Mobile WiMAX system operation

This chapter provides a detailed description of the operation of IEEE 802.16m entities (i.e., mobile station, base station, femto base station, and relay station) through use of state diagrams and call flows. An attempt has been made to characterize the behavior of IEEE 802.16m systems in various operating conditions such as system entry/re-entry, cell selection/reselection, intra/inter-radio access network handover, power management, and inactivity intervals.

This chapter describes how the IEEE 802.16m system entities operate and what procedures or protocols are involved, without going through the implementation details of each function or protocol. The detailed algorithmic description of each function and protocol will be provided in following chapters. Several scattered call flows and state diagrams were used in reference [1] to demonstrate the behavior of the legacy mobile and base stations, making it difficult to coherently understand the system behavior.

The IEEE 802.16 standards have not generally been developed with a system-minded view; rather, they specify components and building blocks that can be integrated to build a working and performing system. An example is the mobile WiMAX profiles where a specific set of IEEE 802.16-2009 standard features (one out of many possible configurations) were selected to form a mobile broadband wireless access system.

Detailed IEEE 802.16m entities' state transition diagrams comprising states, constituent functions, and protocols within each state, and inter-state transition paths conditioned to certain events would help the understanding and implementation of the standards specification [2–5]. It further helps to understand the behavior of the system without struggling with the distracting details of each constituent function.

State diagrams are used to describe the behavior of a system. They can describe possible states of a system and transitions between them as certain events occur. The system described by a state diagram must be composed of a finite number of states. However, in some cases, the state diagram may represent a reasonable abstraction of the system.

There are many forms of state diagrams which differ slightly and have different semantics. State diagrams can be used to graphically represent finite state machines (i.e., a model of behavior composed of a finite number of states, transitions between those states, and actions). A state is defined as a finite set of procedures or functions that are executed in a unique order. In the state diagram, each state may have some inputs and outputs, where deterministic transitions to other states or the same state happen based on certain conditions.

In this chapter, the notion of mode is used to describe a sub-state or a collection of procedures/protocols that are associated with a certain state. The unique definition of states and their corresponding modes and protocols, and internal and external transitions, is imperative to the unambiguous behavior of the system. Also, it is important to show the reaction of the system to an unsuccessful execution of a certain procedure. The state diagrams described in the succeeding sections are used to characterize the behavior of IEEE 802.16m system entities.

This chapter provides a top-down systematic description of IEEE 802.16m entities' state transition models and corresponding procedures, starting at the most general level and working toward the details or specifics of the protocols and transition paths. An overview of 3GPP LTE/LTE-Advanced states and user equipment state transitions is further provided to enable readers to contrast the corresponding terminal and base station behaviors, protocols, and functionalities. Such contrast is crucial in the design of inter-system interworking functions.

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