Multidimensional Index Modulation in Wireless Communications

In index modulation schemes, information bits are conveyed through indexing of transmission entities such as antennas, subcarriers, times slots, precoders, subarrays, and radio frequency (RF) mirrors. Index modulation schemes are attractive for their advantages such as good performance, high rates, and hardware simplicity. This paper focuses on index modulation schemes in which multiple transmission entities, namely, {\em antennas}, {\em time slots}, and {\em RF mirrors}, are indexed {\em simultaneously}. Recognizing that such multidimensional index modulation schemes encourage sparsity in their transmit signal vectors, we propose efficient signal detection schemes that use compressive sensing based reconstruction algorithms. Results show that, for a given rate, improved performance is achieved when the number of indexed transmission entities is increased. We also explore indexing opportunities in {\em load modulation}, which is a modulation scheme that offers power efficiency and reduced RF hardware complexity advantages in multiantenna systems. Results show that indexing space and time in load modulated multiantenna systems can achieve improved performance

Efficient Signaling Schemes for mmWave LOS MIMO Communication Using Uniform Linear and Circular Arrays

High spatial correlation in line-of-sight multiple-input multiple-output (LOS MIMO) channels in mmWave communication is a cause for the channel matrices to have low rank. However, with proper placement of the transmit and receive antennas, the channel matrix can be made full/high rank. While optimum placements for full rank can be realized with uniform linear arrays (ULA), this may not be the case with uniform circular arrays (UCA). This motivates the need to investigate efficient signaling schemes for LOS MIMO schemes for different array configurations. Accordingly, in this work, we study various signaling schemes including spatial multiplexing (SMP), spatial modulation (SM), and generalized spatial modulation (GSM) in the context of both ULA and UCA. Our analytical and simulation results show that GSM achieves better performance compared to SMP and SM. We also propose a new signaling scheme, termed as subarray index modulation (SAIM) scheme, where groups of antennas in the array (subarrays) are indexed to convey information bits and each antenna within an activated subarray carries an independent modulation symbol. It is found that the proposed SAIM scheme can achieve better performance compared to SMP, SM, and GSM schemes