Techniques for reducing out-of-band radiation in OFDM based transmission systems

Abstract

Orthogonal frequency-division multiplexing (OFDM) suffers from high out-of-band radiation that prohibits the efficient use of the available spectrum particularly in OFDM based overlay systems. Recently, three different techniques for sidelobe suppression have been proposed and are recapitulated in this paper. One approach referred to as subcarrier weighting is based on weighting the individual subcarriers such that their sidelobes cancel each other. Alternatively, cancellation carriers are inserted at the edges of the spectrum in order to cancel the sidelobes of the transmit (Tx) signal. Thirdly, with the multiple choice sequences method, the symbol vector is transformed into multiple equivalent Tx sequences and the one with the lowest sidelobe power is transmitted. Sidelobes are reduced significantly at the expense of a slightly ncreased bit error rate or a reduced throughput. In order to further improve performance, in the paper, the combination with Tx windowing and reasonable combinations of the three methods are proposed and investigated. Simulation results show that the suppression achieved with the joint application of two techniques considerably exceeds the suppression achieved with the methods applied separately.