Simulation of Third Generation CDMA Systems - Virginia Tech

the receiver filters are cascaded and they constitute a Raised Cosine (RC) filter. The noisehas to be passed through a Root RC filter before it is added to the received frame. Thisrearrangement is shown in Figure 3.9. The noise variance is calculated as described in section3.2.4.1.Only the first three lobes of the Raised Cosine were considered for implementing thefilters and all the filters were implemented as symmetric FIR filters. Symmetric FIR filtershave a delay equal to half the order of the filter. So to take this delay into account we paddedeach transmitted data block by an additional data segment whose size is equal to the delay.So if the delay of the filter is N D samples we repeated the first N D samples of the data at theend of the data block. After the filtering, we removed the first N D output of the filter. Weignored the transient of the filter. However the transient can be easily removed by passing asmaller data block through the filter and store the state before passing the data frame forpulse shaping.3.2.6 Rake ReceiverMultipath is resolved for WCDMA system because of the wide bandwidth. Rakereceiver [18] is used to exploit the consequent time diversity. The default number of fingersat the base station receiver is four. However any number of finger between three and six canbe chosen. The simple case of one finger is also provided as an option. The block diagramshown in Figure 3.10 illustrates the implementation of the rake receiver. It is assumed thatthe receiver has perfect channel estimation. Maximal Ratio Combining (MRC) is employedfor rake combining [19], [20].40