analysis of vertical and horizontal handoff

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ANALYSIS OF VERTICAL AND

HORIZONTAL HANDOFFS

Wireless and Mobile Communication Project Subject Code - ECE 403

BY

Tauseef Khan-11BEC0511

Rajesh Thomas-11BEC0097

Under the Guidance of:

Prof. Pavithra Balaji

Assistant Professor (Selection Grade)

School of Electronics Engineering

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CONTENTS

ABSTRACT..........................................................................3

CHAPTER 1:

1.1 Introduction……….……………………...……….4

1.2 Related Work…………………………….........….5

CHAPTER 2: THEORY

2.1 Handover Management Process……........….........6

2.2 Horizontal Handover……………………....…......6

2.3 Vertical Handover……………………….........….6

2.4 Always Best Connected Concept………...............7

CHAPTER 3:

3.1 Algorithm ……………………………….…........8

3.2 Programme..........................................................10

3.3 Simulation and Result….............….……….…...11

CHAPTER 4:

4.1 Conclusion……………………….......…….…...13

4.2 References…………………………………........13

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LIST OF FIGURES

CHAPTER 1

1 Vertical and Horizontal Handoff………………………….…..4

2 Horizontal vs. Vertical Handoff …………………………...…5

CHAPTER 2

3 Always Best Connected Concept………………………..……7

CHAPTER 3

4 Algorithm flow chart.................................................................9

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ABSTRACT

In broadband wireless access network, continuous high speed data communication can be provided to mobile subscribers by well-designed mobility management, where handover is a key element in maintaining air link to base station even in high velocity. When a mobile station changes

its geographical position, it may also need to change its attachment point in the network in order

to retain the quality of the connection. Currently, the mobility of a terminal is a requirement of

great importance, supported by a procedure known as handover. Horizontal Handover (HHO) is a

symmetric process and happens within the same technology and vertical handover or inter-system

handoff occurs between PoA supporting different network technologies, The results showed that

vertical handoff is done near access point due to power and antenna height in access point is less

than in base station. But vertical handoff will maintain the throughput stable, when the MS move

away from access point to base station. The effect of user speed on throughput also studied

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CHAPTER 1

1.1 INTRODUCTION

The rapid growth in the area of communication has generated the need of mobility during

communication. Currently, the mobility of a terminal is a requirement of great importance,

supported by a procedure known as handover. To maintain the connection between base station

and mobile terminals is the key to customer satisfaction. In the 3G or 4G wireless environment, a

mobile user is able to continue using the mobile device while moving from one point of attachment

to another. Such process is called a handoff, by which a MT keeps its connection active when it

migrates from the coverage of one network access point to another. Depending on the access

network that each point of attachment belongs to, the handoff can be either horizontal or vertical

Horizontal Handoff:

A horizontal handoff or intra-system handoff takes place between PoA (Point of Access)

supporting the same network technology, e.g., two geographically neighboring BSs of a 3G

cellular network

Vertical Handoff:

A vertical handoff or inter-system handoff occurs between PoA supporting different

network technologies, e.g., an IEEE 802.11 AP and a 3G BS. An example of horizontal and vertical

handoffs is illustrated in Figure 1.1

Figure 1. Vertical and Horizontal Handoff

Where a horizontal handoff happens between two cellular BSs and a vertical handoff takes

place between an AP of a WLAN and a BS of a cellular BS. Vertical handoffs are implemented

across heterogeneous cells of access systems, which differ in several aspects such as bandwidth,

data rate, frequency of operation, etc. The different characteristics of the networks involved make

the implementation of vertical handoffs more challenging as compared to horizontal handoffs.

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Figure 2. Horizontal vs Vertical Handoff

Wireless LAN connections generally provide higher speeds, while cellular technologies

generally provide more ubiquitous coverage. Thus the laptop user might want to use a wireless

LAN connection whenever one is available, and to 'fall over' to a cellular connection when the

wireless LAN is unavailable. Vertical handovers refer to the automatic fall over from one

technology to another in order to maintain communication. This is different from a 'horizontal

handover' between different wireless access points that use the same technology in that a vertical

handover involves changing the data link layer technology used to access the network.

