Patent Publication Number: US-6337754-B1

Title: Optical conversion relay amplification system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical conversion relay amplification system for use as a relay amplification system to cover a dead spot of mobile communications, particularly relates to an optical conversion relay amplification system achievable of economic constitution avoiding a beat noise. 
     2. Description of the Related Art 
     Public mobile communications systems (hereafter referred to as mobile communications systems) such as car phone, portable phone system, PHS, paging system, etc. have a base station of the mobile communications (hereafter, base station) linked to a network of the higher rank than public networks, etc. (PSTN and ISDN) by a wire to allow the base station to communicate with mobile stations such as portable phones by wireless systems. 
     The communicable area (cover area) of the base station by wireless systems is exemplified by some kilometers to some ten kilometers in car phone and portable phone systems and some hundred meters in PHS. In addition, so-called “cellular system” is applied to locate base stations in cover areas like cells in order to keep wider areas effectively using frequencies. 
     Further, to solve the problem of frequency resource according to an increased demand of radio waves, 1.5 GHz frequency band has been newly assigned to car/portable phone systems for use in addition to the conventional 800 MHz band and 1.9 GHz frequency band has been assigned to PHS for use. Furthermore, 2 GHz band is probably assigned to the portable phone of the next generation. All these band changes to high frequency bands have been carried out for mobile communications. 
     In these mobile communications systems using the cellular system, generally, wireless communications are done in high quality on outdoor ground, etc. However, even in a cover area of a base station, a radio wave difficultly reaches the inside of a tunnel, an underground shopping center, a basement of a building, and stories above ground of a big building, and thus, any auxiliary means are required to communicate with mobile wireless terminals in these sites by wireless systems. 
     These areas are named “dead spots”. The dead spot generally appears in radio wave wireless communications not only of mobile communications systems, but also of such as official radios exemplified by police radio, fire radio, and train radio, TV broadcast, and radio broadcast. 
     As auxiliary means to allow wireless communications in these dead spots, an apparatus named “relay amplification apparatus is generally used”. 
     The first antenna is located in a site capable of high quality wireless communications with a base station (a broadcast station in broadcasting) and the second antenna is located in a dead spot to amplify a high frequency signal arrived in the first antenna, transmit to the second antenna located in the dead spot by a wire, and radiate the high frequency signal amplified via the second antenna. 
     By such steps, downlink communications from the base station to the mobile station are kept. Besides, wireless communications in the dead spot become possible by that communications of a downlink line from the base station to the mobile station are established, and also by that in uplink communications from the mobile station to the base station, the high frequency signal radiated by the mobile station is caught by the second antenna to amplify and transmitted to the first antenna with a wire, and the amplified high frequency signal is radiated via the first antenna to output for transmission to the base station. 
     In addition, on the background of the popularized, wired, high quality communications networks of higher rank such as ISDN, there is a plan that a radio modem is equipped for the dead spot, e.g., underground shopping center where communications have a particularly large demand, directly connected to higher rank network such as ISDN by a wire. 
     Such radio modem modulates a high frequency signal by a signal inputted from the higher rank network, distributes the high frequency signal from the radio modem to an antenna (said second antenna) located in the dead spot, receives the frequency signal through the antenna, and demodulates the signal from the mobile station to output to the higher rank network. 
     The conventional relay amplification systems are specifically exemplified by a method in which in a dead spot such as tunnel, a leaky coaxial cable suitable to achieve a linear service area is used as the second antenna to link to the first antenna with a high frequency coaxial cable, and a method in which the second antenna is located in various sites to link to the first antenna with a high frequency coaxial cable. 
     However, a connection distance between the first antenna and the second antenna requires some kilometers on the situation. In this case, an attenuation (transmission loss) occurs as a problem in the high frequency coaxial cable. Particularly in latest years, frequencies assigned to mobile communications are moved to higher bands to require coaxial cables with a large diameter resulting in a problem of difficulty of laying construction. 
     Thus, to avoid transmission loss, the optical conversion relay amplification system has been proposed and partially practiced using analog optical fiber transmission technology in replacement to conventionally used the high frequency coaxial cable and leaky coaxial cable having a function as an antenna. 
     The technical situations of these optical conversions have been detailedly described in reference  1 : Kuganuma et al., “A tunnel booster 1.5 GHz digital mobile communications”, NTT DoCoMo technical Journal, Vol. 2, No. 2 (1994), for example, for relay system, and also for example, reference  2 : Sanada et al., “An optical transmission system for wireless base stations”, National Technical report, Vol. 39, No. 4 (1993) for optical transmission system to link to the system of a base station. 
     Besides, a detailed description has been given in the following general review about the application of transmission technology using an analog optical fiber for mobile communications: reference  3 , Morita, K., et al., “The new generation of wireless communications based on fiber-radio technologies”, IEICE Trans. Comm., Vol. E76-B, No. 9 (1993), etc. 
     On the other hand, the following two main systems are conventional to accomplish these analog optical fiber transmission systems in a structure of optical transmission line: a star distribution connection used for point-to-multipoint connection to connect an optical transmitter/receiver of the first antenna side with an optical transmitter/receiver of the second antenna side for the downlink line from the base station of the mobile communications (simply, base station) with the mobile station (portable machine); on the contrary, transmission by connecting both optical transmitters/receivers as point-to-point connection in the uplink line from the portable machine to the mobile base station. 
     However, this connection system requires many optical fiber conductors. Therefore, A multibranching optical transmission system has been proposed to make the system economic by reducing the required optical fiber conductors. 
     This means that the number of optical fiber conductor is reduced to one for the downlink to distribute optical signals in a site requiring the distribution of the optical signal by using a point-to-two point optical branching device. The uplink, as well, transmits an optical signal from respective sites through a single optical fiber by multiplex using a point-to-two point optical multiplexer. 
     By this process, in the uplink, the optical fiber as transmission line is one in number and, in addition, an optical signal multiplexed by a single photo-detector is collectively received to make the scale of a photo-detector circuit small as an advantage. 
     As a specific example appeared in Japanese Published Unexamined Patent Application No.153255/94, a system has been described as that radio signals received by a plurality of antennae—corresponding to the second antenna/e—put in a tunnel is converted to optical signals with different wavelengths keeping enough difference among E/O converters making pairs with respective antennae, respective optical signals are connected with optical couplers to transmit to objective sites using a single optical fiber to convert to electric signals using O/E converters for supplying to radio receiver. 
     In Japanese Published Unexamined Patent Application No.130322/97, a technology has been described that relay is carried out by connecting a ground relay station having the first antenna with a relay station in a dead spot having a leaky coaxial cable—corresponding to said second antenna—laid in a tunnel or an underground shopping center using an optical fiber. 
     As specific action, a radio signal from the base station of a mobile communication is received by a ground relay station via the first antenna, the high frequency electric signal thereof is converted to an optical signal to send via an optical fiber, the optical signal received by the relay station in the dead spot is converted to a high frequency electric signal and finally send through the leaky coaxial cable to the mobile station. 
     On the contrary, a radio signal sent from the mobile station is received by the leaky coaxial cable, the high frequency electric signal is converted to an optical signal in the relay station located in the dead spot to send via an optical fiber, the optical signal received by the ground relay station is converted to the high frequency electric signal to send to the base station of the mobile communications from the first antenna resulting in relay. 
     Particularly, as an example considering impossible area coverage caused by attenuation in a single leaky coaxial cable in a very long tunnel, etc., a technology has been described as that a plurality of the leaky coaxial cables is laid, a plurality of relay stations is established in the dead spot to service respective areas, an optical fiber is made as an optical transmission line of a single core multibranch type using a point-to-two points optical branching device/optical joint located near relay stations in respective dead spots. 
     As in said conventional examples 1 and 2, the use of the optical branching device/optical joint requires that branching ratio of the optical branching device in the downlink line is determined on situation in a system using a single optical fiber for an optical transmission line of the single core multibranch type. 
     On the other hand, in the uplink as like as the downlink, the multiplexing ratio of the optical multiplexer should be determined on situation. Besides, it should be considered that a beat noise caused by frequency difference among a plurality of optical signals multiplexed as electromagnetic waves should not affect the frequency band of the objective high frequency signal. 
     Said optical branching device and optical multiplexer can be made by using an optical coupler of fiber fusion type, for example. A single optical coupler can be used for both branching and multiplexing; a marketed optical coupler with branching ratio (multiplexing ratio) of each 5% class from 50%: 50% (power ratio) to 5% to 95% can be easily used. 
     Concerning methods to avoid a beat noise in the uplink, as shown in the first method of reference  4 , it is the method proposed that a beat noise is detected positively to control to prevent abutting of emitting wavelengths (i.e., frequency) of a light emission diode to avoid the effect of the beat noise. 
     Reference  4 : Taresawa et al., “a single core, multibranching type optical fiber link for mobile communications employing automated frequency offset control”, IECIE Tech. Rep., RCS97- 70 (1994.) 
     However, in the first method, there are problems that more numbers of wavelengths cannot be used, light source for transmission is expensive, the optical multiplexing loss is high, and maintenance is difficult. 
     On the other hand, as the second method to avoid the beat noise, the following method has been proposed: no positive control of wavelength is carried out and the wavelength of a semiconductor laser—a light source of the optical signal—is selected to multiplex previously. According to the experiment of the inventors of the second method, a semiconductor laser of multilongitudinal mode oscillation, and in the optical signal of multipoint multiplexing using Fabry-Perot type laser as a light source of which condition of avoiding the beat noise is more strict in comparison with that of DFB (Distributed FeedBack) laser, a difference around 10 nm between central wavelengths is required to inhibit an effect on a frequency band of portable phones; the multiplex of 3-4 per single fiber is a limit in consideration of economic system, easy availability of the light source. 
     The reference  5  presents the proposal of application of said second method to the mobile communications systems. 
     Reference  5 : Hukuie et al., “Constitution of a multibranching optical transmission system for mobile the communications”, 1996 IECIE Communications Society Meeting, B-492. 
     Avoiding the beat noise in the uplink is the most crucial technical problem in said high frequency signal transmission systems by analog optical modulation using the optical transmission lines of said multibranching and multinode multiplexing type. 
