JPH07288496A - Radio communication system - Google Patents

Abstract

PURPOSE:To provide a repeater device which ensures the large without changing the frequency and then to obtain a simple and practical radio communication system. CONSTITUTION:A repeater station 12 is provided with a receiver antenna 14 and a transmitter antenna 16 which have the substantially same directivity and placed so that their mutual degree of coupling can be minimized. The signals received by the antenna 14 are amplified by a reception amplifier 15 and sent to a transmission power amplifier 17 via a transmission/reception connector device. The signals amplified by the amplifier 17 are transmitted through the antenna 16. It is desirable to add a directive antenna 13 to each terminal station 11 to point the station 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system, and more particularly to a wireless communication system for relaying wireless signals in a base station.

[0002]

2. Description of the Related Art A wireless communication system is the most suitable system for easily performing communication in an area where a communication network is not established and communication between mobile units. An example of such a wireless communication system is a personal wireless system.

In a personal radio system, as shown in FIG. 7, a plurality of personal radios 71 directly transmit / receive radio signals to / from other personal radios 71 via antennas 72 connected to the respective radios. It is a system that does.

In the personal radio system used in Japan, 80 channels are allocated to 900 MHz band,
A multi-channel access (MCA) method in which users jointly use these channels is adopted. Note that one of the above channels is used as a control channel.

In this type of wireless communication system, each wireless device automatically searches for a free channel and sets a channel. That is, the radio device that is trying to transmit is the carrier (Carr
ier) Detects an empty channel using the detection method, and when it detects an empty channel, it sends a connection request signal containing the channel number and the destination number, and the called partner's radio sets the instructed channel. Then you can talk.
The call channel is a Press to Talk method that uses the same frequency for both transmission and reception.

As described above, the personal radio system is characterized in that the system configuration and its operation are extremely simple and the price of the radio device is low. Therefore, in Japan, it is widely used for various purposes such as delivery business, car travel, and leisure.

On the other hand, worldwide, two thirds of the population live without telephones, and due to lack of communication means,
We have many social difficulties. Therefore, it is extremely effective to use the personal wireless system in order to bring the communication means to these areas at the lowest cost.

However, if the above personal radio system is used as it is as a basic communication network, there are the following problems. That is, since the personal wireless device uses an omnidirectional antenna in the horizontal direction, there is a problem that the reach of radio waves is short and the communicable range is limited. Specifically, the (B) station shown in FIG. 6 can communicate with any of the other (A), (C), and (D) stations, while it can communicate with the (A) station. There is a problem that it cannot communicate with (D).

To solve this problem, a base station may be provided, and each radio may communicate with another radio via this base station. Since it is only necessary for each radio to communicate with the base station, a directional antenna can be used, and the communicable range becomes long. In addition, if it is a radio that can communicate with the base station, communication can be performed regardless of the distance to the other station with which communication is actually performed. Further, each radio can be connected to the public communication network simply by connecting the base station to the public communication network (PSTN). In this way, if the base station is combined with the personal wireless system, the basic communication network should be able to be prepared at low cost.

However, in the personal radio system, since the same RF frequency is used for transmission and reception, there is a problem that relay amplification cannot be performed by the usual method. That is, there is a problem that the signal transmitted from the transmitting antenna at the base station wraps around to the receiving antenna side and stable amplification cannot be performed.

Conventionally, there is a device as shown in FIG. 8 as a wireless relay device which solves the problem of wraparound. This wireless relay device includes a receiving antenna 81, a directional coupler 82,
Detection circuit (DET) 83, variable attenuator (ATT) 84,
Control circuit (CONT) 85, frequency converter (CONV)
86, an oscillator 87, a high power amplifier 88, and a transmitting antenna 89.

This radio relay device is basically a device that a reception signal received by the reception antenna 81 is amplified by a high power amplifier 88 and transmitted from a transmission antenna 89. However, in this wireless relay device, instead of simply amplifying the received signal, the frequency converter 86 and the oscillator 87 are used to give an offset to the frequency. As a result, between the frequency of the received signal and the frequency of the transmitted signal,
A difference equal to the offset frequency is generated, and the detection circuit 83 can detect the wraparound amount of the transmission signal.
The control circuit 85 controls the variable attenuator 84 based on the wraparound amount detected by the detection circuit 83, and controls the amplification factor in this relay device so that loop oscillation does not occur.
Thus, in the conventional wireless relay device, loop oscillation is suppressed and stable amplification is achieved. Such a wireless relay device is disclosed in, for example, Japanese Patent Laid-Open No. 63-79429.

