Hybrid Reflection Modulation

Abstract

Reconfigurable intelligent surface (RIS)-empowered communication has emerged as a novel concept for customizing future wireless environments in a cost-and energy-efficient way. However, due to double path loss, existing fully passive RIS systems that purely reflect the incident signals into preferred directions attain an unsatisfactory performance improvement over the traditional wireless networks in certain conditions. To overcome this bottleneck, we propose a novel transmission scheme, named hybrid reflection modulation (HRM), exploiting both active and passive reflecting elements at the RIS and their combinations, which enables to convey information without using any radio frequency (RF) chains. In the HRM scheme, the active reflecting elements using additional power amplifiers are able to amplify and reflect the incoming signal, while the remaining passive elements can simply reflect the signals with appropriate phase shifts. Based on this novel transmission model, we obtain an upper bound for the average bit error probability (ABEP), and derive achievable rate of the system using an information theoretic approach. Moreover, comprehensive computer simulations are performed to prove the superiority of the proposed HRM scheme over existing fully passive, fully active and reflection modulation (RM) systems.

Over-the-Air Beamforming with Reconfigurable Intelligent Surfaces

“…Then, at the transmitter side, without requiring any additional signal processing approaches for interference mitigation, the overall signal is conveyed to the users through the RIS. Towards this aim, the RIS elements are assumed to be equipped with additional power circuitry to modify both the magnitude and the phase of the incident signal (Zhang et al, 2021;Nguyen et al, 2022;Yigit et al, 2021b). Hence, unlike the traditional beamforming techniques that employ complex and power-hungry signal processing hardware (Sohrabi and Yu, 2016;El Ayach et al, 2014), the RIS is designed as a beamformer to alleviate multi-user interference by adjusting the amplitude and phase of each reflecting element.…”

“…In a recent study on designing active RISs, a dynamic and fixed hybrid RIS architectures are constructed via leveraging power amplifiers and radio frequency (RF) chains as active elements (Nguyen et al, 2022). Further, for improving the data rate, a new RM design, which employs the sub-groups of a hybrid RIS as information transfer units, is presented in (Yigit et al, 2021b). In follow-up studies, the concept of the active RIS is deployed for beamforming optimization of the RIS-aided multi-user systems (Gao et al, 2022;Thanh Nguyen et al, 2022).…”

Hybrid Active-Passive Reconfigurable Intelligent Surface-Assisted UAV Communications

“…They can thus overcome the potential limitations of the passive RIS, especially in harsh transmission scenarios such as with low transmit power and/or severe path loss. As a result, the hybrid RIS is shown to provide significant improvement the system spectral efficiency [22], [26], secrecy rate [27], harvested energy [28], and reliability [29]. A fully active RIS with all active elements can achieve better spectral efficiency [30]- [32], which, however, requires higher power consumption and hardware cost compared to the hybrid one.…”