Dither Signal Design for PAPR Reduction in OFDM-IM over a Rayleigh Fading Channel

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a novel scheme where the information bits are conveyed through the subcarrier activation pattern (SAP) and the symbols on the active subcarriers. Unfortunately, OFDM-IM inherits the high peak-to-average power ratio (PAPR) problem from the classical OFDM. The OFDMIM signal with high PAPR induces in-band distortion and out-of-band radiation when it passes through high power amplifier (HPA). There are attempts to reduce PAPR by adding dither signals in the idle subcarriers, where the dither signals can have various amplitude constraints according to the characteristic of the corresponding OFDM-IM subblock. But, there is no result for the specific amplitude constraint for the dither signals over a Rayleigh fading channel. In this letter, based on pairwise error probability (PEP) analysis, a specific constraint for the dither signals is derived over a Rayleigh fading channel.

Low Complexity Suboptimal ML Detection for OFDM-IM Systems

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a novel multicarrier scheme, which uses the k out of n subcarriers as active subcarriers to transmit data. For detecting the subcarrier activation pattern (SAP) at the receiver, maximum likelihood (ML) detection cannot be used because of its high computational complexity. Instead, the detector selecting the most likely active k subcarriers is used, which is called a k largest values (klv) detector. However, this method degrades the detection performance especially if the ratio of illegal SAPs to SAPs is high. In this letter, the suboptimal ML detector is proposed, which is a slight modification of the klv detector. However, the proposed detector has a similar detection performance compared to the ML detection, which is suitable for flexible implementation of OFDM-IM systems.