1.2 RELATED WORK

Experimental Analysis of Horizontal and Vertical Handovers in Wireless Access Networks

by Sahana Bhosale Department of E & TC, BV’s College of Engineering for Women, Pune &

International Institute of Information Technology (I2IT) Pune, India and R.D. Daruwala

Department of Electrical Engineering, Veermata Jijabai Technological Institute (VJTI)

Mumbai, India,

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CHAPTER 2

2.1 HANDOVER MANAGEMENT PROCESS

The most basic way of describing a handover (HO) is when a phone call in progress is

redirected from its current cell to a new cell. This normally happens when the mobile device

making the call is in movement and detects that it is losing coverage, so it needs to “jump” to

another antenna. When the HO is within the same technology, for example, between Wi-Fi cells,

it is called a horizontal HO or traditional handover as depicted in Figure 1.2. If it is executed

between different technologies, for example, WiMAX to Wi-Fi, then it is called vertical HO.

Horizontal HOs are easy to implement because the operation is typically made under the same

operation domain. Vertical HOs, on the other hand, are typically executed between different

operators and require a much more complex signaling the main distinction between VHO and

HHO is symmetry. While HHO is a symmetric process, VHO is an asymmetric process in which

the MT moves between two different networks with different characteristics

2.2 HORIZONTAL HANDOVER

Horizontal handover always occurs in same Radio Access Technology (RAT) means

handover process occurs in different cells of same network. In homogeneous networks, horizontal

handovers are typically required when the serving access router becomes unavailable due to MT’s

movement In heterogeneous networks, the need for vertical handovers can be initiated for

convenience rather than connectivity reasons. HHO mainly use received signal strength (RSS) to

decide the handoff.

2.3 VERTICAL HANDOVER

In heterogeneous wireless networks the handover process is divided into two parts, one is

handover decision process and other is handover execution process. In handover decision process

both the mobile node and network decides that when will be the handover process occur. After the

completion of handover decision process, the handover execution process continues. The handover

execution process collects the supplementary network information such as the address detection

time in Mobile IPv6 and when will be the handover decision and detection process overlaps. The

handover delay process can be classified in to three main mechanisms:

1) Discovery time

2) Address Configuration Period

3) Network Registration Period

Vertical handover is slightly different from the traditional Horizontal handover

mechanism. They are further classified into two parts on signal strength-basis. The first

classification is upward VHO and downward VHO [4]. An upward VHO occurs from a network

with small coverage and high data rate to a network with wider coverage and lower date rate.

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On the other hand, a downward VHO occurs in vice-versa direction. The second

classification is imperative and alternative [5]. An imperative VHO occurs due to low signal

received from the BS or AP. In other words, it can be considered as a Horizontal handover. The

process for an imperative VHO has to be fast to keep connected the on-going connections. On the

other hand, an alternative VHO provides the user with better performance eg: more bandwidth or

lower access cost. Since this VHO occurs when the subscriber cone ted with a 3G network enters

the coverage area of WLAN network, even if the signal of the connection to the 3G cellular

networks does not lose any signal strength, the user may consider the connection to the WLAN a

better option.

2.4 ALWAYS BEST CONNECTED (ABC) CONCEPT

Always Best Connected is not refers to being not only always connected but also being

connected to the best available device and access technology all the times. ABC concept gives the

ability to user to get IP connectivity at any point of time to access internet according to his or her

needs. In this concept various wireless services (GSM/UMTS, WiMAX/802.16e and Wi-

Fi/802.11) will be accessible and these services share the same physical location. There will be

different points of Attachment (PoA) to access this service and these PoA includes different BSs

and APs offers different ways to connect the MS to communication server.

When the MS is turned on, the wireless card that is NIC in the MS starts active scanning and will

wait for the probe request. The probe request will return the available APs or BSs. Since the

authentication process in vertical handover is to be done at the communication server. The reply

gateway will grant access to the IP address to the wireless NIC card. In this way MS will be able

to reach the communication server and then the authentication will be started. The whole process

will run only for once for all the wireless interfaces. Gateway is just a delivery medium between

MS and server. At the MS, all the traffic should passed through Agent. This Agent is an application

which has a full control over all the wireless networks or interfaces. The role of the Agent is to

evaluate the quality of every available connection and then it will pick the best affordable service.

At the server the incoming data from the MS will be encapsulated with MIP address and then send

to the destination address. On the other side when the data is received, it replaces the MIP with

one of the available delivery IP address. Now the communication server will pick the last updated

best link. This process will provide us a simple Vertical Handover.

Link Quality table is continuously updating its values to connect the best available network without

affecting the performance or without any user interaction with the system. This will optimize all

the parameters in order to deliver the best affordable QoS with seamless connectivity. One of the

biggest key factor of this concept is that it will not add any complexity to handsets or MS.

Figure 3.

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CHAPTER 3

3.1 ALGORITHM

3.1.1 To Find the the received signal strength, radius of the cell, the power density,

cumilative distribution and the time threshold parameter from the required inputs.

