Using Constellation Shaping to Reduce the Peak and Average Power of OFDM Signals

Abstract

We suggest applying constellation shaping to reduce the peak and average power of orthogonal frequency division multiplexing (OFDM) signals using quadrature amplitude modulation (QAM) in all subcarriers without clipping or reducing the data rate. Adopting the successful shell mapping algorithm for high data rate transmission over telephone channels, as described in the V.34 Recommendation of ITU-T, we build a shell mapping algorithm for multidimensional constellation in the frequency domain for OFDM communication systems with N subcarriers. We give closed-form expressions of the functions needed to apply the constellation shaping algorithm for any N being a power of two. No side information needs to be transmitted and the data rate remains the same as for the basic OFDM system. Our simulation results show that we are able to reduce the peak and mean power by about 1 dB for OFDM signals with N = 16. For a higher number of subcarriers, we expect that we obtain more freedom in power minimization and the resulting gain will be higher. The only price to be paid is the enhanced complexity of the system by an amount that is rather acceptable.