Seminar Report Final

Wireless network 3G and 4G

Department of electronics and communication Page 1

ABSTARCT

4G is a term used to describe the next complete evolution in wireless

communications.4G system will be able to provide a comprehensive IP

solution where multimedia can be given to users higher data rates than

previous generations.

2G was a total replacement of the 1G networks and handsets,and the 3G was

a total replacement of 2G networks and handsets,4G cannot be an

incremental evolution of current 3G,but rather the total replacement of the

current 3G networks and handsets.

4G will be capable of providing between 100 Mbps-1 Gbps speeds both

indoors and outdoors,with premium quality and high security.



CHAPTER 1:

1. INTRODUCTION:

The approaching 4G (fourth generation) mobile communication systems are projected to

solve still-remaining problems of 3G (third generation) systems and to provide a wide

variety of new services, from high-quality voice to high-definition video to high-data-rate

wireless channels.

The term 4G is used broadly to include several types of broadband wireless access

communication systems, not only cellular telephone systems. One of the terms used to

describe 4G is MAGIC—Mobile multimedia, Anytime anywhere, Global mobility

support, Integrated wireless solution, and Customized personal service.

As a promise for the future, 4G systems, that is, cellular broadband wireless access

systems, have been attracting much interest in the mobile communication arena. The 4G

systems not only will support the next generation of mobile service, but also will support

the fixed wireless networks.

This paper presents an overall vision of the 4G features, framework, and integration of

mobile communication. The features of 4G systems might be summarized with one word-

Integration. The 4G systems are about seamlessly integrating terminals, networks, and

applications to satisfy increasing user demands.

The continuous expansion of mobile communication and wireless networks shows

evidence of exceptional growth in the areas of mobile subscriber, wireless network

access, mobile services, and applications. An estimate of 1 billion users by the end of

2003 justifies the study and research for 4G systems.



CHAPTER 2:

2.1 HISTORY:

The history and evolution of mobile service from the 1G (first generation) to fourth

Generation are discussed in this section. Table1 presents a short history of mobile

telephone technologies. This process began with the designs in the 1970s that have

become known as 1G. The earliest systems were implemented based on analog

technology and the basic cellular structure of mobile communication. Many fundamental

problems were solved by these early systems.

Numerous incompatible analog systems were placed in service around the world during

the 1980s.The 2G (second generation) systems designed in the 1980s were still used

mainly for voice applications but were based on digital technology, including digital

signal processing techniques. These 2G systems provided circuit-switched data

communication services at a low speed.

The competitive rush to design and implement digital systems led again to a variety of

different and incompatible standards such as GSM (Global System Mobile), mainly in

Europe : TDMA (Time Division Multiple Access) (IS-54/IS- 136)

U.S. : PDC (Personal Digital Cellular)

Japan : CDMA (Code Division Multiple Access) (IS-95)

These systems operate nationwide or internationally and are today's mainstream systems,

although the data rate for users in these system is very limited.

During the 1990s, two organizations worked to define the next, or 3G, mobile system,

which would eliminate previous incompatibilities and become a truly global system. The

3G system would have higher quality voice channels, as well as broadband data

capabilities, up to 2 Mbps. Unfortunately, the two groups could not reconcile their

differences, and this decade will see the introduction of two mobile standards for 3G.

In addition, China is on the verge of implementing a third 3G system. An interim step is

being taken between 2G and 3G, the 2.5G. It is basically an enhancement of the two



major 2G technologies to provide increased capacity on the 2G RF (Radio Frequency)

channels and to introduce higher throughput for data service, up to 384 kbps.

A very important aspect of 2.5G is that the data channels are optimized for packet data,

which introduces access to the Internet from mobile devices, whether telephone, PDA

(personal digital assistant), or laptop. However, the demand for higher access speed

multimedia communication in today's society, which greatly depends on computer

communication in digital format, seems unlimited. According to the historical indication

of a generation revolution occurring once a decade, the present appears to be the right

time to begin the research on a 4G mobile communication system.

Table 1. Short History of Mobile Telephone Technologies



2.1.1 First Generation (1G):

1G was based on analog technology and basically intended for analog phones. It was

launched in the early 1980s.

It introduced the first basic framework for mobile communications like the basic

architecture, frequency multiplexing, roaming concept etc. Access technology used was

AMPS (Advances Mobile Phone Service).

2.1.2 Second Generation (2G):

2G was a revolution that marked the switching of mobile communication technology

from analog to digital. It was introduced in the late 1980s and it adopted digital signal

processing techniques.

GSM was one of the main attractive sides of 2G and it introduced the concept of SIM

(Subscriber Identity Module) cards.

Main access technologies were CDMA (Code Division Multiple Access) and GSM

(Global System for Mobile Communication).

2.1.3 2.5 Generation (2.5G):

2.5 G was basically an extension of 2G with packet switching incorporated to 2G.

It implemented hybrid communication which connected the internet to mobile

communications.

2.1.4 Third Generation (3G):

The basic idea of 3G is to deploy new systems with new services instead of just provide

higher bandwidth and data rate. Support for multimedia transmission is another striking

feature of 3G. It employs both circuit switching and packet switching strategies.



The main access technologies are CDMA (Code Division Multiple Access), WCDMA

(Wideband CDMA), and TSSDMA (Time division Synchronous CDMA).

2.2 Current Technology:

Most modern cellular phones are based on one of two transmission technologies:

time-division multiple access (TDMA) or code-division multiple access (CDMA)

(Riezenman 2000, 40).

These two technologies are collectively referred to as second-generation, or 2G.

Both systems make eavesdropping more difficult by digitally encoding the voice

data and compressing it, then splitting up the resulting data into chunks upon

transmission.

2.2.1 TDMA:

TDMA, or Time Division Multiple Access, is a technique for dividing the time domain up

into subchannels for use by multiple devices. Each device gets a single time slot in a

procession of devices on the network, as seen in Figure 3.

During that particular time slot, one device is allowed to utilize the entire bandwidth of

the spectrum, and every other device is in the quiescent state.The time is divided into

frames in which each device on the network gets one timeslot.

