JPH01233838A - Method and device for eliminating inter-code interference by decision feedback - Google Patents

Abstract

PURPOSE:To eliminate interference in a symbol waveform by receiving an error signal and a demodulated data series by a 1st adaptive filter to revise the coefficient, receiving the polarity of the 1st half of the succeeding symbol waveform predicted by a 2nd adaptive filter, revising the coefficient when the demodulated 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 first half of 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.

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.

(Prior Art) A decision feedback type fixture is known as a known technology for removing intersymbol interference that occurs during waveform transmission (IEEE T
RANSACTIONS ONCOMMUNICAT
IONS; Vol. 32, No. 3, 1984, pp. 258-266).

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 1, 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, and produces a difference signal (=received signal including residual intersymbol interference component, [residual intersymbol interference component ]=[Intersymbol interference component]−
[Pseudo intersymbol interference signal]) is obtained and supplied to the determiner 3 and the subtracter 6. Gain adjuster (AGC) 7 and 7 doubletape filter 5
supply to. The intersymbol interference signal adaptively generated by the adaptive filter 5 is supplied as one input to the subtracter 2 . The output signal of the determiner 3 supplied to the AGC 7 is multiplied by γ and input to the subtracter 61C.

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 inter-bone interference component.
Correct. That is, the closed loop circuit consisting of the subtracter 6 and the AGC 7 operates to extract only the residual sign interference component in the difference signal that is the output of the subtracter 2. This is A.G.
This is achieved by adaptively determining the gain of the output signal of the AGC 7 by correlating the output signal of the subtracter 6 and the output signal of the determiner 3 in C7. The residual intersymbol interference component output from the subtracter 6 is also supplied to the adaptive filter 5 and used for coefficient updating. Subtractor 2゜Judgment device 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.

(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 51. 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 filler 5 will be lost. Therefore, conventionally, the subtractor 6. shown in FIG. AGC7
A method has been used in which the adaptive operation of the adaptive filter 5 is guaranteed by extracting the residual intersymbol interference component. 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 drawback of increasing the size of the software. Further, although the conventional decision feedback type equipment can remove intersymbol 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 intersymbol interference cancellation using decision feedback, which is simple and has a small hardware scale. An object of the present invention is to provide a method and apparatus for intersymbol interference cancellation using decision feedback, which is capable of canceling not only intersymbol interference caused by a sequence of symbols, but also interference within a symbol waveform.

(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 t intersymbol interference to obtain a difference signal, and demodulates the difference signal. The demodulated data sequence obtained by the received signal is used to extract already stored data corresponding to the symbol waveform of the received signal, and is added or subtracted from the difference signal to obtain a residual intersymbol interference signal. Memo I corresponding to the symbol waveform of the signal
An error signal and the demodulated data sequence obtained by storing JK and 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. a second adaptive filter receives the polarity of the first half of the next symbol waveform predicted from the polarity of the difference signal and the demodulated data sequence, and the demodulated data sequence becomes a specific value. The pseudo intersymbol interference signal is generated by updating the coefficients and adding the outputs of the first and second adaptive filters.

The intersymbol interference canceling device using decision feedback according to the present invention includes: a subtracter that obtains a difference between a received signal and a pseudo intersymbol interference signal; a first determiner that receives the output of the subtracter and generates a demodulated data sequence; a first adaptive signal receiving the demodulated data sequence and the first error signal supplied from the first determiner;
a filter, 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, and 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 arithmetic unit that obtains the sum or difference between the output of the delay element and the output of the first selector, and a pre-subtractor. a second switch that distributes output based on the phase of the received signal; a polarity prediction circuit that receives the demodulated data sequence and predicts the polarity of the first half of the next symbol waveform; and a prediction supplied from the polarity prediction circuit. a second adaptive filter that receives the signal and a second error signal; a second selector that selects either one contact output or zero of the second switch based on the demodulated data sequence; The output of the arithmetic unit and the second
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 switch that selects one of the outputs based on the phase of the received signal; and an adder that adds the outputs of the first and second 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 as the second error signal to the second adaptive filter. It is configured to feed back to the filter.

