Vertical Handover works

7/27/2019 Vertical Handover works

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BATTERY BASED HANDOVER BETWEEN WLAN

AND WIMAX TECHNLOGIES (Malak,salwa

,Magdy,Hussein )

The paper proposes a methodology for triggeringbetween different wireless technologies based on

the user terminal battery level status since different

access technologies have different terminal battery

power consumption during handover. This will save

battery energy of user terminal.

Assume user terminal equipped with both WLAN

and Wimax access technologies and the user uses

Wimax when there is WLAN in the same coverage.

Also assume limited user mobility to have both

networks in same coverage. The user terminalbattery will become weak after using Wimax

technology for some time and this will trigger a

desire to handover to WLAN which consumes less

energy. The triggering info is mapped into the

battery based handover flag and its exchanged

between the user terminal device and the network

through the handover option IP header. The

Network node reads the battery field information

and makes the handover decision based on the

battery level.

The battery level indicator field consists of 3 bits

hence enabling 8 levels of battery indicators. Level

zero (000) is assigned the strongest battery level

indicator while level 7 (111) is the weakest battery

level indicator. The presence of this field depends

on the value of the value of the battery based

handover flag with a value of 1 indicating the

presence of the battery level information in the

handover IP header. The user can activate this field

anytime he feels he needs to handover based on the

terminal battery level. The flag triggering conditioncan be set at a specific terminal energy level that

can be determined by the user required setting.

This set level can be transferred to the network side

using the field in the option IP header. The battery

level for each wireless technology can be manually

chosen by the user or the software can do it for him.

Under this state, handover is not only triggered due

to user mobility but also depends on battery level

hence handover can be forced by user.

Simulations are made for the mathematical models

which give energy consumption when user use onlyone access technology ie WLAN or Wimax and the

battery energy gain when user equipment makes a

battery based vertical handover from WiMAX to

WLAN.

Simulation results show that as the number of

exchanged packets is increased, the battery energy

consumption is increased and the battery level

decreases. Also the energy degradation of WiMAX is

higher than that of WLAN.

-Using the WLAN instead of WiMAX at some timessaves the battery energy levels of the terminal by

more than 540.5 times. Simulations also that it is

always better to handover to WLAN as long as there

is coverage in cases of low mobility of user terminal.

No Simulation tools mentioned

A SEAMLESS VHO APPROACH ( Rastin Pries, Dirk

S, Thorsten Gutbrod)

The paper Suggests use of VHO protocol based on

tight coupled architecture so that handover is

performed on link layer hence reducing handover

delays. The tight coupled architecture has the

WLAN APs integrated into the UMTS network

architecture.

Wireless technologies characteristics complement

one another making their integration feasible and

attractive. Existing mobile handover technologies

are based on mobile IP which simulation have

shown to be low in performance due to theiroperation on Network layer. Mobile IP sends out

messages periodically to look for connection

changes and handover will occur if 3 consecutive

massages are lost which results into handover

delays.


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For handover from WLAN to UMTS; The WLAN AP

is an integral part of UMTS connected directly to

SGSN and the ME is equipped with two interfaces to

WLAN and UMTS which are connected to each other

and the network layer by the handover module.VHO

is initiated whenever ME moves out of coverage forWLAN indicated by measurement reports to the

SGSN.VHO occurs in 3 main phases/steps ie

connection establishment, handover procedure and

connection release. Its initiated by sending a UMTS

device activation request from SGSN to theme using

the existing WLAN connection. The ME then sends a

packet data protocol context request over the

UMTS shared channel back to the SGSN.

Radio access bearer is set up and tunnel created

between RNC and SGSN. When quality of serviceclasses are active, ME is connected to both networks

and transmits a positive UMTS device activation

response to the SGSN. After successful connection

establishment, the SGSN initiates the vertical

handover and switching of the networks. The ME

first switches to UMTS and indicates change of

device to the SGSN through a handover response

message. The SGSN then activates the IP-over IP

tunnel to the RNC and updates its address of the ME

so that all the traffic is forwarded to the RNC which

is responsible for the ME. The old connection to

WLAN is then deallocated hence releasing the

tunnel between the SGSN and the AP and the ME

disassociates itself.

