QPSK MODULATION FOR DSSS-CDMA TRANSMITTER AND RECEIVER USING FPGA
Susan Kuriakose, Miji Jacob · 2014
Direct sequence spread spectrum technique, which also known as direct sequence code division multiple access (DS-CDMA), is one of the two approaches to spread spectrum modulation for digital signal transmission. Direct sequence CDMA is the most popular of CDMA techniques. The DS-CDMA transmitter multiplies each of user signals by a distinct code waveform. The detector receives a signal composed of the sum of all user signals. In a conventional DS-CDMA system a particular user's signal is detected by correlating the entire received signal with the user's code waveform. DS-CDMA transmitter and receiver are implemented in Verilog for FPGA .Transmitter module mainly consist of user data generator, programmable chip sequence generator (PN sequence generator) and QPSK modulator. The receiver module mainly consists of QPSK demodulator, PN sequence generator, matched filter and threshold detector block. QPSK is a form of phase shift keying in which 2 bits are modulated at once. QPSK allows the signal to carry twice as much information as ordinary PSK using same bandwidth. Modelsim tool will be used for functional and logic verification. Xilinx synthesis technology will be used for synthesis of transmitter and receiver on FPGA Spartan 3E.