JPS62213441A - Cross polarization interference compensation method - Google Patents

Abstract

PURPOSE:To facilitate the compensation of mutual interference in a compensation circuit by inserting a pilot signal respectively at the sending side to two signal sent by the cross polarized wave transmission system. CONSTITUTION:The data of a signal processing unit 1 and the output of a pilot signal generator 4 are mixed by transmitter 2, 3 and the result is sent via a coupler 5 and an antenna 6. After the signal is received by an antenna 7, the result is separated by a demultiplexer 8, compensated by an interference compensation circuit 10, the phase of the pilot signal of each polarized wave recovered by carrier recovery circuits 13, 14 are compared by using a signal from demodulator 11, 12 and its output controls a variable phase shifter 9 so that the phases of both the pilot signals are made coincident.

Description

[Detailed Description of the Invention] [Summary] A pilot signal is inserted into two signals transmitted by a cross-polarization transmission method on the transmitting side, and the phases of both pilot signals in the received signals match on the receiving side. By adjusting the phase of the intermediate frequency of one of the signals at the stage before the interference compensation circuit provided in the intermediate frequency stage, mutual interference compensation in this compensation circuit can be made easy and appropriate. I did it like that.

[Industrial application field]

The present invention utilizes two polarized waves (hereinafter referred to as cross-polarized waves) that can transmit signals independently from each other, such as horizontally polarized waves and vertically polarized waves of the same frequency, or right-handed circularly polarized waves and left-handed circularly polarized waves. The present invention relates to a digital wireless transmission system that transmits digital signals by combining two transmission paths. In this transmission method, cross-polarization discrimination characteristics (X
PD) is degraded, causing interference between signals of each polarization. Therefore, it is necessary to compensate for this interference on the receiving side.

[Conventional technology]

Conventionally, in order to remove this interference, the signals of each polarization are
After converting the signals into baseband signals for the I channel and Q channel, compensation is performed using a transversal filter, or as shown in Figure 3, after converting the received signal to an intermediate frequency band, transversal A compensation signal is obtained by delaying the received polarized signal by a time width T using a filter, and weighting and combining the preceding and subsequent polarized signals with control signals from a control circuit. .

[Problem that the invention seeks to solve]

In the above conventional technology that performs compensation at the baseband, transversal signals are applied to both the ■ channel and the Q channel.
There is a problem in that the circuit scale becomes large because it is necessary to provide a filter, and in systems that perform compensation in the intermediate frequency band, it is also necessary to compensate for the phase difference between polarized waves due to differences in propagation time of each polarized wave, etc. However, there was a problem that the compensation was not sufficient.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a transmitter that transmits the pilot signal from the viroft signal generator 4 using each polarization, as shown in the principle diagram of FIG. 2 and transmitter 3 transmit the signal together with data information from signal processing device 1 to a receiver via coupler 5 and antenna 6.

On the receiving side, after the above signals are received by the antenna 7, each polarized signal is extracted individually by the splitter 8, and one polarized signal is directly sent to the interference compensation circuit 10.
The other polarized signal is also supplied to the interference compensation circuit 10 via the variable phase shifter 9.

A phase comparator 15 compares the phases of the pilot signals of each polarization regenerated by the carrier regeneration circuit 13.14 using the signal from the demodulator 11.12, and based on the phase comparison output from the phase comparator 15, The variable phase shifter 9 provided at the front stage of the interference compensation circuit 10 in the intermediate frequency stage is controlled so that the phases of both pilot signals coincide with each other.

[For production]

With the above configuration, the phases of the intermediate frequency input signals of each polarization to the interference compensation circuit match each other, so there is no need for the interference compensation circuit to compensate for the phase shift between these two signals, and the appropriate Compensation can be made.

〔Example〕

Figure 2 shows an embodiment in which the present invention is applied to the transmission of a digital quadrature amplitude variable (hereinafter referred to as CAM) signal using a cross-polarization transmission method.The left side of the figure is the transmitter, and the right side is the receiver. These transmitters and receivers are connected by a wireless line. The signal processing device 20 in FIG. 2 has digital-to-analog converters 21 to 22 added to the signal processing device 1 in FIG.
, low-pass filters 25 to 26, power supply 29, mixer 32
~33, the part consisting of the hybrid circuit 36 is the first
The transmitter 3 in the figure is equipped with digital-to-analog converters 23 to 2.
4, low pass filters 27-28, power supply 30. Mixer 3
4 to 35 and the hybrid circuit 37 are included in the transmitter 2 in FIG.
The interference compensation circuit 10 composed of transversal filters 105-106 is included in the interference compensation circuit 10 in FIG. 1, the synchronous detectors 41-42 are included in the demodulator 11 in FIG. The demodulator 12 in FIG.
162 is the discriminator 16 of FIG.
correspond to the discriminator 17 in FIG. In addition, the above quadrature amplitude variation Uni (QAM: Quadratu
re Amplitude Modulation
) method modulates the phase component (Q) and amplitude component H) on the transmission data carrier (ill transmission), and since any point on the modulation vector plane can be selected as the code point, it is easy to use on the code arrangement. This is a modulation method with a high degree of freedom.