There are n timeslots in each frame, one each for n devices on the network. In practice,

every device gets a timeslot in every frame. This makes the frame setup simpler and more

efficient because there is no time wasted on setting up the order of transmission.

This has the negative side effect of wasting bandwidth and capacity on devices that have

nothing to send (Leon-Garcia and Widjaja 2000). One optimization that makes TDMA

much more efficient is the addition of a registration period at the beginning of the frame.



During this period, each device indicates how much data it has to send. Through this

registration period, devices with nothing to send waste no time by having a timeslot

allocated to them, and devices with lots of pending data can have extra time with which to

send it.

This is called ETDMA (Extended TDMA) and can increase the efficiency of TDMA to

ten times the capacity of the original analog cellular phone network.

The benefit of using TDMA with this optimization for network access comes when data is

“bursty.” That means, at an arbitrary time, it is not possible to predict the rate or amount

of pending data from a particular host.

This type of data is seen often in voice transmission, where the rate of speech, the volume

of speech, and the amount of background noise are constantly varying. Thus, for this type

of data, very little capacity is wasted by excessive allocation.

Figure 1: Time Division Multiple Access



2.2.2 CDMA:

CDMA, or Code Division Multiple Access, allows every device in a cell to transmit over

the entire bandwidth at all times. Each mobile device has a unique and orthogonal code

that is used to encode and recover the signal (Leon-Garcia and Widjaja 2000).

The mobile phone digitizes the voice data as it is received, and encodes the data with the

unique code for that

phone. This is accomplished by taking each bit of the signal and multiplying it by all bits

in the unique code for the phone.

Thus, one data bit is transformed into a sequence of bits of the same length as the code for

the mobile phone. This makes it possible to combine with other signals on the same

frequency range and still recover the original signal from an arbitrary mobile phone as

long as the code for that phone is known.

Once encoded, the data is modulated for transmission over the bandwidth allocated for

that transmission. A block diagram of the process is shown in Figure 2.

Figure 2: Sending Data using Code Division Multiple Access



Figure 3: Receiving Data using Code Division Multiple Access

The process for receiving a signal is shown in Figure 3. Once the signal is demodulated, a

correlator and integrator pair recovers the signal based on the unique code from the

cellular phone. The correlator recovers the original encoded signal for the device, and the

integrator transforms the recovered signal into the actual data stream.

CDMA has been patented in the United States by Qualcomm, making it more expensive

to implement due to royalty fees. This has been a factor for cellular phone providers when

choosing which system to implement.

By keeping security in mind while designing the new system, the creators of 2G wireless

were able to produce a usable system that is still in use today. Unfortunately, 2G

technology is beginning to feel its age. Consumers now demand more features, which in

turn require higher data rates than 2G can handle.

A new system is needed that merges voice and data into the same digital stream,

conserving bandwidth to enable fast data access. By using advanced hardware and

software at both ends of the transmission, 4G is the answer to this problem.



CHAPTER 3:

3.1 VISION OF 4G:

This new generation of wireless is intended to complement and replace the 3G systems,

perhaps in 5 to 10 years. Accessing information anywhere, anytime, with a seamless

connection to a wide range of information and services, and receiving a large volume of

information, data, pictures, video, and so on, are the keys of the 4G infrastructures.

The future 4G infrastructures will consist of a set of various networks using IP (Internet

protocol) as a common protocol so that users are in control because they will be able to

choose every application and environment.

Based on the developing trends of mobile communication, 4G will have broader

bandwidth, higher data rate, and smoother and quicker handoff and will focus on ensuring

seamless service across a multitude of wireless systems and networks.

The key concept is integrating the 4G capabilities with all of the existing mobile

technologies through advanced technologies. Application adaptability and being highly

dynamic are the main features of 4G services of interest to users.

3.1.1 Limitations of 3G:

The reasons for a new generation of mobile communication are listed below:

� Difficulty of CDMA to provide higher data rates.

� Need for continuously increasing data rate and bandwidth to meet the multimedia

requirements.

� Limitation of spectrum and it’s allocation.

� Inability to roam between different services.



� To provide a seamless transport end-to-end mechanism.

� To introduce a better system with reduces cost.

3.2 Some main desired Features of 4G:

High usability and 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.

Multimedia support:

The user should be able to receive high data rate multimedia services. This demands

higher bandwidth and higher data rate.

Personalization:

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.

3.3 Main Challenges:

3.3.1 Security and Privacy:



In the development of 4G Networks, security measures must be established that enable

data transmission to be as safe as possible. Specifically, “The 4G core addresses mobility,

security, and QoS through reuse of existing mechanisms while still trying to work on

some mobility and handover issues”.

Therefore, it is necessary for the organization to develop an effective series of tools that

support maximum 4G security measures as a means of protecting data that is transmitted

across the network from hackers and other security violations. Because of the nature of

the 4G network, there is an increased likelihood of security attacks, and therefore,

multiple levels of security, including increased requirements for authentication, will be

necessary to protect data and information that is transmitted across the network.

One of the main goals of G4 networks is to blanket very wide geographic area with

seamless service. Obviously, smaller local area networks will run different operating

systems. The heterogeneity of these wireless networks exchanging different types of data

complicates the security and privacy issues.

The encryption and decryption methods being used for 3G networks are not appropriate

for 4G networks as new devices and services are introduced for the first time in 4G

networks.

To overcome these security and privacy issues, two approaches can be followed. The first

is to modify the existing security and privacy methods so that they will be applicable to

heterogeneous 4G networks. Another approach is to develop new dynamic

reconfigurable, adaptive, and lightweight mechanisms whenever the currently utilized

methods cannot be adapted to 4G networks.

3.3.2 Quality of Service (QoS):

With respect to network quality, many telecommunications providers are promising that

there will be enhanced connectivity, and the quality of data that is transmitted across the



network will be of the highest possible quality, as in the case of Ericsson’s 4G Network

for TeliaSonera .

The company promises that “The new 4G network will do for broadband what mobile

telephony did for voice. With real-time performance, and about 10 times higher data rates

compared to today's mobile broadband networks, consumers can always be connected,

even on the move” .