[0013]

As described above, the conventional radio relay apparatus gives an offset to the frequency of the received signal and transmits the transmitted signal having a frequency slightly different from the frequency of the received signal. Therefore, if the conventional wireless relay device is directly applied to a personal wireless communication system, there is a problem that it becomes difficult to perform a receiving operation in a personal wireless device that uses signals of the same frequency for transmission and reception.

Further, in the conventional radio relay apparatus, when the isolation between the transmitting and receiving antennas is not sufficient, the relay amplification factor cannot be increased and the relay distance becomes short.

An object of the present invention is to provide a repeater capable of performing large amplification without changing the frequency, and thus to provide a simple yet practical wireless communication system.

[0016]

According to the present invention, a plurality of terminal stations that use the same frequency signal for transmission and reception, and a base station that amplifies and sends out the signals transmitted from the plurality of terminal stations In a wireless communication system in which each of the plurality of terminal stations communicates with another terminal station via the base station, a directional antenna that directs the base station to the plurality of terminal stations is provided. At the same time, the base station is provided with a receiving antenna and a transmitting antenna having a predetermined directivity, and the receiving antenna and the transmitting antenna are arranged so that the directional directions thereof coincide with each other and the degree of coupling is minimized. A characteristic wireless communication system is obtained.

Further, according to the present invention, the base station includes a receiving device connected to the receiving antenna, a transmitting device connected to the transmitting antenna, and a transmitting / receiving device connecting the receiving device and the transmitting device. A wireless communication system having a connection device is obtained.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The wireless communication system according to the present embodiment includes a plurality of terminal stations (personal wireless devices) 1
1 and a base station 12. Each terminal station 11 is equipped with a high-gain directional antenna 13, and communicates only with the base station 12. By using the directional antenna 13, the communication distance between the personal wireless device and the repeater becomes longer than the communication distance between the conventional personal wireless devices. Also, the base station 1
2 includes a reception (RX) antenna 14, a reception amplifier 15, a transmission (TX) antenna 16, a transmission power amplifier 17, and a transmission / reception connection device 18 that connects the reception amplifier 15 and the transmission power amplifier 17.

The receiving antenna 14 and the transmitting antenna 16 of the base station 12 have radiation patterns 21 and 2 as shown in FIG.
Have two. That is, these antennas have maximum directivity in the horizontal direction and minimum directivity in the vertical direction. In the base station of this embodiment, if these two antennas are arranged vertically, the degree of coupling between these two antennas can be minimized.

The transfer characteristic of the base station 12 of this embodiment will be described with reference to FIG. X (ρ) is the transfer function of the received signal,
Y (ρ) is the transfer function of the transmission signal, Gr is the amplification factor of the reception amplifier, Gt is the amplification factor of the transmission power amplifier, and F (ρ)
Is the transfer characteristic of the transmission / reception transfer device, and L (ρ) is the coupling transfer function between the transmitting antenna and the receiving antenna. The transfer characteristic T (ρ) of this base station is expressed by Equation 1 from FIG.

[0021]

[Equation 1] As is clear from Equation 1, in order to perform normal amplification in this repeater, 1-Gr · Gt · F (ρ) · L (ρ)>
Must be 0. That is, Gr · Gt · F (ρ)
• L (ρ) <1 must be satisfied.

Here, consider a coaxial cable as the transmission / reception connecting device 7. In this case, the transfer characteristic of the coaxial cable is
F (ρ) = 1. Therefore, the condition for performing normal amplification is Gr · Gt · L (ρ) <1. That is,
Gr · Gt <1 / L (ρ), which must be satisfied. Thus, when a simple transmission / reception coupling device such as a coaxial cable is used, the relay amplification factor of the base station is limited by the reciprocal of the coupling degree of the transmission / reception antenna.

