Joint angle and delay estimation for 2D active broadband MIMO-OFDM systems

Mobile data traffic is expected to have an exponential growth in the future. In order to meet the challenge as well as the form factor limitation at the base station, 2D “Massive MIMO”, combined with OFDM, has been proposed as one of the enabling technologies to significantly increase the spectral efficiency of a broadband wireless system. In 2D broadband MIMO-OFDM systems, a base station will rely on the spatial information extracted from uplink sounding reference signals to perform downlink MIMO beam-forming. Accordingly, multi-dimensional parameter estimation of a ray-based multipath wireless channel becomes crucial for such systems to realize the predicted capacity gains. In this paper, we study joint angle and delay estimation for 2D broadband MIMO-OFDM systems and analytically assess its estimation performance. To be specific, a tensor-based standard ESPRIT algorithm is naturally applied to estimate the corresponding 3D channel parameters. Further, we give out the closed-form mean square error expressions for DoA estimation. It is found that the dimensionality of the antenna array at the base station, as well as the implementation of OFDM, play an important role in determining the estimation performance. Simulation is conducted to evaluate the performance of the tensor-based ESPRIT algorithm, and the empirical results match very well with that from the derived analytical expressions. These insights will be useful for designing practical 2D broadband MIMO-OFDM systems in future mobile wireless communications.