  Quality of Service (QoS) is provided in IEEE 802.11e protocol by means of HCF
Controlled Channel Access (HCCA) scheduler which is efficient for supporting
Constant Bit Rate (CBR) applications. Numerous researches have been carried out
to enhance the HCCA scheduler attempting to accommodate the needs of Variable
Bit Rate (VBR) video traffics which probably demonstrates a non-deterministic
profile during the time. This paper presents an adaptive TXOP assignment
mechanism for supporting the transmission of the prerecorded video traffics
over IEEE 802.11e wireless networks. The proposed mechanism uses a feedback
about the size of the subsequent video frames of the uplink traffic to assist
the Hybrid Coordinator (HC) accurately assign TXOP according to the fast
changes in the VBR profile. The simulation results show that our mechanism
reduces the delay experienced by VBR traffic streams comparable to HCCA
scheduler due to the accurate assignment of the TXOP which preserve the channel
time for data transmission.
