The ASN is the access network of WiMAX and it provides the interface between the user and the core service network. Mandatory functions as defined by the WiMAX forum include the following:
- Handover
- Authentication through the proxy authentication, authorization, and accounting (AAA) server
- Radio resource management
- Interoperability with other ASN’s
- Relay of functionality between CSN and mobile station (MS), e.g., IP address allocation
Base station (BS): The cell equipment comprises the basic BS equipment, radio equipment, and BS link to the backbone network. The BS is what actually provides the interface between the mobile user and the WiMAX network. The coverage radius of a typical BS in urban areas is around 500–900 m. In rural areas the operators are planning cells with a radius of 4 km. This is quite a realistic number now and quite similar to the coverage areas of GSM and UMTS high-speed downlink packet access (HSDPA) BSs today.
Deployment is driven either by the bandwidth required to meet demand, or by the geographic coverage required to cover the area. Based on the cell planning of other previous technologies, urban and suburban segments cell deployment will likely be driven by capacity. Rural segment deployment will likely be driven by the cell radius. For BTS systems, the emphasis is more on performance than on cost and size, although there still is an interest in low cost because WiMAX is a new deployment.
ASN gateway: The ASN gateway performs functions of connection and mobility management and interservice provider network boundaries through processing of subscriber control and bearer data traffic. It also serves as an Extensible Authentication Protocol (EAP) authenticator for subscriber identity and acts as a Remote Authentication Dial-In User Service (RADIUS) client to the operator’s AAA servers.
