JP3458834B2 - Cross polarization interference cancellation system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross polarization interference cancellation system by controlling transmission power in microwave communication, and more particularly to a cross polarization interference cancellation system provided with cross polarization interference compensation means on the receiving side.

[0002]

2. Description of the Related Art In a case where a two-route microwave communication line is constructed by using vertically polarized waves (V polarized waves) and horizontal polarized waves (H polarized waves) which are orthogonal to each other between facing stations, fading, etc. Due to the influence, cross polarization interference occurs on the receiving side. In order to eliminate such cross polarization interference, the reception side sends the transmission power control information from the reception side to the transmission side according to the reception status, and the transmission side transmits the V polarization and the H polarization based on the transmission power control information. The polarization transmission power is controlled individually.

A conventional cross polarization interference canceling system using transmission power control is disclosed in, for example, Japanese Patent Laid-Open No. 4-252223.
It is disclosed by the publication. FIG. 8 is a block diagram showing its configuration.

In FIG. 8, a reception level determination circuit 44 on the reception side is provided with an AGC voltage Lv of a V-polarized AGC amplifier (AGCA) 41v and an AGC voltage of an H-polarized AGC amplifier 41h.
The reception levels of the V polarization and the H polarization are determined based on the GC voltage Lh, and the determination result is transmitted to the transmission side. The transmission side controls the transmission power of the V polarization and the H polarization based on the determination result from the reception side.

For example, when the reception level of the V polarization is lowered due to fading and the reception level of the H polarization is higher than the reception level of the V polarization, the one with the higher reception level (H polarization) is detected. By controlling the transmission output and controlling the variable attenuator 12h so that the reception level of the H polarization becomes an appropriate level, cross polarization interference caused by fading is removed.

[0006]

In the above-mentioned conventional example,
The reception side determines the reception levels of the V polarization and the H polarization, and the transmission side controls the transmission powers of the V polarization and the H polarization according to the determination result based on the reception level, so that crossing due to fading occurs. Polarization interference is removed.

However, when the receiving side is provided with means for compensating cross-polarization interference by generating an interference compensation signal by a different polarization demodulator and a transversal filter, the reception level is detected as in the conventional example. Even if the transmission power control is performed after that, the amount of interference compensation differs depending on the characteristics of the transversal filter on the V polarization side and the H polarization side or the characteristics of the different polarization demodulator. It is difficult to detect, and there is a problem that proper transmission power control cannot be performed.

An object of the present invention is to provide a system including cross polarization interference compensating means on the receiving side, which enables appropriate and fine control of transmission power according to the interference situation, and improves cross polarization interference compensation characteristics. It is to provide a cross polarization interference cancellation system.

[0009]

A cross polarization interference canceling system according to the present invention is a transversal filter for generating an interference compensation signal for compensating cross polarization components of two orthogonal polarizations on a receiving side. With each,
A cross polarization interference cancellation system comprising means for generating transmission power control information so as to improve interference compensation characteristics in accordance with an interference situation and transmitting the transmission power control information to a transmission side, wherein a tap coefficient supplied to the transversal filter is used. Based on the interference compensation signal, it is determined that the level of the interference compensation signal is close to a saturation state, and the interference power level determining unit generates the transmission power control information.

In the interference level determining means, at least one tap coefficient of a transversal filter for generating an interference compensation signal on one polarization side of the two orthogonal polarizations reaches a value close to its upper limit value. Then, the transmission power control information is generated so as to increase the transmission power on the other polarization side of the two polarizations. Specifically, a comparison circuit that compares a tap coefficient of the transversal filter corresponding to each of the two orthogonal polarizations with a preset threshold value close to the upper limit value of the tap coefficient, and these comparison circuits, When it is detected that at least one of the tap coefficients has reached the threshold value, a determination circuit that generates the transmission power control information so as to increase the transmission power on the different polarization side with respect to the detected polarization side. Have and.

Further, the threshold value set in the comparison circuit is
It may be a plurality of values close to the upper limit value of the tap coefficient.

