This paper focuses on 3D localization of transmitting satellites in low Earth orbits (LEO). 3D localization of transmitters in low orbits is an important emerging problem for many applications such as spectrum management, orbit determination, and backup for GPS failures in orbit. We present StarLoc - a system to geolocate transmitters in space using a combination of orbital modeling and a new interferometric 3D angle-of-arrival estimation technique. StarLoc's design relies on a unique insight - the motion of satellites is governed by orbital dynamics and is therefore along a 2D manifold in a 3D space. This reduces the degrees of freedom in satellite motion and allows us to 3D-locate and track a satellite with just three antennas in a 2D plane. We evaluate StarLoc using signal transmissions from 81 Starlink satellites. Our results show that StarLoc can estimate the 3D-angle of a satellite within 0.7° and the orbital range within 5 km. Our dataset and implementation are available at: https://connectedsystemslab.github.io/starloc.

Reconfigurable intelligent surface (RIS) has been envisioned as a promising research direction for future wireless communications. As an important indicator of RIS-assisted communication systems in green wireless communications, energy efficiency (EE) receives intensive research interest as an optimization target. Recently, an increasing number of works have been devoted to EE maximization in RIS-assisted systems, in which the power consumptions of the base station and RIS are jointly optimized. However, most existing works ignored the different power consumption between the ON and OFF states of the RIS elements, which mismatches the characteristics of the realworld physical components. To construct a more correct power dissipation model for EE optimization in RIS-aided systems, in this paper, we establish a novel ON-OFF aware power dissipation model for the RIS elements. Based on this new model, the EE optimization problem is re-formulated, and corresponding lowcomplexity algorithms are proposed by leveraging the mathematical structures of the problem. Simulation results verify the effectiveness of the proposed algorithms across a wide range of scenarios.