RED-TXOP scheme for video transmission in IEEE802.11E EDCA WLAN

With the growth of multimedia services in today's IEEE 802.11 WLAN, the new standard IEEE 802.11e is presented to support QoS in WLAN. A concept called transmission opportunity (TXOP) has been proposed in 802.11e to limit the maximum time duration (named TXOPlimit) that a station can be allowed to retain the channel after winning a contention or receiving a QoS-poll from the AP (Access Point). Multiple frames can be transmitted within one acquired TXOP without any additional contention or QoS-poll as long as the total transmission time does not exceed the TXOPlimit duration. Unfortunately, the adoption of a unique value for its TXOPlimit for all stations, included the AP, results in an unfair behavior that provokes an unbalance between uplink and downlink throughputs and consequent QoS degradation. We propose an algorithm, Random Early Detection TXOP (RED-TXOP) for dynamical tuning the TXOPlimit, in order to dynamically change its channel resources according to the current traffic conditions. Extensive simulations show that the proposed algorithm allows to enhance significantly QoS performance of multimedia traffic and to increase the global WLAN throughput.