JPS6412135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cross-polarization interference cancellation circuit, and more particularly, to a baseband signal that receives digitally modulated signals of two orthogonal polarizations and removes cross-polarization interference from each received polarization signal. This invention relates to a cross-polarization interference cancellation circuit for restoring.

In recent years, in microwave wireless communications, orthogonal polarization communication methods, which utilize frequencies effectively by using two orthogonal polarized waves (vertical and horizontal or left-handed circularly polarized waves and right-handed circularly polarized waves) of the same frequency, have attracted attention. ing. Such orthogonal polarized waves generate cross polarized waves due to anisotropy such as rainfall, causing interference between both polarization channels. Therefore, in orthogonal polarization communication systems, it is necessary to improve the polarization characteristics of antennas and power supply devices, as well as develop cross-polarization interference cancellation circuits that compensate for deterioration of polarization characteristics in radio wave propagation due to rain, etc. is also an important issue.

Conventionally, cross-polarization interference cancellation circuits in microwave band digital wireless communications control transversal filters based on demodulated baseband signal information, as proposed in Japanese Patent Application Laid-Open No. 133156/1983. This eliminates cross-polarization interference. However, as will be described later, in this method, a compensation signal that cancels cross-polarization interference is generated by a transversal filter that is directly branched from the reception output of each polarization, so it is difficult to use when waveform distortion due to fading etc. is large. has the disadvantage that cross-polarization interference cannot be removed sufficiently.

An object of the present invention is to provide a negotiated polarization interference cancellation circuit that eliminates the above-mentioned drawbacks and can eliminate cross-polarization interference even when waveform distortion is large, in a cross-polarization interference cancellation circuit for digital communication using a transversal filter. The goal is to provide the following.

The cross-polarization interference removal circuit of the present invention includes a first transversal filter that receives the received output of the first polarized wave and performs waveform equalization, and a first transversal filter that receives the received output of the second polarized wave and performs waveform equalization. at least one delay circuit connected to the output of at least one of the first and second transversal filters and providing a constant delay time; and the first and second transversal filters at least one third branching signal that is branched and connected to at least one output of the third polarized wave and generates a compensation signal that cancels an interference signal of the first or second polarized wave that is included in the received output of the second or first polarized wave. a transversal filter, at least one signal synthesis circuit for synthesizing the output of the delay circuit and the output of the third transversal filter, and the first and second signal synthesis circuits including at least the output of this signal synthesis circuit.
and a control signal generation circuit that receives the output of the transversal filter and generates a control signal for controlling each of the variable weighting circuits of the first, second, and third transversal filters.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of a conventional example of a cross-polarization interference removal circuit using a transversal filter. In FIG. 1, a transversal filter 1 receives a demodulated V-polarized wave 101 and performs waveform equalization. Similarly, the transversal filter 2 receives the demodulated H polarized wave 102 and performs waveform equalization. Further, the transversal filter 3 branches the V-polarized wave 101 and generates a compensation signal 103 that cancels the interference signal of the V-polarized wave included in the H-polarized wave 102. Similarly, the transversal filter 4 branches the H polarized wave 102 and generates a compensation signal 104 that cancels the interference signal of the H polarized wave included in the V polarized wave. A signal synthesis circuit 5 synthesizes the outputs of transversal filters 1 and 4, and a signal synthesis circuit 6 synthesizes the outputs of transversal filters 2 and 3. Control signal generation circuit 7
are control signals 710, 720, 730 and 740 which receive the outputs of the signal synthesis circuits 5 and 6 and control the transversal filters 1, 2, 3 and 4, respectively.
occurs.

