Performance analysis of CE-OFDM-CPM Modulation using MIMO system over wireless channels

Abstract

Orthogonal Frequency-Division Multiplexing (OFDM) is a multicarrier modulation that has expanded attractiveness and is used for wireless communication system. However one key weakness of OFDM signal is the high Peak-to-Average Power Ratio (PAPR). The high PAPR of OFDM signal cause nonlinear distortions by the power amplifier, which in turn affects negatively the OFDM transmission signal. These nonlinearities in amplifiers cause both Inter-Symbol Interference (ISI) and inter-carrier interference (ICI) in the system. A “power back-off” is required to prevent spectral broadening and performance degradation from inter-modulation distortion. To overcome this problem we propose Constant Envelope OFDM (CE-OFDM) which provides a good solution to the high PAPR issue in OFDM. OFDM signal is transformed, by way of Phase Modulation (PM), to a constant envelope signal, thereby alleviating the need for a power back-off and allowing for the most efficient power amplifier operation possible. In this paper the implementation of Maximum-Likelihood Sequence Estimation (MLSE) channel equalization in CE-OFDM-PM is proposed, a performance gain comparison and evaluation over fast fading channels well be presented and discussed. At the same time, Multiple-Input Multiple-Output (MIMO) system is found to provide better performance over wireless channels by providing communication links with substantial diversity and capacity. Likewise for MIMO system, simulation results are given in terms of BER (Bit Error Rate) to show the performance gain of the Alamouti code and of the proposed receiver. The simulation results show that the Minimum Mean Square Error (MMSE) is the best one to avoid ISI.