A multimode CDMA scheme with reduced intercell interference for LMDS networks

This paper investigates the application of code-division multiple access (CDMA) to local multipoint distribution services (LMDS) networks. Our analysis shows that while conventional CDMA is superior to time-division multiple access (TDMA) in terms of worst-case interference on the upstream channel, it leads to higher interference on the downstream channel. Next, based on the observation that strong interference occurs only for a small range of user locations, we introduce a multimode CDMA concept which assigns orthogonal spreading sequences whose number and length are a function of the user position with respect to the base station (BS). We show that in terms of worst-case signal-to-interference ratio (SIR), the proposed technique leads to a substantial improvement with respect to conventional CDMA and TDMA.