JPS6119188B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a space diversity reception system that reduces the effects of frequency selective fading that occurs in wireless communication lines.

Conventionally, microwave FM lines use an in-phase synthesis space diversity reception system.
FIG. 1 shows the basic configuration of this system, in which signals received by antennas 1 and 4 are combined using a combiner 3 so that they are in phase. The phase shifter 5 is
At this time, it is used to vary the relative phase difference between the two received signals. A phase modulator 2, a sensing oscillator 7, and a synchronous detection circuit 16 are control circuits for combining two received signals into the same phase, and automatically detect the same frequency component as the sensing oscillator output contained in the amplitude fluctuation contained in the combined signal. Gain control circuit 2
5, and the polarity of this signal is used to determine the control direction of the phase shifter. This technique is generally called a sensing method in the field of diversity methods. (Reference: British Patent No. 810698) On the other hand, frequency selective fading is caused by multiple waves with path differences, and the dominant waves among these multiple waves are the main wave and the interference wave. It is known that there is (two-wave model). Figure 2 shows an example of frequency selective fading calculated using this two-wave model, in which a and b are the frequency characteristics of the signals received by each antenna, and c is the conventionally used d is the frequency characteristic when the in-phase combining space diversity reception method is used, and d is the frequency characteristic when the interference wave components received by two antennas are combined so that they are in antiphase with each other. .

As can be seen from the figure, the conventional in-phase synthesis space diversity reception system aims to maximize the reception level, and therefore has the drawback of insufficient improvement in frequency characteristics.

The present invention aims to eliminate these drawbacks, and by combining the signals received by two antennas so that the in-band deviation is small, the interference wave components included in the signals are made to have opposite phases. This is to flatten the frequency characteristics of the combined signal, and the drawings will be described in detail below.

FIG. 3 shows an embodiment of the present invention, in which 1 is an antenna, 2 is a phase modulator, 3 is a combiner, 4 is an antenna, 5 is a phase shifter, 6 is a receiver, 7 is a sensing oscillator, and 8 is a band A characteristic detection circuit, 9 indicates a control circuit.

To make this work, two antennas 1 and 4 are required.
The signals e ₁ and e ₂ received by are passed through a phase modulator 2 and a phase shifter 5, respectively, and then combined by a combiner 3, and converted by a receiver 6 into an IF signal having a constant signal level. do. This IF signal is branched into two, one is added to the band characteristic detection circuit 8, the amplitude or delay frequency characteristic after synthesis is observed, and the amplitude or delay deviation within the required band is detected (hereinafter referred to as in-band deviation). ). This in-band deviation signal is applied to the control circuit 9, and the phase shifter 5
control. By carrying out such control, the amount of phase shift that minimizes the deviation becomes a phase that makes the interference wave have an opposite phase, and the band characteristics are completely flattened as shown in d of FIG. The sensing oscillator 7 and the phase modulator 2 are an example of a detection circuit for detecting the direction in which the deviation becomes smaller, and their operation is similar to that of the conventional sensing method.

In addition, as a means for detecting the direction in which the in-band deviation becomes smaller, it is also possible to detect by changing the amount of phase shift of the phase shifter 5.

Furthermore, FIG. 4 shows a specific example of the band characteristic detection circuit 8 and the control circuit 9 shown in FIG.
and 12 is a bandpass filter, 11 and 13 are detectors, 14 is a subtraction circuit, 15 is a full-wave rectifier circuit, 1
6 represents a synchronous detection circuit, and 17 represents a drive circuit. The example shown in the figure shows a method of using the deviation component of the amplitude frequency characteristic of the composite signal as an in-band deviation signal for control, and two signal components separated by ±Δω from the center frequency ω ₀ are The absolute value of the difference is detected using the circuits 12 and 13, and the subtraction circuit 14
and is detected using the full-wave rectifier circuit 15. However, as a signal having a frequency component of ω ₀ ±Δω, the pilot signal inserted at the time of transmission is generally used, but if the average level of the main signal is constant at the frequency of ω ₀ ±Δω, the pilot signal is It can be used as a signal equivalent to a signal.
The control circuit 9 is composed of a sensing signal synchronous detection circuit 16 and a drive circuit 17 including an integrator, and detects a signal having the same frequency as the sensing signal from the output signal of the band characteristic detection circuit 8, and equivalently detects the band deviation. Detect the differential coefficient of .

Fig. 5 explains this operation in detail. The differential coefficient d|Δx|/dφ of the absolute value |Δx| of the in-band deviation Δx with respect to the phase shift φ is detected, and the shift is performed according to the sign of the differential coefficient d|Δx|/dφ. If the control direction of the phase shifter is determined as indicated by the arrow in C in the figure, the amount of phase shift can be stabilized at the position shown by the white circle in P or Q in the figure. Here, point P indicates the amount of phase shift at which the interference wave has an opposite phase, and Q indicates the amount of phase shift at which the main wave has an opposite phase, but since the frequency characteristics are flat in both cases, it will be the same regardless of which stable point it is pulled into. characteristics can be obtained.

FIG. 6 shows an example of operation when the amplitudes of interference waves included in received signals are not equal. As shown in Figure a, the in-band deviation Δx is minimum at the interference wave antiphase point (φ=0), but Δx=0 is not achieved. However, even in this case, the differential coefficient d|Δx
If the control direction of the phase shifter is determined by the sign of |/dφ, a stable point exists at white circle point R or S, as shown in FIG. Therefore, even if the state of the propagation path deviates from the two-wave model, it is possible to control the phase shifter to a position that minimizes the in-band characteristics.

