JPS6239861B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technology for compensating for cross-polarization interference that occurs when orthogonal polarizations are shared in wireless transmission.

Microwave band wireless communications are rapidly developing, centering on terrestrial communications and satellite communications. The demand for wireless communications is expected to further increase in the future due to the expansion of mobile communication services, etc., and along with the development of sub-millimeter wave and higher frequency bands, so-called frequency reuse of current frequency bands with high practical value is expected. Thoughts are growing. The use of orthogonal polarization is already specified in the CCIR (Consultative Committee on International Radio Communications) recommendations regarding FM radio frequency allocation in the 4 to 6 GHz range.
In addition, in satellite communications, INTELSAT (International Telecommunication Satellite Organization) is expected to commercialize orthogonal polarization sharing technology in the 4 to 6 GHz band, which has been used with single polarization on V-series satellites.

Originally, free space is independent of two orthogonal polarized waves, and is a transmission line that can simultaneously transmit both polarized waves. However, in actual propagation paths, there is anisotropy in media such as rain, and orthogonal polarized waves If a shared system is adopted, coupling between polarized waves due to the generation of cross-polarized waves will cause interference between different polarization channels.

In order to achieve this shared use of orthogonal polarization, it is important to improve the polarization characteristics of antennas and power supply equipment, as well as develop cross-polarization compensation circuits that compensate for deterioration of polarization characteristics during radio wave propagation due to rain, etc. This has become an issue.

Cross polarization compensation technology automatically compensates for such coupling between polarized waves by providing a compensation circuit within an antenna feeder or wireless device.

Conventionally, microwave band communication has centered on analog transmission, mainly FM, but in recent years, digital transmission has come to be used in the microwave band as well, and cross-polarization compensation methods have also been developed to take advantage of the characteristics of digital transmission. Proposals for more efficient methods are requested.

Conventionally, this type of circuit receives two mutually orthogonal polarized waves, multiplies the received signal of one (the interfering side) by a compensation coefficient, and subtracts it from the received signal of the other (the desired receiving side) to eliminate the interference. We are trying to remove the ingredients. For example, considering horizontal polarization and vertical polarization,
When independent data H and V are placed on each, due to the polarization interference αV and βH that occurred during propagation, the horizontally polarized received signal H ₀ and the vertically polarized received signal V ₀ become H ₀ = H + αV …… (1) V ₀ =V+βH ...(2) Now, if we consider the case where we want to receive data H, it is common to multiply the vertically polarized received signal V ₀ by a compensation coefficient Ω and add it to the horizontal received signal H ₀ to obtain the interference cancellation signal He. be. That is, He=H ₀ +ΩV ₀ ...(3) Therefore, He=H+αV+Ω(V+βH)=H+(α+Ω)V+Ω・β・H≒H+(α+Ω)V
...(4) That is, by setting α=-Ω, He≒H ...(5) and polarization interference is removed. At this time, Ω is generally controlled so that Ω ⁽ⁱ⁺¹⁾ = Ω ⁽ⁱ⁾ −kV ₀ ^* ·(He−H^e) (6). Here, H^e is the discrimination value of He, and He-H^e is the discrimination error e, which includes interference from vertically polarized waves. Therefore, e and
If Ω is controlled in a direction that minimizes the correlation with V ₀ , α=−Ω, and interference will be removed.

However, V ₀ ^* ·e is a complex multiplication and requires an expensive analog multiplier, which is very expensive especially when the transmission rate is high.

The purpose of the present invention is to solve the above-mentioned conventional drawbacks and
The object of the present invention is to provide an inexpensive polarization interference cancellation circuit that can obtain a value proportional to the above V ₀ ^* ·e without using multiple multipliers.

The interference cancellation circuit of the present invention receives two mutually orthogonal polarized waves, multiplies one received signal by a compensation coefficient, and adds it to the other received signal to remove the polarization interference component. , an identification error detector that detects an error between the compensated received signal and its identification value; an adder that outputs the sum and difference between the real part and the imaginary part of the identification error signal output from the error detector; a subtracter, an interference side discriminator that detects that the absolute values of the real part and the imaginary part of the received signal on the interference polarization side are equal and outputs a control signal according to which quadrant it belongs to; and the interference side discriminator. a switch that changes the sign combination of the output signals of the adder and the subtracter in response to a control signal output from the switch, and a low-frequency wave generator that smooths the output of the switch; The present invention is characterized in that the compensation coefficient is obtained from the output of the wave generator.

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

First, the principle of the present invention will be explained. Now, let V _R be the real part of the received signal V ₀ , V _I be the imaginary part, e _R be the real part of the identification error signal e, and e _I be the imaginary part, then V ₀ = V _R +jV _I ...(7) e=e _R +je _I ...(8) Therefore, V ₀ ^*・e=(V _R −jV _I )(e _R +je _I ) =(V _R e _R +V _I e _I )+j(V _R e _I − V _I e _R ). Here, when _VR = V _I > 0 ... (9), V ₀ ^* e∝ (e _R + e _I ) + (e _I − e _R ) ... (10), so the above (10 ) can be obtained using only an adder. Therefore, the interference wave component can be removed by outputting the value of equation (10) only when equation (9) is satisfied and thereby controlling the compensation coefficient.

