Performance comparison of different transmission schemes in uplink massive MIMO systems with dual-antenna users

In this paper, we consider an uplink massive MIMO systems with dual-antenna users, and investigate the performance of several popular transmission schemes, such as orthogonal space-time block coding (OSTBC), transmit beamforming (TB) and transmit antenna selection (TAS). The achievable sum rate lower bound and asymptotic power scaling performance when M →∞ are presented, where M is the number of base station antennas. The analytical findings suggest that all the mentioned schemes achieve the same power scaling law as the system with only single-antenna users, indicating a rather pessimistic conclusion that using multiple antennas at the users does not bring much performance gain. Therefore, advanced transmission schemes shall be designed to fully exploit the additional spatial degrees offered by the multiple antenna users. Through simulation, we find that user scheduling is one of such promising techniques to further improve the system performance.