As a result, it is important for providers to develop an effective approach to the 4G

Network that will enhance quality, provide effective security measures, and will ensure

that all users are provided with extensive alternatives for downloading video, music, and

picture files without delays.

The main challenge that 4G networks are facing is integrating non-IP-based and IP-based

devices. It is known that devices that are not IP address based are generally used for

services such as VoIP. On the other hand, devices that are IP address based are used for

data delivery. 4G networks will serve both types of devices. Consequently, integrating the

mechanisms of providing services to both non-IP-based as well as IP-based devices is one

of key challenges 4G networks have to address.

3.3.3 Complex Architecture:

Multimode End-User Terminals

To reduce operating costs, devices that operate on 4G networks should have the capability

to operate in different networks. This will not only reduce the operating cost but will also

simplify design problems and will reduce power consumption. However, accessing

different mobile and wireless networks simultaneously is one of the major issues 4G

networks have been addressing.

One mechanism that has been proposed to handle this problem is termed “multi-mode

devices”. This mechanism can be achieved through a software radio that allows the end-

user device to adapt itself to various wireless interfaces of the networks. Figure 4 shows

an example of such solution.



Figure4: Accessing multiple networks and services through multi-mode software

System Discovery and Selection:

Due to the heterogeneity of 4G networks, wireless devices have to process signals sent

from different systems, discover available services, and connect to appropriate service

providers.

Various service providers have their own protocols which can be incompatible with each

other as well as with the user’s device. This issue may complicate the process of selecting



the most appropriate technology based on the time, place and service provided, and thus,

may affect the Quality of service provided to the end user.

One solution to resolve this issue is called “System-initiated discoveries”. This

mechanism allows automatic download of software modules based on the wireless system

the user is connected to.

Another approach to handle this problem is based overlay networks. In such case, the

end-user device is connected to different networks through an overlay network. The

overlay network performs all necessary tasks such as protocol translation and Quality of

service negotiation as depicted in Figure 5.

Figure5: Automatic system discovery is one of the features provided by 4G

networks.



Service and Billing

Managing user accounts and billing them has become much more complicated with 4G

networks. This is mainly due to heterogeneity of 4G networks and the frequent interaction

of service providers. The research community addressed this concern and proposed

several frameworks to handle the customers’ billing and user account information.



CHAPTER 4:

4.1 WIRELESSARCHITECTURE:

The 4G Mobile communications will be based on the Open Wireless Architecture

(OWA)to ensure the single terminal can seamlessly and automatically connect to the

local high-speed wireless access systems when the users are in the offices, homes,

airports or shopping centers where the wireless access networks (i.e. Wireless LAN,

Broadband Wireless Access, Wireless Local Loop, HomeRF, Wireless ATM, etc) are

available.

When the users move to the mobile zone (i.e. Highway, Beach, Remote area, etc.),the

same terminal can automatically switch to the wireless mobile networks (i.e.GPRS,W-

CDMA,cdma2000, TD-SCDMA, etc.).

Greatly increase the spectrum efficiency Mostly ensure the highest data-rate to the

wireless terminal Best share the network resources and channel utilization Optimally

manage the service quality and multimedia applications Figure 3 shows the wireless

evolution to 4G mo bile communications based on OWA platform, where 3G,Wireless

LAN and other wireless access technologies will be converged into 4G mobile platform

to deliver the best infrastructure of mobile communications with optimal spectrum

efficiency and resource management.

In fact, this OWA model had already been accepted by most wireless industries, for

example, the W-CDMA/W-LAN/Bluetooth 3-in-1 terminal is being designed in many

companies.

The global 4G Mobile R&D focuses on the following Open Wireless Architecture:



Figure 6:Wireless evolution to 4G mobile based on wireless architecture

4.2 Mobile IPv6 Protocol:

Mobile IPv6 [Johnson and Perkins, 2001, Montavont and Noel, 2002, Beloeil, 2002] is

proposed to keep any communication between a mobile node and a correspondent node

(CN) while the mobile node moves from one IPv6-based sub-network to another one.

In this design, each MN has a home address identifying its home network. Within its

home network, each MN uses the traditional routing functions to exchange IP datagram

with its CN.

Whenever an MN moves from its local network to a new network, its home address

becomes invalid. And then the MN can create a new address called care-of address (CoA)

from a router advertisement message sent by the new visited network.



A binding between MN’s CoA and its home address is updated to the MN’s home agent

to keep continuous communications between the MN and its correspondent(s). In this

way, MN’s home agent can always detect coming communication packets to MN with

MN’s home address, and locate the current position of MN with MN’s CoA.

At the beginning of the handover procedure, an MN can use “Neighbor Discovery"

scheme, which is based on reception of Router Advertisement (RA) sent by current access

router (AR), to detect its movement to a new subnet, as shown in Figure 7

After verifying the uniqueness of its linklocal address on the new link, the MN will create

an IPv6 address called CoA from the corresponding prefix in RA. After that, MN will

exchange binding update information which include MN’s CoA with its HA and its CN to

allow all of them to maintain their connections, shown in Figure 7

Mobile IPv6 can reasonably keep track of MN’s new address by timely binding update

between the MN and its home agent. However, before finishing binding update, data

packet communications are interrupted. The MN needs to spend time discovering new

subnet, establishing new care-of address, and exchanging information between MN and

its home agent.

For 4G high-speed data multimedia communications, all of them will create a lot of

signaling traffic and latency, resulting in packet loss.

It is even worse when an MN roams between two ARs several times. This frequent

roaming will cause pingpong effects, which refer to the situation in which too frequent

and unnecessary location updates and handoffs occur in a short time. In this case, MN

cannot keep normal continuous communications with its CN. In the meantime, all packets

destined for the old care-of address are dropped.

Therefore, we need to improve binding update procedure of Mobile IPv6 handover

schemes to reduce handoff latency and signaling traffic.



Figure7 : Mobile IPv6 wireless network

4.3 Hierarchical Mobile IPv6:

Hierarchical Mobile IPv6 (HMIPv6) [Soliman et al., 2001, Pack and Choi, 2003] is

developed to reduce the amount of signalling traffic required, which affects handoff

latency of MN’s communications.

