Trade-Offs of Spatial Gain for QoS-Guaranteed Services in the MIMO Broadcast Channels

Although the capacity of multiple-input multiple output (MIMO) broadcast channels (BCs) can be achieved by dirty-paper coding (DPC), it is difficult to apply the results directly to practical quality-of-service (QoS)-guaranteed multiuser wireless systems. In this paper, we propose a new multiuser scheduling algorithm which exploits spatial gain of MIMO techniques for QoS-guaranteed services and analyze its performance with several MIMO preceding techniques. We assume that there are real-time (RT) users and best effort (BE) users in the MIMO BC. Numerical results demonstrate that the average delay of RT users can be guaranteed within certain delay thresholds by trading off spatial multiplexing for different user classes. Nonlinear Tomlinson-Harashima precoding (THP) is more robust to different types of user selection algorithms and shows better performance than linear zero-forcing beamforming (ZFBF) both in delay and throughput performance.