Nortel Networks DCT1900 Roaming and Handover Handling by the Portable Telephone, Locked Situation

Technical Product Manual - DCT1900

System Description, System Overview

2.2Roaming 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.

System-DCT1900/R8/mw	2-9
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