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Mobility Support for IEEE 802.16e System
Hyun-Ho Choi and Dong-Ho Cho
CONTENTS
1.The Emerging Wireless Internet Architecture: Competing 6
and Complementary Standards to WiMAX Technology 3 6
2.IEEE 802.16 Standards and Amendments 19 6
3.MAC Layer Protocol in WiMAX Systems 35 6
4.Scheduling and Performance Analysis of QoS for IEEE 802.16 Broadband Wireless Access Network 57 6
5.Propagation and Performance 77 6
6.Mobility Support for IEEE 802.16e System 103 6
7.Measured Signal-Aware Mechanism for Fast Handover 6
in WiMAX Networks 129 6
8.802.16 Mesh Networking 147 6
9.WiMAX Testing 175 6
10.An Overview of WiMAX Security 197 7
11.Privacy and Security in WiMAX Networks 205 7
12.WiMAX Security: Privacy Key Management 229 7
Index 251 7
6.1Overview of Mobility-Supporting Functions 104
6.2Power-Saving Mechanism 105
6.2.1Power-Saving Class of Type I 106
6.2.2Power-Saving Class of Type II 107
6.2.3Power-Saving Class of Type III 109
6.3Handover 110
6.3.1Network Topology Acquisition 110
6.3.2Basic Handover Operation 117
6.3.3Macro Diversity Handover and Fast BS Switching 121
6.4Paging and Location Update 124
6.4.1Basic Paging Operation 125
6.4.2Location Update 127
6.4.3Network Reentry from Idle Mode 128
6.5Summary 129
References 130
103
Overview of Mobility-Supporting Functions
The IEEE 802.16e system called Mobile WiMAX [1] has been standardized to add user mobility to the original IEEE 802.16 system (WiMAX) [2]. Since mobility causes a number of problems and requirements in wireless systems, to support user mobility, a mobile station (MS) and a base station (BS) in the mobile WiMAX system need to introduce several mobility-supporting functions to the existing WiMAX system [3].
First of all, terminals in mobile environments must rely on portable power sources, such as batteries. Since batteries provide a limited amount of energy, it is important for mobile terminals to have an efficient power-saving mechanism. The basic approach to power saving in wireless systems is dis- continuous reception in which an MS periodically powers off its reception units (enters sleep state) to save power instead of continuously listening to radio channels [4]. On this basis, the IEEE 802.16e system also provides a sim- ilar sleep mode operation that provides efficient power-saving mechanisms that take into account the traffic attributes of various application services.
Second, an MS may move out of the coverage range of the current BS due to its mobility. Hence, to maintain a seamless service connection, the MS should find another BS that can serve it and establish a connection with that BS. We call this operation of transferring an ongoing connection to another BS to prevent loss or interruption of service as handover. The HO function enables the MS to have unlimited mobility and continuity of service, and hence is one of the most important functions in wireless cellular networks. The IEEE 802.16e system provides not only a basic HO function to support MS mobility, but also various techniques that enhance HO performance [5].
Finally, in cellular networks, the location of MSs is managed by two pro- cesses: paging and location update [6]. Paging is a process by which a network searches for dormant MSs by broadcasting/multicasting a paging message in predetermined areas. Location update enables MSs to inform the network of their location. A wireless system that supports the paging scheme allows MSs to operate in two modes: active mode and idle mode. If there is no traffic to or from an MS for a given period, the MS is allowed to change its mode to idle. In idle mode, the MS does not have to maintain the connection with the network and performs location update less frequently, since there is no need for the location of the MS to be traced precisely. Therefore, the MS can reduce its consumption of battery power and radio resources significantly, and the BS can eliminate unnecessary air interface and HO traffic. To allow networks to take advantage of the benefits of paging and location update, the IEEE 802.16e system also provides MSs’ idle mode operation as an optional support function.
We now explain in detail the operation of the main mobility functions
defined in the medium access control (MAC) layer of the IEEE 802.16e system: power-saving mechanism, HO operation, and paging and location update.
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