Transcript
CHAPTER-1
WIRELESS COMMUNICATION SYSTEM
1.1 BRIEF HISTORY OF CELLULAR NETWORKS
The history of cellular communication is long and the background of mobile
networks thereby is also long however in this topic we focus on brief historic evolution
of cellular networks in terms of network architecture and services .ST Louis Missouri
invented the first car based telephone in 1946.This system consists of a single
transmitter installed on the top of a building. This system was a single channel and
only one way communication was possible at same time. In this system a single button
was used. Button was pushed for talk and released to listen. Police and taxi drivers still
use this half duplex CB radio system even today. This system was modified into a two
channel system called Improved Mobile Telephone System (IMTS) in 1960.In
Advanced Mobile Phone System (AMPS) the cellular radio system was implemented
to support more users by reuse of frequencies. AMPS are an analogue mobile phone
system.
Wireless communications mobile are commonly seen as one of the most highly
developed form of human transportation ever. Cellular technology has acquired over
three generations since 1979, when the first national cellular network was congenital in
Jan. The evolution of mobile system starting from 1G (First Generation), 2G, GSM
(Global System for Mobile Communication) and ultimately become Universal
Mobile Telecommunication System (UMTS).
1.2 ADVANCEMENTS
The advancement is necessary to provide new and more services at reasonable
cost as well as provides existing services in a better and efficient way. The analog
cellular system supported plain old telephony services that were the voice with some
supplementary services. As we all know that technology has been change day by day
and growing very fast, so for this changes comes rapidly for regarding this we have we
have Universal mobile telecommunication system (UMTS) and the goal of third
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generation (3G) is to deliver the multimedia services to the users. This requires the
provision of user data rates and that are much higher than previously provided by
second-generation (2G) network. In GSM the data rate is available 9.6 kbps currently
supported until yet. If we compare to this situation in case of UMTS user will provide
with higher data rates up to 144 kbps and if we change our environments like, if I talk
about macro cellular environments up to 384 kbps and 2 Mbps in indoor for Pico
cellular environments [8,9]. For meeting this and increasing demands of all kind of
data transfer wireless technology placed. Wireless technology has gone through many
steps in order to improve QoS and try to overcome the limitation of pervious systems.
Now we have successfully passed three generations in history of cellular domains.
First generation
Second generation
Third generation
1.2.1 First Generation
In this generation generally analog techniques is used. Gradually it was felt that
certain limitation have been raised small problems and the main issue is long call setup
time, take full efficient use of bandwidth and insecure transmission. This is pure
analog systems and offering mainly voice services, NMT 450/900, Comvik450, AMPS
and TACS.
1.2.2 Second Generation
In this generation, cellular system brought digital modulation techniques, due
to this digital technique major changes come in the field of cellular domain and caused
the considerable improvement in the efficient bandwidth usage, much better secure
quality and advance mobility management. Importantly it starts encryption
mechanism. This is digital systems offering voice, data services: GSM 900/1800/1900,
DAMPS, IS-54, IS-136, TDMA, CDMA/IS-95 (cdmaOne) and PDC.
In this generation mainly enforced by internet success and it is also offers
HSCSD (circuit switched data) bundling of traffic channels, GPRS (packet-switched 2
data) in this addition of packet-data a network core, EDGE (efficient modulation
schema, 8-PSk, increase system capacity (bit rate per user).
1.2.3 Third Generation
In this generation, we get everything in quite better way and regarding our
requirements. Although second-generation present better QoS but the data rate was
quite low as we need today’s. Luckily in third generation system is tend to provide all
kinds of service for example, data rate, audio, video etc. On the other hand, we get
much smaller call setup delay and it is user friendly. Open System Architecture (OSA)
is promising to provide such API’s which will perform authentication and
authorization of user secure and independent of vendor specific solution and
independent of programming languages. Services and application offers in 3G system
are as follows.
A Multimedia service provides high quality image, video, telephone etc.
Internet services provide web browsing, file download, streaming audio and video.
Service multiplexing provides different requirements share same logical connection;
web browsing and voice call in parallel. Increased bit rates and minimum 144 kbps
rural outdoors, maximum 500 km/h and minimum 384 kbps, suburban outdoors,
maximum 120 km/h [10].
Bandwidth offers different bit rates and its depending upon user and service
requirements. QoS supports to decrease delay, jitter and BER. Asymmetrical or
symmetrical connections provide data voice.
Today mobile wireless communications are commonly seen as one of the most
advanced form of human communications ever. The last decade GSM technology has
been a leading force in this revolution. Simultaneously with the phenomenal
deployment of wireless networks and distribution of user terminals, also the Internet
has seen a similar revolutionary growth. The success of both technologies offers a
great opportunity to provide integrated services using a wireless network.
In order to support multimedia, web, email and other data services in a
broadband wireless network, standards have been proposed by the 3GPP leading to the
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creation of the Universal Mobile Telecommunications System (UMTS) [2]. Besides
providing changes in the network infrastructure the UMTS specifications point out the
evolution path from GSM circuit switched networks towards packet switched
technologies offering higher transmission rates.
Based on the service requirements the UMTS Terrestrial Radio Access
Network (UTRAN) has been designed. A key requirement in the bearer capabilities is
the handover. Principally handover is necessary to support mobility of users and to
enable the interoperability of different network technologies (e.g. between UMTS and
2nd generation systems as GSM).
Based on the demand of the users, next generation cellular system is being able
to provide a variety of applications for users’ satisfaction. The Universal Mobile
Telecommunication (UMTS) System is one of the features of cellular communication
that is able to yield the different types of services as per users’ satisfaction. Video and
voice conferencing have a great deal of demand over the cellular network. The quality
of service (QoS) is the major concern for real time application in this area [8].
For suitable service to fulfill the users’ demand it is necessary to improve the
QoS, Next generation/4G network will be intelligent and common platform to
integrate all other wireless technologies.
Universal Mobile Telecommunications System (UMTS) is the third-generation
(3G) cell phone technology. UMTS offers telecommunications services (like speech or
SMS) and bearer services, which provide the capability for information transfer
between access points. It is possible to negotiate and renegotiate the characteristics of a
bearer service at session or connection establishment and during ongoing session or
connection. Both connection-oriented and connectionless services are offered for
Point-to-Point and Point-to-Multipoint communication. The radio interface of UMTS
is called UTRAN (UMTS Terrestrial Radio Access Network) which uses W-CDMA as
the underlying air interface.
4G technology is also being developed for the heterogeneous networks e.g.
WiMAX. Today mobile wireless infrastructure is commonly-seen as one of the most
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advanced form of human communications. The last decade GSM technology has been
a leading force in this revolution. Simultaneously with the phenomenal deployment of
wireless networks and distribution of user terminals, also the Internet has seen a
similar revolutionary growth.
Handover means changing/switching of a mobile transmission from one
channel to another. The main purpose of handover is to maintain an ongoing call when
the hardware changes the channel, whether it is in the same cell or a different cell.
Whenever a handover occurs there is always a handover delay which dictates that we
cannot guarantee the service continuity.
Though the handover time is millisecond but if there is long handover latency,
it will results in high packet losses and degradation of end-to-end TCP performance in
case of packet switched data. Delay sensitive real-time applications demands packet
lossless and low latency Quality-of-Service (QOS) guarantee during handover.
The goal of this research is to study some factors that affect the handover
process and hence the overall quality of the mobile network. Before going into details
of the UMTS handover process, some background information on general concepts in
mobile communications will be presented. Also some considerations concerning
network modelling and the outline of this project are also discussed.
1.3 WiMAX INTRODUCTION
Since the inception of the telephone, service providers have staved off
competition by relying on the exorbitant capital investment necessary to deploy a
telephone network. The cost of deploying copper wires, building switches, and
connecting the switches created an insurmountable barrier to entry for other
competitors. In most of the world, the high cost of this infrastructure limited telephone
service to the wealthy and the fledging middle class.
The Public Switched Telephone Network (PSTN) was the earliest example of
traffic engineering to deliver Quality of Service (QoS) guarantees. It consists of three
major components: access, switching and transport. Each element has evolved over the
hundred years plus history of the PSTN. This network was designed originally to
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handle voice; later, data was introduced. As data traffic on the PSTN grew, high
capacity users found it inadequate, so these subscribers moved their data traffic to
data specific networks [3]. Many data users then found themselves limited to an
infrastructure that was dependent on wires, either fiber optic cable, coaxial cable or
twisted pair copper wire. Using wireless means to bypass wired monopolies is
now a practicality for subscribers of both voice and data services. The primary form
of bypass is the use of cellular phones.
A cellular network is a radio network made up of a number of radio cells (or
just cells) each served by a fixed transmitter, known as a cell site or base station. These
cells are used to cover different areas in order to provide radio coverage over a wider
area than the area of one cell. Cellular networks are inherently asymmetric with a set
of fixed main transceivers each serving a cell and a set of distributed (generally, but
not always, mobile) transceivers which provide services to the network's users [4].
Cellular networks offer a number of advantages over alternative solutions such as
increased capacity, reduced power usage, better coverage etc.
The use of multiple cells means that, if the distributed transceivers are mobile
and moving from place to place, they also have to change from cell to cell. The
mechanism for this differs depending on the type of network and the circumstances of
the change. For example, if there is an ongoing continuous communication and we
don't want to interrupt it, then great care must be taken to avoid interruption. In this
case there must be clear coordination between the base station and the mobile station.
