SELF-ADAPTIVE HANDOFF MODEL FOR 4G

1. INTRODUCTION

The 4G wireless networks will integrate heterogeneous technologies such as wireless

LAN (WLAN) and third generation (3G) cellular network because no single wireless

network technology simultaneously can provide a low latency, high bandwidth, and wide

area data service to a large number of mobile users.

The movement of a user within or among different types of networks can be referred as

the vertical mobility. One of the major challenges for seamless service in the vertical

mobility is a vertical handoff, where handoff is the process of maintaining a mobile user's

active connection by changing its point of attachment. In the 4G wireless systems,

seamless handoff with small latency and packet losses should be executed. Handoff

latency is one of important factors that decide the quality of service (QoS) in the 4G

wireless networks. In the deployment of multimedia services with real-time requirements,

the handoff process can significantly degrade the QoS from the user's perspective. Since

many packets can be typically lost before vertical handoff by the unstable channel

condition, this article presents a design mobile architecture which is seen suitable for

envisioned various network architectures and technologies for 3G and beyond.

The continuing evolution of micro electronics, telecommunication, audio-visual

techniques and information services is delivering the technology to fulfill the vision of

omnipresent services. Today many technologies are available that can be combined to

exploit the business potential of application that work anywhere anytime in a seamless

and intuitive way.

The wide spread success of wireless and mobile communication has resulted in the

creation of a large variety of wireless technologies, including 2G and 3G cellular,

satellite, Wi-Fi, and Bluetooth. Each technology is tailored to reach a particular market.

The advantage of these diverse networks is that they offer many choices for increasing

bandwidth, accessing the internet and increasing the coverage area for the average user.

Expanding services to the use and co-ordination of diverse networks creates the challenge

of developing novel interoperable network protocols to manage user mobility, between

different types of systems-a level of interoperability currently not available in 3G

systems. The evolutionary goals of beyond 3G (B3G) and 4G include building on packet

based CDMA networks. Some goals may be forecast by emerging issues, such as

spectrum efficiency, dynamic bandwidth allocation, security, quality of service (QoS)

and transceiver technology.

Universal wireless access refers to the ability of the user to connect any where at any time

from any network. The change in connection may be initiated by the user or by the

network, transparent to the user. For instance, a user may choose to access a wireless

LAN (WLAN) to send a large a data file, but may choose a cellular network for voice call

on the other hand, a network may decide to handoff a stationary data user to a WLAN

user in order to increase bandwidth availability for mobile users in a 3G cellular

networks. To achieve seamless mobility, network management operations must be

conducted without causing degradation of services, and without need for user

intervention. The movement of a user within or among different types of networks can be

referred to as intersystem or vertical mobility. Handoff research has been based on

evaluation of the signal strength received at the mobile node, followed by a change in

access point, if needed and up dated.

2. HAND OFF

When a mobile user travels from one area of coverage or cell to another cell within a

call’s duration the call should be transferred to the new cell’s base station. Otherwise, the

call will be dropped because the link with the current base station becomes too weak as

the mobile recedes. Indeed, this ability for transference is a design matter in mobile

cellular system design and is call hand off

Fig1 han off

Initiation of the handoff may begin when the signal strength at the mobile received from

base station 2 is greater than that of base station 1

Any hand off operation is a three stage process, that includes hand off decision, radio link

transfer and channel assignment. Hand off decision is performed based on a perception of

channel quality reflected by the received signal strength and other measurements and the

availability of resources in a new cell. The base station usually measures quality of the

radio link channels being used by mobile nodes in its surface area. This is done

periodically so that degradation in signal strength below a prescribed threshold can be

detected and hand off is initiated by the base station. Radio link transfer refers to the

responsibility of the network to form links to the call at its new point of attachment. It

may require hand off rerouting operations. The third handoff stage channel assignment

consists of allocations of resources to the hand off at the new point of attachment.

While performing handoff, the mobile user connection may be created at the target base

station before the old base station connection is released. This is soft hand off. On the

other hand the new connection may be set up after the old connection is released. This is

hard hand off. Also we have hand off between different networks termed as vertical

handoff and handoff between same networks known as horizontal handoff. The handoff

model developed here can suite any network

2.1 HANDOFF INITIATION

A hard handoff occurs when the old connection is broken before a new connection is

activated. The performance evaluation of a hard handoff is based on various initiation

criteria [1, 3, 13]. It is assumed that the signal is averaged over time, so that rapid

fluctuations due to the multipath nature of the radio environment can be eliminated.

