OFDM Multipath Transmission with 4QAM Modulation: Performance Analysis and Algorithm Comparison

This research investigates OFDM multipath transmission systems employing 4QAM modulation, with comprehensive comparison of bit error rate performance across different channel estimation algorithms and analysis of influencing factors. In this study, we conduct an in-depth exploration of 4QAM modulation scheme applied to OFDM multipath transmission systems. The implementation typically involves MATLAB-based simulation frameworks where we first generate 4QAM symbols using qammod() function, then apply OFDM modulation through IFFT operations with appropriate cyclic prefix insertion. Our analysis focuses on comparing channel estimation algorithms including LS (Least Squares), MMSE (Minimum Mean Square Error), and LMMSE (Linear MMSE) approaches, evaluating their BER performance using Monte Carlo simulations with varying SNR conditions. We then investigate key influencing factors such as carrier frequency offset (compensated using algorithms like Moose's method), timing synchronization errors, and channel delay spread characteristics. The performance metrics are analyzed through BER curves generated using semilogy() plots, with channel impulse responses modeled using Rayleigh fading channels with exponential power delay profiles. Through this systematic investigation, we enhance the understanding of 4QAM-modulated OFDM systems in multipath environments, providing valuable guidance for future system optimization and algorithm improvements in wireless communication design.