JPH09284233A - Optical transmission repeater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in the S/N of a transmission signal by applying electrooptic conversion to a received RF signal after it is converted into a digital signal so as to configure the optical transmission system at a low cost. SOLUTION: A radio wave from a base station is received by a counter-base station antenna 101, and the received signal is subjected to band limit and amplification by a band pass filter (BPF) 102 and an amplifier(AMP) 103, and converted into a digital signal by an A/D converter(A/D) 104. Its output is converted into a serial signal by a parallel-serial converter(P/S) 105. The serial signal is converted into a digital optical signal at an electrooptic converter (E/O) 106 and fed to an optical fiber cable 2. The sent digital optical signal is converted into an electric signal by an optoelectric converter(O/E) 306 of a counter mobile station repeater 3, converted into a parallel signal at serial- parallel converter(S/P) 305, converted into an analog RF signal by a D/A converter(D/A) 304, subjected to band limit and amplification by a band pass filter(BPF) 302 and an amplifier(AMP) 303, and sent to a mobile station by a counter mobile station antenna 301.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay system for covering an area where radio waves are hard to reach in a service area of a mobile communication system such as an analog / digital mobile phone or a pager, and particularly as a transmission line. The present invention provides a relay system that uses an optical fiber at a low cost and has a small SN ratio deterioration.

[0002]

2. Description of the Related Art In recent years, mobile communication businesses such as mobile phones, MCA, and radio calls (pagers) have been developed nationwide, and their service areas are rapidly expanding. Along with this, it is necessary to take measures for areas where radio waves are hard to reach and communication is difficult, such as in the shade of buildings, tunnels, and underground malls. On the other hand, as shown in FIG. 4, the base station repeater is installed in a place where the radio wave condition with the base station is good, and the mobile station repeater is installed in the place where the above communication is difficult. There is an analog optical transmission repeater system that transmits signals by connecting optical fiber cables between them.

FIG. 3 is a block diagram of an analog optical transmission repeater system for a mobile phone. However, in FIG. 3, only a block diagram of a device for a downlink for relaying radio waves of a base station to a mobile station is shown. In an actual relay system, a device for the uplink is also necessary, but the same block diagram is used, so it is omitted here. In FIG. 3, a radio wave from a base station is received by an antenna of a repeater for a base station and then converted into an IF signal by a mixer. This is the mobile phone RF
Direct signal (for example, 800MHz to 2GHz) electricity
Light conversion is difficult because of high frequency.
A system for directly electro-optically converting an RF signal has already been disclosed in Japanese Patent Application No. 4-157932.
An electric-optical converter (E / O) for analog transmission capable of converting the frequency (800 MHz to 2 GHz) has not been obtained at a commercial level. Therefore, the signal is once converted to an IF frequency (for example, 90 MHz), and then electro-optical conversion (E / O) is performed to convert the analog optical signal. The analog optical signal propagates through the optical fiber, and the optical-electrical conversion (O
/ E), is converted into an RF signal by the mixer, undergoes necessary power amplification, and then transmitted from the antenna to the mobile station.

Here, the received signal frequency fB from the base station
And the transmission signal frequency fM to the mobile station must match with high accuracy (for example, 0.05 ppm). The frequency matching accuracy depends on the matching accuracy between the local signal frequency fLB of the base station repeater and the local signal frequency fLM of the mobile station repeater. If different reference oscillators are used for both repeaters, even if a high-precision crystal oscillator is used,
An accuracy of 5 ppm cannot be realized. Therefore, the desired frequency matching accuracy is obtained by superimposing the signal of the reference oscillator (TCXO) of the base station on the IF signal and sending the superimposed signal to the mobile station repeater.

[0005]

However, the analog optical transmission repeater system has the following problems. (1) Since it is an analog optical transmission system that directly converts an analog electric signal into an optical signal for transmission, the C / N of the optical transmission system is used.
(Carrier to noise ratio) characteristics and dynamic range are problems. Generally, required values for C / N and dynamic range are very strict as compared with digital optical transmission for transmitting binary signals. For this reason, in particular, the electro-optical converter (E /
O) and the opto-electric converter (O / E) are difficult to select, and become very expensive. (2) Since the signal of the reference oscillator (TCXO) is superimposed and transmitted, unless the transmission signal and the reference signal are completely separated on the receiving side, the SN ratio of the transmission signal deteriorates. There was a problem that it was difficult to separate. The present invention has been made in order to solve the problems of the conventional optical transmission repeater system as described above, and it is possible to configure an inexpensive optical transmission system, and at the same time, to improve the SN ratio of the transmission signal. It is an object of the present invention to provide an optical transmission repeater system without deterioration.

