JPS6169227A - Space diversity reception system - Google Patents

Abstract

PURPOSE:To improve the S/N to about 3dB and also to attain the cost reduction of a device by inserting a phase shifter to a microwave stage to change the phase of the output wave of a reception local oscillator which is mixed with the 2nd reception signal. CONSTITUTION:The 1st reception signal received through a primary antenna 13 is supplied to a synthesizer 4 after the conversion of frequency. While the 2nd reception signal received through an SD antenna 14 is amplified by a low noise amplifier 8 and mixed with the output wave of a reception local oscillator 6 passed through a phase shifter 16 of a microwave band by a reception mixer 9 to be converted into an intermediate frequency. The converted 2nd reception signal is synthesized with the 1st reception signal by the synthesizer 4 and amplified up to a prescribed level by a primary intermediate frequency amplifier 5. This amplified signal is delivered to the outside through a terminal 15. Then the gain of the amplifier is controlled automatically so that the output level of the amplifier 5 is kept constant. At the same time, the shifter 16 is controlled by an SD control part 12 so as to set the output of the amplifier 5 at the maximum level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a space diversity reception method used in a microwave line with multipath fading.

Generally, multipath fading is a phenomenon in which a plurality of radio waves received by an antenna through different propagation paths interfere with each other and the reception level fluctuates.

When multipath fading occurs, a deviation occurs in the amplitude characteristics within the band, and the error rate of the digital signal passing through this deviation worsens.

Therefore, a space diversity reception method (hereinafter abbreviated as SD reception method) is used to reduce the influence of this fading.

In the SD reception/reception method, two received waves are combined so that the in-band amplitude characteristic deviation is flat, and the two received waves are combined with the same phase so that the combined level is maximized. There are two commonly used methods.

In particular, in the latter case, ideally the signal-to-noise ratio of the composite wave should be improved by 3 dB, but in reality it is difficult to obtain this value.

Therefore, SDD, which further improves the signal-to-noise ratio of the synthesized wave,
A reliable method was requested.

[Conventional technology]

FIG. 2 shows a block diagram of a conventional example of the SDD communication system.

In the figure, a first reception signal received by a main antenna 13 is amplified by a low noise amplifier 1 and added to a reception mixer 2. Since the output of the receiving local oscillator 6 is added here through the distributor 7, the first received signal is frequency-converted into an intermediate frequency signal. This intermediate frequency signal is amplified by a pre-intermediate frequency amplifier 3 and then applied to a combiner 4.

On the other hand, the second received signal received by the SD antenna is transmitted to the low noise amplifier 8. Receive mixer 9. After passing through a pre-intermediate frequency amplifier 10, a phase shifter 11 configured using a two-ring balanced modulator applies phase rotation so that the signal is in the same phase as the first received signal, and is sent to a combiner 4. Added.

Therefore, the above-mentioned first and second received signals are combined by a combiner 4, and the combined intermediate frequency signal is amplified to a predetermined level by a main intermediate frequency amplifier 5 and sent to the outside from a terminal 15.

The output level of the main intermediate frequency amplifier 5 is detected, and the gain of the main intermediate frequency amplifier is automatically controlled (AGC) so that the level becomes constant, and the output level is maximized. The phase shifter 11 is controlled by the SDD control section 12.

In this way, the phase shifter 11 is inserted into the intermediate frequency stage and the second
When the phase of the received signal is controlled, the level of the received signal varies by about 1 dB, so the signal-to-noise ratio of the synthesized intermediate frequency signal is not improved by 3 dB.

Also, since the digital signal passes through this phase shifter 11,
There was a problem in that flat frequency characteristics were required over the necessary transmission band.

[Problem that the invention seeks to solve]

As explained above, the first signal received by the main and SD antennas
In order to synthesize the second received signal at the intermediate frequency stage, when the phase of the second received signal is rotated by a phase shifter placed in the intermediate frequency stage, the level changes at the same time, and the synthesized intermediate frequency The signal-to-noise ratio of the signal is not improved by 3 dB.

Furthermore, since a digital signal passes through the phase shifter, there is a problem in that the frequency characteristics must be made flat.