Handover protocol between WLAN and UMTS has

been implemented and evaluated using OPNET

Modeler. The simulation results indicate total

handover delay for the two directions of less than

750ms which is less than that of mobile IP. Also the

period with no connection at all lasts less than100ms still out performing mobile IP. The

simulations further show that connection

establishment takes most of the time due to the

complex radio access bearer and tunnel setup and

unfortunately this connection establishment delay

cannot be minimized.

VERTICAL HANDOVER IN B3G WIRELESS

NETWORKS (Enrique S, Ulises Pineda, Jesus

Acosta-Elias)

Beyond 3G refers to the combination of the different

several wireless technologies such as cellular,

metropolitan, wireless and personal area networks.

To guarantee ubiquitous coverage that will offer

connectivity anytime, anywhere, there is need to

integrate complimentary wireless technologies with

overlapping coverage so that the user can use the

best available wireless technology at any given time.

This requires mobile terminals with multiple

interfaces to access different networks. Users canthen switch from one wireless technology to

another without disruption in service thus from BS

to AP and vice versa. This is termed vertical

handover if the BS and AP are using different

technologies.

-Vertical handover can be classified depending on

data rate and coverage into downward and upward

VHO. Upward VHO occurs from a network with

small coverage and high data rate to a network with

wider coverage and lower date rate and vice versa

for downward VHO. It can also be classified further

according to received signal strength and

performance into imperative and alternative VHO.

-VHO decision is divided into 3 steps thus system

discovery, handover decision and execution. During

discovery phase, the mobile terminal identifies

which networks can be used and the available

services in the networks. During decision phase,

depending on a number of metrics such as available

bandwidth, delay, jitter, access cost, the mobile

device determines the network to connect to.Handover execution involves rerouting connections

and transfer ofusers context information from an

existing network to the new network in a seamless

manner. It also involves authentication and

authorization.


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The VHO decision mechanism is formulated as an

optimization problem in which each candidate

network is associated with accost function and the

best network is the one with will minimal cost

value. The cost function depends on parameters

such as delay, bandwidth and power requirementsand appropriate weights are associated to each

parameter depending on its importance in the

decision making. The VHO can be formulated as

fuzzy MADM problem with two classical MADM

methods in use is SAW and TOPSIS. The network

selected is based on analytic hierarchy process

(AHP)which decomposes network selection

problem into several sub problems each with an

assigned weight and also uses Grey relational

analysis to rank the candidate network and selectthe one with the highest ranking.

Comparison is made for performance of VHO, SAW,

TOPSIS, GRA and MEW (multiplicative exponent

weighting). A B3G network scenario with four

wireless networks available for VHO is simulated

using

Stochastic models and several kinds of traffic such

as conversational, streaming, interactive and

background. Handover metrics such as available

band width, jitter, packet delay, probability of error

etc are considered.

Results show close results in performance but GRA

outcompetes the rest in terms of performance in

some situations. Simulation results also show that

MEW, SAW, TOPSIS select the same network for

VHO for more than 90% of the time and the four

algorithms select the same network more than 70%

of the time.

A mobile device in B3G wireless environment

makes decisions about target network eitherperiodically or each time new network is sensed.

This sequential decision can be modeled as a

markov decision process(MDP).Cost and reward

functions are introduced to capture trade off among

network resources utilized by the connection in

terms in terms of available bandwidth and delay

and the signaling and processing load incurred by

the network after VHO execution.The MDP

formulation objective is to is to maximize the

expected total reward per connection.

WLAN WIMAX VHO HYBRID SATIFACTION

MECHANISM (Mohammed S,Nizar , Cosmas

A,Chrsitos)

The paper considers handover between two access

technologies IEEE 802.16e Wimax and the IEEE

802.11n WLAN networks. The user benefit is in

terms of improvement of the obtained quality of

service and date rate and as long as user is satisfied

with Q0S, he wont search for another accesstechnology to perform handover which can even

lead to a connection failure. The incentive for

handover to Wimax is wider coverage and stricter

control on delay. WLAN on the other hand, offer

higher data rates with smaller coverage and lack of

control on delay. Operator benefits entails load

balancing among different cells/access technologies

while the user is motivated by higher data rates or

minimal delays.

