Constant-envelope omni-directional transmission with diversity in massive MIMO systems

The common signals in public channels of cellular networks should be transmitted omni-directionally from the base station to guarantee reliable coverage. In this paper, we propose a transmission scheme for public channels in massive MIMO systems based on the precoding-extended Alamouti code. This proposed space-time code has the following four features: 1) the transmitted signal is omni-directional, i.e., its DFT has constant-envelope; 2) the transmitted signal on each antenna has constant-envelope to achieve the highest power-efficiency; 3) the maximum diversity order 2 can be obtained; 4) it is easy for downlink channel estimation at the user side. Furthermore, we propose two different constellation designs for the two symbols in this space-time code, i.e., these two symbols can be modulated independently or jointly. The independent design has the advantage in fast decoding while the joint design has the advantage in superior performance. Simulations verify the effectiveness of our scheme.