WiMAX, the Worldwide Interoperability for Microwave Access, is a
telecommunications technology aimed at providing wireless data over long distances
in a variety of ways, from point-to-point links to full mobile cellular type access. It is
based on the IEEE 802.16 standard, which is also called Wireless MAN. The name
"WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to
promote conformance and interoperability of the standard [2]. The forum describes
WiMAX as “a standards-based technology enabling the delivery of last mile wireless
broadband access as an alternative to cable and DSL" (and also to HSPA).
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WiMAX will change telecommunications, as it is known throughout the world
today. As this technology enables a lower barrier to entry, it will allow true market
based competition in all of the major telecommunication services: mobile and static
voice, video and data. This thesis handles WiMAX technology from the air interface
perspective as well as from the access network point of view and the mobility support
they provide.
Main concentration is on handover (handoff) performance. IEEE 802.16e-2005
standard, or ’Mobile WiMAX’, defines wireless network access for fixed and mobile
users by specifying Medium Access Control layer (MAC) functionality as well as
Physical layer (PHY) that supports single carrier (SC), Orthogonal Frequency Division
Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access
(OFDMA).
The Mobile WiMAX standard expands previously released IEEE 802.16-2004
specification to support mobility services for subscriber stations (SS) moving at
vehicular speeds and updates the MAC and PHY layer mechanisms with new and
improved features. 802.16j standard expands the mobility support further by
introducing multihop relays (MR) to enhance coverage and performance in WiMAX
network. WiMAX technology beyond the air interface is being developed and defined
by the WiMAX Forum, an organization consisting of operators and component and
equipment manufacturers [6].
The objective of this thesis is to study behavior and performance of the
WiMAX network during handovers on the one hand from the air interface point of
view and on the other hand from the access network perspective. Impact of basic
handover related parameters are being observed to find out preferable values in order
to increase the handover performance.
Usually a handover is performed when the signal quality level of a serving base
station (BS) or a relay station (RS) is deteriorated below the signal quality level of
another BS/RS during mobile station´s (MS) movement from the coverage area of the
serving BS/RS to the coverage area of another BS/RS, although there exist many
additional handover triggering mechanisms. In the simulation part of this thesis only
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signal strength measurements are used for handover initiation, therefore it is studied
quite thoughtfully. Nevertheless, other mechanisms are explained also at theoretical
level.
A decision when to perform a handover is a bit problematic since the signal
levels tend to have fluctuation due to wireless propagation factors, such as shadowing
and fast fading. Therefore overly sensitive handover triggering may result in increased
connection drops, signaling overhead and possibly a so called ping-pong effect in a
circumstance where two or more cells provide almost equally good conditions for the
MS to enter the network. In such case a MS perpetually may switch its traffic anchor
point in the network. However, handovers performed too sparsely will cause prolonged
reduction of the signal power level prior to a handover, thus leading to a bigger
amount of dropped packets and worse throughput performance.
The next-generation wireless systems will acquire increasingly more market
area from the currently dominant 3G and 3.5G systems as the bandwidth demand
grows. Operators are pushed to offer fast, flexible and reliable connections for
subscribers. While fixed and nomadic wireless access has been available for some time
now, full mobility supporting networks reaching very high bandwidth are knocking on
the door. Especially real-time data services, for instance VoIP and video streaming,
depend on continuous, high quality networking. Mix it with high speed mobility up to
120 km/h and the goal for maintaining good quality of service (QoS) becomes
demanding from the technical point of view. One of the key issues in ensuring the
network to be able to handle such cases is proper mobility management (MM), where
well designed handover procedures play a big role [14, 15].
1.4 LITERATURE SURVEY
This book “WCDMA for UMTS – Radio Access for Third Generation Mobile
Communications” by John Wiley and Sons gave us complete idea about the UMTS
evolution and its compatibility with other networks.
This paper study of soft handover in UMTS by Cauwenbridge deals with
UMTS Architecture and soft handover concept of the network [13].
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These papers “Issues and Optimization of UMTS Handover” and
“Investigation of handover in 3G UMTS traffic classes” gave us complete idea of the
handover requirements and modifications required for the UMTS network [15, 17].
This paper “Deployment of Mobile WiMAX by Operators with Existing 2G
and 3G Networks” in WiMAX forum deals with all WiMAX Architecture and its
interfaces for its deployment [1].
This paper “Quality of Service Scheduling for 802.16 Broadband Wireless
Access Systems” enabled us to understand the mobility scenarios for the users with
handover technique [12].
The OPNET modeler online documentation and tutorials enabled us to create
the scenarios required for the simulation.
1.5 ORGANIZATION OF THE THESIS
Chapter 1 introduces wireless network system including cellular networks
evolution and the WiMAX networks.
Chapter 2 discusses the UMTS system and WiMAX system in detail. The
network elements, principle, spectrum, applications and the core network are
discussed.
Chapter 3 deals with the handovers, requirements, Procedure, types are
discussed in detail.
Chapter 4 gives the modelling of a UMTS and WiMAX network. The OPNET
network modeller with its different layers and editors is presented in a first section.
The following part presents the modelling work done. The different models built as
also the iterative process of setting goals, building models, simulating them and
analysing the results obtained for handover are discussed.
Chapter 5 gives the conclusion of our project and future works that can be
presumed from the same and the various references we made for our project.
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CHAPTER-2
EXISTING SYSTEM
2.1 BASIC CONCEPT OF UMTS
The abbreviation of UMTS is Universal Mobile Telecommunication System
and worldwide industry dialogues that favor UMTS idea that goes beyond IMT-2000.
In this technology, fundamental elements form the internet with the IMT-2000 radio
core network and it will use internet-based protocol according to IPv4/IPv6 throughout
the network. UMTS is a wideband, circuit, packet based transmission system for
text, digital voice, video and multimedia with data rates up to 2Mbps. UMTS has
become the dominating 3G standards and even before its starts their service in 2001 or
2002. If UMTS is completely implement than computer, phone users can be
frequently attached to the internet and no matter either you are traveling or roaming
have almost same set of capabilities or functionalities. When UMTS is fully
accomplished, users can have multimedia devices that switch to the available
technologies such as, GSM 900, GSM 1800 and GSM 1900 etc. The new air interface
using WCDMA will offer better-quality performance in relation to GSM in terms of
higher data rates and higher capacity. Uniquely feature in difference to GSM is IP-
based network architecture, which supports both voice, data services via packet
transport and switching [9].
2.2 UMTS Architecture
UMTS network [10] consist of three interface domains as follows
Core Network (CN)
Universal Terrestrial Radio Access Network (UTRAN)
User Equipment (UE)
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a) Core Network
Core network of UMTS provides us transport service for various applications like
packet switching and circuit switching. Generally backbone of network of UMTS is
interconnected UTRAN with public networks. This network provides various kinds of
function and procedures like, we have call management, security, mobility
management and billing. It is using databases, SS7, IWU. Asynchronous transfer
Mode (ATM) is defining for UMTS core transmission. The architecture of the core
network may modify when new features and services are introduced.
The Core network of UMTS is composed of
Circuit Switched Domain
Packet Switched Domain
In UMTS AAL2 (ATM Adaptation Layer 2) deals circuit switched and packet
switched data where as AAL5 is responsible for data delivery. The core network
architecture may subject to change according to services and features are introduced. The
NPDB (Number Portability Data Base) is used to provide the facility to user to change
the network while keeping their old phone number.
b) UTRAN
The UTRAN plays very important role to make establishment and
connection between user equipment and rest of the network. Radio network controller
(RNC) is connect to one or more base transceiver station (BTS) and the function of
RNC is to control radio resource [8,9]. The RNC is belonging to access network and it
connected with core network. Which consist of MSC, SGSN and MPE. The interface
point between RNC and a node is IUB; UE accesses the UTRAN through base station. It
is sub system which controls WCDMA and performs as a medium between UE and CN
named as RAB (Radio access Bearers). UTRAN further contains RNS (Radio Network
Subsystems) RNS is connected with CN (Core Network) via IU interfaces also UTRN
connects UE via Uu interface [10,11].
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Figure 2.1 UMTS Architecture And System Overview
c) User Equipment
The UE consists of two parts ME (Mobile Equipment) .ME is further
subdivided in to two components MT (Mobile Terminal) which performs radio
transmission and related functions the second one is TE (Terminal Equipment) which
ensures the end to end applications. MT is used for communicating Via Uu interface
between UE and UTRAN. The second part of UE is USIM (UMTS subscriber
identity module is a smart card which contains user identity information and
encryption keys.
Smart card industry will be able to offer cards with large memory, good
CPU performance, contactless operation and it is capability for encryption. These
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forward steps in this technology will permit the USIM to add to the UMTS service
package by allowing portable high security data storage. It is not only use to install
software for the operation of any UMTS, but we can save personal files, fingerprint,
images and signature data, download or upload from the card.
2.2.1 Gateway Location Register (GLR)
The GLR (Gateway Location Register) is used to optimize subscriber handling
network boundaries.
2.2.2 Visitor Location Register (VLR)
The combination of mobile switching centre and Visitor Location Register
denoted by MSC/VLR performs switching and as a data base for circuit switched data.
