JP2569902B2 - Interference wave canceller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference wave canceller, and more particularly to adaptive equalization of waveform distortion due to fading and interference wave interference when a strong interference wave exists in a multipath fading channel. The present invention relates to an interference wave removing device that removes interference waves.

(Prior Art) Conventionally, interference by an FM line to a digital microwave line using PSK or QAM may be a problem. Especially when digital transmission is performed at high speed, FM interference waves are regarded as narrowband interference waves. In addition, adaptive equalization technology is indispensable in a strong multipath fading line, and a matched filter (MF) is required in a line with a large propagation distance such as non-line-of-sight communication.
And a receiver using a decision feedback equalizer (DFE). FIG. 4 shows an example of a conventional interference wave eliminator for removing a narrow-band interference wave in a multipath fading environment.

In FIG. 4, 41 is a transversal filter, 42
Is a matched filter (MF), 43 is a decision feedback equalizer (DFE)
Numerals 44 to 51 denote signal spectrums in respective parts of the conventional interference wave removing apparatus.

A transversal filter is usually used to remove the narrow band interference wave. This is to remove the interference wave by lowering the amplitude characteristic of the transversal filter at the frequency of the interference wave. Control of the tap coefficients of the transversal filter is performed by an LMS algorithm, a Kalman algorithm, or the like such that the root mean square value of the error signal output from the determiner is minimized. However, the removal of the interference wave by the transversal filter 41 is basically filtering in the frequency domain, and if it is attempted to sufficiently remove the interference wave, the same frequency component as the interference wave of the desired signal will be removed. In addition to the generated multipath distortion, a strong waveform distortion is generated.

FIG. 4 (a) shows how interference waves are removed from a received signal in which an interference wave overlaps a desired signal. In the received signal input to the transversal filter 41, the interference signal J overlaps the desired signal S as shown at 44. The transversal filter 41 produces a deep dip in the frequency band of the interference wave having the frequency characteristic of the filter in order to remove the interference wave J. Therefore, at the output of the transversal filter 41, the interference wave is removed as indicated by 45, but the frequency characteristic of the desired signal component is reduced. The occurrence of a notch on the frequency axis as in the signal spectrum 45 is equivalent to the impulse response being dispersed as in a two-wave model.
That is, this state is approximated to a multipath state. The matched filter 42 attempts to symmetrically disperse the dispersed impulse response and synthesize the delay-dispersed echo component into the main wave in phase.
Therefore, the ratio of the echo wave to the main wave decreases, and the notch signal such as 45 passes through the matched filter 42 so that the notch becomes shallow as 46. Matched filter 42
Is input to the decision feedback equalizer 43 to remove multipath distortion, and the desired signal wave S is output as indicated at 47. As described above, in FIG. 4A, the interference wave included in the received signal is sufficiently removed, and the desired signal is accurately equalized.

FIG. 4B shows how interference waves are removed from a received signal in which an interference wave overlaps a desired signal in which multipath distortion has occurred.

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 on the transmission line, and the desired signal S is overlapped with the interference wave J. In order to remove the interference wave J, the transversal filter 41 generates a notch in the frequency band of the interference wave having the frequency characteristic of the filter. If the notch frequency due to the multipath already generated in the propagation path and the frequency of the interference wave are different, the signal input to the matched filter 42 has a plurality of notches in the signal band. That is, the frequency interval at which the notch is formed becomes shorter. Generally, a short notch interval corresponds to the presence of an echo wave having a large delay time difference in an impulse response. 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 taps is set to a value corresponding to the delay dispersion generated in the propagation path, and is usually set to the minimum necessary number of taps. Therefore, the occurrence of new distortion in the transversal filter 41 other than the distortion generated in the propagation path as shown in 49 increases the load on the matched filter 42. In particular, if the distribution region of the impulse response exceeds the number of taps of the matched filter 42, not only the impulse response cannot be made symmetrical, but also the distribution may be broadened, and a desired effect cannot be obtained. The output 50 of the matched filter 42 is input to the decision feedback equalizer 43, but the state of the impulse response exceeds the equalization ability, and the equalization is not sufficiently performed, and distortion is left as shown at 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 from which the interference wave is to be removed, the desired signal spectrum is greatly reduced, the desired signal is not accurately equalized, and the adverse effect is large.

(Problems to be Solved by the Invention) In the above-described conventional interference wave elimination apparatus, since the received signal is subjected to distortion accompanying the processing of eliminating the interference wave in addition to the distortion due to multipath fading, the burden on adaptive equalization increases. However, there is a disadvantage that the waveform distortion is not sufficiently removed.

