JPH0435545A - Interference wave eliminating device - Google Patents

Abstract

PURPOSE:To effectively eliminate both of the multipath distortion and an interference wave by extracting an interference component without filtering on the frequency base by subtraction of a desired signal replica from a reception signal and weighting the extracted interference wave so that the error signal of a discrimination feedback equalizer is minimum and subtracting the interference component from the reception signal. CONSTITUTION:A discrimination feedback equalizer 2 eliminates the multipath distortion included in a matched signal outputted from a matching filter 1 to generate a discrimination signal and an error signal of the discrimination result. A convoluter 3 convolutes an inference impulse response to the discrimination signal to obtain an inferred desired signal. A delay element 6 fixedly delays the reception signal, and a subtractor 8 takes the difference between the output signal of this element 6 and the inferred desired signal to extract an interference wave component. A correlator 5 takes correlations of the interference wave component and the error signal to obtain a correlation value, and a multipler 4 multiplies the interference wave component by the correlation value to obtain an ingerred interference wave. Thus, both of the multipath distortion and the interference wave are effectively eliminated.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an interference wave removal device, and in particular, to adaptive equalization of waveform distortion due to fading and removal of interference waves when strong interference waves exist in a multipath fading line. Install an interference wave removal device that performs

(Prior Art) Conventionally, interference caused by an FM line may pose a problem with a digital microwave line using PSK+QAM. Especially when digital transmission is high speed, FM interference waves are considered narrowband interference waves. In addition, adaptive equalization technology is essential for strong multipath fading lines, and in lines with long propagation distances such as non-line-of-sight communication, matched filters (MF) and decision feedback equalizers (DFE) are used. A receiver is required. FIG. 4 shows an example of a conventional interference wave removal device that removes narrowband interference waves in a multipath fading environment.

In FIG. 4, 41 is a transversal filter;
2 is a matched filter (MF), 43 is a decision feedback type equalizer 11
(DFE), and 44 to 51 show the state of the signal spectrum in each part of this conventional interference wave removal device.

A transversal filter is usually used to remove narrowband interference waves. This attempts to remove interference waves by lowering the amplitude characteristics of the transversal filter in the frequency band of the interference waves. Also, i! of the tap coefficient of the transversal filter! JIJ# is performed using the LMS algorithm, Kalman algorithm, or the like so that the root mean square value of the error signal output from the determiner is minimized. However, interference wave removal using a transversal filter is basically filtering in the frequency domain, and if you try to remove the interference wave sufficiently, you will end up removing the same frequency component as the interference wave of the desired signal, which means that the transmission path In addition to the resulting multipath distortion, strong waveform distortion will also be produced.

FIG. 4(a) shows how interference waves are removed from a received signal in which an interference wave is superimposed on a desired signal.The received signal input to the transversal filter 41 has an interference wave J on the desired signal S as shown in 44. overlapping. In order to remove the interference wave J, the transversal filter 41 causes a deep dip in the frequency band of the interference wave in the frequency characteristic of the filter.

Therefore, at the output of the transversal filter 41, interference waves are removed as shown in 45, but the frequency characteristics of the desired signal component are reduced. The occurrence of a notch on the frequency axis as in the signal spectrum 45 is equivalent to the impulse response being dispersed like a two-wave model. That is, this state is approximated to a multipath state.

The matched filter 42 attempts to symmetrize the dispersed impulse response and synthesize the delayed and dispersed echo components into the main wave in phase. Therefore, the ratio of the echo wave to the main wave decreases, and 4
When a signal having a notch like 5 passes through a matched filter 42, the notch becomes shallower like 46. The output of the matched filter 42 is input to a decision feedback equalizer 43 to remove multipath distortion, and the desired signal wave S is generated as shown in 47.
As shown in FIG. 4(a), the interference waves included in the received signal are sufficiently removed and the desired signal is accurately equalized, as shown in FIG. 4(a).

FIG. 4(b) shows how interference waves are removed from a received signal in which interference waves are superimposed on a desired signal with multipath distortion.

