Spectrum sidelobe suppression for discrete Fourier transformation-based orthogonal frequency division multiplexing using adjacent subcarriers correlative coding

Abstract

The large spectrum sidelobes of orthogonal frequency division multiplexing (OFDM) signal lead to the interference with the licensed user working on the adjacent band in spectrum pooling. The power spectral leakage of discrete Fourier transformation (DFT)-based OFDM systems can be divided into two parts, in-band–out-of-subband (IBOSB) spectral leakage and out-of-band (OOB) spectral leakage. A correlative coding technique is proposed to suppress the IBOSB leakage and redistribute the OOB leakage of DFT-based OFDM signal through the subcarrier coding in the frequency domain with appropriate weighting. The correlation is introduced between adjacent subcarriers and mutual cancellation of the spectrum sidelobes reshapes the spectrum of DFT-based OFDM signal. The optimum weighting factor is obtained through optimisation. Analytical results and simulation show that the proposed coding scheme significantly suppresses the IBOSB leakage in contrast with the common OFDM system and introduces least interference with the licensed user. Furthermore, the carrier–interference ratio (CIR) of OFDM system with correlative coding increases by 3 dB. At the same time, maximum likelihood sequence detection (MLSD) can mostly compensate the bit error rate (BER) degradation caused by error propagation at the expense of introducing a little computation complexity.