Tone reservation for SFBC-OFDM transmission systems using null subcarriers

A combination of space-frequency-block-codes (SFBC) with orthogonal frequency division multiplexing (OFDM) has became a promising candidate for high performance 4G broadband wireless communications. However, a widely recognized nonlinear distortion due to the nonlinear power amplifiers reduces the efficiency of the SFBC-OFDM transmission and limits further network deployment. In this paper, we propose the strategy based on using the well-known tone reservation (TR) technique that was initially proposed to be used in conventional single antenna OFDM systems. However, in OFDM systems TR sacrifices a set of subcarrier prior to the transmission in order to reduce the signal envelope fluctuation, thereby reducing the data rate of the transmission. Here, we propose to use the zero tones introduced during the procedure of SFBC encoding using selected orthogonal design instead of reserving the set of subcarriers, which allows for achieving practically full data rate of the transmission. Numerical results indicate that the proposed method can significantly reduce the out-of-band radiation to the adjacent channels and therefore improve the overall performance of the system.