Wednesday, November 11, 2009

Initial Ranging | WiMAX Operation

Initial ranging is the process of estimating the distance or propagation time between a transmitter and receiver. Ranging information may be used to assist in the establishment of operating parameters for the transmitter and receiver. The transmitter power level and packet transmission delay time ensure packets do not overlap with transmission from other devices.

During the initial ranging process, the base station is assigned the basic CID that will be used to control the radio operations of the subscriber device. After the basic CID is assigned, a primary management CID may be assigned to allow for authentication and the establishment of other CID channels. A secondary CID may be assigned to allow the downloading of configuration files and the assignment of an IP address using dynamic host configuration protocol (DHCP).

Figure 1 depicts the basic channel acquisition processes that may be used in the WiMAX system. The subscriber station begins by scanning a set of potential WiMAX frequencies. If it finds a WiMAX radio channel, it synchronizes with the RF channel and acquires the downlink channel descriptor (DCD) and uplink channel descriptor (UCD) messages to determine how to access the system. The subscriber station then sends initial ranging request messages to get the attention of the system and to receive timing adjustment information. This process starts by transmitting at a lower RF power level and gradually increasing until the system responds with an assignment of basic and primary control identifiers (CID). The subscriber station then sends its transmission capabilities to the base station and the WiMAX system responds with an authorization or denial of service for these transmission capabilities.

Figure 1: 802.16 Channel Acquisition and Initial Ranging
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