Furthermore, there is a reception level detection means for detecting the reception electric field levels of the two orthogonal polarized waves, and the interference level determination means has the transmission power control based on the tap coefficient and the reception electric field level. Generate information. Specifically, the interference level determination means is configured to, when at least one of tap coefficients of a transversal filter that generates an interference compensation signal on the own polarization side of the two orthogonal polarizations reaches the threshold value. When the reception electric field level on the polarization side is in a good reception electric field state in which the cross polarization discrimination does not change with respect to the change, the transmission power control is performed so as to increase the transmission power on the different polarization side. When the information is generated and the reception electric field level on the self-polarization side is in a weak reception electric field state in which the cross polarization discrimination degree changes in response to the change, the transmission power on the self-polarization side is increased. The transmission power control information is configured to be generated.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Two routes of microwave communication are carried out by utilizing vertical polarization (V polarization) and horizontal polarization (H polarization) orthogonal to each other. The structure of the transmission side and the reception side which oppose in the system to perform is shown.

Here, the configuration on the transmitting side is basically the same as that of the conventional example shown in FIG. 8, and the same components are designated by the same reference numerals. Further, the symbols “v” and “h” indicate the vertical polarization (V polarization) side and the horizontal polarization (H polarization) side, respectively.

In FIG. 1, on the transmission side, modulators (MODs) 11v and 11h and modulators (MOD) 11v and 11h for modulating the baseband signals S1v and S1h on the V polarization side and the H polarization side, respectively. Variable attenuators (ATT) 12v and 12h for controlling the output levels respectively, and outputs of the variable attenuators (ATT) 12v and 12h are converted into signals of a predetermined transmission frequency and converted into V polarization and H polarization transmission signals. Transmitting transmitters (TX) 13v and 13h, and a V polarization transmission signal and an H polarization transmission signal to the opposite station (reception side) via the antenna 16 and a signal from the opposite station via the antenna 16. A duplexer 15 for receiving and separating
And a signal from the opposite station (reception side) (transmission power control information)
And a variable attenuator (ATT) 12v, 12h based on the demodulated signal (transmission power control information)
And a transmission power controller 18 for controlling the transmission levels of the V-polarized wave and the H-polarized wave.

On the other hand, the receiving side receives the signal from the opposite station (transmitting side) via the antenna 21, and the transmitter 3
A signal transmitter / receiver 22 for transmitting a signal (transmission power control information) from the communication terminal 1 to the opposite station (transmission side) via the antenna 21, and V
Receivers (RX) 24v and 24h for converting the received signals of polarized waves and H polarized waves into intermediate frequency signals, respectively, and receivers (R
X) Self-polarization demodulator (self-polarization DEM) 2 that demodulates the 24v and 24h outputs and outputs them as baseband signals, respectively
5v, 25h, different polarization demodulators (different polarization DEM) 26v, 26h for demodulating different polarization signal components respectively superimposed on the outputs of the receivers (RX) 24v, 24h, and different polarization demodulation Cross polarization interference component (different polarization component) superposed on the own polarization demodulation signal by receiving the output of the output devices (different polarization DEM) 26v and 26h and the tap coefficient supplied from the tap coefficient generators 29v and 29h, respectively. And a transversal filter 2 that generates interference compensation signals of the same level in opposite phases
7v, 27h and self-polarization demodulator (self-polarization DEM) 25v,
A transversal filter 27v for the output signal of 25h,
The interference compensation signals generated by 27h are added to remove the cross polarization interference component and the V polarization demodulation output signal S2v
And adders 28v and 28h for outputting as H polarization demodulation output signal S2h, and demodulation output signals S2v and S2, respectively.
h and the output signals of the different polarization demodulators (different polarization DEM) 26v and 26h, respectively, and receive the transversal filter 2
7v and 27h, tap coefficient generators 29v and 29h that generate tap coefficients respectively, and interference levels are determined based on the tap coefficients output from the tap coefficient generators 29v and 29h to generate transmission power control information. The interference level determiners 30v and 30h and the transmitter 31 that transmits the transmission power control information output from the interference level determiners 30v and 30h to the opposite station (transmission side) via the duplexer 22 and the antenna 21. Have

