Multi-channel Enhancements for IEEE 802.11-Based Multi-hop Ad-Hoc Wireless Networks
Collision avoidance is critical for the performance of contention-based medium access mechanism such as CSMA. In this paper, the IEEE 802.11-based MAC protocol is enhanced for performance improvements in multi-hop ad-hoc wireless networks. The protocol be
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Department of Computer Science KwangWoon University 2 Division of Information and Computer Science DanKook University [email protected]
Abstract. Collision avoidance is critical for the performance of contentionbased medium access mechanism such as CSMA. In this paper, the IEEE 802.11-based MAC protocol is enhanced for performance improvements in multi-hop ad-hoc wireless networks. The protocol behavior of hidden terminals in carrier sensing range[10] is important for end-to-end performance. There are several mechanisms defined in IEEE 802.11 standard such as IFS(Inter Frame Space), but we address a problem that such time interval is not long enough to avoid unnecessary collisions by the hidden terminals in carrier sensing range. We have conducted a comprehensive simulation to study performance improvement. The simulation results indicate that the performance is increased and the number of the dropped packets due to unnecessary collisions can be significantly reduced as much as a half. Keywords: Ad-hoc wireless networks, IEEE 802.11, MAC, Collision, CAI (Collision Avoidance Interval).
1 Introduction In the IEEE 802.11-based MAC protocol[1], two medium access control protocols are specified - PCF(Point Coordination Function) and DCF(Distributed Coordination Protocol). DCF is often used as a referred scheme for multi-hop ad-hoc wireless networks, and is a contention-based medium access protocol - a host that has frames to send can send them only when the medium is available, which means it works in simplex mode. There are several research works to overcome this limitation[7][8][9]. The range covered by the power necessary for transmitting a frame has two disjoint areas, named transmission range and carrier sensing zone (Fig. 1)[10]. In transmission range, a node can sense and decode a signal correctly, whereas a node can sense but can not decode it correctly in carrier sensing zone. To avoid a collision, a node is ∗
This work was supported by the Korea Science and Engineering Foundation(KOSEF) grant funded by the Korea government(MOST) (R01-2005-000-10934-0) and by the Research Grant of KwangWoon University in 2007. ** Corresponding author. M. Denko et al. (Eds.): EUC Workshops 2007, LNCS 4809, pp. 82–92, 2007. © IFIP International Federation for Information Processing 2007
Multi-channel Enhancements
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required to sense the medium first before transmitting a frame. If it finds the medium busy, the behavior of the node in IEEE 802.11 specification is as follows. If the node is in transmission range, it can decode the signal correctly, so it can also recognize NAV(Network Allocation Vector) which indicates the remaining time of on-going transmission sessions, therefore, it defers transmitting a frame during that NAV interval. But if it is in carrier sensing zone, the node can not decode the signal, so it can not recognize NAV. In this paper, we address the importance of the protocol behavior in carrier sensing zone and show that the behavior is required to be modified to avoid unnecessary collisions to improve perfo
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