Movable intelligent surfaces improve wireless communication and sensing
Movable-Element STAR-RIS for 6G: From Programmable Propagation to Programmable Geometry
Emerging Technologies
Summary
Wireless signals often bounce around in complicated ways, making communication tricky. This paper explores a special kind of surface called a movable-element STAR-RIS that can physically shift its parts while controlling how it reflects and transmits signals. By changing both the surface shape and its electronic settings, these surfaces can better direct wireless signals, reduce interference, and improve connection quality. The authors also look at practical challenges for using these movable surfaces in future wireless systems.
Reconfigurable intelligent surfacesSTAR-RISWireless propagationSignal reflectionSignal transmissionSpectral efficiencyNear-field focusingMultipath propagationWireless sensing6G networks
Authors
Wali Ullah Khan, Muhammad Adil
Abstract
Reconfigurable intelligent surfaces (RISs) make the wireless propagation environment programmable, while simultaneously transmitting and reflecting RISs (STAR-RISs) extend this capability to users located on both sides of a surface. However, conventional STAR-RIS architectures retain a fixed physical geometry after deployment. Movable-element STAR-RIS (ME-STAR-RIS) introduces an additional spatial degree of freedom by allowing the surface elements to reposition within prescribed regions while maintaining electronic control of their transmission and reflection responses. This combination of electromagnetic and geometric reconfiguration can alter propagation distances, multipath combinations, spatial correlation, interference, near-field focusing, and sensing geometry. This article presents a system-level perspective on ME-STAR-RIS through the concept of programmable geometry. We discuss its operating principles, movement architectures, and promising applications in communications, security, near-field systems, sensing, and high-mobility networks. A representative case study comparing optimized fixed and movable STAR-RIS architectures illustrates measurable spectral-efficiency gains from limited local displacement and the resulting saturation behavior. Finally, key hardware, channel-acquisition, electromagnetic, energy, reliability, and control challenges are discussed toward practical ME-STAR-RIS deployment.