Here, the different polarization demodulator (different polarization DEM) 26
v, the transversal filter 27 v, and the adder 28
v and the tap coefficient generator 29v constitute cross polarization interference compensating means on the V polarization side, and a different polarization demodulator (different polarization D
EM) 26h, transversal filter 27h,
The adder 28h and the tap coefficient generator 29h constitute cross polarization interference compensating means on the H polarization side. The cross polarization interference compensating means generates an interference compensation signal of the same level as that of the cross polarization interference component (different polarization component) superimposed on the self polarization demodulation signal, and generates the self polarization demodulation signal. It has a function of removing cross polarization interference by adding to.

The transversal filter 27 is, for example, as shown in FIG. 2, a well-known transversal FIR filter having a multi-tap structure. That is, the delay circuit (D) that sequentially delays the different polarization demodulation signal output from the different polarization demodulator 26 by 1/2 of the symbol interval, and each tap output are multiplied by tap coefficients C1, C2, and C3. And a weighting circuit, and a combining circuit that combines the output signals of these multiplying circuits.

Further, the tap coefficient generator 29 for generating the tap coefficients C1, C2, C3 outputs the sign bit of the different polarization demodulation signal output from the different polarization demodulator 26 as shown in FIG. 2, for example. A delay circuit (D) for sequentially delaying at 1/2 of the symbol interval, each tap output and demodulation output signal S2
The output of each exclusive OR circuit and the correlation circuit that takes the exclusive OR with the error bit representing the error component of the correlation circuit to correlate with the input according to the residual distortion (error) amount of the demodulation output signal S2 are obtained. Integrate by counting and tap coefficient C
1, C2 and C3, respectively, and counter circuits.

Such a transversal filter 27
Since cross polarization interference compensating means using the tap coefficient generator 29 and the tap coefficient generator 29 is well known, detailed description thereof will be omitted.

Next, the operation will be described.

On the transmission side shown in FIG. 1, the output signals of the V-polarization side modulators (MOD) 11v and 11h of the H-polarization side are set to appropriate levels by the variable attenuators (ATT) 12v and 12h, respectively. After being attenuated, the transmitter 13v, 1
It is converted into a signal having a predetermined transmission frequency by 3h, and is transmitted to the propagation path as the V polarization and the H polarization through the duplexer 15 and the antenna 16.

On the other hand, on the receiving side, the signal transmitted as the V-polarized wave and the H-polarized wave from the transmitting side passes through the antenna 21 and the duplexer 22 to receive the V-polarized wave received signal and the H-polarized wave.
Each of them is demultiplexed into polarized wave reception signals, and the receiver (RX) 24
v and 24h respectively.

Intermediate frequency signals output from the receivers 24v and 24h are self-polarization demodulators (self-polarization DEM) 2
After being demodulated into baseband signals at 5v and 25h, respectively added at the adders 28v and 28h with the interference compensation signals generated by the transversal filters 27v and 27h, respectively, the cross polarization interference component is suppressed to V.
Polarization demodulation output signal S2v and H polarization demodulation output signal S2
Each is output as h.

By the way, when the cross polarization discrimination of the self-polarization demodulation signal, for example, the V polarization demodulation signal is in a bad state due to the influence of fading generated in the propagation path, that is, the self polarization component (V polarization). Wave component) and different polarization component (H polarization component)
When the power ratio of the self-polarization is deteriorated, the tap coefficient generator 29v on the self-polarization side (V-polarization side) increases the specific tap coefficient and supplies the increased tap coefficient to the transversal filter 27v. The interference compensation signal is generated so as to compensate the different polarization component (H polarization component) superimposed on the wave demodulation signal).
However, since the tap coefficient is limited due to the hardware configuration, the output level of the interference compensation signal becomes saturated, so that it is not possible to sufficiently compensate the different polarization component (H polarization component). There is.