The operation of this cross-polarization interference removal circuit is an extension of an adaptive waveform equalizer using a known transversal filter, and each variable weighting circuit of the transversal filter 3 for removing cross-polarization interference of H polarization. 31, 32, 33, 34 and 35 are H
An error signal given by the difference between the demodulated baseband signal of polarization and its estimated value, and V causing interference
Control is performed to determine the correlation between the polarized wave and the demodulated baseband signal, and to generate a compensation signal that cancels the cross-polarization interference of the H polarized wave. The received outputs 101 and 102 of V polarization and H polarization are V ₁₀₁ and
Assuming H ₁₀₂ , with i as 0, ±1, ±2...V ₁₀₁ =V ₀ + 〓 ^i≠0 α _i V _i +Σβ _i V _i ...(1) H ₁₀₂ = H ₀ + 〓 ^i≠0 It can be expressed as γ _i H _i +Σδ _i V _i ...(2). Here, V ₀ and H ₀ are the reception codes of each polarization that are equal to the transmission code, and the second term is the preceding (i < 0) and subsequent codes (i > 0) based on waveform distortion.
The third term is the interference component from the synchronization code (i=0) of the cross-polarized component, the preceding code, and the subsequent code. The input signals 105 and 106 of the control signal generation circuit 7 have their formation distortion and cross-polarization interference reduced by the action of each transversal filter, but can be displayed in the same format as V ₁₀₅ =V ₀ + 〓 ^i≠0 α ′ _i V _i +Σβ′ _i H _i ……(3) H ₁₀₆ =H ₀ + 〓 ^i≠0 γ′ _i H _i +Σδ′ _i V _i ……(4) H determined by the control signal generation circuit 7
Considering that the estimated polarization value H _k has correctly estimated H ₀ , the error signal E is as follows from equation (4): E= 〓 ^i≠0 γ′ _i H _i +Σδ′ _i V _i ……(5), When we find the correlation between this and V ₁₀₅ in equation (3), we get
Since completely uncorrelated data is transmitted between the V polarized wave and the H polarized wave, and each data series is also uncorrelated in time series, if we ignore the high-order minute terms, Equation (5) (2) Among the terms, only δ′ ₀ V ₀ can be detected. Transversal filter 3 is used to reduce this value.
by controlling the variable weighting circuit 33 of the intermediate tap of
A compensation signal ₀ V ₀ is obtained that cancels the synchronization code component δ ₀ V ₀ of the cross-polarized interference of the H-polarized received output in equation (2). That is, the compensation coefficient ₀ is controlled so that δ ₀ − ₀ = δ′ ₀ →0 (6). Similarly, for the interference components from the preceding code and the subsequent code, by calculating the correlation between the signal obtained by shifting V ₁₀₅ in equation (3) by i bits and the error signal in equation (5), each A compensation signal _i V _i (i≠0) is obtained. A transversal filter 4 that removes cross-polarization interference of V-polarized waves is also controlled in the same manner.

In the circuit shown in Figure 1, transversal filter 3
is connected by branching the receiving output 101, so the compensation signal of the intermediate tap of the transversal filter is ₀ V ₁₀₁ = ₀ V ₀ + ₀ ( 〓 ^i≠0 α _i V _i +Σβ _i H _i ) ...(7). Also, variable weighting circuits 31, 3 for the leading and trailing taps of the transversal filter
Each compensation signal controlled by 2, 34, and 35 is
The signal V _{101 (i)} obtained by shifting V 101 by i bits is multiplied by each compensation coefficient δ _i to obtain _i V _101(i) = _i V _i + _i ( 〓 ^i≠0 α _i+j V _i+j + Σβ _{i+ j} H _i+j ) ...(8).

In both cases, when the waveform distortion is small, the cross-polarization compensation component is only the first term, and the synchronization, preceding, and subsequent interference components are independently controlled and stable and good compensation is performed, but when the waveform distortion becomes large, The control loops of each interference component influence each other, slowing down convergence and making the loops unstable, resulting in insufficient removal of cross-polarization interference and instability, which tends to cause code errors. There is a drawback.

As is clear from the above explanation, one method for eliminating the above-mentioned drawback is to eliminate waveform distortion of the inputs of the transversal filters 3 and 4 for cross-polarization interference removal, that is, to eliminate the waveform distortion of the inputs of the transversal filters 3 and 4 for removing cross-polarization interference is branched from the output side of transversal filters 1 and 2 that equalize waveform distortion. With such a connection, cross-polarization interference can be stably removed even when waveform distortion is large, and the occurrence of code errors can be suppressed.

