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IEEE 802.11e wireless local area networks specify the hybrid coordination function (HCF) controlled channel access (HCCA) method, which includes reference scheduling and an admission control. In the HCCA scheduler, channel interference, bursty traffic streaming and packet loss cause insufficiency in the strict periodic transmission opportunity (TXOP) allocation scheme. It provides quality of service by using the most severe delay requirement and thus over allocating the bandwidth. In order to overcome the disadvantages of HCCA, this study proposes an enhanced HCCA-based adaptive scheduler for delay sensitive traffic. In the proposed scheme, the sender includes the tolerable loss limit along with the traffic specification to estimate the packet loss rate. To estimate the queue size at the end of the previous TXOP, the proposed scheme first calculates the bit error rate based on the specified channel conditions. The mean application data rate for the next TXOP is evaluated. Expected delay and the per hop maximum delay are computed. The rest of per hop delay is calculated based on the remaining delay and the remaining hops of a packet. Then, the queued packets are checked for the required bandwidth and scheduled, so that the probability for transferring the delayed packets can be increased.
Date of Publication: December 2012