QPSK Modulation and Demodulation of Binary Information with Performance Analysis

In this simulation program, we implement QPSK modulation on a binary information sequence. The implementation involves mapping binary pairs (dibits) to one of four phase states (0°, 90°, 180°, 270°) using Gray coding to minimize bit errors. We first generate and plot the time-domain waveform and power spectral density of the QPSK modulated signal, which demonstrates the bandwidth efficiency of this modulation scheme. The modulated signal is then transmitted through a wireless Additive White Gaussian Noise (AWGN) channel model, where we simulate realistic communication conditions by adding Gaussian noise to the signal. The channel model implementation includes configuring the signal-to-noise ratio (SNR) parameter to test different communication scenarios. At the receiver side, we perform coherent demodulation using a phase-locked loop (PLL) for carrier recovery and matched filtering for optimal signal detection. The demodulation process involves phase detection, symbol decision making, and conversion back to binary data. Finally, we analyze system performance by plotting the symbol error rate (SER) versus SNR curve. This performance metric is calculated by comparing the transmitted and received symbols across multiple Monte Carlo simulations with varying noise levels. The SER curve implementation uses statistical averaging to provide reliable performance evaluation under different channel conditions. Through this comprehensive simulation, we gain deeper insights into the QPSK modulation and demodulation process. By examining the waveform and spectral characteristics, we understand how the signal transforms during modulation and its frequency distribution. The AWGN channel simulation helps replicate real-world communication environments. The demodulation recovery process demonstrates practical receiver implementation, while the SER performance curve provides quantitative assessment of system robustness across various SNR conditions. This step-by-step analysis enables thorough understanding of QPSK communication systems and facilitates performance evaluation and optimization, making it particularly valuable for wireless communication system research and design. The simulation code structure typically includes modules for signal generation, modulation, channel modeling, demodulation, and performance analysis, allowing for modular testing and extension to more complex communication scenarios.