1. Field of the Invention
The present invention relates to a radio communication system and a repeater, more particularly, to a radio communication system, which repeats a signal transmitted from a base station by a repeater that is multistage-connected by a leaky coaxial cable (LCX) and communicates with a mobile terminal.
2. Related Art
In the field of a train radio communication and a PHS (Personal Handy-Phone System) base station installed in metropolitan railway stations, a radio communication system using a leaky coaxial cable as antenna has been put into practical use. In such a leaky coaxial cable, a slit for leaking a radio wave is provided at an outer conductor of a coaxial cable.
The radio communication system using the leaky coaxial cable is advantageous in that only one transmitter can cover a long distance communication area and a stable communication can be realized even in an environment with a lot of metallic reflecting objects or obstacles. Furthermore, the radio communication system using the leaky coaxial cable is advantageous in that the communication area can be limited to a peripheral area of the leaky coaxial cable, so that the radio wave cannot be leaked to an unnecessary area, thereby realizing a high security.
FIG. 10 shows a conventional radio communication system using the leaky coaxial cable. Referring to FIG. 10, a signal line 104 from a base station 103 is connected to each pre-amplifier 102 to which a leaky coaxial cable 101 is connected, and a communication is carried out between the base station 103 and a mobile terminal 105 via the leaky coaxial cable 101.
FIG. 11 shows another conventional radio communication system using the leaky coaxial cable, in which a plurality of repeaters 111 are multistage-connected by leaky coaxial cables 101, and each of the repeaters 111 amplifies signal, thereby increasing a communication area. Referring to FIG. 11, the graph shows a relationship between a transmission distance of signals and an electric power (i.e. intensity of the signals), in which L6 indicates an intensity of signals transmitted from the base station 103 and propagated through the leaky coaxial cable 101, L7 indicates an intensity of received signals of a mobile terminal 105 located at a point distant from the leaky coaxial cable 101 with a predetermined distance, and L8 indicates a minimum receiver sensitivity of the mobile terminal 105.
In the structure shown in FIG. 10, it is necessary to transmit the signal to be transmitted from the base station 103 to each pre-amplifier 102 by another cable (a signal line 104) which is different from the leaky coaxial cable 101, so that two kinds of cables i.e. the leaky coaxial cable 101 functioning as an antenna and the signal line 104 are required.
On the other hand, in the structure shown in FIG. 11, the leaky coaxial cable 101 functions as both an antenna and a signal line, so that the number of components can be reduced. Therefore, it is possible to reduce the cost compared with the structure shown in FIG. 10.
Japanese Patent Laid-Open No. 2006-295433 (JP-A 2006-295433), Japanese Patent Laid-Open No. 11-186943 (JP-A 11-186943), and Japanese Patent Laid-Open No. 2004-328121 (JP-A 2004-328121) disclose examples of radio communication system using the leaky coaxial cable.