The Internet Protocol Journal 19 Mobile WiMAX by Jarno Pinola and Kostas Pentikousis, VTT Technical Research Centre of Finland O ne of the technologies that can lay the foundation for the next generation (fourth generation [4G]) of mobile broadband networks is popularly known as “WiMAX.” WiMAX, Worldwide Interoperability for Microwave Access, is de- signed to deliver wireless broadband bitrates, with Quality of Service (QoS) guarantees for different traffic classes, robust security, and mo- bility. This article provides an overview of mobile WiMAX, which is based on the wireless local and Metropolitan-Area Network (MAN) standards IEEE 802.16-2004 [1] and 802.16e-2005 [2] . We introduce WiMAX and focus on its mobile system profile and briefly review the role of the WiMAX Forum. We summarize the critical points of the WiMAX network reference model and present the salient charac- teristics of the PHY and MAC layers as specified in [1] and [2]. Then we address how mobile nodes enter a WiMAX network and explain the fundamentals of mobility support in WiMAX. Finally, we briefly compare WiMAX with High-Speed Packet Access (HSPA), another contender for 4G. The Role of the WiMAX Forum The WiMAX Forum is a nonprofit organization formed in 2001 to enhance the compatibility and interoperability of equipment based on the IEEE 802.16 family of standards. The IEEE 802.16 standards provide a large set of fundamentally different options for designing a wireless broadband system, including, for example, multiple options for Physical (PHY) layer implementation, Media Access Control (MAC) architecture, frequency bands, and duplexing. So many options lead to several possible system variants, which are all com- patible with the IEEE standards. Although such multiplicity allows for deployment in very diverse environments, it may spell either solely vertical, single-vendor deployments or no deployment at all, because operators do not want to be locked in with any particular implemen- tation. Thus, a major motivation for establishing the WiMAX Forum was to develop predefined system profiles for equipment manufac- turers, which include a subset of the features included in the IEEE 802.16 standards. WiMAX Forum-certified products are guaranteed to be interoperable and to support wireless broadband services from fixed to fully mobile scenarios. The aim is to enable rapid market introduction of new standard-compliant WiMAX equipment and to promote the use of the technology in different sectors. From IEEE 802.16 to Mobile WiMAX The IEEE 802.16 standard was originally meant to specify a fixed wireless broadband access technique for point-to-point and point- to-multipoint links. During its development, however, it was decided that mobility support should also be considered.