Back to Single-Carrier for Beyond-5G Communications above 90GHz

Wireless Terabits per second (Tbps) link is needed for the new emerging data-hungry applications in Beyond 5G (B5G) (e.g., high capacity broadband, enhanced hotspot, three Dimensional (3D) extended reality, etc.). Besides, the sub-THz/THz bands are the next frontier for B5G due to scarce sub-GHz spectrum, and insufficient bandwidth for wireless Tbps link in 5G millimeter Wave (mmWave) bands. Even though a wider bandwidth and large-scale Multiple-Input Multiple-Output (MIMO) are envisioned at sub-THz bands, but the system and waveform design should consider the channel characteristics, technological limitations, and high Radio Frequency (RF) impairments. Based on these challenges, we proposed to use an energy-efficient low order single carrier modulation accompanied by spectral-efficient Index Modulation (IM) with MIMO. Firstly, MIMO Spatial Multiplexing (SMX) and spatial IM domain (e.g. Generalized Spatial Modulation (GSM)) are explored, where we reduced their optimal detection complexity by 99% and the high-spatial correlation effect on GSM. Besides, we proposed Dual-Polarized Generalized Spatial Modulation (DP-GSM) that provides higher Spectral Efficiency (SE) via multi-dimensional IM and helps with the latter problem. We derived the theoretical performance of DP-GSM, and all these potential candidates are assessed in sub-THz environment. We also proposed a novel IM domain, called filter IM domain, that generalizes most existing Single-Input Single-Output (SISO)-IM schemes. Within the filter IM domain, we proposed two novel schemes: Filter Shapes Index Modulation (FSIM) and In-phase and Quadrature Filter Shape Index Modulation (IQ-FSIM) to enhance system SE and Energy Efficiency (EE) through indexation of the filters in the bank. In addition, their optimal low complexity detectors and their specialized equalization techniques are designed. Starving for further SE and EE improvement, this filter IMdomain is exploited inMIMO. Besides, we theoretically characterized the performance of FSIM, IQ-FSIM, and Spatial Multiplexing with Filter Shape Index Modulation (SMX-FSIM) systems. To conclude, the proposed SMX-FSIM is compared in sub-THz environment to the previously considered candidates. The results confirm that SMX-FSIM is the most promising solution for low-power wireless Tbps B5G system due to its high SE/EE, robustness to RF impairments, low power consumption, feasible complexity, and low-cost with a simple linear receiver. Finally, the challenging filter bank design problem imposed by the filter IM domain is tackled by optimization to achieve better results.