Pre-equalization of continuous phase modulation for multipath fading channels

In this paper, a channel precoding technique is proposed for M-ary continuous phase modulation (CPM) for multipath downlink channels. The proposed pre-equalizer depends on the approximation of CPM signals by complex exponential functions and applies modulo-arithmetic operations to ensure stability, as in Tomlinson-Harashima precoding. Then spectrally efficient precoded signals are obtained with small envelope variations by employing a transmit selection diversity technique. By transferring the equalization functions to the base station, complexity in the mobile terminals is reduced significantly. The simulation results depict the power spectral density of the transmitted signals and the bit-error rate performance.