Implementation of a digital communication system using QPSK modulation

Abstract

With the advances in high speed, programmable digital signal processing (DSP) chips, modern communications links are using a combination of DSP techniques and digital communications methods to realize faster, reconfigurable, and modular systems. This thesis details the software implementation of a modern digital communication system combining various DSP functions, channel Forward Error Correcting (FEC) algorithms, and digital modulation methods. The digital modulation schemes considered here include both baseband and Quadrature Phase Shift Keying (QPSK) techniques. The proposed communication system will serve as a practical tool useful for simulating the transmission of any digital data. The various modules of the system include source encoders/decoders, data compression functions, channel encoders/decoders, and modulators/demodulators. Implementation consists of coding the various link functions in C and integrating them as a complete system. The results show the viability of a QPSK modulated digital communications link and point the direction of future research towards software radio.