JPH0884134A - Wireless multiple link - Google Patents

Abstract

PURPOSE: To evade an interference wave generated in a radio base station by wirelessly transmitting plural high frequency signals by time division multiplex and providing each radio base station with a switch for sending a light signal to an optical transmission line only at the time of receiving a high frequency signal by a detector. CONSTITUTION: Each of radio base stations 101 to n is constituted of an antenna 23 for receiving a burst high frequency signal (f) from an information terminal, a high frequency amplifier 22 for amplifying the received burst high frequency signal, a high frequency detector 20 for judging the existence of a burst signal and driving an optical switch 19, a semiconductor laser 21 for converting the signal (f) into an optical burst signal, an optical multiplexer 18 for connecting the optical burst signal to an optical fiber, and so on. In each of the stations 101 to n, the optical switch 19 is switched so as not to supply a light carrier to the optical fiber when a burst signal is off. Thereby the generation of a beat signal due to the wavelength difference of the light carrier can be evaded except that the packets of optical burst signals are superposed to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless signal multiplexing system combining an optical fiber link and a wireless link, and accommodates a large number of terminals and requires a large number of wireless base station devices for personal mobile communication and wireless LAN. Etc. relating to wireless multiple links that can be used in such systems.

[0002]

2. Description of the Related Art In a conventional radio signal multiplexing system using an optical fiber, a frequency multiplexing system at an electric stage is used as shown in FIGS. In FIG. 6, each radio base station is composed of an optical combiner 1, a semiconductor laser 2, a high frequency amplifier 3, and an antenna 4, like the radio base station 101, for example. Further, the radio base station 101 receives a high frequency signal of frequency f1 from the information terminal, and the other radio base stations also receive the radio signal of each frequency band from the information terminal. These received signals are continuous signals, and the intensity of the semiconductor laser 2 is modulated with this signal. The radio base stations are connected by an optical fiber 9, and the output of the radio base station at the final stage is input to the photodetector 6 of the radio control station 7 to reproduce the high frequency signal transmitted from the information terminal.

In addition to the configuration of the radio signal multiplexing system described above, there is a configuration in which the radio base station is not provided with a light source, as shown in FIG. FIG. 7 shows a configuration of a wireless multiple link in which optical external modulators are connected in cascade, and an optical carrier is fed from a wireless control station to each wireless base station. In the wireless base station 101, the optical carrier is intensity-modulated at the reception frequency f1. Then, the intensity-modulated optical carrier is transmitted to the wireless base station 102.
And is intensity-modulated again at the reception frequency f2. In this way, the intensity of the optical carrier is sequentially modulated in each radio base station, and finally the optical detector 16 of the radio control station uses the frequency f1.
~ Fn are played.

[0004]

By the way, since the structure of the wireless multiplex link shown in FIG. 6 uses a large number of light sources, when the optical frequencies of the light sources are close to each other, the optical frequency difference of the light sources in the photodetector 6 is increased. A beat signal corresponding to is generated. If this beat signal falls within the band of the wireless signal, it becomes an interference wave, and the transmission characteristics deteriorate. In order to avoid this, it is sufficient to control the oscillation wavelength of each light source, but there is a drawback that the configuration of the wireless base station becomes complicated.

Further, in the structure of the wireless multiplex link shown in FIG. 7, the drawbacks of the structure of the wireless multiplex link shown in FIG. 6 can be avoided, but since it is a cascade connection of intensity modulation, a sum / difference frequency between the frequencies is generated. , These become interference waves. Of each frequency, the sum and difference frequencies of two waves are frequency bands f1 to f1.
This is not a problem because it occurs outside the band of fn, but the sum / difference frequency between the three waves, for example, f1 + f2-f3, f1-f2
Since frequencies such as + f3 are generated in the band, they become interference waves, and there is a problem that signal characteristics are deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radio multiplex link capable of avoiding an interference wave generated in a radio base station.

[0007]

According to the present invention, a plurality of wireless base stations for receiving one of a plurality of wirelessly transmitted high frequency signals and converting it into an optical signal are provided in an optical transmission line. In a radio multiplex link in which a radio control station having a photodetector for detecting the plurality of high frequency signals connected in cascade is arranged at the end of the series of the radio base stations, the plurality of high frequency signals are time-division multiplexed and wirelessly transmitted. Each of the radio base stations is
A wireless multiplex link comprising: a detector that senses reception of the high-frequency signal; and a switch that sends the optical signal to the optical transmission path only when the high-frequency signal is received by the detector. .

According to a second aspect of the present invention, a plurality of radio base stations that receive one of a plurality of radio-frequency signals transmitted by radio and superimpose on an optical signal are cascade-connected by an optical transmission line, and the plurality of radio base stations are connected. In a radio multiplex link in which a radio control station having an optical detector for detecting a high frequency signal is arranged at the end of a series of the radio base stations, the plurality of high frequency signals are time division multiplexed and wirelessly transmitted, and each radio base station. Includes a detector that senses reception of the high-frequency signal, and a switch that modulates the optical signal on the optical transmission line with the high-frequency signal only when the high-frequency signal is received by the detector. Wireless multiple link.

