11'' which is the output of the delay element 207 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 and the first multiplier 20
After being added with the output signals of selectors 204 and 205
is input. Further, the outputs of the delay elements 206 and 207 are also supplied as inputs to selectors 204 and 205, respectively. Furthermore, the outputs of the 1 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. When the data signal 200' is @0'', the selector 208 selects the delay element 2 corresponding to the data signal @0''.
06 is selected and outputted 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 data @0'' is updated. Since the output of the delay element 207 is selected and supplied to the delay element 207 again,
The coefficient corresponding to data @1# 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 the coefficient corresponding to the data '''1#, and outputs it as the output signal 209. At this time, the output signal 209 is output from the adder 20
3, it is input to delay element 2 via selector 205.
07, and the coefficient corresponding to data "1#" is updated.

- On the other hand, the selector 204 selects the output of the delay element 206 and supplies it to the delay element 206 again, so
The coefficient corresponding to the data @O'' is not updated. Based on the principle explained above, the value of the data signal 200'
Selects the coefficient to be used in the adaptive filter operation corresponding to ``or 1'', updates the coefficient for the coefficient that has been used, and retains the original value for the coefficient that has not been used. By this operation, the coefficients of the adaptive filter can be obtained adaptively. Adaptive+
The pseudo intersymbol interference signal caused by the past data series generated by the 1 filter 25 is sent to the subtracter 2 via the adder 22.
and is subtracted from the received signal subjected to intersymbol interference, which is supplied to input terminal l.

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 input to the adaptive filter 19 at the sampling phase 11 via the polarity determination circuit 16 and the second output terminal of the switch 17. The polarity of the difference signal of the sampling phase t is the third
It is used in the adaptive filter 19 as judgment data for the first half of the symbol waveform shown in the figure. On the other hand, the polarity of the difference signal that is the output of the subtracter 2 is input to the selector 8 via the polarity determining circuit 16 and the switch 17 at the sampling phase t. In addition, zero is also input to the selector 18, and using the demodulated data that is the output of the determiner 3, when the data signal is 10", it is set to zero, and when the data signal is 1",
At this time, K selects and outputs the residual intersymbol interference component appearing at the third output terminal of the switch 17, and supplies it to the adaptive filter 19. The selector 18 distinguishes that at sampling phase i=, the symbol waveform representing data ``'01'' does not have a zero crossing point, but data 11'' always does. The selector 18 determines the polarity of the residual intersymbol interference component when the data of the output signal of the discriminator 3 is @1#, and when the data is '0', the polarity of the residual intersymbol interference component is adaptive.
Since the data is supplied to the filter 19, the coefficients are selectively updated only when the data is 11#. sampling phase t.

Of the displacement from zero in K, the component due to interference in the symbol waveform is removed by feeding the pseudo intersymbol interference signal generated by the adaptive filter 19 to the subtractor 2 via the adder 22, and eliminating the intersymbol interference. 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 polarity of the output signal of the second output contact of the switch 17 in the figure, that is, the difference signal at the sampling phase t1, is the input signal. IK corresponds to an error signal representing the polarity or threat of the residual intersymbol interference component at the output of the detector 18, that is, the sampling phase. 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 resulting from interference within the 7 symbol waveform.

In FIG. 6, the polarity 300 of the difference signal is determined by the multiplier 302.
305. Delay element 30 providing a 1 second delay
4 is a coefficient memory whose output is supplied to a multiplier 305 to generate a pseudo intersymbol interference signal 306. Delay element 30
The output of 4 is also fed back via an adder 303, and the output of a multiplier 302 that multiplies the polarity 300 of the difference signal and the error signal is supplied to the adder 303. When the error signal 301 is zero, the output of the multiplier 302 is zero, so the coefficients do not change, and selective updating of the coefficients 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 fist filter 25 in the adder 22. After that, it is supplied to the subtracter 2.

In FIG. 1, switch 9, memories 10t, 10g,...
..., 10m, the selector 11 and the adder 12 extract only the residual intersymbol interference component, but as is clear from the eye pattern in Figure 3, the adder 12 is replaced with a subtracter and the same A similar effect can be obtained by subtracting sample values having the same polarity and absolute value from the current sample value. At this time, in order to avoid subtracting the current sample value, ie, itself, the selector 11 is configured to write the value supplied from the switch 9 into the memory after incrementing the value 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, and in this multiplier, the mode signal of the demodulated data is @1#. It can also be configured to multiply by -1 when @θ'' and by +1 when @θ''.In other words, memory allocation is done based only on the symbol waveform regardless of the polarity K, and even when the waveforms are equal and have different polarities. The same memory VC is stored.Therefore, the number of memory groups is halved.Using the mode signal obtained by the determiner 3, +1 and -1
controls the new selector supplied with + to the multiplier above.
Supply 1 or -1. 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 nonlinearity of the received signal cannot be obtained.

