Adaptive Chip Level Equalization for HSDPA

We consider a chip level decision-directed NLMS equalization scheme which targets estimating the total transmitted base station chip sequence in a decision-directed manner and using it as the desired response for equalizer adaptation. For this purpose, we explicitly use only the knowledge of the user-assigned HSPDSCH codes in order to obtain reliable signal components by hard decisions. By exploiting the equivalence between the actual multirate transmission in the sense of containing multiple spreading factors and the multicode pseudo-transmission at the single HSDPA spreading level we use also the estimated pseudo-symbols of other codes via LMMSE weightings. In addition to its reasonable complexity and Max-SINR achieving performance in realistic HSDPA working regimes, the proposed scheme also has the advantage of not requiring the channel parameters. We evaluate its performance by extensive simulations vis-à-vis the Griffiths equalizer which requires channel parameters.