JPH0616613B2 - Polarization multiplexing wireless communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polarization multiplexing wireless communication system such as a quadrature amplitude modulation (QAM) communication system for improving frequency utilization efficiency of microwave digital communication. In particular, the present invention relates to a transmission apparatus including means for applying a frequency offset at the time of signal transmission in a polarization multiplexing wireless communication system having a cross polarization discrimination compensation circuit in a reception side apparatus.

[Conventional technology]

In microwave digital communication, attention has been paid to an orthogonal polarization communication system using two orthogonal polarizations. In order to effectively use the frequency by sharing the orthogonal polarization, the cross polarization characteristic of the antenna system should be improved, and the cross polarization discrimination (X) caused by fading should be performed.
When the deterioration of (PD) is significant, it is necessary to compensate for it. The deterioration of the cross polarization discrimination degree that occurs in the radio wave propagation path, that is, the cross polarization interference is caused by anisotropic phase shift (DPS) and anisotropic attenuation (DA) during fading. Therefore, a system requiring a high degree of cross polarization discrimination requires a cross polarization discrimination compensation circuit (XPIC) that compensates for the deterioration.

This cross polarization discrimination compensating circuit is a system that removes cross polarization interference by controlling the variable coupler by obtaining the correlation between the error signal corresponding to the interference and the data signal in the receiving side device. For stable operation of this cross polarization discrimination compensation circuit,
When the phase of the error signal changes due to the change in the phase difference of the reproduced carrier signal, it is necessary to correct the error signal so that the correct correlation can be obtained with the data signal. To this end, a means for detecting the phase relationship between the reproduced carrier signals is provided, and an error signal corrected in accordance with the phase difference between the reproduced carrier signals is obtained, and the demodulator on the main polarization side and the different polarization side are obtained. It is necessary to provide means for correctly correlating the reproduced carrier signals with the demodulator in any phase relationship (see "Cross-polarization interference canceling circuit", JP-A-59-112739).

[Problems to be solved by the invention]

However, such a conventional cross polarization interference cancellation circuit is
By means of detecting the phase relationship between the outputs of two demodulators corresponding to two orthogonal polarizations and correcting the error signal obtained as a result, no matter how the phase difference of the reproduced carrier signal changes, This is a method of performing a normal operation. Therefore, depending on the phase difference detecting ability of the means for detecting the phase from the outputs of the two demodulators, for example, the phase difference is 0 °, 90 °, 180 °.
In the very vicinity of ° or 270 °, it may be impossible to judge.

Furthermore, when the received signal undergoes phase rotation due to a change in delay time due to fading, and when it fluctuates and fluctuates, the undetectable region for phase detection may extend for a long time (several seconds).

The present invention has been made in view of such conventional problems. In the cross polarization interference canceling circuit on the receiving side, the phase of the error signal rotates due to the change of the phase difference of the reproduced carrier signal. In addition, it is an object of the present invention to provide a polarization multiplexing wireless communication system that makes it possible to almost ignore the time when the phase difference determination becomes impossible.

[Means for solving problems]

The present invention is characterized in that a frequency offset is applied to a local oscillator of a transmitter for both polarizations.

That is, the first invention of the present invention is to provide a transmitting device including a means for transmitting a radio signal in which different information is modulated to cross polarized waves, and a plurality of demodulating means for receiving the radio signal and demodulating for each polarization. And a receiver including a means for removing cross-polarization interference by the output of the demodulating means, and the transmitting device, in which the carrier frequencies of crossing polarized waves are slightly different from each other. It is characterized by different configurations.

This slight difference in carrier frequency may be within the demodulator capture range.

A second invention of the present invention is a transmission device including a means for transmitting a radio signal in which different information is modulated to cross polarized waves, and a plurality of demodulation means for receiving the radio signal and demodulating for each polarization. In a polarization multiplexing wireless communication system including a receiver including means for removing cross polarization interference by the output of the demodulator, the transmitter has a demodulator capture range whose output frequency is in accordance with a control signal. And a detection circuit for detecting a modulation signal input and sending the detection output as the control signal to the local oscillator.

[Work]

The first aspect of the present invention accelerates the phase rotation between both polarizations by applying a frequency offset to the local oscillator of the transmission device for both polarizations in advance within the demodulator capture range. Therefore, the phase detection means on the receiving side can almost ignore the time when the determination cannot be made, and the stable operation of the cross polarization interference cancellation circuit is established.

The second aspect of the invention changes the oscillation frequency of the local oscillator corresponding to one or both modulation input signals of both polarization transmitters, and a frequency offset between both polarizations can be easily obtained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the first invention of the present invention. In FIG. 1, modulated waves (intermediate frequency signals) are input to input terminals 10 and 20, respectively, and output terminal 1
The microwave signals to be transmitted are output to 9 and 29, respectively. Between the input terminals 10 and 20 and the output terminals 19 and 29, frequency converters 12 and 22 and amplifiers 13 and 23, which receive the outputs of the local oscillators 11 and 21, respectively, are connected.

