Holdoff Algorithms for IEEE 802.16 Mesh Mode in Multi-Hop Wireless Mesh Networks

Abstract

Multi-hop wireless mesh networks (M-WMNs) [Akyildiz, I. F., 2005] are one of the key features of beyond 3G systems because of their flexibility and low-cost deployment. So far, most of existing studies on multi-hop wireless mesh networks have been accomplished based on the IEEE 802.11 ad hoc mode. The IEEE 802.16 working group (WG) specified the IEEE 802.16-2004 standard [IEEE Std. 802.16-2004, 2004] in October 2004 and the standard defined two modes: the point-to-multi-point (PMP) mode and the mesh mode. The IEEE 802.16 mesh standard defines three mechanisms to schedule the data transmission: centralized scheduling (CSCH) [Morge, P. S., 2007], [Han, B., 2007], coordinated distributed scheduling (C-DSCH) [Morge, P. S., 2007], and uncoordinated distributed scheduling (UnDSCH). In the IEEE 802.16 mesh mode with the CSCH, C-DSCH, and Un-DSCH, multi-hop communication is possible between nodes such as mesh base stations (MeshBSs) and mesh subscriber stations (MeshSSs) because all nodes are peers and each node can act as routers to support multi-hop packet forwarding. In particular, in the IEEE 802.16 mesh mode with the C-DSCH, every node competes for channel access using a distributed election algorithm (DEA) based on the scheduling information of the extended neighborhoods (one-hop and two-hop neighbors) in a completely distributed manner and reserves radio resource by a three-way handshaking mechanism in which nodes request, grant, and confirm available radio resource using mesh distributed scheduling (MSH-DSCH) message. Like this, because the IEEE 802.16 mesh mode with the C-DSCH has good flexibility and scalability, it is suitable as an alternative medium access control (MAC) protocol for establishing M-WMNs. For M-WMNs to serve as a wireless network infrastructure, the protocol design for M-WMN should target a high network throughput. In the IEEE 802.16 mesh mode with the C-DSCH, after occupying radio resource, a node cannot transmit any MSH-DSCH message for a holdoff time in order to share radio resource with other nodes in M-WMN. If nodes get a short holdoff time in a heavily loaded network situation, the competition between nodes will happens severe and thus they will experience long contention times before reserving radio resource. On the other hand, if nodes get a long holdoff time in a lightly loaded