Spectral Efficiency Analysis of AF Cooperative Diversity Systems with M-QAM Adaptive Modulation

This research employs MATLAB-based simulation programs to analyze and evaluate spectral efficiency in systems combining AF (Amplify-and-Forward) cooperative diversity with M-QAM adaptive modulation techniques. The simulation architecture incorporates key components including: 1) AF relaying protocol implementation with signal amplification and forwarding mechanisms, 2) Adaptive M-QAM modulation algorithms that dynamically adjust constellation sizes based on real-time channel state information (CSI), and 3) Spectral efficiency calculation modules using bit-per-second-per-Hertz metrics. First, we investigate how AF cooperative diversity techniques enhance system reliability and performance through distributed spatial diversity gains. The MATLAB code implements multiple relay scenarios with path loss models and cooperative combining algorithms at the destination node. Second, we examine how M-QAM adaptive modulation optimizes spectral utilization under varying channel conditions, implementing threshold-based modulation switching algorithms that select optimal QAM orders (4-QAM to 256-QAM) according to instantaneous SNR estimates. Through extensive MATLAB simulations involving Monte Carlo methods and BER vs. SNR performance curves, we gain deep insights into parameter impacts including relay positioning, power allocation ratios, and modulation adaptation thresholds. The simulation framework also incorporates comprehensive channel impairment models analyzing effects of AWGN, multipath fading using Rayleigh/Rician distributions, and antenna configuration parameters. Finally, based on simulation results, we propose optimization strategies including intelligent relay selection algorithms and enhanced modulation adaptation protocols to further improve spectral efficiency while maintaining target error rates. The MATLAB implementation features modular design with separate functions for channel modeling, cooperative processing, and adaptive modulation, allowing systematic performance comparison under various system configurations.