(Function) Unlike the conventional method of multiplying the output of the present invention's determiner by a constant to generate a received signal that does not include residual intersymbol interference components, and subtracting it from the difference signal, the characteristics of the eye pattern of the received signal The system was designed so that residual intersymbol interference components could be extracted accurately. That is, according to the characteristics of the received signal eye pattern of transmission line codes including binary code systems, 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 calculating the sum or difference between the current sample value and the sample value JT seconds ago for the difference signal (=received signal containing the residual intersymbol interference component), only the residual intersymbol interference component can be extracted with a certain positive probability that is not zero. can be extracted. Therefore, if the sum or difference is used as an error signal, the adaptive operation of the adaptive filter is guaranteed. Furthermore, the present invention is configured to be able to eliminate interference within the symbol waveform, which was impossible with conventional methods, by providing a one-tap adaptive filter for eliminating interference within the symbol waveform. ,
Higher tolerance to clock jitter than before,
Performance can be improved.

(Example) Next, the present invention will be described 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.

Figure 2 shows the symbol waveform and shape of an MSK (minimum shift keying) code as an example of a transmission line code. 114 transition is shown. As shown in Figure 2, in the MSK code, 4a
[Prepare symbol waveforms like this. That is, %Ql and %I
For the I data, 2f1 waveforms of %Ol mode and %II mode with inverted polarity are prepared. 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. It has a property that the polarity always inverts at the boundary of this MSN symbol waveform. The transmission path code shown in FIG. 2 is transmitted through the transmission path and is input to the input terminal 1Vc of FIG. 1 after receiving intersymbol interference. 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) gives a delay of 3°MT seconds to the determiner. Delay element 8. The signal is supplied to 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 sent to the output terminal 4, the switch 9, the selectors (SEL) 11, 15, 18, the polarity prediction circuit 24, and the adaptive It is supplied to the filter 25. Additive ψ filter 25. Adder 22. Subtractor 2, delay element 8. Switch 9. Memory 101.10. -・・・・・・1
0o, 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 101. io,...10ffi
, 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 selects the output of the polarity detection circuit 13, the output of the selector 15, or the output of the switch 17.
It is supplied to the filter 25.

Next, the relationship between the output of the adder 12 and the residual intersymbol interference component in the difference signal, which is the output of the 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 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. takes some positive value. Therefore, it is possible to cancel the received signal by storing a sample value every T seconds in a memory corresponding to the symbol waveform to which this sample value belongs, and adding it to the sample value when a waveform of the opposite polarity is received. can.

Next, a note on Figure 1! J 101+, 10□,・
・・・・・・．

The operation of the switch 9 and selector 11 that control the input/output signals of 10ffl will be explained. The switch 9 connects a memory 101.1 (h+...
・Choose from 10m. The eye pattern of the MSK code is a superimposition of four types of waveforms as shown in Figure 3, so m = 4. For example, the eye pattern of the memory 101.10
! , 103.104 are respectively %00#.

It can be considered that this corresponds to the symbol waveform expressed by %01N9%10' and '111. Here, %01' represents a symbol waveform defined by the data signal %Ol and the mode signal %11. The switch 9 uses the data signal and mode signal supplied from the determiner 3 to select the signal supplied from the delay element 8 when these combinations are %QQ#, %01', '10', and %11'. Memory 101.1 respectively
Switch the circuit so that it is stored at 0t+10g, 104. In addition, in FIG. 1, the determiner 3 and the switch 9. Selector 11, 15.18, polarity prediction circuit 24
The path connecting the data signal and the adaptive filter 25 is shown as one line, but when MSK code is adopted, two paths are shown corresponding to the data signal and the mode signal. 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 T seconds by the delay element 8.

