Research On Scheduling Algorithms In Multi-User Mimo Wireless Downlink System

Multiple-Input Multiple-Output (MIMO) technology can improve wireless communication system's capacity and reliability without increasing bandwidth. It also provides rich diversity gains, multiplexing gains and array gains. So, it is considered as one of the key technologies in future mobile communication systems.The object of scheduling algorithm in wireless communication downlink system is to allocate resource fairly among users and to improve system capacity by achieving multi-user gain. Traditional scheduling methods for single antenna downlink can only choose one user each time. With MIMO technique, more users can be chosen each time, which brings scheduling algorithm a new perspective.As measure standards of scheduling algorithm such as system capacity and fairness between users, feedback of channel information is also a key factor. Less feedback ratio can help to reduce feedback uplink's band requirement and base station's burden. An effective scheduling algorithm in a practical system should make a balance between system performance and feedback ratio.In this paper, with inspection of several beamforming scheduling algorithms, three scheduling algorithms are proposed: Proportional Fair Threshold Scheduling algorithm at receiver, MAX Scheduling algorithm at receiver and Proportional Fair MAX Scheduling algorithm at receiver. Simulation shows that these three methods can reduce feedback ratio without losing much system performance, and they also have their own characteristics and applicability. Proportional Fair Threshold Scheduling algorithm at receiver has less feedback ratio with more mobile users in a cell; so it is applicable to a cell where there are many users. MAX Scheduling algorithm at receiver and Proportional Fair MAX Scheduling algorithm at receiver simplify receiver, and they can keep system performance when there are many users in a cell and can reduce feedback ratio with more sub channels; so they are applicable to a cell where there are many users and many sub channels.