QPSK Modulation and Demodulation Process with Performance Analysis

This study provides a detailed analysis of QPSK modulation and demodulation processes under Gaussian white noise and Rayleigh fading channel conditions, excluding multipath interference, while employing quasi-analytical methods for bit error rate performance evaluation. The simulation framework comprises multiple systematic stages: synthetic signal generation using predetermined bit sequences, filter configuration with raised-cosine or root-raised-cosine filters for pulse shaping, QPSK modulation mapping two bits per symbol to four phase states (45°, 135°, 225°, 315°), injection of additive white Gaussian noise with controlled SNR levels, Rayleigh fading channel emulation using complex Gaussian random variables, coherent QPSK demodulation with phase recovery and symbol-to-bit decision mapping, and finally bit error rate calculation through transmitted-received bit comparison. The implementation typically utilizes MATLAB/Simulink with key functions like pskmod(), awgn(), rayleighchan(), and biterr() for respective stages. This comprehensive simulation enables deeper understanding of QPSK system principles and provides quantitative BER performance metrics under varying channel conditions.