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Mobile Computing COE 446

Network OperationTarek Sheltami

KFUPMCCSECOE

http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm

Principles of Wireless Networks

K. Pahlavan and P. Krishnamurth

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Handoff Management

Architectural Issues in Handoff

Handoff Decision Time Algorithms

Types of Handoffs

Outline

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Handoff ManagementHandoff Management

1.Architectural Issues in Handoff

Set of protocols to notify all related entities of a particular connection that a handoff has been executed and the connection has to be redefined

In voice network, MT selects the BS that is serving its location

When an MT moves from one point of attachment to another, the old serving point of attachment has to be informed about the change (dissociation)

Other network components involved in routing mechanism have to be aware of the handoff in order to seamlessly continue the ongoing connection of the call

Mobile Management

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Handoff are classified according to the connection creation

Seamless handoff and hard handoff

Handoffs are classified into:

1. Network Controlled Handoff (NCHO)

2. Mobile Controlled Handoff (MCHO)

3. Mobile Assisted Handoff (MAHO)

Mobile Management

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(Cellular Digital Packet Data)

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Handoff ManagementHandoff Management

2.Handoff Decision Time Algorithms

Traditional handoff algorithms are based on the RSS. Some of them are as follows:

1. RSS

2. RSS plus Threshold

3. RSS plus Hysteresis

4. RSS, Hysteresis and Threshold

5. Algorithms plus Dwell Timer

Mobile Management

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Time051015202530354045BS1-50-57-56-44-49-55-60-60.5-55-52BS2-49-53-46-54-45-47-56-60-55-56BS3-66-55-45-47-57-58-46-54-55-62

A mobile terminal is receiving signals from 3 BSs at the handoff region .The handoff decision is made at each sampling time according to the below table. The MT is initially connected with BS1 .

Show the handoff transitions between BSs for each of the following algorithms:•RSS•RSS + -60 dBm Threshold•RSS + Hysteresis 10 dBm•RSS + Hsyteresis 5 dBm + -55 dBm Threshold

Example

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BS3 BS2 BS1 Time 0 5 10 15 20 25 30 35 40 45

BS3 BS2 BS1 Time 0 5 10 15 20 25 30 35 40 45

BS3 BS2 BS1 Time 0 5 10 15 20 25 30 35 40 45

BS3 BS2 BS1 Time 0 5 10 15 20 25 30 35 40 45

Time051015202530354045BS1-50-57-56-44-49-55-60-60.5-55-52BS2-49-53-46-54-45-47-56-60-55-56BS3-66-55-45-47-57-58-46-54-55-62

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Handoff ManagementHandoff Management

2.Handoff Decision Time Algorithms

The performance of handoff algorithms measures have been considered such as call blocking probability, handoff blocking probability, delay between handoff request and execution, and call dropping probability

Handoff rate is related to the ping-pong effect and algorithms are designed to minimize the number of unnecessary handoffs

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Generic Handoff Management ProcessGeneric Handoff Management Process

1. Handoff decision is made and initiated

2. MT register with new visiting database via handoff messages

3. New visiting database communicates with the home database to get the subscriber profile and for authentication

4. Home database responds to the new visiting database with authentication of the MT

5. Home database sends messages to the old visiting database to cancel registration

6. The old visiting database flushes or redirects to the new visiting database and removes the MT from its list

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Handoff ManagementHandoff Management

Types of Handoffs:

1. Intracell, two channels

2. Intercell intradomain handoff, between two BSs associated with the same database

3. Intercell interdomain handoff, between two BSs with different database

Mobile Management