JPH03135233A - One frequency alternate communication system for mobile communication - Google Patents

Abstract

PURPOSE:To increase an information transmission quantity per unit time by always monitoring the reception levels of signals received through plural antennas and executing diversity in a base station. CONSTITUTION:Receivers (two receivers 251 and 252) are provided in correspondence with plural antennas and the antennas transmitting outgoing signals are selected with the estimation of the reception level of mobile station by using the reversibility of a transmission line from the reception levels of respective incoming signals. Then, respective reception levels of the moving stations in a signal length T are predicted, and transmission diversity for switching the antennas transmitting the outgoing signals when the reception levels are crossed is executed. Thus, a preamble signal and a postamble signal, both of which are conventionally used in level detection are eliminated and the information transmission quantity per unit time can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a mobile communication system in which signals of a single frequency are alternately transmitted and received between a base station and a mobile station. This invention relates to a single frequency alternating communication system for mobile communications that achieves this 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 of (here, two) antennas 73 and 732 for both transmitting and receiving functions for diversity, one receiver, and one transmitter. Mobile station 7
5 is a single transmitting and receiving antenna 77 for miniaturization.
, one receiver, and one transmitter.

Antenna 73 of base station 71. Alternatively, the signal of carrier frequency f1 transmitted from antenna 73□ is received by antenna 77 of mobile station 75. Further, a signal with a carrier frequency r1 transmitted from the antenna 77 of the mobile station 75 is received by the antenna 73° and the antenna 73□ of the base station 71, and one of them is selected. That is, the base station 71 is configured to perform selective diversity in which the received signal from the antenna with the highest received level among the plurality of antennas is demodulated.

Note that the mobile communication system in which the base station 7I and the mobile station 75 perform bidirectional communication using a single frequency is Breathtalk communication in which data is transmitted alternately at a predetermined transmission time T, as shown in FIG. Here, a signal from the mobile station 75 to the base station 71 is an uplink signal, and a signal from the base station 71 to the mobile station 75 is a downlink signal.

FIG. 9 is a block diagram showing the configuration of main parts of a base station and a mobile station. Note that (a) indicates a base station, and (b) indicates a mobile station.

In the figure, a transmitter 81 and a receiver 82 of the base station are connected to antennas 86I and 862 via high frequency switches 84 and 85 which are switched and controlled by a switch control circuit 83.
is connected. An antenna 96 is connected to a transmitter 91 and a receiver 92 of the mobile station via a high frequency switch 94 whose switching is controlled by a switch control circuit 93 .

Note that the high frequency switches 84 and 94 are 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 uplink signal transmitted by the mobile station, the high frequency switch 94 of the mobile station is switched to the transmitter 9I side, and the high frequency switch 84 of the base station is switched to the receiver 82 side. Furthermore, 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 connected to each antenna 86.
．． ．． The reception level of the signal received at 86□ is switched to the higher one.

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

FIG. 10 shows the frame structure of uplink signals and downlink signals transmitted and received within 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 the preamble signal and postamble signal do not include transmission information.

At the base station, the switch control circuit 83 alternately switches the high frequency switch 85 within the reception time of the preamble signal of the uplink signal, and selects the antenna with the higher reception level detected by the receiver 82. Diversity takes place.

On the other hand, since the mobile station has only one antenna, transmit diversity is performed to select a suitable antenna on the transmitting side.

That is, in the base station, the switch control circuit 83 alternately switches the high frequency switch 85 within the reception time L3 of the postamble signal of the uplink signal, detects each reception level, and selects the higher antenna. Note that this transmit diversity utilizes the reversibility of the propagation path where the correlation of the propagation path is sufficiently high for the downlink signal that follows the uplink signal under conditions where fading fluctuations are slow, and the signal is received by the base station. A downlink signal transmitted from an antenna with a high reception level of a postamble signal of an uplink signal is considered to have a high reception level at the mobile station.

In this manner, the base station performs receive diversity using the preamble signal of the uplink signal, and similarly performs transmit diversity for the downlink signal using the postamble signal of the uplink signal. Each diversity works effectively and has a considerable effect if the frequencies of the upstream and downstream signals are the same and the fading pitch is sufficiently larger than the transmission time (signal length) T of the upstream or downstream signals. do.

