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