HHandovers in Fourth andovers in Fourth Generation Heterogeneous Generation Heterogeneous

NetworksNetworks

IntroductionIntroduction

First, second and third – generation mobile systems depend on First, second and third – generation mobile systems depend on the employment of the radio spectrum that was either the employment of the radio spectrum that was either unlicensed (available for public use) or licensed for use by very unlicensed (available for public use) or licensed for use by very small number of service providers and network operators in small number of service providers and network operators in each region.each region.

Difference in bandwidth and coverage areas have led to the Difference in bandwidth and coverage areas have led to the necessity of developing multi network interface devices necessity of developing multi network interface devices (terminals) that are capable of using the variety of different (terminals) that are capable of using the variety of different network service provided.network service provided.

The fourth generation (4G) of the wireless communications is The fourth generation (4G) of the wireless communications is expected to integrate a potentially large number of different expected to integrate a potentially large number of different heterogeneous wireless technologies in what could be heterogeneous wireless technologies in what could be considered a huge step forward towards universal wireless considered a huge step forward towards universal wireless technologies . technologies .

Fourth Generation (4G)Fourth Generation (4G)

Even though 4G is currently under defined, there are Even though 4G is currently under defined, there are many current outlooks that delineate the vision of new many current outlooks that delineate the vision of new wireless technologies. based on the emergent trends of wireless technologies. based on the emergent trends of mobile communication, 4G will have:-mobile communication, 4G will have:-

1. Higher Bandwidth.2. Higher Data rates.3. Quicker Handovers.4. Focus on reducing faultless service.5. Allowing seamless handovers across multitude of

wireless networks.

Network Management in 4GNetwork Management in 4G

Network management will be necessary among different Network management will be necessary among different access systems in terms of:-access systems in terms of:-

1.1. Horizontal (intra system handovers)Horizontal (intra system handovers)

2.2. Vertical (Inter system Handover)Vertical (Inter system Handover)

3.3. Seamless mobilitySeamless mobility

4.4. Quality of serviceQuality of service

5.5. DependabilityDependability

6.6. SecuritySecurity

Classification of HandoversClassification of Handovers

Basically, each mobile node is, at all times, within range of at Basically, each mobile node is, at all times, within range of at least one least one network access pointnetwork access point, also known as , also known as base stationbase station..

The area serviced by each base station is identified as its The area serviced by each base station is identified as its cell.cell.

The dimensions and profile of every cell depends on the:-The dimensions and profile of every cell depends on the:-1.1. Network typeNetwork type2.2. Size of the base stationsSize of the base stations3.3. Transmission and reception powerTransmission and reception power

Usually, cells of same network are adjacent to each other Usually, cells of same network are adjacent to each other and overlap in such a way that, for majority of time, any and overlap in such a way that, for majority of time, any mobile device is within the coverage of more than one base mobile device is within the coverage of more than one base station.station.

Cells of heterogeneous networks, on the other hand, are Cells of heterogeneous networks, on the other hand, are overlaid with each other.overlaid with each other.

The key issue for a mobile host is to reach a decision from The key issue for a mobile host is to reach a decision from time to time as to which base station of which network will time to time as to which base station of which network will handle the signal transmissions to and from a specific host handle the signal transmissions to and from a specific host and handover the signal transmission if necessary.and handover the signal transmission if necessary.

We classify handovers depending on several parameters, We classify handovers depending on several parameters, no longer is the network type the only handover no longer is the network type the only handover classification parameter.classification parameter.

Many more factors constitute categorization of handovers Many more factors constitute categorization of handovers including the administrative domains involved, number of including the administrative domains involved, number of connections and the frequencies engagedconnections and the frequencies engaged

Categorization ParametersCategorization Parameters

HandoverHandover Classifications Classifications

1.1. Network Types InvolvedNetwork Types Involved

Horizontal HandoverHorizontal Handover – The handover process of a mobile – The handover process of a mobile terminal between access points supporting same network terminal between access points supporting same network technology.technology.

E.g.E.g. The change over of signal transmission from IEEE 802.11b The change over of signal transmission from IEEE 802.11b

base station to geographically neighboring IEEE 82.11b base base station to geographically neighboring IEEE 82.11b base station considered as horizontal handover process.station considered as horizontal handover process.

