OSTBC Transmission in Large MIMO Systems

We address the problem of orthogonal space-time block code (OSTBC) transmission in a large multiple-input multiple-output (MIMO) system in Rayleigh fading environment. Because there are hundreds of antennas at the transmitter, a very large dimension OSTBC is required in the case of massive MIMO system. Full rate OSTBC is available only for two transmit antenna-based system with complex symbols. Recently, an implementation of OSTBC for 32 transmit and 32 receive antennas is presented for real symbols. In this letter, we present a scheme of OSTBC transmission for practical large MIMO systems by embedding the OSTBCs of small dimensions with good rate. At the receiving end, the decoding of the OSTBCs is performed by utilizing the concept of null space. It is shown by simulation and analysis that the code rate can be improved at the cost of degraded performance; however, the performance of large MIMO system is not an issue because of the availability of very large antennas at the transmitter and receiver. The expression for the moment generating function (MGF) of the received signal-to-noise ratio at the receiver node is derived for the proposed OSTBC-based scheme. Using the MGF expression, we obtain the analytical symbol error rate for the proposed scheme with M-ary phase-shift keying modulation symbols.