An Adaptive RLS MIMO Equalizer Algorithm for HSDPA

Multiple transmit and receive antennas, more generally known as multiple-input multiple-output (MIMO) systems, are used in an extension to the third generation partnership program (3GPP) standard called high speed downlink packet access (HSDPA) to achieve high throughput. The data rates and capacity demands of HSDPA require MIMO adaptive equalizers, which attempt to undo channel coloration and cross-coupling using the pilot signals defined in the 3GPP standard. However, the convergence of LMS-type algorithms is slow, thereby degrading dynamic performance. Surprisingly, the conventional RLS algorithm does not improve the convergence in this setting. However, we show that an RLS algorithm using an M-chip output correlator provides a dramatic improvement in convergence speed while still being implementable within affordable computational constraints.