JPH0744490B2 - One frequency alternating communication system for mobile communication - Google Patents

Description

The present invention relates to a mobile communication system for alternately transmitting and receiving a signal of a single frequency between a base station and a mobile station, and the present invention relates to a receive diversity and a transmit diversity at the base station. The present invention relates to a one-frequency alternating communication system for mobile communication that realizes the above and improves communication quality.

[Conventional technology]

FIG. 7 is a conceptual diagram illustrating a mobile communication system 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 71 has a plurality (here, two) of antennas 73 ₁ and 73 _{2 for} both transmission and reception for diversity, one receiver, and one transmitter. The mobile station 75 has one antenna 77 for both transmission and reception, one receiver, and one transmitter for downsizing.

Antenna 73 ₁ or the signal of the carrier frequency f ₁ to be transmitted from the antenna 73 ₂ of the base station 71, mobile station 75 antenna
Received at 77. Further, the signal of the carrier frequency f ₁ transmitted from the antenna 77 of the mobile station 75 is the antenna of the base station 71.
73 received ₁ and the antenna 73 _2, one of which is selected. That is, in the base station 71, among the reception levels of the plurality of antennas, selection diversity is performed to demodulate the reception signal from the antenna having the maximum reception level.

The mobile communication system in which the base station 71 and the mobile station 75 perform bidirectional communication at a single frequency is press talk communication in which transmission is performed alternately at a predetermined transmission time T, as shown in FIG. Here, the signal from the mobile station 75 to the base station 71 is an upstream signal, and the signal from the base station 71 to the mobile station 75 is a downstream signal.

FIG. 9 is a block diagram showing a main configuration of a base station and a mobile station. In addition, (a) shows a base station and (b) shows a mobile station.

In the figure, antennas 86 ₁ and 86 ₂ are connected to a transmitter 81 and a receiver 82 of a base station via high frequency switches 84 and 85 which are switched and controlled by a switch control circuit 83.
An antenna 96 is connected to a transmitter 91 and a receiver 92 of the mobile station via a high frequency switch 94 which is switch-controlled by a switch control circuit 93. The high frequency switch 84,
94 is switched according to the transmission / reception switching signal, and the high frequency switch 85 is switched according to the antenna switching signal.

Here, within the transmission time T of the upstream signal transmitted by the mobile station, the high frequency switch 94 of the mobile station is switched to the transmitter 91 side, and the high frequency switch 84 of the base station is switched to the receiver 82 side. Further, within the transmission time T of the downlink signal transmitted by the base station, the high frequency switch 84 of the base station is switched to the transmitter 81 side, and the high frequency switch 94 of the mobile station is switched to the receiver 92 side. Further, the high frequency switch 85 of the base station is switched to the one in which the reception level of the signal received by each of the antennas 86 ₁ and 86 ₂ is higher.

The switching operation of the high frequency switch 85 will be described below.

FIG. 10 shows a frame structure of an upstream signal and a downstream signal transmitted / received in one signal section.

The signal lengths of the upstream signal and the downstream signal correspond to the transmission time T, and are composed of a preamble signal, an information signal and a postamble signal. Note that transmission information is not included in the preamble signal and the postamble signal.

At the base station, the reception time t of the uplink preamble signal
₁ , the switch control circuit 83 alternately switches the high-frequency switch 85, and reception diversity is performed to select the antenna with the higher reception level detected by the receiver 82.

On the other hand, since the mobile station has only one antenna, transmission diversity is performed to select an appropriate antenna on the transmission side.
That is, in the base station, the switch control circuit 83 alternately switches the high frequency switch 85 within the reception time t _{3 of the} postamble signal of the upstream signal, detects each reception level, and selects the antenna with the larger one. Note that this transmission diversity is received by the base station under the condition that the fluctuation of fading is slow, by utilizing the reversibility of the propagation path in which the correlation of the propagation path is sufficiently high for the downlink signal following the uplink signal. It is considered that a downlink signal transmitted from an antenna having a high reception level of an upstream postamble signal has a high reception level at a mobile station.

