Modulation and Demodulation Techniques for Common Modulation Schemes in OFDM Systems

This document presents the modulation and demodulation procedures for several commonly used modulation schemes in OFDM systems, including: BPSK, QPSK, 16QAM, and 64QAM. These modulation techniques play crucial roles in OFDM systems by achieving different data transmission rates and reliability through variations in signal phase, amplitude, and modulation depth. BPSK (Binary Phase Shift Keying) is a fundamental binary modulation scheme that represents 0 and 1 by changing the signal phase. In code implementation, BPSK typically uses two phase states (0° and 180°) with constant amplitude, making it robust against noise but with lower spectral efficiency. QPSK (Quadrature Phase Shift Keying) is a quaternary modulation scheme that transmits two bits per symbol by modifying both phase and amplitude. Implementation-wise, QPSK uses four phase states (45°, 135°, 225°, 315°) with equal amplitude spacing, effectively doubling the data rate compared to BPSK while maintaining reasonable noise immunity. 16QAM and 64QAM are higher-order modulation schemes that transmit more bits per symbol by combining phase, amplitude, and modulation depth variations. In 16QAM implementation, 4 bits are mapped to 16 constellation points with both amplitude and phase variations, while 64QAM maps 6 bits to 64 constellation points. These schemes offer higher spectral efficiency but require better signal-to-noise ratio conditions. The selection of appropriate modulation schemes depends on specific application requirements and channel conditions. Code implementations typically involve constellation mapping at the transmitter and maximum likelihood detection at the receiver, with adaptive modulation algorithms often used to dynamically select the optimal scheme based on real-time channel quality measurements.