An RSSI-Based Multi-Stage 3D Beam Scanning and Alignment Method for Wireless Power Transfer

Accurate spatial alignment is essential for improving the performance of beamforming-based wireless power transfer systems. Nevertheless, conventional search methods usually face a trade-off between scanning complexity and estimation accuracy, especially when the receiver location is unknown in three-dimensional space. In this paper, a Received Signal Strength Indicator (RSSI)-based multi-stage beam scanning algorithm is proposed for joint azimuth, elevation, and distance estimation in a wireless power transfer system. The proposed algorithm performs hierarchical coarse scanning, refined scanning, angular local adjustment, fine distance search, and peak interpolation to determine the optimal spatial focus point. Unlike random search and conventional hierarchical scanning methods, the proposed method not only performs coarse-to-fine beam candidate selection but also introduces sub-grid interpolation and final local 3D refinement to overcome the resolution limitation of discrete grid scanning. Then, near-field focusing beamforming weights are designed according to the estimated spatial parameters to maximize the received signal strength. A simulation model is established at 900 MHz using a 4 × 3 uniform planar transmit array and a four-element receive array under a Rician channel. The results demonstrate that the proposed algorithm reduces both angular and distance estimation errors, thereby improving three-dimensional positioning accuracy. The proposed method is suitable for low-complexity and high-accuracy three-dimensional beam alignment in wireless power transfer applications.