A Robust MMSE Equalizer for MIMO Enhanced HSDPA

In this contribution, we analyze the performance of MIMO enhanced high speed downlink packet access (HSDPA) for UMTS in realistic, frequency-selective propagation channels. At the receiver, an MMSE equalizer is implemented to restore the orthogonality of the UMTS spreading codes and to perform the MIMO detection. The matrix inversion, necessary for the MMSE equalization, is implemented in an iterative manner, requiring only mult-add operations. Since the algorithm is division-free, it is numerically stable, robust, and very well suited for fixed-point implementation. We show that initial convergence of the iterative algorithm can be achieved in only a few iterations. Moreover, we study the equalizer performance in terms of coded block error ratio for low and high code rates and find the proposed algorithm very suitable for approximating matrix inverses.