In FIG. 4(b), the received signal input to the transversal filter 41 is a signal in which multipath distortion has already occurred on the desired signal S in the transmission path, and the interference wave J is superimposed on the desired signal S. In order to remove the interference wave J, the transpersal filter 41 creates a notch in the frequency band of the interference wave in the frequency characteristic of the filter. by the way,
If the notch frequency due to multipath already generated in the propagation path and the frequency of the interference wave are different, the signal input to the matched filter 42 will have a plurality of notches in the signal band. In other words, the frequency interval between the notches becomes shorter.

Generally, a short notch interval corresponds to the presence of echo waves with a large delay time difference in the impulse response. In order to remove distortion from the desired signal in this state, it is necessary to increase the number of taps of the matched filter 42 and the decision feedback equalizer 43. However, the number of these taps is set to a value corresponding to the delay dispersion occurring in the propagation path, and is usually the minimum number of taps necessary. Therefore, as shown in 49, the occurrence of new distortion in the transversal filter 41 in addition to the distortion occurring in the propagation path increases the burden on the matched filter 42. In particular, the distribution area of the impulse response exceeds the number of tags of the matched filter 42. The output of the matched filter 42, 50, is input to the decision equalizer 43, but the impulse response may not be made symmetrical, but may even widen its distribution, and the desired effect cannot be obtained. The impulse response exceeds the equalization ability, and is not sufficiently equalized, leaving distortion as shown in 51.

Further, if the number of interference waves is two or more, filtering on the frequency axis becomes complicated, and it is necessary to considerably increase the number of taps of the transversal filter. If there are a plurality of frequency locations where interference waves should be removed, the desired signal spectrum will be significantly reduced, and the desired signal will not be accurately equalized, which will have a significant negative effect.

(Problem to be Solved by the Invention) In the conventional interference wave canceling device described above, in addition to the distortion due to multipath fading, distortion accompanying the process of removing interference waves is added to the received signal, so the burden on adaptive equalization is increased. There is a drawback that waveform distortion is not sufficiently removed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an interference wave removal device that can effectively remove both multipath distortion and interference waves.

(Means for solving JAM) A first interference wave removal device according to the present invention includes a first subtracter that generates a signal of a difference between a received signal consisting of a desired signal and an interference wave and an estimated interference wave; An estimated impulse response is obtained by estimating the impulse response of the transmission system from the difference signal and the determination signal output from the first subtracter, and a time-reversed complex conjugate response of the estimated impulse response and the previous difference signal are a matched filter that obtains a matched signal convoluted with the matched signal; and a decision feedback equalizer that removes multipath distortion included in the matched signal output from the matched filter and obtains the decision signal and an error signal of the decision result. a convolver that obtains an estimated desired signal by convolving the estimated impulse response and the determination signal; a delay element that provides a certain delay to the received signal; and an output signal of the delay element and the estimated desired signal. a second subtractor that extracts an interference wave component by taking the difference between the two; a correlator that calculates a correlation between the interference wave component and the error signal to obtain a correlation value; and a multiplier for obtaining the estimated interference wave.

Further, a second interference wave removal device according to the present invention includes a first subtracter that generates a difference signal between a received signal consisting of a desired signal and an interference wave and an estimated interference wave, and an output from the first subtracter. An estimated impulse response is obtained by estimating the impulse response of the transmission system from the difference signal and a reference signal, and a matching signal is obtained by convolving the difference signal with a time-reversed complex conjugate response of the estimated impulse response. a matched filter, and a decision feedback method that performs decision feedback equalization on the matched signal using the reference signal to remove multipath distortion included in the matched signal to obtain a decision signal and an error signal of the decision result. a training signal generator that generates a training signal representing an assumed transmission symbol sequence, and selects either the determination signal or the training signal according to the error signal and outputs it as the reference signal. an interpolator that obtains an estimated desired signal by convolving the estimated impulse response and the reference signal, a delay element that provides a certain delay to the received signal, and an output signal of the delay element and the estimated desired signal. a second subtractor that extracts an interference wave component by taking the difference from the desired signal; a correlator that calculates the correlation between the interference wave component and the error signal to obtain a correlation value; and a multiplier that obtains the estimated interference wave by multiplying a value.

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

FIG. 1 is a block diagram showing the configuration of an embodiment of a first interference wave removal device according to the present invention. FIG. 2 is a block diagram showing an embodiment of the second interference wave removal device according to the present invention.