Therefore, an object of the present invention is to provide an interference wave removing device capable of effectively removing both multipath distortion and interference waves.

(Means for Solving the Problems) A first interference wave removing apparatus according to the present invention comprises: a first subtractor for generating a signal representing a difference between a reception signal composed of a desired signal and an interference wave and an estimated interference wave; Estimating an impulse response of a transmission system from the difference signal and the determination signal output from the first subtractor to obtain an estimated impulse response, and obtaining a time-inverted complex conjugate response of the estimated impulse response and the difference signal. A matched filter that obtains a matched signal obtained by convoluting the above, a decision feedback equalizer that generates the decision signal by removing multipath distortion included in the matched signal output from the matched filter, and the estimated impulse response A convolution unit for convolving the received signal with the decision signal, a delay element for providing a predetermined delay to the received signal, and a interference between the output signal of the delay element and the desired signal for estimation. Wave component A second subtractor that outputs the signal, a power detector that detects the power of the difference signal input to the matched filter, and controls the phase of the interference wave component such that the power detected by the power detector is minimized. And an estimated interference wave generator for generating the estimated interference wave.

Further, a second interference wave removing apparatus according to the present invention comprises: a first subtractor for generating a signal representing a difference between a reception signal composed of a desired signal and an interference wave and an estimated interference wave; and an output from the first subtractor. The impulse response of a transmission system is estimated from the difference signal and the reference signal to obtain an estimated impulse response, and a matched signal obtained by convolving the complex conjugate response with the difference signal by time inversion of the estimated impulse response is obtained. A matched filter, a decision feedback equalizer that removes multipath distortion included in the matched signal output from the matched filter to obtain a decision signal and a decision result error signal, and a transmission symbol sequence assumed A training signal generator that generates a training signal, a switching unit that selects one of the determination signal and the training signal according to the error signal and outputs the selected signal as the reference signal, A convolution unit that convolves the estimated impulse response with the reference signal to obtain an estimated desired signal, and a delay element that applies a fixed delay to the received signal.
A second subtractor that extracts an interference wave component by taking a difference between the output signal of the delay element and the estimation desired signal; a power detector that detects power of the difference signal input to the matched filter; An estimated interference wave generator that controls the phase of the interference wave component so as to minimize the power detected by the power detector and generates the estimated interference wave.

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

FIG. 1 is a lock diagram showing the configuration of one embodiment of a first interference wave removing apparatus according to the present invention. FIG. 2 is a block diagram showing the configuration of an embodiment of the second interference wave removing apparatus according to the present invention.

In FIG. 1, 1 is a matched filter (MF), 2 is a decision feedback equalizer (DFE), 3 is a convolution unit, 4 is a multiplier, 5
Is a phase controller, 6 is a delay element having a delay time of τ, 7
And 8 are subtractors, and 9 is a power detector.

In FIG. 2, 21 is a matched filter (MF), 22 is a decision feedback equalizer (DFE), 23 is a convolution unit, 24 is a multiplier, 25
Is a phase controller, 26 is a delay element having a delay time of τ, 27
And 28 are subtractors, 29 is a power detector, 30 is a switch, 31
Is a training signal generator, and 32 is a controller.

In the embodiment shown in FIG. 1, the transmission symbol sequence is represented by a _n (n =
-∞ ... + ∞), when the discrete value h _n of the impulse response of the transmission system to be input to the FM1, the received signal 102 discrete values r
_n is Indicated by Here, J indicates an interference wave in a band narrower than the frequency of the desired signal S.

MF1 is the judgment signal a _n 105 and the reception signal 10 shown in the equation (1).
By taking a correlation with 2, the impulse response of the transmission system is estimated. The following equation shows the correlation process.

The MF 1 performs an operation of convolving the received signal 102 with the complex conjugate response h _−n ^{* by} reversing the estimated impulse response.

On the other hand, the convolution unit 3 calculates the impulse response h estimated by MF1.
convolving the decision signal _n 105 at the output of _n 103 and DFE2. That is, when the determination signal _n 105 is equal to the transmission symbol sequence a _n is
That is, the convolution unit 3 estimates the desired reception signal S. The desired signal replica is delayed by τ due to the desired signal component at the input terminal 11 due to the processing time required to generate the desired signal replica (reproduced waveform) to be estimated. Therefore, the delay of the input signal 101 is adjusted by the delay element 6 and the subtractor 8
Then, the desired signal replica of the output of the convolution unit 3 is subtracted from the output signal of the delay element 6. Therefore, the subtractor 8 outputs the interference wave J delayed by τ. Here, as compared with the desired signal spectrum, a narrow-band interference wave such as an FM wave is targeted. Therefore, when the center frequency of the interference wave is ω, the delay of τ is ex.
It can be approximated by giving a phase shift of p (−jωτ) to the interference wave J. That is, the output of the subtracter 8 is J · exp (−jωτ)
It has become.

