SmartShell: A Near-Field Reflective Surface Enhancing RSS.

Reconfigurable reflective arrays can be used to program the radio propagation environment in order to form favorable wireless channel conditions. Previous designs have used large-scale arrays containing hundreds to thousands of reflecting elements located external to the receiving node, with the reflection coefficients of all array elements managed by a controller. However, these designs can be costly to deploy and are challenging to quickly adapt to the time-varying nature of wireless channels caused by mobility. In this paper, we propose using a small-sized and low-cost reflective surface attached to the mobile device, called SmartShell, to program the micro-environment of radio propagation near the device. We provide a systematic analysis of the near-field reflective surface, laying the theoretical foundation for the feasibility and effectiveness of SmartShell. We then present insight into controlling the surface units of SmartShell, showing that this is fundamentally different from existing far-field designs and can be formulated as a binary quadratic programming (BQP) problem, with performance bounds derived. We develop a prototype of the SmartShell system and conduct comprehensive experiments. Results show that the SmartShell can increase the received signal strength (RSS) of the wireless node by 5--10 dB, which is comparable to far-field large-scale reflective surfaces but at a much lower cost.