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The 802.11e EDCA can deliver quality of service for video transmission over wireless networks during traffic congestions based on the techniques of multiple access category (AC) queues and virtual collision, but its performance is limited by the first-in-first-out (FIFO) characteristic of the reserved AC_VI queue. In order to offer further service differentiation among video packets based on their video frame importance and achieve more enhancement on video transmission quality, this paper proposes a novel probabilistic packet mapping algorithm called Piecewise Mapping. Depending on the congestion level of AC_VI, the proposed algorithm can actively manage AC_VI by proposing four downward transition phases to decide the mapping probabilities among AC_VI and the lower-priority ACs. The four phases include zero transition phase in light congestion, full transition phase in heavy congestion, and two proportional transition phases in medium congestion between the low and high thresholds of the AC_VI queue length. The downward mapping between the two lower ACs is decided by which queue length is shorter. Our results show that the proposed Piecewise Mapping algorithm outperforms the existing works, including EDCA and Adaptive Mapping. Under various congestion levels, the gains can be as high as 4.84 dB and 4.33 dB respectively.
Date of Conference: Nov. 30 2011-Dec. 2 2011