JPH0529992A - Diversity circuit in time division multiple access, single frequency alternate communication system for mobile communication - Google Patents

Abstract

PURPOSE:To improve the communication quality by detecting the error rate of a signal received by plural antennas and comparing the result so as to select a reception signal minimizing a waveform distortion with respect to frequency selective fading. CONSTITUTION:An incoming signal sent from a mobile station is received by each of receivers 521, 522 via a high frequency switch 54 from antennas 551, 552 of a base station. After a demodulated base band signal is decoded by relevant decoders 561, 562 respectively, the signal is inputted to error check circuits 111,112. The circuits 111, 112 are configured corresponding to the error check coding circuit provided to each mobile station and check the parity for each prescribed bit number to output an error bit number. The error bit numbers outputted from the circuits 111, 112 are compared by an error bit number comparator circuit 12, and the reception data signal of a reception system having a least error rate is selected via a base band switch 58 as a signal from the mobile station. Thus, a propagation line best for code transmission is employed 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 relates to a time division multiple access single frequency alternating communication system for mobile communication, in which a single frequency signal is alternately transmitted and received between a base station and a plurality of mobile stations. The present invention relates to a diversity circuit that realizes diversity and transmission diversity to improve communication quality.

[0002]

2. Description of the Related Art FIG. 6 is a diagram for explaining a time division multiple access single frequency alternating communication system for mobile communication in which a signal of a single frequency is alternately transmitted and received between a base station and a mobile station.

In the figure, a base station 71 and a plurality of mobile stations 7 are shown.
5 ₁ to 75 _n have the same carrier frequency f, and the mobile stations 75 ₁ to 75 ₁ to each time slot of the frame configuration shown in FIG.
By assigning 75 _n and transmitting alternately, time division multiple access communication using one frequency is performed. Each frame is composed of a guard time, a preamble, and data. Further, a signal from the mobile stations 75 ₁ to 75 _n to the base station 71 is an up signal, and a signal from the base station 71 to the mobile stations 75 ₁ to 75 _n is a down signal.

[0004] FIG. 8 is a block diagram showing a main structure of a conventional base station, and FIG. 9 is a block diagram showing a main structure 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
Antennas 55 ₁ and 55 ₂ are connected via a high-frequency switch 54 whose switching is controlled by 3. Base station 71
A plurality of mobile stations 75 _{1 to} 7 accommodated in the base station.
When receiving the upstream signal from 5 _n , the high-frequency switch 54 is controlled by the switch control circuit 53 so that the antenna 55
₁ , 55 ₂ and receivers 52 ₁ , 52 ₂ are connected respectively. 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. Further, a transmission data signal is input to the transmitter 61 via an encoder 66, and a baseband signal output from the receiver 62 is output as a reception data signal via a decoder 67.

The uplink signal transmitted from the mobile station 75 _n in the n-th time slot of the uplink signal frame is received by the corresponding receivers 52 ₁ and 52 ₂ via the antennas 55 ₁ and 55 ₂ of the base station 71. To be done. Multiple receivers 52
_The baseband signals output from ₁ and 52 ₂ are input to and decoded by decoders 56 ₁ and 56 ₂ , respectively. In addition, the reception level signals output from the plurality of receivers 52 ₁ and 52 ₂ are input to the level comparator 57, which outputs a level comparison result indicating which receiver has the maximum reception level. The baseband switch 58 selects the one having the maximum reception level from the reception data signals output from the plurality of decoders based on the level comparison result. At the same time, the level comparison result is sent to the storage circuit 59 and stored in the address corresponding to the mobile station 75 _n at the last timing of the time slot. In this way, the base station performs the reception diversity for selecting the reception signal from the antenna having the maximum reception level among the plurality of antennas.

The transmission data signal transmitted from the base station 71 to the mobile station 75 _{n in} the n-th time slot of the downlink signal frame is sent to the transmitter 51 via the encoder 60. Further, since the level comparison result compared at the last timing of the time slot of the upstream signal transmitted immediately before from the mobile station 75 _n is stored in the memory circuit 59, the switch control circuit 53 is based on the level comparison result. Then, the radio frequency switch 54 is controlled to select the antenna having the maximum reception level of the upstream signal and transmit diversity is performed to transmit the downstream signal.

[0007] Such transmission diversity utilizes the reversibility of a channel having a high correlation with respect to a downlink signal subsequent to an uplink signal under the condition that the fluctuation of fading is slow. That is, the situation of the propagation path in the n-th time slot of the upstream signal frame and the situation of the propagation path in the n-th time slot of the subsequent downlink signal frame are approximately equal to each other and are received by the base station. It is assumed that the downlink signal transmitted from the antenna having the higher reception level of the uplink signal has a higher reception level at the mobile station than the case of transmitting from the other antenna.

