Wideband terahertz links face beam squint and phase control limits
Beam Squint and Aperture--Bandwidth Limitations in Wideband RIS-Assisted THz Links
Information TheoryNetworking and Internet Architecture
Summary
Wireless communication using terahertz frequencies can be improved with devices called reconfigurable intelligent surfaces (RIS), which help direct signals. The authors studied how two problems—beam squint, where the signal direction shifts with frequency, and limited precision in controlling signal phases—affect performance. They developed mathematical formulas to predict signal strength and data rates across different frequencies. Their work helps understand limits on how well RIS can control wide frequency ranges in these systems.
What this means in practice
- •For wireless network engineers: Design RIS-assisted terahertz links accounting for beam squint and phase control limits to optimize communication rates over wide bandwidths.
- •For antenna array designers: Adjust antenna and RIS design parameters to mitigate aperture and bandwidth limitations revealed by the first-null bandwidth analysis in wideband systems.
Authors
Waqas Khalid, Chiew Foong Kwong, David Chieng, Qianyu Liu
Abstract
This paper analyzes the ergodic rate of a wideband reconfigurable intelligent surface (RIS)-assisted terahertz link under beam squint and finite-resolution phase control. Independent Rayleigh fading on the two RIS-assisted hops produces double-Rayleigh cascaded amplitudes. Exact second- and fourth-order channel moments are derived by incorporating the frequency-dependent array response and phase-quantization errors. Moment matching then provides a Gamma approximation for the received power on each subcarrier and a tractable closed-form approximation for the wideband ergodic rate. A first-null bandwidth approximation characterizes the aperture--bandwidth limitation of frequency-flat RIS control. Monte Carlo simulations validate the analytical framework.