Optimal Multi-Level ASK Modulations for RIS-Assisted Communications with Energy-Based Noncoherent Reception
Sambit Mishra, Soumya P. Dash, George C. Alexandropoulos
TL;DR
The paper addresses energy-efficient RIS-assisted noncoherent SISO communications by introducing energy-based noncoherent receivers for one- and two-sided ASK and formulating an SER-minimization framework under an average energy constraint. It derives a statistical model where the RIS enables a effectively real-valued channel; two channel-knowledge regimes are analyzed: perfect statistics and statistics up to the fourth moment, with algorithms to obtain SER-optimal constellations in each case. The main contributions are SER-optimal SER designs for both one- and two-sided ASK, scalable algorithms (including bisection-based procedures) to compute constellations under energy budgets, and extensive simulations showing a threshold SNR beyond which the proposed constellations outperform equispaced signaling. The results offer practical design guidelines for RIS-enabled noncoherent systems, highlighting performance gains at higher SNRs and informing decisions on RIS size, modulation order, and channel information requirements.
Abstract
This paper investigates the performance of one- and two-sided amplitude shift keying (ASK) modulations in noncoherent single-input single-output (SISO) wireless communication systems assisted by a reconfigurable intelligent surface (RIS). Novel noncoherent receiver structures are proposed based on the energy of the received symbol and the choice of the modulation scheme for data transmission. The system's performance is assessed in terms of the symbol error rate (SER) and an optimization framework is proposed to determine the most effective one- and two-sided ASKs to minimize the SER, while adhering to average a transmit power constraint. Two scenarios based on the availability of the statistical characteristics of the wireless channel are explored: a) the transceiver pair has complete knowledge of the channel statistics, and b) both end nodes possess knowledge of the statistics of the channel gain up to its fourth moment, and novel algorithms are developed to obtain optimal ASKs for both of them. Extensive numerical evaluations are presented showcasing that there exists a threshold signal-to-noise ratio (SNR) above which the optimal ASKs outperform the traditional equispaced ASKs. The dependencies of the SER performance and the SNR threshold on various system parameters are assessed, providing design guidelines for RIS-assisted noncoherent wireless communication systems with multi-level ASK modulations.