4g Communications Rajendar Bits

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4G: An Ultimate Mobile Solution

(Mobile communications)

By

V.Rajendar V.Arjun rao

[email protected]

[email protected]

III B.TECH

Electronics & Communication Engineering

BALAJI INSTITUTE OF TECHNOLOGY &

SCIENCE

NARSAMPET ,

WARANGAL DIST.
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Abstract

This paper aims to identify and explore the different issues and challenges

related to fourth generation networks. It starts with a brief Introduction, and then

explains the edge of 4G technology over 3G, and defines 4G. It also focuses on the

opportunities for implementation of 4G, and also explains the threats for

implementation of 4G. It also provides a detailed insight on the vision of 4G, and also

discusses about the advantages and limitations of 4G technology. It also compares the

4G technology with all other technologies and also explains the Applications of 4G

technology. This paper also focuses on key technologies to implement 4G technology

as it provides a basic idea on OFDM since with its natural resistance to multipathfading and its ability to support extremely high data rates, orthogonal frequency

division multiplexing (OFDM) is a major candidate for fourth-generation air

interfaces.

Introduction

We are seeing a massive demand for data, audio, image and video services on

mobile phones. These require a faster rate of data transfer.

Though the projected data rate of 3G is around 2 Mbps, the actual data rate is much

slower, especially in crowded areas or when the network is congested. Further, data

rates also depend on the users activity (moving or steady state) and location

(indoor/outdoor).

As expected data services like multimedia are going to play an increasing role and

will dominate the cellular traffic instead of voice in future.

In such a scenario, the present 2G and 3G systems will saturate and have no room to

survive. Also, the demand for increasing data rates leads to higher bandwidth

requirements. These factors force the cellular industry to develop a common standard

or system that over comes almost all limitations imposed by previous cellular

technologies.


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4G services hold out the promise of end-to-end, totally IP (Internet protocol), packet-

switched networks that will be able to handle growing loads of wireless voice, data,

video and audio transmissions more efficiently, at lower cost and at higher

performance levels i.e., 4G systems are expected to allow much higher data rates of

around 100 Mbps, higher bandwidth of the order of hundreds of megahertz, plenty of

services like data, audio and video(as shown in fig1),seamless connectivity and

improved quality of service keeping in mind that all existing networks can be merged

or interconnected to form an all-in-one.

What is 4G?

Fig 2 shows the concept of 4G cellular network. The future 4G infrastructurewill consist of various networks using Internet Protocol (IP) as a common protocol. So

the users will be in control as they can choose every application and environment.

Accessing information any where, in time with seamless connections to a wide range

of information, data, pictures, video andso on will be the benefits of 4Ginfrastructure.


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One of the terms popularly used to describe 4G is MAGIC, which stands for

Mobile multimedia, anytime any where, Global mobility support, Integrated Wireless

solutions and customized personal services.

4G services will be dynamic and adaptable to the application. Faster response and

quality are the prerequisites for full-motion video, home entertainment and advance

location-based services. The expected data rate is 2 Mbps for vehicular applications.

Such high data rates obviously require a high bandwidth of the order of several

hundreds of megahertz.

The ultra WCDMA access technology and orthogonal frequency-division

multiplexing (OFDM)-being spectral-efficient-are the two major options that can help

to realize the expected features of 4G cellular networks.

OFDM/COFDM allows many users to transmit the allocated band, by subdividing the

available bandwidth into many narrow bandwidth carries. Each user is allocated

several carries to transmit his data. The transmission is generated such that the carriesto transmit his data. The transmission is generated such that the carries are orthogonal

to each other, thus allowing them to be packed together much closer than standard

frequency-division multiplexing in OFDM/COFDMA technology.

Seamless connectivity requires fast handoff between different networks as the user

moves from one network to another. This is possible as the core network is IP- based.

While maintaining the connectivity, the emphasis is also on the quality of services at

the cheapest rate.


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Although most service providers are still expanding and improving their existing 2G+

networks, research towards 4G systems is making significant progress in major

companies like Motorola ,Qualcomm ,AT&T , Nokia ,Erickson and NTT(Nippon

Telephone and Telegraph) DoCoMo.

