JPH0529993A - Diversity circuit in single frequency alternate communication system for mobile communication - Google Patents

Abstract

PURPOSE:To improve the communication quality by detecting an error rate of a signal received by plural antennas and comparing the result so as to select a reception signal minimizing a waveform distortion against frequency selective fading. CONSTITUTION:Receivers 521, 522 are connected to antennas 561, 562 in common use for the transmission reception of a base station via high frequency switches 551, 552 and a transmitter 51 is connected to the antennas 561, 562 via switches 551, 552 and a high frequency switch 54. Reception IF signals c1, c2 and burst timing signals d1, d2 outputted from the receivers 521, 522 are inputted to an error rate detection circuit 10. The circuit 10 applies time division processing to the signals c1, c2 in response to the signals d1, d2 and inputs error rate information sets e1, e2 to a comparator circuit 20. The circuit 20 sends an antenna switching control signal to minimize an error rate to a changeover switch 59 and a switch control circuit 53. Thus, effective reception/transmission diversity is implemented and the communication quality is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention realizes a reception diversity and a transmission diversity in a base station in a one-frequency alternating communication system for mobile communication in which a single frequency signal is alternately transmitted and received between a base station and a mobile station. And a diversity circuit for improving communication quality.

[0002]

2. Description of the Related Art FIG. 5 is a diagram for explaining a one-frequency alternating communication system for mobile communication in which signals of a single frequency are alternately transmitted and received between a base station and a mobile station.

In the figure, a base station 41 includes a plurality of (in this case, two) antennas 43 for both transmission and reception for diversity.
_1, and 43 _2, has a two receivers, and one transmitter. The mobile station 45 has one transmission / reception antenna 47, one receiver, and one transmitter for downsizing.

The signal of the carrier frequency f transmitted from the antenna 43 ₁ or the antenna 43 _{2 of the} base station 41 is received by the antenna 47 of the mobile station 45. In addition, the mobile station 4
The signal of the carrier frequency f transmitted from the antenna 47 of _{No. 5 is} the antenna 43 ₁ and the antenna 43 _{2 of the} base station 41.
The receiver connected to one of the antennas is selected. That is, in the base station 41, the selection diversity is performed to demodulate the reception signal from the antenna having the maximum reception level among the reception levels of the plurality of antennas.

The one-frequency alternating communication system in which the base station 41 and the mobile station 45 perform bidirectional communication with a single frequency is shown in FIG.
As shown in, the press talk communication is to alternately transmit at a predetermined time. Here, the signal from the mobile station 45 to the base station 41 is an upstream signal, and the signal from the base station 41 to the mobile station 45 is a downstream signal. FIG. 6 shows the case of N-channel multiplexing, in which each frame from the first channel to the N-th channel has a frame length T, and each frame is composed of a preamble signal and an information signal. Transmission information is not included in the preamble signal. Further, the transmission time of the downlink signal is equal to the frame length T.

FIG. 7 is a block diagram showing a main part configuration of a conventional base station, and FIG. 8 is a block diagram showing a main part configuration of a conventional mobile station. In the figure, the transmitter 51 of the base station
And the receivers 52 ₁ and 52 ₂ include a switch control circuit 5
High-frequency switches 54 and 55 controlled to be switched by
_The antennas 56 ₁ and 56 ₂ are connected via ₁ and 55 ₂ . An antenna 65 is connected to a transmitter 61 and a receiver 62 of the mobile station via a high frequency switch 64 which is switch-controlled by a switch control circuit 63.

Here, within the transmission time T of the upstream signal transmitted by the mobile station, the high frequency switch 64 of the mobile station is operated by the transmitter 6
1 side b, high frequency switch 5 of the base station
5 ₁ and 55 ₂ are switched to the receiver a ₁ and 52 ₂ side a, respectively. The respective reception levels at the receivers 52 ₁ and 52 ₂ are detected by the level detection circuits 57 ₁ and 57 ₂ , respectively, and the levels are compared by the comparison circuit 58.
_{One of} the reception data signals demodulated by the receivers 52 ₁ and 52 ₂ is selectively output by the changeover switch 59. Here, the comparison circuit 58 switches the changeover switch 59 (reception diversity) by the antenna changeover control signal designating the antenna side having the higher reception level. The antenna switching control signal is given to the switch control circuit 53 and used for antenna selection (transmission diversity) at the time of downlink signal transmission.

