Distributed Queueing Collision Avoidance (DQCA) is an efficient MAC protocol designed for infrastructure Wireless LANs. In this chapter, a thorough description of the protocol is given, along with a set of protocol rules and an example of its operation. In continuation, four algorithms are proposed that alter the FIFO scheduling order of DQCA in order to meet specific network requirements. The proposed schemes combine the efficiency of opportunistic scheduling with the QoS provisioning through service differentiation. The opportunistic policy encourages transmissions at higher rates when the channel condition is good and is implemented through a cross-layer dialogue between the PHY and the MAC layers. The key idea of service differentiation is to assign priorities to traffic flows with different requirements in order to provide QoS guarantees. The throughput, delay and jitter performance of the proposed schemes have been evaluated through simulations for a scenario with heterogeneous traffic of voice, video, best-effort and background data traffic flows.
A cellular wireless local area network with QoS guarantees for heterogeneous traffic