The MSC perform switching where as VLR keeps the copies service profile of users.
2.2.3 Home Location Register (HLR)
The user service profile is stored in HLR. When a new user enters to system a
service profile is created as long as user subscription becomes active. The service profile
consists of the information about service type and its roaming characteristics.
2.2.4 Radio Access Network (RAN) Architecture
In UMTS the connection between mobile terminal and the core network is
established by WCDMA RAN (Radio Access Network) besides this all other radio issues
between core network and mobile terminal are handled by RAN.
The WDMA RAN consists of two types of nodes.
RBS (Radio Base Station or Node B)
RNC (Radio Network Controller) Radio Base Station (Node B)
a) Radio Base Station (Node B)
In UMTS radio transmission and reception to mobile terminal, from mobile
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terminal via radio interface is done by RBS. The RNC Radio Network Controller
manages RBC via lub interface. One or more UMTS cells are covered RBS.
b) Radio Network Controller (RNC)
All WCDMA radio access and network functions are handled by RAN. RAN is
also responsible for the connection between WCDMA and core network using IU
interface RNC performs two different roles to serve and to control in serving RNC
manages overall issues of handset or mobile terminal with WCDMA including
connection and termination of protocols.
In controlling RNC it manages the overall control of a specific cell and their
associations. When a mobile terminal uses the resources of a cell which is not controlled
by RNC then serving RNC enquire controlling RNC about these resources. The request is
send via IU interface. In this case controlling RNC is also called Drift RNC. This process
is done in case of soft handover [13].
Its functions are similar to the BTS in the GSM network. The Node-B’s are also
called as the radio network controller. The following are functions of the Node-B,
• Many cells are managed by the Node-B.
• The tasks which are attached to the radio interface is manage in the Node-B.
• The data splitting and the combination is also the duty of this entity.
• It helps in the process of handovers too.
It uses the mechanism for power control known as the inner loop power control.
In the radio access network the RNC is the main node. Between the mobile equipment
and the radio access network a number of the protocols are applied in the radio network
controller through the lub interface with the other RNC’s of the core network. The
function of the RNC is same as the function of the BSC in the GSM network. The radio
resource management is controlled in more than one Node-B by the RNC. The following
are tasks of the RNC,
• Through the radio interface it performs all the data transmission tasks.
• The radio resources are managed by this entity.
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• The connection and the replacement of the radio bearers.
• The admission of the call control through the Call admission control.
• The allocation of the code is also the duty of this entity.
• The control of power.
• Helps in handovers and the scheduling of the packet.
• The relocation of the SRNS and the conversion of the protocol.
• The data coming from other networks are ciphered in the RNC’s.
• To enable the transformation of the various entities RNC can connect and
switch to ATM connection.
There are three types of RNC’s:
• Serving RNC
• Controlling RNC
• Drift RNC
a) Serving RNC
This RNC serves the user equipment because the user equipment is connected to
this RNC. That is why this RNC is called as the serving RNC.
b) Controlling RNC
It works with reference to the Node - B.
c) Drift RNC
It works in the process of handover. Node-B’s has three types which include the
following.
• UTRA-TDD Node B
• UTRA-FDD Node B
• Dual Node B
2.2.5 Radio Network Functionality
For optimal operation of a wireless system i.e. from handset to radio access
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network (RAN) numerous functions are needed to control the radio network and
many handsets are using it. Except for Handover to GSM, all functions are
described in this section are important and necessary for a WCDMA system.
2.2.6 Radio Access Bearers
Radio Access Bearer (RAB) is the main service which is offered by WCDMA
RAN. RAB is needed to begin a call connection between the handset and the
base station RAB. Its characteristics are different depends upon the services or
information which is being transported. Subscriber’s data between core network and
handset is carried by RAB; it is poised of one or more than one Radio Access Bearers
between the Serving RNC and handset, and the IU bearer between the Serving RNC and
core network.
2.2.7 Mobile Switching Center (MSC)
It is the switching entity. It supports the circuit switched connection. It also
supports the mobility of the users. The current location of the user is known to the MSC.
It also works in authentication and the user data encryption.
2.2.8 Gateway Mobile Switching Center
The circuit switch network between the outside network and the core network is
provided by the GMSC.
2.2.9 Serving GPRS Support Node
The user’s current location is stored in SGSN. It performs the functionality of the
routing. Authentication and the copy of information of the user are stored in SGSN.
2.2.10 Gateway GPRS Support Node
The internet is connected to this node. It is the gate way to other packet
networks. Usually firewall is containing in this entity.
2.2.11 GPRS register
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It is the data base that is part of HLR. The packet switch transmission information
is stored in this register.
2.3 BACKGROUND OF WiMAX
WiMAX (also known as IEEE 802.16) is a wireless digital communications
system that is intended for “Wireless Metropolitan Area Networks" (WMAN). It can
provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations,
and 3 - 10 miles (5 - 15 km) for mobile stations. In contrast, the WiFi/802.11 wireless
local area network standard is limited in most cases to only 100 - 300 feet (30 - 100m).
WiFi-like data rates are easily supported in WiMAX [4], but the issue of
interference is less. Operating on both licensed and non-licensed frequencies, it
provides a regulated environment and a viable economic model for wireless carriers.
WiMAX can be used for wireless networking in much the same way as the
WiFi protocol. WiMAX is a second-generation protocol that allows for more efficient
bandwidth use, interference avoidance, and is intended to allow higher data rates over
longer distances. The IEEE 802.16 standard defines the technical features of the
communications protocol. The WiMAX Forum offers a means of testing
manufacturer's equipment for compatibility, as well as an industry group dedicated to
fostering the development and commercialization of the technology. Soon, WiMAX
will be a very well recognized term to describe wireless Internet access all over the
world [3, 4].
The IEEE 802.16 group was formed in 1998 to develop an air-interface
standard for wireless broadband. The group's initial focus was the development of a
LOS-based point-to-multipoint wireless broadband system for operation in the
10GHz-66GHz millimeter wave band. The resulting standard—the original 802.16
standard, completed in December 2001—was based on a single-carrier physical (PHY)
layer with a burst time division multiplexed (TDM) MAC layer. Many of the concepts
related to the MAC layer were adapted for wireless from the popular cable modem
DOCSIS (data over cable service interface specification) standard.
The IEEE 802.16 group subsequently produced 802.16a, an amendment to the
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standard, to include NLOS applications in the 2GHz-11GHz band, using an orthogonal
frequency division multiplexing (OFDM)-based physical layer. Additions to the MAC
layer, such as support for orthogonal frequency division multiple access (OFDMA),
were also included. Further revisions resulted in a new standard in 2004, called IEEE
802.16-2004, which replaced all prior versions and formed the basis for the first
WiMAX solution. These early WiMAX solutions based on IEEE 802.16-2004 targeted
fixed applications, and these will be referred to as fixed WiMAX. In December 2005,
the IEEE group completed and approved IEEE 802.16e-2005, an amendment to the
IEEE 802.16-2004 standard that added mobility support.
The IEEE 802.16e-2005 forms the basis for the WiMAX solution for nomadic
and mobile applications and is often referred to as mobile WiMAX. Note that these
standards offer a variety of fundamentally different design options. For example, there
are multiple physical-layer choices: a single-carrier-based physical layer called
Wireless MAN-SCa, an OFDM-based physical layer called Wireless MAN-OFDM,
and an OFDMA- based physical layer called Wireless-OFDMA. Similarly, there are
multiple choices for MAC architecture, duplexing, frequency band of operation, etc.
These standards were developed to suit a variety of applications and deployment
scenarios, and hence offer a plethora of design choices for system developers. In fact,
one could say that IEEE 802.16 is a collection of standards, not one single
interoperable standard.
With the completion of the IEEE 802.16e-2005 standard, interest within the
WiMAX group has shifted sharply toward developing and certifying mobile WiMAX
system profiles based on this newer standard. All mobile WiMAX profiles use
scalable OFDMA as the physical layer. At least initially, all mobility profiles will use
a point-to-multipoint MAC. It should also be noted that all the current candidate
mobility certification profiles are TDD based. Although TDD is often preferred, FDD
profiles may be needed.
Internet is the preferred mode of communication today. There are basically
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three different options of accessing the internet:
a) Broadband access - In your home, you have either a DSL or cable modem. At the
office, your company may be using a T1 or a T3 line.
b) WiFi access - In your home, you may have set up a WiFi router that lets you surf
the Web while you lounge with your laptop. On the road you can find WiFi hot spots.
c) Dial-up access -If you are still using dial-up, chances are that either
broadband access is not available, or you think that broadband access is too
expensive, but the following are the advantages.
1) The high speed of broadband service
2) Broad coverage like the cell phone network (against small WiFi hotspots)
3) Wireless rather than wired access, so it would be a lot cheaper than cable or
DSL and much easier to extend to suburban and rural areas.
WiMAX is the wireless solution for the next step up in scale, the metropolitan
area network (MAN). A MAN allows areas the size of cities to be connected. In the
same way that many people have given up their "land lines" in favor of cell phones,
WiMAX could replace cable and DSL services, providing universal Internet access
just about anywhere you go and gets connected to nearest WiMAX antenna.