1) Start

2) Get the transmitted power and store it in Ptx

3) Get the path loss and store it in PLref

4) Get the path loss exponent and store it in n

5) Get the reference distance and store it in dref

6) Get the distance between the mobile and the base station and store it in lop

7) Get the standard deviation of the Gaussian distribution function and store it in X

8) Calculate the received signal strength, RSS using the equation

𝑅𝑆𝑆 = 𝑃𝑡𝑥 − 𝑃𝐿𝑟𝑒𝑓 − 10𝑛 log10𝑙𝑜𝑝

𝑑𝑟𝑒𝑓+ 𝑋

9) Get the received signal strength at the edge of the cell and store it in RSSe

10) Calculate the radius of the cell, R using the equation

𝑅 = 𝑑𝑟𝑒𝑓𝑃𝑡𝑥 − 𝑃𝐿𝑟𝑒𝑓 − 𝑅𝑆𝑆𝑒

𝑛

11) Calculate the distance between base station and the sampling point, los using the equation

𝑙𝑜𝑠 = 𝑑𝑟𝑒𝑓𝑃𝑡𝑥 − 𝑃𝐿𝑟𝑒𝑓 − 𝑅𝑆𝑆

𝑛

12) Get the velocity of the mobile user and store it in v

13) Get the time of sampling and store it in ts

14) Get the time of entering the cell and store it in tpi

15) Calculate the travelling time in the cell, T using the equation

𝑇 =𝑅2 − 𝑙𝑜𝑠2 + 𝑣2(𝑡𝑠 − 𝑡𝑝𝑖)2

𝑣2(𝑡𝑠 − 𝑡𝑝𝑖)

16) If the value of T is in between 0 and 2R/v, find the PDF and CDF using

𝑓𝑇 =2

𝜋√4𝑅2 − 𝑣2𝑇2

𝐹𝑇 =2 cos−1(

𝑣𝑇2𝑅)

𝜋

Otherwise fT=0 and FT=1

17) Get the required probability of handoff and store it in Pf

18) Get the handoff delay and store it in Ti

19) Find the time threshold parameter, T1 using the equation

𝑇1 =2𝑅

𝑣sin(sin−1(

𝑣𝑇𝑖

2𝑅) −

𝜋

2𝑃𝑓)

20) Print the required values

21) Stop

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3.1.2 Algorithm to find if vertical handoff is required based on the received signal strength

and velocity of the mobile user

1) Start

2) Get the threshold signal strength and store it in Xwlan

3) Get the threshold velocity and store it in Vt

4) Check if user is near a WLAN

If not, repeat step 3.

If yes, continue with the following steps

5) Measure the received signal strength, RSS

6) Check if RSS is greater than Xwlan

If not, repeat step 3

If yes, continue with the following steps

7) Calculate the velocity of the mobile user, v

8) Check if v is lesser than Vt

If not, repeat step 3

If yes, initiate handoff

9) Stop

Figure 4. This figure shows

the algorithm of the second

programme as a flow chart.

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3.2 PROGRAMME

3.2.1 Programme to find the the received signal strength, radius of the cell, the power

density, cumilative distribution and the time threshold parameter from the required

inputs.

clear all; clc;

Ptx=input('Enter the Transmitted Power in dBm :');

PLref=input('Enter the Path Loss in dB :');

n=input('Enter the Path Loss Exponent :');

dref=input('Enter the reference distance in meter :');

lop=input('Enter the distance between the mobile user and base station in meter :');

X=input('Enter the standard deviation of the Gaussian distribution :');

RSS=Ptx-PLref-10*n*log10(lop/dref)+X;

fprintf('The received signal strength is : %d dBm \n\n',RSS);

RSSe=input('Enter the received signal strength at edge of cell (dBm) :');

R=dref*(Ptx-PLref-RSSe)/n; % Radius of the Cell

fprintf('The radius of the Cell is : %d m \n\n',R);

los=dref*(Ptx-PLref-RSS)/n; % distance between the base station and the sampling point

v=input('Enter the velocity of the mobile user (m/s) :');

ts=input('Enter the time of sampling (s) :');

tpi=input('Enter the time of entering the cell (s) :');

T=(R^2-los^2+v^2*(ts-tpi)^2)/(v^2*(ts-tpi)); % Travelling time in the Cell

if T>=0 && T<=2*R/v

fT=2/(pi*sqrt(4*R^2-v^2*T^2)); % Power Density Function

FT=2*acos(v*T/2/R)/pi; % Cumilative Distribution Function

else

fT=0;

FT=1;

end

fprintf('The PDF is %d and CDF is %d \n\n',fT,FT);