Unlike MIPv6, HMIPv6 addresses the issue of local mobility and global mobility

separately, which means local handoffs are managed locally without notifying home

agent, while global mobility is managed with the

MIPv6 protocol.

In HMIPv6, the global internet is divided into regions for local area mobility and each

region is connected to the rest of IP network with a new node called Mobility Anchor

Point (MAP), which is a kind of anchor point in charge of several ARs (from 1 to k), as

shown in Figure 8.



In this scheme, each mobile node has two care-of addresses. One is a regional care-of

address and the other is a local care-of address. The regional care-of address is local to

the MAP's covered region. An MN communicates with its correspondent nodes via its

regional care-of address.

When an MN moves into a new region or domain, it will first get a regional care-of

address from MAP advertisement information, and then the MN will inform its home

agent and its correspondents about its “regional location” as its raw location information.

When the MN moves between two ARs in the same region covered by a same MAP, MN

will update its localization into the domain and get a new local careof address by sending

local registration to the MAP, instead of sending to its home agent.

The MAP intercepts data packets designated to MN’s regional care-of address and tunnels

them to the corresponding MN’s local care-of address. So in this way, handoff latency

and signaling traffic are reduced because each MN hides its local movements in a region

from its home agent and correspondents, and meanwhile MN can keep unbroken

communications with its correspondent(s).

Figure 8: Hierarchical Mobile IPv6 Architecture



CHAPTER 5:

5.1 SERVICE PROVISION IN THE 4G ERA:

To reap the economical and developmental benefits of competition, namely diversified

service offerings and rapid technological evolution, the mobile value chain must be open

so as to foster and harbor the participation of multiple new players, e.g., value added

service providers, content providers, application developers, etc).

These players will cooperate with the incumbent mobile operators to contribute additional

value to the mobile service provision process but will also compete for the lion’s share of

user revenue.

5.1.1 Analyzing the “ABC” vision:

In the 4G mobile communication era, a plethora of disparate services and multimedia

applications will have to be flexibly yet efficiently deployed over a heterogeneous

multinetwork environment, raising service management requirements.

Nonetheless, mobile users will expect seamless global roaming across these different

wireless networks and ubiquitous access to personalized applications and rich content via

a universal and user-friendly interface. In studying the implications of the heralded

“Always Best Connected” vision of 4G mobile systems, we identify the notion of utility,

implicitly embedded in the “best” adjective.

Utility is a fundamental concept in microeconomic theory that concerns a typically

continuous function representation of the consumer’s preference relation over a set of

commodities.

5.1.2 User utility issues:

Users engage communication-based applications to realize various subjective benefits.

These applications depend on the timely and orderly provision of network bearer services



to exchange application-specific signaling and to move various classes of user

information (e.g., image, video, corporate data) between communicating application

endpoints.

Inasmuch as the network is unable to provide the required levels of service, application

will become dysfunctional and any user-perceived benefits of these applications will

remain elusive, thus leading to a degraded user experience.

Performance of communication-based applications depends on the accommodation of

QoS requirements for their native signaling and the exchange of arbitrary user

information. From a network viewpoint, these factors translate to traffic flows with

different QoS requirements that will – in principle – levy different charges, thereby

decreasing user satisfaction.

Thus, ensuring an adequate performance for communicationbased applications so as to

maximize user satisfaction, translates to honoring the QoS requirements of their traffic.

Personal intelligent agent(s), enjoys untethered connectivity and ubiquitous access to

applications over the most efficient combination of available systems.

Figure 9 provides an illustration of the future 4G mobile network architecture comprising

ad-hoc, cellular, hot-spot, and satellite radio components.



Figure 9: The generic 4G mobile network architecture.

Considering that a single system that optimally meets a wide range of use cases and

satisfies diverse service requirements is likely to remain an engineering utopia, we

understand that heterogeneous architectures that can exploit individual system

capabilities’ to optimally server the instant application and value-added service mix in a

flexible manner are a plausible design approach.

The goal of future mobile communication systems will be to incorporate and integrate

different wireless access technologies and mobile network architectures in a

complementary manner so as to achieve a seamless wireless access infrastructure.

It is widely accepted that the individual (wireless and/or wireline) access networks will

interface to core and/or backbone network elements over the IP protocol, the lingua

franca of networking technology.

Regardless of their particular technological blueprints (e.g., licensed or unlicensed

frequency band, mobility management protocol, etc), these wireless access networks are

expected to have the following in common:



1) A dynamic address assignment mechanism (e.g., DHCP, SLP, IPv6) that is capable of

associating a short-lived or long-lived IP address to the respective wireless interface at the

mobile terminal (e.g., Mobile IP COA association)

2) A transparent IP forwarding service that is accessible over the logical termination of

the IP layer at the mobile terminal and one or more gateways (e.g., GGSN, MobileIP FA)

at the wireless access network infrastructure. The IP forwarding service is set up by

signalling procedures (e.g., PDP context signalling in the UMTS case) specific to the

technical architecture of each wireless access network.

Technical reviews of existing wireless access standards and research contributions on the

similarities of wireless network architectures validate these assumptions.

5.2 HANDOFF MECHANISM:

The subscription and service profile of GMS are maintained by GPRS network at two

entities. Its GPRS profile is stored at home location register (HLR) and its WLAN

profiles are stored at HA.

The subscription and service profile of WH are maintained by its HA in Internet. In our

proposed WLAN/GPRS interworking architecture, two types handoff procedures are

performed..

5.2.1Handoff from GPRS to WLAN:

We take the scenario that a GMS is initially in GPRS network and she maintains a session

with correspondent node (CN) N1 in the Internet through GPRS network. The terminal’s

GPRS system is active and WLAN radio system is in passive scan mode. When the GMS

moves to WLAN hotspot, her WLAN card is activated on receipt of beacon signal from

WLAN access point(AP).

The GPRS sytem is triggered off and terminal performs association with AP.

subsequently she performs MIP based registration with HA at GGSN. After MIP based



handoff completion, she can send packets to CN through WLAN with much higher speed

and packets are directly routed in the Internet.

