JPH0595298A - Interference wave elimination device - Google Patents

Abstract

PURPOSE:To attain proper interference elimination with respect to a broad band interference and a narrow band interference. CONSTITUTION:A correlation device is used as a means to discriminate whether an interference wave occupies a broad band or a narrow band, and a controller 111 controls a changeover device 109 based on the information as a clue. When a D/U (interference versus desired wave ratio) is negative to indicate a broad band interference wave, an output of a power inversion adaptive array of a subtractor 107 is selected, and when the D/U is positive and the interference occupied a narrow band as a CW, an output of an adder 108 resulting from maximum ratio diversity synthesis is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an interference canceller,
The present invention relates to an interference wave canceling apparatus that performs optimum interference cancellation and adaptive equalization for multipath distortion when a wideband interference wave or a narrowband interference wave is present in a multipath fading line that requires a diversity method.

[0002]

[Prior Art]

In the present invention, when there is a wide band interference wave having a strong D / U on the receiving side of the diversity system, the diversity root is used as a power inversion adaptive array to remove the interference wave. If the interference wave can be regarded as a narrow band signal such as an FM signal, the received signals of the diversity routes are combined at the maximum ratio, and the output is the decision feedback with the reference tap set at the center of the front equalizer. Shape equalizer (DF
E), and by removing the CW interference wave here,
Provided is a method capable of optimal interference cancellation for wide band interference and narrow band interference.

FIG. 3 shows a conventional technique relating to interference cancellation in digital radio transmission.

Reference numerals 301 and 302 are A for normalizing the input signal.
GC amplifiers, 303 and 304 are multipliers, 305 and 306
Is a correlator, 307 is a subtractor, 308 is a combiner, 309 is a switch, 310 is an AGC amplifier, 311 is N delay elements of delay time τ, 312 is N + 1 multipliers, 313.
Is a combiner, 314 and 315 are multipliers, 316 is a determiner,
Reference numeral 317 is a delay element in which M delay times are the symbol length T, 318 is M multipliers, and 319 is a combiner.

The principle by which the constituent circuit shown in FIG. 3 cancels interference will be described with reference to FIG. In the dual diversity method, desired waves of diversity routes 1 and 2 are S1 and S2, respectively. Regarding the interference wave, it is assumed that one interference wave source J exists near the receiving antenna. In this case, it can be expressed as J1 = J · A ₁ exp (jφ ₁ ) (1) J2 = J · A ₂ exp (jφ ₂ ) (2).

In FIG. 4, 401 and 402 represent the outputs of AGC amplifiers 301 and 302, respectively. Here, in the case of a strong interference wave in which D / U (interference wave to desired wave ratio) is negative, AGC (automatic gain control) is applied by interference waves J1 and J2, respectively, and the amplitudes of J1 and J2 are both normalized to 1. Be converted. The outputs of the multipliers 303 and 304 are the adder 3
08, and is normalized by the AGC amplifier 310, and then, in the correlators 305 and 306, the AGC amplifiers 301 and 3
02 output is correlated. By multiplying these correlation values by the multipliers 303 and 304, respectively, 403 and 4
As indicated by 04, control is performed so that J1 and J2 are in phase.

Therefore, the output of the adder 308 is in-phase combined with respect to the interference wave, as shown by 406. On the other hand, in the subtractor 307, the normalized interference waves J1 and J2 are combined in anti-phase, and the interference wave is removed. This interference cancellation method is a type of adaptive array and is called a power inversion adaptive array (PIAA).

Reference numeral 405 in FIG. 4 indicates the output of the subtractor 307. However, in-phase synthesis is not performed for the desired wave. Therefore, in some cases, the desired waves may be canceled.

That is, in this system, the diversity root is used as an array, and the drawback is that the diversity gain is not secured.

When there is a strong interference wave having a negative D / U, the switch 309 selects the output of the subtractor 307 and performs the PIAA operation. Its output is component 31
1,312,313,314,315,316,31
A decision feedback equalizer (DF
E), and intersymbol interference due to multipath fading is removed.

When there is no interference wave, the switch 3
09 selects the combiner 308 output. Here, maximum ratio diversity combining for the desired wave signal is performed, and it functions as a normal diversity combining + adaptive equalization receiver.

[0013]

In the above-mentioned conventional technique, when trying to remove the interference wave, the maximum ratio combining or the in-phase combining of the desired waves is not performed, so that the diversity effect cannot be obtained and the multipath fading is not obtained. Optimal reception by adaptive equalization on the line and interference wave cancellation are incompatible, and in some cases the desired signal is lost.

Further, in this system, it is premised that the D / U becomes negative, and when the D / U becomes 0 dB or positive, control is applied by the desired signal wave and the interference wave between the diversity routes is generated. There is a problem that interference cannot be removed because the control to bring them into the same phase is not applied.

In view of the above drawbacks, the technical problem of the present invention is that the D / U is positive and the interference wave is CW in a narrow band.
If it can be regarded as, by eliminating the PIAA operation and removing the reference tap position by the DFE located in the center of the front equalizer, it is possible to prevent the desired wave from disappearing due to the interference removal.
Another object of the present invention is to provide an interference wave elimination device that does not impair the diversity effect.