     Thus, Reference  6  proposed an optical multiaccess using a subcarrier relay node multiplexing system, in which any beat noise does not occur, as the third method to prevent a problem of optical beat noise caused by the optical multiplexing in the uplink. 
     Reference  6 : Domon et al., “A proposal of an optical multiaccess using the subcarrier relay node multiplexing system”, IECIE Tech. Rep., OCS93-99 (1994.) 
     The outline of said system is: an optical signal is once converted to electric signal in respective local nodes to multiplex electrically frequencies of new subcarriers followed by conversion to an optical signal to send to the optical transmission line. 
     The optical signal transmitted by multiplexing electrically the new subcarriers in respective local nodes one after another applying said method is received by an optical receiver in a center node to convert to an electric signal and a signal sent from a local node can be selected with a tuner etc. 
     As a specific example of said system, an optical network for relay and amplification using the optical multiaccess by the subcarrier relay node multiplexing system has been proposed in Japanese Published Unexamined Patent Application No. 191478/96. This system is herewith explained as a conventional optical conversion relay amplification system with reference to FIG.  8 . The FIG. 8 is the diagrammatic illustration of the conventional optical conversion relay amplification system and the optical networks using the system. 
     The conventional optical conversion relay amplification system is, as shown in the FIG. 8, mainly composed of a central station  100 , a mobile terminal station  103 , an intermediate radio base station  102 A and  102 B, an end radio base station  102 C, and a downlink optical fiber line  104 A and an uplink optical fiber line  104 B connecting the central station  100  and respective radio base stations  102 . 
     In the central station  100 , a downlink signal is modulated to send to the mobile terminal  103 , converted to an optical signal to send to the downlink optical fiber line  104 A; on the contrary, the uplink optical signal sent from the mobile terminal  103  to transmit is received from the uplink optical fiber line  104 B to convert to a radio signal followed by demodulation. 
     The intermediate radio base station  102 B is composed of an optical demultiplexer  121 B demultiplexing the downlink optical signal from the downlink optical fiber line  104 A, an optical receiver  123 B converting the optical signal demultiplexed to radio signal, an amplifier  124 B amplifying the radio signal, an antenna  135 B sending the radio signal, an antenna  136 B receiving the radio signal, an amplifier  132 B amplifying the received signal, an optical receiver  125 B converting the optical signal transmitted from a lower rank radio base station to a high frequency signal, a multiplexer  122 B multiplexing the received signal amplified by the amplifier  132 B with the high frequency signal from optical receiver  125 B, and an optical transmitter  134 B converting the multiplexed signal to an optical signal to send to the uplink optical fiber line  104 B. 
     The intermediate radio base station  102 A has the same constitution. 
     The end radio base station  102 C has the constitution in which a function of demultiplexing optical signals in the downlink line and an optical relaying function in the uplink line have been removed from the constitution of the intermediate radio base station  102 B, and is composed of an optical receiver  123 C converting an optical signal from the downlink optical fiber line  104 A to a radio signal, an amplifier  124 C amplifying the radio signal, an antenna  135 C sending the radio signal, an antenna  136 C receiving the radio signal, an amplifier  132 C amplifying the received signal, and an optical transmitter  134 C converting the received amplified signal to an optical signal to send to the uplink optical fiber line  104 B. 
     Further in the action of the conventional optical conversion relay amplification system, a downlink signal is converted to an optical signal in the central station  100  to send through the downlink optical fiber line  104 A, partially demultiplexed by the demultiplexer  121 B in the radio base station  102 B (same in the radio base station  102 A), converted to a radio signal by the optical receiver  123 B, amplified by the amplifier  124 B, and transmitted from the antenna  136 B to the mobile terminal station  103 B. 
     Furthermore, the optical signal transmitted from a lower rank radio base station (for example, radio base station  102 C) to the uplink optical fiber line  104 B is converted to a high frequency signal by the optical receiver  125 B and inputted into the multiplexer  122 B. 
     On the other hand, a radio signal sent from the mobile terminal  103  is received by the antenna  136 B, amplified by the amplifier  132 B, inputted into the multiplexer  122 B, multiplexed with the high frequency arrived from said lower rank radio base station, subsequently, converted to an optical signal by the optical transmitter  134 B and sent to the uplink optical fiber line  104 B, and finally, converted to a radio signal by the central station  100 . 
     Although the beat noise occurring in the uplink line can be avoided in said conventional optical conversion relay amplification system, there is a problem that the optical receiver having same performance is required by respective uplink and downlink lines resulting in an increased circuit size uneconomical. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide an optical conversion relay amplification system capable of a relay with the economical constitution in which the beat noise is avoided in uplink line of the optical transmission line of multibranching and multinode multiplexing type. 
     The present invention is an optical conversion relay amplification system, wherein said optical conversion relay amplification system has a fixed central station for transmission and receiving of a radio signal from a base station and a plurality of fixed relay stations located in intermediate position in the downlink optical fiber line from said fixed central station and an uplink optical fiber line to said fixed central station, 
     said fixed central station is a fixed central station converting a radio signal arrived from said base station to an optical signal to output to said downlink optical fiber line, and also converting the optical signal inputted from said uplink optical fiber line to a high frequency electric signal to send to said base station, and 
     said fixed relay station is a fixed relay station dividing the downlink optical signal from said downlink optical fiber line to multiplex with said uplink optical fiber line, converting the multiplexed optical signal to an electric signal, transmitting the downlink electric signal included in said converted electric signal to portable phone by wireless system, and also receiving the radio signal arrived from the said portable phone to multiplex with an uplink electric signal included in said converted electric signal and converting the multiplexed electric signal to an optical signal to output to said uplink optical fiber line. 
     Thus, the beat noise in the uplink line can be avoided and the communication of a portable phone located in a dead spot with a base station can be relayed in an economic constitution. 
     Further, the present invention has a fixed central station working for transmission/receiving of a signal to/from public networks, and a plurality of fixed relay station located in intermediate position of a downlink optical fiber line from said fixed central station and an uplink optical fiber line toward said fixed central station, in an optical conversion relay amplification system, wherein 
     said fixed central station is a fixed central station modulating a signal received from said public network to make a high frequency signal to convert to an optical signal for output to said downlink optical fiber line, and also converting the optical signal inputted from said uplink optical fiber line to a high frequency electric signal, demodulate to transmit to said public network, and 
     said fixed relay station is a fixed relay station branching the downlink optical signal from said downlink optical fiber line to multiplex with said downlink optical fiber line, converting the multiplexed optical signal to an electric signal, transmitting downlink electric signal contained in the converted electric signals to a portable phone by radio, and also receiving an electric signals from said portable phone to multiplex with uplink electric signals contained in said converted electric signals, and converting the multiplexed electric signals to optical signals to output to said uplink optical fiber line. 
     Thus, communications between a portable phone located in a dead spot and a public network can be relayed with the economical constitution in which the beat noise is avoided in uplink line. 
     Furthermore, the present invention has a fixed central station to receive a radio signal arrived from a base station and a plurality of fixed relay stations located in an intermediate position in downlink optical fiber line from said fixed central station and an uplink optical fiber line to said fixed central station in an optical conversion relay amplification system, wherein 
     said fixed central station is a fixed central station, wherein a radio signal received from said base station is converted to an optical signal to output to said downlink optical fiber line, and also an optical signal inputted from said uplink optical fiber line is converted to an electric signal to receive a surveillance signal of a surveillance result in said fixed relay station, and 
     said fixed relay station is a fixed relay station, wherein a downlink optical signal branches from said downlink optical fiber line to multiplex with said uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signals is transmitted to a radio paging receiver by wireless system, an uplink electric signal contained in said converted electric signals is multiplexed with the surveillance signal, and the multiplexed electric signals are converted to optical signals to output to said uplink optical fiber line. 
     Thus, paging from a base station to a paging receiver located in a dead spot can be relayed with the economical constitution in which the beat noise is avoided in the uplink line, and also a surveillance signal in a fixed relay station can be transmitted to the fixed central station by relaying. 
     Further, the present invention has a fixed central station to receive a signal from a public network and a plurality of fixed relay station located in intermediate position of a downlink optical fiber line from said fixed central station and an uplink optical fiber line to said fixed central station in an optical conversion relay amplification system, 
     said fixed central station is a fixed central station, wherein a signal received from said public network is modulated to a high frequency signal, converted to an optical signal to output to said downlink optical fiber line, and also the optical signal inputted from said uplink optical fiber line is converted to an electric signal to receive a surveillance signal of a surveillance result in said fixed relay station, 
     said fixed relay station is a fixed relay station, wherein a downlink optical signal branches from said downlink optical fiber line to multiplex with said uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signals is transmitted to a paging receiver by wireless system, an uplink electric signal contained in said converted electric signals is multiplexed with the surveillance signal, the multiplexed electric signals are converted to optical signals to output to said uplink optical fiber line. 
     Thus, paging from a public network to a paging receiver located in a dead spot can be relayed with the economical constitution in which the beat noise is avoided in uplink line, and also a surveillance signal in a fixed relay station can be transmitted to the fixed central station by relaying. 
     Furthermore, the present invention has a fixed central station to transmit/receive a radio signal to/from a base station and a plurality of fixed relay station located in intermediate position of respective downlink optical fiber line from said fixed central station and uplink optical fiber line to said fixed central station in an optical conversion relay amplification system, 
     said fixed central station is a fixed central station, wherein a surveillance controlling signal controlling surveillance in said fixed relay station is multiplexed with a radio signal received from said base station, said multiplexed electric signal is converted to an optical signal to output to said downlink optical fiber line, and also an optical signal inputted from said uplink optical fiber line is converted to an electric signal, and said electric signal is separated into a signal to said base station and a surveillance signal of a surveillance result in said fixed relay station to transmit said signal for said base station to said base station, and also said surveillance signal is received, and 
     said fixed relay station is a fixed relay station, wherein a downlink optical signal branches from said downlink optical fiber line to multiplex with said uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signals is separated into a signal for a portable phone and a surveillance controlling signal, the separated signal for a portable phone is transmitted to a portable phone by wireless system, and also surveillance is carried out on the basis of said separated surveillance controlling signal, the surveillance signal yielded by said surveillance, the radio signal received from said portable phone, and an uplink electric signal contained in said converted electric signals is multiplexed, and the multiplexed electric signals are converted to optical signals to output to said uplink optical fiber line. 
