297 research outputs found
Providing Dynamic TXOP for QoS Support of Video Transmission in IEEE 802.11e WLANs
The IEEE 802.11e standard introduced by IEEE 802.11 Task Group E (TGe)
enhances the Quality of Service (QoS) by means of HCF Controlled Channel Access
(HCCA). The scheduler of HCCA allocates Transmission Opportunities (TXOPs) to
QoS-enabled Station (QSTA) based on their TS Specifications (TSPECs) negotiated
at the traffic setup time so that it is only efficient for Constant Bit Rate
(CBR) applications. However, Variable Bit Rate (VBR) traffics are not
efficiently supported as they exhibit nondeterministic profile during the time.
In this paper, we present a dynamic TXOP assignment Scheduling Algorithm for
supporting the video traffics transmission over IEEE 802.11e wireless networks.
This algorithm uses a piggybacked information about the size of the subsequent
video frames of the uplink traffic to assist the Hybrid Coordinator accurately
assign the TXOP according to the fast changes in the VBR profile. The proposed
scheduling algorithm has been evaluated using simulation with different
variability level video streams. The simulation results show that the proposed
algorithm 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 transmission.Comment: arXiv admin note: substantial text overlap with arXiv:1602.0369
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FHCF: A simple and efficient scheduling scheme for IEEE 802.11e wireless networks
The IEEE 802.11e medium access control (MAC) layer protocol is an emerging standard to support quality of service (QoS) in 802.11 wireless networks. Some recent works show that the 802.11e hybrid coordination function (HCF) can improve signi¯cantly the QoS support in 802.11 networks. A simple HCF referenced scheduler has been proposed in the 802.11e which takes into account the QoS requirements of °ows and allocates time to stations on the basis of the mean sending rate. As we show in this paper, this HCF referenced scheduling algorithm is only e±cient and works well for °ows with strict constant bit rate (CBR) characteristics. However, a lot of real-time applications, such as videoconferencing, have some variations in their packet sizes, sending rates or even have variable bit rate (VBR) characteristics. In this paper we propose FHCF, a simple and e±cient scheduling algorithm for 802.11e that aims to be fair for both CBR and VBR °ows. FHCF uses queue length estimations to tune its time allocation to mobile stations. We present analytical model evaluations and a set of simulations results, and provide performance comparisons with the 802.11e HCF referenced scheduler. Our performance study indicates that FHCF provides good fairness while supporting bandwidth and delay requirements for a large range of network loads
A Greedy Reclaiming Scheduler for IEEE 802.11e HCCA Real-Time Networks
The IEEE 802.11e standard introduces Quality of Service (QoS)
support for wireless local area networks and suggests how to design a tailored HCF Controlled Channel Access (HCCA) scheduler.
However the reference scheduling algorithm is suitable to assure
service guarantees only for Constant Bit Rate traffic streams,
whereas shows its limits for Variable Bit Rate traffic. Despite the
numerous alternative schedulers proposed to improve the QoS support for multimedia applications, in the case of VBR traffic satisfactory real-time performance has not been yet achieved.
This paper presents a new scheduling algorithm, Unused Time
Shifting Scheduler (UTSS). It integrates a mechanism for bandwidth reclaiming into a HCCA real-time scheduler. UTSS assigns the unused portion of each transmission opportunity to the next scheduled traffic stream. Thanks to such feature, traffic variability is absorbed, reducing the waste of resources. The analytical evaluation, corroborated by the simulation results, shows that UTSS is suitable to reduce the delay experienced by VBR traffic streams and to increase the maximum burstiness sustainable by the network
Priority-Oriented Adaptive Control With QoS Guarantee for Wireless LANs.
In today’s wireless networks there is a great need
for QoS, because of the time-bounded voice, audio and video
traffic. A new QoS enhanced standard is being standardized by
the IEEE 802.11e workgroup. It uses a contention free access
mechanism called Hybrid Control Channel Access (HCCA) to
guarantee QoS. However, HCCA is not efficient for all types of
time-bounded traffic. This work proposes an alternative protocol
which could be adapted in HCF (Hybrid Coordination Function).
The Priority Oriented Adaptive Control with QoS Guarantee
(POAC-QG) is a complete centralized channel access mechanism,
it is able to guarantee QoS for all types of multimedia network
applications, it enhances the parameterized traffic with priorities,
and it supports time division access using slots. Furthermore, it
instantly negotiates the quality levels of the traffic streams
according to their priorities, supporting multiple streams to the
best quality it can achieve. POAC-QG compared to HCCA,
provides higher channel utilization, adapts better to the
characteristics of the different traffic types, differentiates the
traffic streams more efficiently using priorities, and generally
exhibits superior performance
Dynamic TXOP HCCA reclaiming scheduler with transmission time estimation for IEEE 802.11e real-time networks
IEEE 802.11e HCCA reference scheduler guarantees Quality of
Service only for Constant Bit Rate traffic streams, whereas its as-
signment of scheduling parameters (transmission time TXOP and
polling period) is too rigid to serve Variable Bit Rate (VBR) traffic.
This paper presents a new scheduling algorithm, Dynamic TXOP
HCCA (DTH). Its scheduling scheme, integrated with the central-
ized scheduler, uses both a statistical estimation of needed trans-
mission duration and a bandwidth reclaiming mechanism with the
aim of improving the resource management and providing an in-
stantaneous dynamic Transmission Opportunity (TXOP), tailored
to multimedia applications with variable bit rate. Performance evaluation through simulation, confirmed by the scheduling analysis, shows that DTH is suitable to reduce the transmission queues length.
This positively impacts on the delay and on packets drop rate experienced by VBR traffic streams
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