On the other hand, when interference waves are combined with opposite phases, there is a high probability that the received power after combination will be smaller than the received power when received alone, and deterioration of transmission quality due to thermal noise becomes a new problem.

Moreover, FIG. 7 shows an example of operation when there is a large difference in the amplitude of interference waves included in received signals. Figure c
The broken line is an example of operation when the control method shown in FIG. 4 is used, and a stable point exists at point T in the figure.
This point T is a point where the in-band deviation Δx is large, as shown in FIG.

FIG. 8 shows an embodiment of the present invention that takes into consideration eliminating these drawbacks, in which 18 and 19 are discriminators, 20 and 21 are switches that are switched by the outputs of the discriminators 18 and 19, respectively; 2
5 and 26 indicate filters that pass the phase modulation frequency component.

In this circuit, when the received signal level detected using the receiver 6 falls below a predetermined value, this is detected by the identification 18, the switch 20 is switched to the a side, and the conventional in-phase synthesis is performed. and increase the reception level. On the other hand, if the in-band deviation exceeds a required value, this is detected by the discriminator 19, and the switch 21 is switched to the c side to forcibly rotate the phase shifter in one direction. In this way, it is possible to prevent an extreme drop in the received power, and the control operation becomes as shown by the solid line in FIG.

Furthermore, FIG. 9 shows another embodiment of the present invention, 2
2 is a band wave detector, 23 is a sensing signal detector, and 24 is a weighting circuit. In conventional sensing methods, the phase changed by the phase modulator is constant and is kept as small as possible. However, in the case of the present invention, since a special signal called band characteristic is used, when a certain phase modulation is applied, the fluctuation component of the in-band deviation is small depending on the propagation path conditions, and the control direction can be detected. There are cases in which this is not possible, or conversely, cases in which the fluctuation component of the in-band deviation becomes excessive and adversely affects the main signal. For example, points V and P in FIG. 5c correspond to each other. Therefore, as shown in FIG. 9, if the in-band deviation fluctuation component is detected using the filter 22 and the detector 23, and the weighting circuit 24 is controlled so that the deviation fluctuation component is constant, the above-mentioned drawbacks can be solved. It becomes possible to remove. In the above explanation, a configuration was used in which a phase shifter was inserted into the main signal sequence of the RF stage, but two series of receivers were used to
A similar effect can be obtained by using a method of controlling the phase of the local oscillation wave of one receiver, such as a method of combining signals in stages.

As explained above, by using the configuration of the present invention, it is possible to flatten the in-band amplitude and delay deviation due to fading.

In wideband waveform transmission such as a digital transmission system using a microwave band, inter-symbol interference (waveform distortion) increases due to in-band amplitude deviation or delay deviation caused by fading, and error rate characteristics deteriorate significantly. In addition, in the microwave band SSB method in which multiplexed FDM signals are transmitted by SSB-AM modulation, in-band level deviation due to fading directly changes the transmission level, so strict requirements are placed on in-band level deviation.

By applying the space diversity reception according to the present invention, it is possible to suppress the occurrence of in-band deviations during fading, which greatly contributes to improving the transmission quality of wideband digital and analog transmission in fading propagation paths.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the conventional space diversity reception method (in-phase combining method), Figure 2 is a diagram showing the band characteristics when using the conventional and present invention diversity reception methods, and Figure 3 is the present invention. 4 is a simple block diagram showing an embodiment of the present invention, FIGS. 5 and 6 are diagrams showing the operation of the circuit in FIG. 4, and FIG. 7 is a diagram showing the operation of the circuit in FIG. 4. 8 is a block diagram showing another embodiment of the present invention, and FIG. 9 is a block diagram showing another embodiment of the present invention. be. 1, 4; antenna; 2; phase modulator; 3; synthesizer; 5; phase shifter; 6; receiver; 7; sensing oscillator; 8; band characteristic detection circuit; 9; control circuit.

Claims (1)

[Claims] 1. In a space diversity reception system in which signals are received by two spatially separated antennas, the phase of one signal is controlled by a phase controller, and both received signals are combined. If the subsequent signal level is larger than a predetermined value, the phase controller is controlled in the direction of decreasing the in-band amplitude deviation or delay deviation, and if the signal level is smaller than the predetermined value, the signal level is A space diversity reception method in which the phase controller is controlled in the direction of increasing the value. 2 In a space diversity reception method in which signals are received by two spatially separated antennas and the phase of one signal is controlled by a phase controller to combine both received signals, the band of the combined signal is detecting the absolute value signal of the deviation or delay deviation, and if the absolute value signal is smaller than a predetermined value, controlling the phase controller in a direction in which the in-band amplitude deviation or delay deviation of the combined signal becomes smaller; A space diversity reception method in which if the absolute value signal is larger than a predetermined value, the phase controller is controlled in a predetermined direction. 3 In a space diversity reception method in which signals are received by two spatially separated antennas, and the phase of one signal is controlled by a phase controller to combine both received signals, one received signal is subjected to phase modulation. detect the phase modulation frequency component included in the absolute value signal of the in-band amplitude deviation or delay deviation of the synthesized signal, control the phase modulation degree so that the amplitude is constant, and A space diversity reception method characterized by determining a control direction of a phase controller using the polarity of a component.