     Thus, communications between a portable phone and a base station located in a dead spot can be relayed with the economical constitution in which the beat noise is avoided in uplink line, and also communications of a surveillance controlling signal and a surveillance signal between a fixed central station and a fixed relay station can be relayed. 
     Also furthermore, the present invention has a fixed central station to transmit/receive a signal to/from a public network and a plurality of fixed relay station located in intermediate position of respective downlink optical fiber line from said fixed central station and uplink optical fiber line to said fixed central station in an optical conversion relay amplification system, 
     said fixed central station is a fixed central station, wherein a surveillance controlling signal controlling surveillance in said fixed relay station is multiplexed with a high frequency signal generated by modulating a signal received from said public network, said multiplexed electric signal is modulated and converted to an optical signal to output to said downlink optical fiber line, and also an optical signal inputted from said uplink optical fiber line is converted to an electric signal, and said electric signal is separated into a signal for said public network and a surveillance signal of a surveillance result in said fixed relay station to transmit a signal for said public network to said public network after demodulation, and also said surveillance signal is received, and 
     said fixed relay station is a fixed relay station, wherein a downlink optical signal branches from said downlink optical fiber line to multiplex with said uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signals is separated into a signal for a portable phone and a surveillance controlling signal, the separated signal for a portable phone is transmitted to a portable phone by wireless system, and also surveillance is carried out on the basis of said separated surveillance controlling signal, the surveillance signal yielded by said surveillance, the radio signal received from said portable phone, a surveillance signal outputted from said surveillance controlling signal unit, and an uplink electric signal contained in said converted electric signals are multiplexed, and the multiplexed electric signals are converted to optical signals to output to said uplink optical fiber line. 
     Thus, communications between a portable phone and a public network located in a dead spot can be relayed with the economical constitution in which the beat noise is avoided in uplink line, and also communications of a surveillance controlling signal and a surveillance signal between a fixed central station and a fixed relay station can be relayed. 
     Finally, in an optical conversion relay amplification system of the present invention, the antenna of the relay station is a leaky coaxial cable and with the economical constitution in which the beat noise is avoided in uplink line, and also communications of a portable phone or a paging receiver with a base station of mobile communications or a higher rank network can be relayed for linearly extending dead spots as service areas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an exemplary constitution of the 1st optical conversion relay amplification system of the present invention. 
     FIG. 2 is a block diagram showing an exemplary constitution of the 2nd optical conversion relay amplification system of the present invention. 
     FIG. 3 is a block diagram showing an exemplary constitution of the 3rd optical conversion relay amplification system of the present invention. 
     FIG. 4 is a block diagram showing an exemplary constitution of the 4th optical conversion relay amplification system of the present invention. 
     FIG. 5 is a block diagram showing an exemplary constitution of the 5th optical conversion relay amplification system of the present invention. 
     FIG. 6 is a block diagram showing an exemplary constitution of the 6th optical conversion relay amplification system of the present invention. 
     FIG. 7 is a block diagram showing an exemplary constitution of the 7th optical conversion relay amplification system of the present invention. 
     FIG. 8 is a block diagram of a conventional optical conversion relay amplification system and an optical network employing the conventional system. 
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       1 — 1 ,  1 - 2 ,  1 - 3 ,  1 - 4 ,  1 - 5 ,  1 - 6 : fixed central station;  2 - 1 A,  2 - 1 B,  2 - 2 A,  2 - 2 B,  2 - 3 A,  2 - 39 ,  2 - 4 A, and  2 - 4 B: fixed relay station;  3 A and  32 : portable apparatus (portable phone),  4 A: downlink optical fiber line;  4 B: uplink optical fiber line;  5 : base station of mobile communications;  6 A and  6 B: leaky coaxial cable;  7 : higher rank network;  8 A and  8 B: radio paging receiver;  10 : uplink band pass filter for transmission;  10 ′: band pass filter for surveillance signal;  11 ,  11 ′,  35 A,  35 B,  35 ′A, and  35 ′B: antenna;  12  and  30 : antenna distributor;  13 ,  15 ,  24 ,  27 ,  29 ,  32  and  38 : amplifier:  14  and  34 ; electric/optical converter;  16  and  23 : optical/electric converter;  17 : high frequency modulator;  17 ′: modulator for surveillance controlling signal;  18 : high frequency demodulator;  18 ′: demodulator for surveillance signal;  19 : surveillance processing unit;  19 ′: surveillance controlling indication unit;  20 : power distributor unit;  20 ′: power multiplexer;  21 A and  21 B: optical branching device;  22 A and  22 B: optical multiplexer;  25  and  25 ′: power distributor;  26 : downlink band path filter;  28 : uplink band pass filter for relaying;  31 : uplink band pass filter for receiving  33  and  33 ′: power multiplexer;  36 : modulator for surveillance signal;  37  and  37 ′: surveillance controlling unit;  39 : band pass filter for surveillance controlling signal;  40 : demodulator for surveillance controlling signal. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Mode for carrying out the present invention is herewith described with reference to drawings. 
     First, the first mode for carrying out the present invention is herewith described with reference to drawings. An optical conversion relay amplification system of the first mode for carrying out the present invention relates to claim  1  and claim  7 . 
     An optical conversion relay amplification system of the present invention makes communications between a portable phone located in a dead spot and a base station possible by achieving the economical constitution in which a beat noise in uplink signals caused by optical signal multiplex is avoided on the basis that a downlink radio signal received from the base station is converted to an optical signal in the fixed central station to transmit via a downlink optical fiber line and a downlink optical signal branches in the fixed relay station to subject to optical multiplexing with the uplink optical signal transmitted from a lower rank fixed relay station via uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink signal component contained in the electric signal is transmitted from an antenna to a portable phone by wireless system, an uplink signal components contained in the electric signal is subjected to power multiplex with an uplink signal transmitted from the portable phone followed by conversion to an optical signal to transmit via the optical fiber line and again converted to an electric signal by the fixed central station to transmit to the base station as an uplink radio signal. 
     An exemplary constitution of the first optical conversion relay amplification system of the present invention is herewith described with reference to FIG.  1 . The FIG. 1 is a block diagram showing an exemplary constitution of the first optical conversion relay amplication system of the present invention. The first mode for carrying out the present invention is for the application to the relay amplification system of a portable phone. In the FIG. 1, examples presented are respective two sets of a fixed relay station and a portable phone to simplify the explanation. 
     The first optical conversion relay amplication system (the first system) of the present invention has an outlined constitution composed of a base station of mobile communications  5 , a fixed central station  1 — 1 , a downlink optical fiber line  4 A and an uplink optical fiber line  4 B, one or more fixed relay stations  2 - 1 A and  2 - 1 B having a cascade connection in intermediate position of these lines  4 A and  4 B, and portable apparatus  3 A and  3 B. 
     The base station  5  of mobile communications corresponds to the base station of claims and the portable apparatus  3 A and  3 B correspond to portable phones of claims. 
     Respective units of the first system of the present invention are explained below. 
     The base station  5  of mobile communications—an ordinary base station—is connected to a higher rank network than a public network, etc. by wired system to service a link of portable phone system. 
     The fixed central station  1 — 1  presents in the service area of the base station  5  of mobile communications and is located in a site showing qualified conditions of electric waves to transmit/receive radio waves to/from the base station  5  of mobile communications, and also mutually converts between the radio signal and optical signal for optical signal transmission and receiving. The internal details of the fixed central station  1 — 1  presents are stated later. 
     The fixed relay stations  2 - 1 A and  2 - 1 B are located in a dead spot such as a tunnel and an underground shopping center, etc. where a radio wave difficultly reaches, transmit/receive an optical signal to/from the fixed central station  1 — 1 , and also mutually converts between optical signal and the radio signal for radio signal transmission and receiving. By this process, radio communications between portable apparatus presenting in dead spots and other area make possible. The internal details of the fixed relay stations  2 - 1 A and  2 - 1 B are stated later. 
     The portable apparatus  3 A and  3 B (mobile phone. etc.) present in the range reachable of radio waves from the fixed relay stations  2 - 1 A and  2 - 1 B and transmit/receive radio waves to/from the fixed relay stations  2 - 1 A and  2 - 1 B. 
     The downlink optical fiber line  4 A is the optical fiber line to transmit an optical signal sent from the fixed central station  1 — 1  to the fixed relay stations  2 - 1 A and  2 - 1 B and an uplink optical fiber line  4 B is the optical fiber line to transmit an optical signal sent from the fixed relay stations  2 - 1 A and  2 - 1 B to the fixed central station  1 — 1 . 
     Next, the internal structure of the fixed central station  1 — 1  is described. 
     The fixed central station  1 — 1  has been constituted by an antenna  11  to transmit/receive a radio signal to/from the base station  5  of mobile communications, an antenna distributor  12  to use the antenna  11  for transmission and receiving, an amplifier  13  to amplify received radio signal, an electric/optical converter  14  (E/O in the FIG. 1) to convert the amplified radio signal (an electric signal) to an optical signal to send to the downlink optical fiber line  4 A, an optical/electric converter  16  (O/E in the FIG. 1) to convert the optical signal received from the uplink optical fiber line  4 B to an electric signal, and an amplifier  15  to amplify the converted electric signal. 
     Here, the electric/optical converter  14  corresponds to the first electric/optical converter of claims and the optical/electric converter  16  corresponds to the first optical/electric converter of claims. 
     The electric/optical converter  14  is, for example as stated later, subcarrier multiplexing analog optical modulator and the optical/electric converter  16  is a subcarrier multiplexing analog optical demodulator. 
     Subsequently, the followings are the explanation of the internal structure of the fixed relay stations  2 - 1 A and  2 - 1 B. The fixed relay stations  2 - 1 A and  2 - 1 B have same components and are explained herewith presenting the details of the internal structure of only the fixed relay stations  2 - 1 A in the FIG.  1 . 