4G: Edge over 3G

It is commonly said that 4G is the super- enhanced version of 3G.4G systems

will be deployed with software defined radios, allowing equipmentupgrades for new

protocols and services via software upgrades. In addition, 4G holds the promise of

worldwide roaming using a single handheld device. To summarise,4G means fully

converged services, ubiquitous cellular access, diverse user devices, autonomous

networks and software dependency.

The main aim of 3G was to provide multimedia, multirate, cellular communications

any time and any where. Its uneconomical to meet this requirement with only

cellular radio.4G systems will extend the scenario to an IP network that integrates

broadcast, cellular radio.4G systems will extend the scenario to an IP network that

integrates broadcast ,cellular , cordless ,WLAN/PAN and fixed wire.

4G is a network of networks with which users will be in control. They will be able

to decide the right system and even right terminal for each application and each

environment (mobility, coverage). So personalized services can be providedirrespective of underlying network. This makes the most efficient use of the available

spectrum by directing users to the most appropriate network.

Opportunities for implementation

It is now clear that to meet the requirements of high data rates, seamless

connectivity and cost effective service, the core network for 4G must be IP-based.

Merging all the networks in one core network requires an intermediate layer that

provides an interface between the existing network protocol and the required protocol.

Hence the opportunities are open for all the networks to update their present

architecture and allow the desired change.

In India, GSM is dominating the market, with CDMA competing with it. EDGE and

GPRS are working, while complete 3G services have not been introduced yet. It may

happen that the cellular networks waiting for 3G and upgrading themselves with 2G+

may switch directly to 4G by completely by passing 3G as it seems a better option

cost effectiveness in network upgradation and replacement.


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Since the expected technology for 4G is ultra WCDMA and/or OFDM, the present

GSM networks must upgrade or be replaced with the whole network of CDMA or

OFDM. The migration of all networks like LAN, MAN, WLAN, HIPERLAN, DVB

and DAB also requires a transparent protocol and smart handoffs which should be

able to work for maintaining the quality of service and offering such services at thelow cost.

The path to final 4G may be plotted in four steps:

1. Internet working of 2G+ and 3G and internet.(circuit-switched voice/data)

2. Integration of all networks (circuit-switched voice/data)

3. IP-based harmonization (packet -based voice / data)

4. Full convergence of the networks (all IP-based voice, data and multimedia for end-

to-end quality of service, better security, seamless connectivity, entertainment and so

on)

Fig. 3 shows the advantage of all the networks is possible according to the projected

path. It indicates integration of media, information technology and communication,

which is the major growing, fields in user applications. Merging all the services (like

voice, non-voice, Internet, e-commerce, multimedia, entertainment like news, sports,

video on demand, audio and so on) in one hand set is an attractive proposition ifimplanted with reliable end-to-end quality of service and faster data transfer.


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Threats for implementation

Major issues that need to be resolved before implementing the 4G network are:

Connecting all networks on one common platform. It will bereally be a tough task to merge all the network services on one common platform with

the same quality of service, same tariffs, etc. Take

the example of the existing GSM and CDMA. For merging those on a common

platform to provide of them has to change its standard or both have to compromise on

new interfacing standards. Since 4G has CDMA or OFDM as the only option to use,

definitely all the networks must update themselves to the desired level.

Seamless connectivity and smart handoffs. Providing seamless

connectivity while moving between different networks using smart handoffs is a big

challenge before the designers if all the networks are using different standards.

Therefore it becomes essential to design very complex air interfaces that will decide

the quality of smart hand-offs and the quality of service.


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Acquiring the required data rate and bandwidth. 4G is expected

to have a much higher data rate even when the user is in motion (vehicular).To

support the high data rate, the devices to be designed must be very sensitive and smart

enough to work with vehicular speeds at the both ends (user and the cellular base

station terminal ends) as shown in fig.4.

4G Vision

A 4G mobile communications system offering high-speed transmission of large

volume of data with the wide coverage requires a bandwidth of approximately

100MHz. It is anticipated that 4G speeds could be as high as 100Mbps. Thus, 4G will

represent another quantum leap in mobile Internet speeds of up to 50 times more than

3G networks and offer three-dimensional visual experiences for the first time.

