RIS-Based Over-the-Air Channel Equalization in Resource-Constrained Wireless Networks

Rich scattering yields long channel impulse responses (CIRs) with many taps that thwart communications in resource-constrained wireless networks limited to simple on-off-keying: the modulation rate must be throttled to avoid inter-symbol interference. Relevant examples include Internet-of-Things (IoT) networks and wireless networks-on-chips (WNoCs). If the radio environment is parametrized by a reconfigurable intelligent surface (RIS), the RIS configuration can be optimized to tailor the CIR between selected antenna pairs and make it (almost) pulse-like despite rich scattering by judiciously engineering the interferences of the multi-bounce paths. Thereby, the channel is equalized “over the air” in the physical domain, unlike conventional pre- and/or post-coding strategies. Here, using a physics-compliant model of a RIS-parametrized rich-scattering environment, we explore how the optimal choice of the time delay at which the CIR is shaped to have its most significant tap depends on the amount of reverberation in the environment and the latter's specific geometry.