Abstract—The IEEE 802.11e which is an enhanced version of the 802.11 WLAN standards incorporates the Quality of Service (QoS) which makes it a better choice for multimedia and real time applications. In this paper we study various aspects concerned with 802.11e standard. Further, the analysis results for this standard are compared with the legacy 802.11 standard. Simulation results show that IEEE 802.11e out performs legacy IEEE 802.11 in terms of quality of service due to its flow differentiated channel allocation and better queue management architecture. We also propose a method to improve the unfair allocation of bandwidth for downlink and uplink channels by varying the medium access priority level. Keywords—Wireless; IEEE 802.11e; EDCA; Throughput; QoS; MAC. I. INTRODUCTION EEE 802.11 wireless LAN (WLAN) is becoming one of the most deployed wireless technologies all over the world and is likely to play a major role in next-generation wireless communication networks [1]. The possibility of WLAN’s coexistence with 3 rd and 4 th generation cellular networks [2] makes it more vital for up gradation and improvement. The main characteristics of the 802.11 WLAN technologies are simplicity, flexibility and cost effectiveness. This technology provides people with a ubiquitous communication and computing environment in various places. Further, since multimedia applications have experienced an explosive growth, end users require high speed video, voice and Web services. However, multimedia applications require QoS in terms of guaranteed throughput, minimum delay and low packet loss. Guaranteeing these QoS requirements in 802.11 WLAN is very challenging and substantial amount of work has been done to ensure QoS and higher data rates in WLAN environment [3-5]. IEEE 802.11e [6] and IEEE 802.11n [7] standards are introduced for enabling QoS and for improving data rate requirements respectively. In this paper we focus upon the simulation based results to make an analysis on the QoS issue for both these standards. The paper is organized as follows: the second section gives an overview of IEEE 802.11 legacy WLAN standard while Ammar Abbas 1 and Ibrahim M. Hussain 2 are with the Department of Computer Engineering, Sir Syed University of Engineering and Technology, Karachi 75300-Pakistan. phone: 092-21-4988000-284; fax: 092-21-4982393; e-mail: ammarabbas@gmail.com (1) , hmmiharbi@yahoo.com (2) . Osama M. Hussain is with the Communication & Information Research Center (CIRC) - Sultan Qaboos University, Muscat-Oman. e-mail: osama.mhussain@gmail.com details about IEEE 802.11e standard are presented in section 3. The simulation tools and the simulation environment being used are discussed in section 4. The analysis of these results is provided in section 5. Further, fairness analysis of uplink and downlink throughput in IEEE 802.11e is given in section 6 along with a proposed method to improve such fairness throughput. Finally we make conclusions on these results in section 7. II. AN OVERVIEW OF IEEE 802.11 LEGACY STANDARD An IEEE 802.11 LAN (Local Area Network) is based on a cellular architecture where each cell is called Basic Service Set (BSS). These cells are controlled by a base station called Access Points (APs). The interconnection of these wireless LANs is called Extended Service Set (ESS). Three different physical layers are provided for possible implementation [8]. One is based on Infrared (IR) communications, and the other two are frequency-Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS) techniques. Legacy IEEE 802.11 MAC has two types of medium access methods [9]. The first one is used during contention free period called Point Coordination Function (PCF) and the other is used during contention period called Distributed Coordination Function (DCF). In this paper we confine our study to the DCF as this implementation is more widely used than PCF. DCF is a distributed medium access scheme in which every station must sense the medium before initiating a packet transmission. If the medium is found idle for a time interval longer than Distributed Inter-Frame Space (DIFS), then the station can transmit the packet, otherwise the transmission is restrained and the back off process starts. Back-off procedure is devised as such to minimize the chances of two stations ending up with the same time of sending packets. Each station computes a random time interval called Back-off time which is uniformly distributed between zero and the current Contention Window size (CW). This time slot depends on the type of physical layer being used. The back off timer is decreased only when the medium is idle but when a station starts transmitting, the timer is halted. A positive acknowledgement is used to notify the sender that the transmitted frame has been successfully received. Acknowledgement is send after the Short Inter Frame Space (SIFS) with the reception of frame. SIFS is smaller than the DIFS and hence the receiving station does not need to sense and apply back-off procedure to transmit an Fairness and Quality of Service Issues and Analysis of IEEE 802.11e Wireless LAN Ammar Abbas, Ibrahim M. Hussain and Osama M. Hussain I World Academy of Science, Engineering and Technology International Journal of Electronics and Communication Engineering Vol:4, No:1, 2010 163 International Scholarly and Scientific Research & Innovation 4(1) 2010 scholar.waset.org/1307-6892/2029 International Science Index, Electronics and Communication Engineering Vol:4, No:1, 2010 waset.org/Publication/2029