Vertical HandoverVertical Handover - The handover process of a mobile terminal - The handover process of a mobile terminal between access points supporting different network technologybetween access points supporting different network technology

E.g.E.g. The change over of signal transmission from IEEE 802.11b The change over of signal transmission from IEEE 802.11b base station to overlaid cellular network is considered as base station to overlaid cellular network is considered as vertical handover process.vertical handover process.

2. Frequencies Engaged 2. Frequencies Engaged

Intra frequency HandoverIntra frequency Handover – The handover process of a mobile – The handover process of a mobile terminal among access point operating on same frequency.terminal among access point operating on same frequency.

E.g. This type of handoff is present in code division multiple E.g. This type of handoff is present in code division multiple access ( CDMA) network with frequency –division duplex ( FDD).access ( CDMA) network with frequency –division duplex ( FDD).

Inter frequency HandoverInter frequency Handover - The handover process of a mobile - The handover process of a mobile terminal among access point operating on different frequencies.terminal among access point operating on different frequencies.

E.g. This type of handoff is present in code division multiple E.g. This type of handoff is present in code division multiple access ( CDMA) network with time – division duplex ( TDD) and access ( CDMA) network with time – division duplex ( TDD) and is only handover type supported in GSM cellular systems.is only handover type supported in GSM cellular systems.

3. Number of Connections 3. Number of Connections InvolvedInvolved

Hard HandoverHard Handover – In hard handover the radio link to old base – In hard handover the radio link to old base station is released at the same time a radio link to the new station is released at the same time a radio link to the new base station is established.base station is established.

Soft HandoverSoft Handover – Contrary to hard handover, In soft – Contrary to hard handover, In soft handover a mobile node maintains a radio connection with handover a mobile node maintains a radio connection with no less than two base stations in overlapping handover no less than two base stations in overlapping handover regions and does not release any of the signals until it regions and does not release any of the signals until it drops below a specified threshold value. Soft handover are drops below a specified threshold value. Soft handover are pssible in situaions where the mobile node is moving pssible in situaions where the mobile node is moving between cells operating on same frequency.between cells operating on same frequency.

Softer HandoverSofter Handover – A softer handover is very similar to soft – A softer handover is very similar to soft handover except the mobile terminal switches connections handover except the mobile terminal switches connections over radio links that belong to same access point.over radio links that belong to same access point.

4. Administrative Domains 4. Administrative Domains InvolvedInvolved

An administrative domain is a group of systems and networks An administrative domain is a group of systems and networks operated by single organization of administrative authority.operated by single organization of administrative authority.

Intra – administrative domainIntra – administrative domain – A handover process where – A handover process where the mobile terminal transfers between different networks the mobile terminal transfers between different networks ( supporting the same or different types of network ( supporting the same or different types of network interfaces) managed by same administrative domain.interfaces) managed by same administrative domain.

Inter– administrative domainInter– administrative domain – A handover process where the – A handover process where the mobile terminal transfers between different networks mobile terminal transfers between different networks ( supporting the same or different types of network ( supporting the same or different types of network interfaces) managed by different administrative domain.interfaces) managed by different administrative domain.

5. Necessity of Handover5. Necessity of Handover

Obligatory HandoverObligatory Handover – In some situations it is necessary for – In some situations it is necessary for mobile terminal to transfer the connection to another mobile terminal to transfer the connection to another access point in order to avoid disconnection.access point in order to avoid disconnection.

Voluntary HandoverVoluntary Handover – In other situations transfer of – In other situations transfer of connection is optional and may or may not improve the connection is optional and may or may not improve the quality of servicequality of service

6. User Control Allowances 6. User Control Allowances

Proactive HandoverProactive Handover – In proactive handover the mobile – In proactive handover the mobile terminal’s user is allowed to decide when to handover. The terminal’s user is allowed to decide when to handover. The handover decision can be based on set of preferences handover decision can be based on set of preferences specified by user. Proactive handover is expected to be one specified by user. Proactive handover is expected to be one of the radical features of 4G wireless systems.of the radical features of 4G wireless systems.

