1/10/20151 Mobile Computing COE 446 Network Operation Tarek Sheltami KFUPM CCSE COE Principles of Wireless.

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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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Mobile management

Location UpdatesLocation Updates

PagingPaging

Location Information DisseminationLocation Information Dissemination

Handoff management

Outline

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1. Mobility and location management

2. Radio resources and power management

3. Security

Tetherless access user has the ability to move around while connected to the network and continuously possesses the ability to the service provider

Knowledge of where the destination is (location)

How to reach the destination (route)

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Location ManagementLocation Management

Involves tracking of the location of MT

When a call is made to a mobile number, a dedicated channel has to be set up from the calling party to the called party for the conversation to proceed

It has to be set up over the fixed part of the network and a pair of radio channels have to be allocated to the MT for the voice conversation, this is before the actual conversation takes place

If the MT moves during the course of a conversation, the step taken to handle the continuity of conversation is called handoff

Routers will use the destination address to deliver the packet

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Location Management..Location Management..

Required steps to determine location of the destination are done before the packet is routed to the dest

The status of the MT should be determined by the routing process

Location management has three parts:

1.1. Location UpdatesLocation Updates

2.2. PagingPaging

3.3. Location Information DisseminationLocation Information Dissemination

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Location updates are messages sent by the MT regarding its location to the fixed network

Each time the MT makes an update to reflect its new location, a database in the fixed part of the network has to be updated to reflect the new location

Whether there is a change in the location, the update message will be transmitted to the fixed network

Updates are periodic there will be some uncertainty in the location of MT to something around a group of cells

Paging is used by the network to deliver an incoming message to the MT

The network have to page the MT in such group of cells

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The paged terminal will respond through the point of access that is providing coverage in its cell, which will enable the network to locate accurately the MT

In order to initiate paging, the calling party or incoming message should trigger a location request from some fixed network entity

The fixed network entity will access some kind of database that will contain the most current location related to the particular MT and use this information to generate the paging request as well as deliver the message or set up a channel

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Location information dissemination refers to the procedures that are required to store and distribute the location information related to MTs served by the network

Location management is the tradeoff between the cost of the nature, number and frequency of location updates and the cost of paging

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Location Update AlgorithmsLocation Update Algorithms

Two types: Static and Dynamic

In static location updates, the topology of the cellular network decides when the location updated needs to be initiated

In dynamic location updates, the mobility of the user and call patterns is used in initiating location updates

Most cellular networks use static location update, which is a group of cell assigned a location area (LA) identifiers

Each BS in the LA broadcasts this identification number periodically over some control channels

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An MT is required to continually listen to the control channel for the LA identifier

When LA changes, MT will make an update to the location by transmitting a message with new identifier to the databases containing the location information

If there is an incoming message, paging is performed in the group of cells corresponding to the location identifier stored in the database

The MT usually responds and communication can be established

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In GSM, an LA consists of a group of cells controlled by a base station controller (BSC)

An MT performs the location under the circumstances:

1. Upon powering up, it compares the location area identity

2. When the MT crosses the boundary of the a location area, because the BS broadcasts the LA identity, which an MT is required to monitor and compares it with the stored value

3. After a period of time predetermined by the network, because update mechanism might be costly if MT does not leave an LA for long periods of time

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The primary problem with static LA identifier approach is that if an MT is frequently crossing the boundary of two LAs, there will be a ping-pong effect of continually switching between two LAs

One suggested solution is to employ a dwell timer that persists without location updates for sometime to ensure that location update is worthwhile

Distance-based, where the location update is performed after crossing a certain number of cells

Timer-based, where a location update is performed after a certain time elapse

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Variation of the pervious two schemes take into account the signaling load on control channels and the location and velocity of the MT

Example of dynamic location update schemes are state-base and user-profile-based

State-based location update, the MT makes decision on when to perform an update based on its current state information, includes time elapsed, distance traveled, the number of LAs crossed and number of calls received that could be changed based on the user mobility and call patterns

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User-profile-based location update, maintains a sequential list of LAs that the MT may be located in at different points of time based on the history of the MT

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Paging SchemesPaging Schemes

Broadcasting a message in a cell or a group of cells to obtain a response from the MT for which a call or a message is incoming

Paging only the cell in which the MT is located reduces the cost

It is quite impossible to determine location accurately, especially if the location update cost has to be kept low

Blanket Paging refers to paging the MT in all the cells with LA simultaneously

Closest-Cell-First, first paging the cell where the MT was last seen, then subsequent rings of cells that are equidistant from this cell in each paging cycle

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If there are delay constraints, several rings may be polled simultaneously in a paging cycle

In general, if the first location estimate is not correct, the next page should be performed so that the probability of locating the mobile is the next largest and so on

Paging is performed according to location updates and then subsequent pages based on other parameters (history, distance, …)

A timer is used to declare that the MT as unreachable in a particular cycle (sequential paging)

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Results indicate that blanket polling provides the lowest delay at small load, whereas sequential paging can sustain a higher paging request rate especially when there are several incoming calls to a certain area

Location DisseminationLocation Dissemination

When there is an incoming call to the MT, there is a need for at least one fixed network entity, whose location and address is known, which can be reached to obtain information about the MT (anchor)

The anchor has some information regarding the location and routing information of the MT

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Multiple anchor points are usually employed to avoid congestion and call failure

Every MT is associated with home network and home database

The home database keeps track of the profile of the MT

The location of MT is maintained in terms of a visiting network, where the MT is located

Visiting database keeps track of the MTs in its service area

The home and visiting database communicate with each other to authenticated and update each other

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In GSM, the home and visiting database are call home location register (HLR) and visiting location register (VLR)

When a MT observes a change in the LA identity, it transmits a location update message through its BS to an MSC

The MSC contacts its VLR with the location update, which contacts its HLR via location registration message only if it has no info about the MT

The HLR authenticates and acknowledges the location registration, updates its own database, and sends a message to the old VLR to cancel the registration there

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When a call is made to a mobile phone, the anchor entity contacts the MSC associated with the HLR of the MT

The HLR contacts the VLR that is associated with the MT and enable call setup

Handoff ManagementHandoff Management

Ping-Pong effect refers to several handoffs that occur back and forth between two BSs

This has a severe charge on the both the user’s quality perception and the network load

One way to eliminate the Ping-Pong effect is to persist with a BS for as long as possible

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If the handoff is delayed, a weak signal reception persist unnecessarily, resulting in a lower voice quality, increasing the probability of call drops and degrading QoS

Handoff involves a sequence of events in the backbone network that include rerouting the connection and reregistering to the new point of access (additional load)

Handoff has an impact on traffic matching and traffic density for individual BSs

We can consider handoff as consisting of two different steps

In the first step, the handoff management process determines that a handoff is required (handoff decision and initiation)

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In the second step, the rest of the network is made aware of the handoff and the connection is restructured to reflect the new location of the MT

An anchor in the fixed part must be involved in the handoff management process in a manner similar to location management

Several issues arise during the handoff management, which are divided into two categories: architectural issues and handoff decision time algorithms

Architectural issues are those related to methodology, control and software/hardware elements

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Handoff decision time are types of algorithms, metrics used by algorithms, and performance evaluation methodologies

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Important issues involved in the handoff mechanism

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Two basic actions during handoff

1/10/20151 Mobile Computing COE 446 Network Operation Tarek Sheltami KFUPM CCSE COE Principles of Wireless.

Documents

location of mt

network location management

location identifier

new location

location request

current location

location update algorithms

static location updates