That is, M=1 in the MSN 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 per one symbol waveform is R=4, there are sample values at four types of phases per one symbol waveform. For this reason, the memory 101. Lo2.103+ 1
04 each consists of four sub-memories, each sub-memory corresponding to one symbol waveform in one sample phase.

Conversely, since there is only one memory corresponding to one symbol waveform in one sample phase, the sample values corresponding to the same symbol waveform in the same sample phase are updated at normal pressure, and the latest values are stored in the memory. This is R
The same applies to the case of 〆4. The selector 11 stores memories 101, 10, . ,..., 10
Select from ffl. In the case of MSK code, determiner 3
Using the data signal and mode signal supplied from
10 memory each.

The circuit is switched so that the data stored in 10+, 104, and 103 are 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 taken out. 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. This is K.

The difference signal that is the output of the subtracter 2 is also supplied to the polarity determination circuit 16, and becomes an input to the switch 17 after the polarity of the difference signal is detected. Switch 17 has four output contacts, T/R seconds (assuming R is an even number and R=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. The fourth output contact is used, and this operation is repeated every T seconds. The sampling phase of the operation of switch 17 is shown in FIG.
! 1t3 are respectively the first .1t3 of the switch 17 in FIG. Second
゜＠３． This corresponds to the sampling phase of the fourth output contact. The contact output of switch 170@3 is selector 15
is supplied as one of the inputs. Further, as the other input of the selector 15, the output of the polarity detection circuit 13 is supplied. On the other hand, a data signal that is the determination result of the determiner 3 is input as a line control signal to the selector 15,
When the data signal is slz, the third contact output of the switch 17 is selected and output, and when the data signal is %Ol, the output of the polarity detection circuit 13 is selected and output. That is, as is clear from FIG. 3, the data signal #;'
1' has a zero crossing at the center of the symbol, so the third contact output of switch 17 shown in FIG. 1 becomes a residual intersymbol interference component, whereas at t, the data signal is %ON Since K does not have a zero crossing point at the center of the symbol, the output of the polarity detection circuit 13 becomes a residual intersymbol interference component. Therefore, the output of the selector 15 is the residual intersymbol interference component of the sampling phase t2.
input contacts. The switch 14 is a switch having four input contacts, and is synchronous with the switch 17.
The input is sequentially switched from the first input contact to the fourth input contact in the direction of the arrow in FIG. 1 every /R seconds (assuming R=4 here). From the left of the figure, i@ is the first.
Second. Third. This operation is repeated every T seconds using the fourth input contact. 'On'1+'2+13 shown in Figure 3
are activated by the switches 14 and 17 in FIG. 1, respectively. Second. Third. This corresponds to the sampling phase of the fourth input contact. The first input contact of switch 14 has switch 1
7, the output of the polarity detection circuit 13 is supplied to the second and fourth input contacts, and the output of the selector 15 is supplied to the third input contact, as described above. As shown in FIG. 3, no zero crossing point occurs in the sampling phases t1 and t, so the polarity detection circuit 13 of FIG.
Using the residual intersymbol interference component obtained as the output of
The tap coefficients of the adaptive filter 25 are updated. In the sampling phase t2, the residual intersymbol interference components corresponding to the data signals %OI and 111 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 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 description, R=4, but it is clear that R may be any even number.

Next, the 1 adaptive and filter 25 will be explained in detail. Figure 4 shows the adaptive filter 25 in Figure 1.
This figure shows the detailed configuration of .

The data signal 1061, the mode signal 106, and the output signal 107 of the switch 14, which constitute the output signal of the determiner 3 in FIG. 1, are input to this filter.

Mode signal 106 is delay element 100t + multiplier 101o
.

101, 10IR-1 and coefficient generator 102g, 102t-..., 102R
-IK supplied. Further, the data signal 106' is transmitted through a delay element 1001' and a coefficient generator 1020°1021,
...+102R-IKK is supplied. Delay elements 100o, 100z, each giving a delay of T seconds.
song·.