Passive HandoverPassive Handover – The user has no control over handover – The user has no control over handover process. This type of handover is most common n 1G, 2G process. This type of handover is most common n 1G, 2G and 3G wireless systemsand 3G wireless systems

DESIRABLE HANDOVERDESIRABLE HANDOVER

FEATURESFEATURES

1. RELIABLE1. RELIABLE

A handover algorithm should be reliable. This means that A handover algorithm should be reliable. This means that the call should have god quality after handover. Many the call should have god quality after handover. Many factors help in determining the potential service quality of factors help in determining the potential service quality of a candidate base station. Some of these factors include:-a candidate base station. Some of these factors include:-

1.1. Signal-to-Interference ratio (SIR)Signal-to-Interference ratio (SIR)

2.2. Signal-to-noise ratio (SNR)Signal-to-noise ratio (SNR)

3.3. Received signal strength (RSS)Received signal strength (RSS)

4.4. Bit error ratio (BER)Bit error ratio (BER)

2. SEAMLESS2. SEAMLESS

A handover algorithm should be fast so that mobile A handover algorithm should be fast so that mobile device does not experience degradation or interruption. device does not experience degradation or interruption.

Service degradation may be due to :-Service degradation may be due to :-1.1. Continuous reduction in signal strength Continuous reduction in signal strength

2.2. Increase in co- channel interference (CCI)Increase in co- channel interference (CCI)

Service interruption may be due to hard handover Service interruption may be due to hard handover approach.approach.

3. INTERFERENCE 3. INTERFERENCE PREVENTIONPREVENTION

A handover algorithm should avoid high interference.A handover algorithm should avoid high interference. Co-channel interference is caused by devices transmitting Co-channel interference is caused by devices transmitting

on the same channel.on the same channel. Inter-channel interference is caused by device transmitting Inter-channel interference is caused by device transmitting

on adjacent channel.on adjacent channel. Both CCI and Inter-channel interference may severely limit Both CCI and Inter-channel interference may severely limit

the transfer rates of data network.the transfer rates of data network.

4. LOAD BALANCING4. LOAD BALANCING

A handover algorithm should balance traffic in all cells, A handover algorithm should balance traffic in all cells, whether of same or different network type.whether of same or different network type.

This helps to eliminate the need for borrowing channels This helps to eliminate the need for borrowing channels from neighboring cells that have free channels.from neighboring cells that have free channels.

Which simplifies cell planning and operation.Which simplifies cell planning and operation.

Reduces the probability of new call blocking.Reduces the probability of new call blocking.

5. IMPROVING 5. IMPROVING PERFORMANCEPERFORMANCE

Number of excessive handovers should be minimized Number of excessive handovers should be minimized because excessive handover leads to heavy handover because excessive handover leads to heavy handover processing loads and poor communication and greater processing loads and poor communication and greater chances that a call will be denied access to channel, chances that a call will be denied access to channel, resulting in higher handover call dropping probability.resulting in higher handover call dropping probability.

Excessive handover causes delay in processing of handover Excessive handover causes delay in processing of handover request, which will cause signal strength to decrease over request, which will cause signal strength to decrease over longer time period to a level of unacceptable quality. Call longer time period to a level of unacceptable quality. Call may be dropped if sufficient SIR is not achieved.may be dropped if sufficient SIR is not achieved.

Less handover minimize switching load.Less handover minimize switching load.

HANDOVER PROCESSHANDOVER PROCESS

Horizontal and Vertical handover Horizontal and Vertical handover process consists of three phases:-process consists of three phases:-

Handover DecisionHandover Decision

Radio Link TransferRadio Link Transfer

Channel AssignmentChannel Assignment

HANDOVER DECISIONSHANDOVER DECISIONS

Horizontals Handover Decisions mainly depends on:-Horizontals Handover Decisions mainly depends on:-1.1. Quality of channel mainly reflected by the received signal Quality of channel mainly reflected by the received signal

strength and the resources available in the target cell.strength and the resources available in the target cell.

2.2. Many signals are interference limited, meaning that signal Many signals are interference limited, meaning that signal strength is an adequate indication of channel quality. A strength is an adequate indication of channel quality. A handover is made if RSS from a neighboring base station handover is made if RSS from a neighboring base station exceeds the RSS from the current base station by exceeds the RSS from the current base station by predetermined threshold.predetermined threshold.

Vertical Handover DecisionsVertical Handover Decisions

Many network characteristics have an effect on whether Many network characteristics have an effect on whether or not handover should take place. Most of these or not handover should take place. Most of these characteristics were not needed in horizontal handoverscharacteristics were not needed in horizontal handovers

Vertical Handover DecisionsVertical Handover Decisions

Quality of serviceQuality of service : Handing over to a network with better conditions : Handing over to a network with better conditions and higher performance would usually provide improved service levels.and higher performance would usually provide improved service levels.

