A Two-Stage QoS Aware Scheduler for Wireless LANs Based on MIMO-OFDMA-SDMA Transmission

In this paper, a QoS-aware cross-layer scheduler for wireless LANs is introduced which can handle parallelised transmissions which are provided by OFDMA or SDMA. The scheduler includes two stages: in the hardware-independent stage, data flows are selected according to their QoS requirements such as throughput and delay. In the hardware-dependent stage, the channel resources are adaptively allocated to the flows according to the user priorities. All flows with a sufficiently high channel capacity are transmitted in parallel by assigning different OFDMA subcarriers or different spatial subchannels to the users. It is shown that the proposed QoS aware scheduler efficiently uses the channel resources in case of TDMA, OFDMA or SDMA and meets the quality-of-service requirements of time-critical flows under varying load and channel conditions.