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Presentation on
Handover
By-
Ankita Khadatkar
Pooja Jaiswal
Puja Thosar
Nikita Borikar
THE TERM HANDOVER
The process of transferring an ongoing call
or data session from one channel to another
in a cellular network
The core network performs handovers at
various levels of the system architecture
It is a key component in cellular network
mobility management as it requires a
specific latency on server interruption time.
Basic reasons why a handover might be
conducted:
If the mobile device moves out of the range of one
cell and a different base station can provide it with a
stronger signal
If all channels of one base station are busy then a
nearby base station can provide service
to the device
Handover process
Important one in any cellular network
Must be completed efficiently and without
inconvenience to the user
Different networks use different types of handover
techniques
Two main types of handover
Hard handover - GSM systems
Soft handover - CDMA systems
Hard Handover
Existing radio link must be dropped for a small
period of time
Then taken over by another base station
A call in progress redirected not only from a base
station to another base station but also from its
current transmit–receive frequency pair to another
frequency pair
An ongoing call can not exchange data or voice
for this duration
Call drop in hard handover
Break in call transmission
Handover takes place in a few ms (at best in 60 ms)
Interruption is hardly discernible by the user
Handover to another cell is required when the signal
strength is low and error rate is high. GSM systems
perform hard handovers
Soft Handover
A soft handover is one in which the channel in the
source cell is retained and used for a while in parallel
with the channel in the target cell
In this case the connection to the target is
established before the connection to the source is
broken, hence this handover is called make-before-
break
Soft handovers may involve using connections to
more than two cells: connections to three, four or more
cells can be maintained by one phone at the same time
When a call is in a state of soft handover, the signal
of the best of all used channels can be used for the call
at a given moment or all the signals can be combined
to produce a clearer copy of the signal
Softer handovers are possible when the cells involved
in the handovers have a single cell site.
Inter and Intra System Handover
Inter System Handoff
If during ongoing call mobile unit moves from one
cellular system to a different cellular system which is
controlled by different MTSO, a handoff procedure
which is used to avoid dropping of call is referred as
Inter System Handoff.
An MTSO engages in this handoff system. When a
mobile signal becomes weak in a given cell and
MTSO can not find other cell within its system to
which it can transfer the call then it uses Inter
system handoff.
Before implementation of Inter System Handoff
MTSO compatibility must be checked
In Inter System Handoff local call may become
long distance call.
Intra System Handover
If during ongoing call mobile unit moves from one
cellular system to adjacent cellular system which is
controlled by same MTSO, a handoff procedure
which is used to avoid dropping of call is referred as
Intra System Handoff.
An MTSO engages in this handoff system
In Intra System Handoff local calls always remain
local call only since after handoff also the call is
handled by same MTSO
When a mobile signal becomes weak in a given
cell and MTSO finds other cell within its system to
which it can transfer the call then it uses Intra system
handoff.
Advantages
Overcome fading through micro diversity
Reduce Node Power which in turn decreases
interference and increases capacity
Increases battery life
Disadvantages
Using several radio links requires more channelize
at ion codes
High handover signalling resulting in slower
handover initiation
Summary
Handover when the mobile device moves out of
the range of one cell (base station) and a different
base station can provide it with a stronger signal or
when present cell traffic high
Hard handover in GSM
Call drop for hard handover
Soft handover in CDMA
References :
Wikipedia, The Free Encyclopedia, [Online]: http://en.wikipedia.org
MobileCompChap03L11GSMHandover
handoverinnetworks-13071790379332-phpapp01-110604041918-phpapp01
trial_lecture on handover