The document discusses different types of handovers in cellular networks. A handover occurs when a mobile device moves between different base stations. There are two main types - hard handovers where the existing radio link is dropped briefly as the call is transferred to a new base station, and soft handovers where the call can be transferred without being briefly disconnected by maintaining connections to multiple base stations simultaneously. Handovers are important for mobility in cellular networks to maintain call quality as users move between different coverage areas without dropping calls.

1. Presentation on
Handover
By-
Ankita Khadatkar
Pooja Jaiswal
Puja Thosar
Nikita Borikar

2. 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.

3. 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

4. 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

6. Two main types of handover
Hard handover
- GSM systems
Soft handover
- CDMA systems

8. 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

9. 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

10. 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

11. 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.

12. Inter and Intra System Handover

13. 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.

14. 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.

15. 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.

16.  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.

17. Advantages
Overcome fading through micro diversity
Reduce Node Power which in turn decreases
interference and increases capacity
Increases battery life

18. Disadvantages
Using several radio links requires more channelize
at ion codes
High handover signalling resulting in slower
handover initiation

19. 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

20. References :
Wikipedia, The Free Encyclopedia, [Online]:
http://en.wikipedia.org
MobileCompChap03L11GSMHandover
handoverinnetworks-13071790379332-phpapp01-
110604041918-phpapp01
trial_lecture on handover