[0016]

According to the present invention, when there is a wide band interference wave having a strong D / U at the receiving side of the diversity system, the diversity route is subjected to power inversion adaptive. A means for removing an interference wave used as an array, and a combining means for combining the received signals of the respective diversity routes with a maximum ratio when the interference wave can be regarded as a narrow band signal, and the maximum combined output is a reference tap, CW is passed through the decision feedback equalizer (DFE) set at the center of the front equalizer.
An interference wave removing device is obtained which has a removing means for removing the interference wave.

Further, according to the present invention, the receiving side of the diversity system normalizes the received signal of each diversity route and outputs a first normalized output signal, and the first normalizing means. A branching means for branching the normalized output signal of 1 to pass through the multiplier and the correlator, a combining means for combining the multiplier output signals of the branching means, and an amplitude of the output of the combining means to 1 And a first correlating means for taking a correlation between the second normalized output signal normalized by the second normalizing means and each diversity signal passed through the correlator. Multiplication means for multiplying the received signal passed through the multiplier by the correlation value for each diversity route by the first correlation means, subtraction means for performing subtraction between the multiplier output signals by the multiplication means, and the subtraction means Signal and the output of the multiplier A switching means for switching the signal to the selected signal, a means for passing the signal switched by the switching means to a decision feedback equalizer whose reference tap position is at the center of the front equalizer, and a first tap of the front equalizer. A second correlating means for taking a correlation between the received signals distributed to the first tap and the last tap, and a control means for controlling the switching means by passing a correlation value by the second correlating means through a control circuit. An interference wave removing device is obtained.

[0018]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram of the dual diversity system of this embodiment. FIG. 2 is an explanatory diagram of the interference removal operation of this embodiment.

In FIG. 1, 101 and 102 are AGC amplifiers, 103 and 104 are multipliers, 105 and 106 are correlators, 107 is a subtractor, 108 is an adder, 109 is a switcher, 110 is an AGC amplifier, and 111 is 111. Control circuit, 112
Is a correlator, 113 is 2N delay elements with delay time τ,
114 is 2N + 1 multipliers, 115 is an adder, 116
And 117 are subtractors, 118 is a determiner, 119 is M delay elements whose delay time is equal to the symbol length T, 120 is M multipliers, and 121 is an adder.

In FIG. 2, 201 and 202 are vector diagrams at the outputs of the AGC amplifiers 101 and 102, and S1 and S2.
Is a desired wave of routes 1 and 2, and J1 and J2 are interference waves of routes 1 and 2. 203 and 204 are output vectors of the multipliers 103 and 104, and 205 is an adder 108.
The output vector, 206 is the frequency spectrum at the output of the adder 108, 207 is the frequency spectrum at the output of the adder 115, and 208 is the frequency spectrum of the subtractor 116.

In the configuration diagram of FIG. 1, a structural difference from the conventional system described in FIG. 3 is that the reference tap position of the DFE is located at the center of the front equalizer.

It is known that DFE has a canceling ability especially for CW interference. The literature on this is IEE TRANSACTION on Communication Volcom 31 Number 4 April 1983 Rejection of CW Interference in QPSK Systems Using Decision Feedback Filters.

Here, the CW interference wave elimination capability of the DFE is analyzed, and the standard tap position is not placed at the center of the forward equalizer but the normal DFE set at the final tap.
Is said to have higher CW removal capability. Further, here, the case where the DFE is used for the purpose of removing only the interference wave is targeted.

However, in an actual line, multipath distortion becomes a problem, and compatibility between interference removal and multipath distortion removal is an important issue. It is effective to set the reference tap position of the DFE at the center of the front equalizer in order to simultaneously remove the narrowband interference wave such as CW and the intersymbol interference due to the multipath fading. That is, when the interference wave is not in a wide band and has a CW property, it is preferable to perform CW interference removal by DFE after performing maximum ratio combining between diversity routes, without performing interference removal by PIAA.

Therefore, in FIG. 1 showing the configuration of the present embodiment, the correlator 1 is used to judge whether the interference wave is a wide band or a narrow band.
12 are provided.

With respect to the interference wave, there is only one source, and when the interference wave is the CW interference wave of angular frequency ω, the interference waves of routes 1 and 2 are J1 = A ₁ exp {j (ω + φ ₁ )} (1) J2 = A ₂ exp (j (ω + φ ₂ )} (2)

By the way, as described in the conventional method, the constituent elements 101, 102, 103, 104, 105 and 10 are used.
PI consisting of 6, 107, 108, 109 and 110
The AA circuit is effective only when D / U becomes negative. When D / U becomes positive as shown in FIG. 2, control is performed so that the desired signal wave, instead of the interference wave, is combined in phase by the adder 108. This state is shown by S1 and S2 in 203 and 204. At this time, the subtractor 107
Then, the desired wave signals cancel each other, and the interference wave cannot be canceled. In such a case, the switch 10
The output of the adder 108 is selected by 9 and a signal is supplied to the next DFE.