Four output digital data 8 from the signal processing device 20
1 to S4 are digital-to-analog converters 21 to 1, respectively.
24 into an analog signal. The analog signals pass through low-pass filters 25 to 28, respectively, and are mixed with the carrier wave output of the carrier wave generator 31 by mixers 32 to 35. 33.35, a carrier wave with a phase of 90'' is supplied from the carrier wave generator 31, so the outputs of the mixer 32 and mixer 33, and the outputs of the mixer 34 and mixer 35 are quadrature modulated with respect to each other. The ■ signal and the Q signal are synthesized by the hybrid circuits 36 and 37, respectively, to generate two sets of Q signals.
The AM signals Sv and S8 are transmitted by vertical polarization of the Sv multiplication signal and by horizontal polarization of the SH multiplication signal through the coupler 5 and from the antenna 6 via the wireless transmission path to the receiver.

In addition, the power supplies 29 and 30 shown on the input side of the mixer 32 and 34 provided on the ■ channel side superimpose a DC component on the analog signal of the ■ channel, thereby causing the output of the mixer to be in phase with the carrier wave. It is for generating a pilot signal.

The signal received via the antenna 7 on the receiver side is a signal transmitted by vertical polarization by the splitter 8, Sv
and a signal SH transmitted by horizontal polarization,
Output from local oscillator 3 and mixer 39.40 respectively
The signals iv and IN are mixed together to form intermediate frequency signals iv and IN.

The variable phase shifter 9 added according to the present invention will be explained later.
102, 103, 104 and transversal filters 105, 106 whose transmission characteristics are controlled by the received signals so that cross-polarization interference is minimized in the time domain.
After passing through a known interference compensation circuit 10 consisting of a pilot signal in the received signal, synchronous detection is performed by synchronous detectors 41 to 44 using the carrier regenerated from a pilot signal in the received signal by a carrier regeneration circuit 13 and 14 consisting of a PLL circuit or the like. and demodulated.

The phase of the carrier regenerated by the above carrier regeneration circuits 13 and 14 is determined by the DC power supply 29. 30 as the signal source is obtained which is equal to the phase of the I channel pilot signal inserted. Therefore, the outputs from the synchronous detectors 42.44, which are synchronously detected by the outputs of the carrier regeneration circuits 13.14, are channel signal components of the signals Sv and SH, respectively, and the carrier regeneration circuits 13.1
The outputs from the synchronous detectors 41 and 43, to which the outputs of the synchronous detectors 41 and 43 are respectively applied through 90 degree phase shifters 45 and 46, become the Q channel signal components of the signals Sv and S14, respectively, and the outputs from the discriminator 1
From 61,162,171.172, Sv and SH double signal Q channel signal and! channel signal can be obtained.

Then, the control signal generation circuit 18 generates the transversal filters 105 and 10 of the interference compensation circuit IO from the ■ channel signal and Q channel signal of the signal Sv and the I channel signal and Q channel signal of the signal SH.
A signal controlling the transmission characteristics of 6 is extracted.

Note that the DC components of the Q channel signals of the signal Sv and the signal SH indicate the phase difference between the received wave of each polarization and the regenerated carrier, so the carrier regeneration circuit 13.14 converts the carrier based on this signal. is playing.

In the present invention, the input phases of the signals at the intermediate frequency stage of the signals transmitted by each cross-polarized wave to the interference compensation circuit 10 are made to match, and in this embodiment, the intermediate frequency signal IH of the above-mentioned signal SH is A mixer 40 that outputs
A variable phase shifter 9 is inserted between the carrier regenerating circuit 13 . 1
4 is compared in phase by a phase comparator 15, and the phase comparator 15 is adjusted so that the phase comparison error becomes zero.
The amount of phase shift of the variable phase shifter 9 is controlled by the output of the variable phase shifter 9.

In the above embodiment, the example was explained in which the pilot signal is used both as a pilot signal for obtaining a regenerated carrier used for channel synchronous detection and as a pilot signal indicating the phase of a signal transmitted by vertical or horizontal polarization. It will be obvious that a pilot signal or signal source indicating the phase of the signal can be separately provided on the transmitting side.

〔Effect of the invention〕

According to the present invention, since the phases of the two input signals of the interference compensation circuit provided in the intermediate frequency stage, that is, the signals transmitted by cross-polarized waves match, in the interference compensation circuit, these input signals There is no need to compensate for mutual interference and distortion that occur in the demodulated signal based on the phase difference between the two, and therefore compensation becomes easy and appropriate compensation can be performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a block diagram showing an embodiment of the invention, and FIG. 3 is a diagram showing a conventional example using a transversal filter. 4... Pilot signal generator, 9... Variable phase shifter,
10... Interference compensation circuit, 13.14... Carrier regeneration circuit, 15... Phase comparator.

Claims (1)

[Claims] On the transmitting side, a pilot signal is inserted into each of the two cross-polarized transmission paths for transmission, and on the receiving side, a carrier recovery circuit (13 , 14), the phases of both pilot signals are compared by a phase comparator (15), and the interference compensation circuit of the intermediate frequency stage on the receiving side is configured to match the phases of both pilot signals. (10) A cross-polarization interference compensation system characterized in that a variable phase shifter (9) provided at the front stage of the phase comparator (15) is controlled by the output of the phase comparator (15).