An energy efficient DOA estimation algorithm for uncorrelated and coherent signals in virtual MIMO systems

The multiple input and multiple output (MIMO) and smart antenna (SA) technique have been widely accepted as promising schemes to improve the spectrum efficiency and coverage of mobile communication systems. The definition of direction-of-arrival (DOA) estimation is that multiple directions of incident signals can be estimated simultaneously by some algorithms using the received data. The conventional DOA estimation of user equipments (UEs) is one by one, which is named as sequential scheme. The Virtual MIMO (VMIMO) scheme is that the base station (BS) estimates the DOAs of UEs in a parallel way, which adopts the SA simultaneously. Obviously, when the power is fixed, the VMIMO scheme is much more energy efficient than the sequential scheme. In VMIMO scheme, a set of UEs are grouped together to simultaneously communicate with the BS on a given resource block. Then the BS using multiple antennas can estimate the 2D-DOA of the UEs in the group simultaneously. Based on VMIMO system, the 2D-DOA estimation algorithm for uncorrelated and coherent signals is proposed in this paper. The special structure of mutual coupling matrix (MCM) of uniform linear array (ULA) is applied to eliminate the effect of mutual coupling. The 2D-DOA of uncorrelated signals can be estimated by DOA-matrix method. The parameter pairing between azimuth and elevation is accomplished. Then these estimations are utilized to get the mutual coupling coefficients. Based on spatial smoothing and DOA matrix method, the 2D-DOA of coherent signals can be estimated. The Cramer–Rao lower bound is derived at last. Simulation results demonstrate the effectiveness and performance of the proposed algorithm.