FIG. 2 is a block diagram of the first embodiment of the present invention, which includes the same transversal filters 1, 2, 3 and 4 as in FIG. 1, signal synthesis circuits 5 and 6,
from a control signal generation circuit 7 and delay circuits 8 and 9 inserted between the outputs of transversal filters 1 and 2 and signal synthesis circuits 5 and 6 and giving the same delay time as the third transversal filters 3 and 4; The main difference from FIG. 1 is that transversal filters 3 and 4 are replaced by transversal filter 1.
and 2 are branched and connected from the output side, and time alignment is performed by delay circuits 8 and 9. As mentioned above, cross-polarization interference can be removed without being affected by waveform distortion. will be held. Note that outputs 701 and 702 of the control signal generation circuit 7 are reproduced baseband signals of V and H.

FIG. 3 is a block diagram of a second embodiment of the present invention using an intermediate frequency band transversal filter.
1 and 112, intermediate frequency band transversal filters 13 and 14 connected in the same manner as in FIG. 2, delay circuits 18 and 19, and a signal synthesis circuit 15. 16, the same control signal generation circuit 7 as in FIG. 2, and demodulators 17, 17' inserted between the signal synthesis circuits 15, 16 and the control signal generation circuit 7.
It is composed of. The technique of controlling a transversal filter in the intermediate frequency band using demodulated baseband information to perform waveform equalization is based on a technique in which the carrier frequency of the input modulation signal, that is, the intermediate frequency _c , is a positive integer of the modulation frequency _s of the input modulation signal. It has not been used in general microwave band wireless communications in which the intermediate frequency cannot necessarily be selected to be _c = N _s (N is a positive integer).
However, in Japanese Patent Application No. 56-215271, _c ≠
A method has been proposed that can also be applied to the case of N _s . According to this technique, a cross-polarization interference removal circuit using a transversal filter in the intermediate frequency band can also be used in general, and the present example The circuit produces the same effect as shown in FIG.

FIG. 4 is a block diagram of a third embodiment of the present invention, which uses a baseband transversal filter when both V and H polarized waves are subjected to orthogonal modulation. Transversal filters 21 and 22 each receive in-phase and orthogonal two-line baseband signals, compensate for waveform distortion and orthogonal symbol interference, and send in-phase and orthogonal outputs to delay circuits 28, 28', 29, 29' and It is sent to transversal filters 23, 23', 24, 24'. The transversal filter is configured to generate two sets of compensation signals that are each controlled separately by two sets of control signals, and the outputs thereof are sent to a signal combining circuit 2 with orthogonal and in-phase outputs of opposite polarization, respectively.
5, 25', 26, 26'. The control signal generation circuit 27 generates in-phase and quadrature signals 10 of each polarization.
5, 105', 106, 106' and each error signal to generate respective control signals. Transversal filter 2
The control signals 271 and 272 of No. 1 and 22 include four sets of control signals for eliminating in-phase and orthogonal waveform distortion and interference between orthogonal symbols, respectively. With the above configuration, cross-polarization interference between two orthogonally modulated polarized waves can be removed even when waveform distortion is large.

FIG. 5a is a block diagram of an embodiment of the transversal filters 23, 23', 24, 24' of FIG. and two sets of variable weighting circuits 41 to 41 branched from before and after each delay circuit 40 and controlled by separate control signals, respectively.
45 and 41' to 45', and two adders 46 and 46' that add the outputs of each variable weighting circuit to generate two sets of compensation signals 401 and 402.
It is a tap transversal filter. This is a set of delay circuits that performs the functions of two transversal filters 3 shown in FIG. 1, and 23, 23', 24, and 24' in FIG. Can be replaced with a transversal filter. Conversely, among the two outputs of the transversal filters 23 and 23', 24 and 24', the same signal combining circuit 26 or 26', 2
5 or 25' are synthesized in advance, and this synthesis circuit and the transversal filters 23, 23' shown in FIG. 5a have the same two inputs and outputs as the transversal filters 21, 22. It can also be configured as one transversal filter that receives four sets of control signals.

