ISM band has been approved for spread spectrum communication in radio LAN in Japan since December 1992. This frequency band extends from 2.474 GHz to 2.5 GHz with 26 MHz bandwide. In an indoor environment, the maximum observed delay spread is 100-200 ns in a room, it is too short to generate a selective fading, thus flat fading conditions are often observed. Serve as an alleviation, we propose a new system of multi-antenna in base station (BS) and single antenna in mobile station (MS). In this system, MS should have a simple structure for its small size and energy-saving.

Indoor radio communications is an important component of the emerging personal communication systems service. It is also the basis for wireless local area networks. The indoor radio channel is characterized by fading multipaths as well as noise. Direct sequence spread spectrum (DSSS), with its inherent resistance to multipath interference is an attractive technique for this environment. To allow multiple users within the limited bandwidths available, code division multiple access is needed. This paper analyzes the performance of a DSSS scheme employing random orthogonal codes over fading multipath indoor radio channels using actual channel measurements from five different locations. A RAKE receiver is used to study the effects of power control, code length and receiver structure. The average probability of error as a function of signal-to-noise ratio or as a function of the number of simultaneous transmitters is used as the performance criteria.