In the thesis work, an all digital phase shift keying(QPSK) direct sequence code division multiple access(DS-CDMA) mobile demodulator is designed which conforms to the TIA/EIA/IS-95 digital cellular standard. The demodulator has the RAKE receiver structure which utilizes up to three multipath signals with maximal ratio combining. After simulating the demodulator using the XACT development system, we implement it using FPGA chips from xilinx.
The CDMA mobile demodulator consists of three main blocks : a pseudo noise(PN) acquisition block, a finger block with three fingers which can track and demodulate three PN sequences, and a symbol combiner block. The PN Acquisition block synchronize three PN sequences to corresponding three multipath signals within 1/2 chip timing with appropriate receiver delay. Each finger can track a PN sequence within 1/8 chip timing and demodulate symbols for one multipath signal. The symbol combiner combines three demodulated symbols from three fingers with maximal ratio combining.
Computer simulation results show that the acquisition block and the finger block for PN synchronization reveal superior performance in the multipath fading channel environment. The bit error rate(BER) performance of the proposed demodulator is numerically derived. The results show that as the number of the symbol demodulations increases BER performance is improved.
