OFDM-based SDMA networks: signal model under imperfect synchronization and channel state information

Abstract

Space-Division Multiple Access (SDMA) is envisioned as a key component in future multiuser wireless networks. While the capacity limits of such networks are becoming well understood, there is still little knowledge about the performance degradation that may result from poor synchronization and imperfect channel knowledge. We focus on this problem and derive a signal model for OFDM-based SDMA networks whose transmissions are impaired by carrier frequency offset and sampling frequency offset. Applying the result to the analysis of the SDMA uplink, we find that using a downlink beacon for synchronizing the mobiles’ uplink transmissions is virtually unavoidable. Our analysis of the downlink also includes the effect of imperfect channel state information. We find that poor knowledge of the channel state severely limits the maximum number of users that can be served, and is more important in this respect than fine synchronization.