Distributed MIMO-CDMA system: effects of spreading sequences on sum capacity

Distributed multiple-input multiple-output (MIMO) system is a new architecture for a wireless communication system with distributed multiple antennas. In this paper, the uplink sum capacity of distributed MIMO system with wideband code-division multiple-access (CDMA) technology under multipath fading channels is studied carefully. Single-user decoders with different assumptions of interference knowledge are used in the receivers. The spreading sequences of the CDMA system are assumed to employ loosely synchronized (LS) spreading sequences and random spreading sequences, respectively. LS codes exhibit a so-called interference free window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS sequences have the promise of mitigating the effects of inter symbol interference (ISI) and multiple access interference (MAI) in multipath fading channels. Simulation results show that due to the perfect correlation properties of LS spreading sequences, the uplink sum capacity of the distributed MIMO-CDMA system using LS sequences can substantially outperform that of the system using random spreading sequences.