100N/R-1 and 1001', 1002', =,
100N/R-1' is IC in this order! They are connected together, and each can be implemented with a flip-flop. Here, the number of taps NFi is a positive integer, 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 100+(i=1.2
．． ··song.

The outputs of N/R-1) are multipliers]01+, 10, respectively.
11+n- and coefficient generator 102J, 1023+
t,=,1023+u−t. Also, 10
(1' (i=1.2......, N/R-1)
The outputs of coefficient generators 102+ and 1021+ respectively
1. Song.

]0210m-1. However, j = i
It is R.

To the multiplier 101, +n to 101, ・”−, 101
k+s-R (k=0.l.

......,ll'! -1), the coefficient generator 102h102h+i+, ......, +N to IQ2, respectively.
Each coefficient that is the output of -H and the input mode signal (+1 or -
1), all the multiplication results are sent to the adder 103.
It is input to k and added. R adders 1036.1
The outputs of 03t, . . . +, 103R-1 become contact inputs of the switch 104. The switch 104 is a multi-contact switch with a period of T seconds, and R adders 1030
．． 1031. "..., selects and outputs the output of 103n-t in this order every 1cT/R seconds, and transmits the pseudo intersymbol interference signal-1ii) 108 caused by the past transmission data sequence 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, the switch 105 transmits the input signal 107 every T/R seconds.
It performs the function of sequentially distributing to R contacts.

Each contact output of the switch 105 is fed to a coefficient generator present in the signal path input to the corresponding contact of the switch 104 which operates synchronously.

Next, the coefficient generator will be explained in detail. FIG. 5 shows the coefficient generator 102z (fi=0.1...) in FIG.
....

This figure shows the detailed configuration of N-1). The mode signal 200 in FIG. 5 is the mode signal 106 in FIG. 4 or the delay elements 100s, 10(h, . . . + 100R)
It corresponds to the mode signal output from -1. Similarly, data signal 200' in FIG. 5 corresponds to data signal 1 in FIG.
06' or delay element tool', 100g', ++
++e+, corresponds to the data signal output from 100u-t'. In addition, the input signal 201 in FIG.
This corresponds to the contact output of switch 105 in the figure.

Further, output signal 209 in FIG. 5 corresponds to the output of coefficient generator 102□ in FIG. In FIG. 5, a data signal 200' indicating %OI or %11 is supplied as a control signal to each of selectors 204, 205, and 208. Further, a mode signal 200 that takes %Ol or %lj corresponding to the data signal 200' is supplied as one of the inputs of the multiplier 202. On the other hand, as the other manual input of the multiplier 202, the error signal 2 consisting of the residual intersymbol interference component is
In the 0 multiplier 202 to which 01 is supplied, the mode signal 2
00 and the error signal 201, the multiplication result is provided as one input of the adder 203. here,
Delay elements 206 and 207 providing a delay of T seconds are coefficient memories corresponding to %ON and %11K of data signal 200', respectively, and their outputs are both supplied as inputs to selector 208. On the other hand, the data signal 200' is input as a control signal to the selector 208, and the data signal 200' is inputted as a control signal.
When 0' is %OI, the output of delay element 206 is %
Select and output the coefficient corresponding to OI, and generate the data signal 20
When 0' is %ll, the coefficient corresponding to %II, which is the output of the delay element 207, is selected and output, and in either case, the output signal 209 representing the coefficient is obtained. Furthermore, the output signal 209 is fed back to the adder 203, and the multiplier 20
After being added to the output signals of selectors 204 and 20
5 is input. Furthermore, 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, selectors 204, 205 . The operation of 208 will be explained. When data signal 200' is %OI, selector 208 selects delay element 2 corresponding to data signal %QI.
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 the data %QI 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 data %11 is not updated.

