JPH06169272A - Diversity signal transmission system - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the quality of a received signal when a base station selects the best branch by transmitting a plurality of diversity signals received by a repeater to a base station through one optical fiber. With the goal. [Structure] A wireless signal from a terminal (1) is diversity-received by a repeater (2), and this wireless signal is converted into an optical signal,
In the communication system for converting the optical signal transmitted to the base station (4) through the optical fiber (3) into the original wireless signal, the wireless signal from the terminal (2) received by the plurality of antennas (8, 9) is , F with different center frequencies for each path (8, 9)
After converting to M wave and frequency-multiplexing each FM wave,
It is converted into an optical signal and transmitted to the base station (4) through one optical fiber (3), the optical signal is converted into an FM wave in the base station (4), and the path with the best signal quality is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system for converting an electric signal into an optical signal by E / O (electrical-optical conversion) and transmitting the optical signal through an optical fiber, and in particular, it is received by a plurality of antennas in a repeater. The present invention relates to a method for collectively transmitting wireless signals from terminals to a base station via an optical fiber.

[0002]

2. Description of the Related Art In a conventional diversity configuration in which a plurality of antennas are used, each path (transmission path from the antenna to the demodulator) is set independently, and the transmission paths are not integrated. Therefore, when transmitting a radio signal input to a plurality of antennas in a repeater to a base station by an optical fiber, optical fibers, E / Os, and O / Es are required for the number of paths connected to each antenna. , There was a problem in economics. Further, when the installation place of the repeater is limited, there is a problem in downsizing the device. Furthermore, when transmitting a wireless signal through an optical transmission line,
There is a problem that the signal quality deteriorates due to distortion and noise characteristics.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to transmit a plurality of diversity signals received by a repeater to a base station with one optical fiber and improve the quality of received signals.

[0004]

A feature of the present invention for achieving the above object is that a wireless signal from a terminal is diversity-received by a repeater, the received signals of a plurality of branches are converted into an optical signal, and the optical signal is received. Is transmitted to the base station via an optical fiber, the base station converts the optical signal into an electric signal to restore each of the received signals, and in the diversity transmission system in which one branch is selected, the repeater is a radio signal. Antennas for receiving a signal and an FM that frequency-modulates with a received signal of each antenna
The base station includes a modulator and an electro-optical converter that converts a composite wave obtained by frequency-multiplexing the FM waves of each branch into an optical signal and sends the optical signal to an optical fiber. An optical-electrical converter for converting the optical signal of to an electric signal,
A means for separating each FM wave from the output, an FM demodulator for demodulating each separated FM wave, and a quality of the received signal obtained from the output of each FM demodulator are determined, and the quality of the received signal is good. A diversity signal transmission in which a plurality of received signals received by a repeater are frequency-multiplexed with FM waves having different center frequencies, and transmitted to a base station through one optical fiber. There is a method.

[0005]

According to the present invention, since a plurality of antenna input signals in the repeater are converted into FM waves having different center frequencies, diversity reception signals from the same terminal can be multiplexed on the frequency axis. Therefore, this frequency-multiplexed signal can be converted into an optical signal by one E / O and transmitted by one optical fiber, and a more economical diversity signal transmission system can be provided. Further, as described in the patent application “Mobile communication system (Japanese Patent Application No. 3-178243)”, a technique of FM-modulating a reception signal whose level fluctuates depending on a wireless transmission path and optically transmitting the FM wave is described in E / Since it is possible to improve the non-linear distortion of O and at the same time improve the noise resistance characteristic due to the FM wide band gain, it is possible to improve the communication quality of the entire transmission line from the repeater to the base station. That is, since the diversity signals can be FM-converted and the center frequencies thereof can be changed, the diversity signals can be multiplexed, so that both improvement of signal quality and economical efficiency can be satisfied.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention. A description will be given with a configuration in which a signal is transmitted from the terminal 1 to the base station 4 via the repeater 2. Wireless transmission is performed between the terminal 1 and the repeater 2, and optical fiber transmission is performed between the repeater 2 and the base station 4. In the repeater 2,
The transmission signal from the terminal 1 is received by the antennas 8 and 9,
The respective received signals are input to the FM modulators 12 and 13 via the receivers 10 and 11 and frequency-modulated. FMs having different center frequencies output from the FM modulators 12 and 13
The waves are combined by a coupler 14 and then input to an E / O (electrical-optical converter) 15 to be converted into an optical signal. In this case, one or both FM waves may be frequency-converted and frequency-multiplexed by using FM modulators having the same center frequency. This optical signal is transmitted to the base station 4 via the optical fiber 3.