The output of the subtracter 8 is multiplied by the phase control coefficient W, which is the output of the phase controller 5, by the multiplier 4 and supplied to the subtractor 7. Assuming that the output of the multiplier 4 is = W · Jexp (−jωτ) (3), the output of the subtractor 7 is (S + J−). The output signal of the subtractor 7 is the received signal 102 input to the MF1, and the power detector 9 detects the power P of the received signal 102. The power P is shown as follows.

P = (S + J−) · (S + J −) ^* = SS ^* + (JJ ^* −J ^* −J ^* + ^* ) + Δ (4) where Δ is a component of the product of S and J, and the interference wave It becomes zero if J is removed by.

P is a function of the tap coefficient W of the multiplier 4, and W at which P is the minimum is W ^opt = exp (jωτ) (6) using equation (3).

The tap coefficient W in the equation (6) is output by the multiplier 4 to the output J of the subtractor 8.
By multiplying exp (−jωτ), the interference wave J in the input signal 101 can be estimated. The estimated interference wave J, which is the output of the multiplier 4, is input to the subtractor 7 by the input signal 101.
The interference wave J can be removed by subtracting from S + J. Therefore, the phase controller 5 supplies the phase control coefficient W, which is the tap coefficient, to the multiplier 4 and performs feedback control so that P is minimized. The interference wave J is removed by the above operation. At this time, the power of the equation (4) indicates the minimum value, and only the desired wave component of SS ^* is obtained.

Even if the interference wave fluctuates in the subsequent operation, the interference wave is adaptively removed. On the other hand, waveform distortion due to multipath fading is removed by an MF / DFE receiver composed of MF1 and DFE2 independently of interference removal.

Next, the above operation will be described with reference to a vector diagram and a spectrum shown in FIG. The case where the narrow-band interference wave J exists in the desired signal spectrum that has undergone multipath distortion in the propagation path is shown in the spectrum column of FIG. The vector relationship is shown in the column of the vector diagram. Notches occur in the spectrum of the desired signal S due to multipath distortion.
The output of the convolution unit 3 makes a replica of the desired signal S. Since this replica is delayed by τ from the desired signal S at the input terminal 11, the replica is shifted in phase from the S vector in FIG. b) as shown in the S vector. (A)
(C) shows the result obtained by subtracting the desired signal replica of (b) from the signal obtained by delaying the signal by τ. That is, the interference wave J component is extracted from the output of the subtracter 8. The output of the multiplier 4 shown in (d) is obtained by controlling the phase of the interference wave component so that the power of the received signal 102 input to the MF 1 is minimized. By subtracting the estimated interference wave J of (d) from the input of (a), it is possible to extract only the desired signal component that has undergone multipath distortion as shown in (e), and the MF / DFE receiver , (F) are adaptively equalized.

In the above operation, distortion due to interference wave elimination other than multipath distortion is not given to the desired signal S. As described above, in the present embodiment, the interference wave is removed without performing the filtering in the frequency domain, so that even if there are a plurality of interference waves, the interference wave can be removed.

By the way, when starting up the MF / DFE receiver, the MF / DEF receiver cannot output a correct determination signal if there is already a strong interference wave such that the D / U ratio becomes negative. If the determination signal is incorrect, the MF cannot perform a correct impulse response estimation. Thus, the desired signal replica is no longer correct. In this case, if it is left as it is, it will not be possible to stand up forever.

The embodiment shown in FIG. 2 solves this initial pull-in.

