JPS6159572B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a diversity reception method used to reduce the effects of fading that occurs in a wireless transmission path, and more specifically, it monitors the line quality in the IF band to provide optimal diversity. The present invention relates to a diversity switch that selects a city branch.

Well-known diversity methods include space diversity (hereinafter abbreviated as SD) and frequency diversity (F´requency).
Diversity is hereinafter abbreviated as FD. ) etc. These methods attempt to maintain line quality by combining or selecting each diversity branch, with the expectation that there will be uncorrelated fading between spatially separated antennas or between different frequencies. It is something to do.

In such cases, linear combining methods such as selection combining, maximal-ratio combining, and equal-gain combining are often used in the prior art. However, all of these synthesis methods depend on the signal-to-noise ratio (hereinafter referred to as
Shown in SNR. ) are subject to evaluation. For this reason, it is extremely effective in cases such as non-selective fading, where the increase in thermal noise associated with a decrease in the received electric field has a dominant effect on line quality deterioration; however, as in selective fading, it is It is not very useful in cases where amplitude first-order and second-order distortion or delay distortion occurs on the amplitude frequency characteristics, which causes fatal waveform deterioration.

This is because selective fading does not necessarily occur without a reduction in the received electric field, so the conventional synthesis method that evaluates only the received electric field is insufficient.

An object of the present invention is to select a diversity branch with the best quality by detecting selectivity fading that occurs in the propagation path, thereby maintaining line reliability. The purpose is to provide circuits.

In order to achieve the above object, the uninterrupted diversity switching circuit according to the present invention converts the received electric field of each branch of a receiving system having two or more diversity branches and the amplitude on the amplitude frequency characteristic generated in the transmission line of each branch. A detection circuit installed in each branch that detects first-order distortion and second-order distortion from frequency components on the power spectrum of the received signal, and a detection circuit installed in each branch that detects the carrier wave phase of each signal of all branches by changing the carrier wave phase of any one branch. a calculation control circuit that generates a signal that performs calculations according to a preset algorithm using the outputs of all of the detection circuits and selects the branch with the least waveform distortion among all the branches; a switch that selects one output from the circuit outputs for aligning the phases according to the output of the control circuit, and selects the branch with least waveform distortion due to selective fading among the plurality of branches to obtain a received signal. It is structured as follows.

According to the above configuration, the object of the present invention can be completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a diversity switching circuit according to the present invention. In the figure,
No. 1 to No. N (N≧2, integer) are the first to Nth diversity branches.

The received signals of these N diversity branches are N
The signal is input to a circuit 3 that aligns the phase of each branch with the phase of one of the carrier waves.

One of the signals whose phases have been aligned in the circuit 3 is selected by the switching circuit 4.

The present invention enables uninterrupted switching of the switching circuit 4 in which the circuit 3 selects the diversity branch of the best quality. On the other hand, each of the N diversity branches has a circuit 1 that detects the first-order and second-order distortion of the amplitude frequency characteristic (hereinafter referred to as amplitude characteristic) of the transmission path by detecting the received electric field and the frequency of the power spectrum of the received signal. is provided. All the outputs of the detection circuit 1 of each branch are sent to the arithmetic control circuit 2.
Here, the best branch is calculated using a predetermined algorithm and the above-mentioned switching circuit 4 is controlled. The present invention is characterized in that it detects selective fading compared to conventional examples, and the circuit 3 and switching circuit 4 are not particularly different from the conventional examples already proposed in terms of configuration. A detailed explanation of 4 will be omitted. Therefore, the description will focus on the detection circuit 1.

Details of the circuit for detecting the first-order and second-order distortion of the amplitude characteristic in the detection circuit 1 are shown in FIG.

The received signals from the aforementioned branches are respectively guided to low-pass filters 5, 6, and 7 having amplitude-frequency characteristics as shown in FIG. In FIG. 3, A or center frequency (f ₀ +f ₁ ) is of filter 5, B or center frequency (f ₀ - f ₁ ) is of filter 6, and C or center frequency f ₀ is of filter 7. The characteristics of each are shown (here, f ₀ is the center frequency of the signal band, and f ₁ is an appropriate frequency). The signals passing through each filter are level detected by level detectors 8, 9, and 10, respectively. The output of the level detector 8 is input to the non-inverting input terminal of the differential amplifier 11, and the output of the level detector 9 is input to the inverting input terminal of the differential amplifier ₁₁ . The signal components (signal power) on the high frequency side are compared, the difference is extracted, and the first-order distortion is detected.

On the other hand, the differential amplifier 12 has the average value of the outputs of the level detectors 8 and 9 (averaged by resistors R ₁ and R ₂ ).
is input to the non-inverting input terminal, and the output of the level detector 10 is input to the inverting input terminal, signal components in the vicinity of f ₀ are compared, the difference is extracted, and second-order distortion of the amplitude characteristic is detected. The primary and secondary distortions of each branch extracted in this way are calculated by the calculation control circuit 2 as described above, and a control signal for selecting the best quality is sent to the switching circuit.

As explained in detail above, the present invention focuses not only on the SNR (determined by the received electric field) of each transmission line, but also on the first-order amplitude characteristic, which causes fatal signal waveform deterioration for the line. Since secondary components are also monitored, an even better diversity reception system is possible.

In particular, in wireless transmission systems for large-capacity digital data, the outage rate of the line has a strong correlation with various distortions caused by selective fading, and during the outage period due to a drop in the received electric field (increase in thermal noise), the outage rate is extremely high. Known to be small portions. Therefore, the diversity switching circuit according to the present invention is an extremely effective means for diversity systems in terrain where selective fading such as k-type fading and duct fading occurs frequently.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the uninterrupted diversity switching circuit according to the present invention, and FIG.
FIG. 3 is a block diagram of an embodiment of the amplitude first-order and second-order distortion detection circuit, and FIG. 3 is an amplitude-frequency characteristic diagram of the narrow band filter shown in FIG. DESCRIPTION OF SYMBOLS 1... Amplitude primary and secondary distortion detection circuit, 2... Arithmetic control circuit, 3... Circuit for aligning the phase of carrier waves of N branches to the phase of any one branch, 4... Switch, 5. 6, 7...Narrowband filter, 8, 9, 10
... Level detector, 11, 12 ... Differential amplifier.

Claims (1)

[Claims] 1 In a receiving system with two or more diversity branches, the received electric field of each branch and the amplitude first-order distortion and second-order distortion on the amplitude frequency characteristics generated in the transmission path of each branch are calculated from the frequency components on the power spectrum of the received signal. To detect,
A detection circuit provided in each branch, a circuit that aligns the carrier wave phase of each signal of all branches to the carrier wave phase of any one branch, and the output of all the detection circuits described above are used to perform a preset an arithmetic control circuit that calculates according to an algorithm and generates a signal that selects the branch with the least waveform distortion among all the branches; and a circuit that aligns the phases using the output of the arithmetic control circuit and selects one output. a switch that selects a branch with the least waveform distortion due to selective fading from among the plurality of branches, and is configured to obtain a received signal.