Thus GGSN acts as an anchor point of GMS while she is in a WLAN hotspot. The

incoming packets from the Internet are routed to GGSN. If destination WMS is in a

WLAN hotspot, GGSN forwards the packets to responsible FA using MIP tunneling.

5.2.2 Handoff from WLAN to GPRS:

The AAA (authentication, authorisation and accounting) profiles of a WH are maintained

at HA in Internet. A WH has the capability to access GPRS network.

GPRS entertains IP connection for a WH because the GPRS operator has an agreement

with the Internet. The GPRS network maintains the profiles for service and QoS that a

WH can avail through GPRS network. A WH may have subscriptions to access GPRS

network from selected cells or routine area also.

When WH comes out of a WLAN hotspot, she will in cellular coverage. Therefore, her IP

based ongoing sessions can continue through GPRS network. She will perform MIP

based signaling for mobility and handoff management through GPRS netowrk.

GPRS network provides the bearer service for IP packets in conjunction with PDP

context maintained at SGSN and GGSN. The MIP registration request is a IP packet

which needs PDP context for transportation through GPRS network.

This packet is dealt by FA at GGSN. Hence, after GPRS attach procedure, a WH needs

two passes for MIP registration. In first pass, PDP context is created in GPRS network

and in second pass, MIP registration is performed . The handoff delay in two-pass method

is substantially larger.

We propose a one-pass technique for both PDP context activation and MIP registration to

reduce the handoff delay.



Before sending the activate-PDP-context request message, the GPRS session management

(GSM) entity retrieves the MIP registration request [MRR] packet from network layer.

Then, it inserts this packet in the information field of PDP request message.

5.2.3. One-pass Method:

Following sequential operations are performed by a WH and GPRS network for hand off

management.

- WH performs GPRS attachment signalling with GPRS network and terminal equipment

attains the GPRS attached state.

- GSM sub-layers of terminal retrieves the MRR packet from network layer.

- WH sends a modified activate-PDP-context request message to SGSN and it contains

MRR packet.

- SGSN sends a modified create-PDP-context request to GGSN and it contains MRR

packet.

– GGSSN creates PDP context and sends create-PDP-context response to SGSN.

- GGSN fills the care-of-address field of MRR message with the PDP address and gives

the MRR packet to FA.

- Now FA processes the MRR packet for MIP signaling with HA and simultaneously,

create-PDP-context response message travel through GPRS network.

- FA receives the MIP registration response packet from HA and gives this packet to

GGSN addressed to WH.

- Now PDP is already established. Therefore the MIP response packet is tunneled to

SGSN using GTP protocol and SGSN sends this packet to WH.



Figure 10: The sequence of signaling for MIP based handoff from WLAN to GPRS



CHAPTER 6:

6.1 Basic Multi-Carrier Multiple Access Schemes:

Before deciding on the probable access technique for 4G wireless communication

systems, we here briefly summarize the basic properties of three fundamental multi-

carrier based multiple access techniques, namely Orthogonal Frequency Division

Multiple Access (OFDMA), Orthogonal Frequency Division Multiplexing - Time

Division Multiple Access (OFDM-TDMA) and Orthogonal Frequency Division

Multiplexing - Code Division Multiple Access (OFDM-CDMA).

6.1.1 Definition of Basic Schemes:

OFDM-TDMA:

In OFDM-TDMA, a particular user is given all the sub-carriers of the system for any

specific OFDM symbol duration. Thus, the users are separated via time slots. All symbols

allocated to all users are combined to form a OFDM-TDMA frame.

The number of OFDM symbols per frame can be varied based on each users requirement.

Frequently, an error correcting code is applied to the data to compensate for the channel

nulls experienced by several random bits.

This scheme allows MS to reduce its power consumption, as the MS shall process only

OFDM symbols which are dedicated to it. On the other hand, the data is sent to each user

in bursts, thus degrading performance for delay constrained systems delay constrained

systems.



OFDMA:

In OFDMA, available sub-carriers are distributed among all the users for transmission at

any time instant.

The subcarrier assignment is made for the user lifetime, or at least for a considerable time

frame.

The scheme was first proposed for CATV systems and later adopted for wireless

communication systems.

OFDMA can support a number of identical downstreams, or different user data rates, [e.g.

assigning a different number of sub-carriers to each user].

Based on the sub-channel condition, different baseband modulation schemes can be used

for the individual sub-channels, e.g. QPSK, 16-QAM and 64-QAM etc.

This is investigated in numerous papers and referred to as adaptive subcarrier, bit, and

power allocation or Quality of Service (QoS) allocation.

In OFDMA, frequency hopping, one form of spread spectrum, can be employed to

provide security and resilence to inter-cell interference.

OFDM-CDMA:

In OFDM-CDMA, user data is spread over several subcarriers and/or OFDM symbols

using spreading codes, and combined with signal from other users .

The idea of OFDM-CDMA can be attributed to several researchers working

independently at almost the same time on hybrid access schemes combining the benefits

of OFDM and Code Division Multiple Access (CDMA).

OFDM provides a simple method to overcome the Inter-Symbol Interference (ISI) effect

of the multi-path frequency selective wireless channel, while CDMA provides the

frequency diversity and the multi-user access scheme.



Different types of spreading codes have been investigated. Orthogonal codes are preferred

in case of DL, since loss of orthogonality is not as severe in DL as it is in UL.

Several users transmit over the same sub-carrier. In essence this implies frequency

domain spreading, rather than time domain spreading, as it is conceived in a Direct

Sequence Code Division Multiple Access (DS-CDMA) system.

The channel equalization can be highly simplified in DL, because of the one tap channel

equalization benefit offered by OFDM.

6.2 Characteristics of Basic Schemes:

6.2.1 Flexibility:

OFDM-TDMA

Different OFDM symbols can be allocated to different users based on certain allocation

conditions. Since

the OFDM-TDMA concept allocates the whole bandwidth to a single user, a reaction to

different subcarrier

attenuations could consist of leaving out highly distorted sub-carriers .

The number of OFDM symbols per user in each frame can be adapted accordingly to

support heterogeneous data rate requirements.

