Bandwidth Efficiency Optimization for Constant Envelope Multicarrier Modulation with Power Allocation and Bit Loading

This research presents an enhanced Constant Envelope Orthogonal Frequency Division Multiplexing (CE-OFDM) scheme optimized for systems requiring high spectral efficiency. While multi-carrier modulation techniques like OFDM enable high data rates, their practical implementation is hindered by the peak-to-average power ratio (PAPR) issue, which degrades power efficiency and increases hardware complexity. CE-OFDM overcomes this limitation by generating constant-amplitude signals through phase modulation, thereby improving amplifier efficiency and reducing nonlinear distortion. We study a frequency-dependent power allocation scheme where the amplitudes of high-frequency subcarriers are suppressed more than those of low-frequency subcarriers, thereby reducing bandwidth and improving system efficiency. Additionally, as high-frequency subcarriers are allocated less power, bit-loading is enabled to better align channel conditions. The modulation order (M-value) for M-ary quadrature amplitude modulation (QAM) is dynamically adjusted in response to variations in the signal-to-noise ratio (SNR), ensuring maximal bandwidth efficiency with a guaranteed error performance. Numerical results demonstrate substantial improvements in spectral efficiency while maintaining acceptable bit error rates (BER), making CE-OFDM more viable for 5G/6G applications where both power efficiency and spectral utilization are critical.