JPS61131625A - Space diversity reception system - Google Patents

Abstract

PURPOSE:To improve the S/N regardless of the quantity of a reception electric field strength and to attain a flat in-band amplitude characteristic by changing the gain of two amplifiers respectively based on a level of each input signal and an amplitude level after synthesis. CONSTITUTION:A signal received by an antenna 11 and a signal received by an antenna 12 are given to a phase shifter 32, where the phase of them is matched and the result is symthesized. In a space diversity device constituted in this way, variable gain amplifiers 101, 102 are provided at the post-stage of each antenna. Further, level detectors 51, 52 detecting a reception level of each antenna and an amplitude detector 7 detecting a signal amplitude after synthesis are provided so as to control the gain of the two amplifiers 21, 22 based on the detection signal. Through the constitution above, a nonlinear distortion when the reception electric field strength is high is decreased and the S/N when the reception electric field strength is low is improved. Even when an interference wave level incident in each antenna differs, the in-band amplitude characteristic is made flat.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a space diversity reception system suitable for microwave digital communication.

[Conventional technology]

By controlling the mutual phase difference and combining the signals received by the two antennas so that the in-band amplitude characteristic deviation after combining is small, the interference wave components included in the signals are made to have opposite phases to each other, A space diversity reception method that flattens the frequency characteristics has been used (see prior art Japanese Patent Application Laid-open No. 72548/1983).

[Problem that the invention seeks to solve]

However, this method is effective when the levels of the interference waves are equal, but has the drawback that it is not effective when the levels are unequal. In general, in order to improve the noise figure of a receiver, if the gain of the amplifier at the front stage is set high, this will lead to saturation of the amplifier and increase distortion when the received electric field strength is high. If the gain is limited by , the signal-to-noise ratio deteriorates due to thermal noise when the received field strength is low.

The present invention solves the above-mentioned drawbacks by flattening the in-band amplitude characteristic deviation even when there is no level difference between interference waves and when there is a level difference, and also suppressing the occurrence of distortion when the received electric field strength is high. It is an object of the present invention to provide a space diversity reception method that can reduce the received electric field strength and obtain a good signal-to-noise ratio even when the received electric field strength is low.

[Means for solving problems]

The present invention provides two amplifiers that amplify the received signals of two antennas, a phase shifter that adjusts the mutual phase shift of the output signals of the two amplifiers, and a phase shifter that adjusts the mutual phase shift of the output signals of the two amplifiers. A synthesizer that combines two signals, an amplitude detector that measures the in-band amplitude frequency characteristic deviation of the output signal of this synthesizer, and an output signal of this amplitude detector that makes the in-band amplitude frequency characteristic approach flat. In the space diversity receiving system, the gain of each of the two amplifiers is substantially controlled by a control means for controlling the phase shifting means, and an automatic gain control amplifier for amplifying the output signal of the combiner to a predetermined level. and level detection means for detecting the respective levels of the input signals of the synthesizer; The present invention is characterized in that it includes means for controlling the variable gain control means so that the amplitude frequency characteristic approaches flatness, less nonlinear distortion is generated in the two amplifiers, and the signal-to-noise ratio is improved.

The invention can be implemented with a level detector in which the level detection means is provided separately at the input of the synthesizer. Furthermore, if control is to be performed so that the in-phase synthesis state is always maintained, this can be implemented by means for detecting the gain control voltage of the automatic gain control amplification means.

[For production]

The present invention detects the level of each input signal of the synthesizer with a level detector, and controls the variable gain control means with the control means based on the detected output and the output signal of the amplitude detector, thereby adjusting the gains of the two amplifiers. By making each substantially variable, even when the received field strength is high, there is little nonlinear distortion in the amplifier, etc., and the signal-to-noise ratio is good even when the received field strength is low, and the antenna system Even when the levels of incident interference waves are different, the in-band amplitude characteristics can be flattened. In addition, if control is to be performed so that the in-phase synthesis state is always maintained, the same effect can be achieved by controlling the variable gain control means by the control means using the gain control voltage of the automatic gain control amplifier and the output signal of the amplitude detector. can do.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a space diversity receiving apparatus according to an embodiment of the present invention. In FIG. 1, the feature of the present invention is a variable gain amplification portion surrounded by a dashed line. That is, the signals received by the antennas 11.1□ are respectively connected to the inputs of the variable gain amplifiers 28.2□. The amplified output signal from variable gain amplifier 2□ is connected to phase shifter 3□. The amplified output signal from the variable gain amplifier 2) is connected to one input of the combiner 4 and to the input of the level detector 5°. The phase-adjusted output signal from the phase shifter 3□ is connected to the other input of the synthesizer 4 and the input of the level detector 5□, and the output signals of the variable gain amplifier 2I and the phase shifter 3□ are combined. be done. The output signal of the synthesizer 4 is connected to an automatic gain control amplifier 6, amplified to a specified level, and connected to a demodulator (not shown). The output signal of the synthesizer 4 is branched and connected to the human power of the amplitude detector 7, and the detected signal is connected to the human power of the controller 8. Also level detector 59.5
The detection outputs of □ are respectively connected to the human power of the controller 8.

A control signal from the controller 8 is sent to each variable gain amplifier 2).
It is connected to the control input of phase shifter 2□ and phase shifter 3□, and has low nonlinear distortion even when the received field strength is high, and has a good signal-to-noise ratio even when the received field strength is low. Control is performed to flatten the in-band amplitude characteristics even when the levels of interference waves incident on the system differ.