In FIG. 1, 1 is a matched filter (MP), 2 is a decision feedback equalizer (DFE), 3 is a convolver, 4 is a multiplier,
5 is a correlator, 6 is a delay element having a delay time of τ, and 7 and 8 are subtracters.

In FIG. 2, 21 is a matched filter (MF), 22 is a decision feedback equalizer (DFE), and 22a is a forward equalizer!
(FE), 22b is a backward equalizer (BE), 22e is a determiner, 22d and 22e are subtracters, 23 is a convolution
4 is a multiplier, 25 is a correlator, 26 is a delay element having a delay time of τ, 27 and 28 are subtracters, 29 is a switch, 30 is a training signal generator, and 31 is a controller.

In the embodiment of FIG. 1, 1, the transmission symbol sequence is a m
(n ''-ω...+■), and the discrete value of the impulse response of the transmission system until it is input to the MFI is R, then the discrete value r of the received signal 102 is r, = S + J = Σa *
h k−m + , J =·(1). Here, J indicates an interference wave having a band narrower than the frequency band of the desired signal S.

The MFI takes the correlation between the determination signal aa 106 and the received signal 102 shown by equation (1), and the zero-order equation for estimating the impulse response of the transmission system shows the correlation process.

=h,
... (2> The MFI performs an operation of time-reversing the estimated impulse response to incorporate the complex conjugate response 1° and the received signal 102.

On the other hand, the convolver 3 convolves the estimated impulse response of the MF1, 103, with the determination signal a, 106 output from the DFE2. That is, when the determination signal amlO6 is equal to the transmission symbol sequence a, the convolver 3 estimates the signal S desired to be received. Due to the processing time required to create this estimated desired signal replica (reproduced waveform), the desired signal replica is delayed by τ from the desired signal component at the input terminal 11. Therefore, the input signal 101 is delayed and adjusted by the delay element 6, and the desired signal replica of the output of the interpolator 3 is subtracted from the output signal of the delay element 6 by the subtracter 8. Therefore,
The subtracter 8 outputs an interference wave delayed by τ, ■. Here, compared to the desired signal spectrum, we are targeting a narrowband interference wave such as an FM wave, so if the center frequency of the interference wave is ω, the delay of τ is the phase shift of exp (-Jωτ), which is the interference wave, J It can be approximated by giving That is, subtractor 8
The output of is J-exp(jωτ).

The output of this subtracter 8 is the correlation value W1 which is the output of the correlator 5.
07 is multiplied by the multiplier 4 and supplied to the subtracter 7.

If the output of this multiplier 4 is set as J=W−J−exp(Jωτ) (3), the output of the subtracter 7 becomes (S+J−J), DFE2
The determiner inside has MFI and DFE at the output of subtractor 7.
The error signal ε output from the determiner in the DFE 2, which receives the signal multiplied by the transfer function H of the DFE 2, includes an error component due to the interference wave J. In particular, when code amount interference (ISI) due to multipath fading exists at the same time, the determiner error signal ε includes both an error component due to ISI and an error component due to interference wave J.
The error signal ε is used to control D. However, since the interference wave component in the error signal ε is independent of the component due to ISI, D
It does not affect the modification of the tap coefficient of FE2, that is, the ISI is MFI and DFE2.
If removed by the B receiver, the error signal ε is approximated as follows.

ε=H・(J-J)...(4
) The evaluation interval number ξ, which is the root mean square value of this error signal ε, is displayed as an average value as ξ=E[ε・ε11] when the speed of fading and fluctuation of the interference wave J is slower than the desired signal speed. E can be omitted.

ξ is a function of the tap coefficient W of the multiplier 4, and the W at which ξ is the minimum is given by + + “-・]1 day = 0 (5), and using equation (3), W0?t=exp (Jωr) = (6)
becomes.

By the way, in order to adaptively follow this ideal value of W, a gradient method is used for the evaluation function ξ. The slope of the ξ plane at a certain value of W is shown as follows, omitting the average value E.

=-ε-J"exp(Jωr)H"...-(7
>That is, if the tap coefficient W is corrected using the following equation, it will converge to the ideal value of equation (6).

