JPH06188791A - Diversity signal transmission system - Google Patents

Abstract

PURPOSE:To improve the quality of a received signal when the best branch is selected at a base station by sending plural diversity signals, received by a repeater, to the base station by one optical fiber. CONSTITUTION:A communication system which performs the diversity reception of a radio signal from a terminal 1 by a repeater 2, converts the radio signal into a light signal, and converts the light signal sent to the base station 4 by the optical fiber 3 into the original radio signal multiplexes radio signals from the terminal 2 received by plural antennas 8 and 9 by frequency conversion. The composite signal is modulated by an FM modulator 16 and then converted into the light signal, which is sent to the base station 4 by one optical fiber 3; and the light signal is converted into an FM wave at the base station 4 and the path having 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 and transmitting the optical signal through an optical fiber, and particularly to a wireless communication from a terminal which is received by a plurality of antennas in a repeater. The present invention relates to a method of transmitting a signal to a base station via an optical fiber.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional configuration of a diversity signal transmission system. In the conventional diversity configuration using a plurality of antennas, each path (transmission path from the antenna to the demodulator) is set independently, and the transmission paths are not integrated.

[0003]

Therefore, when the radio signals input to the plurality of antennas in the repeater are transmitted to the base station by the optical fibers, the number of optical fibers, E / E, and E / E are equal to the number of paths connected to the respective antennas. O, and O /
E was required, and there was a problem in economic efficiency. 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 signal quality is deteriorated due to distortion generated by the non-linearity of the laser diode, intensity noise generated in the laser diode, and shot noise generated in the photodiode.

According to the present invention, a plurality of diversity signals received by a repeater are transmitted to a base station through a single optical fiber to make the apparatus economical and compact, and by using FM, distortion characteristics of received signals. And to improve the noise characteristics.

[0005]

A feature of the present invention for achieving the above object is that 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, 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. A plurality of antennas for receiving the received signals, a device for frequency converting at least one of the received signals, a combiner for combining the received signals directly or via frequency conversion, and an FM modulator for frequency modulating the combined signals, The base station has an optical-electric converter that converts the FM wave of the composite wave into an optical signal and sends it to an optical fiber, and the base station converts the optical signal from the repeater via the optical fiber into an electric signal. An electrical converter, An FM demodulator that demodulates the FM wave of the output of the device, a device that branches the output of the FM demodulator into a plurality of units, performs frequency conversion into one with a small number of branched outputs, and restores each of the received signals. And a determination circuit that determines the quality of the received signal and selects a signal of good quality among the received signals, modulates a plurality of received signals received by the repeater with FM waves, and outputs a single optical signal. It is a diversity signal transmission method that transmits to a base station via a fiber.

[0006]

According to the present invention, the radio signal from the terminal is diversity-received by the repeater, the radio signal is converted into an optical signal, and the optical signal transmitted to the base station by the optical fiber is converted into the original radio signal. In the communication system, radio signals from terminals received by a plurality of antennas are frequency-multiplexed, and the frequency-multiplexed waves are collectively FM-modulated. Since the present invention frequency-converts a plurality of antenna input signals in a repeater and further performs FM modulation of this frequency multiplexed wave, it is superior to the conventional method in the following two points. First, an FM wave can be converted into an optical signal by one E / O and can be transmitted by one optical fiber, and an economical diversity signal transmission system can be provided. By performing FM modulation, a signal with a constant envelope is input to the E / O as a modulated wave, so that the nonlinear distortion of the E / O can be improved, and at the same time, the S / N ratio can be improved by the FM wide band gain. The communication quality of the entire transmission line from the repeater to the base station can be improved. That is, by frequency-multiplexing the diversity signal and performing FM modulation, it is possible to satisfy both the multiplexing of the diversity signal and the improvement of the signal quality.