Furthermore, polarity detection circuits 13 and 16 are removed, and 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 filter 19.25 is LMS
Although it operates on an algorithm, all the effects mentioned so far are valid.

Up to now, one embodiment of the present invention has been described using an MSN code as an example, but a pi-phase code, for example, can be used as the transmission path code. (When using the e-phase code, the received signal is different from the MSK code in that the received signal eye pattern shown in Figure 3 is shifted by T72 seconds. /Glue value is stored in the memory corresponding to the symbol waveform to which this temple value belongs and the sample phase, while the memory value corresponding to the symbol waveform with the same absolute value as the symbol waveform to which the current sample value belongs is saved to the current sample value. The received signal components are canceled by addition or subtraction.However, in the case of a biphase code, the input signal to switch 9 and selector 11 is only a data signal.Also, the symbol waveform one second after the current one is I can't know anything in advance, so
The coefficients are updated after waiting until the symbol waveform one second after the current one is determined. Therefore, in the case of the Pi7 code,
If M=2, then the delay element 8 is 2? A delay of seconds shall be given. In the case of the pi-phase code, the control signal of the selector 15 is further different from that of the MSK code. That is,
t! in Figure 3! The selector 15 selects the output signal depending on whether the received signal takes a value of zero at the sample point of t! Since this is the boundary between the symbol waveforms, it is necessary to use a circuit for switching the selector 15 corresponding to two consecutive symbol waveforms. Considering transmission line codes other than these codes in the same way, the memory 101m1F+... is based on the received signal eye pattern corresponding to FIG.

It is clear that residual intersymbol interference can be extracted accurately if 101Tl is assigned and used to update the coefficients of the adaptive filter 25 after canceling the received signal.

〔Effect of the invention〕

As described in detail above, according to the present invention, the residual intersymbol interference component contained in the received signal can be calculated by taking the difference between the current value and the value JT seconds ago. It is extracted accurately with a probability of a certain positive value that is not zero. Therefore, if the above sum or difference is used to control the 7-adaptive filter by updating the coefficients while selecting the above sum or difference and difference signals corresponding to the sampling phase pressure, adaptive operation is guaranteed from K, It is possible to provide an intersymbol interference removal method and apparatus using decision feedback that is simple and does not require complicated control and has small hardware scale.

Further, according to the present invention, it is possible to match the zero crossing points of the received signal with the sample points and simultaneously eliminate not only intersymbol interference caused by past symbol waveform sequences but also interference within symbol waveforms. It has the advantage that the judgment timing phase can always be optimally maintained regardless of the transmission distance, and is 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 MS
A diagram showing symbol waveforms and state transitions of K code, Figure 3 is M
4 is a diagram showing the eye number pattern corresponding to the SN code. FIG. 4 is a configuration diagram of the adaptive filter 25 in FIG. 1.
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 block diagram showing a conventional example of the decision feedback type equalizer. . 1...Input terminal, 2...Subtractor, 3.
...Judgment device, 4...--Output terminal, 19.2
5...Adaptive filter, 8...
・M extension element, 9, 14.1? ...Switch, 1
01,102~10m...Memory, 11.1
5.18...Selector, 12.22...
- Adder, 13.16...Polarity detection circuit. Agent Patent attorney Susumu Uchihara 2nd previous 3rd concave ro t112 13 Kaya 5 Figure Kaya Otsu skin 3ρI〆” cow

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, and update the coefficients only when the demodulated data series becomes a specific value, and
and the output of a second 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 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 adaptive filter that receives one contact output of a second switch that distributes the output of the subtracter based on the phase of the received signal and a second error signal; and a second selector that selects either one contact output of the second switch or zero based on the demodulated data series, and an output of the arithmetic unit and one contact output of the second switch. a third selector that selects one of the following based on the demodulated data series;
a third switch that selects one of the contact outputs 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; an adder that adds the outputs of two 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 selector is used as the second error signal.
An intersymbol interference removal device using decision feedback, characterized in that feedback is fed back to an adaptive filter.