In this way, the base station performs reception diversity using the preamble signal of the uplink signal and similarly performs transmission diversity for the downlink signal using the postamble signal of the uplink signal. It should be noted that each diversity works effectively and exerts a considerable effect as long as the frequencies of the upstream signal and the downstream signal are the same and the fading pitch is sufficiently larger than the transmission time (signal length) T of the upstream signal or the downstream signal. To do.

[Problems to be Solved by the Invention]

However, when the reception level at the base station or the mobile station is relatively lowered during the transmission time T of the upstream signal or the downstream signal by using the selected antenna, the effect is significantly reduced.

FIG. 11 is a diagram explaining a case where the reception levels at the base station and the mobile station are reversed.

FIG. 11 (a) shows changes in the reception level of each antenna of the base station. The base station receives the reception level r of each antenna 86 ₁ and 86 ₂ at the reception time t ₁ of the preamble signal of the uplink signal.
₁ and r ₂ are compared. Here, since the reception level r ₁ is large, the reception diversity in which the antenna 86 ₁ is selected is performed. However, during the transmission time (signal length) T of the upstream signal, the reception levels r ₁ and r ₂ may be reversed as shown in the figure.

Further, FIG. 11 (b) shows a change in the expected reception level at the mobile station of the signal transmitted from each antenna of the base station.
In the base station, the reception levels r ₁ and r _{2 of the} antennas 86 ₁ and 86 ₂ are received at the reception time t ₃ of the postamble signal of the uplink signal.
To compare. Here, since the reception level r ₂ is high, transmission diversity is performed in which the antenna 86 ₂ is selected for transmitting the downlink signal. In the mobile station is the downlink signal sent from the antenna 76 ₂ of the base station is received, during the estimated reception level r ₂ is the downstream signal transmission time (signal length) T, as shown in FIG. However, a reversal of the expected reception level r ₁ may occur.

As described above, in the conventional receive diversity and transmit diversity, since the antennas are fixed during the transmission time T, there is a problem that the diversity effect is reduced in the situation where the reception level shown in FIG. 11 is reversed. .

INDUSTRIAL APPLICABILITY The present invention is intended to minimize the deterioration of the reception quality while receiving one frame signal corresponding to the transmission time of the upstream signal or the downstream signal, and to effectively bring out the diversity effect. The purpose is to provide a communication method.

[Means for Solving the Problems]

FIG. 1 is a block diagram showing the principle configuration of the method of the present invention.

The present invention alternately transmits and receives a signal of a single frequency 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 one-frequency alternating communication method for mobile communication, the base station performs reception diversity using an antenna with a high reception level, and transmission diversity using the antenna with a high reception level to transmit to the next mobile station. The station has a plurality of receivers corresponding to a plurality of antennas, a reception diversity control means for sequentially selecting a receiver having the maximum reception level of each receiver, and a receiver having the maximum reception level at the time of transmission. The transmission diversity control means is configured to select a corresponding antenna, predict the value of each reception level after a predetermined time, and successively select the antenna having the maximum predicted value.

[Work]

According to the present invention, in the reception diversity of the base station, it is possible to successively monitor the reception level at each receiver corresponding to a plurality of antennas, and it becomes possible to perform the reception process using the maximum receiver. , The highest reception level can always be secured during the reception period.

Further, in the transmission diversity of the base station, each reception level immediately before switching to transmission is selected and the transmission is started while selecting the antenna, while predicting the value of each reception level at each time within the transmission time, By sequentially selecting the antenna with the maximum predicted value, the mobile station can always have the highest reception level during the transmission period of the base station.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of an embodiment of a base station according to the method of the present invention.

In the figure, a plurality in the antennas 21 _1, 21 ₂ of both transmission and reception of (here two), the transmitter via the high-frequency switch 22
23 are connected, and receivers 25 ₁ and 25 ₂ are connected via a high-frequency switch 24 which is switched in conjunction with each other.

