In recent years, studies are being actively conducted on technical approaches to realize a high transmission rate using a high frequency radio band in a cellular mobile communication system represented by, for example, a cellular phone set. When a high frequency radio band is used, attenuation due to a transmission distance increases, compared with the case of using a low frequency radio band so that the area where the realization of a high transmission rate can be expected is limited to a relatively short distance area. Therefore, more base station apparatuses need to be installed in the system. The cost is commensurate with installing base stations and there is a strong demand for realization of a high transmission rate in restraining the increase in the number of base station apparatuses.
For example, Non-Patent Document 1 gives two types of relay systems as a technique responding to this demand. Here, the relay system means a communication system to relay a transmission signal. Non-Patent Document 1 evaluates a decode and forward system whereby a transmission signal is decoded once at a relay station apparatus that executes relaying and an amplify and forward system whereby a transmission signal is not decoded at a relay station apparatus from the standpoint of an error rate characteristic. It is proven that the decode and forward system has a gain of 2 dB over the amplify and forward system in a flat Rayleigh fading model.    Non-Patent Document 1: “Cooperative Relaying Technique with Space Time Block Code for Multihop Communications among Single Antenna Terminals”, RCS2003-365