Antenna selection based user scheduling for downlink of multiuser MIMO systems

Future wireless communication systems are required to support extreme high-speed packet data transmission. MIMO system and channel-aware scheduling are announced to be two promising technologies to achieve this target for PHY layer and MAC layer, respectively. However, recent research results showed that an improper synergy of these two technologies induces a destructive consequence. In order to overcome this drawback, a cross layer joint design for downlink of multiuser MIMO system is proposed here. In particular, we aim to solve the problem with following assumptions: a) number of receive antenna n_R at each mobile station (MS) is smaller than number of transmit antenna n_T at base station (RS). b) there is no perfect but partial channel state information (CSI) available at BS side. Under these assumptions, it is infeasible for each MS to build an interference-free channel for each transmit antenna so that the method in R.W. Heath et al (2001) can not be used. This paper starts with an investigation of impact of scheduling on LAST-based MIMO system and point out that redundant transmit antennas have an adverse effect. Based on this finding, a transmit antenna selection based user scheduling method is proposed. The key point is that the scheduled user should be allocated a set of transmit antennas whose number is no more than the number of its receive antennas. Furthermore, When n_T is extremely larger than n_R, we come up with an adaptive multiple user scheduling by assign the unselected transmit antennas to other users. Simulation results show that, compared with existing x-number multiple user scheduling schemes, our adaptive method can provide around 10% capacity enhancement.