At the base station 4, the optical signal from the repeater 2 is O
/ E (optical-electrical converter) 16 and an electric signal (FM
Wave). This FM wave is a band pass filter BP designed according to the center frequency of each FM wave.
The signals are input to the FM demodulators 20 and 21 via F1-18 and BPF2-19, respectively. The output signals of the FM demodulators 20 and 21 are input to the determination circuit 48, and a signal with good signal quality is output to the output terminal 25.

FIG. 2 shows a configuration example of the determination circuit. (A) is a configuration example of claim (2), in which the levels of the output signals of the FM demodulators 20 and 21 are compared, and the switch 24 inputs the high level signal to the demodulator 28. (B) is claim (3)
In the configuration example of 1, the output signals of the FM demodulators 20 and 21 are input to the demodulators 22 and 23, and from the comparison result of the levels of the output signals of the FM demodulators 20 and 21, the path of the high level signal is switched by the switch 24. The output signal of either one of the demodulators 22 and 23 included in 1 is output from the output terminal 25. Also, the determination circuit may detect the output signals of the FM demodulators 20 and 21 by the demodulators, compare the error rates of the detected baseband signals, and output a signal with a good error rate from the output terminal 25. good.

FIG. 3 shows a spectrum when a diversity signal is frequency-multiplexed with FM waves having different center frequencies.
Radio signals f ₁ and f ₂ transmitted from the two terminals 1 and 1 '
Are center frequencies f in the FM modulators 12 and 13, respectively.
Converted to FM waves of _C1 and f _C2 . These FM signals are combined by the combiner 14 and input to the E / O 15. On this occasion,
By utilizing the wide band property of the optical fiber, each FM wave can be arranged with a sufficient frequency interval.

FIG. 4 shows a block diagram of the determination circuit when there are a plurality of terminals. The FM waves collectively FM-modulated for each path are detected by the FM demodulators 20 and 21 in the base station 4, and the signals from the respective terminals are demultiplexed and demodulated by the channel filters 30 and 31. It represents. Path selection is performed for each channel.

[0011]

As described above, in the method of transmitting the diversity signal between the repeater and the base station by the optical fiber, the signals received by the plurality of antennas are converted into FM waves having different center frequencies, and this frequency is converted. Multiplexed F
One optical fiber or E /
O and O / E can be combined into a pair. Therefore, it is possible to realize a diversity signal transmission method which is economical and has good transmission quality.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration example of a determination circuit.

FIG. 3 is a spectrum when a diversity signal is frequency-multiplexed with FM waves having different center frequencies.

FIG. 4 is a configuration diagram of a determination circuit when there are a plurality of terminals.

FIG. 5 shows a conventional configuration example.

[Explanation of symbols]

 1, 1'Terminal 2 Repeater 3, 40, 41 Optical fiber 4 Base station 5 Modulator 6 Transmitter 7, 8, 9 Antenna 10, 11 Receiver 12, 13 FM modulator 14 Combiner 15, 42, 43 E / O 16,44,45 O / E 17 distributor 18 BPF1 19 BPF2 20,21 FM demodulator 22,23,28,46,47 demodulator 24 switch 25,37,38,39 output terminal 27,29 level comparison Device 31, 31 Channel filter 34, 35, 36, 48 Judgment circuit

Claims (3)

[Claims] 1. A radio signal from a terminal is diversity-received by a repeater, a received signal of a plurality of branches is converted into an optical signal, the optical signal is transmitted to a base station by an optical fiber, and the optical signal is transmitted by the base station. In the diversity transmission system in which each of the received signals is restored by converting it to an electrical signal and one branch is selected, the repeater frequency-modulates the plurality of antennas for receiving the wireless signal and the received signals of each antenna. The base station includes an FM modulator and an electro-optical converter that converts a composite wave obtained by frequency-multiplexing the FM waves of each branch into an optical signal and sends the optical signal to the optical fiber. The base station is a repeater via the optical fiber. From the output of each FM demodulator, the optical-electrical converter that converts the optical signal from the to the electrical signal, the means that separates each FM wave from the output, the FM demodulator that demodulates each separated FM wave, Get received signal Judge quality,
A decision circuit for selecting a signal of good quality among the received signals, and by frequency-multiplexing a plurality of received signals received by the repeater with FM waves having different center frequencies, a single optical fiber is used. A diversity signal transmission method characterized by transmitting to a base station. 2. The determination circuit compares the levels of the output signals of the FM demodulators, selects the output signal with the highest level, and inputs the selected signal to the demodulator for detection. The diversity signal transmission system according to claim 1. 3. The decision circuit has a plurality of demodulators for detection connected to the output of each FM demodulator, and a demodulator for detection of a branch having the highest output signal level of the FM demodulator is selected. The diversity signal transmission method according to claim 1, wherein the diversity signal transmission method is selected.