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An Enhanced EDD QoS Scheduler for IEEE
802.11e WLAN
Dong-Yul Lee, Sung-Ryun Kim, and Chae-Woo Lee
School of Electrical and Computer Engineering, Ajou University
San 5 Wonchon-dong Yeongtong-gu, Suwon, Korea
{ dreamhunting,srkim,cwlee }
Abstract. The IEEE 802.11e standard was proposed to guarantee QoS
in the MAC layer. It uses new HCF(Hybrid Coordination Function) pro-
tocol, which is composed of two access functions: A distributed
contention-based channel access function(EDCA) providing prioritized
QoS and a centralized polling-based channel access function(HCCA) pro-
viding parameterized QoS. In this paper, we propose a new scheduling
algorithm to improve the performance of HCCA. The proposed scheduler
guarantees QoS by changing suitably service intervals and transmission
opportunities. The service schedule is based not only on the TSPEC pa-
rameters of a flow but also on the trac queueing. Simulation results
show that the proposed scheduling algorithm is superior to the reference
scheduler and SETT-EDD scheduler in terms of throughput, end-to-end
delay and jitter.
In recent years, with increasing demands of real-time multimedia service, a lot of
attention has been given to quality of service(QoS) support in wireless networks.
To maintain QoS of multimedia services we need to control packet loss, delay
and jitter. But it is dicult to guarantee QoS especially when the network is
overloaded since traditional wireless LANs provide a best effort service only [1].
In order to guarantee the QoS for IEEE 802.11 WLAN, the IEEE 802.11
Task Group has proposed a new protocol IEEE 802.11e [2]. In IEEE 802.11e, to
provide QoS a new MAC control mechanism called HCF(Hybrid Coordination
Function) is defined, which replaces the role of DCF(Distributed Coordination
Function) and PCF(Point Coordination Function) in 802.11. HCF is composed of
EDCA(Enhanced Distributed Channel Access) which controls the channel access
in contention period and HCCA(HCF Controlled Channel Access) which controls
the channel access in non-contention period. HCF is backward compatible with
the legacy WLAN MAC.
While PCF operates only in CP(Contention Period), HCCA of HCF operates
in CFP(Contention Free Period) as well as CP. In PCF, AP(Access Point) does
This work was supported by the new faculty research fund of Ajou University.
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