JP2737348B2 - Cross polarization interference canceller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-polarization interference canceller used in an orthogonally polarized digital radio communication system using two orthogonally polarized waves, and more particularly, to a method for removing a code error or the like. The present invention relates to a cross-polarization interference canceller that prevents an adverse effect.

[Conventional technology]

As is well known, in digital wireless communication, two orthogonal polarizations (for example, horizontal polarization and vertical polarization, right circular polarization and left circular polarization, etc.) of the same frequency are used in order to increase the frequency utilization efficiency. The orthogonal polarization communication system has been put to practical use.
In the case of using such orthogonal polarization, if cross polarization interference occurs due to anisotropy of a medium such as raindrops during rainfall, the line quality is significantly deteriorated. A cross-polarization interference canceller has been put to practical use when it was developed.

The cross-polarization interference canceller is configured using a cross-polarization interference canceller having a transversal filter as a whole.
As is well known, transversal filters include an IF type configured with an intermediate frequency (IF) band and a baseband type configured with a baseband. The transversal filter composed of a baseband includes an analog type using an analog delay line and an analog integrator, and a digital type using a shift register as a delay circuit and an up / down counter as an integrator.

FIG. 3 shows an example of a cross polarization interference canceller using a conventional digital cross polarization interference canceller. This cross-polarization interference canceller is composed of a self-polarization side demodulation system (input terminal 1, demodulator
101 and A / D converter 103) and demodulation system on different polarization side (input terminal
2, demodulator 012 and A / D converter 104), cross polarization interference canceller 11A, and output terminal 3. The cross polarization interference canceller 11A includes a subtractor 105 and a transversal filter 106.
And a tap coefficient controller 107 for performing an interference removal operation by digital signal processing.

In this cross-polarization interference canceller, the self-polarization-side IF signal input to the input terminal 1 is synchronously detected by the demodulator 101 to become an analog baseband signal. The signal is quantized to become a demodulated digital signal, which is one input of the subtractor 105.

The different-polarization-side IF signal input to the input terminal 2 is synchronously detected by the demodulator 102 to become an analog baseband signal, and further sampled and quantized by the A / D converter 104 to be demodulated digitally. Signal. The demodulated digital signal is supplied to the transversal filter 106 and the tap coefficient controller 107 as a control signal.

In the tap coefficient controller 107, the error information signal of the digital signal output from the subtractor 105 and the A / D converter 1 on the different polarization side are output.
04 and an identification information signal (polarity signal) of the output digital signal, and generates a tap coefficient control signal by correlating the two signals.
Control the tap coefficient of.

The transversal filter 106 includes, for example, flip-flop circuits 301 and 302 as shown in FIG.
, Tap weighting circuits 303 to 305, and an adder 306. The A / D converter 1 on the different polarization side is connected to the input terminal 31.
04, the output tap coefficient control signal of the tap coefficient controller 107 is received at the terminals a to c, and the same amplitude and the same amplitude as the signal component on the different polarization side leaked to the own polarization side.
A cross-polarization interference compensation signal having a phase characteristic is generated, and is supplied from the output terminal 32 to the other input of the subtractor 105.

The subtractor 105 performs a digital subtraction process between the two input signals, and outputs a self-polarized-side demodulated data signal from which cross polarization interference has been removed to the output terminal 3.

The operation of the digital cross-polarization interference canceller described above is described in the literature (eg, “Digital cross-polarization interference compensator for ultra-multilevel modulation” (IEICE Transactions Vol.
J70-B No. 8 pp. 977-986), and Japanese Patent Application Laid-Open No. 62-269429).

[Problems to be solved by the invention]

The above-described conventional cross-polarization interference canceller generates a tap coefficient control signal by correlating both the error information signal on the own polarization side and the identification information signal (polarity signal) on the different polarization side. Then, the upcoefficient of the transversal filter is controlled to eliminate leakage from the different polarization signal. That is, in FIG.
If the self-polarization side signal is delayed from the different polarization side signal by T seconds from the center tap b of the above, the weighting circuit a of the -1 tap is controlled, and the inverse characteristic of the interference delayed by T seconds is obtained. The generation eliminates interference. However,
If there is interference 2T seconds behind the center tap, that is, if interference is received outside the tap of the transversal filter (outside the tap), correct compensation operation is not possible because there is no corresponding weighting circuit Becomes
This has an adverse effect such as giving a code error to the own polarization side.

As a result, as shown in the interference elimination characteristic of FIG. 5 (b), for the interference in which the tap of the transversal filter is delayed by T seconds or advanced by T seconds, a sufficient compensation operation is performed.
When interference occurs outside the tap as in 2T and −2T, there is a problem that the compensating operation capability is reduced as compared with the case where the tap coefficient of the transversal filter is fixed (reset) to the initial value.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cross polarization interference canceller that prevents a reduction in compensation ability when interference is received outside a tap.

[Means for solving the problem]

The cross-polarization interference canceller of the present invention outputs a reset signal when the other demodulated signal wetted into one demodulated signal of two orthogonal polarizations leaks outside the tap of a transversal fighter, and outputs a reset signal. A reset control circuit for initializing each tap coefficient of the versal filter is provided.

That is, a transversal filter that generates a compensation signal having the same amplitude and the same phase as the other signal leaked into one demodulated signal, and controls the tap coefficient of the transversal filter according to the advance and delay of the leaked signal. A tap coefficient control circuit, a reset control circuit that resets or cancels the reset of the tap coefficient control circuit in accordance with the advance or delay of the leaked signal, and a subtractor that subtracts a compensation signal from the one demodulated signal. Make up.

[Action]

According to the present invention, when the leakage on the different polarization side is outside the tap of the transversal filter, the reset control circuit initializes the transversal filter, so that the output of the erroneous compensation signal from the transversal filter is stopped. This prevents the demodulated signal on the polarization side from being adversely affected by a code error or the like.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention, and is a block diagram of an interference canceller using a three-tap cross-polarization interference canceller. The device of this embodiment is basically the same as the conventional device shown in FIG. That is, the self-polarization side demodulation system (input terminal 1, demodulator 101, and A / D converter 103) and the different polarization side demodulation system (input terminal 2, demodulator 012, and A / D converter 104).
, A cross polarization interference canceller 11, and an output terminal 3. Here, the cross polarization interference canceller 11 includes a subtractor 105, a transversal filter 106, a tap coefficient controller 107, and a reset control circuit 108.

For example, as shown in FIG. 2, the reset control circuit 108 includes flip-flop circuits 201 to 205, exclusive OR circuits 206 and 207 as correlation detection circuits, up / down counters (U / D counters) 208 and 209, It is composed of a talk circuit 210.

The error information signal of the digital signal output from the subtractor 105 is applied to one input terminal 21. Also,
The other input terminal 22 is applied with a polarity signal of the digital signals output from the A / D converter 104 on the different polarization side. Further, the output terminal 23 is connected to a reset signal input terminal of the tap coefficient controller 107.

According to the cross polarization interference canceller having such a configuration, the self-polarization-side IF signal input to the input terminal 1 is synchronously detected by the demodulator 101 to become an analog baseband signal.
The sample is quantized by the A / D converter 103 and becomes a demodulated digital signal, which is input to the subtractor 105.

The different-polarization-side IF signal input to the input terminal 2 is synchronously detected by the demodulator 102 to become an analog baseband signal, and further sampled and quantized by the A / D converter 104 to be a demodulated digital signal. Becomes The demodulated digital signal is transmitted to the transversal filter 106, the tap coefficient controller.
107 and a reset control circuit 108 are supplied as control signals.

In the tap coefficient controller 107, the error information signal of the digital signal output from the subtractor 105 and the A / D converter 1 on the different polarization side are output.
04 and an identification information signal (polarity signal) of the output digital signal, and generates a tap coefficient control signal by correlating the two signals.
Control the tap coefficient of.

The transversal filter 106 receives the output digital signal of the A / D converter 104 on the different polarization side and the output tap coefficient control signal of the tap coefficient controller 107 as shown in FIG. A cross-polarization interference compensation signal having the same amplitude and phase characteristics as the signal component on the different polarization side leaked to the side is generated and supplied to the other input of the subtractor 105.

The subtractor 105 performs digital subtraction processing between the two input signals, and outputs a self-polarized-side demodulated data signal from which cross polarization interference has been removed to the output terminal 3. The error information signal of the output digital signal is input to the tap coefficient controller 107 and is also input to the reset control circuit 108.