[Means for solving problems]

The problem mentioned above is that the first received signal received by the main antenna is mixed with the output wave from the receiving local oscillator.
and a second intermediate frequency signal obtained by mixing a second received signal received by the SD antenna with an output wave from the receiving local oscillator that has passed through a microwave band phase shifter. This problem can be solved by the SD receiving/receiving method of the present invention in which a synthesizer synthesizes the signals to obtain a composite intermediate frequency signal.

[Effect]

In the present invention, the first received signal received by the main antenna is mixed with the output wave of the receiving local oscillator, converted into an intermediate frequency signal, and then applied to the combiner.

On the other hand, the second received signal received by the SD antenna is mixed with the output of the receiving local oscillator that has passed through a phase shifter, is converted into an intermediate frequency signal, and is combined with the intermediate frequency signal in a combiner. did.

That is, the insertion position of the phase shifter is different from that of the conventional intermediate frequency stage, and the phase shifter is inserted into the microwave stage to change the phase of the output wave of the receiving local oscillator that is mixed with the second received signal. did.

Therefore, even when the phase shifter was operated, the level of the second received wave hardly changed, and the signal-to-noise ratio of the synthesized intermediate frequency signal was improved by approximately 3 dB.

Further, since the data signal does not pass through the phase shifter, the frequency characteristics of the phase shifter do not matter.

〔Example〕

FIG. 1 (al is a block diagram of one embodiment of the present invention).

Note that the same reference numerals indicate the same objects throughout the figures.

The first received signal received by the main antenna 13 is frequency converted as described above and is applied to the combiner 4.

On the other hand, the second reception signal received by the SO antenna is amplified by a low-noise amplifier 8, mixed with the output wave of the reception local oscillator 6 that has passed through a microwave band phase shifter by a reception mixer 9,
converted to an intermediate frequency.

The second received signal converted to the intermediate frequency is sent to the synthesizer 4
is combined with the first received signal at the main intermediate frequency amplifier 5.
The signal is amplified to a predetermined level and sent out from the terminal 15.

Then, the gain of the main intermediate frequency amplifier 5 is automatically controlled (8GG) so that the output level of the main intermediate frequency amplifier 5 is constant.
), and the SD control unit 12 controls the phase shifter 16 so that the output level is maximized.

Incidentally, since the phase shifter 16 operates in the microwave band, the ring modulator is constructed using, for example, a strip line.

FIG. 1(b) is a diagram of receive local oscillator output level versus conversion loss.

As shown in the figure, for example, the receiving local oscillator output is
If it is set to dBm, the conversion loss remains approximately constant even if this value changes by several dB.

That is, even if the output from the reception local oscillator 6 applied to the reception mixer changes somewhat by operating the phase shifter 16, the level of the intermediate frequency signal applied to the synthesizer 4 remains unchanged.
The signal-to-noise ratio of the synthesized intermediate frequency is improved by approximately 3 dB.

〔Effect of the invention〕

As explained above, in the present invention, even if the phase shifter is operated to rotate the phase of the received signal, the amplitude of the received signal remains approximately constant. The noise ratio is improved by approximately 3 dB, and the system gain is improved by 3 dB.

Further, since the data signal does not pass through the phase shifter, frequency characteristics are not required, which reduces the cost of the device.

[Brief explanation of the drawing]

FIG. 1(a) is a block diagram of an embodiment of the present invention. In the figure, 1.8 is a low noise amplifier, 2.9 is a receiving mixer, 3, IO is a pre-intermediate frequency amplifier, 4 is a combiner, 12 is an SD controller, and 16 is a phase shifter. Fig. 4 (a) (b) Zo4ro, town τP℃i IkS 2nd 4-tOdbs db L Hell 2nd figure light 41 tube Shigemura Mae, tcp between L father Yuku Aosagi 5
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Claims (1)

[Claims] When performing space diversity reception, the first intermediate frequency signal obtained by mixing the first received signal received by the main antenna with the output wave from the receiving local oscillator, and the second intermediate frequency signal received by the SD antenna. A synthesizer combines the received signal with a second intermediate frequency signal obtained by mixing the received signal with an output wave from the receiving local oscillator through a microwave band phase shifter to obtain a composite intermediate frequency signal. A space diversity reception method that is characterized by