2168-6750 (c) 2015 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TETC.2015.2432745, IEEE Transactions on Emerging Topics in Computing JOURNAL OF L A T E X CLASS FILES, VOL. 13, NO. 9, SEPTEMBER 2014 1 A Pragmatic VBR Stream Scheduling Policy for IEEE 802.11e HCCA Access Method Che-Yu Chang, Hsu-Chun Yen, Abderrahim Benslimane, Der-Jiunn Deng Abstract—Nowadays, transferring variable bit rate (VBR) video streaming on mobile devices is getting popular and necessary. Such traffic streams usually have stringent transferring requirements and in many cases they should be indeed delivered as they were generated. Hence, the IEEE 802.11e HCCA (HCF Controlled Channel Access) access method was proposed to provide better QoS (quality-of-service) requirements for real-time traffic in the wireless network. However, the reference scheduler of HCCA offered in the standard of IEEE 802.11e is insufficient for VBR video stream since it only considers a few characteristics. Hence, choosing the right parameters to meet the QoS requirements of VBR stream remains an unsolved and opened issue. In this paper, we propose a pragmatic packet scheduling policy for VBR stream and try to enhance the transmission efficiency for IEEE 802.11e HCCA access method. The proposed scheduler considers not only traffic characteristics, but also the queue state and the real-time information of the packet. An efficiency analysis is provided to evaluate the transmission efficiency of the proposed scheduler. The result shows that our method can reach higher transmission efficiency than the reference scheduler. Simulations on the transmission of VBR video stream are also performed to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a better performance than the reference and other well-known schedulers. Index Terms—IEEE 802.11e, QoS, HCCA, VBR, Wireless LAN backoff, BER. ✦ 1 I NTRODUCTION T HE last few years we have witnessed an explosive growth in the applications of the wireless network. These applications, especially the multimedia applications [1] [2] [3] seem to be announced daily. In terms of the mul- timedia transmission, the transmitted data can be classified into two kinds of the traffic stream namely Constant Bit Rate (CBR) traffic and Variable Bit Rate (VBR) traffic. In CBR, the data of a traffic stream will be generated with constant interval and constant data size. The widely used voice service, Voice Over IP (VOIP) [4] with G.711 or G.729 can be considered as CBR stream. In VBR, three kinds of stream can be seen as VBR one, as shown in Fig.1, that are data gener- ated with 1) constant data size and variable interval (CSVI), 2) variable data size and constant interval (VSCI) and , and 3) variable data size and variable interval (VSVI). For trans- mitting video over the internet, the compression techniques such as MPEG4, H.263 and H.264 [5] are used to rescale the video size. According to the compression technique, the compressed video will be formed as different kinds of VBR. On the other hand, most multimedia applications such as voice communication, video conference, and live multimedia content also consider the real-time degree since it affects the user experience. In video application, a higher • C.Y. Chang is with the Department of Electrical Engineering, National Taiwan University, Taiwan. E-mail: D99921030@ntu.edu.tw • H. C. Yen is with the Department of Electrical Engineering, National Tai- wan University, Taiwan. E-mail: hcyen@ntu.edu.tw • A. Benslimane is with the Laboratoire Informatique d’Avignon, Universite d’Avignon, 84914 Avignon Ce’dex 9, France • D.J. Deng is with the Department of Computer Science and Infor- mation Engineering, National Changhua University of Education, Tai- wan. D.J. Deng is the corresponding author of this paper. E-mail: dj- deng@cc.ncue.edu.tw real-time degree causes the higher quality of presentation while, in the voice application, a higher one causes clear and smooth communication. In order to attach this goal, Qual- ity of Service (QoS) should be considered in multimedia transmission. Providing guaranteed QoS in a wired network is so far robust and reliable, but it suffers big challenge in a wireless network. The legacy wireless standard IEEE 802.11 [6], which is designed for best effort service has been proposed for several years. A station of IEEE 802.11 uses the channel access method called Distributed Coordination Function (DCF) based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to perform data transmis- sion. The DCF has the advantages of easy implement and scalable; however, it is hard to handle the real-time services due to the property of random access, much less providing guaranteed QoS. 1.1 IEEE 802.11e To overcome this problem, IEEE Task Group E (TGe) defined a QoS-oriented specification amendment referred to IEEE 802.11e [7]. The significant change is that the IEEE 802.11e introduces Transmission Opportunity (TXOP) as the unit of one-time transmission rather than the number of packets. A station gains a TXOP when it obtains the channel resource. A TXOP is defined as a time duration that is used for data transmission. Following this, the transmission time can be accurately handled, and at the same time, the station can transmit more than one packet within a TXOP. Based on the feature, IEEE 802.11e provides an additional function called Hybrid Coordination Function (HCF). HCF contains two access mechanisms namely Enhanced Distributed Chan- nel Access (EDCA) and HCF Controlled Channel Access (HCCA).