Non-orthogonal pilot design and analysis for CoMP systems

In this paper, a non-orthogonal pilot scheme is proposed for the downlink of the coordinated multi-point (CoMP) systems to reduce the pilot overhead. Compared with the conventional orthogonal pilot schemes resulting in a heavy burden of the system along with the increasing number of transmit antennas, our proposed scheme doesn´t need the necessary orthogonality between different antennas´ pilot sequences. By exhaustively searching the non-orthogonal vectors over proper different unitary spaces, the optimal pilot sequences based on the criteria of minimal cross-correlation can be obtained for different antennas in CoMP systems. Analysis and simulations show that the proposed scheme provides a tradeoff between the accuracy of channel estimation and the total pilot overhead. In particular, when the number of cooperative transmitting antennas is large, our proposed scheme outperforms the orthogonal one at the same pilot overhead, with regard to available system capacity by linear beamforming.