Numerous studies have been done to determine the shape as well as the length of the

averaging window and the older measurements may be unreliable. Figure 2 shows a MS

moving from one BS (BS1) to another (BS2). The mean signal strength of BS1 decreases

as the MS moves away from it. Similarly, the mean signal strength of BS2 increases as

the MS approaches it. This figure is used to explain various approaches described in the

following subsection.

1.2.1 Relative Signal Strength

This method selects the strongest received BS at all times. The decision is based on a

mean measurement of the received signal. In Figure2 , the handoff would occur at

position A. This method is observed to provoke too many unnecessary handoffs, even

when the signal of the current BS is still at an acceptable level.

1.2.2 Relative Signal Strength with Threshold

This method allows a MS to hand off only if the current signal is sufficiently weak (less

than threshold) and the other is the stronger of the two. The effect of the threshold

depends on its relative value as compared to the signal strengths of the two BSs at the

point at which they are equal. If the threshold is higher than this value, say T1 in Figure

2, this scheme performs exactly like the relative signal strength scheme, so the handoff

occurs at position A. If the

threshold is lower than this value, say T2 in Figure 2, the MS would delay handoff until

the current signal level crosses the threshold at position B. In the case of T3, the delay

may be so long that the MS drifts too far into the new cell. This reduces the quality of the

communication link from BS1 and may result in a dropped call. In addition, this results in

additional interference to cochannel users. Thus, this scheme may create overlapping cell

coverage areas. A threshold is not used alone in actual practice because its effectiveness

depends on prior knowledge of the crossover signal strength between the current and candidate

BSs

1.2.3 Relative Signal Strength with Hysteresis

This scheme allows a user to hand off only if the new BS is sufficiently stronger (by a

hysteresis

margin, h in Figure 2) than the current one. In this case, the handoff would occur at point

C. This technique prevents the so-called ping-pong effect, the repeated handoff between

two BSs caused by rapid fluctuations in the received signal strengths from both BSs. The

first handoff, however, may be unnecessary if the serving BS is sufficiently strong.

1.2.4 Relative Signal Strength with Hysteresis and Threshold

This scheme hands a MS over to a new BS only if the current signal level drops below a

threshold and the target BS is stronger than the current one by a given hysteresis margin.

In Figure 2, the handoff would occur at point D if the threshold is T3.

3 TYPES OF HAND OFF

There are mainly two types of handoff

a) Soft handoff

While performing handoff, the mobile user connection may be created at the

target base station before the old base station connection is released. This is soft

hand off

Soft handoff is used in voice-centric cellular networks such as GSM or

CDMA(code-division multiple access). It uses a make-before-break approach

whereas a connection to the next BS is established before a SS leaves an ongoing

connection to a BS. This technique is suitable to handle voice and other latency-

sensitive services such as Internet multiplayer game and video conference. When

used for delivering data traffic (such as web browsing and e-mail), soft handoff

will result in lower spectral efficiency because this type of traffic is bursty and

does not require continues handover from one BS to another.

In CDMA, all base station use the same frequency channel for each mobile phone

set, no matter where the set is located. Each set has an identity based on a code,

rather than on a frequency (as in FDM) or sequence of time slots (as in TDM).

Because no change in frequency or timing occurs as a mobile set passes from one

base station to another, there are practically no dead zones. As a result,

connections are almost never interrupted or dropped.

A soft handoff may involve using connections to more than two cells, e.g.

connections to three, four or more cells can be maintained by one phone at the

same time

b) Hard handoff

New connection may be set up after the old connection is released. This is hard

hand off

Mobile WiMAX has been designed from the outset as a broadband technology

capable of delivering triple play services (voice, data, video). However, a typical

Mobile WiMAX network is supposedly dominated by delay-tolerant data traffic.

Voice in Mobile WiMAX is packetized (what is called VoIP) and treated as other

types of IP packets except it is prioritized. Hard handoff (HHO) is therefore used

in Mobile WiMAX.

In hard handoff, a connection with a BS is ended first before a SS switches to

another BS. This is known as a break-before-make approach. Hard handoff is

more bandwidth-efficient than soft handoff, but it causes longer delay. A

network-optimized hard handoff mechanism was developed for Mobile WiMAX

to keep a handoff delay under 50 ms.

