Abstract—In this paper, we propose the EDCA-TM, a new architecture which tunes the enhanced distributed channel access (EDCA) for multi-hop networks. In EDCA-TM, we suggest a new module for dynamic access category adaptation (DACA) over the existing channel access mechanism such as EDCA. It processes received data packets for assigning an appropriate access categories (AC) to provide delay and rate guarantee to the QoS traffic. In addition, we adopt the earliest deadline first queuing (EDF) scheme to reschedule buffered packets in the AC queues according to their urgency for actual transmission. We have simulated our proposal in the network simulator, ns-2.31, and compared it with EDCA and APHD. Results show that our schemes outperform existing protocols and provide quality service for the traffic flows within the stated requirements. Index Terms—IEEE 802.11e, medium access control, QoS, wireless multi-hop network I. INTRODUCTION HE WLAN mesh network based on the IEEE 802.11 radio is widely becoming popular for home, community and enterprise networking etc. Due to the use of unlicensed radio spectrum and accessible off-the-shelf components, wireless networking has provided user convenience and marketability compared to wired-LANs. However, performances in terms of throughput, latency and quality of service (QoS) have been remaining as major challenges that the wireless community still faces today for its wider deployment. The present IEEE 802.11 MAC operates in two distributed modes: (i) Distributed Coordinated Access (DCA) [1] and (ii) Enhanced DCA (EDCA) that supports QoS [2]. Since these protocols are designed for a single-hop WLAN network, several design aspects of these systems have low compatibility with multi-hop wireless mesh networks. For example, physical and virtual carrier sensing mechanisms used in a single-hop WLAN network have been reported inadequate for mitigating the hidden and exposed terminal problems in multi-hop scenarios [3]. Similarly, enhancements in EDCA for supporting QoS are not capable of providing end-to-end service guarantees in multi-hop environment. This is primarily because packets are treated in a similar fashion with each intermediate node as with the source node regardless of varying conditions. In this paper, we focus on these issues and propose a multi-hop service differentiation to satisfy end-to-end requirements for multihop sessions. The dynamic AC adaptation in EDCA has been previously proposed in [4]-[6]. Lera et al [4] proposed a scheme to improve QoS and throughput in single and multi-hop WLAN through a dynamic priority assignment where traffic priorities are determined dynamically at each hop, which is distinguishable from the fixed traffic categorization in EDCA. Each node computes the average transmission delay for an ACs based on the delay incurred by transmitted packets. When a station has a frame ready for transmission, the maximum transmission delay required for that frame is compared with the average delay. The packet is expedited if the maximum delay becomes larger than the average by setting a higher priority. Li et al [5] proposed a scheme, called “Adaptive Per Hop Differentiation (APHD)” that computes a per-hop delay budget at each participating node for the packet based on end-to-end delay requirement supplied by the application. The per-hop delay budget is the amount of time a packet is allowed to spend at one node such that it can meet the total delay requirement. When a node is aware that the budget is low, it speeds up the transmission by raising the priority level of such packets over those that have higher budget. ReAP scheduler proposed in [6] is similar to that of [5] in that the variation on the mechanism of how delay is calculated. In this scheme, each packet has a deadline based on which the laxity is computed at each hop. The priority is then recomputed as a ratio of current laxity to the remaining hops, giving higher priority to those that have high laxity and longer hops to traverse. Our work in this paper is based on the similar observations, in which application requirements are embedded in the data packets during transmission. We consider a bit-rate requirement and delay that could be specified for any network applications [7]. For instance, multimedia streaming requires guaranteed throughput to ensure minimum quality, likewise voice over IP (VoIP) requires strict limits on jitter and delay whereas link emulation requires guaranteed throughput, jitter and latency. In our proposed architecture, which tunes EDCA for multi-hop networks, we implement a dynamic AC adaptation (DACA) module over existing channel access mechanism. It considers these requirements and other varying parameters, based on which we confirm whether a packet can be delivered within a pre-assigned duration. This decision EDCA-TM: IEEE 802.11e MAC Enhancement for Wireless Multi-hop Networks Min-Soo Kim, Deepesh Man Shrestha and Young-Bae Ko College of Information & Communication, Ajou University, Suwon, Republic of Korea {ms7777, deepesh, youngko}@ajou.ac.kr T “This research was supported by the MIC(Ministry of Information and Communication), Korea, under the ITRC(Information Technology Research Center) support program supervised by the IITA(Institute of Information Technology Advancement)” (IITA-2008-C1090-0801-0015) 978-1-4244-2948-6/09/$25.00 ©2009 IEEE This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2009 proceedings.