Ws=W''-'-p, -t - (Jexp (Jωτ))° ...(8) Here, μ
is the correction coefficient.

The tap correction operation described above is performed by the correlator 5 in FIG. The correlator 5 receives the signal Jexp from the subtractor 8.
By taking the average of the products of the complex conjugate of (-j(11)τ> and the error signal ε105 from the DFE2, the tap correction shown in equation (8) is realized.

Through the above operations, the output of the multiplier 4 receives the input signal 10
An estimated value of the interference wave J in 1 is obtained. This estimated interference wave J
The interference wave J can be removed by subtracting from the input signal S+J101 using the subtracter 7.

Even if the interference waves fluctuate in subsequent operations, the interference waves are adaptively removed. On the other hand, waveform distortion due to multipath fading is removed by the MP/DFE receiver independently of interference removal.

Next, the above operation will be explained using the vector diagram and spectrum shown in FIG. The spectrum column of FIG. 3(a) shows a case where a narrowband interference wave J exists in the spectrum of the desired signal that has undergone multipath distortion in the propagation path. In addition, the vector function is shown in the vector diagram column.
The output of the convolver 3 creates a replica of the desired signal S, but since this replica is delayed by τ from the desired signal S at the input terminal 11, it is out of phase with the S vector in FIG. 3(a). It is shown as S vector in b). (a
) is delayed by τ and the desired signal replica of (b) is subtracted from that shown in (C). In other words, the output of the subtractor 8 estimates the interference wave J. This is multiplied by the tap coefficient W, which is the output of the correlator 5, and becomes the output of the multiplier 4 in (d). This (d) estimated interference wave,
By subtracting J from the input in (a), only the desired signal component subjected to multipath distortion can be extracted as shown in (e), and the MF/DFE receiver performs adaptive equalization as shown in (f). be done.

In the above operation, no distortion other than multipath distortion is imparted to the desired signal S due to interference wave removal.

In this way, in this embodiment, interference waves are removed without performing frequency domain filtering, so even if a plurality of interference waves exist, they can be removed.

By the way, when starting up the MF/D FE receiver, if there is already an interference wave strong enough to make the D/U ratio negative, the MF/D FE receiver will not be able to output the correct judgment signal6. If the decision signal is wrong, the MP cannot make a correct impulse response estimation, and therefore the desired signal replica is no longer correct. In this case, if you leave it as it is, you will be unable to stand up forever.

Therefore, the embodiment shown in FIG. 2 solves this initial pull-in problem.

In Figure 2, 21, 22, 23, 24, 25, 26
．． 27 and 28 are 1°2.3, 4, respectively in Figure 1.
5, 6.7, and 8, these components in FIG. 2 perform the same operations as the components in FIG.
Until the transmission symbol sequence a is removed, the training signal generator 30 outputs the same training signal as the transmission symbol sequence a, and this training signal is selected by the control signal 202 in the switch 29, and the convolver 23, MP21, and DF
E22. In this case, the MF 21 estimates the impulse response of the transmission system by correlating the training sequence a with the received signal 102 expressed by equation (1). At this time, since the correlation value between the interference wave J and the determination signal a, 106 becomes zero, the estimated impulse response becomes a correct value even if the interference wave J has not been removed yet. Further, the convolution unit 23 has a training sequence a,
Since the output is the correct desired signal replica. If the desired signal replica is a correct value, the subtracter 28
The interference wave component Jexp(Jωτ) is extracted.

On the other hand, the training signal is transmitted to the subtracter 22e in the DFE 22.
Therefore, the determiner error signal ε105 that correctly includes the interference wave component can be obtained. Furthermore, if an incorrect determination signal is used in the backward equalizer (BE) 22b in the DFE 22, an incorrect signal is fed back to the subtracter 22d, thereby disturbing the error signal ε105. Therefore, in this embodiment, the output signal of the switch 29 is also supplied to the BE 22b.

In this way, by using the training signal at the time of initial pull-in, the correlation value of the correlator 25 is controlled so that the error signal ε105 is minimized. That is, a correct estimated value of the interference wave J is obtained as the output of the multiplier 24, and the interference wave can be removed by the subtracter 27.