     The fixed relay stations  2 - 1 A is composed of an optical branching device  21 A, optical multiplexer  22 A, an optical/electric converter  23  (O/E in the FIG.  1 ), an amplifier  24 , a power distributor  25 , a downlink band pass filter  26 , an amplifier  27 , a relaying uplink band pass filter  28 , an amplifier  29 , an antenna distributor  30 , an antenna  35 A, a receiving uplink band pass filter  31 , an amplifier  32 , a power multiplexer  33 , and the electric/optical converter  34  (E/O in the FIG. 1.) 
     The optical/electric converter  23  corresponds to the second optical/electric converter of claims and the electric/optical converter  34  corresponds to the second electric/optical converter of claims, the power distributer  25  corresponds to the first power distributer of claims, and the power multiplexer  33  corresponds to the first power multiplexer of claims. 
     The optical branching device  21 A divides an optical signal and has one input end and two output ends (branched output ends.) the upstream end of the downlink optical fiber line  4 A is connected to the input end, one of the two output ends is connected to the downstream end of the downlink optical fiber line  4 A, and another end is connected to the first input end of the optical multiplexer  22 A. 
     The branching ratio in the optical branching device  21 A is determined in consideration of the multiplex ratio of the optical multiplexer  22 A to equalize inputted optical powers into the optical/electric converters  23 A,  23 B, . . . n of respective fixed relay stations  2 - 1 A,  2 - 1 B, . . . n with cascade connection, and generally a value other than 50:50 (as a power ratio.) 
     In addition, the setting method of optical branching ratio, etc. for the optical branching device  21 A is exemplarily determined according to “Single Fiber Multi Terminal Optic Links for Mobile Radio Communications using Automatic Wavelength-Offset Control”, by Tarusawa et al., The Institute of Electronics Information and Communication Engineers, Technical Report of IEICE RCS94-70 (1994-09) as the followings. 
     Concerning the branching ratio in the optical branching device  21 A for the downlink line, it is economic that amplifier gains, etc. of respective fixed relay stations  2 - 1 A, B, . . . n can be commonly designed by fixing the strength Pr of an optical signal inputted into the optical/electric converters  23  of respective fixed relay stations  2 - 1 A, B, . . . n. 
     Thus, the branching ratio (connection coefficient) Ki of the optical branching device  21 A of i-th fixed relay station is determined by the following [Formula 1.]         K   i     =       K   L     i   -   2             ∑     i   =   1       N   -   2            K   L   i       +   2                       
     Where, KL represents the loss of an optical fiber, i is 3 or more. The connection coefficient KN of the optical multiplexer  22 A nearest the fixed central station  1 — 1  is presented in the following [Formula 2.]         K   N     =       K   L     N   -   2             ∑     i   =   1       N   -   2            K   L   i       +   2                       
     Making the strength of an optical signal as Ps to be outputted by the electric/optical converter  14  of the fixed central station  1 — 1 , the photo-detecting level Pr in respective fixed relay stations  2 - 1 A, B, . . . n is as following [formula 3.]         P   r     =         K   L     N   -   1             ∑     i   =   1       N   -   2            K   L   i       +   2       ·     P   s                       
     The connection coefficient of the optical multiplexer  22 A of the uplink line can be also calculated as same as the downlink line. 
     The optical multiplexer  22 A multiplexes an optical signal and has two input ends (multiplex input end) and one output end. The one of the two input ends is connected to the second output end of the optical branching device  21 A and the other end is connected to the upstream end of the uplink optical fiber line  4 B, and the output end is connected to the input end of the optical/electric converters  23 . 
     The multiplex ratio in the optical multiplexer  22 A is as same as the branching ratio in the optical branching device  21 A and is determined in consideration of the branching ratio of the optical branching device  21 A to equalize inputted optical powers into the optical/electric converters  23 A,  23 B, . . . n of respective fixed relay stations  2 - 1 A,  2 - 1 B, . . . n. 
     The optical/electric converters  23  is, same as the optical/electric converter  16  of the fixed central station, a subcarrier multiplexing analog optical demodulator to convert an analog optical signal to an electric signal, and multiplexes a downlink optical signal from the fixed central station  1 — 1  with an uplink optical signal from the fixed relay station  2 - 1 B in the optical multiplexer  22 A to convert a multiplexed analog optical signal to an electric signal for outputting. 
     The amplifier  24 , amplifier  27 , amplifier  29 , and amplifier  32  are ordinary amplifiers to amplify an electric signal to an appropriate level. 
     The power distributer  25  is ordinary distributor to output an inputted signal to two output ends, as it is. 
     The downlink band pass filter  26  is an ordinary band pass filter to pass frequency of the downlink signal only from the fixed central station  1 — 1 . 
     The receiving uplink band pass filter  28  is an ordinary band path filter to pass a frequency band of only upstream electric signal from the fixed relay station (the fixed relay station  2 - 1 B in the FIG. 1) located in upstream of the uplink line. 
     The antenna  35 A is an ordinary antenna to transmit and receive a radio wave. 
     The antenna distributor  30  is an ordinary antenna distributor to use the antenna  35 A for both transmission and receiving. 
     The receiving uplink band pass filter  31  is an ordinary uplink band pass filter to pass a frequency band of only upstream signal from a mobile apparatus  3 A. 
     The power multiplexer  33  is an ordinary power multiplexer to subject to simple power multiplex of two electric signals. 
     The electric/optical converter  34  is, as same as the electric/optical convertor  14  of the fixed central station, the subcarrier multiplexing analog optical modulator modulates the multiplexed electric signal to an analog optical signal to output. 
     Next, the action of the first system of the present invention is explained with reference to the FIG.  1 . 
     In the first system of the present invention, a downstream radio wave transmitted from the base station  5  of mobile communications is received by the antenna  11  of the fixed central station  1 — 1 , amplified by the amplifier  13  to an appropriate level via the antenna distributer  12  followed by analog optical modulation by the electric/optical converter  14  to generate an optical signal, and sent to the downlink optical fiber line  4 A. 
     Subsequently, this optical signal is divided by the optical branching device  21 A of the first fixed relay stations  2 - 1 A, and inputted to the one of the optical multiplexer  22 A, and uplink optical signal from the second fixed relay station  2 - 1 B is inputted to the other of the optical multiplexer  22 A, multiplexed in the optical multiplexer  22 A to yield a multiplexed analog signal. 
     The multiplexed analog signal is converted to an electric signal by the optical/electric converter  23  and amplified by the amplifier  24  if necessary, and divided into two signals by the power distributer  25 . 
     A frequency of the downlink signal is extracted from the one of the divided two signals by the downlink band path filter  26  to become the downlink high frequency band signal, amplified by the amplifier  27  if necessary, and radiated as a radio wave from the antenna  35 A of the first fixed relay stations  2 - 1 A via the antenna distributor  30  to keep radio communications in the downlink direction toward a portable apparatus  3 A. 
     On the other hand, only the uplink electric signal frequency is extracted from the other signal—divided by the power distributer  25 —by the relaying uplink band path filter  28  to become an uplink high frequency band signal, amplified by the amplifier  29  if necessary, and inputted to one of the power multiplexer  33 . 
     Concerning the uplink line from portable apparatus  3 A to the base station  5  of mobile communications, the uplink radio signal transmitted from the portable apparatus  3 A is received by the antenna  35 A of the fixed relay stations  2 - 1 A, limited its band by the receiving uplink band pass filter  31 , amplified to an appropriate level by the amplifier  32  if necessary, and inputted to another power multiplexer  33 . 
     The power multiplexer  33  multiplexes the power of uplink signal—outputted from the amplifier  29 —from the second fixed relay station  2 - 1 B with that of the uplink signal in the fixed relay stations  2 - 1 A and the multiplexed output is modulated to an analog signal by the electric/optical converter  34  to send to the uplink optical fiber line  4 B. 
     In the fixed central station  1 — 1 , the uplink analog optical signal from the uplink optical fiber line  4 B is demodulated to a high frequency signal by the optical/electric converter  16 , amplified to an appropriate level by the amplifier  15  if necessary, and radiated from the antenna  11  to space via the antenna distributor  12  to send to the base station  5  of mobile communications. 
     For reference, in this mode for carrying out the present invention, the optical branching device  21 A and the optical multiplexer  22 A have been illustrated as located in a case of the fixed relay stations  2 - 1 A. However, as shown with the dotted line L of the FIG. 1, the optical branching device  21 A and the optical multiplexer  22 A can be located in an optical fiber termination box for optical wiring to the fixed relay stations  2 A. 
     According to the first system of the present invention, there is an effect to make possible radio communications between a portable apparatus  3  presenting in a dead spot and the base station  5  of mobile communications by locating the antenna  11  of the fixed central station  1 — 1  in a site giving an environment allowing high quality radio communications with the base station  5  of mobile communications and also locating a plurality of the fixed relay stations  2 - 1 A,  2 - 1 B, . . . n—connected to the fixed central station  1 — 1  with an optical fiber—in a dead spot, such as a tunnel and an underground shopping center, where is difficult to receive a radio wave. 
     Besides, in the first system of the present invention, avoiding the occurrence of a beat noise in two optical waves is only required, because the fixed relay stations  2 - 1 A receives a signal made by multiplex of two optical waves that are an optical signal of the downlink optical fiber line  4 A and an optical signal from a lower rank fixed relay stations  2 - 1 B linked by cascade connection. On principle, an optical generator exemplified by a semiconductor laser, etc. of two groups with previously selected wavelengths is only required. 
     This means that a complicated operation such as an automated frequency offset control is quite unnecessary concerning optical wavelengths from respective fixed relay stations  2 - 1 A,  2 - 1 B, . . . n. Therefore, an effect of constituting an economic system can be yielded in comparison with conventional systems. 
     In addition, in the first system of the present invention, an optical signal from the lower rank fixed relay stations  2 - 1 B is once converted an electric signal to superimpose by power multiplex with a high frequency signal from the portable apparatus  3 A existing in the area of the fixed relay stations  2 - 1 A to convert to an optical signal again, in order to transmit an optical signal of the uplink line avoiding a beat noise. 
