Centralized Scheduling Algorithms for 802.16 Mesh Networks

IEEE 802.16 protocol [1, 2] specifies two different modes of operation. The first mode of operation is the point-to-multipoint (PMP) mode. In the PMP mode, each 802.16 access point has a dedicated broadband connection to the Internet. Wireless terminals connect to the access points on their first hop and their traffic goes to the Internet through the access point’s broadband connection. The second mode of operation is the mesh mode, where access points are interconnected with wireless links. In the mesh mode, wireless terminals connect to the access points on their first hop. Then, the wireless mesh carries their traffic to the Point-of-Presence (POP) where it goes to the Internet (Fig. 1.1). Mesh networks decrease the cost of running the access points, since all access points in the same area share a single broadband connection. Current mesh networks use 802.11a technology to interconnect the mesh backbone [3, 4]. However, 802.11a technology is a decade old and was not designed for mesh networks. In particular, 802.11 Medium Access Control (MAC) lacks the extensions to provide Quality–of–Service (QoS) in multihop wireless environments [5]. IEEE 802.16 introduces QoS in the mesh with Time Division Multiple Access (TDMA) MAC technology [1]. In 802.16, access points negotiate their endto-end bandwidth with the POP. IEEE 802.16 MAC enforces end-to-end QoS by scheduling wireless transmissions on the links connecting the access point to the POP. IEEE 802.16 mesh protocol specifies two TDMA scheduling protocols: centralized and decentralized scheduling protocols. The base station (POP) uses the centralized scheduling protocol to establish network wide schedules. In the centralized scheduling protocol, mesh nodes request bandwidth from the base station. The base