In such a case, if the transmission side is controlled so as to increase the transmission power on the different polarization side (H polarization side), the reception level of the different polarization demodulator 26v on the receiving side rises and the transformer. Since the input level of the Versal filter 27v rises, even if the tap coefficient is saturated, interference of a level sufficient to compensate for the different polarization component (H polarization component) superimposed on the own polarization demodulation signal (V polarization demodulation signal). A compensation signal can be generated.

In the present invention, the tap coefficient supplied from the self-polarization side tap coefficient generator to the transversal filter is monitored, and when it is detected that the tap coefficient has reached a value close to the upper limit value, an abnormal deviation is detected. The interference compensation capability is improved by controlling the transmission power on the wave side to increase. For this reason, the interference level determiner 30
v and 30h are provided.

The interference level determiner 30 is, for example, as shown in FIG. 3, a tap coefficient comparison circuit for comparing the tap coefficients C1, C2, C3 output from the tap coefficient generator 29 with a specific constant value Cs. 301, 302, 303
And an OR circuit 304 that ORs the outputs of the comparison circuits 301, 302, and 303, and a determination circuit 305 that receives the output of the OR circuit 304 and generates transmission power control information. Here, as the specific constant value Cs (threshold value), a value close to the upper limit value of the tap coefficient is set.

The comparator circuits 301, 302, 303 compare the tap coefficients C1, C2, C3 with the threshold value Cs, respectively, and output a signal of level "1" when the tap coefficient is greater than or equal to the threshold value Cs, and less than the threshold value Cs. If it is, a signal of level "0" is output. The OR circuit 304 uses the comparison circuits 301, 302, 303 to generate tap coefficients C1,
When it is detected that either C2 or C3 has reached the threshold value Cs, a signal of level "1" is output.

The determination circuit 305 of the interference level determination device 30v on the V polarization side increases the transmission power on the H polarization side (different polarization side) when the OR circuit 305 outputs a signal of level "1". To transmit to the transmitter 31. Similarly, the determination circuit 305 of the interference level determination device 30h on the H polarization side increases the transmission power on the V polarization side (different polarization side) when the OR circuit 305 outputs a signal of level "1". To generate transmission power control information. This transmission power control information is modulated by the transmitter 31 and sent to the transmission side via the duplexer 22 and the antenna 21.

On the transmission side, the transmission power control information from the reception side demodulated by the receiver 17 is sent to the transmission power control circuit 18
To control the attenuation amount of the variable attenuator 12 so as to increase the transmission power on the different polarization side specified by the transmission power control information.

As a result, the reception level on the different polarization side rises on the receiving side, and the input level of the transversal filter 27 rises as the receiving level on the different polarization demodulator 26 rises. It is possible to generate an interference compensation signal that can sufficiently compensate the different polarization component.

In the above description, the case of using a 3-tap transversal filter is taken as an example.
It is also possible to implement the configuration with a plurality of taps (N is an odd number).

Further, the interference level judging device 30 shown in FIG.
In the comparison circuits 301, 302, and 303, one value close to the upper limit value of the tap coefficient is compared as the threshold value Cs. However, a plurality of values close to the upper limit value of the tap coefficient are set as the threshold value, and the plurality of threshold values are set. May be output, and the transmission power may be finely controlled based on these comparison results.

By the way, generally, the relationship between the cross polarization discrimination degree (power ratio between a desired polarization component and the cross polarization component) and the received electric field level has a characteristic as shown in FIG. 4, for example. . That is, when the received electric field level is higher than the specific level Ls, the cross polarization discrimination degree hardly changes with respect to the change of the received electric field level and has a substantially constant value, but the received electric field level is the specific level. When it is lower than Ls, the degree of cross polarization discrimination changes according to the level of the received electric field, and when the level of reception electric field decreases, the degree of cross polarization discrimination deteriorates. In addition,
This characteristic differs depending on the propagation path, antenna, and the like.

