Improved Out-of-Band Emissions Reduction for OFDM Systems

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is its large out-of-band (OOB) emissions. These emissions may cause harmful interference to adjacent users. In this paper, we investigate the ability of combining two existing OOB emissions reduction techniques. The chosen techniques are the subcarrier weighting (SW) technique and the constellation expansion (CE) technique. Each technique, individually, can achieve significant reduction in the OOB emissions, however, at the expense of degrading the performance of the OFDM system. This paper presents a heuristic algorithm for combining these two techniques so that significant OOB emissions reduction can occur with less degradation as will be shown in the paper. Due to the simplicity of the proposed algorithm, it is implemented in a software defined radio tested for real-time transmissions.