Handover [Under GSM >> Signaling] §
As MS passes through different location areas, it does location updates with the network. This is when MS do not have a connection (TCH/SDCCH not assigned) with the network. When it does, related signaling and procedures are known as "Handover".
Who takes a decision about Handover ?
Decision of
handover is always done by (serving) BSC.
Based on what parameters BSC decide ?
Based on regular
measurement results (signal quality, strength) received from MS
and BTS. TCH has associated signaling channels, FACCH and SACCH.
FACCH is used during initial stages of call setup as seen in
earlier "Voice Call" articles. Once call has been setup, SACCH is
used for signaling required later (like DTMF signaling, exchanging
measurement results etc.).
Note that MS need to do measurements on both serving (i.e. current) cell and neighboring cells. Neighboring cell information is given to MS by BTS.
Based on measurement results, BSC may suggest BTS (downlink) and MS (uplink) to adjust their powers or it may trigger Handover.
Below diagram shows related signaling during after call is setup.
| MS |  | BTS | | BSC |
|
1: Required MS power level is sent to MS through Layer 1 header of (next) SACCH.
In next article, we will see different types of Handovers and related signaling.
References: GSM Networks book by Heine, GSM book by Mouly and Pautet, Signaling diagrams from 24.007/24.008 (R99), 04.18 (RR procedures).
© Copyright Samir Amberkar 2010
| Voice Call - 8 « | GSM Index | » Intra-BTS HO |