DART 200 CDPD Modem User’s Guide | 2 Installation and Setup |
3.If the channel is not available for CDPD use, the DART continues searching, dropping the allowable signal level by 10 dB after each pass through all the cellular channels on the side it is searching, until it finds a usable channel or reaches the weakest allowable signal level
4.If an available CDPD channel was not found, the search starts over again at
5.When a CDPD channel is found the modem checks that the block error rate (BLER) is acceptable.
6.If the BLER is adequate, the DART extracts the network operating parameters (continuously being broadcast by the MDBS) from the data stream, then stays on the channel as long as possible awaiting commands from the Mobile Application Subsystem (MAS); the attached device. If the BLER is not acceptable the search continues.
7.While on the CDPD channel, the modem accepts operating parameters (called XID parameters) broadcast by the base station, including thresholds, threshold time limits, and adjacent channel lists. The modem continually monitors its radio environment and compares the current signal quality to the thresholds and time limits; if any of the thresholds are exceeded for longer than their permissible time limit, the modem must go find a better channel. To speed up this search the modem makes use of the adjacent channel lists picked up from the base station along with the operating parameters.
This process allows a modem to stay on an acquired channel, until the signal strength or BLER fails the threshold test. In a situation where the
∙CDPD Version 1.1 mode operation
In the system types already described the channel acquisition process is:
1.The DART 200 powers up and immediately searches for a CDPD channel to use. It searches sequentially, from the lowest number channel to the highest, on the side (A or B) it is configured to use recording the signal strength (RSSI) of every active cellular channel encountered.
2.The DART then sorts the channels in descending order of strength and evaluates them to find the best available (strongest signal) CDPD channel (in a dedicated system many in the list are voice only channels).