The Author considers metric to offer handover

benefit to both operator and customer. The

proposed metric tackles both user and operator

satisfactions. The metric indicates VHO mechanism

to start or not start providing the system designer

with the ability to offer both advantages at the same

time or modified to account for single objective.

Focus is on downlink channel where N receivers

each of them equipped with single antenna are

being served by singe BS equipped with single

transmitting antenna. Single access technology is

considered between BS and user on each time andfor each one of them, a channel h(t) is considered

between users and BS with static block fading

model being assumed which keeps constant

through the coherence time and independently

changes between consecutive time intervals with iid

complex Gaussian distributions. Hence each user is


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assumed to be fixed during each fading block where

the duration of each symbol is 20ms to match with

practical wireless systems.

-Let si(t) denotes the uncorrelated data symbol to

the ith user with E{}=1.

The received signal yi(t)=hi(t) si(t)+zi(t) where zi(t)is an additive iid complex noise component with

zero mean and E{}=2

Proposed Hybrid model;

The switch between different technologies should

be transparent and cause no disruption in the

service. The handover should be seamless and this

is facilitated by use of IP protocol standard where

each user is assigned an IP that is fixed as the client

moves within broadband wireless technology.The VHO is carried out on basis of hybrid

satisfaction indicator given as

Th=Sc +(1- )Sop

Where Sc indicates customer satisfaction indicator

and Sop indicates operator satisfaction metric. The

importance of SC and Sop is determined by the

optimization parameter . setting to zero or one

gives a single objective metric for operator or

customer satisfaction respectively. Varying

between 1 and 0 gives degree of freedom depending

on system conditions on load and customer

requirements. Satisfaction indicator definition for

both operator and customer are based on

thresholds to guarantee a marginal increase in

satisfaction if the performance is above threshold

and a drastic decrease in the satisfaction indicator if

the performance is below the demand.

The customer satisfaction Sc has value less than one

if the user is not satisfied and value above 1 for a

satisfied user.

Sc = if yob yth

if yob < yth

The decay below 1 is exponential while the increase

above 1 is small. The performance is presented

through the SNR as its metric as it links both the

data rate and probability of error performance.

Due to economical considerations, the operator

satisfaction doesnt follow exponential distribution.

The formulated metric also shows a value less than

1 if the load is more than threshold hence customer

is not satisfied and returns a value above one

otherwise. The objective of the operator is to makeload balancing.

Sop = 1 +

if

1 +

if <

The proposed algorithms are tested using computer

simulations considering one Wimax BS with 1km

coverage and several WLAN BS each covering 30m

diameter. Simulations are made under different

conditions of by varying load Wimax and WLAN cellloads and changing SNR of user as he moves

through the considered area. Tests are run for 50%

of their maximum load conditions and simulations

show an increase in threshold values for customer

connected to WLAN for regions close to the WLAN

BSs due to large data rate offered by WLAN and

operator load remains the same for both access

technologies under this condition.

In the first extreme case when the Wimax if fully

loaded and WLANs are not loaded, the operator

desires customers to handover to WLAN to

decrease Wimax congestion and the users also

desire to go to WLAN due to larger data rate. In case

Wimax system is not loaded and WLAN is fully

loaded, the satisfaction indicator controlled by

Wimax system leads to customers to desire to

handover to Wimax system. The satisfaction

remains high and stable as long as the received SNR

is above the set threshold and it decreases

dramatically when the received SNR drops below

the threshold and this occurs at the cell edges due

to path loss effect.

-A plot of satisfaction indicator shows that

satisfaction increases greatly in regions close to the

BSs while it is below one in all other regions

implying users in Wimax coverage regions alone are


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not satisfied and hence they always desire to

handover to WLAN if its in its coverage region to

increase satisfaction.

-Also the data rate for each user increases with

increase in number of WLANs Bs.

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Vertical Handover works