How CDMA Call Initiation
The user then decides to make a call. The number is keyed in and the send key is hit. This initiates an Access Probe. The mobile uses a special code channel called the Access Channel to make contact with the cell site.
CDMA mobiles can transmit two types of channels on the single physical channel provided by the reverse link. These two channel are distinguished by the types of coding that are used. The Access Channel is used by the mobile to initiate calls. The other possible channel is the traffic channel that is used once a call is established.
The long code mask used for access probes is determined from parameters obtained from the Sync and Paging channels: the access channel number, the paging channel number, the base station ID, and the Pilot PN offset used by the base station.
As no link is yet established, closed-loop power control is not active. The mobile uses open-loop control to guess an initial level. Multiple tries are allowed with random times between the tries to avoid collisions that can occur on the Access Channel.
This is necessary since there is no mechanism to prevent multiple users attempting to access the system at the same time. For each cell site there is also a limited number of access channels that are supported. Because of the limited number of access channel receivers in the base station, the odds of collisions occurring are increased.
- Dial Numbers, Then Press Send
- Mobile Transmits on a Special Channel Called the Access Channel
- The Access Probe Uses a Long Code Mask Based On:
- Access & Paging Channel Numbers
- Base Station ID
- Pilot PN Offset