A Differentiated Cooperative MAC for QoS enhancement in Wireless LANs

The quality of service (QoS) support in wireless local area networks (WLANs) faces a big challenge due to time-correlated fading channel. Conventional automatic repeat reQuest (ARQ) schemes based on time diversity may result in consecutive retransmission failures degrading QoS severely. This paper proposes a novel Differentiated cooperative medium access control (MAC) protocol, called DC-MAC, to enhance QoS in WLANs based on the IEEE 802.11e architecture. The retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source to exploit spatial diversity. A novel negative acknowledgement (NAK) feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Simulations conducted on the OPNET platform show that the proposed scheme significantly improves the performances of both multimedia applications and data applications in terms of throughput and delay while supporting service differentiation.