Network Entry, Initialization & Ranging Process | WiMAX Mobility Management

1. Network Entry and Initialization

A SS needs to successfully complete the network entry process with a desired BS to join the network. The network entry process is composed of four stages. The first stage is capability negotiation. After successful completion of initial ranging, the SS will request the BS to describe its available modulation capability, coding schemes, and duplexing methods. During this stage, the SS shall acquire a DL channel. Once the SS finds a DL channel and synchronizes with the BS at the PHY level, the MAC layer will look for DCD (downlink channel descriptor) and UCD (uplink channel descriptor) to get modulation and other parameters. The SS remains in synchronization with the BS as long as it continues to receive the DL-medium access protocol (MAP) and DCD messages. Finally, the SS will receive a set of transmission parameters from UCD as its UL channel. If no UL channel can be found after a suitable timeout period, the SS shall continue scanning to find another DL channel. Once the UL parameters are obtained, the SS shall perform the ranging process.

The second stage is authentication. In this stage, the BS authenticates and authorizes the SS. Then the BS performs key exchange with the SS, such that the provided keys can enable the ciphering of transmission data. The third stage is registration. To register with the network, the SS and the BS will exchange registration request/response messages. The last stage is to establish IP connectivity. The SS gets its IP address and other parameters to establish IP connectivity. After this step, operational parameters can be transferred and connections can be set up.

2. Ranging Process

Ranging is the process of acquiring the correct timing offset and power adjustments such that the SS's transmission is aligned to the BS's timing. Two types are supported for ranging process in the IEEE 802.16e-2005 specification. One is initial ranging, and the other is periodic ranging.

Initial ranging is performed during network initialization and registration/reregistration to allocate CDMA codes in UL ranging opportunities. Then the SS is allowed to join the network to acquire correct TX parameters (timing offset and TX power level). On the other hand, periodic ranging is performed when transmission is on-going on a periodic basis. It uses regular UL burst to allow SS to adjust TX parameters so that the SS can maintain UL communications with the BS.