The oscillation frequency of the local oscillator 11 or 21 is offset in advance within the demodulator capture range. For example, one local oscillator with respect to the other
When shifted by about 100 kHz, the time required for 90 ° rotation of the phase was about 1 second when the offset was not applied, but it can be rotated rapidly to about 10 μsec.

However, in the case of performing the frequency offset, the first invention adopts a method of previously offsetting the carrier frequency of the modulator or the frequency of the local oscillator of the transmitter, but the adjustment is quite complicated, and Confusion tends to occur in maintenance or device manufacturing management.

Therefore, the second invention is characterized by including means for applying a frequency offset only when the modulated signal is input to the transmitter. Therefore, the constituent circuits of the transmitters of both polarizations may have the same standard, and the manufacturing control of the device can be extremely facilitated.

FIG. 2 is a block diagram showing an embodiment of the second invention of the present invention. In FIG. 1, modulated waves (intermediate frequency signals) are input to input terminals 10 and 20, and microwave signals to be transmitted are output to output terminals 19 and 29, respectively. Between the input terminals 10 and 20 and the output terminals 19 and 29,
The frequency converters 12 and 22 and the amplifiers 13 and 23 thereof, which receive the outputs of the local oscillators 11 and 21, respectively, are connected. Further, in one of the transmitting devices, an input signal is branched and connected to the modulation signal detector 14, and the output of the modulation signal detector 14 is configured to control the oscillation frequency of the local oscillator 11.

Modulation signal is input from input terminals 10 and 20, frequency converter
At 12, 22 they are mixed with the outputs of local oscillators 11, 21 and converted to the microwave band, then amplified by amplifiers 13, 23 and output terminal 1
It is sent from 9 and 29 to each polarization input terminal of the antenna system.

Here, the feature of the second invention of the present invention is that the modulation signal detector 14 in one of the transmitters determines whether or not a modulation signal is input, and if there is a modulation input signal, the local signal A control signal for offsetting or wobbling the oscillation frequency is output to the local oscillator 11.

Therefore, a modulation signal detector 14 and a local oscillator whose oscillation frequency is controlled by its output control signal
By providing 11, the frequency offset can be easily applied.

In this embodiment, an example of the heterodyne system is shown, but in the case of the direct modulation system, the frequency converters 12 and 22 are microwave band modulators, and the input signal is a digital signal.

In this embodiment, the frequency offset shift amount is 100 k
Although the example of Hz has been shown, any frequency offset that can rotate the phase at a high speed for a time sufficiently shorter than the detection time constant of the phase difference detection means of the cross polarization interference cancellation circuit may be used.

Further, in the present invention, the local oscillation frequency of the transmitter is offset or wobbled. However, in the case of using a modulator of the intermediate frequency band, a method of similarly offsetting or wobbling the carrier wave by judging the presence of an input data signal is provided. The present invention can also be practiced by using it.

〔The invention's effect〕

According to the present invention, by applying a frequency offset to one of both polarizations of the orthogonal polarization communication system within the demodulator capture range, the phase rotation of the error signal becomes faster and the cross polarization provided in the receiving side device is increased. The phase detection means of the wave interference elimination circuit can almost ignore the time when the phase cannot be determined.
That is, stable operation of the cross polarization interference cancellation circuit is guaranteed.

Further, by adding the means for applying the frequency offset only when the modulated signal shown in the second invention is input, the transmitters of both polarizations may be of the same standard, and manufacturing management and maintenance management are very easy. There is an excellent effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the first invention of the present invention. FIG. 2 is a block diagram showing an embodiment of a second invention of the present invention. 10, 20 …… Input terminal, 19,29 …… Output terminal, 11,21 ……
Local oscillator, 12, 22 ... frequency converter, 13, 23 ... amplifier, 14 ... modulation signal detector.

Claims (2)

[Claims] 1. A transmission device including a means for transmitting a radio wave signal obtained by modulating different information in crossed polarizations, a plurality of demodulation means for receiving the radio wave signal and demodulating it for each polarization, and the demodulation means. And a receiver including means for removing cross-polarization interference by the output of the above, the transmitting apparatus is capable of demodulating the carrier frequencies of the crossed polarizations by the demodulating means. A polarization multiplexing wireless communication system characterized in that the configurations differ in the following ranges. 2. A transmitting device including a means for transmitting a radio wave signal in which different information is modulated in crossed polarizations, a plurality of demodulation means for receiving the radio wave signal and demodulating for each polarization, and the demodulation means. And a receiver including means for removing cross-polarization interference by the output of the above, in the above-mentioned transmitter, the output frequency of the transmitter can be demodulated by the demodulator according to a control signal. A polarization multiplexing wireless communication system comprising: a local oscillator that changes within a range; and a detection circuit that detects a modulation signal input and sends the detection output as the control signal to the local oscillator.