Here, as indicated by 205 and 206, the desired signal is subject to multipath distortion, but maximum ratio combining is performed. The interference waves are vector-multiplied by the multipliers 103 and 104 and combined, but CW
Holds sex. Components 113, 114 and 11
The forward equalizer consisting of 5 acts as a linear filter. 2N
The tap coefficients of the +1 multiplier adaptively converge to a linear sum of the solution of the steep notch filter that frequency-filters the CW interference wave and the solution that removes the multipath distortion due to the Precursor of the impulse response. The influence of the notch filtering by the front equalizer on the desired signal is DF
Since it is compensated by the backward equalizer of E, higher interference removal characteristics can be obtained as compared with a mere transversal filter having no decision feedback.

The notch-filtered signal spectrum shown at 207 in FIG. 2 is returned to the original spectrum of the roll-off transmission system by the backward equalizer composed of the components 119, 120, and 121 so as to obtain the Nyquist distortion-free condition. The situation is shown at 208.

As described above, when D / U is not negative and the interference wave is in a narrow band such as CW, the PIA is intentionally performed.
It is more effective to return to normal maximum ratio diversity combining instead of the A operation and perform interference cancellation by DFE.

The received signals on the C _-N and C _{+ N} taps of the forward equalizer are correlated by the correlator 112. Here, when the interference wave is CW, the linear combination of the interference waves shown in the above equations (1) and (2) is distributed as C- _N and C _{+ N} taps as J- _N and J _{+ N.} To do.

Assuming that the delay time τ of the delay element 113 is T of the symbol length, J _−N = Jexp {j (ωt + φ)} (3) J _{+ N} = Jexp {j (ωt + 2NωT + φ)} ( 4) is shown.

[0034] Accordingly, the correlator 112 output is _{E {J -N · J + N} *} = J 2 exp {-j2NωT} (5).

Time interval 2NT between C- _N and C _{+ N} taps
If the number of taps of the front equalizer is selected so that is longer than the delay dispersion time of the multipath propagation path, the correlation value due to the desired signal component is not output to the output of the correlator 112. If the interference wave is not a narrow band signal but a wide band signal that has been modulated, there is no correlation due to a 2NT time shift, and the output of the correlator 112 is zero.

That is, the correlator 112 can be used as a means for judging whether the interference wave is in a wide band or a narrow band, and the controller 111 controls the switch 109 by using this information as a clue. When the interference wave has a wide band, the PIAA output of the subtractor 107 is selected as in the conventional method. When the interference wave has a narrow band such as CW, the output of the adder 108 subjected to maximum ratio diversity combining is selected and output instead of PIAA.

[0037]

As described above, according to the present invention, the D / U
In case of negative and wide band interference wave, it is removed by the conventional power inversion adaptive array method, and D / U
Is positive and the interference wave is in a narrow band, the diversity route is switched to the normal maximum ratio combining, and the narrow band interference wave is removed by the DFE that sets the reference tap at the center of the forward equalizer. And, there is an effect that enables optimum removal according to the band of the interference.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a dual diversity system of the present invention.

FIG. 2 is an explanatory diagram of an interference removal operation of the present invention.

FIG. 3 is a block diagram of a conventional interference wave cancel device in digital wireless transmission.

FIG. 4 is a diagram illustrating the principle of the conventional technique shown in FIG.

[Explanation of symbols]

101,102 AGC amplifier 103,104 Multiplier 105,106 Correlator 107 Subtractor 108 Adder 109 Switcher 110 AGC amplifier 111 Control circuit 112 Correlator 113 2N delay elements with delay time τ 114 2N + 1 multipliers 115 Adder 116, 117 Subtractor 118 Determinator 119 M delay elements with delay time equal to the symbol length T 120 M multipliers 121 adder

Claims (2)

[Claims] 1. The receiving side of the diversity system,
When there is a wide band interference wave having a strong D / U that is negative, a means for removing the interference wave using the diversity route as a power inversion adaptive array, and a case where the interference wave can be regarded as a narrow band signal Is a combining means for maximizing the ratio of received signals of the diversity routes, and the maximally combined output is passed through a decision feedback equalizer (DFE) whose reference tap is set at the center of the forward equalizer.
An interference wave removing device comprising: a removing unit for removing a CW interference wave. 2. A first normalizing means for normalizing a received signal of each diversity route and outputting a first normalized output signal at a diversity side receiving side, and the first normalized output signal. Branching means for branching to the multiplier and correlator, synthesizing means for synthesizing the multiplier output signal of the branching means, and second normalization for normalizing the amplitude of the output of the synthesizing means to 1. Means, first correlating means for correlating the second normalized output signal normalized by the second normalizing means with each diversity signal passed through the correlator, and the first correlation Multiplication means for multiplying the received signal passed through the multiplier by the correlation value for each diversity route by the means, subtraction means for performing subtraction between the multiplier output signals by the multiplication means, the signal by the subtraction means and the multiplier The output is combined with the signal Switching means for switching, means for passing the signal switched by the switching means to a decision feedback equalizer whose reference tap position is at the center of the front equalizer, first tap and final tap of the front equalizer And a control means for controlling the switching means by passing a correlation value obtained by the second correlation means through a control circuit. Interference wave remover.