AN2253, Channel Estimation for a WCDMA Rake Receiver

The third-generation universal mobile telecommunications system (UMTS) uses direct-sequence code division multiple access (DS-CDMA) to transmit data. DS-CDMA is well suited to transmit data over the multipath fading channel. The high signal bandwidth for the WCDMA system (5 MHz) allows the received signal to be split into distinct multipaths with high resolution. For the first generation of UMTS handsets, a rake receiver is the receiver of choice because it allocates one rake finger to each multipath, thus maximizing the amount of received signal energy. The rake receiver combines these different paths into a composite signal with substantially better characteristics for demodulation than a single path. To combine the different paths meaningfully, the rake receiver needs such channel parameters as the number of paths, their location (in the delay domain), and their (complex-valued) attenuation. In a WCDMA system, the necessary channel parameters must be estimated and tracked throughout the transmission.