According to a third aspect of the invention, there is provided the wireless multiple link according to the first aspect, wherein each of the wireless base stations has a light source. According to the invention described in claim 4, in the wireless multiple link according to claim 3, the switch is an optical switch for switching an optical signal, which is a wireless multiple link.

According to a fifth aspect of the present invention, there is provided the wireless multiple link according to the third aspect, wherein the switch is an electric switch for switching a bias current to the light source. . Claim 6
According to the described invention, in the wireless multiple link according to the second aspect, each of the wireless base stations modulates an optical signal by an external modulator.
According to the invention described in claim 7, in the wireless multiple link according to claim 6, the switch is an electric switch for switching a bias voltage to the external modulator.

[0011]

According to the present invention, since the burst high frequency signal is converted into an optical signal and the optical signal is transmitted in bursts to the optical fiber, the same radio frequency can be used in each information terminal. Since each radio base station multiplexes signals on the time axis, there is no unnecessary wave generated by the product of each frequency, and even if each light source is installed in the radio base station, it is generated by the frequency difference between the light sources. It is possible to construct a wireless multiplex link that does not generate a beat signal that generates Also,
Even in a configuration in which optical external modulators are cascaded, unnecessary waves are not generated due to the reception frequency, and by changing the bias condition of the optical external modulator when the burst signal is off, a link with low optical insertion loss is configured. it can.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described.
FIG. 1 is a diagram showing a configuration of a wireless multiple link according to the first embodiment of the present invention. In this figure, the radio base stations are connected in cascade, and each radio base station receives a burst high frequency signal from an information terminal (not shown). The received burst high frequency signal is converted into an optical burst signal, multiplexed on the time axis and transmitted to the radio control station. With such a configuration, there is an advantage that there is no intermodulation between frequencies and no unnecessary wave is generated. However, since the burst signals are combined on the time axis, it is necessary to control the transmission times so that the burst signals do not interfere with each other during radio signal transmission.

Here, the burst signal is a burst-like signal obtained by switching a carrier wave (which may be a wireless GHz-order carrier or an optical μm-order carrier). In the case of a wireless carrier, an analog-modulated (FM or the like) or digitally-modulated (QAM or the like) signal is transmitted in a burst form. The burst-shaped signal of the optical carrier is formed by intensity-modulating the burst-shaped wireless signal.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing in more detail the configuration of the wireless multiple link of FIG. 1 referred to in the first embodiment. In this figure, a radio base station 101 has an antenna 23 for receiving a burst radio frequency signal f (T1) from an information terminal (not shown), a radio frequency amplifier 22 for amplifying the received burst radio frequency signal, an optical signal by judging the presence or absence of a burst signal. It comprises a high frequency detector 20 for driving the switch 19, a semiconductor laser 21 for converting the burst high frequency signal into an optical burst signal, and an optical combiner 18 for connecting the optical burst signal to an optical fiber. Also, the wireless base stations other than the wireless base station 101 have the same configuration as the above-described configuration.

With these configurations, in each radio base station,
The optical switch is switched so that the optical carrier is not supplied to the optical fiber when the burst signal is turned off. Therefore, there is an advantage that the generation of the beat signal due to the wavelength difference of the optical carriers can be avoided as long as the packets of the optical burst signals do not overlap. Further, the radio control station 27 reproduces the burst high frequency signal multiplexed in each radio base station by using the optical detector 29. As shown in FIG. 3, a bias switch with a built-in power source that switches the bias current to the semiconductor laser 21 is used in place of the optical switch 19 described above, and switching is performed so that the optical carrier is not supplied to the optical fiber when the burst signal is off. Good.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of the wireless multiple link in the third embodiment. In this figure,
The radio base station 101 has an antenna 36 for receiving a burst high frequency signal f (T1) from an information terminal (not shown), a high frequency amplifier 35 for amplifying the received burst high frequency signal, a bias switch 3 with a built-in power source by judging the presence or absence of the burst signal.
3, a high frequency detector 34 for driving 3, a synthesizer 32 for synthesizing the amplified burst high frequency signal and the DC voltage from the bias switch 33 with a built-in power source, and an optical external modulator 31 for intensity modulation of the optical carrier. Also, the wireless base stations other than the wireless base station 101 have the same configuration as the above-described configuration. Further, in the third embodiment, the light source 30 is installed in the wireless control station 27, and the optical carrier is installed in each wireless base station, and the optical external modulator (in the case of the wireless base station 101, the optical external modulator 31 is used). ) Is supplied to.
In the configuration described above, the procedure for reproducing the burst high frequency signal is the same as in the second embodiment.

