JPS62195935A - Diversity reception system - Google Patents

Abstract

PURPOSE:To improve the error rate characteristic due to a delay distortion by selecting a diversity branch having the highest reception level when the reception level is low and selecting the diversity branch having the least delay distortion when the reception level is high. CONSTITUTION:A signal received by diversity branches 1, 2 is inputted to receivers 3, 4, subject to identification and discrimination by demodulation circuits 5, 6 and an envelope level is extracted by envelope detection circuits 7, 8. The amplitude of the beat component of the envelope level signal extracted by high pass filters 11, 12 is fed to a delay distortion comparator circuit 17, where which diversity branch has lesser delay distortion is discriminated and when the mean reception level is higher than or equal to the threshold value, the result of the delay distortion comparator 17 is outputted respectively to the selection circuit 19. Thus, the diversity branch having the lowest mean error rate is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aims to improve transmission characteristics in digital mobile communication where bit error rate characteristics are severely degraded due to multipath 7-enong (especially propagation delay time dispersion), etc. This relates to a diversity reception method used to achieve this.

[Conventional technology]

Conventional diversity reception methods select and combine outputs from a plurality of diversity techniques according to the respective reception levels or S/N ratios of the diversity techniques. This works effectively against a drop in reception level (envelope #!7A song) caused by multipath 7 aging, and is useful for improving transmission characteristics in the low electric field region.

[Problem that the invention seeks to solve]

In the conventional diversity reception method described above, when transmitting a high-speed digital signal with a transmission rate of 64 kbps or higher over a mobile radio channel, as in the case of mobile communication, code amount interference caused by propagation delay time dispersion is detected. This causes large distortion (delay distortion) in the waveform, resulting in a phenomenon called a "floor" in which the error rate does not fall below a certain value even if the reception level becomes high.

The above-mentioned conventional method has a drawback in that it cannot sufficiently improve the delay distortion.

Figure 1 shows 128kbps actually measured in the Tokyo area.
MS K (Minimum 5hift Keyin)
g) Average error rate characteristics of the signal.

Here, the figure shows that selection diversity after two-branch spatial detection is used as diversity, and code errors due to delay distortion are not significantly reduced even with diversity, and the error rate is low even in the strong electric field region (30 clB or more). 6X10-
'You can see that it doesn't go below.

In view of these conventional problems, the present invention reduces the influence of the envelope 7enong by selecting the diversity branch with the highest reception level when the reception level is low, as in the conventional method, and also reduces the reception level by selecting the diversity branch with the highest reception level. When the delay distortion is high, the diversity technique with the least delay distortion is selected (controlled), and the objective is to provide a diversity reception method that can improve the floor of error rate characteristics due to delay distortion.

[Means for solving problems]

According to the present invention, the above object is achieved by the means described in the claims.

The effects and the like will be explained below in relation to the actual state of the received signal.

FIG. 12 is a diagram showing an example of instantaneous reception level fluctuations observed in a mobile radio channel.

In the tIS2 diagram, the gradual fluctuation is due to envelope 7 aging, and the fluctuation frequency is approximately 30 when the carrier frequency is 800 MHz and the moving speed is 40 km/h.
H2, which is relatively low.

On the other hand, the high-frequency beat components that can be seen in several places in the figure are caused by interference between the direct wave and the delayed wave, and the fluctuating frequency can range up to several tens of kHz, making it difficult for the digital signal to be transmitted. transmission speed close to that of When the average reception level is low, code errors 9 occur intensively in areas where the instantaneous reception level drops, so it can be said that the main factor in the deterioration of the transmission characteristics is envelope aging.

However, when the average reception level becomes high, the code errors due to the decrease in the reception level almost disappear, and instead code errors due to delay distortion occurring in the region where the beat component appears become dominant. In the case of the measured values in Figure 1, the area where the ift') rate decreases almost linearly as the average received level increases (average received level -10 to 10 dBμ)
In the fit range (average reception level 10 to 40 dBμ) where the error rate is approximately constant, delay distortion is the dominant factor.

In the present invention, when the reception level is low, by selecting the diversity branch with the highest reception level, the envelope +Ii
By reducing the influence of the 7-enong and selecting the diversity branch with the least delay distortion when the reception level is high, the floor of the error rate characteristic due to delay distortion is improved.

〔Example〕

FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention (selection diversity after two-branch detection), in which 1.2 is the diversity technique (antenna), 3.4 is the receiver, and 5.6 is the demodulation circuit, 7.8 is an envelope detection circuit, 9.10 is a low-pass filter, 11.12 is a high-pass filter, 13 is a reception level comparison circuit, 14 is an averaging circuit, 15 is a comparison circuit, 16 is a threshold generation circuit, 17 is a delay distortion comparison circuit, 18 is a date circuit, 19 is a selection circuit, and 20 is an output terminal.

In FIG. 3, the signal received by the diversity branch 1.2 is input to the reception @3, 4, is discriminated by the demodulation circuit 5.6, and the envelope level is detected by the envelope detection circuit 7.8. The extracted 6-envelope level signal is passed through a low-pass filter 9.
At ゜10, only the instantaneous fluctuation component of the reception level is extracted,
The signal is input to the reception level comparison circuit 13.

The reception level comparison circuit 13 determines which of the two diversity branches has a higher reception level, outputs the result to the date circuit 18, and outputs the higher reception level to the averaging circuit 14. The reception level averaged by the averaging circuit 14 is compared with a threshold value by the comparison circuit 15, and the comparison result is output to the date circuit 18.

