JPS6239860B2 - - 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 currently used frequency bands with high practical value is expected. Thoughts are growing.

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.

Therefore, in order to achieve cross-polarization sharing, it is necessary to improve the polarization characteristics of antennas and power supply equipment, as well as develop a cross-polarization compensation circuit that compensates for the deterioration of polarization characteristics during radio wave propagation due to rain, etc. This has become an important 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 adopted 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 (interfering side) by a compensation coefficient, and subtracts it from the received signal of the other (desired side) to eliminate 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 _V0 by a compensation coefficient Ω to obtain the interference cancellation signal He in addition to the horizontal received signal _H0 . . 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 object of the present invention is to overcome the above-mentioned conventional drawbacks and to
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 a complex multiplier.

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 the error between the compensated received signal and its identification value, and an interference side that outputs when the real component and imaginary component of the interference side reception signal are both positive and equal in magnitude. a discriminator, an adder and a subtracter that output the sum and difference between the real component and the imaginary component of the output value of the discrimination error detector, and outputs of the adder and subtracter as outputs of the interference side discriminator. The present invention is characterized in that it includes a switch that conducts through the switch, and a low frequency generator that smoothes the output of the switch and outputs the compensation coefficient.

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, if the real part of the received signal V ₀ is _VR , the imaginary part V _I , the real part of the identification error signal e is e _R , and the imaginary part e _I , then V ₀ = _VR + jV _I ...(7) e= _{E _ _} ^_ _{_ _ _ _ _ _ _ _ _ _ IeR )} . Here, when _VR = V _I > 0 ... (9), V ₀ ^* e∝ (e _R + e _I ) j (e _I − e _R ) ... (10), so the above (10 ) can be obtained using only an adder. That is, the present invention removes the interference wave component 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 side reception 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 outputted by the comparator circuit 33. |V _R |≒|V _I | is detected by comparing. 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 one embodiment of the present invention. 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 vertically polarized received signal V ₀ is inputted to the input terminal 601. The vertical polarization received signal V ₀ is sent to the multiplier 61
is multiplied by a compensation coefficient Ω and added to the horizontally polarized received signal H ₀ in an adder 60 . Therefore, the interference cancellation signal He is output to the output terminal 602. In other words, equation (3) is realized. The interference cancellation signal He is
connected to the input terminal 100 of the identification error detector 1;
The discriminator 10 outputs the discrimination value H^e, the subtracter 11 calculates the difference from the above He, and the discrimination error e is output from the terminal 101. The real part e _R and the imaginary part e _I of the identification error e are added by an adder 22 built in the correlator 2 and subtracted by a subtracter 23 . The output of the adder 22 is (e
_R +e _I ) is given, and the output of the subtracter 23 gives (e _R −e _I ) on the right side of equation (10). These outputs are supplied to integrators 50 and 51, respectively, when the switch 4 (switches 40, 41) is closed, and are subjected to the integration operation shown in equation (6) 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 an 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 51 to become the imaginary part of the compensation coefficient Ω. Ω _I. Integrators 50 and 51 constitute a complex low-pass filter 50. That is, (6)
Ω in the equation can be obtained without using a multiplier.
As described above, the compensation coefficient Ω is multiplied by the vertically polarized received signal V ₀ by the multiplier 61 and added to the horizontally polarized received signal H ₀ to cancel polarization interference. The remaining compensation becomes the identification error signal e, and the next compensation coefficient is corrected by the above-described operation.

In addition, the condition for the output of the interfering side discriminator is not limited to equation (9); it also detects a signal that satisfies |V _R |= |V _I |, and determines the polarity of the correlator depending on the quadrant to which V ₀ belongs. You may try changing it.

As described above, in the present invention, an interference cancellation signal is obtained by multiplying the interfering side polarized signal by a compensation coefficient and adding it to the signal on the receiving side, and the difference between the interference cancellation signal and the identification signal, i.e. Since the system is configured to modify the compensation coefficient only when the interfering signal satisfies certain conditions using the sum and difference signals of the real and imaginary parts of the identification error signal, no multiplier is used. The compensation coefficient can be changed optimally and automatically. That is, there is an effect that a good interference wave cancellation signal can be obtained and the quality of received data is improved. According to the present invention, it is possible to quickly and accurately follow changes in polarization interference due to Faraday rotation in outer space in satellite communications.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing each signal point of a 16-level amplitude phase modulation signal and signal points that satisfy specific conditions, Fig. 2 is a circuit diagram showing an example of an interference side discriminator used in the present invention, and Fig. 3 is a diagram showing signal points that satisfy specific conditions. FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, 1...Identification error detector, 2...Correlator, 3...Interfering side discriminator, 4...Switch, 5...
...Low frequency filter, 6...Polarization interference subtraction circuit, 10...
... Discriminator, 11 ... Subtractor, 22 ... Adder, 2
3...Subtractor, 30, 33...Comparator, 31...
Subtractor, 32... folding circuit, 34... 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 interference side discriminator that outputs an error when both the real component and the imaginary component of the interfering side received signal are positive and equal in magnitude; an adder and a subtracter that output the sum and difference between the real component and the imaginary component of the output value of the detector; and a switch that connects the output of the adder and subtracter with the output of the interference side discriminator. , and a low frequency device that smoothes the output of the switch and outputs the compensation coefficient.