     Therefore, a factor limiting possible cascade connection numbers is accumulation of distortion and noise occurring in respective ranks. 
     Concerning this point, a result has been reported in the reference already introduced: the reference  6 , Domon et al., “A proposal of an optical multiaccess using the subcarrier relay node multiplexing system”, IECIE Tech. Rep., OCS93-99 (1994.) 
     According to this reference, an example has been calculated using a Fabry-Perot laser, that shows a 45 dBc tertiary intermodulation distortion in modulating with a double tones using two waves of a 135 dB/Hz relative noise intensity (RIN) and a 20% optical modulation, as a light source of a fixed relay station, and also using 10 pA/(Hz) ½  noise current density by input conversion and a 0.9 mA/mW optical conversion efficiency, as the characteristics of photo-detector. 
     Thus, 20 cascade connections are possible in transmission of an FM signal with 27 MHz noise band width under the condition of a receiving CNR&gt;17 dB. 
     According to the condition, 20 fixed relay stations in the cascade connection yields about 47 dB receiving CNR, when a radio signal for mobile communications of about 25 kHz noise band width is transmitted. The value can be improved by reducing the number of fixed relay stations in a whole system or by using a high performance laser such as DFB laser for light emission device. 
     In addition, in the first system of the present invention, at least one set of the optical/electric converter  23  is required in a fixed relay station to multiplex an optical signal of the downlink optical fiber line  4 A with an optical signal of the uplink optical fiber line  4 B by the optical multiplexer  22 A followed by modulating it to an analog optical signal by the optical/electric converter  23 . This processing means possible effect of a simple, economic constitution in comparison with conventional systems. 
     Next, the second mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the second mode for carrying out the present invention relates to claim  2  and claim  8 . 
     The second optical conversion relay amplification system related to the second mode for carrying out the present invention is an applied example of the first system already described and has a structure of direct linking of the fixed central station with a higher rank network (a public network); in the fixed central station, a signal received the public network is modulated into a high frequency, converted to an optical signal, and outputted to the uplink optical fiber line, and an optical signal inputted from the uplink optical fiber line is converted to a high frequency electric signal, demodulated, and transmit to the public network. Communications by the system between portable phone in dead spots and the public network becomes possible by avoiding a beat noise caused by multiplex of an optical signal in the uplink signal and accomplishing an economic system constitution. 
     First, as an example of constitution of the second optical conversion relay amplification system (the second system) related to the present invention, an applied example of constitution of the first system is herewith described with reference to FIG.  2 . The FIG. 2 is a block diagram showing an example of constitution of the second optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG. 1 are described with same symbols. 
     The second relay amplification system (the second system) by optical conversion related to the present invention is same as the first system, and the outlined structure is composed of a fixed central station  1 - 2  directly linked with a higher rank network  7 , a downlink optical fiber line  4 A and an uplink optical fiber line  4 B, one or more fixed relay stations  2 - 1 A and  2 - 1 B linked by cascade connection in intermediate position of these lines  4 A and  4 B, and portable apparatus  3 A and  3 B (mobile phone. etc.) 
     In the second system, the downlink optical fiber line  4 A and the uplink optical fiber line  4 B, the fixed relay stations  2 - 1 A and  2 - 1 B, and the portable apparatus  3 A and  3 B are quite same as those of the first system, and the constitution of the fixed central station  1 - 2  somewhat differs from that of the first system. 
     The fixed central station  1 - 2  in the second system is, as same composition as that of the first system, composed of an amplifier  13  amplifying a downlink signal from a higher rank network  7 , an electric/optical converter  14  (E/O in FIG. 2) converting the amplified electric signal to an optical signal, an optical/electric converter  16  (O/E in FIG. 2) converting the optical signal to an electric signal, and an amplifier  15  amplifying the electric signal to send, and the second system is characterized by a high frequency modulator  17  (MOD in FIG. 2) modulating the downlink signal from the higher rank network  7  to a high frequency signal, and a high frequency demodulator  18  (DEM in FIG. 2) demodulating an uplink high frequency signal to the higher rank network  7 . 
     In the action of the second system of the present invention, the downlink signal from the higher rank network  7  is modulated to a high frequency signal by the high frequency modulator  17  of the fixed central station  1 - 2 , amplified to an appropriate level by the amplifier  13 , and subjected to the analog optical modulation by the electric/optical converter  14  to make an optical signal followed by sending the downlink optical fiber line  4 A. 
     The subsequent actions in the fixed relay stations  2 - 1 A and  2 - 1 B are quite same as those of the first system. 
     On the other hand, in the uplink line from the portable apparatus  3 A to the higher rank network  7 , an uplink optical signal is sent to the uplink optical fiber line  4 B, the optical signal is converted to a high frequency electric signal by the optical/electric converter  16  of the fixed central station  1 - 2 , amplified to an appropriate level by an amplifier  15  if necessary, and demodulated by a high frequency demodulator  18  to output to the higher rank network  7 ; all these actions are quite same as those of the fixed relay stations  2 - 1 A and  2 - 1 B in the first system. 
     In the FIG. 2, only respective one figure has been presented for the high frequency modulator  17  and the high frequency demodulator  18  of the fixed central station  1 - 2  in order to simplify. However, in the downlink line, a plurality of the high frequency modulator  17  may be equipped for frequency multiplexing different frequency outputs from respective high frequency modulator  17  to subject to collectively the analog optical modulation by the electric/optical converter  14  followed by sending as a subcarrier multiplexing analog optical signal. 
     Further, the uplink line may have a constitution, in which a plurality of the high frequency demodulator  18  is equipped for simultaneous processing of multichannel signals. 
     There is almost no instance of a single wave in radio waves radiated by the base station of the portable phone system; a plurality of modulated waves of different frequencies is generated, multiplexed in frequencies, and radiated from another antenna. 
     In constitution of the apparatus of the present invention, it is preferable to adopt such subcarrier multiplexing system, because not only a single wave from a single high frequency modulator  17 , but also a plurality of modulated waves from a plurality of the high frequency modulator  17  can be collectively transmitted. 
     According to the second system of the present invention, an effect can be accomplished for a simple, economic constitution of radio communications of the higher rank network  7  with the portable apparatus  3  existing in dead spots avoiding a beat noise, by making up the fixed central station  1 - 2  connecting directly with the higher rank network  7 . 
     Next, the third mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the third mode for carrying out the present invention relates to claim  3  and claim  9 . 
     The third optical conversion relay amplification system related to the third mode for carrying out the present invention is another applied example of said described first system; the radio paging system is replaced to the portable phone system and a surveillance signal in respective fixed relay stations transmitted to the fixed central station using the uplink line. This system has achieved an economic system constitution avoiding a beat noise caused by multiplexing of optical signals in uplink signals. By the system, radio paging communications from the base station of mobile communications to a radio paging receiver in a dead spot has become possible, and also the function of surveillance of fixed relay stations by the fixed central station can be simultaneously achieved. 
     First, as an exemplary constitution of the third optical conversion relay amplification system (the third system) of the present invention, an exemplary constitution by applying the first system is described with reference to FIG.  3 . The FIG. 3 is a block diagram showing an example of constitution of the third optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG. 1 are described with same symbols. 
     The radio paging (i. e., a pager or a pocket bell) system has paging function alone, and therefore, only a downlink signal exists as primary radio communications signal. However, the FIG. 3 is an example having a function of an uplink signal to send signals such as a system surveillance signal and emergency reporting signal, etc. from respective fixed relay stations  2 — 2  to higher rank systems (the fixed central station  1 - 3 .) 
     The third optical conversion relay amplification system (the third system) related to the third mode for carrying out the present invention has an outlined constitution, same as that of the first system as shown in the FIG. 3, composed of the base station  5  of mobile communications, the fixed central station  1 - 3 , the downlink optical fiber line  4 A and the uplink optical fiber line  4 B, one or more the fixed relay stations  2 - 1 A and  2 - 1 B linked by cascade connection in intermediate position of these lines  4 A and  4 B, and radio paging receivers  8 A and  8 B replaced to mobile phones as mobile apparatus. 
     However, the constitution of the fixed central station  1 - 3  and the fixed relay stations  2 - 2 A and  2 - 2 B of the third system somewhat differs from that of the first system. 
     The fixed central station  1 - 3  of the third system is composed of an antenna  11  to receive a radio signal, an amplifier  13  to amplify received radio signal, an electric/optical converter  14  (E/O in the FIG. 3) to convert amplified radio signal (an electric signal) to an optical signal to send to the downlink optical fiber line  4 A, an optical/electric converter  16  (O/E in the FIG. 3) to convert the optical signal received from the uplink optical fiber line  4 B to an electric signal, and an amplifier  15  to amplify the converted electric signal, as same components as those of the first system. In addition, the third system is characterized by equipping a demodulator for surveillance signal (DEM in FIG. 3)  18 ′ demodulating an uplink high frequency electric signal to receive a surveillance signal and a surveillance signal processing unit  19  to process the surveillance signal demodulated. 
     The amplifier  13 , the electric/optical converter  14 , the optical/electric converter  16 , and the amplified  15  in the fixed central station  1 - 3  of the third system are quite same as those of the first system and no description is given herewith. 
     The antenna  11 ′ is an antenna for exclusive receiving use to receive a radio signal from the base station  5  of mobile communications. 
     The demodulator for surveillance signal  18 ′ is a demodulator to demodulate a high frequency electric signal converted from an uplink optical signal, that is transmitted after conversion from a surveillance signal sent from the fixed relay stations  2 - 2 A, B, . . . n., to extract finally the surveillance signal demodulated. 
     The surveillance signal processing unit  19  processes the demodulated signal as a surveillance signal; the specific processing entity of the surveillance signal processing unit  19  is not restricted in the present invention. 
     Next, the fixed relay stations  2 — 2  of the third system of the present invention is explained. Respective fixed relay stations  2 - 2 A, B, . . . n have same components and FIG. 3 shows a detail of the internal structure of the fixed relay stations  2 - 2 A only to explain herewith. 