An efficient multiple access scheme should grant a high flexibility when it comes to the

allocation of time-bandwidth resources.

On the one hand, the behavior of the frequency- selective radio channel should be taken

into account, while on the other hand the user requirements for different and/or changing

data rates have to be met.



For example, both for OFDMA and OFDM-TDMA, the usage of AMC on different sub-

carriers, as proposed in figure 7, may increase overall system throughput and help in

further exploiting CSI.

OFDMA

In OFDMA, the granularity of resource allocation is higher than that of OFDM-TDMA,

i.e. the flexibility can be accomplished by suitably choosing the sub-carriers associated

with each user.

Here, the fact that each user experiences a different radio channel can be exploited by

allocating only “good” sub-carriers with high SNR to each user.

Furthermore, the number of sub-channels for a specific user can be varied, according to

the required data rate. Thus, multi-rate system can be achieved without increasing system

complexity very much.

OFDM-CDMA

In OFDM-CDMA, the flexibility lies in the allocation of all available codes to the users,

depending on

the required data rates. As OFDM-CDMA is applied using coherent modulation, the

necessary channel

estimation provides information about the subcarrier attenuations; this information can be

used when

performing an equalization in the receiver.



6.2.2 Time-Frequency Resource Allocations:

OFDM-TDMA

Unit resource is one OFDM symbol. Thus, in a frame unit (consists of a number of basic

OFDM symbols), the symbols can be wholly assigned to any particular user.

Thus, similar to OFDMA, static and dynamic allocation can be implemented. In largely

static environment, such as indoor scenario, Dynamic Sub- Carrier Allocation (DSA)

based on CSI may not give much improvement in OFDM-TDMA compared to static

allocation scheme.

For very dynamic environment, DSA can be very beneficial for this scheme. But, from

another point of view, channel changes very frequently for a very dynamic wireless

channel, and so, static allocation may be enough to avoid fading. It can be safely assumed

that resource allocation is much simpler in this scheme than OFDMA.

OFDMA

Different methods of allocating and re-allocating different sub-carriers to different users

may be used:

Static:

Sub-carriers are allocated to a user for the entire duration of the connection time without

considering CSI. If the user is allocated some sub-carriers that are in fade, the signal will

remain faded until the user moves out of the fade or the sub-carriers are re-allocated after

some number of frames. So, when a user is in fade in allocated sub-carriers, it remains

there for long time, which is not desirable.



Dynamic:

Sub-carriers are allocated dynamically, assuming that the base station has instantaneous

(or near-instantaneous) knowledge of the CSI for each user. This is called DSA. In this

case, the subcarriers are allocated in real-time based on the knowledge of channel strength

at all sub-carriers for all users.

The sub-carriers are assigned into sub-channels in a contiguous or interleaved manner.

For contiguous assignment, the sub-carriers are divided into contiguous sub-channels,

where one benefit is the simplicity, but a disadvantage is the possible throughput

degradation due to channel fading.

In the interleaved case, the sub-carriers are successively assigned to the different users

and then interleaved over the total number of sub-carriers. One important advantage is

that it has potential to reap more channel diversity gain.

The disadvantage is that issues like synchronization for the entire OFDM symbol become

crucial, as the user sub-channel is scattered over the OFDM symbol.

In the dynamic sub-carrier assignment case, CSI is used to assign the sub-carriers best

suited for each user. This is advantageous in the sense that users at different locations

have different channel conditions, and most likely different optimal sub-carriers.

The benefit is that high throughput rate can be obtained, the disadvantages are that;

channel information is needed, sub-carriers must be reassigned whenever conditions

change, leading to additional signalling overhead whenever sub-carriers are reassigned.

OFDM-CDMA

All sub-carriers are shared by all the users. Thus, resource allocation does not include

sub-carrier allocation. In this scheme, user code allocation is the resource allocation.

Practically, any well-known code allocation scheme used in Wideband Code Division

Multiple Access (WCDMA) system can be adopted for OFDM-



CDMA scheme. The resource allocation scheme is much simpler in OFDM-CDMA

compared to other two schemes.

6.2.3 Variants of the Basic Schemes:

OFDM-TDMA

Besides static and dynamic allocation of OFDM symbols for different users, symbol

hopping can also be implemented in OFDM-TDMA system. As it is mentioned earlier,

this can bring some benefits for severely time and frequency selective outdoor scenario.

OFDMA

When it is not possible to be obtained CSI at the transmitter, an alternative to DSA can be

Subcarrier hopping (SCH) schemes. Frequency hopping in OFDMA systems can be

obtained in two ways: contiguous sub-band hopping and sub-carrier hopping.

Sub-Carrier Hopped Orthogonal Frequency Division Multiple Access (SCH-OFDMA)

system combines all the capabilities of an OFDMA system with sub-carrier hopping

spread-spectrum techniques. When users hop randomly on the available sub-carriers, then

we can call the system as Random Sub-Carrier Hopped Orthogonal Frequency Division

Multiple Access (RSCH-OFDMA).

This is very similar to Fast Low-Latency Access with Seamless Handoff Orthogonal

Frequency Division Multiplexing (FLASH-OFDM) system. Depending on the frequency

of the hopping schemes, SCH-OFDMA can be divided into two kinds of systems, namely

Fast Sub-Carrier Hopped Orthogonal Frequency Division Multiple Access

(FSCHOFDMA) and Slow Sub-Carrier Hopped Orthogonal Frequency Division Multiple

Access (SSCH-OFDMA).

In an FSCH-OFDMA system, once sub-carriers are allocated to users, the index of the

assigned subcarrier



is changed, i.e. hopped at every OFDMA symbol. Users are separated by non-overlapping

subcarrier hopping patterns.

These patterns constitute the hop-set available at the BS. The arrangement of the hop-set

available at neighboring cells depends on the cellular structure of the system. SSCH-

OFDMA system is very similar to FSCH-OFDMA system, except that the hopping

duration is at least a number of OFDM symbols.

OFDM-CDMA

The OFDM-CDMA scheme that we are referring here was actually proposed in the name

of Multi-Carrier Code Division Multiple Access (MC-CDMA).