The receiver IF (intermediate frequency) signals a ₁ and a ₂ output from the receivers 25 ₁ and 25 ₂ are level detection circuits 26 that detect and compare their reception levels, and past and present values of the reception levels. Is input to the level prediction circuit 27 that estimates the reception level of the mobile station after a predetermined time. Changeover switch demodulated signal c _1, c ₂ the level detection circuit 26 is output from the control signal b and the receivers 25 _1, 25 ₂ outputs is inputted
28 selects and outputs _{one of} the demodulated signals c ₁ and c ₂ according to the control signal b.

The switch control circuit 29, which selects the transmission antenna of the downlink signal output by the level prediction circuit 27 and switches the transmission antenna after a predetermined time and the transmission / reception switching signal e, is input to the switch control circuit 29. The switches 22 and 24 are switched alternately, and the transmitter 23 and each antenna 21
₁ , 21 ₂ , or receivers 25 ₁ , 25 ₂ and antenna 21 ₁ ,
21 Switch to the connection with ₂ and transmit 23 according to the control signal d.
And the antenna 21 ₁ or the antenna 21 ₂ are mutually switched.

A feature of the present invention is that a receiver (in this embodiment, two receivers 25 ₁ and 25 ₂ ) corresponding to a plurality of antennas is provided, and the reversibility of the propagation path is determined from the reception level of each upstream signal. An antenna that transmits a downlink signal is selected by estimating the reception level of the mobile station by using the antenna, the reception level of the mobile station within the signal length T is predicted, and the downlink signal is transmitted when they intersect. This is where transmission diversity is performed to switch between.

In addition, in the reception diversity, by using a plurality of receivers corresponding to each antenna, the reception level of the upstream signal received by each antenna is constantly monitored, and the higher receiver output is sequentially selected. , It is possible to minimize the deterioration of the reception level (communication quality). In the conventional receive diversity and transmit diversity, one receiver alternately receives the preamble signal and the postamble signal of the upstream signal and selects one of them. Since the preamble signal and the postamble signal for detection are unnecessary, the entire signal length T can be used as the information signal.

FIG. 3 is a diagram showing an example of waveforms of the mobile station reception level estimation values ₁ and ₂ estimated based on the reception level information of the base station.

In the figure, the reception end time of the base station and the reception start time of the mobile station are almost equal, and the reception level at the reception start time t _b of the mobile station is the reception level at the reception end time t _b of the base station due to the reversibility of the propagation path. be equivalent to.

Note that the reception level estimated values ₁ and ₂ of the mobile station are
_b in a _{1 <2,} from _{1 <2} at the time _{t b} + _τ
If it is reversed to ₁ > ₂ (provided that 0 <τ <T), the level prediction circuit 27 tells the switch control circuit 29 that
At time t _b , the high frequency switch 24 is disconnected from the receiver side,
_{t b ≦ t <t b +} τ antenna 21 ₂ of the high-frequency switch 22 in
And the control signal b for switching the high frequency switch 22 to the antenna 21 ₁ side is transmitted when t _b + τ ≦ t ≦ t _c .

FIG. 4 is a block diagram showing a configuration example of the level prediction circuit 27.

In the figure, the receivers output from the receivers 25 ₁ and 25 ₂
The IF signals a ₁ and a ₂ are input to the differentiating circuits 31 ₁ and _{3 12,} and the gradient (derivative coefficient) of the current (t _b ) receiving level is calculated based on the past receiving levels, and the differentiating circuits 31 ₁ , 31 ₂ and the receiver IF signals a ₁ and a ₂ into the arithmetic circuit 33,
Time τ at which the mobile station reception level estimates ₁ and ₂ intersect
Is a configuration for obtaining.

FIG. 5 is a diagram for explaining the calculation principle of the time τ at which the reception level estimated values ₁ and ₂ of the mobile station intersect.

Assuming that the reception levels corresponding to the antennas of the base station at time t _b are r ₁ (t _b ) and r ₂ (t _b ), the reception levels of the mobile station are t ₁ (t _b ), r as described above.
_It can be said that it is equal to ₂ (t _b ). Further, a differential coefficient r ₁ ′ (t at time t _b obtained from each reception level of the base station
_b ) and r ₂ ′ (t _b ) are also equal.