     The fixed relay stations  2 - 2 A of the third system is composed of an optical branching device  21 A, an optical multiplexer  22 A, an optical/electric converter  23  (O/E in the FIG.  3 ), an amplifier  24 , a power distributer  25 , a downlink band path filter  26 , an amplifier  27 , a relaying uplink band path filter  28 , an amplifier  29 , an antenna  35 ′A, an amplifier  32 , a power multiplexer  33 , and the electric/optical converter  34  (E/O in the FIG.  3 ;), as same constitution as that of the fixed relay station  2 - 1 A of the first system; the third system is characterized by the modulator  36  (MOD in FIG. 3) for a surveillance signal and the surveillance controlling unit  37 . 
     Where, the surveillance controlling unit  37  corresponds to the first surveillance controlling unit in claims. 
     The optical branching device  21 A, the optical multiplexer  22 A, the optical/electric converter  23 , the amplifier  24 , the power distributor  25 , the downlink band pass filter  26 , the amplifier  27 , the relaying uplink band pass filter  28 , the amplifier  29 , the amplifier  32 , the power multiplexer  33 , and the electric/optical converter  34  in the fixed relay stations  2 — 2  of the third system are the same as those of the first system, and no description is given herewith. 
     The antenna  35 ′ is an antenna for exclusive receiving use to receive a radio signal from the radio paging receiver  8 A. 
     The surveillance controlling unit  37  monitors respective units inside the fixed relay station  2 — 2 , receives a signal indicating the situation of respective units, prepares a surveillance signal to output; the specific prepared contents are not restricted in the present invention. 
     The modulator  36  for a surveillance signal is a modulator modulating the surveillance signal to a high frequency signal to transmit the surveillance signal as an uplink optical signal. 
     Next, the action of the third system of the present invention is described with reference to FIG.  3 . However, the actions of the third system related to the downlink line from the base station  5  of mobile communications with radio paging receiver  8  are quite same as those of the first system, and no description is given herewith. 
     In the uplink line in the third system of the present invention, a surveillance signal is prepared by monitoring respective units of the fixed relay station  2 - 2 A at the surveillance controlling unit  37 , modulated to a high frequency signal by the modulator  36  for a surveillance signal, amplified to an appropriate level by an amplifier  32  if necessary, and subjected to power multiplex with a high frequency signal—outputted from the amplifier  29 —of the surveillance signal from a lower rank fixed relay station  2 - 2 B in the power multiplexer  33 ; the multiplexed output is modulated to an analog optical signal by the electric/optical converter  34  to send out to the uplink optical fiber line  4 B. 
     In the fixed central station  1 - 3 , an uplink analog optical signal from the uplink optical fiber line  4 B is demodulated to a high frequency signal by the optical/electric converter  16  and amplified to an appropriate level by an amplifier  15  if necessary; the demodulator  18 ′ for surveillance signal demodulate a surveillance signal and the surveillance signal processing unit  19  processes a necessary monitoring. 
     Changing a modulation frequency of the surveillance signal of respective fixed relay stations  2 - 2 A,  2 - 2 B, . . . n allows to know the situation of an optional fixed relay station by changing the tuned frequency of the demodulator  18 ′ for surveillance signal of the fixed central station  1 - 3 . 
     Changing a modulation frequency of the surveillance signal of respective fixed relay stations  2 - 2 A,  2 - 2 B, . . . n allows simultaneous monitoring the situation of all the fixed relay stations, if the fixed central station  1 - 3  has a plurality of the demodulator  18 ′ for surveillance signal tuned to a modulated frequency of the surveillance signal of respective fixed relay stations. 
     Using the time division multiplexing system allows to monitor the situation of all the fixed relay stations, even if the modulated frequency of the surveillance signal of respective fixed relay stations are identical and the demodulator  18 ′ for surveillance signal of the fixed central station  1 - 3  is only one set. 
     In this case, a direct transmission is also possible by using no modulator  36  for a surveillance signal of the fixed relay stations  2 — 2  to keep a base band. 
     Next, the fourth mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the fourth mode for carrying out the present invention relates to claim  4  and claim  10 . 
     The fourth optical conversion relay amplification system related to the fourth mode for carrying out the present invention is another applied example by combination of the second system with the third system aforementioned, has a constitution with a direct link of the fixed central station to a higher rank network (public network), and outputs a signal received from the public network to the uplink optical fiber line by modulation and following conversion to an optical signal, in the fixed central station; this system has achieved an economic system constitution avoiding a beat noise caused by multiplexing of optical signals in uplink signals; by the system, radio paging communications from the higher rank network to a radio paging receiver in a dead spot has become possible, and also the function of surveillance of the fixed relay stations by the fixed central station can be simultaneously achieved. 
     First, as an exemplary constitution of the fourth optical conversion relay amplification system (the fourth system) of the present invention, an exemplary constitution by applying the second and third systems is described with reference to FIG.  4 . The FIG. 4 is a block diagram showing an example of constitution of the fourth optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG.  2  and FIG. 3 are described with same symbols. 
     In the fourth optical conversion relay amplification system (the fourth system) of the present invention, the constitution and action of the fixed relay station  2 — 2  are quite same as those of said third system, and the constitution of the fixed central station  1 - 4  somewhat differs from that of the third system. 
     The fixed central station  1 - 4  of the fourth system is composed of an amplifier  13  amplifying a radio signal received, an electric/optical converter  14  (E/O in the FIG. 4) to convert an amplified radio signal (an electric signal) to an optical signal to send to the downlink optical fiber line  4 A, an optical/electric converter  16  (O/E in the FIG. 4) to convert the optical signal received from the uplink optical fiber line  4 B to an electric signal, an amplifier  15  to amplify the converted electric signal, a demodulator for surveillance signal (DEM in FIG. 4)  18 ′ demodulating an uplink high frequency electric signal to receive a surveillance signal, and a surveillance signal processing unit  19  to process the demodulated signal as the surveillance signal, as the same parts as those of the third system; the fourth system is characterized by equipping a high frequency modulator (MOD in FIG. 4)  17  modulating the downlink signal from the higher rank network  7  to a high frequency signal. 
     The downlink line receives a signal from the higher rank network  7 , modulates to a high frequency signal by the high frequency modulator  17  of the fixed central station  1 - 4 , and finally works like the third system. 
     The actions of the uplink line are quite same as those of the third system. 
     As described in the third system, changing a modulation frequency of the surveillance signal of respective fixed relay stations allows to know the situation of an optional fixed relay station by changing the tuned frequency of the demodulator for surveillance signal  18 ′ of the fixed central station  1 - 4 , and simultaneous monitoring of the situation of all the fixed relay stations is possible by equipping a plurality of the demodulator  18 ′ for surveillance signal tuned to a modulated frequency of the surveillance signal of respective fixed relay stations. 
     Besides, it is possible the surveillance signal of respective fixed relay stations is sent after modulating with the same modulation frequency by the time division multiplexing system and monitored by one set of the demodulator  18 ′ for surveillance signal in the fixed central station  1 - 4 . In this case, a direct transmission is also possible by using no modulator  36  for a surveillance signal of the fixed relay stations  2 — 2  to keep a base band. 
     The systems  3  and  4  of the present invention have achieved a simple, economic system constitution avoiding a beat noise and making radio communications with a radio paging receiver  8  existing in a dead spot possible; also the surveillance of respective fixed relay stations  2 — 2  can be simultaneously achieved by transmitting a surveillance signal of respective fixed relay stations  2 — 2  to the fixed central station  1 - 3  in the uplink line using the downlink line for the transmission of paging signal of the radio paging system. 
     Next, the fifth mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the fifth mode for carrying out the present invention relates to claim  5  and claim  11 . 
     The fifth optical conversion relay amplification system related to the fifth mode for carrying out the present invention is an applied example by combination of the first system with the third system aforementioned and has an additional surveillance signal transmission system to the first system. In the fixed central station, a surveillance controlling signal for surveillance is multiplexed with downlink radio signal, converted to an optical signal for optical transmission, and also converted to an electric signal by the fixed relay station to extract the surveillance controlling signal, respective parts are monitored, the surveillance signal as a monitoring result is multiplexed with an uplink signal and converted to an optical signal for optical transmission; in the fixed central station, the surveillance signal is extracted from a signal converted to an electric signal to process for surveillance. Thus, this system has achieved an economic system constitution avoiding a beat noise caused by multiplexing of optical signals in uplink signals. By the system, communications of a portable apparatus in a dead spot have become possible, and also the function of surveillance of fixed relay stations by the fixed central station can be simultaneously achieved. 
     First, as an exemplary constitution of the fifth optical conversion relay amplification system (the fifth system) of the present invention, an exemplary constitution by applying to the first systems is described with reference to FIG.  5 . The FIG. 5 is a block diagram showing an example of constitution of the fifth optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG.  1  and FIG. 3 are described with same symbols. 
     The internal structure of the fixed central station  1  and the fixed relay station  2  of the fifth system of the present invention somewhat differs from that of the first system explained with reference to the FIG.  1 . 
     The fixed central station  1 - 5  of the fifth system is composed of an antenna  11 , an antenna distributor  12 , an amplifier  13 , an electric/optical converter  14 , optical/electric converter  16 , and an amplifier  15 , as the same components as those of the fixed central station of the first system. 
     In addition to said constitution, the fifth system is characterized by equipping a surveillance control indication unit  19 ′ to prepare a control signal (surveillance controlling signal) for monitoring the fixed relay station, a modulator (MOD in FIG. 5)  17 ′ for modulating a surveillance control signal by high frequency modulation of the surveillance control signal, a power multiplexer  20 ′ to multiplex the modulated surveillance control signal with a radio signal from the base station  5  for mobile terminals, a power distributor  20  to distribute a signal generated by conversion from an optical signal of the uplink line to an electrical signal to amplify, an uplink band pass filter  10  for transmission to extract an uplink signal—toward the base station for mobile terminals—from the distributed signal, a band pass filter  10 ′ for a surveillance signal to extract the surveillance signal from the distributed signal, a demodulator  18 ′ for surveillance signal (DEM in FIG. 5) demodulating a surveillance signal extracted, and a surveillance signal processing unit  19  to process the demodulated signal as a surveillance signal. 
