A novel segment-level MMSE-MUD design for rapidly time-varying channel conditions in TD-SCDMA down-link channel

This paper proposes a novel segment-level MMSE-MUD for TD-SCDMA systems, to improve the receiver performance for rapidly time-varying channels due to high mobile speeds or non-ideal automatic frequency control at the receiver. The algorithm suggests how to acquire multiple channel estimates for each timeslot by taking into account the special frame structure in TD-SCDMA. The new algorithm can be applied in a TD-SCDMA system without any changes in the standard specifications. Simulations show that the novel segment-level MMSE-MUD outperforms the traditional MMSE-MUD, based on uniform channel estimation, significantly for rapidly time-varying channels. By studying the un-coded bit error performance in a TD-SCDMA downlink system it is possible to conclude that three channel estimates per timeslot is sufficient for mobile speeds up to 120 km/h (or a frequency offset up to 200 Hz). Furthermore, the simulations show that a 1.2 dB gain can be obtained in the case of a single-user, and 3.5 dB gain in an 8-user case over a typical urban channel at 120 km/h.