Adaptive fair channel allocation for QoS enhancement in IEEE 802.11 wireless LANs

The emerging widespread use of real-time multimedia applications over wireless networks makes the support of quality of service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 wireless ad-hoc networks. First, we review limitations of the upcoming IEEE 802.11e enhanced DCF (EDCF) and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad-hoc networks. Then, we describe a new scheme called adaptive fair EDCF that extends EDCF, by increasing the contention window during deferring periods when the channel is busy, and by using an adaptive fast backoff mechanism when the channel is idle. Our scheme computes an adaptive backoff threshold for each priority level by taking into account the channel load. The new scheme significantly improves the quality of multimedia applications. Moreover, it increases the overall throughput obtained both in medium and high load cases. Simulution results show that our new scheme outperforms EDCF and other enhanced schemes. Finally, we show that the adaptive fair EDCF scheme achieves a high degree of fairness among applications of the same priority level

WLAN performance evaluation in different wireless access techniques (DCF, PCF, HCF)

IEEE 802.11x Wireless Local-Area-Network (WLAN) considered a powerful solution for the last mile wireless broadband(BB) access. WLAN becomes important element in 4G and 5G mobile networks because it can provide services to mobile users in areas not covered by eNBs. However, the 802.11 legacy protocol doesn’t support delay-sensitive services like VoIP because it adopts the best-effort method. In 2001 IEEE 802.11e standard was proposed to deploy QoS with new access techniques introduction. There are many parameters related to MAC layer which affect the WLAN network performance from the prospective of delay, and throughput. This study presents performance evaluation of voice traffic and FTP traffic in IEEE802.11 legacy protocol WLAN and IEEE802.11e WLAN via OPNET computer simulation. Network performance will be tested against different MAC access protocols and different MAC parameters

Analisis Perbandingan Antara Skema Adaptive Enhanced Distributed Coordination Function(AEDCF) dengan Skema Seasonal Enhanced Distributed Coordination Function(SEDCF) pada IEEE 802.11e Wireless LAN

ABSTRAKSI: Pada Tugas Akhir ini, dibahas mengenai Quality of Service (QoS) pada jaringan wireless LAN. Mode arsitektur wireless yang digunakan adalah mode adhoc. Pada standard IEEE 802.11e sudah mendukung QoS dengan menggunakan skema EDCF. Namun EDCF masih belum optimal dalam menjaga kualitas layanannya, terutama pada saat kondisi jaringan yang mulai padat. Oleh karena itu, terdapat skema AEDCF dan SEDCF yang memperbaiki kekurangan EDCF. Setelah dilakukan simulasi ternyata memang AEDCF dan SEDCF terbukti memiliki performansi yang jauh lebih baik dari EDCF. Tetapi diantara skema AEDCF dan SEDCF, skema SEDCF menampilkan performansi yang lebih baik, terutama pada AC dengan prioritas rendah. Hal ini dikarenakan perhitungan Contention Window(CW) pada SEDCF menggunakan metode seasonal forecasting.Kata Kunci : wireless, adhoc, EDCF, AEDCF, SEDCF.ABSTRACT: This final assignment discussed about Quality of Service (Qos) in wireless LAN. The wireless architecture that is used is an ad hoc mode. Actually, IEEE 802.11e standard has support QoS by using EDCF scheme. But, EDCF still not optimal in maintaining the quality of its service, especially when the network is in high load. Therefore, two schemes are proposed to improve the lack of EDCF. After simulations, AEDCF and SEDCF show better performance than EDCF. And between AEDCF and SEDCF, SEDCF scheme shows better performance, especially in low priority AC. This is because SEDCF uses seasonal forecasting method in calculating Contention Window (CW).Keyword: wireless, adhoc, EDCF, AEDCF, SEDC

A Novel Method of Serving Multimedia and Background Traffic in Wireless LANs.

Wireless local area networks (LANs) require the efficient integration of multimedia and traditional data traffic. This paper proposes the priority-oriented adaptive polling (POAP) protocol that could be used in place of the enhanced distributed channel access (EDCA) part of the IEEE 802.11e access scheme. EDCA seems capable of differentiating traffic; however, it exhibits great overhead that limits the available bandwidth and degrades performance. POAP is collision free, prioritizes the different kinds of traffic, and is able to provide quality of service (QoS) for all types of multimedia network applications while efficiently supporting background data traffic. POAP, compared to EDCA, provides higher channel utilization, distributes resources to the stations adapting to their real needs, and generally exhibits superior performance

A fair access mechanism based on TXOP in IEEE 802.11e wireless networks

IEEE 802.11e is an extension of IEEE 802.11 that provides Quality of Service (QoS) for the applications with different service requirements. This standard makes use of several parameters such as contention window; inter frame space time and transmission opportunity to create service differentiation in the network. Transmission opportunity (TXOP), that is the focus point of this paper, is the time interval, during which a station is allowed to transmit packets without any contention. As the fixed amounts of TXOPs are allocated to different stations, unfairness appears in the network. And when users with different data rates exist, IEEE 802.11e WLANs face the lack of fairness in the network. Because the higher data rate stations transfer more data than the lower rate ones. Several mechanisms have been proposed to solve this problem by generating new TXOPs adaptive to the network's traffic condition. In this paper, some proposed mechanisms are evaluated and according to their evaluated strengths and weaknesses, a new mechanism is proposed for TXOP determination in IEEE 802.11e wireless networks. Our new algorithm considers data rate, channel error rate and data packet lengths to calculate adaptive TXOPs for the stations. The simulation results show that the proposed algorithm leads to better fairness and also higher throughput and lower delays in the network.

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