[Problem to be solved by the invention]

However, if the reception level at the base station or mobile station is relatively lower when the selected antenna is used during the transmission time T of the uplink signal or downlink signal, the effect is significantly reduced.

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

FIG. 11(a) shows changes in the reception level of each antenna of the base station. The base station compares the reception levels rl and r2 of each antenna 861.86□ at reception time 1+ of the preamble signal of the uplink signal. Since the reception level r1 is high here, reception diversity is performed in which the antenna 86° is selected. However, during the transmission time (signal length) T of the upstream signal, the reception levels r and r2 may be reversed as shown in the figure.

Further, FIG. 11(b) shows changes in the expected reception level at the mobile station of signals transmitted from each antenna of the base station. At the base station, each antenna 86 . ．． 86□ reception level r+
Compare srz. Here, since the reception level r2 is high, transmission diversity is performed in which the antenna 86□ is selected for transmitting the downlink signal. The mobile station receives the downlink signal transmitted from the antenna 76□ of the base station, and the estimated reception level r2 is as shown in the figure during the transmission time (signal length) T of the downlink signal. A reversal of the expected reception level r1 may occur.

In this way, in conventional receive diversity and transmit diversity, each antenna is fixed during the transmission time T, so there is a problem that the diversity effect decreases in the situation where the reception level is reversed as shown in FIG. .

The present invention provides a mobile communication system that can minimize the deterioration of reception quality while receiving a one-frame signal corresponding to the transmission time of an uplink signal or a downlink signal, and can effectively bring out the diversity effect. The purpose is to provide a frequency alternating communication system.

[Means for Solving the Problems] FIG. 1 is a block diagram showing the basic configuration of the system of the present invention.

The present invention alternately transmits and receives a single frequency signal at a predetermined period between a base station having multiple antennas for both transmitting and receiving purposes and a mobile station having one antenna for both transmitting and receiving purposes,
In the single-frequency alternating communication system for mobile communications, the base station performs receive diversity, in which the base station performs reception using an antenna with a high reception level, and transmit diversity, in which the base station uses an antenna with a high reception level to transmit to the next mobile station. The station has multiple receivers compatible with multiple antennas, a receive diversity control means that sequentially selects the receiver with the highest reception level for each receiver, and a receiver with the highest reception level during transmission. In addition to selecting the antenna that
and transmit diversity control means that predicts the value of each received level after a predetermined time and sequentially selects the antenna with the highest predicted value.

[For production]

In the present invention, in the receive diversity of a base station, the reception level at each receiver corresponding to multiple antennas can be sequentially monitored, and the reception processing can be performed using the receiver with the highest level. , it is possible to always ensure the highest reception level during the reception period.

In addition, in base station transmit diversity, while selecting the antenna with the highest reception level immediately before switching to transmission and starting transmission, the value of each reception level at each time within the transmission time is predicted, By sequentially selecting the antenna with the highest predicted value, it is possible to ensure that the mobile station always receives the highest reception level during the base station's transmission period.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

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

In the figure, a transmitter 23 is connected to a plurality of (two in this case) transmitting/receiving antennas 21+ and 21□ via a high frequency switch 22, and a receiver is connected via a high frequency switch 24 that is switched in conjunction with each other. 25. ．． 25
□ is connected.

Each receiver 25. ．． The receiver IF (intermediate frequency) signals at and a2 outputted from the receiver IF (intermediate frequency) signals at and a2 are sent to the level detection circuit 26 that detects and compares the reception level and the mobile station after a predetermined period of time from the past and current values of the reception level. It is manually inputted to a level prediction circuit 27 that estimates the reception level. The control signal output from the level detection circuit 26 and each receiver 25
．． ．． The changeover switch 28 to which the demodulated signal 'I%CZ outputted from 25□ is input selects and outputs either one of the demodulated signals CI and C2 according to the control signal.

A control signal d for selecting a transmitting antenna for a downlink signal outputted by the level prediction circuit 27 and switching the transmitting antenna after a predetermined time, and a switch control circuit 29 to which a transmitting/receiving switching signal e is manually input, transmit a high frequency signal according to the transmitting/receiving switching signal e. The switches 22, 24 are alternately connected to the transmitter 23 and each antenna 218, 21□, or the receiver 25. ．． 25
□ and antenna 21. ．． 21□, and the transmitter 23 and antenna 21. Alternatively, mutual switching with the antenna 21□ is performed.