[0006]

In order to achieve the above object, according to the present invention, an optical transmission is performed by converting a received RF signal into a digital signal and then performing a digital optical transmission of electro-optical conversion (E / O). It is possible to reduce the demands on the C / N and the dynamic range of the system. Further, the transmission clock of the digital optical signal is generated from the reference oscillator, and the clock is regenerated on the receiving side so that the transmission of the reference oscillator signal is unnecessary and the deterioration of the S / N ratio is eliminated.

[0007]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, 1 is a base station repeater, 3 is a mobile station repeater, and 2 is an optical fiber cable. The radio wave (frequency fB) from the base station is for the base station antenna 1
01, and the band pass filter (BPF) 102
And the amplifier (AMP) 103 receive the required band limitation and amplification, and then the RF signal remains the analog-digital converter (A
/ D) 104 and converted into a digital signal. The sampling frequency at this time is fSB, and sampling is performed by the output signal of the reference signal generator (TCXO) 107. Next, the analog-digital converter (A / D) 10
4 output to parallel-serial converter (P / S) 105
To convert it to a serial signal. The frequency of this serial signal is fbB and is determined by the output signal of the PLL oscillator 108. Since the reference signal of the PLL oscillator 108 is the output of the reference signal generator (TCXO) 107, its frequency stability is equal to the frequency stability of the reference signal generator (TCXO) 107. The serial signal is converted into a digital optical signal by the electro-optical converter (E / O) 106 and input to the optical fiber cable 2. The transmission rate of this digital optical signal is fbB bits per second. The digital optical signal transmitted by the optical fiber cable 2 is converted into an electric signal by the optical-electrical converter (O / E) 306 of the mobile station repeater 3, and the serial-parallel converter (S / P) 305.
After being converted into a parallel signal by, the digital-analog converter (D / A) 304 converts the signal into an analog RF signal. At this time, the clock for serial-parallel conversion is generated by the clock recovery circuit 309, and its frequency fbM is equal to fbB. There are several ways to recover the transmission rate clock from a digital signal, but it is a well established technique and will not be described in detail here. As one example, there is a method in which a zero-cross point of an eye pattern of a digital signal is detected and a clock having that point as a change point is generated. The clock of the digital-analog converter (D / A) 304 is generated by dividing the reproduction clock in the frequency dividing circuit 310, and its frequency fSM is equal to fSB. The analog RF signal output from the digital-analog converter (D / A) 304 is subjected to necessary band limitation and amplification by a bandpass filter (BPF) 302 and an amplifier (AMP) 303, and then an antenna for mobile stations. At 301, it is transmitted to the mobile station.

Here, as described above, the reception signal frequency fB from the base station and the transmission signal frequency fM to the mobile station must match with high accuracy (for example, 0.05 ppm). The frequency matching accuracy is determined by the sampling frequency fSB of the analog-digital converter (A / D) 104 of the base station repeater and the clock frequency fSM of the digital-analog converter (D / A) 304 of the mobile station repeater. Depends on the matching accuracy of. In the present invention, the sampling frequency fSB of the analog-to-digital converter (A / D) 104 and the frequency fbB that is the transmission speed of the digital optical signal are created by the reference oscillator (TCXO) 107 on the side of the repeater 1 to the base station. Since the clock of the digital-analog converter (D / A) 304 is generated by dividing the clock (fbM) reproduced from the digital optical signal on the side of the repeater for the mobile station, the clock of the reference oscillator (TCXO) is generated. High matching accuracy can be obtained without transmitting signals. Further, considering an actual system, a frequency band for one telecommunications carrier to cover one area is, for example, 10 MHz. To convert a band-limited analog signal from analog to digital, the Nyquist condition must
Double or more sampling frequency is required. Therefore, for example, if oversampling of 2.5 times is performed, the sampling frequency fSB becomes 25 MHz. On the other hand, due to the demand for the dynamic range of the analog signal, the number of bits of the analog-digital converter needs to be about 12 bits. From the above, the output of the analog-digital converter is 12
Bit x 25MHz = 300M bits per second, so
fbB is 300 MHz, that is, the transmission speed of the digital optical signal is 300 Mbit / sec. The problematic electro-optical converter (E / O) 106 and opto-electrical converter (O / E) 30
Regarding No. 6, linearity is not required because it is conversion of a binary digital signal, and as described above, since the transmission speed of the digital optical signal is about 300 MHz, it is necessary to use an expensive device as in the prior art. There is no.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, 1 is a base station repeater, 3 is a mobile station repeater, and 2 is an optical fiber cable. In this embodiment, in addition to the configuration of the first embodiment, the base station repeater 1
In front of the A / D converter 104 and D of the mobile station repeater 3
A / A converter 304 is followed by mixers 112 and 31.
2. A frequency conversion circuit including the bandpass filters 111 and 311, and the PLL oscillators 113 and 313 is provided to perform A / D and D / A conversion in the IF band. With the above configuration, A / D and D
Since the condition for the frequency characteristic of the / A converter is relaxed, it is possible to configure a repeater in a higher frequency band. still,
The matching accuracy of the received signal frequency fB and the transmitted signal frequency fM is
When it is not required with high accuracy, or when the signal of the reference oscillator is transmitted by another cable, the PLL oscillator 108
The clock recovery circuit 309 is unnecessary, and the parallel-serial converter 105 and the serial-parallel converter 30 are not necessary.
5, and the digital-analog converter 304 can clock the signal from its own simple oscillator.

