Greedy Scheduling of MIMO OFDMA: TDMA, FDMA/TDMA, or SDMA/FDMA/TDMA

In multiuser MIMO system, multiuser multiplexing and diversity gain can be achieved by spatial scheduling. However, the limited battery life and terminal size of the User Equipment (UE) in a cellular system put a constraint on MIMO when the tranmitter has more antenna than the receiver in downlink, the conventional MIMO schemes can only exploit partial multiplexing gain and diversity gain. In a multiuser MIMO OFDMA system, multiuser diversity gain can be achieved by exploiting the independent frequency and spatial selective fading one another by joint spatial and frequency scheduling. In this paper, different multiuser multiple access schemes with greedy scheduling of MIMO OFDMA are investigated, e.g. TDMA, FDMA/TDMA and SDMA/FDMA/TDMA. For full spatial-frequency multiuser diversity gain and spatial multiplexing gain can be achieved, SDMA/FDMA/TDMA obtains highest spectrum efficiency. Its gain exceeds that of TDMA and FDMA/TDMA at least 80% and 40% respectively. The more antennas configured, the more gain can be observed from SDMA/FDMA/TDMA.