Within the transmission time T of the downlink signal transmitted by the base station, the high frequency switches 55 ₁ and 55 ₂ are switched to the transmitter 51 side b by the transmission / reception switching signal output from the switch control circuit 53, and the high frequency of the mobile station is reached. Switch 64
Is switched to the receiver 62 side a. Here, since the mobile station has one antenna 65, the high frequency switch 54 of the base station receives each of the receivers 52 by the transmission antenna switching signal output from the switch control circuit 53 based on the final level determination result of the upstream signal. The reception level at ₁ , 52 ₂ is switched to the one with the higher reception level.

Such transmission diversity utilizes the reversibility of a channel having a high correlation with respect to a downlink signal following an uplink signal under the condition that the fluctuation of fading is slow,
It is considered that the downlink signal transmitted from the antenna with the higher reception level of the uplink signal received by the base station has a higher reception level at the mobile station than when transmitted from another antenna.

In this way, the base station performs reception diversity on the upstream signal and transmission diversity on the downstream signal.

[0011]

In land mobile communication, the amplitude and phase of the received wave may fluctuate irregularly due to fading caused by multipath propagation, and the transmission quality may be significantly deteriorated. The reception diversity and the transmission diversity described above have a great improvement effect on such fading in narrow band signal transmission. However, in the transmission of wideband signals, especially high speed digital signals,
An error that is difficult to reduce occurs due to the influence of waveform distortion caused by frequency selective fading, and a sufficient improvement effect cannot be expected with selective diversity by comparing levels in the same frequency band.

That is, the frequency selective fading is
Since the frequency characteristics of the received signal are distorted due to the combined reception of incoming waves with different propagation delay times, the signal transmission characteristics deteriorate significantly when the difference in propagation delay time with respect to the symbol length of the signal cannot be ignored. . Figure 9
Is when there is distortion due to frequency selective fading,
It is a diagram showing the spectrum of the received wave when there is no such signal, but it can be seen that when there is distortion, the level falls within the band, and therefore selective diversity by level comparison does not provide sufficient improvement.

It also shows that, in a configuration in which transmission diversity is performed according to reception diversity, the influence of frequency selective fading also appears in transmission diversity.

The present invention can prevent the deterioration of the reception quality at the base station at the time of receiving the uplink signal, minimize the deterioration of the reception quality at the mobile station at the time of the downlink signal transmission, and effectively bring out the diversity effect. An object of the present invention is to provide a diversity circuit in a one-frequency alternating communication system for mobile communication that can be used.

[0015]

According to the present invention, a signal of a single frequency is transmitted in a predetermined cycle between a base station having a plurality of antennas for both transmission and reception and a mobile station having one antenna for both transmission and reception. In the diversity circuit in the one-frequency alternating communication system for mobile communication that alternately transmits and receives at the base station, and performs reception diversity and transmission diversity at the base station, the base station captures a reception signal from each receiver corresponding to the plurality of antennas. Receiving diversity means for detecting an error rate of a signal obtained by sequentially demodulating each received signal, and selecting a received signal from a receiver having the minimum error rate,
And a transmission diversity means for selecting an antenna connected to the receiver that has obtained the minimum error rate from the immediately preceding received signal at the start of transmission to the mobile station.

[0016]

In the present invention, instead of comparing the levels of the signals received by a plurality of antennas, the error rate is detected and compared, so that the received signal with the minimum waveform distortion against frequency selective fading is detected. You can choose. That is, the reception diversity and the transmission diversity can be effectively operated, and the communication quality can be improved.

Furthermore, since the error rate is detected by sequentially demodulating each received signal output from the receivers corresponding to the plurality of antennas by one error rate detecting section, the deviation from each received signal is detected. It is possible to realize an error rate detection process without any error.

[0018]

1 is a block diagram showing the configuration of an embodiment of a base station according to the present invention. The mobile station has the same configuration as the conventional one shown in FIG.

In FIG. 1, a plurality of (two in this embodiment)
The both transmission and reception antennas 56 _1, 56 ₂ of the high-frequency switch 55 _1, 55 ₂ receiver 52 ₁ through 52 ₂ are connected, the high-frequency switch 55 _1, 55 ₂ and the transmitter via the high-frequency switch 54 51 is connected. The high frequency switches 54, 55 ₁ and 55 ₂ are switched according to a transmission antenna switching signal or a transmission / reception switching signal output from the switch control circuit 53. Receiver 5
_{One of} the reception data signals output from 2 ₁ and 52 ₂ is selected by the changeover switch 59. In addition,
The above configuration is similar to the conventional configuration shown in FIG.