As described above, the base station performs the reception diversity on the upstream signal and the transmission diversity on the downstream signal, so that the deterioration of the reception quality due to the fading can be improved even in the mobile station.

[0009]

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. ..

Since an error occurs due to intersymbol interference in a propagation path in which a delayed wave exists in this way, even if the diversity branch that maximizes the reception level is selected, the best propagation path in terms of code transmission is not necessarily found. It was not always the choice.

Further, it 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 time division multiple access single frequency alternating communication system for mobile communication.

[0014]

According to the present invention, a signal of a single frequency is predetermined between a base station having a plurality of antennas for both transmission and reception and a plurality of mobile stations having a single antenna for both transmission and reception. In a diversity circuit in a time division multiple access single frequency alternating communication system for mobile communication that alternately transmits and receives in a cycle of, the base station performs reception diversity and transmission diversity, the mobile station, the base station in the assigned time slot. The base station is provided with error detection coding means for performing error detection coding of the uplink signal to be transmitted to the base station, and the base station receives the uplink signal from each of the plurality of antennas and demodulates it for each mobile station. Receive diversity means for detecting an error rate of a received signal and selecting a received signal from a receiver having the smallest error rate, and at the time of starting transmission to the mobile station. Characterized by comprising a transmit diversity means for selecting the antenna lowest error rate on the receiving signal is connected to the resulting receiver just before.

[0015]

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.

[0016]

1 is a block diagram showing the configuration of an embodiment of a base station according to the present invention. In the figure, transmitters 51, 2
System receivers 52 ₁ and 52 ₂ , antennas 55 ₁ and 55 ₂
And decoders 56 ₁ and 56 ₂ , a switch control circuit 53,
The configurations of the high frequency switch 54, the baseband switch 58, the storage circuit 59, and the encoder 60 are the same as those of the conventional base station shown in FIG.

The base station in the present invention comprises a level comparator 5
Instead of _No. 7, in this embodiment, error detection circuits 11 ₁ and 11 ₂ that perform error detection on the received data signals output from the decoders 56 ₁ and 56 ₂ and output the number of error bits, and the number of error bits respectively. And an error bit number comparison circuit 12 for determining which receiving system has the lowest error rate, and switching the baseband switch 58 according to the determination result, and determining the determination result. Is stored in the storage circuit 59 for each time slot.

FIG. 2 is a block diagram showing the configuration of an embodiment of a mobile station according to the present invention. In the figure, a transmitter 61,
Receiver 62, switch control circuit 63, high frequency switch 6
The configurations of 4, the antenna 65, the encoder 66, and the decoder 67 are the same as those of the conventional mobile station shown in FIG.

The mobile station according to the present invention is characterized by being provided with an error detection encoding circuit 21 for performing error detection encoding of an upstream signal in order to detect an error in the base station.
In the base station and the mobile station configured as described above, the operation of transmitting and receiving the upstream signal transmitted from the mobile station 75 _n to the base station 71 ₁ will be described first.

The mobile station 75 _n transmits the upstream signal to the base station 71 at the carrier frequency f in the nth time slot of the upstream signal frame. At this time, the transmission data signal is encoded by the encoder 66 and then error detection encoded by the error detection encoding circuit 21, and the transmitter 61 and the high frequency switch 64 are provided.
It is transmitted from the antenna 65 via the. It should be noted that the error detection coding circuit 21 may have a general configuration in which one parity bit is inserted for every 7 bits of the transmission data signal, as shown in FIG. Here, reference numeral 31 is a serial-parallel conversion circuit, reference numeral 32 is an exclusive OR circuit, reference numeral 33 is a latch circuit, and reference numeral 34 is a selector.

In the base station 71, the uplink signals transmitted from the mobile station 75 _n are received by the receivers 52 ₁ and 52 ₂ from the plurality of antennas 55 ₁ and 55 ₂ via the high frequency switch 54. The baseband signals demodulated here are input to the error detection circuits 11 ₁ and 11 ₂ after being decoded by the corresponding decoders 56 ₁ and 56 ₂ . The error detection circuits 11 ₁ and 11 ₂ have a configuration corresponding to the error detection coding circuit 21 as shown in FIG. 4, and perform a parity check for every 8 bits and output the number of error bits. Reference numeral 35 is a serial / parallel conversion circuit, reference numeral 36 is an exclusive OR circuit, reference numeral 37 is a latch circuit, and reference numeral 38 is a counter.