One variation of this scheme is Orthogonal Frequency Division Multiplexing with Code

Division Multiplexing (OFDMA-CDM), where one user is given a set of sub-carriers and

all the data symbols it has to transmit, are spread on those subcarriers only and

transmitted in OFDM fashion.

There is a need of such variation of the original OFDMCDMA scheme to make it even

more usable. The afore-mentioned scheme has the advantage that it does not introduce

Multiple Access Interference (MAI) as MC-CDMA does.

A variation of OFDMACDM is DoCoMo’s well published Variable Spreading Factor -

Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM), where variable

spreading factors for users are used in different environment. SCH can be incorporated

along with OFDMA-CDM to create a scheme called, Sub- Carrier Hopped Orthogonal

Frequency Division Multiple Access with Code Division Multiplexing (SCHOFDMA-

CDM), which can also give substantially good scheme for indoor environment.

By changing the spreading procedure, several other variant of OFDM-CDMA schemes

are studied and analyzed, such as Orthogonal Frequency Division Multiplexing - Code

Division Multiple Access - Slow Frequency Hopping (OFDM-CDMA-SFH), Multi-



Carrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA), Multi-Tone

Code Division Multiple Access (MT-CDMA) etc.

6.2.4 Processing Requirements:

OFDM-TDMA

Users need to process the data symbols that are intended for them only. This is a feature

that gives OFDM-TDMA a little advantage over other two schemes.

OFDMA

As all the active users are present at every OFDM symbol in OFDMA, it is a requirement

that all active

users need to receive, detect and decode every OFDM symbol. This is expensive, in terms

of power

requirement etc.

OFDM-CDMA

Similar to OFDMA, all the users need to receive and decode all the symbols in OFDM-

CDMA system.

6.2.5 Synchronization:

In the DL, synchronization requirements for OFDM-TDMA, OFDMA and OFDM-

CDMA are similar and they are not different from the basic OFDM technique. Once the

timing- and frequency-offset are estimated and corrected, the OFDM symbol can be

decoded without MUI penalty.

In the UL, OFDMA and OFDM-CDMA require that active users be synchronized in time

and frequency to maintain orthogonality among themselves. Otherwise, MUI will occur.



6.2.6 Peak to Average Power Ratio

A multi-carrier signal consists of a number of independently modulated sub-carriers,

which can give a large Peak to Average Power Ratio (PAPR) when added up coherently.

Thus, all access techniques discussed here suffer from PAPR problem.

A large PAPR brings disadvantages like an increased complexity of the analog-to-digital

(A/D) and digital-to-analog (D/A) converters and a reduced efficiency of the Radio

Frequency (RF) power amplifier .

Complex solutions to solve this problem are devised in the literature. In the DL, BS

transmitter can perform the complex calculations to solve the PAPR problem. It can be a

severe problem in UL, where only a small number of sub-carriers are used, thus, PAPR

can be very high. This is the case for all the schemes being discussed in the document.

6.2.7 BER Performance:

OFDM-TDMA

The Bit Error Rate (BER) performance in this scheme is not different from basic OFDM

scheme, unless a form of AMC is used.

OFDMA

The BER of an OFDMA system is given by the modulation scheme used and averaged

over the channel distribution. For the same channel conditions, the overall BER of an

OFDMA system does not differ from the one found for OFDM systems.

When CSI-based resource allocation is used to exploit Multi-user Diversity (MuD), then

the BER performance of OFDMA gets much better compared to single-user basic OFDM

system.



OFDM-CDMA

The amount of MAI depends on particular combining scheme. This dominates the BER

performance. In

general, BER degrades with increasing number of users

.

Using schemes such as soft interference cancellation or Maximum Likelihood Symbol-

by-Symbol Estimation (MLSSE) can improve the performance. Otherwise the

performance depends a lot on the channel estimation and equalization.

6.2.8 Spectral Efficiency:

OFDM-TDMA

The spectral efficiency is equals to that of OFDM for a single user case. The spectral

efficiency depends on the baseband modulation scheme, and the code rate used.

OFDMA

OFDMA might have lower spectral efficiency than OFDM-TDMA when it is used in the

uplink.

Due to Inter-Carrier Interference (ICI), a guard band must be introduced between

different users, leading to a

loss in spectral efficiency.

OFDM-CDMA

OFDM-CDMA is a highly spectral efficient in the DL, as long as orthogonality of the

codes can be preserved. In non-ideal conditions, it is not possible to operate under full

load because of the MAI produced by the orthogonality loss.



High throughput under ideal conditions can be achieved. Due to the available frequency

diversity via spreading across all the sub-carriers, BER performance improves, which in

turn also improves the throughput.

6.2.9 Delay Spread Tolerance:

In the DL, delay spread tolearance of all basic schemes does not differ from the basic

OFDM scheme: Delay spread can be tolerated, provided that the guard interval is larger

than maximum delay spread.

In the uplink, due to different timing-offset between users, the delay spread tolerance of

OFDMA and OFDM-CDMA might be affected.

6.2.10 Mobility

OFDM-TDMA

Mobility gives Doppler spread, and this causes ICI. In OFDM-TDMA, a single user is

allocated all the sub-carriers of any particular symbol, thus, MAI due to ICI does not

happen in this scheme, while this happens in other two schemes.

Because of this, the error floor due to Doppler spread in OFDM-TDMA happens at a

much lower BER and higher SNR than in other schemes.

OFDMA

Mobility can simply be evaluated on the ratio between OFDM symbol duration and

channel coherence time, where Ts < Tc. In Appendix A.2, coherence time for different

user speeds is shown.



If compared to the IEEE 802.14.4c downstream mode from Table 4.1, it is obvious that

for the 2k mode, extreme mobility cannot be handled, whereas low mobility is not a

problem.

OFDM-CDMA

Maximum doppler spread tolerance is dependent on the sub-carrier spacing. As such there

is MAI due to non-ideal channel compensation under synchronous environment as well.

Doppler spread leading to frequency spread will add to it since inter sub-carrier

interference will come into play, further worsening the situation.