     Where, the power multiplexer  20 ′ as the characteristic part of the fifth system corresponds to the second power multiplexer of claims and the power distributor  20  corresponds to the second power distributor of claims. 
     Although the surveillance control indication unit  19 ′ and the surveillance signal process unit  19  are described as separate components in the FIG. 5, the functions of the surveillance control indication unit  19 ′ and the functions of the surveillance signal process unit  19  can be composed as a single circuit. 
     Next, the fixed relay station  2 - 3  in the fifth system has the following same components as those of the fixed relay stations  2 - 1  of the first system: an optical branching device  21 A, an optical multiplexer  22 A, an optical/electric converter  23 , an amplifier  24 , a power distributor  251 , a downlink band pass filter  26 , an amplifier  27 , a relaying link band pass filter  28 , an amplifier  29 , an antenna distributor,  30 , an antenna  35 A, a receiving uplink band pass filter  31 , an amplifier  32 , a power multiplexer  33 ′, and an electric/optical converter  34 . 
     The fifth system differs from the first system in the point that the power distributer  25 ′ has a single input and three outputs and that the power multiplexer  33 ′ has three inputs and a single output. 
     In addition to the said constitution, the fifth system is characterized by a band pass filter  39  for a surveillance controlling signal to extract a surveillance controlling signal, a demodulator for surveillance controlling signal  40  (DEM  40  in the FIG. 5) to demodulate a surveillance controlling signal, a surveillance controlling unit  37 ′ monitors and controls respective parts of the fixed relay station according to the surveillance controlling signal and preparing a surveillance signal from a signal indicating the situation of respective units, a modulator (MOD in FIG. 5)  36  for a surveillance signal modulating the surveillance signal to a high frequency signal, and an amplifier  38  amplifying a modulated surveillance signal to an appropriate level. 
     Where, The surveillance controlling unit  37 ′ corresponds to the second surveillance controlling unit of claims. 
     Next, the action of the fifth system of the present invention is described with reference to FIG.  5 . 
     In the fifth system of the present invention, the downlink signal sent from the base station of mobile communications (not shown) is received by an antenna  11  of the fixed central station  1 - 5 , inputted to the one of the power multiplexer  20 ′ via the antenna distributor; on the other hand, the surveillance controlling signal outputted from the surveillance control indication unit  19 ′ is modulated by the modulator  17 ′ for a surveillance control signal to input to the other of the power multiplexer  20 ′. 
     Subsequently, the received signal and the surveillance controlling signal are subjected to power multiplexing by the power multiplexer  20 ′, amplified to an appropriate level by the amplifier  13 , and subjected to the analog optical modulation by the electric/optical converter  14  to become an optical signal to be sent to the downlink optical fiber line  4 A. 
     Next, the optical signal branches in the optical branching device  21 A of the first fixed relay station  2 - 3 A, said branched optical signal and an uplink optical signal from the second fixed relay station (not shown) are multiplexed by the optical multiplexer  22 A, converted to an electric signal by the optical/electric converter  23 , amplified by the amplifier  24  if necessary, and finally distributed in three signals by the power distributer  25 . 
     Only the frequency of the surveillance controlling signal is extracted from the one of three distributed signals by the band pass filter  39  for a surveillance controlling signal, the surveillance controlling signal is demodulated in the demodulator  40  for a surveillance controlling signal, outputted to the surveillance controlling unit  37 ′, and used for the surveillance control in the fixed relay station. 
     The downlink radio signal from the base station of wireless communications and uplink radio signal from the second fixed relay station—the remain of three divided signals by the power distributer  25 —are processed like the first system. 
     The situation of respective parts in the fixed relay station  2 - 3  is monitored by the control of the surveillance controlling unit  37 ′, the surveillance signal to send to the fixed central station  1 - 5  is prepared, the surveillance signal is modulated to a high frequency signal by the modulator  36  for a surveillance signal, and amplified by the amplifier  38  as one input to the power multiplexer  33 ′. 
     On the other hand, as the action as that if the first system, the uplink radio signal from a portable apparatus (not shown) and the uplink radio signal from the second fixed relay station become remained two signals of the power multiplexer  33 ′ to subject the three signals to power multiplexing, the multiplexed output is modulated to an analog optical signal by the electric/optical converter  34  to send out to the uplink optical fiber line  4 B. 
     In the fixed central station  1 - 5 , the uplink analog optical signal from the uplink optical fiber line  4 B is demodulated to a high frequency signal by the optical/electric converter  16 , amplified to an appropriate level by the amplifier  15  if necessary followed by division into two signals by the power distributor  20 , only uplink signal to the base station of mobile communications is extracted from the one by the uplink band pass filter  10  for transmission, and radiated from the antenna  11  to space via the antenna distributor  12  to transmit to the base station (not shown) of mobile communications. 
     Besides, only a surveillance signal is extracted from the other of divided two signals in the power distributor  20  by the band pass filter for surveillance signal  10 ′, the surveillance signal is demodulated by the demodulator  18 ′ for surveillance signal, the surveillance signal processing unit  19  processes a necessary surveillance. 
     Next, the sixth mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the sixth mode for carrying out the present invention relates to claim  6  and claim  12 . 
     The sixth optical conversion relay amplification system related to the sixth mode for carrying out the present invention is an applied example by combination of the second system with the fifth system aforementioned; the fixed central station is directly linked with the higher rank network (the public network). A surveillance controlling signal is multiplexed with a high frequency signal generated by modulation of a signal received from the public network in the fixed central station to convert to an optical signal for outputting to the uplink optical fiber line. Thus, this system has achieved an economic system constitution avoiding a beat noise caused by multiplexing of optical signals in uplink signals. By the system, wireless communications of a portable phone in a dead spot with a higher rank network has become possible, and also the function of surveillance of fixed relay stations by the fixed central station can be simultaneously achieved. 
     First, as an exemplary constitution of the sixth optical conversion relay amplification system (the sixth system) of the present invention, an exemplary constitution by applying the second and fifth systems is described with reference to FIG.  6 . The FIG. 6 is a block diagram showing an example of constitution of the sixth optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG.  2  and FIG. 5 are described with same symbols. The internal details of the fixed relay stations  2 - 3  are not given with any figure, because of quite same constitution thereof as that of said fifth system. 
     In the sixth optical conversion relay amplification system (the sixth system) of the present invention, the constitution and action of the fixed relay station  2 - 3  are quite same as those of said fifth system, and the constitution of the fixed central station  1 - 6  somewhat differs from that of the third system. 
     The fixed central station  1 - 6  of the sixth system is composed of an electric/optical converter  14 , optical/electric converter  16 , and an amplifier  15 , as the same components as those of the fifth system. 
     The fixed central station of the sixth system is, as same components as that of the fifth system, composed of a surveillance control indication unit  19 ′ to prepare a surveillance control signal, a modulator (MOD in FIG. 6)  17 ′ for a surveillance controlling signal for high frequency modulation of the surveillance controlling signal, a power multiplexer  20 ′ multiplexing the modulated surveillance control signal with a signal from the unlink network  7 , an amplifier  13  amplifying a multiplexed signal, 
     an electric/optical converter  14  converting the multiplexed signal to an optical signal, 
     an optical/electric converter  16  converting the optical signal received from the uplink line to an electric signal, 
     an amplifier  15  amplifying an electric signal, 
     a power distributor  20  distributing an amplified signal, 
     an uplink band pass filter  10  for transmission to extract an uplink signal from the distributed signal toward a higher rank network, 
     a band pass filter  10 ′ for a surveillance signal to extract the surveillance signal from the distributed signal, 
     a demodulator  18 ′ (DEM in FIG. 6) for surveillance signal demodulating a surveillance signal extracted, 
     a surveillance signal processing unit  19  processing the demodulated signal as a surveillance signal. 
     In addition, the sixth system is characterized by equipping a high frequency modulator  17  (MOD in FIG. 6) modulating the downlink signal from the higher rank network  7  to a high frequency signal, and 
     a high frequency demodulator  18  (DEM in FIG. 6) demodulating a high frequency electric signal of the uplink signal toward the higher rank network  7 . 
     This means that the downlink line receives a signal from the higher rank network  7  and modulates to a high frequency signal by the high frequency modulator  17  of the fixed central station  1 - 6  to work as same as the fifth system. 
     On the other hand, in the work of the uplink line, a high frequency signal distributed by the power distributer  20  and restricted a band by the uplink band path filter  10  for transmission is demodulated by the high frequency demodulator  18  to send to the higher rank network  7 , as same as the third system. 
     For reference, in said mode for carrying out the present invention for the fifth and sixth systems, it has been exemplified that a control signal for surveillance is superimposed to the downlink line and a surveillance signal is superimposed to the uplink line. However, the constitution only composed of the followings is possible: the controlled contents of surveillance are fixed and a surveillance signal is superimposed to the uplink line, as same as the third and fourth systems. 
     Besides, as described for the third and fourth systems, changing a modulation frequency of the surveillance signal of respective fixed relay stations allows to know the situation of an optional fixed relay station by changing both the passed frequency of the band pass filter  10 ′ for a surveillance signal and the tuned frequency of the demodulator  18 ′ for surveillance signal in the fixed central station  1 - 5  and  1 - 6 , and simultaneous monitoring of the situation of all the fixed relay stations is possible by equipping a plurality of the band pass filter  10 ′ for a surveillance signal tuned to a modulated frequency of the surveillance signal of respective fixed relay stations and the demodulator  18 ′ for surveillance signal. 
     Besides, it is possible that the surveillance signal of respective fixed relay stations is sent after modulating with the same modulation frequency by the time division multiplexing system and monitored by one set of the demodulator  18 ′ for surveillance signal in the fixed central station  1 - 5  and  1 - 6 . In this case, a direct transmission is also possible by using no modulator  36  for a surveillance signal of the fixed relay stations  2 - 3  to keep a base band. 