The operation of the space diversity receiving device having such a configuration will be explained. In FIG. 1, the controller 8 controls the phase shifter 3□ so that the in-band amplitude frequency characteristic deviation of the output of the amplitude detector 7 is reduced, that is, the interference waves are in opposite phases. The variable gain amplifiers 22.22 are controlled to equalize the magnitudes of the phased interference waves, and the relative levels of the received signals from the antennas 11, □□ are controlled, and the level detectors 53.5 The magnitude of the pre-synthesis level is detected by the variable gain amplifier 20.2 □, and the variable gain amplifier 2. ．． Controls 2t.

When the received field strength is low, use variable gain amplifiers 2I and 2□
It is possible to reduce deterioration of demodulation characteristics due to thermal noise by controlling the gain to increase.

In this embodiment, the circuit addition from the conventional system is a variable gain amplifier 2). 2□ and a level detector 51.5□, and furthermore, the level detectors 5° and 5□ are necessary and sufficient as long as they can only detect high levels where nonlinear distortion occurs, and they do not particularly require band limitation, so they are inexpensive. It can be implemented.

FIG. 2 is a block diagram of a space diversity receiver according to another embodiment of the present invention. In FIG. 2, circuits that are the same as those in FIG. 1 are designated by the same reference numerals.

12.12 is an antenna, 10+ and 10□ are variable attenuators, 111.11□ is a pre-high frequency amplifier, and 13 is a local oscillator. The local oscillator signal is branched into two, one being sent to a frequency converter 12. The other signal is input directly to the frequency converter 12□ after its phase is controlled through the infinite phase shifter 14.

5. ．． 5. , the pre-synthesis level is too thick (so that the pre-high frequency amplifier 112, 112 and frequency converter 12...
This is a level detector to prevent distortion from occurring at 12□. 4 is a synthesizer for synthesizing the main signals, 7 is an amplitude detector, 6 is an automatic gain control amplifier, and 8 is a controller. The controller 8 controls the infinite phase shifter 14 so that the in-band amplitude frequency characteristic deviation of the output of the amplitude detector 7 is small, that is, the interference waves are in opposite phases, and the interference waves that are in opposite phases are The variable attenuators 10, . 1
The relative value of the attenuation amount of 0□ is controlled, and the level detector 5
7.5□ detects the magnitude of the pre-synthesis level and converts the pre-high frequency amplifier 11+, Hz and frequency converter 12I,
The variable attenuator 10. ．． Controls the absolute attenuation amount of 10□.

When the received electric field strength is low, the variable attenuators 10I, 10
By controlling the absolute attenuation amount of 2 to be small, it is possible to reduce deterioration of demodulation characteristics due to thermal noise.

In this embodiment, the circuit addition from the conventional system is a variable attenuator 10. ．． 10. and a level detector 58.5□, and furthermore, this level detector 51.5□ can be realized at low cost like the embodiment shown in FIG.

Further, when control is performed such that the in-phase synthesis state is always maintained, the gain control voltage of the automatic gain adjustment amplifier 6 can be used in place of the detection signal of the level detector 51.5□.

〔Effect of the invention〕

As explained above, the present invention reduces the occurrence of nonlinear distortion when the received electric field strength is high, has a good signal-to-noise ratio when the received electric field strength is low, and has the advantage of preventing interference from entering mutually independent antenna systems. This has the excellent effect of flattening the in-band amplitude characteristics even when the wave levels are different, and that the device can be realized at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a space diversity receiver according to an embodiment of the present invention. FIG. 2 is a block diagram of a conventional space diversity receiver. 1... Antenna, 2... Variable gain amplifier, 3...
Phase shifter, 4... Combiner, 5... Level detector, 6.
...Automatic gain control amplifier, 7...Amplitude detector, 8...
- Controller, 10... Variable attenuator, 11... Pre-high frequency amplifier, 12... Frequency converter, 13... Local oscillator, 14... Infinite phase shifter. ivy 1 diagram

Claims (3)

[Claims] (1) Two amplifiers that amplify the received signals of the two antennas, a phase shifter that adjusts the mutual phase shift of the output signals of these two amplifiers, and two amplifiers that are adjusted by the phase shifter. an amplitude detector that measures the in-band amplitude-frequency characteristic deviation of the output signal of this synthesizer; and an amplitude detector that measures the in-band amplitude-frequency characteristic deviation of the output signal of this synthesizer. In a space diversity reception system comprising control means for controlling the phase shifting means and an automatic gain control amplifier for amplifying the output signal of the combiner to a predetermined level, the gains of the two amplifiers are substantially variable. and level detection means for detecting the levels of the input signals of the synthesizer, and the control means detects the in-band amplitude by the level detection means and the amplitude detector. A space diversity reception system characterized by comprising means for controlling the variable gain control means so that the frequency characteristics are close to flat, nonlinear distortion is less generated in the two amplifiers, and the signal-to-noise ratio is good. (2) The space diversity reception system according to claim (1), wherein the level detection means is a level detector individually provided at the input of the synthesizer. (3) The space diversity reception system according to claim (1), wherein the level detection means is means for detecting a gain control voltage of an automatic gain control amplifier.