[0010]

Since the present invention is configured as described above, when configuring an optical transmission repeater system, the transmission of the reference oscillator signal is not required and the SN ratio is improved, so that the performance is improved. -The requirement for linearity of the optical and optical-electrical converters can be reduced, so that the cost can be reduced, and the use of the system of the present invention has a large effect in that the used frequency band can be used in a wide range.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a digital optical transmission repeater system of the present invention.

FIG. 2 is a diagram showing a second embodiment of the digital optical transmission repeater system of the present invention.

FIG. 3 is a diagram showing a conventional analog optical transmission repeater system.

FIG. 4 is a diagram showing an optical transmission repeater system.

[Explanation of symbols]

 1 ... To base station repeater 2 ... Optical fiber cable 3 ... To mobile station repeater 101 ... To base station antenna 102, 302 ... Band pass filter (BPF) 103, 303 ... -Amplifier (AMP) 104 ... Analog-digital converter (A / D) 105 ... Parallel-serial converter (P / S) 106 ... Electro-optical converter (E / O) 107 ... Reference signal generator (TCXO) 108 ... PLL oscillator 301 ... Mobile station antenna 304 ... Digital-analog converter (D / A) 305 ... Serial / parallel converter (S / P) ) 306 ... Optical-electrical converter (O / E) 309 ... Clock recovery circuit 310 ... Frequency divider circuit

Claims (5)

[Claims] 1. A means for converting an RF analog signal received from an antenna into a digital signal, a means for converting a parallel signal of the digital signal into a serial signal, and then converting the serial signal for output as an optical signal, and externally. Means for converting a serial signal into a parallel signal after converting the transmitted optical signal into an electric signal, means for converting a digital signal of the parallel signal into an RF analog signal, and an antenna for outputting the RF analog signal An optical transmission repeater comprising: 2. A unit for converting an analog signal received from an antenna into a digital signal, a unit for converting a parallel signal of the digital signal into a serial signal, and then converting the serial signal for output as an optical signal, and the digital unit. A highly stable oscillator that supplies a clock signal to the signal conversion unit and the serial signal conversion unit, a unit that converts an optical signal transmitted from the outside into an electric signal and then converts the serial signal into a parallel signal, and a digital signal of the parallel signal. Means for converting a signal into an analog signal, an antenna for outputting the analog signal, a clock signal is extracted from the electric signal after the photoelectric conversion, and the clock signal is supplied to the parallel signal converting means and the analog signal converting means. The optical transmission repeater according to claim 1, further comprising: 3. A means for converting an RF analog signal received from an antenna into an IF signal, a means for converting the IF analog signal into a digital signal, a parallel signal of the digital signal after being converted into a serial signal, and then the serial signal. Means for converting a signal into an optical signal and outputting it, means for converting an optical signal transmitted from the outside into an electric signal, and then converting a serial signal into a parallel signal, and a digital signal of the parallel signal into an IF analog signal Means, a means for converting the IF analog signal into an RF analog signal, and an RF output from the RF analog signal converting means.
An optical transmission repeater, comprising: an antenna that outputs an analog signal. 4. A means for converting an RF analog signal received from an antenna into an IF signal, a means for converting the IF analog signal into a digital signal, a parallel signal of the digital signal after being converted into a serial signal, and then the serial signal. A means for converting a signal into an optical signal and outputting the signal, a highly stable oscillator for supplying a clock signal to the IF converting means, the digital signal converting means and the serial signal converting means, and an optical signal transmitted from the outside to an electric signal. After that, means for converting a serial signal into a parallel signal, means for converting a digital signal of the parallel signal into an IF analog signal, means for converting the IF analog signal into an RF analog signal, and output from the RF analog signal converting means RF
An antenna for outputting an analog signal and a clock reproducing circuit for extracting a clock signal from the electric signal after photoelectric conversion and supplying the clock signal to the parallel signal converting means, the analog signal converting means and the RF analog signal converting means. The optical transmission repeater according to claim 3, further comprising: 5. An optical transmission repeater system comprising a plurality of optical transmission repeaters according to claim 1 connected by an optical fiber cable.