Admission Control and Scheduling for QoS Provisioning in WiMAX Networks

Admission Control and Scheduling for QoS Provisioning in WiMAX Networks

Juliana Freitag Borin, Nelson L.S. da Fonseca
DOI: 10.4018/978-1-61520-680-3.ch009
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Although the IEEE 802.16 standard, popularly known as WiMAX, defines the framework to support real-time and bandwidth demanding applications, traffic control mechanisms, such as admission control and scheduling mechanisms, are left to be defined by proprietary solutions. In line with that, both industry and academia have been working on novel and efficient mechanisms for Quality of Service provisioning in 802.16 networks. This chapter provides the background necessary to understand the scheduling and the admission control problems in IEEE 802.16 networks. Moreover, it gives a comprehensive survey on recent developments on algorithms for these mechanisms as well as future research directions.
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The architecture of a network utilizing the IEEE 802.16 standard has two main elements: Base Station (BS) and Subscriber Station (SS). The BS makes the communication between the wireless network and the core network, whereas the SS provides the user access to the core network by establishing connections with the BS in a Point-Multipoint (PMP) topology. The standard also allows Mesh topologies (optional). The main difference between the PMP and Mesh topologies lies on the fact that in a PMP network the traffic flows only between the BS and the SSs, whereas in the Mesh mode, the traffic can be routed through the SSs and can occur directly between two SSs. In this chapter we will analyze PMP topology networks.

The physical layer operates in a frames format, which are subdivided in time intervals called physical slots. In each frame, the slots are organized in a downlink sub-frame and an uplink sub-frame. The downlink sub-frame is utilized by the BS for the transmission of data and control information to the SSs. The uplink sub-frame is shared among all SSs for transmissions addressed to the BS.

The IEEE 802.16 standard allows two physical medium access modes: Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD). In the FDD mode the downlink and uplink channels operate simultaneously in different frequencies. In the TDD mode the uplink and downlink sub-frames share the same frequency, and so it is not possible to perform simultaneous transmissions in both directions. Each TDD frame has a downlink sub-frame followed by an uplink sub-frame.

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