Adaptive modulation with limited peak power for fading channels

This paper investigates the problem of maximizing the spectral efficiency for adaptive modulated systems with a peak power constraint. The solutions for both the continuous constellation case and the discrete constellation case are derived by the Lagrangian method,and an iterative algorithm solving the Karush-Kuhn-Tucker (KKT) optimality conditions are proposed. Our simulation results show that the spectral efficiency loss due to the peak power constraint is small and the target bit error rate (BER) can be guaranteed by our algorithm. In particular, the spectral efficiency loss remains within 1 [bps/Hz] for the continuous constellation case and 2 [bps/Hz] for the discrete constellation case at average signal-to-noise ratio (SNR) of 20 dB.