Accurate AoA Tracking Method in MIMO Communication Systems

In this chapter, we investigate the problem of AoA tracking for the large-scale array in THz communication, which has a large size and a narrow beam, highly demanding an accurate angle estimation. On the one hand, the system usually adopts a hybrid structure with limited RF chains, which increases the difficulty of angle estimation; on the other hand, the rapid mobility of users also brings new challenges to angle estimation. To address the above challenges, a two-stage tracking framework is proposed in this chapter, which employs the random phase matrix and orthogonal long pilots in the first stage to reduce the complicated multi-user estimation to multiple single-user estimations, followed by using both wide and narrow beams in the second stage to serve high-speed and low-speed users. Furthermore, a GAMP method is proposed for facilitating a low-accuracy estimation of the angles, followed by adopting a modified expectation maximization (EM) algorithm-based phase estimation to unbiasedly estimate the instantaneous angle with the help of high-gain characteristics of the beams. The proposed structure can not only simplify the estimation complexity but also improve the estimation accuracy due to its capability of transferring the non-linear problem of angle observation into a linear Gaussian model. In addition, the Kalman tracking framework is employed for performing continuous angle tracking. Numerical results show that the angle estimation based on the random phase matrix in the initial stage can obtain a high enough estimation accuracy, while the GAMP algorithm implemented in the second stage can quickly capture the angle range under the Rayleigh limit. The performance of the proposed EM-based tracking method is shown to outperform the traditional extended Kalman filter (EKF) method.