Hierarchical QoS Admission Control Mechanism for IEEE 802.16j Mobile Multi-Hop Relay WiMAX Network

Hierarchical QoS Admission Control Mechanism for IEEE 802.16j Mobile Multi-Hop Relay WiMAX Network

Rohaiza Yusoff (Universiti Teknologi MARA, Malaysia), Mohd Dani Baba (Universiti Teknologi MARA, Malaysia) and Muhammad Ibrahim (Universiti Teknologi MARA, Malaysia)
DOI: 10.4018/978-1-4666-4888-3.ch011
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This chapter presents some performance issues in Worldwide Interoperability for Microwave Access (WiMAX) network and focus on the capability of non-transparent relay in Mobile Multi-Hop Relay (MMR) WiMAX Network. In this work, an admission control mechanism with hierarchy Quality of Service (QoS) is developed for the relay architecture. An open source-based simulator is used to evaluate the three types of QoS classes, which are Unsolicited Grant Access (UGS), Real Time Polling Service (rtPS), and Non-Real Time Polling Service (nrtPS). Two scenarios of non-transparent relay topologies are set up for different numbers of subscribers with different types of QoS application classes. Three performance metrics, which are bandwidth utilization, number of slots used, and number of admitted service flow, are observed and plotted in graph. The results show the hierarchy-based QoS admission control mechanism can enhance the throughput of provided services by 35% compared to the conventional method without the admission control approach.
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The field of wireless communications have experience tremendous changes recently in response to user demand for ubiquitous communication from anywhere, anytime and anyone. The role of government in supporting the vendors to deliver the most efficient services will convince the users of their continuous support. Therefore, many approaches were developed and deployed in order to satisfy the user demands.

WiMAX enables the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and Digital Subscriber Line (DSL). WiMAX provides fixed, nomadic, portable and mobile wireless broadband connectivity. The two driving forces of modern internet are broadband and wireless. The WiMAX standard combines the two, delivering high-speed broadband internet access over a wireless connection.

With the rapid advancement in telecommunication technology today, Mobile Multi-hop Relay (MMR) Worldwide Interoperability for Microwave Access (WiMAX) network standard was introduced in early 2009 through IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Broadband Wireless Access Systems Amendment 1: Multiple Relay Specification to enable mobile communication with low cost base station offered.

Role of Relay Station

A Relay Station (RS) is a radio system that helps to amplify and retransmit the signal to the uncovered Base Station (BS) area. The implementation of RS in certain topology is to enhance the network capacity especially for shadowed places. RS is also effective in extending the network coverage region at the edge of cell boundary. There are few types of RS which is categorized according to their functionality. Fixed RS is usually for permanent deployment and long term purpose. It is used to eliminate the coverage holes at valley area, penetration into large building and to enhance coverage for shadowed area. Fixed RS is also used for multi-hop relay in order to penetrate targeted area. Sometimes fixed RS can be found in underground facilities to provide signals for users. Another position for fixed RS is near the edge of the cell to support weak signal from BS and to helps handoff process efficiently.

Figure 1 shows several usages of fixed RS in WiMAX architecture. Another type is Mobile RS which is placed on moving object such as an RS on underground train to ensure the passengers in the train able to continuously communicate while travelling. This RS has to connect and handoff from immediate BS to another in the fastest way while serving its subscribers.

Figure 1.

Usages of relay stations in WiMAX architecture


Ad-hoc RS is a temporary RS which can be deployed for a certain time period such as to provide coverage in a big event or peak usage season. The main purpose of ad-hoc RS is to increase the network capacity being served by existing BS so that user did not get any difficulties to get connected in crowded area. This kind of portable RS give benefits not only to user but also to vendor in order to broadcast any live events.

As for this work, the focus is on fixed type RS with non-transparent mode and distributed scheduling. Several enhancement and features of the fixed RS have also been done.

The biggest difference between conventional WiMAX and MMR WiMAX is that in MMR network, the system enables mobile stations to communicate with a base station through intermediate relay stations. In conventional WiMAX network architecture, signals are transferred between base station and mobile terminals. In MMR network architecture, the whole cell is divided into two regions: BS region and RS region. The users near the base station which belong to BS region are connected directly to BS while users in the relay region, out of BS region are connected to RS. Hence, RS pretends to be a Mobile Station (MS) for BS and to be a BS for MS.

Two different relay modes are defined in the IEEE 802.16j which are transparent and non-transparent relay. Transparent relay usually used to enhance the network capacity while non-transparent relay is to enhance the network coverage. Transparent relay does not forward framing information to BS and this mode has lower complexity which only operates in two-hop network topology in centralized scheduling. Scheduling is one of the most crucial factors which influence the quality of service (QoS) in WiMAX network.

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