On the other hand, the amplitude value of the beat component of the envelope level signal extracted by the high-pass filters 11 and 12 is determined by the delay distortion comparison circuit 1.
7, it is determined which diversity branch has less delay distortion, and the result is output to the date circuit 18. Based on the comparison result of the comparator circuit 15, the date circuit 18 delays the result of the reception level comparison circuit 13 when the average reception level is lower than the threshold; and ■ delays the result of the reception level comparison circuit 13 when the average reception level is higher than or equal to the threshold. The results of the distortion comparison circuit 17 are output to the selection circuit 19, respectively. With the support of the date circuit 18, the selection circuit 19 selects one of the demodulated data in the two diversity techniques and outputs it to the terminal 20.

Although this embodiment uses a method of detecting the magnitude of the beat component appearing in the envelope of the received signal as a means of detecting delay distortion, it is also possible to detect delay distortion by monitoring the frequency spectrum of the received signal. Various methods can be considered, such as a method of determining the frequency characteristics of a transmission path and a method of detecting the degree of waveform distortion of a demodulated signal.

FIG. 4 shows an example of measuring the average bit error rate in the diversity reception method of the present invention, where curve 30 is for the conventional method and curve 31 is for the method of the present invention.

In addition, under the measurement conditions, the modulation and demodulation method is MSK (Mi
nimus 5hift Keying) Frequency detection, transmission speed is 128 kbps, 7 ainong bit is 4
0Hz, average CNR is 50dB, number of arriving waves is 2 waves,
Each arriving wave undergoes mutually independent Rayleigh 7 aging,
The propagation delay time difference was 2 μs.

In addition, the number of diversity techniques is 2, and the D/U in branch 1 is
The ratio (power ratio of direct wave and delayed wave) was set to OdB. The vertical axis is the average bit error rate, and the horizontal axis is the D/U ratio in Technique 2.

The figure shows that when the D/U ratio of sheet 2 is OdB, there is no difference between the present method and the conventional method, but as the D/U ratio increases, the present method shows a greater error rate reduction effect. When the D/U ratio is 20 dB, an improvement of about two orders of magnitude is obtained compared to the conventional method. The present measurement results show that the present method is particularly effective in directional diversity, which has the property that large differences in the A/U ratio occur between diversity techniques.

Furthermore, in the configuration shown in FIG. 3, a diversity technique with the lowest bit error rate is determined from the output signals of the reception level detection means and the delay distortion detection means, and a demodulated signal in that diversity technique is selected and output. You can also take

If an index indicating the degree of delay distortion, such as a D/U ratio or a propagation delay time difference, and an average reception level are given, then the average bit error rate at that time can be determined.

Therefore, by monitoring the degree of delay distortion and reception level in each diversity branch, it is possible to find the diversity branch with the lowest average error rate, and select and output the demodulated signal in this diversity technique.

In this case, each of the circuits 13 to 19 in the block diagram of tJS3 may be replaced with a control circuit that performs the above-described operation.

〔Effect of the invention〕

As explained above, when the reception level is low, the diversity reception method of the present invention reduces the influence of the envelope 7enong by selecting the diversity branch with the highest reception level, as in the conventional method, and when the reception level is high. Envelope #17 x
- It has the advantage of having a large improvement effect on delay distortion caused not only by the non-contact but also by propagation delay time dispersion.

Note that the present invention is particularly effective when the average D/U ratio for each diversity technique is not equal, such as in directional diversity.

[Brief explanation of drawings]

Figure 1 shows 128kbps actually measured in the Tokyo area.
(Minimum 5hift Keying) Signal average error rate characteristics, j@2 Figure 3 shows an example of instantaneous reception level fluctuation observed in a mobile radio channel.
The figure shows an example of the present invention (selection diversity after two-prong detection)
FIG. 4 is a block diagram showing the configuration of , and is an example of measuring the average bit error rate in the diversity reception system of the present invention. 1.2 ...Diversity branch, 3,4 ・
...Receiver, 5.6 ...Demodulation circuit,
7g8 ... Envelope detection circuit, 9.10
...low-pass filter, 11.12 ...
...High-pass filter, 13 ...Reception level comparison circuit, 14 ...Averaging circuit, 15 ...
...Comparison circuit, 16 ...Threshold generation circuit, 17 ...Delay distortion comparison circuit, 1st
...Date circuit, 19 ...Selection circuit, 20 ...Output terminal, 30 ...
...Characteristics of the conventional method, 31 ...Characteristics of the method of the present invention Agent Patent attorney Souhei Honma 3-17 Receptor input strength dB) t) Raku l Figure 2 Figure 3 Zufu 20hei → Sθθ ratio (dB) 4th

Claims (1)

[Claims] (1) A digital mobile communication system, comprising a plurality of diversity branches, means for detecting the reception level in each diversity branch, and means for detecting the degree of delay distortion in each diversity branch. , when the average reception level is lower than a predetermined value, the diversity branch with the highest instantaneous reception level is selected, and when the average reception level is above the predetermined value, the diversity branch with the least delay distortion is selected. Diversity reception method. (2) The diversity reception system according to claim (1), which uses unidirectional antennas with mutually different pointing directions as the diversity branches. (3) The diversity reception system according to claim (1), which uses a method of detecting the magnitude of a beat component appearing in the envelope of a received signal as means for detecting the degree of delay distortion.