As the interference wave is removed, the determiner error signal ε105 becomes smaller, and the controller 31 outputs the determiner error signal ε10.
5 is input, and its root mean square value ξ is monitored, and when this becomes less than a preset threshold value, it is determined that the interference wave has been correctly removed, and the switch 29 is controlled, and the DFE 22 The determination signal 106 is selectively output. Thereafter, the convolver 23, MF 21, and DFE 22 are supplied with the decision signal 106 and continue the same interference wave removal operation as described in the embodiment of FIG. Note that there are two methods for inserting a training signal on the transmitting side; one is a method of periodically inserting the training signal into the transmitting signal sequence in a burst form, and the other is a method of inserting or canceling the training signal according to a signal from the receiving side.

The embodiment shown in FIG. 2 described above makes it possible to eliminate narrow band interference waves that solve the initial pull-in problem.

(Effects of the Invention) As explained above, the present invention extracts the interference component by subtracting the desired signal replica from the received signal without performing filtering on the frequency axis, and Since the interference waves are removed by weighting the extracted interference waves to minimize the error signal and subtracting the interference component from the received signal, the interference wave removal does not affect the desired signal that has undergone multipath distortion. Even if multiple interference waves exist, both multipath distortion and interference waves can be effectively removed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a first interference wave canceling device according to the present invention, and FIG. 2 is a block diagram showing the configuration of an embodiment of the second interference wave canceling device according to the present invention. 3 are diagrams explaining the operation of the embodiment of FIGS. 1 and 2, and FIG. 4 is a diagram showing a conventional interference wave removal device and its interference wave removal. 1.21...Matched filter (MP), 2.22...
Decision feedback equalizer (DFE), 3.23... Convolver, 4, 24... Multiplier, 5, 25... Correlator, 62
6...Delay element having a delay time of τ, 7.8°27
．． 28...Subtractor, 11...Input terminal, 12...
Output terminal, 22a...Forward equalizer (FB), 22b...
... Backward equalizer (BE), 22c... Determiner, 22d
. 22e...Subtractor, 29...Switcher, 30...
Training signal generator, 31...controller.

Claims (2)

[Claims] (1) Transmission from a first subtracter that generates a difference signal between a received signal consisting of a desired signal and an interference wave and an estimated interference wave, and the difference signal and determination signal output from the first subtractor. A matched filter that estimates an impulse response of a system to obtain an estimated impulse response and also obtains a matched signal that is time-reversed and convolved with a complex conjugate response of the estimated impulse response and an earlier difference signal; and a matched filter that is output from the matched filter. a decision feedback equalizer for removing multipath distortion included in the matching signal to obtain the decision signal and an error signal of the decision result; and convolving the estimated impulse response and the decision signal to generate an estimated desired signal. a delay element that gives a certain delay to the received signal; a second subtractor that extracts an interference wave component by taking the difference between the output signal of the delay element and the estimated desired signal; An interference wave comprising: a correlator that correlates the interference wave component with the error signal to obtain a correlation value; and a multiplier that multiplies the interference wave component by the correlation value to obtain the estimated interference wave. removal device. (2) A first subtracter that generates a difference signal between a received signal consisting of a desired signal and an interference wave and an estimated interference wave, and transmission from the difference signal and a reference signal output from the first subtractor. a matched filter that estimates the impulse response of the system to obtain an estimated impulse response and also obtains a matched signal that is a time-reversed complex conjugate response of the estimated impulse response and the difference signal; A decision feedback equalizer that performs decision feedback equalization on a matching signal to remove multipath distortion included in the matching signal to obtain a decision signal and an error signal of the decision result; a training signal generator that generates a training signal representing the reference signal; a switch that selects either the determination signal or the training signal according to the error signal and outputs it as the reference signal; and the estimated impulse response and the reference signal. a convolver that obtains an estimated desired signal by convolving the received signal, a delay element that provides a certain delay to the received signal, and an interference wave component that takes the difference between the output signal of the delay element and the estimated desired signal. a second subtractor for extracting; a correlator for correlating the interference wave component with the error signal to obtain a correlation value; and a multiplier for multiplying the interference wave component by the correlation value to obtain the estimated interference wave. An interference wave removal device comprising: