JPH0756970B2 - Cross polarization receiver circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for digital radio communication for transmitting separate signals by orthogonal polarization. In particular, the present invention relates to a circuit that removes interference between cross-polarized waves generated in a transmission line on the receiving side.

[Conventional technology]

FIG. 4 is a block diagram of a conventional cross polarization receiver circuit. This cross-polarized wave reception circuit includes a cross-polarized wave interference compensation circuit 17 that removes cross-polarized wave interference in the baseband.
Here, a circuit having a 5-tap configuration will be described as an example.

The received signal of the main polarization (horizontal polarization or vertical polarization) receiving the interference and the received signal of the different polarization giving the interference (vertical polarization or horizontal polarization) are independent local oscillators 1. 2 are used to be converted into intermediate frequency signals by the reception frequency converters 3 and 4. The intermediate frequency signal on the main polarization side is input to the demodulator 5, and the intermediate frequency signal on the different polarization side is input to the demodulator 6.

The demodulator 5 demodulates the baseband signal on the main polarization side, regenerates the clock 102, and supplies these signals to the analog / digital converter 7. The analog / digital converter 7 digitizes the baseband signal by the clock 102.

Similarly, the demodulator 6 demodulates the baseband signal on the different polarization side and reproduces the reproduction clock 103. The analog / digital converter 7 digitizes the baseband signal on the different polarization side by the recovered clock 103.

To remove the different polarization signal that leaked to the main polarization side,
The two baseband signals are digitized with the same clock and supplied to the cross polarization interference canceling circuit 17. That is, the baseband signal output from the demodulator 6 is branched and input to the analog / digital converter 9, and digitized by the clock 102 reproduced by the demodulator 5. The digitized signal and the output signal of the analog-digital converter 7 are input to the cross polarization interference canceling circuit 17.

The cross polarization interference canceling circuit 17 is provided with a transversal filter 19 which operates in the clock cycle T reproduced by the demodulator 5, and the output of the analog-digital converter 9 is supplied to the transversal filter 19. The transversal filter 19 controls the amplitude and phase characteristics of the signal from the analog-digital converter 9, and then outputs this signal to the subtractor 18. The output of the analog-digital converter 7 is supplied to the subtractor 18 via the delay circuit 20, and the output signal of the transversal 19 is subtracted from this signal. The output of the subtracter 18 is output from this cross polarization reception circuit as a main polarization signal and is also supplied to the transversal filter 19 as an error signal. The transversal filter 19 correlates the most significant bit (polarity signal) of the analog / digital converter 9 with the error signal, and subtracts the subtracter 18
The weighting coefficient of each tap is controlled so that the error in the output of 1 is minimized.

[Problems to be solved by the invention]

However, in the conventional cross polarization receiver circuit, the clock cycle T
Since cross-polarization interference is compensated for by using a weighting circuit that operates for each, the relative delay time between the different polarization signal leaking to the main polarization side and the different polarization signal that is the source for interference compensation , The cross polarization interference can be compensated. However, if the relative delay time fluctuates due to the influence of the transmission line etc., the compensating ability of the cross polarization interference compensating circuit is significantly reduced. Will end up. This will be described with reference to FIGS. 5, 6 and 7.

FIG. 5 shows an example of a propagation path of digital radio communication using orthogonal polarization. The radio wave emitted from the transmitting antenna 51 spreads and propagates according to the beam characteristics of the transmitting antenna 51, so that not only the direct wave is transmitted to the receiving antenna 52,
Radio waves reflected at a reflection point r on the ground or the surface of water or radio waves complicatedly refracted by a duct generated on the propagation path are combined and received.

Here, it is assumed that the transmitting antenna 51 transmits the V polarization and the H polarization, and the receiving antenna 52 receives the V polarization as the main polarization and the H polarization as the different polarization. At this time, the cross polarization interference canceling circuit compensates the interference signal included in the reception signal of the V polarization based on the reception signal of the H polarization. Considering only the direct wave, even if the H polarization is mixed (interference) with the V polarization, H
There is no difference in path length between the polarization reception signal and the interference signal, and there is no relative delay time difference. The problem is that the H polarized wave is reflected at the reflection point r and mixed into the V polarized wave, or mixed into the V polarized wave via the duct.

As is well known, radio waves generate different polarization components as they are reflected. In addition, the duct is generated by the inversion of the vertical refractive index distribution of the atmosphere under the influence of weather conditions (passage of the front, etc.), and when radio waves propagate in this duct due to complex reflection and refraction. A different polarization component is generated. In such a case, the path difference between the different polarization received by the receiving antenna 52 as a direct wave and the interference wave leaking to the main polarization side is (a) the path difference ΔL (r) due to the reflection point r. ΔL (r) = Lr−L (b) The path difference ΔL (d) due to the duct ΔL (d) = Ld−L. Here, L is the path length of the direct wave, Lr is the path length of the radio wave reflected by the reflection point r, and Ld is the path length of the radio wave passing through the duct. Path difference ΔL due to reflection point r
(R) has different conditions depending on the reflecting object, but in the case of the sea surface, it changes depending on the tide. In the case of paddy fields, there are seasonal changes. Passage difference ΔL due to duct
(D) shows that the duration of the duct is several minutes to several hours,
It fluctuates greatly with it.

In this way, the reflection of radio waves and the influence of the duct fluctuate with time, and the path difference (relative time difference) between the interference wave and the direct wave caused thereby also fluctuates with time.

6 and 7 show the output R _V (t) of the analog-digital converter 7 and the reference signal input from the analog-digital converter 9 to the transversal filter 19 in the conventional example shown in FIG. R _H (t), the compensation signal output from the transversal filter 19, and the compensated signal obtained at the output of the subtracter 18 are shown. If there is no relative delay time difference between the different polarization signal leaked into the main polarization signal and the reference signal, or if the relative delay time difference is an integral multiple of the period T, an accurate compensation signal is obtained from the reference signal. Thus, the interference component can be sufficiently compensated. On the other hand, when the relative delay difference fluctuates due to reflection or a duct, the correlation detection sensitivity is reduced, an accurate compensation signal cannot be obtained, and an interference component remains in the compensated signal.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a cross polarization receiver circuit that effectively removes interference signals from different polarizations and outputs a main polarization signal.

[Means for solving problems]

The cross-polarization receiving circuit of the present invention has two demodulators for separately demodulating the main polarization signal and the hetero-polarization signal respectively received from two polarizations orthogonal to each other, and the outputs of these two demodulators are common. Two analog-to-digital converters that convert each to a digital signal by the clock and the outputs of these two analog-to-digital converters are supplied, and the leaked component is removed from the hetero-polarization signal included in the main polarization signal. The cross-polarization interference compensation circuit is provided with the cross-polarization interference compensation circuit, which is supplied with the output of the analog-digital converter on the different polarization side and operates according to the clocks of the two analog-digital converters. Type transversal filter and a subtractor that subtracts the output of this transversal filter from the output of the main polarization side analog-digital converter In the cross-polarized wave receiving circuit including, the operating clocks of the two analog-to-digital converters and the transversal filter are faster than the clocks (regenerated clocks) of the received signals regenerated by the two demodulators, respectively, and the output signal of the subtractor Is provided with a signal reproduction circuit for synchronizing with a clock of a reception signal reproduced by either one of the two demodulators.

[Work]

The output of the demodulator is processed faster than the cycle T of the recovered clock, and the tap weighting coefficient of the transversal filter is adjusted at high speed. That is, the observation density on the time axis is increased so that fluctuations in the relative delay difference caused by reflection and ducts can be dealt with. As a result, even if the relative delay time difference between the different polarization signal leaking to the main polarization side and the different polarization signal itself that is the source of the interference signal changes, good compensation characteristics can always be obtained. .

〔Example〕

FIG. 1 is a block diagram of a cross polarization receiver circuit according to the first embodiment of the present invention. In this embodiment, 1 / the cycle T of the reproduced clock is used.
An example using a transversal filter that adjusts the tap weighting coefficient at intervals of 2 will be described.

This receiving circuit outputs two demodulators 5 and 6 for separately demodulating a main polarization signal and a hetero-polarization signal respectively received from two polarizations orthogonal to each other, and outputs of these two demodulators 5 and 6. The two analog-to-digital converters 7 and 9 for converting into digital signals respectively and the outputs of the two analog-to-digital converters are supplied to remove the leaked component from the hetero-polarization signal included in the main polarization signal. And a cross polarization interference canceling circuit (17).

The input circuit of the demodulator 5 includes a reception frequency converter 3 for converting a reception signal of the main polarization (horizontal polarization or vertical polarization) which is interfered into an intermediate frequency signal, and the reception frequency converter 3. A local oscillator 1 for supplying a local oscillation signal.
Further, in the input circuit of the demodulator 6, a reception frequency converter 4 for converting a reception signal of different polarization (vertical polarization or horizontal polarization) giving interference to an intermediate frequency signal, and this reception frequency converter 4 and a local oscillator 2 for supplying a local oscillation signal.

The cross polarization interference canceling circuit 17 includes a transversal filter 19 to which the output of the analog-digital converter 9 on the different polarization side is supplied, and an output of the transversal filter 19 on the main polarization side. 7 and a subtracter 18 for subtracting from the output. A delay circuit 20 is provided between the analog / digital converter 7 and the subtractor 18 in order to match the delay times of the main polarization signal and the output of the transversal filter 19. As the delay circuit 20, for example, a flip-flop that operates at an interval of T / 2 is used.

The transversal filter 19 is a means for controlling the tap weighting coefficient by the output of the subtractor 18, and the correlation detector C
R ₂ , CR ₁ , CR ₀ , CR _-1 , CR _-2 and tap weight circuit W ₂ ,
It has W ₁ , W ₀ , W _-1 , and W _-2 . Also, a delay element for delaying the output signal of the analog-digital converter 9 by T / 2
T ₂ , T ₁ , T _-1 , T _-2 and tap weight circuits W ₂ , W ₁ , W ₀ ,
And an adder Σ that adds the outputs of W ₋₁ and W ₋₂ .

The two analog-to-digital converters 7 and 9 and the transversal filter 19 are connected to the recovered clock 102 of the demodulator 5.
The clock operates at a higher speed clock (double speed in this embodiment). Therefore, a clock 102D that is twice the reproduction clock 102 is provided between the demodulator 5 and the analog-digital converters 7 and 9. There is provided a multiplier 21 that outputs

In addition, this receiving circuit outputs the output signal of the subtractor 18 to the demodulator 5
The signal reproduction circuit 22 for synchronizing with the reproduced clock 102 of FIG. As the signal reproduction circuit 22, for example, a flip-flop is used. The signal reproduction circuit 22 restores this data rate to the original data rate because the output signal of the subtractor 18 has a repetition frequency twice the data rate. The output of the signal reproduction circuit 22 is output as the main polarization reception signal from which the interference signal has been removed, and the correlation detectors CR ₂ , CR ₁ , CR ₀ , C of the transversal filter 19 are output.
The error signal E is supplied to R ₋₁ and CR ₋₂ .

The output of the demodulator 6 on the different polarization side is supplied to the analog / digital converter 9 as well as the analog / digital converter 8 which operates by the recovered clock 103 of the demodulator 6. The analog-digital converter 8 is output as a different polarization reception signal.

Here, the control of the tap weighting coefficient in the transversal filter 19 will be described. Correlation detector CR ₂ , CR ₁ ,
CR ₀ , CR _-1 , and CR _-2 are the error signal E, the output signal of the analog-digital converter 9 and this signal, and the delay element T ₂ ,
Signals D ₂ , D ₁ , D ₀ , D sequentially delayed by T ₁ , T _-1 , T _-2
-1 and D _-2 are respectively correlated and the signal reproduction circuit 22
The tap weighting circuit W ₂ ,
Controls the coefficients of W ₁ , W ₀ , W _-1 , W _-2 .

In this way, the relative delay between the different polarization signal component included in the input of the main polarization side analog-digital converter 7 and the different polarization signal at the input of the different polarization side analog-digital converter 8 Even if the time difference fluctuates, the clock cycle T
Since the tap weighting coefficient can be controlled at an interval of 1/2, there is no deterioration of the compensation characteristic and a good compensation characteristic can always be obtained.

FIG. 3 is a block diagram of a cross polarization receiver circuit according to the second embodiment of the present invention.

The receiving circuit of this embodiment is provided with a multiplier 23 for generating N times the clock 102N instead of the multiplier 21 for generating the clock twice the clock cycle T, and the transversal filter 19 is provided.
Has 2N + 1 taps, and the analog / digital converters 7 and 9 and the transversal filter 19 operate at N times the clock recovered by the demodulator 5 (N is an integer of 3 or more). Different from the first embodiment.

FIG. 3 is a block diagram of a cross polarization receiver circuit according to a third embodiment of the present invention. In this embodiment, the cross polarization interference compensation circuit equivalent to that in the second embodiment is provided on both the main polarization side and the different polarization side.

That is, the demodulation output of the demodulator 5 on the main polarization side is the analog / digital conversion circuit 7 for the main polarization signal and the analog / digital conversion circuit 7 for compensating the cross polarization interference from the main polarization to the different polarization.
It is supplied to the digital converter 9C. The analog-digital converter 9C is a multiplier for the recovered clock 103 on the different polarization side.
The output of the demodulator 5 is digitized by the clock 103N multiplied by N at 3C.

Similarly, the demodulation output of the demodulator 6 on the different polarization side is converted to an analog / digital converter 8 for the different polarization signal and an analog / digital conversion for cross polarization interference compensation from the different polarization to the main polarization. Supplied to the vessel 9I. Analog-digital converter 9I
Outputs the output of the demodulator 6 by a clock 102N obtained by multiplying the reproduction clock 102 on the main polarization side by N in the multiplier 23I.