For example, among the 16-level amplitude phase modulation (16QAM) signals shown in FIG. 1, the signals marked with black circles satisfy equation (9).

FIG. 2 is a circuit diagram showing an example of an interference side discriminator that outputs an output signal when formula (9) is satisfied. That is, the real part V _R and the imaginary part V _I of the interfering received signal are respectively input to the terminals 300 and 301, subtracted by the subtracter 31, outputted as the absolute value of the difference by the folding circuit 32, and then sent to the comparator circuit. By comparing at 33, |V _R |≒|V _I | is detected. V _R >
0 is detected by comparator 30. Comparators 30 and 34
Both outputs are ANDed by an AND circuit 34 and output to an output terminal 302.

FIG. 3 is a block diagram showing an example of a polarization interference removal circuit using the above-described circuit. That is,
For example, the horizontally polarized received signal H ₀ is input to the input terminal 600 of the polarization interference subtraction circuit 6, and the input terminal 601
The vertically polarized received signal V ₀ is input to . The vertically polarized received signal V ₀ is multiplied by a compensation coefficient Ω in the multiplier 61, and the horizontally polarized received signal H ₀ is outputted in the adder 60.
added to. Therefore, the interference cancellation signal H _e is output to the output terminal 602. In other words, equation (3) is realized. The interference cancellation signal H _e is connected to the input terminal 100 of the discrimination error detector 1 , the discriminator 10 outputs the discrimination value H^e, and the subtractor 11 calculates the difference from the above H _e. The identification error e is output from the terminal 101. Real part e _R and imaginary part e _I of identification error e
are added by an adder 22 built in the correlator 2 and subtracted by a subtracter 23. Adder 2
The output of the subtracter 23 gives (e _R +e _I ) on the right side of equation (10), and the output of the subtracter 23 gives (e _R −e _I ) on the right side of equation (10). These outputs are connected to switch 4 (switch 4
0, 41) are respectively supplied to integrators 50 and 51, where the integral operation shown in equation (6) is performed and smoothed. The switch 4 is a switch that is closed by the output of the interference side discriminator 3, and the interference side discriminator 3 is configured as shown in FIG. Give output. Therefore, since the switch 4 becomes conductive only when the equation (9) is satisfied, the output of the correlator 2 at this time is proportional to the V ₀ ^* e according to the equation (10). The output of the adder 22 is smoothed by the integrator 50 to become the real part Ω _R of the compensation coefficient Ω, and the output of the subtracter 23 is smoothed by the integrator 50.
The compensation coefficient Ω is smoothed by the imaginary part Ω _I of the compensation coefficient Ω. Integrators 50 and 51 constitute a complex low-pass filter 5. That is, Ω in equation (6) can be obtained without using a multiplier. The compensation coefficient Ω is calculated by the multiplier 61 as described above for the vertically polarized received signal.
Polarization interference is canceled by multiplying by V ₀ and adding it to the horizontally polarized received signal H ₀ . The remaining compensation becomes the identification error signal e, and the next compensation coefficient is corrected by the above-described operation.

However, in the above method, only two points of the 16-value amplitude phase modulation (16QAM) signal shown in FIG. 1 are used, so the control speed is slow. In order to increase control speed, it is necessary to use more signals. Therefore, in the present invention, the control speed is increased by using all the signal points satisfying |V _R |=|V _I |. For example, in the case of 16QAM, in Figure 4 ●,
Use the 8 points (4 sets) indicated by ▲, ■, and ▼. ●
The signal marked satisfies Equation (9) above, and according to the right side of Equation (10),
As mentioned above, a signal proportional to V ₀ ^* ·e can be obtained. In the signal marked ■, the real number is negative and the imaginary number is positive, so V ₀ ^* e∝−(e _R −e _I )−j(e _R +e _I )……(11), and the signal marked ▼ is , V ₀ ^* ∝−(e _R +e _I )+j(e _R −e _I ) ……(12) The signal marked with ▲ is V ₀ ^* e∝(e _R −e _I )+j(e _R −e _I )
...(13) becomes. Detection of a signal point group for which equations (10) to (13) hold can be performed, for example, by an interference side discriminator as shown in FIG. That is, for example, the real part V _R of the vertically polarized received signal V ₀ is input to the terminal 300, and the imaginary part V _I is input to the terminal 301. Signs of the real part V _R and the imaginary part V _I are determined by the positive/negative comparators 35 and 36, and the outputs are sent to AND circuits 39a to 39d.
input. The AND circuit 39a outputs a high level for the signal in the first quadrant, and
9b to 39d output high level signals for the second to fourth quadrants, respectively. On the other hand, the real part V _R ,
Input the imaginary part V _I to folding circuits 37 and 38,
These outputs are input to a subtracter 31 and subtracted. The output of the subtracter 31 is compared with a constant level by a comparator 33 via a folding circuit 32, and |V _R
|≒|V _I | is determined, and the output of the comparator 33 is used as one input of the AND circuits 34a to 34d. The outputs of the AND circuits 39a-39d are connected to the other inputs of the AND circuits 34a-34d, respectively. Therefore, the AND circuit 34a outputs a high level for the signal indicated by a circle in FIG. 4, and the AND circuits 34b to 34d each output
Outputs high level for the signals indicated by marks, ▼ marks, and ▲ marks. Therefore, by using these outputs as control signals and combining the identification error signals, equation (10) can be obtained.
The right-hand side of ~(13) can be created.

