Omnidirectional Space–Time Block Coding Design for Three-Dimensional Massive MIMO Systems

Common signals in public channels of cellular systems are usually transmitted omnidirectionally by the base station (BS) to ensure cell-wide coverage. In this paper, two categories of omnidirectional space-time block codes (STBCs) are proposed to broadcast the common information omnidirectionally in three-dimensional (3D) massive multiple-input multiple-output (MIMO) systems. By utilizing Zadoff-Chu sequences, we propose a discrete omnidirectional STBC, through which constant received signal power at discrete angles is achieved while guaranteeing equal-power transmission per antenna. Then, by utilizing two-dimensional orthogonal complementary codes (2D-OCCs), we also propose a consecutive omnidirectional STBC, which is insensitive to the number of BS antennas, and can realize constant received sum power at any angle through one STBC transmission. Besides, through theoretic analyses, we also demonstrate that all the proposed STBC designs can achieve full diversity order. Simulation results verify the effectiveness of the proposed omnidirectional STBC designs.