In a base station using this coaxial cable, if the degree of coupling between the transmitting and receiving antennas is sufficiently small, that is, if Equation 2 holds, the transfer characteristic T (ρ)
Can be expressed by Equation 3. In other words, this base station is just an amplifier with a gain of Gr · Gt.

[0024]

[Equation 2]

[0025]

[Equation 3] The base station of the present embodiment can reduce the degree of coupling between the transmitting and receiving antennas by using the antenna shown in FIG. can do. As a result, the communicable distance is extended and the communication service can be provided to a wide area.

Next, with reference to FIG. 4, a transmission / reception connection device capable of further increasing the repeater gain of the base station will be described. 4 includes a down converter (D / C) 41 connected to the reception amplifier 15, a reception filter bank demultiplexing circuit (RX Filter Bank) 42, and a transmission filter bank multiplexing circuit (TX Filter Bank). 43 and an up converter (U / C) 44 connected to the transmission power amplifier 17.

FIG. 5 shows the structure of a transmission / reception filter bank using a transmultiplexer. The reception filter bank demultiplexing circuit 42 includes a reception local oscillator 51 and a π / 2 phase shifter 5
2, mixers 53 and 53, A / D converters 54 and 54, a processing clock generator 55, an N frequency divider 56, and a transmultiplexer demultiplexing circuit (T-DUX) 57.
The transformer multiplexer / demultiplexer circuit 57 includes a serial / parallel converter 58, a digital filter 59, and an FFT 60.
have.

On the other hand, the transmission filter bank multiplexing circuit 43
Is a transmultiplexer multiplexing circuit 64 including an inverse FFT (IFFT) 61, a digital filter 62, and a parallel-serial converter 63, a D / A converter 65, a transmission local oscillator 66, a π / 2 phase shifter 67, Mixer 68 and adder 6
Have nine.

For details of the transmultiplexer, refer to the document: MG Bellanger, JLDaguet, "TDM-FDM Tr.
as-multiplexer: Digital Polyphase and FFT ", IEEE TRA
NSACTIONS ON COMMUNICATIONS, VOL. COM-22, No.9, Se
ptember 1974, detailed.

The signal transfer characteristics of the transmultiplexer depend on the characteristics of the digital filter used. Here, considering a channel (corner) frequency interval Δω and an N-channel transmultiplexer, the transfer characteristic of the transmultiplexer is expressed by Expression 4.

[0031]

[Equation 4] Here, C (l) is the tap count of the filter.

The processing speed of the transmultiplexer (output frequency of the processing clock generator 55) is 1 / T (1 / sec)
), Expressions 5 and 6 are established.

[0033]

[Equation 5]

[0034]

[Equation 6] Here, in order to see the general appearance of the transfer characteristic, C (l)
When the transfer characteristic in the case of = 1 and (l = 0, 1, ..., N−1) is obtained, the following Expression 7 is obtained.

[0035]

[Equation 7] Formula 7 is based on Formula 6 and becomes Formula 8. However,
It is assumed that N is sufficiently larger than 1.

[0036]

[Equation 8] FIG. 6 shows the transfer characteristic of Equation 8.

In the transmission / reception connecting device of the present embodiment, the transmultiplexers having the transfer characteristics shown in the formula 8 are cascade-connected in two stages, and the total characteristic is represented by the formula 9.

[0038]

[Equation 9] Therefore, the loop transfer function K (ω) of the relay device in FIG.
Is as in Expression 10.

[0039]

[Equation 10] Here, since the leak characteristic from the transmitting antenna to the receiving antenna is constant in the frequency band used in this system, L (ω) = L.

In this repeater, oscillation occurs when the phase of the open loop transfer function K (jω) is 2π, but in this case, | K (jω) | = 0,
No oscillation occurs. In an actual device, as shown by a broken line in FIG. 6, when ω = Δω / 2, the transfer characteristic of the filter F (jω) is generally set to 1 / a. The relay amplification factor that can be realized by the equipment is Gr · Gt <
(1 / L) · a. That is, in the repeater of the present embodiment, it is possible to obtain an amplification factor a times as large as that when a coaxial cable is used. Note that a is the out-of-band attenuation of the channel filter, and depending on the filter design, for example,
A very large value of 60 dB can be easily realized.

