JPS60149234A - Preventing system for deterioration of signal-noise ratio - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a signal-noise ratio S/N by providing a control circuit to control an attenuator which detects the reception power levels of two antennas and attenuates each reception wave according to the detected levels. CONSTITUTION:An antenna circuit of an in-phase synthetic space diversity system contains filters 6 and 7 which extract reception waves, level detectors 8 and 9, attenuators 10 and 11 and a control circuit 12. The attenuation values of attenuators 10 and 11 are set at zero in a normal mode. Then the attenuation degree of the attenuator 10 is increased in case the reception power of an antenna 1, for example, is lowered by fading and then the detection level of the detector 8 is lowered less than a standard level by >=50db. Then the circuit 12 works to give virtually no noise power to a synthesizer 3. Thus the synthesizer 3 does not synthesize the reception wave received through an antenna 2 and noises. This prevents the deterioration of the S/N.

Description

[Detailed description of the invention] Q A M Bokujo temporary? This invention relates to a method for preventing deterioration of the signal-to-noise ratio, which prevents deterioration of the signal-to-noise ratio when the received power of one antenna decreases due to fading, which is related to the most popular in-phase combining space diversity method.

(b) Prior art and problems Figure 1 is a block diagram of a conventional in-phase combining space diversity system, in which 1 and 2 are antennas, 3 is a combiner, 4 is a detector, and 5 is a variable phase shifter. shows.

Specifically, the received wave received by the antenna 2 passes through the variable phase shifter 5, and then is combined with the received wave received by the antenna 1 in the combiner 3. A part of the output of the synthesizer 3 is sent to the detector 4
The detector 4 controls the variable phase shifter 5 so that the power is maximized at the same time as the detected wave is detected.

In this case, when the received power of antenna 1 decreases due to fading, for example, the output of antenna 1 becomes almost only the noise of the transmission path, and in synthesizer 3, this noise power and the received power received by antenna 2 are combined. As a result, the signal-to-noise ratio of the output of the combiner 3 deteriorates. The conventional in-phase synthesis space dyno system has these drawbacks.

(e) Purpose of the Invention In view of the above drawbacks, the purpose of the present invention is to provide a signal-to-noise ratio deterioration prevention method that can prevent deterioration of the signal-to-noise ratio when the received power of one antenna decreases due to fading. be.

(d) Structure of the Invention In order to achieve the above object, the present invention provides an attenuator or switch that attenuates the received waves received by two antennas, and each received power received by the two antennas. A level detector is installed to detect the level of the signal, and the attenuator that reduces the received wave on the received power side whose level has decreased to a predetermined value due to fading is increased, or if a switch is used, it is turned off. The received wave, which has become mostly noise on the transmission line due to fading, is controlled so as not to be input to the combiner.

(e) Examples of the invention An embodiment of the present invention will be explained below according to the drawings.

FIG. 2 is a block diagram of the in-phase synthesis space diversity system according to the embodiment of the present invention. In the figure, the same functions as those in FIG.
8 and 9 are level detectors, 10 and 11 are attenuators, and 12 is a control circuit.

In FIG. 2, a part of the received wave is taken out by single wave generators 6 and 7, which are different from those in FIG. 1, and the level is detected by level detectors 8 and 9. The point is that a control circuit 12 is provided to control the amount of attenuation of 11.

These different points will be explained below.

When the attenuators 10 and 11 are normal, the attenuation is O, but due to fading, for example, the reception power of the antenna 1 decreases, and the level detected by the level detector 8 becomes the standard level. When the noise power decreases by 50 db or more (below the predetermined value), the attenuator 10 is set to -E#'t-dog, and the control circuit is set so that almost no noise power is input to the synthesizer 3. 12.

As a result, in the combiner 3, the received wave received by the antenna 2 and noise are not combined, so that the signal-to-noise ratio does not deteriorate.

In addition, a switch is used instead of attenuator 10.11, and when it is normal, the switch is turned on and the attenuation of the received wave received by antenna 1゜2 is set to O, and the received wave level decreases due to the f-zinc. In this case, the same effect as described above can be obtained by turning off the switch in which the noise has decreased to prevent noise from being input to the synthesizer 3.

(f) Effects of the Invention As explained in detail above, according to the present invention, received waves that have become mostly transmission line noise due to fading are not input to the combiner, so there is an effect of preventing deterioration of the signal-to-noise ratio. There is.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional in-phase combining space diversity system, and FIG. 2 is a block diagram of an ItYl sum combining space diversity system according to an embodiment of the present invention. In the figure, 1 and 2 antennas, 3 a combiner, 4 a detector, 5 a flexible phase shifter, 6 and 7 a single wave generator, 8 and 9 a level detector,
10.11 shows the acid 2 killer, and 12 shows the control 11D circuit.

Claims (1)

[Claims] A transmission wave sent from one transmission system is received by two antennas, one of the received waves received by the two antennas is combined into two waves via a variable phase shifter, and a part of the combined output is an attenuator or switch that attenuates each of the received waves received by the two antennas in an in-phase combining space diversity method that detects a wave and controls the variable phase shifter using the detected signal so that the combined output is maximized; and a level detector that detects the level of each received power received by the two antennas, and the attenuator or switch that attenuates each received wave according to the level of each received power detected by the level detector. A signal-to-noise ratio deterioration prevention method characterized by providing a control control qB old 0] path.