The feature of the present invention is that the receivers (in this embodiment, two receivers 25, .25□
), the antenna for transmitting the downlink signal is selected by estimating the reception level of the mobile station using the reversibility of the propagation path from the reception level of each uplink signal, and furthermore, the reception level of each mobile station within the signal length T is selected. Transmission diversity is performed by predicting the levels and switching the antenna for transmitting the downlink signal at the point where they intersect.

Note that receive diversity uses multiple receivers corresponding to each antenna to constantly monitor the reception level of the upstream signal received by each antenna, and sequentially selects the higher receiver output. , deterioration in reception level (communication quality) can be minimized. Furthermore, in conventional receive diversity and transmit diversity, a single receiver alternately receives preamble signals and postamble signals of uplink signals and selects one of them, but in the present invention, the Since a preamble signal and a boost amplifier signal for level detection are not required, the entire signal length T can be used as an information signal.

Figure 3 shows the estimated reception level of the mobile station based on the reception level information of the base station. +,? It is a figure which shows an example of the waveform of z.

In the figure, the base station reception end time and the mobile station reception start time are almost equal, and the reception level at the mobile station reception start time t5 is equal to the reception level at the base station reception end time t5 due to the reversibility of the propagation path. .

Also, what is the estimated reception level of the mobile station? I,? Z is
What about the time? +<'Fz, time, 10τ? .

<? 2 to 71>72 (however, 0<τ<T
), the level prediction circuit 27 is the switch control circuit 2
9, at time t, the high frequency switch 24 is disconnected from the receiver side, and when ≦t<tb+τ, the high frequency switch 24 is disconnected from the receiver side.
2 is selected on the antenna 21□ side, and tb+τ≦L≦
1c, the high frequency switch 22 is connected to the antenna 21. Sends a control signal to switch to the side.

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

In the figure, each receiver 25. The received 51F signal at at output from 25□ is transmitted to each differentiating circuit 31+,
31□, and based on the past reception level, the current <t,
b) The slope (differential coefficient) of the reception level is calculated, and the output of each differentiating circuit 311.31□ and the receiver IF multiplied signal lsa2 are input into the arithmetic circuit 33, and the estimated value of the reception level of the mobile station? ＋、? This configuration calculates the time τ at which z intersects.

Figure 5 shows the estimated reception level of the mobile station? FIG. 3 is a diagram illustrating the principle of calculating the time τ at which + and rZ intersect.

If the reception levels corresponding to each antenna of the base station at time tb are r+(tb) and rz(tb), the reception levels after the transfer are r+(tb) and rz(tb), respectively, as described above.
It can be said that it is equal to rz(tb). Also, the differential coefficient r + at time 1+, which is determined from each reception level of the base station.
'(tb), r, 'Dt,) are similarly equal.

Here, each antenna 21 . ．． The reception level r 1 (tb+
r ), r z (tb+τ) is r+(tb+T)=
r+(tb)+r+'(tb)'r ・(1)rz
(tb+τ)=rz(tb)+r2'(t
t, )・τ ...(2), and r + (tb
+ r) = r z (tb+ r ), so the time τ at which the reception levels of the mobile station cross can be determined as.

That is, in the level prediction circuit 27, the differentiating circuits 31, .
31□ and the arithmetic circuit 33, the receiver IF multiplied signal l
, a2 and its differential value, the time τ at which the reception level of the mobile station corresponding to each antenna of the base station intersects is estimated.

On the other hand, the level prediction circuit 27 sends a control signal d to the switch control circuit 29 so that the antenna corresponding to the higher reception level is selected as the transmitting antenna at time t, and the calculated time τ is 0≦ If τ≦T (T is the signal length), a timer in the arithmetic circuit 33 is started at the same time as time Lb, and a control signal d for switching the transmitting antenna is sent out at time t, +τ. Note that the switch control circuit 29 operates to select one of the antennas 2121□ connected to the transmitter 23 for the high frequency switch 22 according to the control signal d.

Here, we have explained a method 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 transmitting antenna is switched at time Lb+τ. The same applies to the method of selecting antennas.

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

In the figure, an antenna 211.21□ for transmitting and receiving, a high frequency switch 22.24, a transmitter 23, a receiver 25I,
252, the level detection circuit 26, the level prediction circuit 27, the changeover switch 28, and the switch control circuit 29 are similar to those in the base station embodiment shown in FIG.