Contrary to this case, when the data signal 200' is %ll, the selector 20B selects the output of the delay element 207, which is a coefficient corresponding to the data %II, 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 %11 is updated. On the other hand, since the selector 204 selects the output of the delay element 206 and supplies it again to the delay element 206, 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 calculation according to the value %Ol or antIN of ', the coefficients used are updated, and the coefficients not used are updated By holding the value of
The coefficients of the adaptive filter are obtained adaptively. The pseudo intersymbol interference signal caused by the past data sequence generated by the adaptive filter 25 is supplied to the subtracter 2 via the adder 22, and the received signal subjected to the intersymbol interference supplied from the input terminal 1 is is subtracted from.

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 filter 19 via the polarity prediction circuit 24. 1st
In the figure, there is one line connected to the polarity prediction circuit 24, but in the case of an MSK code, there are two lines connected to the polarity prediction circuit 24 to supply a data signal and a mode signal. 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 waveform boundary, the mode signal of the current received signal waveform can be found by using the mode signal output from the determiner 3, which is the determination result of the received signal waveform T seconds ago. be able to. For example, when the data signal is %QI and the mode signal is %11, and when the data signal strength is Z%1z and the mode signal is %Ql, the polarity of the first half of the next symbol waveform is positive, and this is called %OI. If defined, it matches the mode signal obtained as an exclusive NOR. This is also clear from FIG.

The output signal of the polarity prediction circuit 24 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 output from the subtracter 2 is input to the selector 18JC via the polarity determination circuit 16 and the switch 17 at the sampling phase t2. Further, 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 %Ol, zero is input, and when the data signal is %II, it is input to the third output terminal of the switch 17. The residual intersymbol interference component that appears is selected and output, and is supplied to the adaptive filter 19. The selector 18 distinguishes that at the sampling phase t2, the symbol waveform representing data %O1 does not have a zero crossing point, but data %11 always does. The selector 18 determines that when the data of the output signal of the determiner 3 is slt, K is the polarity of the residual intersymbol interference component and the data is %o.
When K is 1, zero is supplied to the adaptive filter 19, so coefficients are selectively updated only when the data is %II. Of the displacement from zero at sampling phase t2, the component due to interference in the symbol waveform is:
The pseudo intersymbol interference signal generated by the adaptive filter 191C is supplied to the subtracter 2 via the adder 22, and is subtracted from the received signal K by receiving the 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 polarity prediction circuit 24 shown in the figure, that is, the polarity of the difference signal at the sampling phase t1, is input to the input signal 301, that is, the polarity of the difference signal at the sampling phase t2.
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 sent to multiplier 3.
05 to generate a pseudo intersymbol interference signal 306. The output of the delay element 304 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 301 is zero, the multiplier 302
Since the output of is zero, 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.

In FIG. 1, switch 9. Memo! J 101.102.
...10ffl, selector 11. Adder 1
2 extracts only the residual intersymbol interference component, but
1 adder 1 as is clear from the eye pattern in Figure 3.
A similar effect can be obtained by replacing 2 with a subtracter and configuring sample values having the same polarity and the same absolute value to be subtracted from the current sample value. At this time, the current sample value,
That is, in order to avoid subtracting itself, the selector 11 is configured to write the value supplied from the switch 9 into the memory after taking out the value from the memory. When using a subtracter, sample values with the same polarity and the same absolute value are subtracted from the current sample value, so if the amplitude of the positive and negative pulses differs due to the nonlinearity of the received signal, special operations must be performed. The same effect can be expected without any changes.

Further, an absolute value port 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 Sometimes -1, 10' and @t/C
It can also be configured to multiply by +1. 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 -1, 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 nonlinearity of the received signal cannot be obtained.

Furthermore, the unipolarity detection circuits 13, 16 can also be removed. At this time, the adaptive filter 19°25 is LM
Although it operates using the S algorithm, all the effects described so far are valid.