Next, how the bias condition of the optical external modulator in the third embodiment is controlled when the burst signal is turned on and off will be described. FIG. 5 shows the bias voltage dependence of the output of the optical external modulator. The optical output of the optical external modulator is
It is well known that it changes periodically with respect to the applied bias voltage. Normally, when an optical external modulator is modulated with an analog signal such as a microwave signal, the bias voltage (point A in FIG. 5) that maximizes the modulation efficiency is set. Therefore, when the burst signal is on, the bias point of the optical external modulator is point A, while when the burst signal is off, the bias voltage is point B, and the optical insertion loss is the smallest.

In the conventional example shown in FIG. 7, since the high frequency signal is always received, the bias voltage is set at the point A, which has a drawback that the optical insertion loss becomes large. In the case of the third embodiment, when the burst signal is off, each optical external modulator only needs to pass the light and the bias voltage is set to the point B, so that the insertion loss of the entire link can be reduced. is there. Furthermore, there is an advantage that a high frequency signal (microwave to millimeter wave) can be transmitted over a wide frequency band by using an ultra wide band external optical modulator. Therefore, it is possible to configure a system capable of supplying a huge amount of information to the information terminals in the wireless zone covered by each wireless base station.

In the configurations of the wireless multiple links of the first to third embodiments described above, some wireless base stations are provided with optical amplifiers in order to improve optical insertion loss due to an increase in the number of wireless base stations. May be.

[0020]

As described above, according to the present invention,
Since the wireless signals are multiplexed in a large number of cascaded wireless base stations, it is sufficient to provide only one light source and one electro-optical converter in the wireless control station. Even if it is done, it is possible to greatly simplify the radio control station and make it economical. Further, in each radio base station, when converting a burst high frequency signal into an optical burst signal, not only the generation of a beat signal due to optical switching when the burst signal is turned on and off can be suppressed, but also optical insertion loss due to bias switching can be reduced. Can be achieved. Further, the application of the optical amplifier has an effect that it is possible to improve the optical loss, increase the number of wireless base stations thereby, and expand the wireless zone that can be covered by one wireless control station.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless multiple link according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a wireless multiple link according to the second embodiment.

FIG. 3 is a block diagram showing a configuration of a wireless multiplex link when a bias switch with a built-in power source is used instead of an optical switch in the second embodiment.

FIG. 4 is a block diagram showing a configuration of a wireless multiple link according to the third embodiment.

FIG. 5 is a diagram showing the bias voltage dependence of the output of the optical external modulator.

FIG. 6 is a block diagram showing a configuration of a conventional wireless multiple link.

FIG. 7 is a block diagram showing the configuration of another conventional wireless multiplex link.

[Explanation of symbols]

18 ... Optical combiner, 19 ... Optical switch, 20, 34 ...
… High frequency detector, 21 …… Semiconductor laser, 22,35
...... High frequency amplifier, 23,36 …… Antenna, 24,2
5, 26, 37, 38, 39 ... Burst high frequency signal,
27 ... Radio control station, 28, 40 ... Photodetector output port, 29 ... Photodetector, 30 ... Light source, 31 ... Optical external modulator, 32 ... Synthesizer, 33 ... Power supply bias switch

Claims (7)

[Claims] 1. An optical detector for detecting a plurality of high-frequency signals by cascade-connecting a plurality of wireless base stations for receiving one of a plurality of high-frequency signals transmitted by radio and converting the high-frequency signals into an optical signal. In a radio multiplex link in which a radio control station having is arranged at the end of the series of radio base stations, the plurality of high frequency signals are time-division multiplexed and wirelessly transmitted, and each of the radio base stations receives the high frequency signal. A wireless multiplex link, comprising: a detector that senses that; and a switch that sends the optical signal to the optical transmission line only when a high-frequency signal is received by the detector. 2. An optical detector that receives one of a plurality of radio-frequency-transmitted high-frequency signals and cascade-connects a plurality of radio base stations that superimposes the optical signals on the optical signal to detect the plurality of high-frequency signals. In a radio multiplex link in which a radio control station having is arranged at the end of the series of radio base stations, the plurality of high frequency signals are time-division multiplexed and wirelessly transmitted, and each of the radio base stations receives the high frequency signal. A wireless multiplex link, comprising: a detector that senses that; and a switch that modulates the optical signal on the optical transmission line with the high frequency signal only when the high frequency signal is received by the detector. 3. The wireless multiplex link according to claim 1, wherein each of the wireless base stations has a light source. 4. The wireless multiplex link according to claim 3, wherein the switch is an optical switch for switching an optical signal. 5. The wireless multiplex link of claim 3, wherein the switch is an electrical switch that switches a bias current to the light source. 6. The wireless multiplex link according to claim 2, wherein each of the wireless base stations modulates an optical signal with an external modulator. 7. The wireless multiplex link of claim 6, wherein the switch is an electrical switch that switches a bias voltage to the external modulator.