Cost of ServiceCost of Service : Different broadband wireless internet service provides : Different broadband wireless internet service provides and cellular service providers may provide a variety of billing plans and and cellular service providers may provide a variety of billing plans and options that will probably influence the customer’s choice of network.options that will probably influence the customer’s choice of network.

Security: Security: Power requirements: Power requirements: Wireless devices operate on limited battery Wireless devices operate on limited battery

power. When the level decreases, handing over o network with low power. When the level decreases, handing over o network with low power consumption elongated time.power consumption elongated time.

Proactive Handover:Proactive Handover: By permitting the user t choose a preferred By permitting the user t choose a preferred network, the system is able to accommodate the users special network, the system is able to accommodate the users special requirements.requirements.

Velocity: Velocity: In vertical handover, the velocity factor has a larger weight In vertical handover, the velocity factor has a larger weight and imperative effect on handover decision than in horizontal and imperative effect on handover decision than in horizontal handover. Because of overlaid architecture of heterogeneous network. handover. Because of overlaid architecture of heterogeneous network. Handing over off to an embedded network when availing at high Handing over off to an embedded network when availing at high speeds is discouraged since a handover back to original network would speeds is discouraged since a handover back to original network would occur very shortly.occur very shortly.

RADIO LINK TRANSFERRADIO LINK TRANSFER

Radio link transfer, the second part of handover process, refers to Radio link transfer, the second part of handover process, refers to the task of forming link to call at the new base station.the task of forming link to call at the new base station.

Intra-cell Handover – The radio link transfer is within the currently Intra-cell Handover – The radio link transfer is within the currently serving cell. No new link transfer are requiredserving cell. No new link transfer are required

Inter-cell handover – A handover made from one cell to another, Inter-cell handover – A handover made from one cell to another, requires rerouting operations to link the mobile’s current requires rerouting operations to link the mobile’s current communication path to the new base station.communication path to the new base station.

Backward handover – The ld serving base station prepares the Backward handover – The ld serving base station prepares the handover and no access to the target base station is made until handover and no access to the target base station is made until the control unit of the new base station has confirmed the the control unit of the new base station has confirmed the allocation of resources.allocation of resources.

Forward Handover – The process is initiated by means of the Forward Handover – The process is initiated by means of the target base station without relying on the old base station during target base station without relying on the old base station during preliminary phase of handover.preliminary phase of handover.

CHANNEL ASSIGNMENTCHANNEL ASSIGNMENT

The final handover stage is channel assignment which The final handover stage is channel assignment which consists of the allocation of resources at the new base consists of the allocation of resources at the new base station.station.

If a new call is admitted to access the network, a call If a new call is admitted to access the network, a call admission control ( CAC) algorithm will make a decision to admission control ( CAC) algorithm will make a decision to accept or reject it according to amount of available accept or reject it according to amount of available resources vs QoS requirements and the effect on QoS of resources vs QoS requirements and the effect on QoS of existing connection that may occur as result of the new existing connection that may occur as result of the new connection. Channel assignment is part of CAC and connection. Channel assignment is part of CAC and resource management.resource management.

Vertical handover decision Vertical handover decision function function ( VHDF)( VHDF)

VHDF is used to measure the improvement gained by VHDF is used to measure the improvement gained by handing over to a particular network. We choose the handing over to a particular network. We choose the following network parameters for VHDFfollowing network parameters for VHDF

1.1. Cost of Service ( C)Cost of Service ( C)

2.2. Security ( S)Security ( S)

3.3. Power Consumption ( P)Power Consumption ( P)

4.4. Network Conditions ( D)Network Conditions ( D)

5.5. Network performance ( F)Network performance ( F) As the mobile roams across different networks, VHDF is As the mobile roams across different networks, VHDF is

evaluated for all the accessible networks. The network evaluated for all the accessible networks. The network with highest calculated value for VHDF is most desirable with highest calculated value for VHDF is most desirable for the user based on specified preferences.for the user based on specified preferences.

The network quality Qi which provides, which provides a The network quality Qi which provides, which provides a measure of appropriateness of a certain network i, is measure of appropriateness of a certain network i, is measured via the function.measured via the function.

The larger the weight of specific factor, the more important The larger the weight of specific factor, the more important that factor is to user and vice versa.that factor is to user and vice versa.

These weights are obtained from user via user interface .These weights are obtained from user via user interface .