Omnidirectional transmission precoding for uniform planar antennas arrays

Common signals in cellular communications, e.g., synchronous signals or broadcast signal, should be transmitted omni-directionally for reliable cell-wide coverage. However, when the multiple antennas are employed, the transmit signals are not inherently omni-directional unless precoding is properly designed. In this paper, we investigate the omni-directional precoding (OP) transmission in uniform planar array (UPA) equipped massive antenna communication systems. Based on the signal model of the line of sight (LOS) transmission for UPA, we derive the mathematical condition of OP matrix. For discrete angles, the Zadoff-Chu sequence that has been used in the design of OP matrix for the uniform linear array (ULA), can be extended to the UPA case by using Kronecker product. As such design does not result exact constant sum-power at any angles if there are a finite number of antennas, we then propose m sequences based OP matrices. The proposed precoding matrices guarantee the transmitted signal on each antenna has constant envelope thus achieving the full power-efficiency. Simulation results are presented in the term of cell-wide coverage. It shows that the proposed m sequence based precoding matrix has better omni-direction performance than existing ZC sequence based precoding that has been proposed for ULA.