A Low Complexity Millimeter Wave Channel Tracking Algorithm in Reconfigurable Intelligent Surface

In this paper, a low complexity channel tracking scheme based on Newton algorithm is proposed for the millimeter wave communication system assisted by Reconfigurable Intelligent Surfaces (RIS). The proposed tracking algorithm is used to track the slow variation of the angle between the user and the RIS. In the proposed scheme, some elements of RIS are connected to the Radio Frequency (RF) chains. The two Dimensional Fast Fourier Transform (2D-FFT) algorithm is used to initialize the angle estimation, and then the Newton algorithm is used to track the angle parameters in each time slot. The channel gain of each slot is estimated by maximum likelihood algorithm. The channel abrupt changes is caused by sudden environmental change and slow change of user terminal. If the abrupt change is detected, the angle parameters are initialized again, otherwise the Newton algorithm is still used to track the angle parameters. Simulation results show that the proposed channel tracking scheme not only achieves the lowest complexity but also ensures excellent performance, which achieves a great tradeoff between computational complexity and channel estimation performance.