[Paper Review] Performance Analysis of Millimeter-Wave Relaying: Impacts of Beamwidth and Self-Interference

Guang Yang, Ming Xiao|arXiv (Cornell University)|Oct 21, 2017

Full-Duplex Wireless Communications3 citations

TL;DR

This paper analyzes the maximum achievable rate in millimeter-wave amplify-and-forward (AF) relaying systems using a two-ray channel model and Gaussian-type directional antennas. It shows that full-duplex (FD) relaying outperforms half-duplex (HD) only when beamwidth is narrow and self-interference is low; otherwise, direct transmission is superior. Ground reflections significantly impact performance, either constructively or destructively.

ABSTRACT

We study the maximum achievable rate of a two-hop amplified-and-forward (AF) relaying millimeter-wave (mm-wave) system, where two AF relaying schemes, i.e., half-duplex (HD) and full-duplex (FD) are discussed. By considering the two-ray mm-wave channel and the Gaussian-type directional antenna, jointly, the impacts of the beamwidth and the self-interference coefficient on maximum achievable rates are investigated. Results show that, under a sum-power constraint, the rate of FD-AF mm-wave relaying outperforms its HD counterpart only when antennas with narrower beamwidth and smaller self-interference coefficient are applied. However, when the sum-power budget is sufficiently high or the beamwidth of directional antenna is sufficiently small, direct transmission becomes the best strategy, rather than the AF relaying schemes. For both relaying schemes, we show that the rates of both AF relaying schemes scale as $ \mathcal{O}\left(\min\left\lbraceθ_m^{-1},θ_m^{-2} ight brace ight) $ with respect to beamwidth $ θ_ m $, and the rate of FD-AF relaying scales as $ \mathcal{O}\left(μ^{-\frac{1}{2}} ight) $ with respect to self-interference coefficient $ μ$. Besides, we show that, ground reflections may significantly affect the performance of mm-wave communications, constructively or destructively. Thus, the impact of ground reflections deserves careful considerations for analyzing or designing future mm-wave wireless networks.

Motivation & Objective

• To analyze the maximum achievable rate in two-hop mm-wave AF relaying under realistic channel and antenna models.
• To investigate the impact of beamwidth and self-interference coefficient on system performance.
• To evaluate whether direct transmission can outperform AF relaying under high power or narrow beam conditions.
• To incorporate ground reflections via the two-ray channel model and assess their constructive or destructive effects.
• To provide a tractable performance analysis using Gaussian-type directional antennas that capture the roll-off feature of real radiation patterns.

Proposed method

• Uses a two-ray mm-wave channel model to include line-of-sight and ground-reflected paths.
• Employs a Gaussian-type directional antenna model to represent continuous main-lobe to side-lobe roll-off, improving realism over flat-top or sectorized models.
• Analyzes both half-duplex (HD) and full-duplex (FD) AF relaying schemes under a sum-power constraint.
• Derives closed-form expressions for the maximum achievable rate and analyzes their scaling behavior with respect to beamwidth and self-interference coefficient.
• Applies asymptotic analysis to derive scaling laws: O(min{θ⁻¹ₘ, θ⁻²ₘ}) for beamwidth and O(µ⁻¹ᐟ²) for self-interference coefficient.
• Uses mathematical proofs (e.g., monotonicity and convexity analysis) to validate key performance trends.

Experimental results

Research questions

• RQ1 Under what conditions does FD-AF relaying outperform HD-AF relaying in mm-wave systems?
• RQ2 How do beamwidth and self-interference coefficient jointly affect the maximum achievable rate?
• RQ3 When does direct transmission become superior to AF relaying in mm-wave networks?
• RQ4 How do ground reflections influence mm-wave relaying performance, and when do they cause constructive or destructive interference?
• RQ5 What are the fundamental scaling laws of achievable rate with respect to beamwidth and self-interference coefficient?

Key findings

• FD-AF relaying outperforms HD-AF relaying only when beamwidth is narrow and self-interference coefficient is small.
• When sum power is sufficiently high or beamwidth is sufficiently narrow, direct transmission achieves higher rates than both AF relaying schemes.
• The maximum achievable rate scales as O(min{θ⁻¹ₘ, θ⁻²ₘ}) with respect to beamwidth θₘ, indicating a trade-off between beamwidth and rate gain.
• For FD-AF relaying, the rate scales as O(µ⁻¹ᐟ²) with respect to self-interference coefficient µ, showing high sensitivity to residual interference.
• Ground reflections significantly affect performance, causing either constructive or destructive interference, and must be carefully modeled for accurate system evaluation.
• The performance gap between FD-AF relaying and its ideal upper bound (µ=0) is small even with moderate self-interference cancellation, reducing the need for ultra-strong cancellation hardware.