Up to now, an embodiment of the present invention has been described using an MSK code as an example, but a bi-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 is a waveform obtained by shifting the received signal eye pattern shown in Figure 3 by T/2 seconds, but samples are still sampled every R77 seconds.) The value is stored in the memory corresponding to the symbol waveform to which this sample value belongs and the sample phase, while the value in the memory corresponding to the symbol waveform having the same absolute value as the symbol waveform to which the current sample value belongs is added to the current sample value. The received signal components are canceled by subtraction.However, in the case of a biphase code, the input signal to switch 9 and selector 11 is only a data signal.Also, if the symbol waveform T seconds after the current one is Since it is impossible to know, wait until the symbol waveform T seconds after the current time is determined.
Update the coefficients. Therefore, for biphase codes,
Since M=2, the delay element 8 must provide a delay of 2T seconds. In the case of a bi-phase code, the control signal of the selector 15 is further different from that of the MSK code. That is,
The selector 15 selects the output signal depending on whether the received signal takes a value of zero at the sample point t in FIG. It is necessary to use a circuit for switching the selector 15 in accordance with the two symbol waveforms. Considering the transmission line codes other than these codes in the same way, the memory 101.1 (h, . . . ) is stored based on the received signal eye pattern corresponding to FIG.

After allocating Ion and canceling the received signal, adaptive
It is clear that if this is used to update the coefficients of the filter 25, the residual intersymbol interference can be extracted accurately.

(Effects of the Invention) As described in detail above, according to the present invention, the residual intersymbol interference component contained in the received signal is calculated by calculating the sum or difference between the current value and the value JT seconds ago for the difference signal. is extracted accurately with a probability of a certain positive value that is not zero. 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 in accordance with the sampling phase, adaptive operation is guaranteed and complicated filtering is performed. 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.

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 pattern corresponding to the SK code, FIG. 4 is a configuration diagram of the adaptive filter 25 in FIG. 1, and FIG.
This figure is a block diagram of the coefficient generator in FIG. 4, FIG. 6 is a block diagram of the adaptive filter 19 in FIG. 1, and FIG. 7 is a block diagram showing a conventional example of a decision feedback type fixture. ]°°°゛°°Input terminal, 2... Subtractor, 3.
...Judgment device, 4...Output terminal, 19.2
5...Adaptive filter, 8...S...
Delay element, 9.14.17...Switch, 10
1.102-10. ,...Memory, 11,1
5゜18...Selector, 12.22...
・Adder, 13゜16...Polarity detection circuit, 24
...Polarity prediction circuit. Agent: Patent Attorney Susumu Uchihara 2y! J 3rd WJ 5th ffi

Claims (2)

[Claims] (1) Obtain a difference signal by subtracting the pseudo intersymbol interference signal from the received signal that has undergone intersymbol interference, and use the demodulated data sequence to extract the already stored data corresponding to the symbol waveform of the received signal. The residual inter-symbol interference signal is obtained by adding or subtracting it from the difference signal, the difference signal is stored in a memory corresponding to the symbol waveform of the received signal, and the residual inter-symbol interference signal is extracted by a first adaptive filter. and the difference signal is selected based on the sampling phase and the demodulated data series, and the coefficients are updated by receiving the error signal and the demodulated data series, and a second adaptive filter updates the coefficients of the difference signal. The coefficients of the first and second adaptive filters are updated only when the demodulated data series reaches a specific value in response to the polarity of the first half of the next symbol waveform predicted from the polarity of the demodulated data series and the demodulated data series. An intersymbol interference removal method using decision feedback, characterized in that the pseudo intersymbol interference signal is generated by adding outputs. (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; and a second switch that receives the demodulated 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 based on the demodulated data series; and 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; 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, and feeds back the output of the third switch to the first adaptive filter as the first error signal. An intersymbol interference removal device using decision feedback, characterized in that the output of the second selector is fed back to the second adaptive filter as the second error signal.