MANkm radius (approx)
IEEE 802.16
Connects devices up to 50 km radius (approx)
LANradius (approx)
IEEE 802.11
Connects devices up to 300 ft radius (approx)
PANradius (approx)
IEEE 802.15
Connects devices up to 33ft radius (approx)
Table 2.1 Types of Networks
2.3.1 WiMAX Architecture19
The WIMAX reference architecture takes some requirements into account, such as:
High performance packed-based network.
Full scalability of services and applications.
Roaming and interworking with both fixed and mobile networks.
A large variety of services and applications.
The WiMAX Network Reference Model (NRM), is a logical representation of the
network architecture being composed of three components that are inter-connected, in a
logical domain, by standardised interfaces or reference points (RPs) R1 to R5. Different
elements of the network are: Mobile Station (MS) or Subscriber Station (SS), Access
Service Network (ASN) and Connectivity Service Network (CSN). RPs are logical
interfaces between several entities belonged to the WiMAX network [4,8].
The ASN includes all functionalities related to radio connectivity to WiMAX sub-
scribers defining a logical boundary. ASN is responsible for not only RRM aspects,
like handover control and consequent execution, but also for establishing connectivity
between WiMAX subscribers and Layer 2 and Layer 3, using the air interface and the
CSN respectively.
One or several ANSs are interconnected through reference point R4, and may be
deployed by a Network Access Provider (NAP), which provides radio access
infrastructure to one or several Network Service Providers (NSP). According to the
existing Service Level Agreements (SLA), NSP enables IP connectivity and WiMAX
services to subscribers. The ASN usually consists of several BSs connected to
respective ASN Gateways (ASN-GWs). BS is the element that is responsible for
physical layer and MAC mechanisms, and also contributes to the scheduling of user
and to exchange of signalling messages with the ASN-GW through the R6 interface.
The CSN is defined as a set of network functions that provide IP connectivity to
WiMAX subscribers. CSN functions comprise:
User connection authorisation and Layer 3 access.
20
QoS management.
Mobility support based on Mobile IP.
Tunnelling with other equipments and networks based on IP protocols.
WiMAX services.
CSN is deployed by the NSP and includes, among others, network elements, such
as routers, Authentication Authorisation and Accounting (AAA) server or proxy,
firewalls, data bases and interworking gateways. With these components,
interworking, interoperability, protection and security aspects are achieved. In order to
implement ASN, there are three different ASN profiles: A, B and C. They differ in the
fact that several functionalities are implemented by the BS and others by the ASN-GW
or another entity [1, 2].
Figure 2.2 WiMAX Architecture
21
Figure 2.3 WiMAX Protocol Stacks
2.3.2 Operating Principle
A WiMAX system consists of two parts:
WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX
tower can provide coverage to a very large area as big as 8,000 square kilometers
(~3,000 square miles).
WiMAX receiver - The receiver and antenna could be a small box or PCMCIA
card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-
bandwidth, wired connection (for example, a T3 line). It can also connect to another
WiMAX tower using a line-of-sight, microwave link. This connection to a second tower
(often referred to as a backhaul), along with the ability of a single tower to cover up to
3,000 square miles allows WiMAX to provide coverage to remote rural areas. Hence
22
WiMAX actually can provide two forms of wireless service. There is the non-line-of-
sight (NLOS), WiFi sort of service, where a small antenna on your computer connects
to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz
(similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by
physical obstructions -- they are better able to diffract, or bend, around obstacles.
There is line-of-sight service (LOS) [5, 6], where a fixed dish antenna points
straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is
stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-
sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz.
At higher frequencies, there is less interference and lots more bandwidth.
2.3.3 WiMAX Spectrum
As with any other spectrum based technology, successful WiMAX
deployment will depend largely upon the availability and suitability of spectrum
resources. For entities providing wireless communications services, two sources of
spectrum are available:
Licensed spectrum
Unlicensed spectrum
Licensed spectrum requires an authorization/license from the Commission,
which offers that individual user or “Licensee” the exclusive rights to operate on a
specific frequency (or frequencies) at a particular location or within a defined
geographic area. In contrast, unlicensed spectrum permits any user to access specific
frequencies within any geographic area inside the United States without prior
Commission authorization. While users of this spectrum do not have to apply for
individual licenses or pay to use the spectrum, they are still subject to certain rules.
First, unlicensed users must not cause interference to licensed users and must accept any
interference they receive. Second, any equipment that will be utilized on unlicensed
spectrum must be approved in advance by the Commission.
23
Because of its broad operating range, licensed and unlicensed spectrum options
for WiMAX technology are extensive. To take best advantage of the benefits provided
by WiMAX systems, large block spectrum assignments are most desirable. This
enables systems to be deployed in TDD mode with large channel bandwidths,
flexible frequency re-use and with minimal spectral inefficiencies for guard-bands
to facilitate coexistence with adjacent operators. Another key activity for the WiMAX
Forum is collaborating with standards and regulatory bodies worldwide to promote the
allocation of spectrum in the lower frequency bands (< 6 GHz) that is both application
and technology neutral. Additionally, there is a major push for greater harmonization in
spectrum allocations so as to minimize the number equipment variants required to cover
worldwide [7].
The initial system performance profiles that will be developed by the WiMAX
Forum for the recently approved 802.16-2005 air interface standard are expected to be
in the licensed 2.3 GHz, 2.5 GHz and 3.5 GHz frequency bands. The 2.3 GHz band has
been allocated in South Korea for WiBro services based on the Mobile WiMAX
technology. With a 27 MHz block of spectrum assignment to each operator, this band
will support a TDD deployment with 3 channels per base station and a nominal
channel bandwidth of 8.75 MHz The 2.5 to 2.7 GHz band is already available for
mobile and fixed wireless services in the United States. This band is also currently
underutilized and potentially available in many countries throughout South America
and Europe as well as some countries in the Asia-Pacific region. The 3.5 GHz band is
already allocated for fixed wireless services in many countries worldwide and is also
well-suited to WiMAX solutions for both fixed and mobile services.
2.3.4 Usage
WiMAX operates on the same general principles as WiFi -- it sends data from
one computer to another via radio signals. A computer (either a desktop or a laptop)
equipped with WiMAX would receive data from the WiMAX .The fastest WiFi
connection can transmit up to 54 megabits per second under optimal conditions.
WiMAX should be able to handle up to 70 megabits per second. The biggest
difference isn't speed; it's distance. WiMAX outdistances WiFi by miles. WiFi's range is
about 100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with 24
wireless access. The increased range is due to the frequencies used and the power of
the transmitter.
2.3.5 Applicability
WiMAX doesn't just pose a threat to providers of DSL and cable-modem
service. The WiMAX protocol is designed to accommodate several different methods
of data transmission, one of which is Voice over Internet Protocol. VoIP allows
people to make local, long-distance and even international calls through a broadband
Internet connection, bypassing phone. If WiMAX-compatible computers become very
common, the use of VoIP could increase dramatically. Almost anyone with a laptop
could make VoIP calls.
2.3.6 WiMAX Merits
a) Flexible Architecture
WiMAX supports several system architectures, including Point-to-Point, Point-to-
Multipoint, and ubiquitous coverage. The WiMAX MAC (Media Access Control)
supports Point-to-Multipoint and ubiquitous service by scheduling a time slot for
each Subscriber Station (SS). If there is only one SS in the network, the WiMAX Base
Station (BS) will communicate with the SS on a Point-to-Point basis. A BS in a Point-
to-Point configuration may use a narrower beam antenna to cover longer distances.
b) High Security
WiMAX supports AES (Advanced Encryption Standard) and 3DES (Triple
DES, where DES is the Data Encryption Standard). By encrypting the links between the
BS and the SS, WiMAX provides subscribers with privacy (against eavesdropping)
and security across the broadband wireless interface. Security also provides operators
with strong protection against theft of service. WiMAX also has built-in VLAN
support, which provides protection for data that is being transmitted by different users on
the same BS.
c) Quick Deployment
25
Compared with the deployment of wired solutions, WiMAX requires little or no
external plant construction. For example, excavation to support the trenching of cables is
not required. Operators that have obtained licenses to use 5 one of the licensed bands, or
that plan to use one of the unlicensed bands, do not need to submit further applications to
the Government. Once the antenna and equipment are installed and powered, WiMAX is
ready for service. In most cases, deployment of WiMAX can be completed in a
matter of hours, compared with months for other solutions.
d) Multi-Level Service
The manner in which QoS is delivered is generally based on the Service Level
Agreement (SLA) between the service provider and the end-user. Further, one service
provider can offer different SLA s to different subscribers, or even to different users on
the same SS.
e) Interoperability
WiMAX is based on international, vendor-neutral standards, which make it
easier for end-users to transport and use their SS at different locations, or with
different service providers. Interoperability protects the early investment of an operator
since it can select equipment from different equipment vendors, and it will continue
to drive the costs of equipment down as a result of mass adoption.
f) Portability
As with current cellular systems, once the WiMAX SS is powered up, it
identifies itself, determines the characteristics of the link with the BS, as long as the
SS is registered in the system database, and then negotiates its transmission
characteristics accordingly.
g) Mobility
The IEEE 802.16e amendment has added key features in support of mobility.