     In the fifth and sixth systems of the present invention, the surveillance from the fixed central station  1 - 6  to the fixed relay station  2 - 3  is controlled by multiplexing the surveillance controlling signal with the downlink signal to transmit optically in the downlink line; a simple, economic system constitution is accomplished by avoiding a beat noise and making radio communications with a portable apparatus existing in a dead spot possible and the surveillance of respective fixed relay stations  2 - 3  can be simultaneously achieved by multiplexing the surveillance signal of respective fixed relay stations  2 - 3  with an uplink signal in the uplink line to transmit optically the surveillance signal to the fixed central station  1 - 6 . 
     Next, the seventh mode for carrying out the present invention is herewith described with reference to drawings. The optical conversion relay amplification system related to the seventh mode for carrying out the present invention relates to claim  13 . 
     The seventh optical conversion relay amplification system related to the seventh mode for carrying out the present invention is an applied example of the first to the sixth systems aforementioned, having a constitution using a leaky coaxial cable replaced to an antenna in respective fixed relay stations, and having possible communications of portable apparatus (a portable phone and a radio paging receiver) existing in a linearly extended dead spot with the base station of mobile communications and the public network, and also a possible economic system constitution avoiding a beat noise caused by multiplexing of optical signals in uplink signals. 
     As an exemplary constitution of the seventh optical conversion relay amplification system (the seventh system) of the present invention, an exemplary embodiment by applying the first system is described with reference to FIG.  7 . The FIG. 7 is a block diagram showing an example of constitution of the seventh optical conversion relay amplification system related to the present invention. Parts having same composition as those of the FIG. 1 are described with same symbols. 
     The outlined constitution of the seventh optical conversion relay amplification system (the seventh system) of the present invention and the internal details of the fixed central station  1 — 1  are quite same as those of the first system; however, somewhat differs from the first system in the internal constitution of the fixed relay stations  2 - 4 A,  2 - 4 B, . . . n. 
     Specifically, the seventh system of the present invention differs from the first system in equipping leaky coaxial cables  6 A,  6 B, . . . n replaced to the antenna  35  in the fixed relay stations  2 - 4 A,  2 - 4 B, . . . n; others are quite same. 
     Also for the second to the sixth systems, the seventh system can be made by equipping leaky coaxial cables  6 A,  6 B, . . . n replaced to the antenna  35  or antenna  35 ′. 
     The seventh system of the present invention, as same as the first to the sixth systems, has a possible economic system constitution avoiding a beat noise, particularly, a possible communication of a portable apparatus and a radio paging receiver existing in a service area of a linearly extended dead spot with the base station of mobile communications and the higher rank network. 
     Also in the mode for carrying out the present invention, the structure of optical transmission line of the downlink line has been explained with reference to the multibranching type to branch into 1:2 around the fixed relay station. The range to which the present invention is applied is not restricted to this type, but covers a star type transmission line or a combination of the star type with multibranching type, etc. in which the output of the electric/optical converter  6  of the fixed central station is distributed by a star coupler. 
     The optical conversion relay amplification system of the mode for carrying out the present invention makes communications between a portable phone, etc. located in a dead spot and the base station of mobile communications or the higher rank network possible by achieving the economical system constitution in which a beat noise caused by optical signal multiplex in uplink signals is avoided on the basis that a downlink optical signal is branched by the fixed relay station to subject to optical multiplexing with the uplink signal transmitted from a lower rank fixed relay station via uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink signal component contained in said electric signal is transmitted from an antenna, etc. to a portable apparatus, etc., an uplink signal component contained in said electric signal is subjected to power multiplex with an uplink signal transmitted from the portable apparatus, etc. followed by conversion to an optical signal to transmit via the uplink optical fiber line, and an additional conversion to an electric signal to send as an uplink radio signal by the fixed central station. 
     The present invention is an optical conversion relay amplification system that makes possible the relay of communications between a portable phone located in a dead spot and a base station by achieving the economical constitution in which a beat noise in uplink signals is avoided on the basis that the fixed central station converts a radio signal received from the base station to an optical signal to output to the downlink optical fiber line and the fixed relay station processes branching of a downlink optical signal from the downlink optical fiber line to multiplex with the uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signal is transmitted to a portable phone by wireless system, and also an uplink electric signal contained in the converted electric signal is multiplexed with a radio signal received from the portable phone, the multiplexed electric signal is converted to an optical signal to output to the uplink optical fiber line, and the fixed central station converts the optical signal inputted from the uplink optical fiber line to a high frequency electric signal to send to the base station. 
     According to the optical conversion relay amplification system of the present invention, a signal received from the public network is modulated to a high frequency, converted to an optical signal, and outputted to the downlink optical fiber line in the fixed central station, and the downlink signal in branches from the downlink optical fiber line to multiplex with the uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, and a downlink electric signal contained in the converted electric signal is transmitted to a portable phone by wireless system, and also an uplink electric signal contained in the converted electric signal is multiplexed with a radio signal received from the portable phone, the multiplexed electric signal is converted to an optical signal to output to the uplink optical fiber line in the fixed relay station, and the fixed central station converts the optical signal inputted from the uplink optical fiber line to a high frequency electric signal, demodulate, and send to the public network. The relay of communications through the system between portable phone in dead spots and the public network becomes possible by avoiding a beat noise in the uplink line and accomplishing an economic system constitution. 
     Also according to the optical conversion relay amplification system of the present invention, the fixed central station converts a radio signal received from the base station to an optical signal to output to the downlink optical fiber line and the fixed relay station divides a downlink optical signal from the downlink optical fiber line to multiplex with the uplink optical fiber line, converts the multiplexed optical signal to an electric signal, and transmits the downlink electric signal contained in the converted electric signals to a paging receiver by wireless system, and also multiplex the uplink electric signal contained in the converted electric signals with the surveillance signal, and converts the multiplexed electric signals to optical signals to output to the uplink optical fiber line, the fixed central station converts an optical signal inputted from the uplink optical fiber line to a high frequency electric signal to receive a surveillance signal. The system provides a possible economic system constitution avoiding a beat noise in the uplink line, a possible paging communication of the base station with a radio paging receiver existing a dead spot, and a possible transmission of a surveillance signal in the fixed relay station to the fixed central station by relaying. 
     Further according to the optical conversion relay amplification system of the present invention, a signal received from the public network is modulated to a high frequency, converted to an optical signal, and outputted to the downlink optical fiber line by the fixed central station, the downlink optical signal branches from the downlink optical fiber line to multiplex with the uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, a downlink electric signal contained in the converted electric signal is transmitted to a radio paging receiver by wireless system, and also an uplink electric signal contained in the converted electric signal is multiplexed with a surveillance signal, the multiplexed electric signal is converted to an optical signal to output to the uplink optical fiber line in the fixed relay station, and the fixed central station converts the optical signal inputted from the uplink optical fiber line to a high frequency electric signal to receive the surveillance signal. By the system, the relay paging from the public network to a radio paging receiver in dead spots becomes possible and the relay transmission of surveillance signal in the fixed relay station to the fixed central station also becomes possible, avoiding a beat noise in the uplink line and accomplishing an economic system constitution. 
     Furthermore according to the optical conversion relay amplification system of the present invention, the fixed central station multiplexes a surveillance controlling signal with a radio signal received from the base station to generate an electric signal, converts the multiplexed electric signal to an optical signal to output to the downlink optical fiber line; in fixed relay station, the downlink optical signal from the downlink optical fiber line branches to be multiplied with the uplink optical fiber line, the multiplexed optical signal is converted to an electric signal, the downlink electric signal contained in the converted electric signal is separated in a signal for a portable phone and a signal for surveillance control, the separated signal for a portable phone is sent to a portable phone by wireless system, the separated surveillance control signal is outputted to the surveillance controlling unit, and also an uplink electric signal contained in the converted electric signal, a radio signal received from the portable phone, and a surveillance signal from the surveillance controlling unit are multiplexed, the multiplexed electric signal is converted to an optical signal to send to the uplink optical fiber line; in the fixed central station, the optical signal inputted from the uplink optical fiber line is converted to a high frequency electric signal to separate a signal for the base station and a surveillance signal, the signal for the base station is sent to the base station, and the surveillance signal is received; thus, this system has achieved an economic system constitution avoiding a beat noise in uplink signals, the relay of communications of the base station with a portable apparatus in a dead spot becomes possible, communications of the surveillance controlling signal and the surveillance signal between the fixed central station and the fixed relay stations become possible. 
     Also furthermore according to the optical conversion relay amplification system of the present invention, the fixed central station multiplexes a surveillance control signal with an electric signal generated by modulation of a signal received from the public network to a high frequency signal in order to convert to an optical signal to output toward the downlink optical fiber line, the fixed relay station divides a downlink optical signal from the downlink optical fiber line to multiplex with the uplink optical fiber line, converts the multiplexed optical signal to an electric signal, and separates the downlink electric signal contained in the converted electric signals in a signal for a portable phone and a surveillance control signal, the separated signal for a portable phone is sent to the portable phone by wireless system, the separated surveillance control signal is outputted to the surveillance controlling unit, and also an uplink electric signal contained in the converted electric signal, a radio signal received from the portable phone, and a surveillance signal from the surveillance controlling unit are multiplexed, the multiplexed electric signal is converted to an optical signal to send to the uplink optical fiber line; in the fixed central station, the optical signal inputted from the uplink optical fiber line is converted to a high frequency electric signal to separate a signal for the public network and a surveillance signal, the signal for the public network is demodulated to send to the public network, and the surveillance signal is received; thus, this system has achieved an economic system constitution avoiding a beat noise in uplink line, the relay of communications of a portable apparatus in a dead spot with the public network becomes possible, the relay communications of the surveillance controlling signal and the surveillance signal between the fixed central stations and the fixed relay station becomes possible. 
     The present invention is said optical conversion relay amplification system employing a leaky coaxial cable as an antenna for the fixed relay station, allowing an economic system constitution avoiding a beat noise in the uplink line, and also allowing a relay communication of a portable phone or a radio paging receiver existing in a service area of a linearly extended dead spot with the base station of mobile communications and/or the higher rank network.