In this embodiment, the received IF (intermediate frequency) signals c ₁ and c ₂ and the burst timing signals d ₁ and d ₂ output from the receivers 52 ₁ and 52 ₂ are detected by their error rates. Input to the rate detection circuit 10. The error rate detection circuit 10 is one, and time-divisionally processes the reception IF signals c ₁ and c ₂ according to the burst timing signals d ₁ and d ₂ . Each reception IF detected by the error rate detection circuit 10
Error rate information e ₁ of the signal c _1, c _2, e ₂ is the comparison circuit 20
The antenna switching control signal corresponding to the comparison result is sent to the changeover switch 59 and the switch control circuit 53.

The feature of the present invention is that the error rate detection circuit 10 shared by the receivers 53 ₁ and 53 ₂ corresponding to a plurality of antennas is provided, and the error rate of each upstream signal is detected to minimize the error rate. The configuration is such that reception diversity for selecting a reception data signal output from the receiver is performed, and further transmission diversity is performed for transmitting a downlink signal using an antenna corresponding to the receiver.

FIG. 2 is a frame structure of an upstream signal used in the present invention. The frame structure shown here is
This corresponds to the signal for one channel of the upstream signal shown in FIG.
Moreover, it corresponds to the case where diversity is performed using two antennas.

The frame of FIG. 2 (1) has preamble signals 21 and 22 having a signal length T _d , an information signal 23, and a signal length T.
The postamble signals 24 and 25 of _d . When receiving the upstream signal, first, the reception IF signal c output from the receiver 52 ₁ between the preamble signals 21.
₁ of measuring the error rate, receiving the next error rate of the received IF signal c ₂ output from the receiver 52 ₂ between the preamble signal 22 is measured and is outputted from the receiver side with the smaller error rate A data signal is selected and its information signal 23 is processed (receive diversity). In addition, when transmitting the downlink signal, the receiver 5 is placed between the postamble signals 24 of the uplink signal.
The error rate of the received IF signal c ₁ output from 2 ₁ is measured, and then the error rate of the received IF signal c ₂ output from the receiver 52 ₂ between the postamble signals 25 is measured to determine the error rate. Perform transmit diversity to select the antenna corresponding to the lesser receiver output. It should be noted that such a frame configuration requires a number of preamble signals and postamble signals according to the number of antennas, so that the frame utilization efficiency decreases.

Note that if each bit of the preamble signal and the postamble signal is divided into times corresponding to the number of antennas, and the error rate is measured by sequentially fetching them from each receiver, one bit shown in FIG. It can be realized by a frame configuration using only the preamble signal 21 and the postamble signal 24.

FIG. 3 is a block diagram showing the configuration of an embodiment of the error rate detection circuit 10. It should be noted that the case where a signal having the frame structure shown in FIG. 2A is received is shown here. In the figure, reception I output from receivers 52 ₁ and 52 ₂
The F signals c ₁ and c ₂ are connected to the contacts a and b of the changeover switch 11. One of the reception IF signals output from the changeover switch 11 is input to the decoding circuit 13 via the demodulation circuit 12, and the decoded data is output. Decoded data corresponding to the received IF signals c ₁ and c ₂ are alternately taken out (,) via the changeover switch 14 and input to the bit collating circuits 15 and 16, respectively. The bit matching circuits 15 and 16 output the results of bit matching as error rate information e ₁ and e ₂ .

Further, burst timing signals d ₁ and d ₂
The timing generation circuit 17 to which the
The head of the burst is detected according to the burst timing signals d ₁ and d ₂ with reference to the clock signal supplied from
Demodulation circuit 12 and decoding circuit 1 as a burst synchronization signal
3 and also to the switch control circuit 19 for switching the changeover switches 11 and 14 by generating the switching timing of the time T _d of the preamble signal and the postamble signal on the basis of the burst synchronization signal. The switch control circuit 19 generates a switching signal for alternately switching the switching switches 11 and 14 according to the switching timing.

FIG. 4 is a time chart showing an example of the signal waveform of each part of the error rate detection circuit. The change-over switches 11 and 14 are switched at each time T _d of the preamble signal, and the decoded data of the preamble signal of each of the reception IF signals c ₁ and c ₂ is taken out alternately. Decoded data alternately fetched from the changeover switch 14 are processed by the bit collating circuits 15 and 16, respectively. The bit matching circuits 15 and 16 have a built-in circuit that generates a repeating pattern signal of 1,0 when a repeating pattern signal of 1,0 is used for the preamble signal and the postamble signal, and the result of bit matching is performed. Are output as error rate information e ₁ and e ₂ . Note that here, the error rate information e ₁ and e ₂ are exclusive OR results, and the logic “1”
Indicates an error, and the ratio is the error rate.