Improvements have been made to the OFDM and OFDMA physical layers to support
devices and services in a mobile environment. These improvements, which
include Scalable OFDMA, MIMO, and support for idle/sleep mode and hand-off,
26
will allow full mobility at speeds up to 160 km/hr.
h) Cost-effective
WiMAX is based on an open, international standard. Mass adoption of the
standard, and the use of low-cost, mass-produced chipsets, will drive costs down
dramatically, and the resultant competitive pricing will provide considerable cost
savings for service providers and end-users.
i) Wider Coverage
WiMAX dynamically supports multiple modulation levels, including BPSK,
QPSK, 16-QAM, and 64-QAM. When equipped with a high-power amplifier and
operating with a low-level modulation (BPSK or QPSK, for 6 example),WiMAX systems
are able to cover a large geographic area when the path between the BS and the SS is
unobstructed.
j) Non-Line-of-Sight Operation
NLOS usually refers to a radio path with its first Fresnel zone completely
blocked. WiMAX is based on OFDM technology, which has the inherent capability
of handling NLOS environments. This capability helps WiMAX products deliver
broad bandwidth in a NLOS environment, which other wireless product cannot do.
CONCLUSION
This chapter highlights the basic concept of UMTS, its architecture and
also about WiMAX architecture. It infers about the basic ideas to know about
the BBU’s so that the packet rate during the handover between the base station
and the user equipment does not drops to zero but provides a minimum rate
without any abrupt connection termination. Thus studying about the existing
system provides the specifications of the UMTS and WiMAX networks which
helped in completing the initial phase of this project.
27
CHAPTER-3
PROPOSED SYSTEM
3.1 UMTS ROAMING
3.1.1 Handover Overview
Handover is the basic criteria of mobility of the user in cellular networks. The
UMTS handover is to provide the link of mobile services to a user moving over
cell boundaries in a cellular communication network. During an ongoing
communication of a user when the user crosses the cell boundary it is better to use
the radio resources of the new cell also called the target cell because the strength of
signal in the preceding cell is weaker than the next one that is the target cell. Now the
whole process of the terminating of connection of user from previous cell and
establishing the new connection to target cell is called handover.
In other words handover can be defined as the transformation of user connection
from one radio channel to another radio channel. This definition was composed before
the launch of UMTS. After this, new definition was composed by adding the new
concepts to the older ones. The main purpose of handover is to maintain the ongoing call
of user during its mobility because the mobility of the user may be in high speed. In this
situation sometimes the call may drop. Also in the case of multiple users with ongoing
calls changing the cell area the network needs to change the frequency of an ongoing call.
Also there will be a chance user enters an area where the UMTS network coverage ends
and the user is required to hand over to a GSM/GPRS network [11, 13, 15].
The attitude of cellular network to perform efficient handovers is vital to offer
signal-services as real time applications or streaming media as planned in third
generation networks. The number of handover failure in which the handover procedure
cannot be completed has to further minimize the previous generation cellular-
communication system as GSM. The cause for handover failure range from signaling to
the lack of resources in the target cell makes impossible for a new user to be considered.
28
In the network of high-performance there is a tendency the use of smaller cells in
order to increase the capacity-The handover process is more important as more efficient
handover is required. An efficient algorithm of handover can be implemented with
resource and user location management. Resource management means way to establish
release, continue, and manage connections in the radio access layer. In UMTS systems
the Radio Resource Control (RRC) protocols implement the control signaling between
UE and UTRAN-.User location management means the way of the UEs location. This
Information is saved in the functional entities in the core-network.
3.1.2 Objectives of Handover
Handover can be described in the following ways.
During the mobility of user across the boundaries of cellular network the
guarantee of the network service continuity.
To maintain the required quality of service.
The roaming between different networks.
Load balancing between the cells. To keep connected the mobiles with
strong base stations to reduce interference level.
3.1.3 Handover Requirements
There are four possible situations when handover is required to a user [15].
When UE moves from one cell to another cell
In overlapping area of adjacent cells
UE experiencing interference from adjacent cell
Fast motion of UE
3.1.4 Handover Procedure
There are two main functions contributing soft handover in UMTS as listed
below [10, 14].
To acquire and process the measurements.
To execute the handover algorithm.
29
Some terms have to be defined before starting measurements in handover
process.
Set: list of cells.
Active set: list of cells having connection with mobile station.
Monitored cell: list of neighboring cells whose signal strength is not so
strong to be added to active set.
The handover procedure has three stages.
Measurement
Decision
Execution
Figure 3.1 Handover Procedure
a) Measurement
In measurement phase the downlink measurement calculated by mobile is Ec /Io2
of common pilot channel of serving and neighboring cells. In WCDMA relative
timing between the cells is required to measure. For adjustment of transmission timing
to permit coherent combining.
30
b) Decision
The measurement results are compared with predefined values in decision
phase. Then it is decided whether handover or not. There are different triggers in
handover algorithms.
c) Execution
In this phase the Mobile Station starts or leaves the soft handover process, a
new base station is either added or left, the power of each channel is adjusted and
active set is updated during the soft handover process.
3.1.5 Handover Initiation
Handover is an important part of mobility management in a cellular system
especially it is very crucial in UMTS network using micro cells [17]. Handover can be
initiated in three ways.
a) Mobile Initiated
The mobile measures the quality and it switch to the best base station in the
network. This procedure is done due the poor link quality measured by mobile.
b) Mobile Assisted
In this case the network and mobile both make measurements and mobile reports
the nearby BS results.
c) Network Initiated
In this case RNC gets information from the measurements of BS and decide
whether to handover or not. This handover is done by Traffic Reason Handover
(TRHO). It is a load based algorithm which changes handover threshold.
d) Network Assisted
In network assisted handover only networks makes measurements and report to
MS.
31
3.1.6 Handover Types
There are different types of handovers in UMTS [8, 10].
Horizontal Handover
Vertical Handover
Intra Cell Handover
Inter System Handover
Hard Handover
Soft Handover
Softer Handover
a) Horizontal Handover
The term Horizontal Handover means the process of transferring an ongoing call
or data session from one channel connected to the core network to another channel. In
other words when UE moves between two cells using same technology then handover is
said to be horizontal.
b) Vertical handover
Vertical Handover is defined as the changing of access technology of a network
node in connection establishing during mobility. Let us consider the example of vertical
handover in laptop that uses both technologies for internet access, high speed wireless
LAN and cellular technology. Laptop user uses the wireless LAN connection due to
higher speed other than cellular connection. In case of mobility the type of connectivity
or technology is changed then vertical handover occurs.
Vertical handover involves the automatic switching of the access technology. The
data link layer technology to access the network is changed during vertical Handover
between the UMTS and wireless LAN. In the vertical Handover between the WLAN and
UMTS two interworking architectures are used.
Loose coupling
Tight coupling
Private users use loose coupling scheme when the Cellular network operator is
32
not using WLAN so data transmitted by the WLAN will not go through cellular network.
Tight-coupling scheme adopted by the 3GPP, launches two elements Wireless
Access Gateway (WAG), Packet Data Gateway (PDG).WLAN transfers the data to the
node on the internet must go through UMTS core network.
c) Intra cell Handover
In the intra cell handover cell is not changed. Source and target lies in the same
cell, during the handover process only channel is changed .The purpose of intra cell
handover is to change the channel, which may be interfered, or fading with a new clearer
or less fading channel.
d) Inter system Handover
Now for the compatibility between two different network systems with different
architectures these handovers are used. Specially during the rolling out of UMTS
network inter system handovers between UTRAN and GSM will be used. Since
WCDMA networks did not coverage in many rural areas in the beginning so GSM was
still used in those areas. Later 3GPP release offered handover to GSM networks.
e) Hard Handover
Hard handover is the type of handover where the old connection is break before
the new one is established between user and radio network. Hard handover is known as
the break before the make. This type of handover is used in the GSM cellular systems
where each cell was assigned a different frequency. When a user want to establish a new
call first the old one will be disconnected before the new connection established at
different frequency in the desired cell. The hard handover uses simple algorithm. When
the strength of signal in new cell is greater than that of previous cell then hard handover
is used by mobile station with a given threshold. Due to change of radio frequency band
the UE and UTRAN use hard handover In UMTS. During the process for allocation of
frequency for UMTS, it has been planned that each UMTS operator will have the
opportunity to maintain additional band to improve the capacity when optimistic usage
level will be reached. In this case a number of bands about 5MHz will be in use by one
operator for the need for handovers between them. Hard handovers are also applied to
33
change the cell on the same frequency when no network support of macro diversity
exists. When a UE with a dedicated channel allocated roam into a new cell of a UMTS
network hard handover is chosen when soft and softer handover is impossible.
A third case of hard handovers are called inter mode handovers. This allows for
changes between the FDD and TDD modes. This handover type is also called the inter
system handovers as the measuring methods used are similar to WCDMA-GSM
handovers. In the technical point of view these inter system handovers can be considered
as a type of hard handovers. In the GSM network when user enters in the new cell
sometimes high blocking probabilities are present during hard handover. This probability
can be reduced by giving preference to handover users over new users by reserving a
certain part of the network resources in each cell for users with ongoing communication.
On the other hand this gives a less efficient use of the network resources of the cellular
systems or higher blocking probabilities for new users. These considerations and
other CDMA specific arguments have lead to the choice of additional handover types to
coexist in the WCDMA access networks.
Advantages and Disadvantages
In the hard handover one call uses only one channel at any instant of the time.
In the hard handover the phone hardware does not require to accomplish to receive
two or more parallel channels.