Wherein each antenna 21 ₁ of the base _station, 21 ₂ signal transmitted from the reception level at the time t _{b +} tau reception level when being received by the mobile station crosses _{r 1 (t b + τ)} , r
₂ (t _b + τ) is r ₁ (t _b + τ) = r ₁ (t _b ) + r ₁ ′ (t _b ) · τ
(1) r ₂ (t _b + τ) = r ₂ (t _b ) + r ₂ ′ (t _b ) · τ
Since it is approximated to (2) and r ₁ (t _b + τ) = r ₂ (t _b + τ), the time τ at which the reception level of the mobile station crosses is Can be asked as

That is, in the level prediction circuit 27, differentiating circuits 31 ₁ , 31 ₂
By calculating the receiver IF signals a ₁ and a ₂ and their differential values by the arithmetic circuit 33, the time τ at which the reception levels of the mobile stations corresponding to the respective antennas of the base station intersect is estimated.

On the other hand, the level prediction circuit 27 sends the control signal d to the switch control circuit 29 so that the antenna corresponding to the one with the higher reception level at time t _b is selected as the transmission antenna, and the calculated time τ is 0 ≦. if τ ≦ T (T is the signal length), time t _b at the same time starts a timer in the arithmetic circuit 33, and sends a control signal d to switch the transmitting antennas in at time t _b + tau. The switch control circuit 29 responds to the control signal d to the high frequency switch 22 by transmitting the transmitter.
It operates to select one of the antennas 21 ₁ , 21 ₂ connected to 23.

Here, a method has been described in which the time τ at which the reception level of the mobile station corresponding to each antenna of the base station intersects is estimated and the transmission antenna is switched at time t _b + τ. The same applies to the method of selecting the larger antenna.

FIG. 6 is a block diagram showing the configuration of another embodiment of the base station.

In the figure, the antennas 21 ₁ and 21 _{2 for} both transmission and reception, high frequency switches 22 and 24, transmitter 23, receivers 25 ₁ and 25 ₂ , level detection circuit 26, level prediction circuit 27, changeover switch 28 and switch control circuit 29 are shown. The configuration is similar to that of the embodiment of the base station shown in FIG.

The feature of the present embodiment is that it includes a fading frequency detection circuit 41 that takes in the output of the level detection circuit 26 and detects a fading frequency, and the transmission time T of each of the base station and the mobile station according to the detected fading frequency. (Signal length) is variable.

That is, the transmission data is input to the transmitter 23 via the encoder 43, but the encoder 43 uses the fading frequency detection circuit 41.
Sets the signal length according to the fading frequency signal f output by the. The encoder 43 also adds information for setting the signal length of the upstream signal to the mobile station.

The mobile station transmits an uplink signal addressed to the base station with a signal length according to this information.

In this embodiment, _one of the demodulated signals c ₁ and c ₂ of the receivers 25 ₁ and 25 ₂ selected by the changeover switch 28 is used as a decoder.
The transmission / reception switching signal e input to the switch control circuit 29 is taken out from the encoder 43 and the decoder 45 while being received in 45 for reception processing.

The receiving diversity in such a configuration is the same as that of the embodiment shown in FIG. 2, and the level detecting circuit 26 receives each of the receivers 25 ₁ and 25 ₂ corresponding to the antennas 21 ₁ and 21 _2.
The level detection of the IF signals a ₁ and a ₂ is performed. Changeover switch
28 selects a demodulation signal with a higher reception level by the control signal b corresponding to the detection result and sends it to the decoder 45,
Uplink signal information is reproduced.

On the other hand, the fading frequency detection circuit 41 detects the fading frequency from the output of the level detection circuit 26, and the encoder
Notify 43 by fading frequency signal f. Encoder
At 43, when the fading frequency is low, the signal length T of the downlink signal is lengthened, and when the fading frequency is high, the signal length T is shortened. Also, the fading frequency value is included in the downlink signal information to the mobile station and transmitted,
The signal length T of the upstream signal is set.

