Chip-level Channel Equalization with Automatic Depth Determination for Downlink WCDMA Systems

In this paper, a low complexity multicode MMSE chip-level channel equalizer for the downlink UMTS FDD mode is proposed. This equalizer has a Rake-like structure and does not need the knowledge of the spreading codes to compute the equalizer filter coefficients. Moreover, the equalizer depth is determined automatically using the knowledge of the channel impulse response and the noise variance. Thus, the structure of the equalizer changes as the channel conditions change and the equalizer can be reduced to a Rake receiver if the depth is equal to one chip (e.g., in low signal-to-noise ratio conditions and/or in weak frequency selective channels). This property is very important and can be used to optimize the power consumption, which is a major constraint that has to be accounted for in the user equipment design.