In this device, when only the delay of the different polarization side signal is delayed by 2T or −2T seconds from the center tap of the transversal filter 106, one of the outputs of the correlation detection circuits 206 and 207 is “1” continuous or “0”. Continuous, U / D counter 20
It is input to 8,209 and counted for a certain period of time. When the count output value becomes a certain level or more or a certain level or less, the outputs of the U / D counters 208 and 209 become “1” level,
Output to the OR circuit 210. In the OR circuit 210, when "1" level is input to one of the inputs of the OR circuit 210, it is output as "1" level, and the signal level of the output terminal 23 becomes "1" level.

If the leakage of the different polarization side signal is within the tap of the transversal filter, the correlation detection circuits 206 and 20
The output signal of 7 has almost the same number of “1” and “0”.
The signal level of 3 becomes “0” level.

The output signal from the output terminal 23 is input as a reset signal to the tap coefficient control circuit 107. When the reset signal is at “1” level, the transversal filter 10
The tap coefficient of 6 is initialized (reset) and the state is maintained. When the reset signal goes to “0” level,
The reset state is released, and the automatic compensation operation of the cross polarization interference canceller 11 is restarted.

As a result, as shown in FIG. 5 (a), when the leakage of the different polarization side signal is outside the tap of the transversal filter 106, the cross polarization interference canceller is reset and its automatic compensation operation is performed. Therefore, the transversal filter 106 generates an erroneous compensation signal, thereby preventing a code error or the like from occurring in the self-polarization-side demodulated signal.

Although the above embodiment has been described with respect to a case where a three-tap transversal filter is used, the present invention is not limited to this. The reset control is also performed when the different polarization signal leaks only at a position + 2T and −2T away from the center tap. However, the present invention is not limited to this. ± 3T, ± 4T,... Obviously, it can be extended even if it leaks into a remote location.

〔The invention's effect〕

As described above, the present invention provides a reset control circuit that initializes the tap coefficient of the transversal filter when leakage on the different polarization side is outside the tap of the transversal filter. The output of the erroneous compensation signal from the transversal filter at the time of outside is stopped, and thereby there is an effect that it is possible to prevent the self-polarization-side demodulated signal from having an adverse effect such as a code error. Further, since the reset control circuit can be easily formed into an LSI by being included in the tap coefficient control circuit, there is an effect that the size can be reduced and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an interference canceller constituted by a cross polarization interference canceller of the present invention, FIG. 2 is a block diagram of a reset control circuit, and FIG. 3 is an interference constituted by a conventional cross polarization interference canceller. FIG. 4 is a block diagram of a transversal filter, and FIGS. 5 (a) and 5 (b) are diagrams showing interference elimination characteristics of the present invention and conventional cross-polarization interference elimination devices, respectively. . 11,11A cross polarization interference canceller 101,102 demodulator 103,104 A / D converter 105 subtracter 106 transversal filter 107 tap coefficient control circuit 108 ... Reset control circuit, 201 to 205
…… Flip-flop circuit, 206,207 …… Exclusive OR circuit (correlation detection circuit), 208,209 …… U / D counter, 210
…… OR circuit, 303 to 305… Tap weighting circuit, 306 …… Adder.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-14633 (JP, A) JP-A-1-290334 (JP, A) JP-A-1-200843 (JP, A) JP-A-1-200843 176130 (JP, A) JP-A-64-22130 (JP, A) JP-A-63-199547 (JP, A) JP-A-61-131635 (JP, A)

Claims (2)

(57) [Claims] A cross polarization interference canceller for removing a demodulated signal of one of two orthogonally polarized waves which is wetted by one of two demodulated signals by controlling a tap coefficient of a transversal filter. A cross polarization interference canceller, comprising: a reset control circuit that outputs a reset signal when a demodulated signal leaks outside a tap of the transversal filter and initializes each tap coefficient of the transversal filter. . 2. A transversal filter for generating a compensation signal having the same amplitude and the same phase as one of the other signals leaked into one demodulated signal, and a tap of the transversal filter according to the lead and delay of the leaked signal. A tap coefficient control circuit for controlling a coefficient, a reset control circuit for resetting or canceling the reset of the tap coefficient control circuit in accordance with the advance or delay of the leaked signal, and subtraction for subtracting a compensation signal from the one demodulated signal. 2. The cross polarization interference canceller according to claim 1, wherein said cross polarization interference canceller is constituted by a filter.