An advantage of the hard handoff is that at any moment in time one call uses only

one channel. Another advantage of the hard handoff is that the phone's hardware

does not need to be capable of receiving two or more channels in parallel, which

makes it cheaper and simpler.

4 HANDOFF ARCHITECTURE FOR 4G

The mobile host has a multi-mode card that can access the WLAN (such as

802.11b) and cellular (such as CDMA2000) networks. Their hierarchical foreign

agents and multi-path structure used is shown in Figure 2. For conventional

handoff techniques, the criteria that select the initial mode in mobile host are the

radio link quality, data rate, service type, speed of mobile host, and capacity of

cellular network. If its data rate is low and fast moving, then the mobile host can

select the CDMA2000 network. For high data rates, then the WLAN is selected.

For accessing the internet, we know that the uplink and downlink traffics are not

balance. Normally, user prefers a wider downlink frequency than the uplink. Here

our goal is to use the combination of cellular network for uplink traffic services

and WLAN network for downlink traffic services to provide an efficient

application for mobile user to access the internet

In figure 1, structured mobility anchor point (MAP) can offer a mobile

node (MN) seamless mobility when it moves from MAP2 to MAP3 while

communicating with a corresponding node (CN). In this approach, different

mechanisms and protocols can handle authentication, billing and mobility

management in the cellular and 802.11 portions of the network [4-7]. When an

MN enters a new foreign subnetwork, it first acquires a new physical care-of

address (PCoA) by means of address autoconfiguration, in which the MN uses it

as the source address for all datagrams that it sends. The MN will also register a

unique virtual care-of address (VCoA) with a home agent (HA) and CN for each

level of the hierarchy. It all starts when the MN receives a router advertisement

with the mobility information option that contains a new hierarchy, in which it

will send a binding update. That binding update binds its PCoA to its lowest

VCoA (i.e. at the lowest MAP).

After that the lowest MAP will send a surrogate binding update to the next

higher MAP. That binding forms a binding between the VCoAs of the mobile

node in the MAPs hierarchy. This continues until the highest MAP receives a

surrogate binding update when it will check whether that MN is allowed to use

the network and finally sends a binding acknowledgement to the next lower MAP.

These surrogate acknowledgements are sent until the lowest MAP receives one.

Then the lowest MAP sends acknowledgement to the MN.

In figure 2, mobile node sends binding update to the MAP2, which is the

lowest MAP (VCoA2®PCoA). MAP2 sends a surrogate binding update to MAP1

(VCoA1®VCoA2). MAP1 is the highest MAP and it processes the authentication

header of the original binding update and authenticates the mobile node. In figure

1 and figure 2, multiple paths are maintained while mobile node transits the

overlapping area of two adjacent cells, keeping connections for both

cells.

To avoid drastic quality degradation and stream disruptions, Yi Pan et al.

[9] proposed a scheme that reduces packet loss and maintains high throughput

during handoffs by transmitting packets on multiple paths. Meanwhile, high

throughput is maintained by exploiting all the available bandwidth on multiple

paths. To allow a source node to be able to maintain multiple paths

simultaneously, mobile IP simultaneous binding [10, 11] and route optimization

option [12] are used. Simultaneous binding option allows a mobile node to

simultaneously register multiple CoAs, and route optimization option allows the

sender to be always informed of the CoA registration directly form the receiver.

5 HANDOFF ALGORITHM AND ANALYSIS

Based on our architecture, we proposed a 4G mobile control handoff algorithm

showed in figure 3. In our proposal, we hope that the MN request with go through

the first connection (MN ® MAP2 ® MAP1 ® CN) and the reply from the second

connection (CN ® MAP1 ® MAP3 ® MN) showed in figure 2. In order to

implement this, path management is needed to distribute different task by

different path based on different bandwidth. In order to realize this function, a

cache is configured in MAP1 which is used for bandwidth option. When a mobile

node send a request out, it travels from mobile node to MAP2 to MAP1 and

finally reach the CN. A reply from CN will have to come into MAP1. In MAP1,

the reply needs to be rerouted. There is a database in the cache of MAP1, which

include the mobile node ID. It will go into MAP3 but not to MAP2 after

comparing the mobile node ID if it is the same mobile node. As a result, a more

effective use of the available bandwidth can be realized which result in achieving

a higher speed data rate connection.