The main disadvantage of the hard handover is the call may be terminated during
the handover process.
f) Soft Handover
Soft Handover is that in which channel in the source cell is retained and used
for a while in parallel with the channel in the target cell. In this scenario before the
connection to the source is broken the connection to the target is made. This handover is
called make before break.
UMTS uses the CDMA technology. In the CDMA every cell has a same
frequency and the mobile device can communicate the multiple cells at the same time,
in the soft handover two parallel connections is established between the cells.
34
Advantages
In the Soft handover source cell connection is broken when the reliable
connection is established with the target cell.
In the Soft handover in multiple cells channels are at the same time maintained,
when the channels are interfered then call could be fail.
Disadvantages
More complex hardware will be needed in order to continue the processing in
several parallel channels.
In soft handover in single call several parallel channels are used.
g) Softer Handover
The softer handover is a special type of soft handover in which all the radio
links belong to same Node B that is the coverage area of correlated base stations
from which several cells can be served. In softer handover Node B utilizes the
maximum ratio combining of macro diversity also down link macro diversity with
selection combining.
In other words softer handover is not a real handover. In this case to
improve the reception quality UE adds more than one radio link.
3.1.7 Challenges in UMTS Handover
Now days the wireless communication demand has increased tremendously. So
to fulfill this demand cell sizes of the network have to decrease which results in to
problems during handover.
Now using micro cells networks in Personal Communication Service (PCS)
environment the major challenges in case of Handover are the following
The blocking probability of new calls during a handover.
To increase the capacity of the network or in other words reduction of the
infrastructure of the network.
To improve the quality of service either to minimize the delay and interference.
35
3.2 MOBILITY IN WiMAX
The principle of allowing the end-users to move and change the point of
attachment (PoA) while using wireless network services is a distinct feature of the
developed telecommunication technologies. Providing reliable and sufficiently fast data
connections for fixed and nomadic subscribers across the air interface has been a
minimum requirement for wireless technologies ever since the 3G networks emerged.
Current technical and infrastructural status favors development of high speed BWA
systems. On the one hand, now clients are enticed by small, portable equipment allowing
them to get online in spite of the location and still have full mobility support. On the
other hand, now that dial-up based wired network access methods are vanishing and are
not replaced everywhere by newly distributed fiber-optic links, wireless access may be
the only way people can connect themselves to the Internet [7].
The handover process from the air interface perspective is divided into five
sections: cell reselection, handover decision and initiation point, synchronization to new
BS, ranging process with the new BS and context termination at the old BS. In addition
to these, handover cancellation procedure is a mandatory feature quantified by the
standard. Furthermore, actions in the access network between a BS, ASN and CSN are
defined in detail. These topics are reviewed in this section.
Exploring the handover performance should not confine to mere air interface
investigation since many operations are performed inside the access and core network.
This thesis concentrates on handovers from wide perspective by exploring ASN-
anchored mobility and CSN-anchored mobility but the simulator extension used in this
thesis does not support it. The following subsections provide knowledge on handover
types presented by the IEEE 802.16, handover process and mobility types.
3.2.1 Handover Process
During normal operation the MS continuously surveys signal level from the
serving BS. To receive signal strength information from neighbor BSs it may decode
periodical neighbor advertisement messages (MOB_NBR-ADV) sent by the serving BS
or it may transmit a request to the serving BS to schedule a scanning interval for the MS
´s neighbor BS RSSI measurements.
36
If periodical transmission of the neighbor advertisement messages is enabled, the
serving BS includes suitable neighbor BS information in a MOB_NBR-ADV, which it
sends to the MS. This will facilitate scanning process because the MS then knows which
neighbor BSs it should prefer while seeking a target BS. The serving BS uses backbone
network to gather information on the neighboring BSs.
When the MS utilizes scanning of neighbor BSs, it may decide to transmit a
scanning interval request message (MOB_SCN-REQ) to the serving BS if the handover
trigger conditions defined in the DCD message are met. The serving BS may then grant a
scanning interval allocation encoded in MOB_SCN-RSP management message.
Scanning is used for distinguishing suitable target BSs for the handover. During the
scanning intervals the MS is able to create basic association with the neighbor BSs for
synchronization and registration to mitigate signal quality measurements. During the
scanning phase user data is buffered but not transmitted in UL or DL. This phase of the
handover produces quite long packet delays and optimization of which has been of
interest to many studies.
As specified the MS may define one of the following scanning types in the
MOB_SCN-REQ message which it uses for requesting initial ranging parameters and
service availability information from neighboring BS. Performing association is not
mandatory for a mobile station [1-5].
Scanning with association level 0: The serving BS allocates periodical contention
based ranging allocations for the MS to perform ranging with neighboring BS but
the neighboring BSs have no knowledge on the MS.
Scanning with association level 1: The MS transmits a MOB_SCN-REQ to the
serving BS with a list of neighbor BSs it wishes to associate with. Then each of these
BSs provides a predefined ranging interval to the MS.
Scanning with association level 2: This is a network assisted association method
pretty similar to association level 1. In this type the neighbor BSs do not have to
transmit RNG-RSP messages since the information on the PHY offsets is sent over
the backbone network between the neighbor BSs and the serving BS. The serving
BS transmits all ranging related information in a MOB_ASC_REPORT to the MS.
37
The handover process can be initiated by the mobile itself or it can be network
initiated. When a decision to migrate the MS from one BS to another is made, the first
action in the handover preparation is transmission of a handover request message; in
mobile initiated handover a MOB_MSHO-REQ message is transmitted by the MS and in
network initiated HO a MOB_BSHO-REQ is sent by the BS.
A handover request message contains information on pending handover type
(hard HO, FBSS or MDHO) and identifiers of suitable target BSs. When the
MOB_MSHO-REQ is received the serving ASN transmits a HO_Req on R4 to each
target ASN. This message contains especially MS’s service flow information needed for
re-establishment of the connections after the HO. When the target ASN receives a
HO_Req message it may retrieve the Authorization Key (AK) context from the
authenticator ASN if it is not included in the message. Furthermore, at this stage data
path may be pre-established between the target ASN and the anchor ASN.
Upon processing the HO_Req the target ASN transmits a HO_Rsp message on
R4 reference point containing possible information on data path pre-registration. When
the serving BS notices the HO_Rsp it performs a transmission of the MOB_BSHO-RSP
to the MS over the air interface and it also sends an acknowledgment message to all
candidate BSs over the R4 to complete the handover preparation.
The purpose of the MOB_BSHO-RSP is to inform the MS on BSs it may attach
itself during the actual handover. The message may also contain information on pre-
allocated fast ranging time interval that will boost the network re-entry after the HO.
The MS determines the final target BS and includes this information to a
MOB_HO-IND message before transmitting it to the serving BS. The handover
indication message is the last message to the serving BS before the actual HO. After its
transmission the MS removes old connections and initiates ranging with the target BS.
Upon reception of the MOB_HO-IND the serving BS will transmit a HO_Cnf
message to the target ASN over the backbone network to finalize the HO from its part.
The target ASN then replies with a HO_Ack message.
38
After the MS has performed a network re-entry with the target BS, a data path
registration has to be carried out between the target ASN and the anchor ASN for bearer
plane procedures. If the optional data path pre-establishment was done before then this
stage requires only confirmation of the data path registration. Otherwise a full
registration procedure has to be performed using Path_Reg_Req, Path_Reg_Rsp and
Path_Reg_Ack messages. When the path registration exchange is completed a
HO_Complete message is transmitted from the target ASN to the serving ASN to inform
about completion of the handover depicts a successful, MS initiated HO process and
message exchanges. Note that context retrieval procedure and the data path pre-
registration procedure may be performed at various points during a HO.
During the handover message exchanges parts of the MS´s context may have been
transmitted to the target ASN, which at this stage can be omitted. If the target BS did not
receive the context it may request it from the serving BS over the backbone network. This
sort of optimized HHO is designed to keep the handover interruption times less than 50
ms to make usage of VoIP and other real-time applications possible.
3.2.2 Handover types
Usually a handover is understood as a change of physical connection point
through which the terminal communicates with network services. In WiMAX this is
called inter-cell handover. There exists also so called intra-cell handover which basically
means changing from one frequency to another while the serving BS remains the same.
This feature could be exploited for example in a femto cell scenario where a user moves
from outdoors to indoors. From wide perspective handovers may be split into two
groups: horizontal HO and vertical HO. In the horizontal HO network technology
remains the same, whereas the latter is an inter-technology HO type. Media Independent
Handover (MIH) is a vertical HO method defined in 802.21 specifications. In this thesis
only inter-cell horizontal handovers are examined closely [4, 6].
There are different handover triggering ways. One natural method is based on
signal level measurements. If the received signal level from the serving BS is deteriorated
enough, resulting in better signal quality from one or more neighboring BSs, then it is
reasonable to perform a HO. This method is also used in the simulations later in this
document. Depending on the network characteristics and properties there might exist
39
several other reasons for HO initiation, including lack of BS´s capacity, interference from
other cells, fluctuating MS conditions and another network type offering a better
performance.
