An Efficient Cross-Layer Scheduler for Multimedia Traffic in Wireless Local Area Networks with IEEE 802.11e HCCA

This paper proposes a scheduling algorithm, namely Wireless Timed Token Protocol (WTTP), for the Hybrid Coordination Function (HCF) Controlled Channel Access (HCCA) in IEEE 802.11e. WTTP provides traffic streams with a minimum reserved rate, as required by the standard, and it accounts for two types of traffic streams simultaneously, depending on the corresponding application: constant bit rate, which are served according to their rate, and variable bit rate traffic streams. The latter are guaranteed a minimum rate, but they are also allowed to exploit unused bandwidth, which preserves small access delays in case of bursty arrivals. Additionally, WTTP shares the capacity which is not reserved for QoS traffic streams transmissions among traffic flows with no specific QoS requirements. We also propose a strategy for the QoS Access Point to infer the idle/busy status of the uplink transmission buffers, based on cross layer information made available at the MAC by the application layer, which allows channel capacity to be saved. WTTP exhibits O(1) per packet computational complexity. We evaluate the performance of WTTP via simulation under different traffic conditions, and we investigate its resilience to variations of different system parameters.