But if the sub-carrier spacing is large enough, which is again a system design issue as in

an OFDM system, such that the doppler frequency is very small compared to the sub-

carrier spacing, i.e. normalized doppler frequency is small and the ICI will be less.

Otherwise the system will become

interference limited.

6.2.11 Latency:

OFDM-TDMA

Processing is done on every OFDM symbol, but a user gets service once in every U _ Ts,

given that there are U number of users in the system and everyone is given one OFDM

symbol per frame.

OFDMA

In OFDMA the processing is made on one OFDM symbol, giving that the latency is equal

to Ts.

OFDM-CDMA

Latency is similar to OFDMA system.



6.2.12 Intra-cell Interference:

OFDM-TDMA

No intra-cell interference is present also as only one user is transmitting at any certain

OFDM symbol duration.

OFDMA

For OFDMA, there will be no Intra-Cell interference, since all users are using a unique

sub-set of the available sub-carriers.

Depending on ICI and Doppler spread, the users who occupy neighboring subcarriers,

may interfere each other.

OFDM-CDMA

In DL, the effect of MAI is already mentioned before. It occurs due to orthogonality loss

among spreading

codes because of channel fading.

It has also been noted that channel estimation error introduces intra-cell interference and

highly influences the performance of the system.

6.2.13 Inter-cell Interference:

OFDM-TDMA

Inter-cell interference happens only if other cells are using the same time-slot and carrier

frequency as the current cell.



OFDMA

In a multi-cell environment there will be interference, assuming that the same carrier

frequency is used. The reason is that sub-carriers are assigned to sub-channels, and when

a neighbor cell uses the same sub-carriers there will be interference.

OFDM-CDMA

With proper choice and allocation of codes to users based on location and co-ordination

between BS, inter-cell interference can be kept to a quite low value, but in general, the

system is susceptible to intercell

interference.

6.2.14 Narrowband Interference Rejection:

One of the major problems associated with transmitting information from subscriber

premises is so called

NarrowBand Interference (NBI). In OFDM-based systems, the effect can be loss of sub-

carriers and degraded BER performances.

OFDM-TDMA

OFDM-TDMA much more severely than OFDMA systems. As only one user occupies

the whole bandwidth, if the particular user is subdued with high Signal to Interference

Noise Ratio (SINR), then the whole system collapses.

This is evident in the results mentioned in the above mentioned paper, where it is shown

that OFDM-TDMA collapses at around 2dB of SINR, which is a staggering 30dB higher

than OFDMA systems. In summary, a low interference level jams a few carriers in

OFDMA and slightly reduces the system capacity, whereas an OFDM-TDMA system can

still operate at its full capacity.



However, as the interference level exceeds a certain threshold OFDM-TDMA entirely

breaks down, whereas OFDMA only loses a small percentage of its total capacity.

OFDMA

OFDMA performs better when NBI is present in the system. NBI affects certain sub-

carriers, thus, only the users who are allocated those sub-carriers are affected by

increasing NBI.

Thus, number of users operating at a certain BER when NBI increases is reduced

gradually, and only at very low SINR, i.e. at -30dB level, all users are out of service due

to NBI.

OFDM-CDMA

Users spread their signals over whole of the bandwidth, thus, NBI does not affect the

system as it does in OFDM-TDMA. This is one of the benefits that is brought by

incorporation of CDMA with OFDM.

6.2.15 Frequency Reuse Factor:

OFDM-TDMA

The same result mentioned below in case of OFDMA should be valid for OFDM-TDMA

system also.

OFDMA

It was shown that the reuse factor for OFDMA in multi-cell environments is at least 3.

This is shown by simulation.



OFDM-CDMA

This does not have unity frequency re-use factor, but using a PN-sequence might provide

this benefit.

6.2.16 Signalling Overhead:

Usual network control related signalling overhead is almost similar to all of the systems.

The main difference appears when the amount of signalling is compared for resource

allocation purpose.

OFDM-TDMA

Signalling overhead in OFDM-TDMA is much smaller compared to DSA-based OFDMA

system. When dynamic allocation is used, then only an average value of channel strength

for all users are required in OFDM-TDMA scheme.

This means that MSs need to send much less information to BS for allocation purposes.

Similarly, the BS needs to send only the information of OFDM symbol by symbol

allocation. This is much smaller compared subcarrier by subcarrier allocation information

in OFDMA systems, especially for large bandwidth with large number of subcarriers in

the system.

With different number of users in the system, OFDM-TDMA requires the least amount of

signalling compared to OFDMA and OFDM-CDMA schemes.

OFDMA

For static allocation, once the allocation information is conveyed to the user, the BS does

not need any other resource allocation based signalling. For DSA, CSI is required

continuously, thus significant signalling is needed for transmitting both channel

information and subcarrier allocation.



In case of SCH systems, conveying the hopping seed at the beginning of communication

is enough for the system to perform perfectly.

OFDM-CDMA

The signalling overhead is very limited compared to above two schemes. Some

information about spreading code is enough for MS to start transmitting.

6.2.17 Implementation Complexity:

OFDM-TDMA

Implementation complexity is very much similar to basic OFDM system. Even when

dynamic allocation is used, the decision about resource allocation needs to be taken once

per symbol, which requires much smaller effort than deciding on every sub-carrier.

OFDMA

In the case of static subcarrier assignment, the complexity of OFDMA is identical to a

traditional OFDM system, only adding the mapping and de-mapping of subchannels. For

the dynamic subcarrier assignment, CSI is required and huge computational effort is

expected to compute the best subcarrier assignment policy.

Thus, continuous channel estimation for all the users on whole band and computationally

extensive resource assignment policy increases the system complexity very much.

OFDM-CDMA

OFDM-CDMA is simpler compared to DS-CDMA rake receiver because of frequency

domain combining. The complexity depends upon the detection strategy used.



Equal Gain Combining (EGC), Maximal Ratio Combining (MRC) and Controlled

Equalization (CE) are some of the simple methods of detection. Several other complex

detection schemes exist such as Soft Interference Cancellation and MLSSE.

The performance of the scheme increases with the complexity of the detection scheme. It

is a purely implementation tradeoff that needs to be decided for a particular situation.



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