Low complexity space-time MMSE equalization in WCDMA systems

In this paper we propose a low complexity frequency-domain method for finding the minimum mean square error (MMSE) equalizer. Special properties of circulant matrices are exploited in the method. Simulations show that only a minor performance loss is experienced compared to time-domain processing. We also compare joint space-time processing to decoupled equalization and spatial combining. The complexity reduction due to the decoupled processing is evident, while the performance loss remains small. Consequently, the proposed low complexity frequency-domain method can also be used with multiple receive antennas with tolerable performance loss compared to joint space time equalization. Additionally, different MMSE equalizer definitions for multiple receive antennas are considered, and their performance is studied in simulation using estimated channels. Simulations are carried out in high data rate WCDMA system model.