The number of error bits output from the error detection circuits 11 ₁ and 11 ₂ corresponding to each diversity branch is
The error bit number comparison circuit 12 compares the error bit numbers to determine which receiving system has the lowest error rate, and the base band switch 58 is controlled based on the determination result. That is, the received data signal of the receiving system with the smallest error rate is selected as the signal from the mobile station 75 _n .

Therefore, the mobile station 75 _n to the base station 71
Among the propagation paths to the plurality of antennas 55 ₁ and 55 ₂ , the information can be transmitted using the best propagation path in code transmission, and the communication quality can be improved.

Further, the determination result of the error bit number comparison circuit 12 is stored in the storage circuit 59 for each mobile station in the same manner as the conventional level comparison result. That is, in the storage circuit 59, as shown in FIG. 5, the determination result of the error bit number comparison circuit 12 is sent to the memory 42 via the data bus 41. Further, a clock signal (burst synchronization signal) for time division multiple access is input to the memory circuit 59, the address conversion circuit 43 creates an address corresponding to the mobile station 75 _n in accordance with the clock signal, and the address conversion circuit 43 generates the address via the address bus 44. It is given to the memory 42. The contents of the memory 42 are rewritten at the last timing of the time slot in which both the address and the data are fixed, and the determination result is stored in the address corresponding to each mobile station.

Next, the transmission operation of the downlink signal transmitted from the base station 71 ₁ to the mobile station 75 _n in the base station and the mobile station will be described. Here, the determination result of the number of error bits detected at the last timing of the time slot of the uplink signal transmitted immediately before from the mobile station 75 _n is the storage circuit 5
9, the corresponding address is generated in the n-th time slot of the downlink signal frame, and the determination result is read from the memory 42 of the storage circuit 59. The switch control circuit 53 controls the high-frequency switch 54 based on the read test result, selects the antenna with the smallest error rate of the upstream signal, and performs transmission diversity to transmit the downstream signal.

Therefore, even if the mobile station 75 _n does not have a diversity circuit, the transmission diversity in the base station 71 enables the receiving operation using the best propagation path for code transmission, and improves the communication quality. You can

[0027]

As described above, the present invention detects the error rate of each upstream signal received by the receiver corresponding to a plurality of antennas, and the received data signal output from the receiver having the minimum error rate. It is possible to perform receive diversity to select, and to perform transmit diversity by transmitting the downlink signal using the antenna corresponding to that receiver, so select an antenna that is less affected by waveform distortion due to frequency selective fading. You can That is, each diversity effect can be sufficiently brought out, and the communication quality of both the base station and the mobile station can be improved.

[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 block diagram showing a configuration of an embodiment of a mobile station according to the present invention.

FIG. 3 is a block diagram showing a configuration example of an error detection coding circuit.

FIG. 4 is a block diagram showing a configuration example of an error detection circuit.

FIG. 5 is a block diagram illustrating a configuration example of a memory circuit.

FIG. 6 is a diagram illustrating a time division multiple access single frequency alternating communication system for mobile communication.

FIG. 7 is a diagram illustrating alternate communication between a base station and a mobile station.

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

FIG. 9 is a block diagram showing a main part configuration of a conventional mobile station.

[Explanation of symbols]

11 ₁ , 11 ₂ error detection circuit 12 error bit number comparison circuit 21 error detection coding circuit 51 transmitter 52 ₁ , 52 ₂ receiver 53 switch control circuit 54 high-frequency switch 55 ₁ , 55 ₂ antenna 56 ₁ , 56 ₂ decoder 57 level comparator 58 baseband switch 59 memory circuit 60 encoder 61 transmitter 62 receiver 63 switch control circuit 64 high frequency switch 65 antenna 66 encoder 67 decoder 71 base station 75 ₁ to 75 _n mobile station

Claims (1)

Claim: What is claimed is: 1. A base station having a plurality of antennas for both transmission and reception, and a plurality of mobile stations having a single antenna for both transmission and reception. In the diversity circuit in the time division multiple access single frequency alternating communication method for mobile communication, which alternately transmits and receives at the base station, and performs reception diversity and transmission diversity at the base station, the mobile station transmits to the base station at an assigned time slot. An error detection encoding means for performing error detection encoding of an upstream signal is provided, wherein the base station receives an upstream signal from each of the plurality of antennas to a corresponding receiver and demodulates the received signal corresponding to each mobile station. Receiving diversity means for detecting the error rate of the mobile station and selecting the received signal from the receiver that minimizes the error rate; Diversity circuit in time division multiple access first frequency alternating communication scheme for mobile communication, characterized in that a transmission diversity means that a minimum of the error rate at the receiving signal to select an antenna connected to the obtained receiver.