In view of such characteristics, in the reception electric field state in which the reception electric field level is higher than the specific level Ls, that is, in the favorable reception electric field state in which the cross polarization discrimination degree does not change with respect to the change of the reception electric field level. In the case of the system, as described above, when the tap coefficient supplied to the transversal filter reaches a value close to the upper limit value, the cross power is controlled by increasing the transmission power on the side of the different polarization. The amount of polarization interference can be reduced.

However, the received electric field level is a specific level L.
In the case of a system having a reception electric field state lower than s, that is, a system having a weak reception electric field state in which the cross polarization discrimination degree changes with changes in the reception electric field level, the tap coefficient supplied to the transversal filter has an upper limit. When it reaches a value close to the value, by controlling to increase the transmission power of the self-polarization side, the reception electric field level of the self-polarization rises,
As a result, the degree of cross polarization discrimination is improved, and the amount of cross polarization interference can be reduced.

As described above, in a system in which the reception electric field state is not stable, when the tap coefficient reaches a value close to the upper limit value, the transmission power on the different polarization side is increased or the transmission power on the own polarization side is increased. It is necessary to choose whether to increase the transmission power.

Next, another embodiment will be described.

FIG. 5 is a block diagram showing another embodiment of the present invention, showing a system applicable to a wide reception electric field range. The same components as those shown in FIG. 1 are designated by the same reference numerals.

Here, the difference from the system shown in FIG. 1 is that reception electric field level detectors 32v and 32h for respectively detecting the reception electric field levels of the V polarized wave and the H polarized wave are provided on the receiving side and the received electric field is detected. The interference level determiners 33v and 33 are configured to perform transmission power control by determining whether the level is lower or higher than the specific level Ls shown in FIG.

In FIG. 5, the received electric field level detector 32 is shown.
v and 32h detect the reception electric field levels of the V polarization and the H polarization, respectively, and detect the detection results as interference level determiners 33v and 3h.
Send to 3h respectively.

As with the interference level determiner 30, the interference level determiner 33 determines the tap coefficients C1, C2, C3 output from the tap coefficient generator 29 and a specific constant value Cs, as shown in FIG. Comparing circuits 331, 332, 333 of tap coefficients to be compared and comparing circuits 331, 33, respectively.
It has an OR circuit 334 which takes the logical sum of the outputs of 2, 333. Further, a comparison circuit 335 for comparing the reception electric field level detected by the reception electric field level detector 32 with a specific electric field level Ls, and an output of the OR circuit 334 and an output of the comparison circuit 335 are respectively received to obtain transmission power control information. It has a determination circuit 336 to generate.

The reception electric field level comparison circuit 335 outputs a signal of level "1" when the reception electric field level detected by the reception electric field level detector 32 is Ls or more, and when the reception electric field level is less than Ls. The signal of level "0" is output.

FIG. 7 shows the interference level determiners 33v and 33h.
3 is a flowchart showing the operation of FIG.

The interference level determiner 33v on the V polarization side is
The output of the OR circuit 334 indicating the state of the tap coefficient of the polarization receiving system is monitored, and the interference level determiner 33 on the H polarization side is also provided.
The h monitors the output of the OR circuit 334 indicating the state of the tap coefficient of the H-polarized wave reception system (steps 501 and 51).
1). Then, if the output of the OR circuit 334 indicates the level "1", that is, if it is detected that the tap coefficient reaches the value Cs close to the upper limit value, the state of the reception electric field level is checked (step 502, 512), if the reception electric field level comparison circuit 335 outputs the level “1”, that is, when the reception electric field level is higher than the specific electric field level Ls, the transmission power on the different polarization side is increased. Transmission power control information for instructing the above is generated (steps 503 and 513).

In steps 502 and 512, if the reception electric field level comparison circuit 335 outputs the level "0", that is, when the reception electric field level is lower than the specific electric field level Ls, the polarization side of the own polarization side is detected. Transmission power control information instructing to increase the transmission power is generated (steps 504 and 514).

As described above, by controlling the transmission power according to the state of the tap coefficient and the state of the reception electric field level, it is possible to construct a system applicable to a wide reception electric field range.