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

That is, the transmission data is sent to the transmitter 23 via the encoder 43.
However, the encoder 43 sets a signal length according to the fading frequency signal f output by the fading frequency detection circuit 41. The encoder 43 also adds information for setting the signal length of the uplink 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.

Note that in this embodiment, each receiver 25 . One of the demodulated signals C1 and c2 of 25□ is taken into the decoder 45 and subjected to reception processing, and the transmission/reception switching signal e inputted to the switch control circuit 29 is taken out from the encoder 43 and the decoder 45.

Reception diversity in such a configuration is similar to the embodiment shown in FIG. ．． Receiver 25□, 25□ corresponding to 21□
The level of each receiver IF multiplied signal a2 is detected. The changeover switch 28 selects the demodulated signal with the higher reception level and sends it to the decoder 4 using a control signal according to the detection result.
5, and the 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 notifies the encoder 43 using the fading frequency signal f.

The encoder 43 increases the signal length T of the downlink signal when the fading frequency is small, and shortens the signal length T when the fading frequency is large. Further, the value of this fading frequency is included in the downlink signal information and transmitted to the mobile station, and the signal length T of the uplink signal is set.

That is, the level prediction circuit 27 specifies the transmission antenna for the downlink signal via the switch control circuit 29 according to the last received level of the uplink signal, and after switching from uplink signal reception to downlink signal transmission, the encoder A downlink signal with a code length T set to 43 is transmitted from the transmitter 23 to the high frequency switch 22.
and transmit via the selected antenna.

The mobile station receives the downlink signal with the code length T, and when transmitting the uplink signal again, the code length T is set in accordance with the notified fading frequency.

The above operations are repeated between the base station and the mobile station to perform bidirectional communication using a single frequency, but the signal length T of the downlink signal and uplink signal can be made variable in accordance with the fading frequency. This makes it possible to reduce the probability of level deterioration when the fading frequency increases.

In this embodiment as well, the diversity effect is maximized by estimating the reception level of the mobile station during the variable signal length T and switching the transmitting antenna of the base station at a predetermined time. However, it is possible to obtain the desired effect simply by changing the signal length T according to the fading frequency.

[Effects of the Invention] As described above, the present invention performs diversity by constantly monitoring the reception level of signals received at a base station via a plurality of antennas, so that the preamble signal conventionally used for level detection is This eliminates the need for a postamble signal and increases the amount of information transmitted per unit time.

In addition, the base station predicts the reception level at the mobile station,
By switching the transmitting antenna each time when the reception levels change relative to each other during the transmission time,
It is possible to minimize the level drop in the mobile station and reduce deterioration in communication quality.

[Brief explanation of the drawing]

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 present invention. FIG. 3 is a diagram showing an example of the waveform of the estimated value of the reception level of the mobile station estimated based on the reception level information of the base station. FIG. 4 is a block diagram showing a configuration example of a level prediction circuit. FIG. 5 is a diagram illustrating the principle of calculating the time τ at which the estimated reception level 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 signals of a single frequency are alternately transmitted and received between a base station and a mobile station. FIG. 8 is a diagram illustrating alternate communication between a base station and a mobile station. FIG. 9 is a block diagram showing the configuration of main parts of a base station and a mobile station. FIG. 1O is a diagram showing the frame structure of uplink signals and downlink signals transmitted and received within one signal section. FIG. 11 is a diagram illustrating a case where the reception levels at the base station and 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.
...Differential 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 multiple antennas for both transmission and reception,
between a mobile station that has one antenna for both transmitting and receiving,
Receive diversity involves transmitting and receiving a single frequency signal alternately at a predetermined period, using an antenna with a high reception level at the base station for reception, and transmitting to the next mobile station using an antenna with a high reception level. In a single-frequency alternating communication system for mobile communications that performs transmission diversity, the base station includes a plurality of receivers corresponding to the plurality of antennas, and a receiver whose reception level of each receiver is maximized is sequentially selected. Receive diversity control means selects an antenna corresponding to the receiver that maximizes the received level during transmission, predicts the value of each received level after a predetermined time, and successively selects the antenna that maximizes each predicted value. 1. A single frequency alternating communication system for mobile communication, characterized in that it is equipped with a transmission diversity control means.