FIG. 6 is a block diagram showing one embodiment of the present invention. That is, the horizontally polarized received signal H ₀ is input to the terminal 600, and the vertically polarized received signal V ₀ is inputted to the interference side discriminator 3'' via the terminals 601 and 603.The interference side discriminator 3'' It has the configuration shown in the figure, and controls the opening and closing of the switch 4' by outputting a control signal according to the conditions of the input signal.

On the other hand, the vertically polarized received signal V ₀ is multiplied by the compensation coefficient Ω input from the terminal 604 in the polarization interference removal circuit 6, and then added to the horizontally polarized received signal H ₀ .
The interference canceled signal He is output from the terminal 602.
The interference wave cancellation signal He is connected to terminal 1 of identification error detector 1.
00, and the identification error signal e is input from the terminal 101.
outputs. The real part e _R and imaginary part e _I of the identification error signal e are correlators 2, 2', 2'', and 2, respectively.
(e _R +e _I ) and (e _R −e _I ) are calculated within the equation, and each correlator outputs a signal corresponding to the right side of equations (10) to (13). The switch 4' selectively selects the output of each of the correlators in response to the control signal output from the interference side discriminator 3'' and inputs the selected output to the input terminal 500 of the low frequency filter 5. The waveform generator 5 smoothes the input signal and outputs it from an output terminal 501 as a compensation coefficient Ω.

In this example, 8 out of 16 signals shown in FIG.
Since these signals can be used to control the coefficient Ω, rapid control is possible. In other words, it is possible to respond even when the interference polarization fluctuates significantly, and the response time is approximately 4
Double the control speed. Therefore, it is possible to quickly and precisely follow changes in polarization interference due to Faraday rotation in outer space, for example in satellite communications.

In addition, in the above, adders and subtracters were provided in correlators 2, 2', 2'', and 2, respectively, and the right sides of equations (10) to (13) were found in the correlators, but for example, correlator 2 The two outputs (e _R +e _I ) and (e _R −e
_I ) If configured to add or decrease in accordance with the control signal in the switch 4', the correlators 2', 2'',
2 can be omitted.

As described above, in the present invention, an adder that adds the embodiment of the identification error signal and the imaginary part, and a subtracter that subtracts are provided, so that the magnitudes of the real part and imaginary part of the interference polarization received signal are When they are equal, the compensation coefficient is controlled by changing the output combination of the adder and subtracter in accordance with the quadrant to which they belong, so the number of signal points that can be used for compensation coefficient control increases, resulting in rapid control speed. can be obtained. Furthermore, the configuration is simple because the compensation coefficient can be optimally and automatically changed without using a multiplier.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing each signal point of a 16-level amplitude phase modulation signal and a signal point that satisfies a specific condition, Fig. 2 is a circuit diagram showing an example of an interference side discriminator that detects the above specific condition, and Fig. 3 The figure is a block diagram showing an example of a polarization interference removal circuit that changes the compensation coefficient under the above specific conditions. Figure 4 shows a signal in which the real part and imaginary part of a 16-value amplitude phase modulation signal are equal in size. FIG. 5 is a circuit diagram showing an example of an interference side discriminator for detecting the above conditions for use in the present invention, and FIG. 6 is a block diagram showing an embodiment of the present invention. In the figure, 1...discrimination error detector, 2,
2', 2'', 2... Correlator, 3, 3''... Interfering side discriminator, 4, 4'... Switch, 5... Low frequency device, 6... Polarization interference subtraction circuit, 10 ...discriminator,
11...Subtractor, 22...Adder, 23...Subtractor, 30, 33, 35, 36...Comparator, 32,
37, 38... Return circuit, 34, 34a to 34
d, 39a to 39d...AND circuit, 40, 41
... Switch, 50, 51 ... Integrator, 60 ... Adder, 61 ... Multiplier.

Claims (1)

[Claims] 1 In a polarization interference removal circuit that receives two mutually orthogonal polarized waves and removes the polarization interference component by multiplying one received signal by a compensation coefficient and adding it to the other received signal, the received signal after compensation is an identification error detector that detects an error between the identification error signal and its identification value; an adder and a subtractor that output the sum and difference between the real part and the imaginary part of the identification error signal output by the error detector; and an interference polarization detector. An interfering side discriminator that detects that the absolute values of the real part and imaginary part of the side received signal are equal and outputs a control signal according to which quadrant it belongs to, and corresponds to the control signal output from the interfering side discriminator. a switch that changes the sign combination of the output signals of the adder and the subtracter and outputs the output signals, and a low-frequency wave generator that smoothes the output of the switch, and the compensation is performed using the output of the low-frequency wave generator. A polarization interference removal circuit characterized in that a coefficient is obtained.