Wideband CDMA
Kluwer Academic Publishers eBooks · 2005
The coherent RAKE reception of wideband code division multiple access (Wideband CDMA) signals with complex spreading is considered in this chapter. A general multipath-fading channel model is assumed. A dedicated pilot channel, which is separate from data channels, is used for the purpose of channel estimation. Based on a digital implementation, the coherent demodulation scheme is presented. Pilot channel estimation error due to multiple access and multipath interference is studied. System performance is evaluated by means of bit error rate. The analysis shows that the error of channel estimation significantly degrades system performance and can be effectively suppressed by low pass filters (LPFs). A discussion on the envelope variation of complex spread signals is also included, which illustrates that the complex spread signal has more stable envelope than the dual-channel spread signal. The power ratio of pilot to data channels should be chosen in the range of 0.2 to 0.4 (−7 dB to −4 dB) in order to achieve maximum system capacity.