The output of the analog-digital converter 9I is supplied to the cross polarization interference canceling circuit 17I for the main polarization. This cross polarization interference canceling circuit 17I is provided with a transversal filter 19I, and the error signal EI on the main polarization side, the output signal of the analog-digital converter 9I, and this signal are delayed by the delay elements T _N ... T ₁ ,
The signals delayed by T _-1 ... T _-N are correlated with the polarity signals of the signals D _N ... D ₁ , D ₀ , D _-1 ... D _-N , and the error in the output of the signal regeneration circuit 22I is minimized. So that the tap weighting circuit W _N ... W ₁ ,
The coefficient of W ₀ , W _-1 ... W _-N is feedback controlled.

The output of the analog-digital converter 9C is supplied to the cross polarization interference compensation circuit 17C for different polarization. The cross-polarization interference compensation circuit 17C is equipped with a transversal filter 19C similarly to the cross-polarization interference compensation circuit 17I, and outputs the error signal EC on the main polarization side, the output signal of the analog-digital converter 9C, and this signal. Delay element T _N ... T ₁ , T _-1 ... T _-N delayed signals D _N ... D ₁ , D ₀ , D _-1 ... D _-N Correlate with the polarity signal of the signal and a signal regeneration circuit The coefficients of the tap weighting circuits W _N ... W ₁ , W ₀ , W _-1 ... W _-N are feedback-controlled so that the error of the output of 22C is minimized.

〔The invention's effect〕

As described above, the cross-polarized wave reception circuit of the present invention is configured so that the interference signal from the different polarization that leaks into the main polarization side and the signal on the different polarization side that is the source of this interference signal Even if the delay time difference fluctuates, the compensation characteristic does not deteriorate, and the main polarization reception signal containing almost no interference signal can always be output stably.

INDUSTRIAL APPLICABILITY The present invention has an effect of improving the signal-to-noise ratio of a received signal by utilizing it in digital wireless communication in which separate signals are transmitted by orthogonal polarization.

[Brief description of drawings]

FIG. 1 is a block diagram of a cross polarization receiver circuit according to a first embodiment of the present invention. FIG. 2 is a block diagram of a cross polarization receiver circuit according to a second embodiment of the present invention. FIG. 3 is a block diagram of a cross polarization receiver circuit according to a third embodiment of the present invention. FIG. 4 is a block diagram of a conventional cross polarization receiver circuit. FIG. 5 is a diagram showing an example of a propagation path of digital wireless communication using orthogonal polarization. FIG. 6 is a diagram showing an example of signal waveforms of the conventional example shown in FIG. 4, showing a case where there is no relative delay time difference between the different polarization signal leaked into the main polarization signal and the reference signal. . FIG. 7 is a diagram showing an example of signal waveforms of the conventional example shown in FIG. 4, showing a case where there is a relative delay time difference between the different polarization signal leaking into the main polarization signal and the reference signal. . 1, 2 ... Local oscillator, 3, 4 ... Reception frequency converter,
5, 6 ... Demodulator, 7, 8, 9, 9I, 9C ... Analog
Digital converter, 17, 17I, 17C ... Cross polarization interference compensation circuit, 18, 18I, 18C ... Subtractor, 19, 19I, 19C ... Transversal filter, 20, 20I, 20C ... Delay circuit,
21, 23, 23I, 23C …… Multiplier, 22, 22I, 22C …… Signal regeneration circuit.

Claims (1)

[Claims] 1. Two demodulators (5, 6) for separately demodulating a main polarization signal and a different polarization signal respectively received from two polarizations orthogonal to each other, and the outputs of these two demodulators are common. Two analog-to-digital converters (7, 9) that convert each to a digital signal by the clock of 2 and the outputs of these two analog-to-digital converters are supplied, and leaks from the hetero-polarization signal included in the main polarization signal. Cross-polarization interference compensation circuit (17) that removes the included components, and the cross-polarization interference compensation circuit is supplied with the output of the analog-digital converter on the different polarization side and operates according to the common clock. Negative feedback control type transversal filter (19) and a subtractor (1 that subtracts the output of this transversal filter from the analog-digital converter output on the main polarization side.
8) In the cross-polarization receiving circuit including and, the common clock is faster than the clocks of the received signals regenerated by the two demodulators, and the output signal of the subtractor is one of the two demodulators. On the other hand, a cross-polarized wave receiving circuit is provided with a signal regenerating circuit that synchronizes with the clock of the received signal regenerated.