When the mobile node serving in the cellular network region enters the WLAN

service region, it connects to the network (in our case the 802.11 network). In this

case, handoff happen between cellular network and WLAN network. For our

proposed handoff algorithm showed in figure 3 based on three novel idea: (i) the

handoff point is not a critical factor, because the cellular network overlaid the

802.11 region; (ii) multi-path is used for both networks; (iii) bandwidth

optimization, which try to combine cellular network for uplink traffic services and

802.11b Wi-Fi network for downlink traffic service during and after handoff

according to internet characteristics which uplink traffic services is one of fourth

of downlink traffic service. In our proposed algorithm, the mobile node receives

a beacon signal from the access point through activating the 802.11 card. If the

mobile node receives an agent advertisement message from the MAP3, it sends a

handoff ready request message to the MAP2 which is the currently serving

cellular network. Then the MAP1 transmits in-bound packets to the MAP3. After

that, the mobile node checks the received beacon signals continuously to

determine whether to handoff or not. If the conditions for the handoff are

satisfied, then the handoff procedure is performed. At this point, the mobile node

requests to keep the channel that is currently allocated to the cellular network and

transmits a reassociation request message to the access point in the WLAN. So

two connections are used by the mobile node. From now on, the mobile node

communicates with both networks. i.e. the 802.11

Figure 3. 4G Handoff Algorithm

when a mobile node enters 802.11 region it gets an advertisement from access

point and try to measure the signal strength in order to get a best access point for

service, this is the fist step of our proposed handoff algorithm showed in figure 3.

In the mobile controlled handoff algorithm the signal strength measurements are

taken by the mobile device, as indicated by step two in figure 3. if a candidate

access point having better signal strength is detected then the handoff execution

process is initiated. Since mobile controlled handoff is scalable and more

distributed, it can continuously monitor signal strength measurements. A handoff

adapter object located at the mobile device drives handoff execution. Mobile

controlled handoff is executed as a forward, soft handoff. To accomplish soft

handoff and select a best access point, the mobile device can simultaneously

receives data from multiple access point, but handoff only can be taken place at

one access point, so a best AP is selected by step three in figure 3. It is similar

with other handoff procedure after selected a best AP, that is registration and

setting up a connectivity, and then transfer parameter in order that a new data path

can be setup by step 4,5 ,6and 7 in figure 3.Handoff notice by step 8 in figure 3 is

different from traditional handoff procedure, since old data path will be kept

continuously, so path management is needed by step 9 in figure 3 in order that to

make sure multiple path can service for the seam mobile device. Actually, they

are two data path distributed both of WLAN and cellular network serving the

seam mobile device by sending request and getting reply from both network based

on their own characteristics which is the different bandwidth. Since WLAN have

more wide bandwidth with cellular network, and the internet characteristics is that

reply could need more wide bandwidth with request. Consequently, bandwidth

selected by last step in figure 3 should be necessary. Thus our algorithm has been

optimized bandwidth to increase data transmission.

6 VERTICAL HAND-OFF SCENARIO

Today's wireless access networks consist of several overlapping tiers. The

combination of 3G and WLAN technologies enable the internet access from

anywhere and anytime thereby bringing benefits to both end users and service

providers. A horizontal handoff is defined as a handoff between base stations

(BSs) that use the same type of wireless network interface. This is the traditional

definition of handoff for homogeneous cellular systems. A vertical handoff is

defined as a handoff between BSs that uses different wireless network

technologies such as the WLAN and the 3G cellular network. The heterogeneous

networks (3G cellular network and WLAN) have some important properties. First,

the network service areas are overlapped as shown in Fig. [1].

For example, the 3G cellular network acts as an umbrella network to the WLAN

network. Also the different cells of the same network are overlapped. To reduce

service disruption, we can utilize this overlapping by simultaneously connecting

to the different networks at the boundary of one network during vertical handoff.

Second, two networks may support different data rates. The WLAN can support a

data rates in Mbps, while 3G cellular network can only supply tens of Kbps. In

our scenario, we focus on the vertical handoff between the WLAN and the 3G

cellular network. Fig. 1 shows the vertical handoff when the mobile station (MS)

moves from the location A in the WLAN to the location C in the 3G cellular

networks. As the MS leaves the access point (AP), the strength of the beacon

signal received from the AP periodically weakens. If its strength is decreased

below the threshold value, the MS tries connecting to the 3G cellular network and

starts synchronizing with the system to prepare the handoff.

