Performance of adaptive chip equalization for the WCDMA downlink in fast changing environments

Cellular WCDMA systems are characterized by multiple access interference (MAI) and multipath interference (MPI). Thus, optimal receivers deploy the signal and channel parameters of all active users for detection of the desired data stream. For the WCDMA downlink, we study receiver concepts that reduce interference without knowledge of the multiuser parameters. A promising concept is the principle of channel equalization at chip-level that is trying to compensate for the channel. Four receiver types are investigated, the LMMSE (linear minimum mean squared error) approach and three adaptive approaches. The adaptive receivers are based on the Griffith algorithm and adaptive chip separation. A receiver deploying a modification of the RLS (recursive least squares) algorithm is introduced. Adaptation errors are studied for the example of the Griffith algorithm. To evaluate the performance of the four receivers, they are compared to the conventional RAKE receiver for a fast changing fading channel under low spreading factor conditions.