A novel ML combining RAKE receiver for DS-CDMA

Tapped delay line RAKE receivers are commonly used to achieve path diversity gain in DS-CDMA systems. Maximum ratio combining is typically considered the optimal combining scheme when fading parameters can be perfectly tracked. Lee and Milstein (see IEEE Transactions on Communications vol.47, no.12, p.1897-1904, 1999) noted that MRC is not optimal because different diversity branches have different MAI power. However, Lee and Milstein's combining scheme used inaccurate estimations of the MAI power. In this paper, the optimal combining scheme for DS-CDMA RAKE receivers based on the maximum likelihood criteria is derived. Simulation over Rayleigh frequency selective fading channels indicates the benefits over other combining schemes.