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 ${k}$ 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 ( ${k}$ lv) 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 simple modification of the ${k}$ lv detector, but very efficient. The proposed detector has a similar detection performance compared to the ML detection, which is suitable for flexible implementation of OFDM-IM systems.

I. Introduction

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) [1] is an emerging technique which is the application of the spatial modulation (SM) [2] principle to the subcarriers in OFDM systems. In OFDM-IM, the subcarriers are partitioned into subblocks. In each subblock, the subcarriers have two states, active or inactive. Then, OFDM-IM conveys information by not only modulated symbols but also the indices of the active subcarriers. OFDM-IM systems have a better energy efficiency compared to the classical OFDM [1], [3].