Scheduling Technologies In MU-MIMO System

For serving multiple users, Multi-user MIMO system can obtain multi-user diversity gain and thereby improve the quality and rate of the system, which benefit capacity of system. When there are a large number of users, the system has to eliminate multi-user interference, resulting in fewer users to be scheduled. How to select users is a problem worth studying. Fast and efficient scheduling techniques attract researcher.This paper is studying user scheduling algorithms in multiuser MIMO systems and the work of this paper mainly focuses on three questions.Firstly, the paper studies scheduling algorithm for the scenario of users equipped with single-antenna, which is based on Zero-Forcing BeamForming(ZFBF) precoding techniques.Then this paper proposes an adaptive user scheduling algorithm(AUS) and improves the space semi-orthogonal user scheduling algorithm(S-SUS). According to the number of antennas and number of candidate users, AUS can control threshold parameter adaptively and make a reasonable compromise between multi-user diversity and equivalent channel gain. Meanwhile, the improved S-SUS reduces complexity of S-SUS. The simulation results show that AUS greatly reduces floating-point operations, and the throughput of AUS algorithm is almost same of the optimal semi-orthogonal user scheduling algorithm(SUS), and the floating-point operations of improved S-SUS algorithm is evidently less than those of the S-SUS algorithm.Secondly, the paper studies scheduling algorithm for the scenario of users equipped with multi-antenna, which is based on high-complexity Block Diagonalization(BD) precoding techniques. Then this paper proposes an iterative scheduling algorithm based on norm. The proposed algorithm used low-complexity iterative BD precoding algorithm instead of the traditional BD precoding algorithm. In addition, the proposed algorithm adopted a novel user scheduling guidelines which derived from an upper bound of capacity. Simulation results show that the throughput of the proposed algorithm is higher than that of volume-based scheduling algorithm and norm-based scheduling algorithm, but the proposed algorithm has a lower complexity. Also, this paper takes fairness among users into account when studying the scheduling algorithms, and applies the proportional fairness scheme to scheduling algorithms.Finally, this paper researches on channel quality information(CQI) and channel direction information(CDI) of the limited feedback system, then improves both SUS algorithm and volume-based scheduling algorithm. The modified algorithms can schedule users just relying on CQI and CDI. The simulation results show that the modified algorithms can reach larger sum rates of system, when treating the signal to interference noise ratio as the feedback CQI.