N O V A T E L W I R E L E S S T E C H N O L O G I E S L T D .
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A T C o m m a n d S p e c i f i c a t i o n - E x p e d i t e a n d M e r l i n
W i r e l e s s I P M o d e m s
Channel Scan Mode
Description:
The Expedite Wireless IP Modem modems can be programmed to scan for available CDPD channels in
three different manners. Each manner has different operating characteristics and is targeted for specific
applications.
Channel scan mode 0 has the NRM performing an initial scan of all cellular channels associated with the
selected side preference (see AT\N). Service is initially obtained on the CDPD channel with the highest
RSSI. This mode was the first mode developed and was the default mode until mode 2 was developed.
New issue modems default to mode 2 operation.
Channel scan mode 1 has the NRM using only those cellular channels defined in the channel scan list,
regardless of which side they are on. Service is initially obtained on the CDPD channel with the highest
RSSI. This is useful in restricting the modem to obtaining service on only a selection of channels. Once
service is obtained, automatic handoffs may occur sending the modem to a channel not present in the
channel list. If the modem looses the channel, it will only re-scan those channels present in the channel
list.
Channel scan mode 2 has the NRM using the channel list as a “Hot List” scanning those channels first
before scanning outside the list. If service cannot be found on a channel contained in the channel list the
modem will perform a wide scan in an effort to located a suitable channel. If a channel is found which is
not present in the list, it is appended to the list for future use. The modem automatically updates and
maintains the channel list.
The addition of mode 2 operation also expanded the channel list from 16 to 32 entries. The use of the “Hot
List”, offers the advantage of faster connection times since there is a good chance that the channel list will
contain an active channel. Because the modem maintains this list itself, there is no need for the operator
to initialize the modem channel list, the modem will do this itself. When the modem has filled the 32
location list the software will overwrite the oldest entry in the list and continue rewriting old values with new
ones.
Format:
ATS112?
To determine the current channel scan mode
ATS112=0
Any channel
ATS112=1
Hot List Only
ATS112=2
Hybrid
Validity:
The channel scan mode can only be altered in Program mode.
Other Considerations:
To optimize performance for mobile applications which use many channels and may roam from city to city,
it may be advantageous to clear the channel scan list when entering a new area. This would eliminate
channels that are not active in one city from affecting the operation of the modem. Doing this will result in
a longer time for primary initialization of the modem as it refills the channel list.