6.1 PROPOSED MOBILE MODEL

Even today researchers are looking in innovative point of view about the handoff

feature in soft vertical handoff which facilitates 4G. We have worked out such

that we give less work to the BTS, BSC, MTC etc and mould the mobile handset

in order to provide more complex operations which is carried out in a simpler

fashion and also flexible as compared to the present approach models (vertical

handoff and other models).

Proposed model

MICRO

CONTROLLER

MEMORY

D

U

P

L

E

X

BAND

PASS

FILTER

A/D CONVERTER

MEMORY

MICROCONTROLLER

AND DSP

CONTROLLER

MASTER ALGORITHM-OUTLOOK OF THE SOFTWARE PART

READ THE VOLTAGE OF THE NTH NETWORK

COMPARE VOL WITH RANGE VOL

STORE VALUE

INR N

N=0

GET ALL PARAMETERS OF NTH NETWORK

IF Vn=Vr

V n=V

V n=V r

v

V n=V r

IF N=M

N=M

CAL EFFCIENCY OF THE NTH NETWORK

THE NTH NETWORK

CALL SCORE OF NTH N\W

HANDOVER TO NEW NETWORK

NO HANDOVER

HANDOVER

RECOLLET THE SCORES

AND LARGEST

N=0

INR N

USER PREFERENCE

STORES VALUE

IF N=M

N=M

IF N=M

N=M

Here we introduce a block which contains both hardware and software

sectors as shown in fig 3 and fig 4. In the hardware sector we have a block which

can be an integral part of mobile with various available chips like DSP,

Microprocessors, A/D Converters Memory.

6.2 Comparison between 3G and 4G

PARAMETERS 3G 4G

Major Requirement

Driving Architecture

Predominantly voice driven

- data was always add on

Converged data and voice over

IP

Network Architecture Wide area cell-basedHybrid - Integration of Wireless

LAN (Wi-Fi, Bluetooth)

Speeds 384 Kbps to 2 Mbps 20 to 100 Mbps in mobile mode

Frequency BandDependent on country or

continent (1800-2400 MHz)

Higher frequency bands (2-8

GHz)

Bandwidth 5-20 MHz 100 MHz (or more)

Switching Design

BasisCircuit and Packet All digital with packetized voice

Access Technologies W-CDMA, 1xRTT, Edge OFDM and MC-CDMA

Forward Error

CorrectionConvolution rate 1/2, 1/3 Concatenated coding scheme

Component DesignOptimized antenna design,

multi-band adapters

Smarter Antennas, software

multiband and wideband radios

IP A number of air link

protocols, including IP 5.0 All IP (IP6.0)

7. NEED FOR 4G

4G has sprung from a usage –driven research frame work to invent new

technologies to wireless world vision. The evolution of such a wireless system

(also called ‘Beyond 3G ‘or ‘B3G’) is closely linked to rapid advances in digital

and component technologies. So future mobile devices will be capable of

supporting multiple wireless standards, and operate in multi-mode, multiband

fashion. The 4G wireless communication system can be integrated with the

Internet protocol (IP) backbone network to provide quality of service (QoS)

support for multimedia applications. It will support dynamical scheduling, link

adaptation and frequency selection as well as full roaming capabilities. 4G also

mean mobile telephony at a data rate of 100Mbps globally (between any two

points in the world) and 1Gbps locally.

• Need for 4 G 3G performances may not be sufficient to meet needs

of future high- performance applications like multi-media, full-motionvideo,

wireless teleconferencing. We

need a network technology that extends 3G capacity by an order of magnitude.

• There are multiple standards for 3G making it difficult to roam and inter operate

across networks. we need global mobility and service portability

• 3G is based on primarily a wide-area concept. We need hybrid networks that

utilize both wireless LAN concepts.

8. 4G APPLICATIONS

1. PUBLIC SAFETY:

One of the most notable advanced applications for 4G systems is location-based

service.. This database could be accessed by a subscriber in a moving vehicle

equipped with the appropriate wireless device, which would provide the platform

on which would appear a virtual representation of the environment ahead. For

example, one would be able to see the internal layout of a building during an

emergency rescue. This type of application is sometimes referred to as

"Telegeoprocessing", Telegeoprocessing over 4G networks will make it possible

for the public safety community to have wireless operational functionality and

specialized applications for everyday operations, as well as for crisis

management.

