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