Sierra Wireless DART 200 CDPD Modem manual Problem determination

DART 200 CDPD Modem User’s Guide 2 Installation and Setup

3.If the CDPD channel’s BLER is acceptable, the DART acquires the power product, current CDPD operating parameters, and adjacent channel lists from the MDBS. If the channel BLER is not satisfactory, the modem goes to the next best CDPD channel in the list and repeats this step using the next best channel.

4.Once a channel is acquired, there is no guarantee that the modem stays there very long. In a sniff-and-hop system it is forced to continuously hop from one channel to another because voice traffic has priority. Even in a dedicated system, if the modem is mobile, it is forced to frequently change channels as it travels from one cell coverage area to another.

5.The XID parameters broadcast by the base station, in addition to the thresholds, threshold time limits, and adjacent channel lists used with CDPD 1.0, include an evaluation frequency (scan time), and a signal strength change (scan delta) value. As in CDPD 1.0 mode, the modem continually monitors its radio environment and compares the current BLER value to the XID threshold and time limit; if the threshold is exceeded for longer than the permissible time limit, the modem finds 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.

CDPD Version 1.1 requires that the DART periodically evaluates alternative channels to ensure that it is still operating on the best available channel. Also, CDPD Version 1.1 requires that if the DART detects an RSSI changes of more than a predetermined amount, from the initial acquisition value, it must check that it is still using the strongest channel in the area. These features, scan time (usually 90 seconds), and scan delta (usually +/- 8 dB), help to keep the M-ES on the best available channel, and avoids the cell dragging phenomenon common to mobile M-ESs operating in CDPD 1.0 mode.

Whenever the RSSI threshold or scan delta is exceeded, or the scan timer expires the modem must locate a better channel if possible. 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.

Problem determination

There are three ways to determine if a channel was acquired:

∙By observing the OPR light (simplest way). At power on this light flashes at the rate of about once per second. When the DART 200 acquires a channel the rate of flashing speeds up to at least twice per second and flashes faster as the signal strength increases. A very strong signal causes the light to glow steadily

∙By viewing S-Register 101 with the ATS101? command. A value of 1 indicates that a channel has been acquired

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