Pf=input('Enter the required Probability of Handoff :');

Ti=input('Enter the Handoff Delay (s) :');

T1=2*R*sin(asin(v*Ti/2/R)-pi*Pf/2)/v; % Time Threshold Parameter

fprintf('The delay required before handoff initiation = %0.4f \n',T1);

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3.2.2 Program to find if vertical handoff is required based on the received signal strngth

and velocity of the mobile user

clear all;

Xwlan=input('\nEnter the threshold signal strength (dBm): ');

Vt=input('Enter the threshold velocity (m/s): ');

fprintf('\n');

y=true;

while y

wlan=input('Is user near a WLAN (1=Yes, 0=No)? ');

if wlan~=1

fprintf('Handoff not Possible\n\n');

continue;

else

RSS=input('Enter the recived signal strength (dBm): ');

if RSS<=Xwlan


continue;

else

v=input('Enter the velocity of the user (m/s): ');

if v>=Vt


continue;

else

fprintf('Execute Handoff\n');

break;

end

end

end

end

3.3 RESULTS

The program has been executed successfully and the desired output has been obtained. A

sample input and the corresponding output for both programmes is shown below:

3.3.1 Program 1

Enter the Transmitted Power in dBm :50

Enter the Path Loss in dB :1

Enter the Path Loss Exponent :2.5

Enter the reference distance in meter :10

Enter the distance between the mobile user and base station in meter :100

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Enter the standard deviation of the Gaussian distribution :4

The received signal strength is : 28 dBm

Enter the received signal strength at edge of cell (dBm) :5

The radius of the Cell is : 176 m

Enter the velocity of the mobile user (m/s) :20

Enter the time of sampling (s) :1

Enter the time of entering the cell (s) :0.1

The PDF is 0 and CDF is 1

Enter the required Probability of Handoff :0.01

Enter the Handoff Delay (s) :0.1

The delay required before handoff initiation = 0.1765

3.3.2 Program 2

Enter the threshold siganl strength (dBm): 5

Enter the threshold velocity (m/s): 30

Is user near a WLAN (1=Yes, 0=No)? 1

Enter the recived signal strength (dBm): 10

Enter the velocity of the user (m/s): 40

Handoff not Possible








Enter the velocity of the user (m/s): 25

Execute Handoff

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CHAPTER 4

4.1 CONCLUSION

In 1984, when Marconi had seen practical reality, he had also seen the commercial

possibility for a system of telegraphy, which is absolutely free from the limitations of wires. The

invention of transistor a century later has led to the ability for everyone to communicate while on

the move. Today, it is purely a matter of convenience; to make and receive calls at your leisure,

any place and any time. This has been made possible largely due to handoff technologies.

Thus handoffs are very important in today’s wireless technology. Without handoff, it is

impossible to support the large number of users that are currently supported under such wide

areas. As described, roughly, handoff is the porcess of a user getting connected to a new antenna

from and old one. This is required especially when the user is moving. In the near future, wide

variety of wireless networks will be merged into the internet and allow users to continue their

application with higher degree of mobility.

4.2 REFERENCES

[1] Pallavi Shital Yevale and Santosh S. Sambare “A Survey of Vertical Handoff Algorithms to

Minimize Probability of False Handoff”, International Journal of Engineering Research and

Applications (IJERA) ISSN: 2248-9622, Vol. 3, Issue 1, January-February 2013

[2] Jang-Sub Kim, Erchin Serpedin, Dong-Ryeol Shin, and Khalid Qaraqe, “Handoff Triggering

and Network Selection Algorithms for Load-Balancing Handoff in CDMA-WLAN Integrated

Networks”, Hindawi Publishing Corporation EURASIP Journal on Wireless Communications

and Networking Volume 2008, Article ID 136939

[3] Ling-Jyh Chen, Tony Sun, Benny Chen, Venkatesh Rajendran and Mario Gerla, “A Smart

Decision Model for Vertical Handoff”.

[4] Qing-An Zeng and Dharma P. Agrawal, “Handoff in Wireless Mobile Networks”, Department

of Electrical Engineering and Computer Science, University of Cincinnati

[5] Richa Agarwal and Inderjeet Kaur, “Comparative Analysis Of Vertical Handoff In

IEEE 802.11 WLAN and CDMA Network”, International Journal of Engineering Research

and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue4, July-August 2012.

[6] Sahana Bhosale and R.D. Daruwala, “Experimental Analysis of Horizontal and Vertical

Handovers in Wireless Access Networks using NS2”, 2011 World Congress on Information

and Communication Technologies