Fading Cancellation in WCDMA Rake Receiver

The main principle of RAKE receiver is that they exploit multipath propagation by receiving the multipath components of the transmitted signal separately and combining their energies. The complete design, for this purpose, can be segmented into distinct stages or blocks based on their functionality. The incoming data is fed to different fingers after different delays. In each finger the data is descrambled and then despreaded through a matched filter. For descrambling, a Gold code generator also has been implemented, which can be initialized by external controls. For despreading the OVSF code sequence is taken as input to the chip. From matched f ilter outputs we separate the information and pilot symbols. [6] The pilot symbols are used to estimate the channel. After the channel characteristics are estimated finally the outputs of all the fingers are combined together through a fading cancellation block. Rake receiver handles QPSK data hence containing two parallel blocks, which interact with each other only in the ‘Descrambling’ & ‘Fading Cancellation’ blocks to process the in-phase and quadrature components of the data. The main objective of using a RAKE receiver is to combine the energies of all the multipath signals that reach the receiver within a reasonable time window. The RAKE receiver is used to tackle the problems of time dispersion (echoes) caused by multipath propagation in mobile communication. KeywordsW-CDMA, Fading, RAKE receiver