This presentation will show you how handoff works on Mobile communication

1. HELLO!
👨 Noushad Hasan (2014-3-50-025)
👩 Maliha Rahman(2014-3-50-007)
👨 Sauradip Roy(2014-3-50-008)
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2. “Hand-off
in
Mobile
Communication”

3. What is Handoff ?
Let’s start with the first set of slides

4. “In mobile communication, handoff is the transition
for any given user of signal transmission from one
base station to a geographically adjacent base
station as the user moves around. Each base-
station transition, as well as the switching
processor sequence itself, is called handoff.
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5. 📌 Handoff Strategies
 Handoff is encouraged to maintain call quality as
subscribers move in and out of range of base station.
 New voice & Control channel frequencies.
 Prioritizing handoff over a new call initiation by
allocating unused channels of new base station.
 Before handoff the base station monitors the signal
level for a certain period of time.
 Avoid unnecessary handoff by measuring the signal
strength and ensuring the handoff is completed before
the termination of call.
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6. 📌 Handoff Strategies(Cont.)
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 Handoff should be performed under the following
circumstances-

7. 📌 Handoff Strategies(Cont.)
 The call will be dropped when there is an
excessive delay in MSC due to huge traffic in
assigning handoff
 The call will be dropped if no channels are
available.
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8. Guard Channel Concept
a fraction of the total available
channels in a cell is reserved
exclusively for handoff request
from ongoing calls which may
be handed off into the cell.
📌 Prioritizing Handoff
Queuing of handoff requests
In such system the probability
that the handoff will not be
served is equal to blocking
probability of new originating
call.A fraction of the total
available channels in a cell is
reserved exclusively for handoff
request from ongoing calls
which may be handed off into
the cell.
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9. 📌What happens when handoff takes
place ???
1.Signal strength falls
below the threshold
level.
2.Base station of the
cell originates a
handoff request.
3.MSC gets the
information from the
candidate cell.
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When mobile is in the edge of cell-
4.MSC asks both the
cell to co-ordinate
with each other.
5.If the handoff is
successful the mobile
is asked to switch to
another voice
channel

10. 📌 Handoff in different cellular systems
Handoff in 1G Cellular System Handoff in 2G Cellular System
Signal strengths are measured and
monitored by MSC
Signal Strengths are monitored by
mobile itself
MSC decides if handoff is necessary
or not.
According to received power from BS
the mobile decides when to handoff
Huge traffic at MSC due to
computational load
MSC is no longer loaded with traffic
since mobile takes the handoff
decision
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11. 📌Types of Handoff
Hard Handoff
• Break before
make.
• Connects to
single BS at a
time.
Soft Handoff
• Make before
break.
• Connects to
multiple BS
simultaneously.
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12. How to
Overcome???
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13. 📌Umbrella Cell Concept for Practical
Handoff Situations
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Figure: Umbrella Cell Approach

14. 📌Umbrella Cell Concept for Practical
Handoff Situations(Cont.)
The Umbrella cell concept ensures that the number of handoff’s is
minimized for the high speed users and provides additional microcell
channels for pedestrian users.
The speed of vehicle may be evaluated by the MSC, by calculating how
rapidly received signal strength varies for each reverse voice channel.
If a high speed user is approaching to the base station, and its speed is
decreasing, then the base station will handover the user to the microcell,
without consulting with the MSC.
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15. 📌 Cell Dragging in practical situations
If a user travels away from the
base station at a slow speed and
the average signal strength doesn’t
decay rapidly then it seems like the
present cell has been dragged into
the adjacent cell , it is called cell
dragging. It occurs when there is a
line of sight communication path
between the mobile unit and the
antenna most of the time.
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16. 📌 Cell Dragging in practical situations
(Cont.)
This phenomenon effects these following occurrences-
Low speed user line of sight to base station
Strong signal changing slowly
User moves into the area of an adjacent cell without handoff
Creates potential interference and traffic management problems because
user has travelled down into the adjacent cell
This can be avoided by adjusting the handoff threshold and ratio
coverage parameters carefully.
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17. THANKS!
Any questions???
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