[0041]

According to the present invention, by arranging the receiving antenna and the transmitting antenna of the base station so that the degree of coupling is minimized, it is possible to amplify the received signal without changing the frequency to form the transmission signal. You can As a result, it is possible to provide an inexpensive and simple wireless communication system using a personal wireless device as a terminal station. In particular, by providing the terminal station with a high-gain directional antenna that directs the base station, it is possible to provide a wireless communication system with a wide communication range. Further, each terminal station can be connected to the public communication network simply by connecting the base station to the public communication network.

Further, since the base station is provided with the transmission / reception filter bank, an amplification factor larger than the amplification factor limited by the reciprocal of the coupling degree between the transmission / reception antennas can be obtained, and a radio communication system capable of providing a wide range of communication services is provided. can get.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a wireless communication system according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining directivity and arrangement of transmitting / receiving antennas of a base station in the wireless communication system of FIG.

FIG. 3 is a diagram for explaining transfer characteristics of a base station.

FIG. 4 is a block diagram of a transmission / reception connection device used in a base station in the wireless communication system of FIG.

5 is a circuit diagram of the transmission / reception connection device of FIG.

6 is a graph of transfer characteristics of a transmultiplexer used in the transmission / reception connecting device of FIG.

FIG. 7 is a diagram for explaining communication by a conventional personal wireless device.

FIG. 8 is a block diagram of a conventional wireless relay device.

[Explanation of symbols]

11 Terminal Station (Personal Radio) 12 Base Station 13 Directional Antenna 14 Reception (RX) Antenna 15 Reception Amplifier 16 Transmission (TX) Antenna 17 Transmission Power Amplifier 18 Transmission / Reception Connection Device 21, 22 Radiation Pattern 41 Down Converter (D / C) ) 42 Receive filter bank branching circuit (RX Filter Ba
nk) 43 Transmit filter bank combining circuit (TX Filter Ba
nk) 44 up-converter (U / C) 51 receiving local oscillator 52 π / 2 phaser 53 mixer 54 A / D converter 55 processing clock generator 56 N frequency divider 57 transmultiplexer branching circuit (T-DU)
X) 58 serial-parallel converter 59 digital filter 60 FFT 61 inverse FFT (IFFT) 62 digital filter 63 parallel-serial converter 64 transmultiplexer combining circuit 65 D / A converter 66 transmitter local oscillator 67 π / 2 phaser 68 mixer 69 adder 71 personal radio 72 antenna 81 receiving antenna 82 directional coupler 83 detection circuit (DET) 84 variable attenuator (ATT) 85 control circuit (CONT) 86 frequency converter (CONV) 87 oscillator 88 high power amplifier 89 Transmission antenna

Claims (5)

[Claims] 1. A plurality of terminal stations that use the same frequency signal for transmission and reception, and a base station that amplifies and sends out signals transmitted from the plurality of terminal stations. In a wireless communication system in which each communicates with another terminal station via the base station, the base station has a predetermined directivity, and a receiving antenna in which the directivity direction is substantially matched, and A wireless communication system, wherein a transmission antenna is provided, and the reception antenna and the transmission antenna are arranged so that the degree of coupling between them is minimized. 2. The wireless communication system according to claim 1, wherein the plurality of terminal stations are provided with directional antennas that direct the base station. 3. The base station has a receiving device connected to the receiving antenna, a transmitting device connected to the transmitting antenna, and a transmission / reception connecting device connecting the receiving device and the transmitting device. The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. 4. The wireless communication system according to claim 3, wherein the receiving device is a low noise amplifier, the transmitting device is a high power amplifier, and the transmission / reception connecting device is a coaxial cable. 5. The receiving device includes a low noise amplifier, and a receiving filter bank connected to the low noise amplifier to perform demultiplexing for each frequency division channel, and the transmitting device performs multiplexing and multiplexing of frequency division channels. A transmit filter bank to do,
A high power amplifier for amplifying an output of the transmission filter bank, wherein the transmission / reception connecting device is a cable group for connecting the reception filter bank and the transmission filter bank for each channel. 3 wireless communication system.