Adaptive MMSE receiver for multirate CDMA systems

We consider the adaptive receiver for multirate code division multiple access (CDMA) systems under a fading channel environment. The main difficulty that arises in the use of the adaptive receiver for multirate CDMA systems is that the adaptation should resume after the rate change. Hence, the adaptive receiver may not provide a reasonable performance during the transient after the rate change. In order to overcome this difficulty, we investigate an approach that allows updating the weight vectors for all rates simultaneously. For example, in a dual-rate system, the weight vector for the lower rate (the higher rate) can be updated during the period of the higher rate (resp., the lower rate) to avoid the transient after the rate change. The resulting adaptive receiver has multiple parallel adaptive filters. The adaptive filters for each rate can carry out the adaptation simultaneously, regardless of what the current rate is. As a result, the performance is not degraded by the rate change.