Abstract—State of the art wireless networking solutions are expected to efficiently support time-bounded traffic, while serving legacy data transmissions. The dominant relevant approach at the Medium Access Control (MAC) layer is the IEEE Enhanced Distributed Channel Access (EDCA) protocol. EDCA achieves traffic differentiation to some degree, however, its distributed nature raises grate limitations. This work introduces a general purpose access mechanism, specialized to operate inside a wireless cell and capable of providing deterministic QoS support, while demanding no resource reservation. The proposed Adaptive Weighted and Prioritized Polling (AWPP) protocol succeeds to differentiate traffic in a predictable and proportional manner, achieve high channel utilization, and provide fairness in resource allocation. AWPP is shown to outperform EDCA. Index Terms— adaptive polling, medium access control in WLANs, QoS in wireless networks, traffic differentiation I. INTRODUCTION HE current wireless networking area is characterized by correlated evolution. Specifically, we witness the wide spread of wireless local area networks, while their features and performance improve, which improvement is related with the increasing demands of the network users and the requirement for effective traffic differentiation in order to simultaneously support multimedia traffic. There are significant advancements in the domain of physical transmission, which now allow relatively high bit rates. A modern key objective is to exploit the available wireless resources in order to satisfy the increasing requirements of the latest multimedia network applications within a general purpose wireless LAN. Thus, efficient medium access control is needed, which would be able to provide complete QoS in a manner that would make possible to estimate in advance the expected resources a prioritized traffic flow will be provided. At this time, the solution which is expected to dominate the market is coming from the IEEE in the form of the 802.11e standard [1]. The main element of the standardized Hybrid Coordination Function (HCF) is the EDCA protocol. The latter is designed to retain backward compatibility with the legacy 802.11 MAC. It has been shown that EDCA suffers from Manuscript received August 2, 2009. This work was supported by the State Scholarships Foundation of Greece. T. D. Lagkas is with the Department of Informatics and Telecommunications Engineering, University of Western Macedonia, Greece. (phone: +306972866899; fax: +302310488974; e-mail: tlagkas@uowm.gr). significant constraints, which are mainly related with its low channel utilization, and result in poor QoS support. There is extensive research work on improving QoS support in wireless LANs via medium access control. Some approaches propose new schemes [2]-[5], whereas others target on optimizing existing standardized algorithms [6]-[8]. The objective of this paper is to introduce a novel resource distribution mechanism for centralized wireless networks, which does not demand resource requests and it is able to provide predictable QoS to mixed type network traffic. The presented AWPP protocol adopts the frame structure and the basic polling scheme of the efficient Priority Oriented Adaptive Polling (POAP) protocol and it introduces a deterministic traffic differentiation engine that operates proportionally to priorities and data rate. It should be mentioned that while EDCA is a distributed protocol, it is also considered to function under the most common centralized topology based on an Access Point (AP) for packet relay and interconnection to the backbone network. AWPP takes advantage of the existing infrastructure by using the AP for access control. This paper assumes that stations are able to communicate directly when in range, however the model where the AP acts as a packet forwarder could be also used. According to [1], the IEEE 802.11e access model also provides a Direct Link Protocol (DLP) as an extra feature. Furthermore, notice that 802.11e also proposes that a centralized protocol, called Hybrid Control Channel Access (HCCA), could be used in parallel. However, HCCA is a different purpose scheme designed to guarantee QoS exclusively to real-time streams based on strict traffic specifications and fixed resource reservation. The rest of the paper is organized as follows. Section II presents the related work focusing on EDCA and POAP. AWPP is analyzed in Section III, where the station and packet selection algorithms are described. Section IV discusses the analytical approach and the simulation results, which reveal the effectiveness of AWPP. The paper concludes in Section V. II. RELATED WORK A. Enhanced Distributed Channel Access EDCA [1] is the basic access mechanism of the IEEE 802.11e MAC and the mandatory part of HCF. Its operation is based on the well known exponential backoff method, which Adaptive Weighted and Prioritized Polling for QoS Provision in Wireless Networks Thomas D. Lagkas, Member, IEEE T 978-1-4244-5661-1/09/$26.00 ©2009 IEEE