FIG. 5b is a block diagram of an embodiment of an intermediate frequency band transversal filter used in the case of orthogonal modulation, in which an intermediate frequency band delay circuit 50 and variable weighting circuits 51 to 51 are connected in the same manner as in FIG. 5a. 55
and 51' to 55' adders 56, 56', and a 90° hybrid 57 that combines the outputs of the adders 56, 56' with a phase difference of 90°, and a pair of inputs and outputs prevents the interference of two orthogonal components. Removal can be performed. Therefore, even when orthogonal modulation is used, it can be handled with almost the same circuit configuration as in FIG. 3, unlike when processing in the baseband band. However, the demodulators 17 and 17' shown in FIG. 3 are used as demodulators for orthogonal modulation that generate two orthogonal baseband outputs, and the control signal generation circuit 7 is used as the demodulator shown in FIG. 4 that inputs the demodulated output. It is necessary to change the control signal generation circuit 27 to the one shown in FIG. A configuration in which one of the intermediate tap variable weighting circuits 53, 53' is omitted from the circuit of FIG. 5b can also be used by correspondingly changing the control signal generating circuit. Although the explanation so far has been made regarding a 5-tap transversal filter having 4 delay circuits, it goes without saying that transversal filters having a number of taps other than 5 can be used in the present invention.

In the above description, the control signal generation circuit is
~ As is clear from Figure 4, the ZF generates a control signal by determining the correlation between the demodulated baseband signal on the side that is causing interference on the output side of the transversal filter and the error signal on the side that is receiving interference. The above explanation assumes that the equalization algorithm of the (zero-focusing) method is used, but when using a baseband transversal filter, the signal and error signal on the input side of the transversal filter, which is also known as the ZF method, can be used. It is also possible to apply the ME method (root mean square equalization method) algorithm to find the correlation of In actual circuits, a simple algorithm is used in which the signal is compared with a certain threshold value, digitized, and controlled. In any of the above methods, demodulated baseband signal information of both polarizations is required to generate a control signal, but a control method using a perturbation signal that does not require demodulated signal information on the side that is causing interference. Special request was made in 1984.
055530, and it is also possible to apply this control method to the present invention. FIG. 6 is a block diagram of an embodiment of a control signal generation circuit using this perturbation signal method, in which an error detector 60 generates an error signal from a demodulated signal of the in-phase or quadrature output of the polarized wave whose interference is to be removed. and an oscillator 7 that generates a perturbation signal to be superimposed on the control signal of the variable weighting circuit.
1. a correlator 72 that calculates the correlation between the error signal and the perturbation signal; an integrator 73 that integrates the output of the correlator 72;
An inverter 74 inverts the sign of the output and sends out a control signal, an adder 75 superimposes the control signal and the perturbation signal, and the magnitude of the superimposed perturbation signal is determined by the average value of the error signal passed through the low-pass filter 76. The controller 70 includes an attenuator 77 to control the attenuator 77. Controllers 70, 70a, 70 that control each variable weighting circuit of the transversal filter 3
The frequencies of the perturbation signals b, 70c, and 70d are selected to be, for example, ω ₀ , 2ω ₀ , 3ω ₀ . . . so as to be orthogonal to each other. In this method, a correlator 72 determines whether the perturbation frequency component of the error signal is positive or negative, the direction in which the control signal is changed is determined, and interference is removed by controlling the signal through an integrator 73 and an inverter 74. The details of this operating principle can be found in the patent application published in 1983.
-055530, so please refer to it if necessary.

The circuits shown in Figures 1 to 4 described above are designed to be used in a terrestrial communication system in which signals of orthogonal polarization are both received and used on the receiving side, but in a satellite communication system. Therefore, it is expected that one ground station will not necessarily use both polarizations, but will use only one polarization. In such stations, there is no need to compensate for interference signals included in polarized waves that are not used, and some circuits can be omitted in the embodiments of FIGS. 2 to 4. For example, in FIG. 2, when only V polarization is used, the transversal filter 3 and signal synthesis circuit 6 are unnecessary, and the delay circuit 9 can be included in the control signal generation circuit 7, simplifying the configuration. can be converted into

As explained in detail above, the cross-polarization interference cancellation circuit of the present invention can stably eliminate cross-polarization interference even when there is a lot of waveform distortion, and can prevent the occurrence of code errors even when there is large faving etc. This has the effect of suppressing the noise and ensuring good communication.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional cross-polarization interference removal circuit, FIG. 2 is a block diagram of a first embodiment of the present invention, and FIG. 3 is a block diagram of a conventional cross-polarization interference removal circuit. 4 is a block diagram of a third embodiment of the present invention applied to quadrature modulation, and FIG. 5a is a block diagram of an embodiment of the transversal filter used in FIG. 3. 5b is a block diagram of an embodiment of an intermediate frequency band transversal filter, and FIG. 6 is a block diagram of an embodiment of a control signal generation circuit using the perturbation signal method. 1, 2, 3, 4, 21, 22, 23, 23',
24, 24'... Transversal filter (baseband band), 11, 12, 13, 14... Transversal filter (intermediate frequency band), 5, 6,
25, 25', 26, 26'... Signal synthesis circuit (baseband band), 15, 16... Signal synthesis circuit (intermediate frequency band), 8, 9, 28, 28', 29, 29',
40...Delay circuit (baseband band), 18, 19,
50... Delay circuit (intermediate frequency band), 7, 27... Control signal generation circuit, 17, 17'... Demodulator, 31-
35, 41-45, 41'-45', 51-55,
51' to 55'...variable weighting circuit, 46, 46',
56, 56', 75...Adder, 60...Error detector,
70, 70a, 70b, 70c, 70d...controller, 71...oscillator, 72...correlator, 73...integrator, 74...inverter, 76...low-pass filter, 7
7...Attenuator.

Claims (1)

[Claims] 1. A first transversal filter that receives the received output of the first polarized wave and performs waveform equalization, and a second transversal filter that receives the received output of the second polarized wave and performs waveform equalization. a transversal filter; at least one delay circuit connected to the output of at least one of the first and second transversal filters and providing a constant delay time; and at least one of the first and second transversal filters. at least one third branch connected to the output and generating a compensation signal that cancels the interference signal of the first or second polarization included in the received output of the second or first polarization;
a transversal filter, at least one signal synthesis circuit for synthesizing the output of the delay circuit and the output of the third transversal filter, and the first and second transformers including at least the output of the signal synthesis circuit. a control signal generation circuit that receives the output signal of the versatile filter and generates a control signal for controlling each of the variable weighting circuits of the first, second, and third transversal filters. removal circuit. 2 the delay circuit, the signal synthesis circuit, and the third
2. The cross-polarization interference removal circuit according to claim 1, wherein said transversal filter is provided symmetrically with respect to both said first and second polarized waves. 3. The received outputs of the first and second polarized waves are demodulated baseband signals, and the first, second, and third transversal filters, the delay circuit, and the signal synthesis circuit operate in the baseband frequency band. Claim 1 consisting of a circuit
The cross-polarization interference removal circuit according to item 1 or 2. 4. The received outputs of the first and second polarized waves are two rows of baseband signals of demodulated orthogonal modulated waves, and the first and second transversal filters each have in-phase and orthogonal input/output. ,
The third transversal filter is branched and connected to the in-phase and quadrature outputs of the first and second transversal filters, respectively, and the signal synthesis circuit is connected to the in-phase and quadrature outputs of the first and second transversal filters, respectively. The output of the delay circuit connected to the output of the third transversal filter is configured to be combined with the output of the third transversal filter connected to the in-phase and quadrature outputs of the second and first transversal filters. A cross-polarization interference removal circuit according to claim 3. 5. The received outputs of the first and second polarized waves are intermediate frequency signals, and the first, second, and third transversal filters, the delay circuit, and the signal synthesis circuit are configured with intermediate frequency band circuits. , the cross-polarized wave according to claim 1 or 2, wherein a demodulator is inserted between the signal synthesis circuit or the first or second transversal filter and the control signal generation circuit, respectively. Interference cancellation circuit. 6. The control signal generation circuit generates the control signal of the third transversal filter, respectively.
An error signal obtained from the difference between the originally independent demodulated baseband signal of the polarized wave whose interference should be removed and its estimated value, and the demodulated baseband signal that is originally independent of the polarized wave that is causing the interference. 6. The cross-polarization interference canceling circuit according to claim 1, wherein the cross-polarization interference canceling circuit is configured to generate the cross-polarization interference by determining the correlation between the two. 7. The control signal generation circuit superimposes perturbation signals of frequencies that are orthogonal to each of the control signals that control each variable weighting circuit of the third transversal filter, so that the originally independent polarized waves whose interference is to be removed are The error signal obtained from the difference between the demodulated baseband signal and its estimated value is generated by determining the correlation between the perturbation signal and the perturbation signal. ，
The cross-polarization interference removal circuit according to item 4 or 5.