We propose a two-way generalized code index modulation scheme with hexagonal QAM (TW-GCIM-HQAM) over Nakagami-m fading. The design combines GCIM and physical layer network coding with energy-efficient HQAM constellations. Using orthogonal Walsh-Hadamard spreading codes, two users exchange data via a half-duplex relay in two time slots (instead of three in conventional two-way DF). Information is carried by both the HQAM symbols and the indices of the spreading codes on the I/Q branches. We compare the scheme with two-way decode and forward at matched rates and evaluate the average bit error rate via Monte Carlo simulations on Nakagami-m channels for several HQAM constellations. Results show competitive or improved error performance, together with better energy use and time slot efficiency.

The growing demands in wireless communication technologies necessitate the development of more advanced and efficient systems. Therefore, this paper introduces a high-performance and data rate index modulation technique called the double media-based modulation (DMBM) system. The proposed system enhances the conventional media-based modulation (MBM) system by doubling the mirror activation patterns (MAPs) and the transmitted symbols within the same transmission duration. Consequently, the DMBM system achieves double the spectral efficiency of MBM while improving error performance through an increased number of bits encoded in the indices. The proposed DMBM scheme undergoes performance evaluation using$M$-ary quadrature amplitude modulation ($M$-QAM) over Rayleigh, Rician, and Nakagami-$m$fading channels. Its error performance is compared with alternative techniques such as spatial modulation (SM), quadrature SM (QSM), MBM, and double SM (DSM) over the Rayleigh channel. Also, to further improve reliability, especially in high-mobility scenarios envisioned for sixth-generation (6G) networks, orthogonal time frequency space (OTFS) modulation is integrated into the proposed DMBM system. The proposed OTFS-based DMBM (OTFS-DMBM) system is compared with the conventional OTFS system and offers better error performance at the same spectral efficiency. Furthermore, comprehensive analyses of throughput, complexity, energy efficiency, spectral efficiency, and capacity are conducted for the DMBM system alongside the benchmark system. The impact of imperfect channel state information (CSI) for the proposed DMBM system is also analyzed, and performance comparisons are presented for both perfect and imperfect CSI conditions. The findings demonstrate that the DMBM system outperforms its counterparts, highlighting its potential as a superior solution for modern wireless communication networks' demands.

Today's wireless communication networks have many requirements such as high data rate, high reliability, low latency, low error data transmission, and high energy efficiency. High-performance index modulation (IM) techniques and reconfigurable intelligent surface (RIS) technology, which has recently attracted the attention of researchers, are strong candidates to meet these requirements. This paper introduces a novel RIS-supported code IM-based receive spatial modulation (RIS-CIM-RSM) system. The proposed RIS-CIM-RSM system uses quadrature amplitude modulation (QAM) symbols, receive antenna indices, and spreading code indices for wireless data transmission. In the proposed system, an RIS applies a phase rotation that maximizes signal-to-noise ratio (SNR) to the signals coming to the reflecting elements and directs them to the selected receive antenna. Performance analyses of the proposed RIS-CIM-RSM system such as data rate, throughput, and energy saving are obtained. The results obtained show that the proposed RIS-CIM-RSM system is superior to the counterpart RIS-based IM systems in the literature in terms of data rate, throughput, energy saving, and error performance.