A Space-Time Code Design for Omnidirectional Transmission in Massive MIMO Systems

Omnidirectional space-time coding has been proposed recently for massive multiple-input multiple-output (MIMO) systems to broadcast common information. In these systems, signals across all transmit antennas have constant power and their discrete Fourier transforms have constant power as well, where the number of discrete frequencies is the number of transmit antennas. When the number of transmit antennas is large, i.e., it is a massive MIMO system, signals received at these discrete angles have constant mean power at any instant time. Furthermore, spatial diversity can be achieved. In this letter, we propose a different design of such a transmission, where the sum of received signal powers in a few consecutive time slots is constant at any angle (not just discrete angles). The other two properties mentioned above, namely, constant transmission power across antennas at any instant time and achieving spatial diversity, are still maintained. Furthermore, it has the fast symbol-wise maximum-likelihood decoding.