Improving receiver performance for pilot-aided frequency selective CDMA channels using a MMSE switch mechanism and multipath noise canceller

The IS-95 downlink channel incorporates a pilot signal to aid the mobile receiver in obtaining coherent channel estimates for use in the rake receiver. At the transmitter, the traffic signals are orthogonal to the pilot signal; however, in frequency selective channels where more than one resolvable multipath component is received, the received traffic channels of one multipath component are no longer orthogonal to the replicate pilot signals of another multipath component. This nonorthogonal multipath noise contribution will cause degradation in the channel estimate and resulting rake output. Since relevant parameters which characterize the pilot signal are known or estimated, the pilot multipath noise at each rake finger input can be reconstructed and removed. However, care must be taken in performing this pilot multipath noise cancellation (MNC) since them may be situations where subtracting off pilot noise from a weak multipath component will actually decrease the reliability of the decision statistic at the rake output.