As mentioned before the WiMAX specification defines three types of handovers:
hard HO (HHO), FBSS and MDHO. From these, only implementation of the HHO is
mandatory. The FBSS and the MDHO are optional.
a) Hard handover
Hard handover is an efficient yet simple mechanism that is based on received
signal strength indication (RSSI) measurements and support for it is mandatory in mobile
WiMAX network. Hard handover is a break-before-make BS switching method where
the MS first stops connectivity with the old BS before engaging to the target one. The
HHO is bandwidth efficient but produces longer delays than MDHO and FBSS which
are considered as soft HO mechanisms.
To improve HHO performance and to keep MS´s unavailability durations small,
many optimization methods are introduced in the specification.
b) MDHO and FBSS
Macro Diversity Handover and Fast Base Station Switching are considered as
soft handover methods. They both utilize a so called ’diversity set’ which is a list of BSs
included in the handover. These BSs in the diversity set are located near the MS. BSs that
are located within the communication range of the MS but are providing low signal fast
feedback channel. Strength level are not included in the diversity set, but are defined as
neighbor BSs. In MDHO the MS is able to communicate in DL and UL with all the BSs
in the diversity set simultaneously instead of only one. In DL diversity combining and in
UL selection diversity are used for improving quality of the received signal.
In FBSS the MS communicates only with one anchor BS over UL and DL
channel. Switching the anchor BS is quite easy due to MS’s continuous monitoring of
other BSs in the diversity set. The anchor BS changing process can be performed either
by using HO messages or by using fast anchor BS selection feedback over the network.
40
Figure 3.2 Fast Base Station Switching
In MDHO and FBSS the diversity set has to be updated from time to time. A BS is
removed from the diversity set if its long-term CINR drops below a preset threshold.
Equivalently, a neighbor BS may be added to the diversity set if the long-term CINR is
high enough. The diversity set update procedure is commenced by the MS or the
(anchor) BS with a transmission of a MOB_MSHO-REQ or a MOB_BSHO-REQ
message, respectively.
3.2.3 ASN-Anchored Mobility
In the ASN-anchored mobility a MS is allowed to move across coverage areas of
BSs without changing Foreign Agent (FA) and Care-of-Address (CoA) points. In other
words, in the ASN-anchored mobility the CSN and the anchor ASN used for
communication do not change. The ASN-anchored mobility can be divided into intra
ASN mobility and inter-ASN mobility. In the first type a MS may transit across different
cells within the same ASN, whereas in the latter the serving ASN can change. The ASN-
anchored mobility management (MM) covers signaling between the ASNs and the BSs
over the R4 and the R6 reference points and packet loss, order and latency control. The
ASN-anchored mobility is logically composed of a Data Path (Bearer plane) function, a
Handover function and a Context function which is responsible of data transmissions and
control message exchanges. These functions are attached to different network entities
depending on their tasks [2, 3].
41
Figure 3.3
ASN-Anchored Mobility Scenario
Data Path function controls data path establishment and transmission of data
packets between entities. A logical division of the Data Path function includes an
anchor DP function, a serving DP function, a target DP function and a relaying
DP function.
Handover function controls handover decision, initiation and signaling. Serving
HO function, relaying HO function and target HO function constitute the overall
Handover function.
Context function addresses the exchanges required in order to setup any state in
network elements during a HO. Context server, context client and relaying context
functions control the Context function procedures.
Functions above are hosted by ASNs participating a HO. The functions may be
divided into following network elements during a HO process: anchor ASN, serving
ASN, target ASN and authenticator ASN. The anchor ASN is an attachment point to
CSN and external network. It hosts the anchor DP function for the MS. Before the
handover the MS is connected to the serving ASN which hosts the serving HO
function. The target ASN managing the target HO function contains a BS that the MS
will attach to after a successful handover. After that it will become a new serving
ASN. The Authenticator ASN provides authentication and security functions for MS.
42
3.2.4 CSN-Anchored Mobility
Figure 3.4 CSN-Anchored Mobility
CSN-anchored mobility comprises set of procedures associated with MS´s
movement and change of PoA. In this type of mobility the anchor CSN remains constant
but the anchor ASN of a MS may change and signaling and traffic via R3 reference point
is exploited. The CSN-anchored mobility means MIP based macro mobility in which re-
anchoring of MS from a current FA to a new FA as well as consequent binding updates
or MIP re-registration are needed in order to redefinition of data forwarding paths.
The R3 mobility may be divided into Intra-NAP R3 mobility or Inter-NAP R3
mobility as in figure . The inter-NAP R3 mobility enables roaming of the MS between
the home NSP and the visited NSP. In non-roaming scenarios the Home Agent (HA) is
located in the CSN of the home NSP whereas in a roaming scenario it may reside at the
home NSP or the visited NSP.
In each cell i ∈ Mc, the network capacity is 2 Mb/s, and the BBU is set to 32 kb/s
based on the 3GPP-supported multimedia bearer services. This implies that the capacity
of each cell is= 62 BBUs. The first service, i.e., s = 1, is voice connections requiring 32
kb/s. The second service, i.e., s = 2, is video connections requiring 64 kb/s. These values
are set according to the multimedia codecs for 3GPP. The third service, i.e., s = 3, is data
connections with Hypertext Transfer Protocol traffic (i.e., web browsing) at 32 kb/s.
Thus, QoS provisioning in cell i stipulates that b1 = 1 BBU, b2 = 2 BBUs, and b3 = 1 43
BBU. In each cell k ∈ Me, according to, the network capacity is 6 Mb/s. To benefit from
the additional capacity, the required data rates of the services are reasonably assumed to
be larger in the 802.16e ASN than the rates in the 3G RAN. We set the BBU to 64 kb/s,
the voice connections to 64 kb/s, video connections to 128 kb/s, and data connections to
64 kb/s. This implies that the capacity of each cell k is Ck =92 BBUs and that QoS
provisioning is b1 =1 BBU, b2 = 2 BBUs, and b3 = 1 BBU [6].
CONCLUSION
This chapter gives the idea of various handover scenarios, objectives of handover,
handover requirements and procedure. Thus knowing about the entire handover process,
selecting the method of handover is up to the decision strategy existing between the user
equipment and the base station in the scenario model in the proposed system. After creating
the model in OPNET Modeler, handover conditions are to be implemented in the proposed
model. Finally this chapter tells about the various handover types involved in the proposed
scenario in both UMTS and WiMAX networks.
44
CHAPTER-4
SIMULATION RESULTS
4.1 INTRODUCTION TO THE OPNET
The OPNET Modeler gives the facility of the graphical user interface in which
the users can model and simulate their networks. For developing different
communication structures and implementing different scenarios’, different hierarchal
layers are present in the environment of the modeling. Users can build a detail model
according to the requirement to do the analysis of the system. The systems are designed
in the object oriented way, on compilation of the model its produces a discrete event
simulation in the C language. After performing the simulation, the results are analyzed
with the different statistics related to the performance provided by the OPNET. The
following are the different layers in the OPNET which are explain below.
Figure 4.1 OPNET Modeler
45
4.1.1 Network Layer
On the graphical map the network layer enables to specify the network topology.
Different elements of the network can be placed on the network layer. Through different
links these network elements can be connected. To perfume the mobility of the user
equipment the trajectories can be created through the radio links. So it being the useful
facility as the mobile UMTS users can be simulated. The sub network can be merging
together in this layer. Using the network layer the network project can be built up.
OPNET contains the wide library of node model having different technologies like
UMTS, ETHERNET, and ATM etc.
4.1.2 Node Layer
The nodes are build up in the node layer. The nodes are made up in the node
editor using different transmitter, receiver, processor etc. These blocks are called as
modules. These modules allow implementing the different node specific characteristics.
4.1.3 Process layer
This layer makes the possibility of programming the various modules which are
used in the node layer in order to design and implement various protocols or the required
behavior of the node. The OPNET has a wide kernel of standard procedures that are
mostly used in the communication networks but it is possible to write the C++ codes
which are the user’s specific function. The process editor uses Proto-C, which is the
programming language which makes the combination of the C/C++ language and the
state transition diagram.
4.2 OPNET UMTS Model
OPNET Modeler presents the specialized models that cover the specific needs
for the simulating and modeling the networks that poured on certain technology area.
UMTS is the one of those models which is based on the 3GPP specification. The model
focuses on UE-UTRAN-CN architecture as shown in the figure [15-17].
46
Figure 4.2 UE-UTRAN-CN Architecture
In the figure 4.2 user equipment model gives the functionality of the mobile
equipment. It is responsible for the radio link termination. The UTRAN model consists of
the Node B and the RNC. The core network is not fully implemented. The SGSN and the
GGSN are included. The UMTS model supports wide range of a feature which resembles
the real network. The four different traffic classes are defined in the model which is
conversation, interactive, background and streaming. Different QoS profiles are defined
for each traffic class. This allows studying various effects in the network.
The overall features of the UMTS OPNET Model are shown in below.
It is based on WCDMA.
It supports the four QoS classes.
It supports the user equipment UE, Node B, RNC, Repeater, GGSN and
SGSN.
It supports the hard, soft and the softer handovers.
It supports the outer loop power control.
It offers the facility of the set up, release and negotiation of the radio access
bearers.
It supports for the dedicated and the common control channels.
It supports for the different modes like acknowledge, unacknowledged and
the transparent RLC.
47
It supports for the multiplexing of logical channel to the transport channel.