That is, the level prediction circuit 27 specifies the transmission antenna of the downlink signal via the switch control circuit 29 according to the final reception level of the uplink signal, and after switching from the reception of the uplink signal to the transmission of the downlink signal, the encoder. Code length T set to 43
The downlink signal of is transmitted from the transmitter 23 via the high frequency switch 22 and the selected antenna.

In the mobile station, the downlink signal having the code length T is received, and when transmitting the uplink signal again, the code length T corresponding to the notified fading frequency is set.

The above operation is repeated between the base station and the mobile station to perform bidirectional communication with a single frequency. However, the signal length T of the downlink signal and the uplink signal should be variable according to the fading frequency. As a result, the probability of level deterioration when the fading frequency becomes high can be reduced.

Also in this embodiment, the diversity effect is maximized by estimating the reception level of the mobile station during the variable signal length T and performing the operation of switching the transmission antenna of the base station to a predetermined time. Although it can be brought out, it is possible to obtain a predetermined effect only by changing the signal length T according to the fading frequency.

〔The invention's effect〕

As described above, according to the present invention, the reception level of the signal received through the plurality of antennas in the base station is constantly monitored to perform diversity, so that the preamble signal and the postamble signal used in the conventional level detection are unnecessary. Therefore, the amount of information transmission per unit time can be increased.

Also, the base station predicts the reception level at the mobile station,
When each reception level is relatively switched within the transmission time, by switching the antenna for transmission each time,
It is possible to minimize the level reduction in the mobile station and reduce the deterioration of communication quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the principle configuration of the present invention. FIG. 2 is a block diagram showing the configuration of an embodiment of a base station according to the method of the present invention. FIG. 3 is a diagram showing an example of a waveform of a reception level estimated value of a mobile station estimated based on reception level information of a base station. FIG. 4 is a block diagram showing a configuration example of a level prediction circuit. FIG. 5 is a diagram for explaining the calculation principle of the time τ when the reception level estimated value of the mobile station intersects. FIG. 6 is a block diagram showing the configuration of another embodiment of the base station. FIG. 7 is a conceptual diagram illustrating a mobile communication system in which a single frequency signal is alternately transmitted and received between a base station and a mobile station. FIG. 8 is a diagram for explaining alternating communication between a base station and a mobile station. FIG. 9 is a block diagram showing a main configuration of a base station and a mobile station. FIG. 10 is a diagram showing a frame structure of an upstream signal and a downstream signal transmitted / received in one signal section. FIG. 11 is a diagram illustrating a case where the reception levels of the base station and the mobile station are reversed. 21 …… antenna, 22,24 …… high frequency switch, 23 …… transmitter, 25 …… receiver, 26 …… level detection circuit, 27 …… level prediction circuit, 28 …… changeover switch, 29 …… switch control Circuit, 31 ... Differentiation circuit, 33 ... Arithmetic circuit, 41 ... Fading frequency detection circuit, 43 ... Encoder, 45 ... Decoder, 71 ... Base station, 73 ... Antenna, 75 ... Mobile station , 77
…… Antenna, 81,91 …… Transmitter, 82,92 …… Receiver,
83, 93 …… Switch control circuit, 84,85,94 …… High frequency switch, 86,96 …… Antenna.

Claims (1)

[Claims] 1. 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, alternately transmitting and receiving a signal of a single frequency at a predetermined cycle, In the one-frequency alternating communication system for mobile communication that performs reception diversity using a high reception level antenna at a station, and transmission diversity that performs transmission to the next mobile station using a high reception level antenna, the base The station has a plurality of receivers corresponding to the plurality of antennas, a reception diversity control unit that sequentially selects a receiver having the maximum reception level of each of the receivers, and a receiver having the maximum reception level at the time of transmission. Transmit diversity that selects the antenna corresponding to each device, predicts the value of each reception level after a predetermined time, and sequentially selects the antenna with the maximum predicted value A single-frequency alternating communication method for mobile communication, characterized by comprising: