Enhanced Orthogonal Frequency Division Multiplexing With Index Modulation
Abstract: Index modulation concept has attracted considerable research interest in the past few years. As a realization of index modulation in the frequency domain, orthogonal frequency division multiplexing with index modulation (OFDM (OFDM-IM) has recently been proposed, proposed, which conveys information bits through both the subcarrier activation patterns and the amplitude phase modulation constellation points. This paper proposes two enhanced OFDM OFDM-IM IM schemes aimed at achieving higher spectral efficiency and diversity gain, res respectively. pectively. The first one, termed OFDM with hybrid in--phase/quadrature phase/quadrature index modulation (OFDM-HIQ-IM), (OFDM explores the I- and QQ dimensions jointly for index modulation, allowing transmission of more index modulation bits in each subcarrier group. The second one, ne, termed linear constellation precoded OFDM OFDM-IQ-IM IM (LP-OFDM-IQ-IM), (LP spreads information symbols across two adjacent active subcarriers through linear constellation precoding to harvest additional diversity gain. By maximizing the minimum squared Euclidean distance, two different realizations of LP-OFDMLP IQ-IM IM are derived, which leads to a rotated and a diamond-shaped diamond shaped constellation, respectively. The proposed OFDM OFDM-HIQ-IM and LP-OFDM-IQ-IM, IM, as revealed by both theoretical analyses and computer simulations, enable enable low low-complexity detection and exhibit superior error rate performance over the existing OFDM OFDM-IM schemes.