After receiving the information signal, the same processing is performed on the postamble signal, and the corresponding error rate information e ₁ and e ₂ is output. When the error rate detection circuit 10 receives a signal having the frame structure shown in FIG. 2 (2), the switching signal is inverted at the timing of dividing each bit into two. That is, each bit of the preamble signal and the postamble signal is divided into two and processed by the demodulation circuit 12 and the decoding circuit 13, respectively, and the bit matching circuit 1
The error rate information e ₁ and e ₂ are obtained in the same manner by being provided to the channels 5 and 16 and can be used for diversity processing.

[0029]

As described above, the present invention is configured to detect the error rate of signals received by a plurality of antennas and perform the receive diversity and the transmit diversity.
An antenna that is less affected by waveform distortion due to frequency selective fading can be selected. That is, each diversity effect can be sufficiently brought out, which is effective in improving communication quality.

Further, since the error rate detecting function is used in a time division manner, deviation between branches is eliminated, and accurate diversity processing can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a base station according to the present invention.

FIG. 2 is a diagram showing an example of a frame structure of an upstream signal in the present invention.

FIG. 3 is a block diagram showing a configuration of an embodiment of an error rate detection circuit 10.

4 is a time chart showing signal waveforms of various parts of the error rate detection circuit 10. FIG.

FIG. 5 is a diagram illustrating a one-frequency alternating communication system for mobile communication.

FIG. 6 is a diagram illustrating alternate communication between a base station and a mobile station.

FIG. 7 is a block diagram showing a main configuration of a conventional base station.

FIG. 8 is a block diagram showing a main configuration of a conventional mobile station.

FIG. 9 is a diagram showing waveform distortion due to frequency selective fading.

[Explanation of symbols]

10 error rate detection circuit 11, 14 changeover switch 12 demodulation circuit 13 decoding circuit 15, 16-bit matching circuit 17 timing generation circuit 18 main oscillator 19 switch control circuit 20 comparison circuit 41 base station 43 ₁ , 43 ₂ , 47 antenna 45 mobile station 51 transmitter 52 ₁ , 52 ₂ receiver 53 switch control circuit 54, 55 ₁ , 55 ₂ high frequency switch 56 ₁ , 56 ₂ antenna 57 ₁ , 57 ₂ level detection circuit 58 comparison circuit 59 selector switch 61 transmitter 62 receiver 63 Switch control circuit 64 High frequency switch 65 Antenna

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[Procedure amendment]

[Submission date] October 7, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

FIG. 7 is a block diagram showing a main part configuration of a conventional base station, and FIG. 8 is a block diagram showing a main part configuration of a conventional mobile station. In the figure, the transmitter 51 of the base station
And the receivers 52 ₁ and 52 ₂ include a switch control circuit 5
A high-frequency switch 54 controlled to be switched by 3 and
Via the contacts a and b of the high frequency switches 55 ₁ and 55 ₂ ,
The antennas 56 ₁ and 56 ₂ are connected. In the transmitter 61 and the receiver 62 of the mobile station, the contacts a and b of the high frequency switch 64 controlled to be switched by the switch control circuit 63.
The antenna 65 is connected via.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

Within the transmission time T of the downlink signal transmitted by the base station, the transmission / reception switching output from the switch control circuit 53 is performed.
The high frequency switch 55 _1, 55 ₂ are switched to the transmitter 51 side b by recombination signals, the mobile station frequency switch 64
Is switched to the receiver 62 side a. Here, since the mobile station has one antenna 65, the high frequency switch 54 of the base station receives each of the receivers 52 by the transmission antenna switching signal output from the switch control circuit 53 based on the final level determination result of the upstream signal. The reception level at ₁ , 52 ₂ is switched to the one with the higher reception level.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

A feature of the present invention is that the error rate detection circuit 10 shared by the receivers 52 ₁ and 52 ₂ corresponding to a plurality of antennas is provided, and the error rate of each upstream signal is detected to minimize the error rate. The configuration is such that reception diversity for selecting a reception data signal output from the receiver is performed, and further transmission diversity is performed for transmitting a downlink signal using an antenna corresponding to the receiver.

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

Claims (1)

Claim: What is claimed is: 1. A base station having a plurality of antennas for both transmission and reception, and a mobile station having a single antenna for both transmission and reception. In the diversity circuit in the mobile communication one-frequency alternating communication method for performing reception diversity and transmission diversity in the base station, the base station, the received signal from each receiver corresponding to the plurality of antennas, respectively, The reception diversity means for detecting the error rate of the signal sequentially demodulating the received signal of, and selecting the received signal from the receiver whose error rate is the minimum, at the start of transmission to the mobile station, the received signal immediately before One-frequency alternating for mobile communication, characterized by comprising: transmit diversity means for selecting an antenna connected to a receiver having a minimum error rate Diversity circuit in the signal system.