In FIG. 2, 21, 22, 23, 24, 25, 26, 27, 28 and 29
Correspond to 1, 2, 3, 4, 5, 6, 7, 8 and 9 in FIG. 1, respectively, and these components in FIG. 2 perform the same operations as the components in FIG. Until interference J is removed, to output the same training signal and the transmission symbol sequence a _n a training signal generator 31 selects the control signal 202 in the switching unit 30 the training signal, convolver 23
And MF21. In this case, MF21 estimates the impulse response of the transmission system by taking the correlation between the received signal 102 shown in training sequence a _n and (1). At this time, since the correlation value between the interference wave J and the determination signal _n 105 becomes zero, the estimated impulse response has a correct value even if the interference wave J has not been removed yet. Further, since the convolver 23 using training sequence a _n, the output is correct desired signal replica. If the desired signal replica has the correct value,
An estimated value of the interference wave J is obtained at the output of the multiplier 24.
Can be removed. The interference wave J is removed, the MF / DFE receiver removes the multipath distortion of the line, and the desired signal S can be correctly determined. In this case, the error signal ε201 of the determiner included in DEF22 becomes smaller. The controller 32 receives the error signal ε201 of the determiner as an input and monitors the root-mean-square value 、. The control unit 30 is controlled to select the determination signal _n 105 from the DFE 22 and make it mainstream. Thereafter, the convolution unit 23 and the MF 21 are supplied with the decision signal _n 105 and continue the same interference canceling operation as described in the embodiment of FIG. There are two methods for inserting a training signal on the transmitting side. One is a method of periodically inserting a burst in a transmission signal sequence, and the other is a method of inserting or releasing the signal by a signal from the receiving side.

According to the embodiment shown in FIG. 2, it is possible to remove the narrow band interference wave in which the initial pull-in is solved.

(Effects of the Invention) As described above, the present invention extracts an interference component by subtracting a desired signal replica from a received signal without performing filtering on the frequency axis, and after performing phase control on the interference component, Since the interference wave is removed by subtracting from the received signal, the multipath distortion and the interference wave can be eliminated even if there are multiple interference waves without affecting the desired signal that has undergone multipath distortion. There is an effect that both can be effectively removed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a first interference wave canceling apparatus according to the present invention, and FIG. 2 is a block diagram showing a configuration of an embodiment of a second interference wave removing apparatus according to the present invention. FIG. 3 is a diagram for explaining the operation of the embodiment shown in FIGS. 1 and 2, and FIG. 4 is a diagram showing a conventional interference wave elimination apparatus and interference wave elimination. 1,21 Matched filter (MF), 2,22 Decision feedback equalizer (DFE), 3,23 Convolution, 4,24 Multiplier, 5,25
...... Phase controller, delay element having a delay time of 6,26 τ
…… Input terminal, 12 …… Output terminal, 30… Switcher, 31…
... training signal generator, 32 ... controller.

Claims (2)

(57) [Claims] 1. A first subtractor for generating a difference signal between a received signal composed of a desired signal and an interference wave and an estimated interference wave, and the difference signal and the determination signal output from the first subtractor. A matched filter that obtains an estimated impulse response by estimating the impulse response of the transmission system from, and obtains a matched signal obtained by convolving the complex conjugate response and the difference signal by time reversal of the estimated impulse response, and an output from the matched filter. A decision feedback equalizer that removes multipath distortion included in the matched signal to generate the decision signal, and a convolution unit that convolves the estimated impulse response and the decision signal to obtain an estimated desired signal. A delay element for giving a predetermined delay to the received signal, a second subtractor for extracting an interference wave component by taking a difference between an output signal of the delay element and the desired signal for estimation, and an input to the matched filter. Said A power detector for detecting the power of the signal; and an estimated interference wave generator for controlling the phase of the interference wave component so as to minimize the power detected by the power detector and generating the estimated interference wave. An interference wave removing device characterized by the above-mentioned. 2. A first subtractor for generating a difference signal between a received signal comprising a desired signal and an interference wave and an estimated interference wave, and the difference signal and the reference signal output from the first subtractor. A matched filter that obtains an estimated impulse response by estimating the impulse response of the transmission system from, and obtains a matched signal obtained by convolving the complex conjugate response and the difference signal by time reversal of the estimated impulse response, and an output from the matched filter. A decision feedback equalizer for removing a multipath distortion included in the matched signal to obtain a decision signal and an error signal of a decision result, and a training signal generator for generating a training signal representing an assumed transmission symbol sequence A switch for selecting one of the determination signal and the training signal in accordance with the error signal and outputting the selected signal as the reference signal; A convolution unit for convolving the signal with a desired signal to be estimated; a delay element for providing a predetermined delay to the received signal; and an interference wave component by taking a difference between an output signal of the delay element and the desired signal for estimation. A second subtractor to be extracted, a power detector for detecting the power of the difference signal input to the matched filter, and controlling the phase of the interference wave component such that the power detected by the power detector is minimized. And an estimated interference wave generator for generating the estimated interference wave.