Implementation of 4QAM Modulation

This repository contains two programs implementing 4QAM modulation. The first program features a well-structured implementation with clear signal mapping logic where bits are mapped to complex symbols (e.g., 00→1+1j, 01→1-1j, 10→-1+1j, 11→-1-1j). My modified version builds upon this foundation. However, the original implementation has a constraint where channel coefficients must be arranged in descending order. Users can experiment with normalized channel coefficients [0.227 0.46 0.688 0.46 0.227] - commonly used in academic simulations - where the sum of squared coefficients equals 1, representing a normalized channel response. The second program doesn't incorporate channel coefficient handling but implements an OFDM framework with 128 subcarriers where 32 null carriers are allocated at both spectrum edges. This OFDM configuration typically uses guard bands to reduce inter-carrier interference, employing techniques like cyclic prefix insertion and FFT-based modulation. The null carrier implementation follows standard OFDM practice where only central subcarriers carry data while edge subcarriers remain unused, effectively reducing out-of-band emissions and improving bit error rate performance through better spectral containment. Both programs demonstrate practical 4QAM implementation approaches: the first emphasizes modular code structure with separate functions for modulation, channel modeling, and demodulation, while the second integrates OFDM-specific features including IFFT/FFT operations and subcarrier allocation management.