[0050]

As described above, according to the present invention, in the system having the cross polarization interference compensating means on the receiving side, the interference situation is judged based on the tap coefficient supplied to the transversal filter for generating the interference compensation signal. By performing transmission power control in this way, appropriate and fine control is possible, and the interference compensation characteristic of the cross polarization interference compensation means can be improved.

Further, by controlling the transmission power according to the state of the tap coefficient and the state of the reception electric field level, it is possible to perform appropriate control in a wide reception electric field range.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a transversal filter 27 and a tap coefficient generator 29 shown in FIG.

FIG. 3 is a diagram showing an example of an interference level determiner 30 shown in FIG.

FIG. 4 is a diagram showing a relationship between a cross polarization discrimination degree and a received electric field level.

FIG. 5 is a block diagram showing another embodiment of the present invention.

6 is a diagram showing an example of an interference level determiner 33 shown in FIG.

FIG. 7 is a flowchart showing an operation of the interference level determiner 33 shown in FIG.

FIG. 8 is a block diagram showing a conventional example.

[Explanation of symbols]

12v, 12h variable attenuator (ATT) 18 Transmit power controller 15,22 duplexer 24 Receiver (RX) 25 Self-polarization demodulator (Self-polarization DEM) 26 Different polarization demodulator (different polarization DEM) 27 Transversal filter 28 adder 29 tap coefficient generator 30,33 Interference level determiner 301, 302, 303 Tap coefficient comparison circuit 331, 332, 333 Tap coefficient comparison circuit 304,334 OR circuit 305,336 Judgment circuit 335 Reception electric field level comparison circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI H04B 1/10 H04B 1/10 L (58) Fields investigated (Int.Cl. ⁷ , DB name) H04J 11/00

Claims (6)

(57) [Claims] 1. The receiving side has a transversal filter for generating an interference compensation signal for compensating the cross polarization component of two orthogonal polarizations, respectively, and
A cross polarization interference cancellation system comprising means for generating transmission power control information so as to improve interference compensation characteristics in accordance with an interference situation and transmitting the transmission power control information to a transmission side, wherein tap coefficients supplied to the transversal filter are A cross polarization interference canceling system comprising: an interference level judging means for judging that the level of the interference compensation signal approaches a saturation state based on the interference level judging means for generating the transmission power control information. 2. The interference level determining means has at least one tap coefficient of a transversal filter that generates an interference compensation signal on one polarization side of the two orthogonal polarizations reaches a value close to its upper limit value. 2. The cross polarization interference canceling system according to claim 1, wherein the transmission power control information is generated so as to increase the transmission power on the other polarization side of the two polarizations. 3. The interference level determination means compares the tap coefficient of the transversal filter corresponding to each of the two orthogonal polarizations with a preset threshold value close to the upper limit value of the tap coefficient. Circuit,
When it is detected that at least one of the tap coefficients has reached the threshold value by these comparison circuits, a determination circuit that generates the transmission power control information so as to increase the transmission power on the different polarization side is included. The cross polarization interference cancellation system according to claim 2. 4. The cross polarization interference cancellation system according to claim 3, wherein the threshold value set in the comparison circuit is a plurality of values close to the upper limit value of the tap coefficient. 5. The reception level detecting means for detecting the reception electric field levels of the two polarizations orthogonal to each other, and the interference level determining means, wherein the transmission power control information is based on the tap coefficient and the reception electric field level. The cross polarization interference cancellation system according to claim 1, wherein 6. The cross polarization interference cancellation system according to claim 5, wherein the interference level determination means generates a tap coefficient of a transversal filter that generates an interference compensation signal of the self-polarization side of the two orthogonal polarizations. When at least one of the two reaches the threshold value, in the case of a good reception electric field state in which the cross polarization discrimination degree does not change with respect to the change of the reception electric field level on the self-polarization side, When the transmission power control information is generated so as to increase the transmission power on the side, and the reception electric field level on the self-polarization side is a weak reception electric field state in which the cross polarization discrimination degree changes in response to the change. 6. The transmission power control information is generated so as to increase the transmission power on the self-polarization side.
The cross polarization interference cancellation system described.