Wireless Communication with Flexible Reflector: Joint Placement and Rotation Optimization for Coverage Enhancement

TL;DR

This work introduces the flexible reflector (FR), a fully passive, mechanically movable surface that enables beam steering by jointly optimizing reflector placements $\{x_m\}$ and rotation angles $\{\omega_m\}$ to maximize the minimum received power over a target area. Through a foundational MR analysis with fixed rotation, the authors derive closed-form and cubic-solve placement rules, then extend to single-/multi-FR designs for both targeted power enhancement and area coverage. They develop sequential placement/rotation algorithms for MR and FR, and provide single/multi-FR solutions that incorporate anti-blockage and non-overlap constraints, with extensive simulations showing significant gains over benchmark schemes. The results highlight FR’s potential to enhance coverage and reduce active transmit power needs, while also outlining practical challenges such as CSI acquisition, inter-user interference in multi-user scenarios, and extension to multipath/MIMO settings.

Abstract

Passive metal reflectors for communication enhancement have appealing advantages such as ultra low cost, zero energy expenditure, maintenance-free operation, long life span, and full compatibility with legacy wireless systems. To unleash the full potential of passive reflectors for wireless communications, this paper proposes a new passive reflector architecture, termed flexible reflector (FR), for enabling the flexible adjustment of beamforming direction via the FR placement and rotation optimization. We consider the multi-FR aided area coverage enhancement and aim to maximize the minimum expected receive power over all locations within the target coverage area, by jointly optimizing the placement positions and rotation angles of multiple FRs. To gain useful insights, the special case of movable reflector (MR) with fixed rotation is first studied to maximize the expected receive power at a target location, where the optimal single-MR placement positions for electrically large and small reflectors are derived in closed-form, respectively. It is shown that the reflector should be placed at the specular reflection point for electrically large reflector. While for area coverage enhancement, the optimal placement is obtained for the single-MR case and a sequential placement algorithm is proposed for the multi-MR case. Moreover, for the general case of FR, joint placement and rotation design is considered for the single-/multi-FR aided coverage enhancement, respectively. Numerical results are presented which demonstrate significant performance gains of FRs over various benchmark schemes under different practical setups in terms of receive power enhancement.

Figures (12)

• Figure 1: Wireless communication enhanced by multiple FRs.
• Figure 2: Single target location power enhancement by a single-MR.
• Figure 3: Values of $f\left(x\right)$, ${{f_1}\left( {x} \right)}$ and ${{f_2}\left( {x} \right)}$ versus the placement position $x$, where the red circle and red dashed line indicate the optimal placement positions obtained by the closed-form and numerical result, respectively.
• Figure 4: The receive power versus the placement position $x$ for single-MR aided single target location power enhancement, where the placement position given in \ref{['maximumReceivedPowerLocation']} is marked by the red circle.
• Figure 5: The receive power versus the placement position $x$ and rotation angle $\omega$ for single-FR aided single target location power enhancement, where the optimal placement position and rotation angle pair $\left( {x^{\star},\omega^{\star} } \right)$ is marked by the red circle.

Theorems & Definitions (5)

• Proposition 1
• Lemma 1
• Lemma 2
• Proposition 2
• Lemma 3