2. VIRTUAL NAVIGATION: As described, a remote database contains the

graphical representation of streets, buildings, and physical characteristics of a

large metropolis. Blocks of this database are transmitted in rapid sequence to a

vehicle, where a rendering program permits the occupants to visualize the

environment ahead. They may also "virtually" see the internal layout of buildings

to plan an emergency rescue, or to plan to engage hostile elements hidden in the

building.

3. TELE-MEDICINE: A paramedic assisting a victim of a traffic accident in a

remote location could access medical records (e.g., x-rays) and establish a video

conference so that a remotely based surgeon could provide “on-scene” assistance.

In such a circumstance, the paramedic could relay the victim's vital information

(recorded locally) back to the hospital in real time, for review by the surgeon.

4. CRISIS-MANAGEMENT APPLICATION: These arise, for example, as a

result of natural Disasters where the entire communications infrastructure is in

disarray. In such circumstances, restoring communications quickly is essential.

With wideband wireless mobile communications, both limited and complete

communications capabilities, including Internet and video services, could be set

up in a matter of hours. In comparison, it may take days or even weeks to re-

establish communications capabilities when a wireline network is rendered

inoperable.

8. FUTURE CHALLENGES

One of the most challenging issues facing deployment of 4G technologies is how

to make the network architectures compatible with each other. The success of 4G

systems would largely depend upon its ability to overcome the capability

challenges. Some of the challenges concerning 4G architectural design issues are

given below:

1. HIGH USABILITY & GLOBAL ROAMING: The end user terminals should

be compatible with any technology, at any time, anywhere in the world. The basic

idea is that the user should be able to take his mobile to any place, for example,

from a place that uses CDMA to another place that employs GSM.

2. MULTIMEDIA SUPPORT: The user should be able to receive high data rate

multimedia services. This demands higher bandwidth and higher data rate.

3. PERSONALISATION: This means that any type of person should be able to

access the service. The service providers should be able to provide customized

services to different type of users.

4. TERMINAL MOBILITY: This is one of the biggest issues the researchers are

facing. Terminal mobility allows the user to roam across different geographical

areas that uses different technologies. There are two important issues related to

terminal mobility. One is location management where the system has to locate the

position of the mobile for providing service. Another important issue is hand off

management. In the traditional mobile systems only horizontal hand off has to be

performed where as in 4G systems both horizontal and vertical hand off should be

performed.

5. SECURITY & PRIVACY: The existing security measures for wireless

systems are inadequate for 4G systems. The existing security systems are

designed for specific services. This does not provide flexibility for the users and

as flexibility is one of the main concerns for 4G, new security systems has to be

introduced.

6.FAULT TOLERANCE : As we all know, fault tolerant systems are becoming

more popular throughout the world. The existing wireless system structure has a

tree like topology and hence if one of the components suffers damage the whole

system goes down. This is not desirable in case of 4G. Hence one of the main

issues is to design a fault tolerant system for 4G.

7. BILLING SYSTEM: 3G mostly follows a flat rate billing system based where

the user is charged just by a single operator for his usage according to call

duration, transferred data etc. But in 4G wireless systems, the user might switch

between different service providers and may use different services. In this case, it

is hard for both the users and service providers to deal with separate bills. Hence

the operators have to design a billing architecture that provides a single bill to the

user for all the services he has used. Moreover the bill should be fair to all kinds

of users.

9. CONCLUSION

4G in its evolutionary and revolutionary contexts does not allow an exact

vision of the future. However if past evolution developments are a indication of

the future, there is need to promote technological adaptability interoperability for

the next generation of wireless communication. The article presents the design for

achieving an adaptable-soft vertical handoff in a multi-network of 4G

environment Possible mobile architecture which we have proposed for 3G, B3G,

or 4G is a significant step towards 4G systems based on all IP networking

technologies. Traditional handoff considered among the various stations requires

support which can be provided by out mobile model.

10. BIBLIOGRAPHY

[1] G. G. Savo, “Advanced Wireless Communications 4G Technologies”.

[2] J. McNair and Zhu. Fang, “Vertical handoffs in fourth-generation

multinetwork environments,” IEEE Wireless Communications, vol. 11, pp. 8-15.

[3] U. Varshney and R. Jain, “Issues in emerging 4G wireless networks,”

IEEE Computer, vol. 34, pp. 94-96.

[4] J. McNair and Zhu. Fang, “Vertical handoffs in fourth-generation

multi- network environments,”