Low-Cost Approximate LMMSE Equalizer Based on Krylov Subspace Methods for HSDPA

Access (HSDPA) sub-system of UMTS suffers significantly from multiple access interference in the wireless channel. A linear minimum mean square error (LMMSE) equalizer at the receiver achieves higher throughput than a conventional RAKE receiver, at the cost of higher complexity. We introduce an iterative algorithm based on Krylov subspace projections, approximating the LMMSE equalizer with negligible loss of performance for the receiver. Slow variations of the channel can be exploited to allow further acceleration of the algorithm. Computational complexity as well as storage requirements are strongly reduced. Index Terms—UMTS, HSDPA, LMMSE, Krylov subspace methods, low complexity equalizer. I