Nortel Networks DCT1900 - Manual (Page 31)

Technical Product Manual - DCT1900
System Description, System Overview
System-DCT1900/R8/mw 2-9
© 2000-2005
2.2 Roaming and Handover Handling by the Portable Telephone
Sections 2.2.1 and 2.2.2 describe when the Portable Telephone starts internal (intra cell, same
Base Station), external (inter cell, another Base Station of the same RE) and inter system
handovers (another Base Station of another RE) and location updates (roaming).
2.2.1 Unlocked Situation
When the Portable Telephone is first turned on, it will regularly scan the air interface. As soon as
the Portable Telephone detects a bearer signal from a Base Station, it will lock to this bearer. A
bearer is an active PWT air interface channel in which transmissions take place. When a Base
Station is idle (there are no calls routed via this Base Station), it transmits a dummy bearer which is
also referred to as a beacon signal. Dummy bearers enable the Portable Telephone to lock on to
an idle Base Station and to scan the environment.
If the synchronizing system number is not part of one of the Portable Telephone subscriptions, the
Portable Telephone will scan the air interface again.
If the synchronizing system number is part of the system range of one of the Portable Telephone
subscriptions, that subscription will be selected and the Portable Telephone will use the bearer as
a standby bearer. From this moment on the Portable Telephone will start to collect data
concerning the situation in other channels on the air interface. This synchronous situation is
described in the paragraphs below.
The Portable Telephone falls back to asynchronous roaming if during a certain period of time no
valid frames are received. In this case all collected data concerning the situation in other channels
is cleared.
To limit the energy consumption during the unlocked situation, the Portable Telephone will go into
a sleep mode if it does not find a bearer within 10 minutes. The sleep mode will be interrupted
every 2 minutes, when the Portable Telephone performs one full scan to see if there are any
systems present.
2.2.2 Locked Situation
Environment Scanning by the Portable Telephone
If the Portable Telephone is locked to a standby bearer, it maintains a list of information for each
channel on the air interface. This is called a history list, which contains the following information:
RSSI:
For each channel, a received "Received Signal Strength
Indication" (RSSI) value is stored. For an active bearer, this is an
indication of the strength of the received signal. For an idle
channel, this is an indication of the noise level.
RQI: For each channel with an active bearer or dummy bearer, a
"Received Quality Indication" (RQI) value is stored. The RQI
value is determined by the number of correctly/incorrectly
received frames.
Base Station & System ID: For each channel with an active bearer, the Portable Telephone
will store the identification of the Base Station and RE.