[0007]

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 signals from the terminal 1 are received by the antennas 8 and 9, and the respective reception signals are input to the receivers 10 and 11. The output signal of the receiver 10 is input to the combiner 15 at the same frequency, but the output signal of the receiver 11 is frequency-converted by the mixer 12 and input to the combiner 15. In this case, the output signals of both receivers may be frequency converted. The frequency multiplexed wave combined by the combiner 15 is input to the FM modulator 16 and frequency-modulated, and this FM wave is E / O1.
It is input to 7 and converted into an optical signal. 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
It is input to / E18 and reconverted into an electric signal (FM wave).
This FM wave is input to the FM demodulator 19 and converted into the original frequency-multiplexed wave. The frequency-multiplexed wave is a band-pass filter BPF2-2 designed according to the center frequency of the reception signal of each path when input to the FM modulator 16 on the repeater side.
1, is input to BPF1-22. The output signal of the BPF2-21 is the same frequency as that of the output signal of the BPF1-22, and the output signal of the BPF1-22 is reconverted by the mixer 23 to the frequency of the signal output from the receiver 11 and input to the determination circuit 26. Judgment circuit 2
In 6, the signal with good signal quality is determined and output to the output terminal 27.

FIG. 2 shows a configuration example of the determination circuit. In the configuration example of (a), the levels of the output signals of the BPFs 2-21 and 25 are compared, and the switch 29 inputs the high level signal to the demodulator 30. In the configuration example of (b), BPF2-2
The output signals of 1, 25 are input to the demodulators 31, 32,
Based on the comparison result of the levels of the output signals of the BPFs 2-21 and 25, the switch 33 outputs the output signal of one of the demodulators 31 and 32 included in the path of the high-level signal from the output terminal 27. Further, the determination circuit is BPF2-
The output signals of 21 and 25 may be detected by a demodulator, the error rates of the detected baseband signals may be compared, and a signal with a high error rate may be output from the output terminal 27.

FIG. 3 shows a spectrum when a frequency-multiplexed received signal is FM-modulated. The radio signals f ₁ and f ₂ transmitted from the two terminals 1 and 1 ′ are input to the receivers 10 and 11. The output signals f ₁ and f ₂ of the receiver 11 are f ₀ + f
_The frequency is converted into ₁ , f ₀ + f ₂ , and the output signal of the receiver 10 is combined with the combiner 15. Frequency-multiplexed combiner 1
The 5 output signals are converted to FM waves having a center frequency f _c , and E /
Input to O17.

FIG. 4 shows a block diagram of the decision circuit when there are a plurality of terminals. The output signals of the BPFs 2-21 and 25 are demultiplexed by the channel filters 34 and 35, and are input to the determination circuits 36 to 38 for each channel.

[0013]

As described above, according to the present invention, in a method of transmitting a diversity signal between a repeater and a base station by optical fiber, signals received by a plurality of antennas are frequency-multiplexed and then converted into FM waves. Since this FM signal is optically converted, it is possible to combine one optical fiber and a pair of E / O and O / E. 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 frequency-multiplexed reception signal is FM-modulated.

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

FIG. 5 is 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 12,23 Mixer 13,24 Local oscillator 14,22 BPF1 15 Coupling Device 16 FM modulator 17 E / O 18 O / E 19 FM demodulator 20 Distributor 21,25 BPF2 26,36,37,38 Judgment circuit 30,31,32 Demodulator 27,39,40,41 Output terminal 28 Level comparator 29,33 Switch 31 Error rate comparator 32,34 Level comparator 34,35 Channel filter

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 a diversity transmission system in which each of the above received signals is restored by converting it to an electrical signal and one branch is selected, the repeater consists of multiple antennas for receiving radio signals and at least one of each received signal Device for converting, synthesizer for synthesizing received signals directly or through frequency conversion, FM modulator for frequency-modulating synthesized signal, and for converting FM wave of synthesized wave into optical signal and transmitting to optical fiber The base station includes an optical-electrical converter that converts an optical signal from a repeater via an optical fiber into an electric signal, and an FM demodulator that demodulates an FM wave output from the base station. , The FM recovery The output of the receiver is divided into a plurality of units, and the frequency conversion is performed for each of the received signals with a small number of branched outputs to restore each of the received signals and the quality of each received signal is determined. A diversity signal transmission system characterized in that it has a decision circuit for selecting various signals, modulates a plurality of reception signals received by a repeater with an FM wave, and transmits the modulated signals to a base station through a single optical fiber. . 2. The determination circuit compares the levels of the output signals of the respective received signals and selects the output signal with the highest level,
2. The diversity signal transmission system according to claim 1, wherein the selected signal is input to a demodulator for detection. 3. The determination circuit has a plurality of demodulators for detection connected to the output of each received signal, and selects the demodulator for detection of the branch having the highest output signal level of the received signal. The diversity signal transmission system according to claim 1, characterized in that.