Figure 4.3 OPNET UMTS Scenario for Single User
48
Figure 4.4 Throughput for UMTS Base Station
Figure 4.4 describes about uplink and downlink throughput in the base station
(Node_B). The user equipment (UE) is requesting the base station to provide a
throughput of 230 bits per second in return from the base station the user equipment is
accessing throughput of 160 bits per second. It implies that the user equipment has a
good throughput and the connection continues even at the handover interval without
immediate data rate drop to zero.
Figure 4.5 UMTS Handover for Single User
49
Figure 4.5 describes about the handover with pilot channel for the user
equipment while moving from one base station (Node_B_0) to another base station
(Node_B_1). Here the declining rate is minimum because of the Basic Bandwidth Unit
(BBU) of 32 Kbps is allocated so that the UE will be handled by other base station
Node_B_1 when it moves from Node_B_0 without connection loss.
Figure 4.6 OPNET UMTS Scenario for Multi-Users
Figure 4.7 Throughput for UMTS Base Station
50
Figure 4.7 describes about average of the total uplink and downlink for
multiple users in the base station (Node_B). the user equipments in this scenario is
requesting at a rate of 10 bits per second for a small interval of time and in return the
user equipments are accessing at a rate of 7 bits per second.though there are many
users the UMTS can continuously provide a good throughput during the entire
handover interval.
Figure 4.8 UMTS Handover for Multi-users
Figure 4.8 shows the successful handover for four different users namely UE,
UE_0, UE_1, UE_5 it is ensured that the with the active pilot channel. It can be
inferred from the graph that the service rate is high when the handover process
commences and service rate declines but the connection is not lost because of the
Basic Bandwidth Allocation.
51
4.3 OPNET WiMAX Model
The WiMAX model suite includes a discrete event simulation model that lets
you analyze network performance in wireless metropolitan area networks. WiMAX
model suite includes the features of the IEEE 802.16 standard. Note that the Wireless
Module and a license for the WiMAX specialized model are needed to run simulations
that use the WiMAX model suite [5, 9].
The WiMAX configuration object includes the following attributes.
• Contention Parameters
• Efficiency Mode
• MAC Service Class Definitions
• OFDM(A) PHY Profiles
• SC PHY Profiles
PHY layer profiles are used for the following:
• Estimating link capacities during admission control
• Determining uplink/downlink boundary information using the configured frame
structure information
• Determining PHY-layer overheads
Figure 4.9 BS-UE WiMAX Block Diagram
52
Figure 4.10 OPNET WiMAX Scenario for Single User
Figure 4.11 WiMAX Traffic Simulation
53
Figure 4.11 shows the traffic sent from the user equipment (MS_0) to the base
station (BS_0) and traffic received to it from the same base station while it is moving
through BS_1, BS_2, BS_3 and returning to the home location.
Figure 4.12 WiMAX Packet Transmission
Figure 4.12 represents the user (MS_0) packet rate transmitted and received
while communicating with all the base stations while it is moving through its described
trajectory path. Here the maximum and minimum uplink–downlink packet drops are
the same in this WiMAX single user scenario. This WiMAX scenario provides
minimum packet loss thus increasing the reliability.
54
Figure 4.13 WiMAX Connection Throughput
Figure 4.13 points out the throughput scale in all the base stations where the
user equipment’s path is defined. First the user requests (downlink throughput) the
base station at a constant bit rate. Whenever the user entering and leaving the coverage
area of base stations BS_0, BS_1, BS_2, BS_3 receives (uplink throughput) the
constant bit rate.
Figure 4.14 OPNET WiMAX Scenario for Multi-user
55
Figure 4.15 WiMAX Traffic Simulation
Figure 4.15 delivers the user equipment’s traffic state in connection with the
base station. Here the traffic sent to BS_0 whether it can respond with the requested
packet rate or not. In return it received more traffic condition from BS_0 but it won’t
reject the user due to the specification of WiMAX where it should provide good
throughput. Thus during handover it has connectivity until it enters the next base
station.
Figure 4.16 WiMAX Packet Transmission
56
Figure 4.16 reports the uplink and downlink packet drops in user equipment
(MS_1) when it travels through BS_2,BS_3,BS_5 and BS_0. Though it requests for
high packet rate of 75 packets per second it receives of about 10 packets per second
throughout its entire trajectory path and it won’t let it to zero.
Figure 4.17 WiMAX Connection Throughput
Figure 4.17 tells about the connection throughput when the user equipment
(MS_9) travels from BS_0 to BS_1. The user requests for 0.35 packets per second and
it receives 1.7 packets per second which again ensures that under real time connection
according to users request, WiMAX networks never rejects the user and in return it
gives a constant packet rate to the user.
CONCLUSION
Finally, this chapter shows the results of the proposed scenario in both
WiMAX and UMTS networks. The main parameters included in this project are
connection throughput, uplink and downlink packet drops, traffic sent and received by
the user equipments while moving through its trajectory path in connection with the
base stations.
57
CHAPTER-5
CONCLUSION AND FUTURE WORK
An important way for improving the cost-efficiency of UMTS networks is
efficient design and use of existing and newly delayed network infrastructure. The
radio access network is considered as one of the most important economic aspects for
the network planning and bandwidth dimensioning due to its limited and
expensive transport resources. With the rapid expansion of the radio access
network as well as the fast growing number of mobile users and traffic volume, there
is a significantly increasing demand for transport capacities in the radio access
network. To achieve a cost-efficient design of the UMTS network, the radio access
networks have to be dimensioned appropriately for the many types of services which
are to be offered.
IEEE 802.16e offers cost reductions to mobile operators who wish to offer
broadband IP services in addition to 2G or 3G voice services, and allows operators to
enter new markets with competitive services, despite owning disadvantaged spectrum.
The capital outlay for WiMAX equipment will be less than for traditional 2G and 3G
wireless networks. The latest developments in the IEEE 802.16 group are driving a
broadband wireless access revolution to a standard with unique technical characteristics.
Initially, WiMAX will bridge the digital divide and thanks to competitive equipment
prices, the scope of WiMAX deployment will broaden to cover markets with high DSL
unbundling costs or poor copper quality which have acted as a brake on extensive high-
speed Internet and voice over broadband. WiMAX will reach its peak by making
Portable Internet a reality. Integrated into new generation networks with seamless
roaming between various accesses, it will enable end-users to enjoy an "Always
Best Connected" experience .
The IEEE 802.16m standard is the core technology for the proposed
Mobile WiMAX Release 2, which enables more efficient, faster, and more converged
data communications. The IEEE 802.16m standard has been submitted to the ITU
for IMT-Advanced standardization. IEEE 802.16m is one of the major candidates for
IMT-Advanced technologies by ITU. Among many enhancements, IEEE 802.16m
58
systems can provide four times faster data speed than the current Mobile WiMAX
Release 1 based on IEEE 802.16e technology. Mobile WiMAX Release 2 will provide
strong backward compatibility with Release 1 solutions. It will allow current Mobile
WiMAX operators to migrate their Release 1 to Release 2 by upgrading channel cards or
software of their systems. Also, the subscribers who use currently available Mobile
WiMAX devices can communicate with new Mobile WiMAX Release 2 systems
without difficulty.
It is anticipated that in a practical deployment, using 4X2 MIMO in the urban
micro cell scenario with only a single 20 MHz TDD channel available system wide,
the 802.16m system can support both 120 Mbit/s downlink and 60 Mbit/s
uplink per site simultaneously. It is expected that the WiMAX Release 2 will be
available commercially in the 2011-2012 time frame The goal for the long-term
evolution of WiMAX is to achieve 100 Mbit/s mobile and 1 Gbit/s fixed-nomadic
bandwidth as set by ITU for 4G NGMN (Next Generation Mobile Network) .
The 3G/4G network will be heterogeneous and able to serve a large number of
subscribers. It will be able to handle Different technologies in a common platform. For
this reason the existing QoS parameters should be upgraded for large number of
subscriber. The service should be improved in different levels of the large networks.
Besides the QoS manager Adaptive Resource Management (ARM) should be consider
for proper adaption of the network resources in the heterogeneous networks. The
integration of IntServ, Diffserv and MPLS can be the potential to improve the service
as well as the existing QoS parameters in 4G network. The RSVP of IntServ can make
resource reservation in the network. It can enable the end user to reserve the resources
for utilization in the network whereas Diffserv can provide better support in the core
network. The integration of two services can maintain the traffic flow and reduce the
packet loss which may improve the other quality of service (QoS) parameters in the
network.
To support IPv6 based networks, MPLS can be efficient to improve the service
in the large network. The Label Switched Path (LSP) of MPLS can make fast
forwarding decision with the support of Diffserv. Moreover the MPLS- traffic
59
engineering and the RSVP can be provisioning the constraint based LSP to avoid the
congestion as well as improve the traffic flow to meet the requirement for improving
the Existing parameters such as packet loss, end to end delay, delay variation,
throughput and jittering 4G network. From the above analysis, it can be concluded that
the performance of these QoS parameter can be improved both in UMTS and B3G/4G
wireless network by adapting and integrating proper QoS scheme.
The 4G is the common platform for all other technologies to interact properly.
In order to make efficient services for the heterogeneous network, it is important to
design a common QoS scheme for the common platform. Our next concentration will
be designed a model of common QoS scheme in heterogeneous network to improve
the overall service for the end user in the network.
60
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