Dissertation Defence: Modulation and Equalization Schemes for Reconfigurable Surface-assisted Wireless Communication

Hibatallah Alwazani, supervised by Dr. Anas Chaaban, will defend their dissertation titled “Modulation and Equalization Schemes for Reconfigurable Surface-assisted Wireless Communication” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering.

An abstract for Hibatallah Alwazani’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.

Abstract

The sixth generation wireless (6G) is hurtling toward dense deployments of low-cost edge devices under tight energy, hardware, and security constraints. This dissertation targets the challenge of excessive usage of costly radio frequency (RF) chains by incorporating a different philosophy: Using reconfigurable electromagnetic surfaces to carry the burdens of baseband processing and information transmission by shaping the propagating waves in the electromagnetic (EM) domain. We examine two contemporary, low-cost technologies: The Reconfigurable Intelligent Surface (RIS), a single-layer reconfigurable surface that smartly reconfigures the wireless environment to reflect electromagnetic waves, and the Stacked Intelligent Metasurface (SIM), a stack of reconfigurable metasurfaces, which can enable wave-domain signal processing.

The thesis begins with physical layer security (PLS) in environments with slow-varying channels. When used for secret key generation, such channels lead to low secret key rates. We propose to use an RIS as a channel modulator that supports PLS by dynamically altering the propagation environment. The RIS randomly switches its phase configurations to inject controllable randomness into the channel, enabling achieving higher secret key rates, and ensuring secure and efficient key exchange between devices. We evaluate the performance of this scheme, focusing on metrics such as key mismatch rate, key rate, and overall secrecy rate under realistic assumptions such as statistical CSI and spatial correlation.

The second part investigates ultra-low power sensing. We study a wireless sensor network (WSN) in which each sensor node is equipped with an RIS rather than active radio-frequency (RF) electronics. The sensor uses the RIS to reflect a carrier signal from a source while modulating its reflection toward the receiver. By modulating the RISs with the information from each sensor instead of using a conventional transmitter, the caveat of battery usage in the sensors will be reduced. Since multiple sensors share the same receiver under “blind” RIS operation, interference from those sensors may occur. Hence, we analyze and compare scheduling strategies: opportunistic scheduling, round-robin, and proportional fairness and quantify throughput, system outage, and fairness trade-offs as the number of RIS elements and sensor nodes scales.

In the final part, we move beyond reflection toward wave-domain signal processing. Building on the concept of the SIM, we introduce delay augmented SIM (DA-SIM) that adds symbol-duration-level dynamic delays on top of the conventional phase-controlled element. This adds a temporal dimension thereby allowing the SIM to act as a passive analog processor. To show the effectiveness of the DA-SIM, we demonstrate its ability in equalizing a slow-fading multipath channel against several digital filter benchmarks.

Overall, this dissertation evaluates the performance of the RIS and the SIM in different wireless applications through theoretical derivations, algorithmic developments, specific applications, and numerical simulations and demonstrates their potential for next-generation wireless networks.