A picture (fig.5) that is worth a thousand words towards understanding the

vision of 4G (IMT-Advanced) is shown below. ITU (International telecommunication

union) named 4G as IMT-Advanced


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Fig.5: Vision of 4G

As can be seen in the picture above, the main requirements for 4G are as

follows:

Peak data rate of 100Mbps for high mobility applications such asmobile access

Approx. 1Gbps for low mobility applications such as nomadic/local

wireless access


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Though 1XEV-DV and W-CDMA are yet to be deployed, research on 4G has

commenced on a global scale. As the wireless market continues to grow at a frenetic

pace, service providers that rely on circuit-switched technology are facing mounting

pressure due to its disadvantages: the systems cannot sustain increasing bandwidth

requirements for new services and applications. The network lacks the capacity tosupport a rise in traffic. Cannot provide services fast enough to keep enough to keep

up with the demand. Due to these reasons, 4G is intended to be an entirely packet-

switched network.

Among the newer wireless technologies under consideration for the use in 4G systems

are OFDM, smart antenna systems and millimeter wireless.

It is believed that 4G will be operational by 2010(see fig.7). It will be built on the

second phase of 3G, when all networks are expected to offer 99.99 percent reliability.

Fig.7: Key elements of 4G vision.

Advantages of 4G

Support for interactive multimedia services like teleconferencing and wireless

Internet.

Wider bandwidths and higher bitrates.

Global mobility and service portability.

Scalability of mobile network.

Entirely Packet-Switched networks.

Digital network elements.

Higher band widths to provide multimedia services at lower cost (up to 100

Mbps).


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Tight network security.

Limitations

Although the concept of 4G communications shows much promise, there are still

limitations that must be addressed. A major concern is interoperability between thesignaling techniques that are planned for use in 4G (3XRTT and WCDMA).

Cost is another factor that could hamper the progress of 4G technology. The

equipment required to implement the next-generation network are still very expensive.

A Key challenge facing deployment of 4G technologies is how to make the network

architectures compatible with each other. This was one of the unmet goals of 3G.

AS regards the operating area, rural areas and many buildings in metropolitan areas

are not being served well by existing wireless networks.

Applications

Location application. 4G location applications will be based on visualized,

virtual navigation schemes that will support a remote database containing graphical

representations of streets, buildings and another physical characteristic of a large

metropolitan area. This data base could be accessed by subscribers in vehicles.

Virtual navigation and telegeoprocessing. You will be able to see theinternal layout of a building during an emergency rescue. This type of application is

some time referred to as telegeoprocessing.

A remote database will contain the graphical representation of streets, buildings and

physical characteristics of a large metropolis. Blocks of this database will be

transmitted in rapid sequence to a vehicle, where a rendering program will permit the

occupants to visualize the environment ahead. They may also virtually see the

internal layout of buildings to plan an emergency rescue or engage hostile elements

hidden in the building.

Telemedicine.A paramedic assisting a victim of a traffic accident in a remote

location could access medical records (X-rays) and establish a video conference so

that a remotely based surgeon could provide on-scene assistance.

Crisis management application. In the event of natural disasters where

the entire communications infrastructure is in disarray, restoring communications

quickly is essential. With wideband wireless mobile communications, limited and


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even total communication capability (including Internet and video services) could be

set up within hours instead of days or even weeks required at present for restoration of

wire line communications.

Comparison of 4G with other mobile technologiesTechnolo

gy

1G 2G 2.5G 3G 4G

Design

began

1970 1980 1985 1990 2000

Implemen

tation

1984 1991 1999 2002 2010

Service Analogue

voice,Synchronous

data

Up to 9.6

kbps

Digital voice,

short messages

Higher-

capacitypacketized

data

Higher-

capacitybroad-

band up to

2 Mbps

Higher-

capacity,compeletely IP-

oriented,

Multimedia

data up to

hundreds of

mega bits

Standards AMPS,

TACS, NMT,

etc

TDMA,CDM

A,GSM,PDC

GPRS,EDG

E,1XRTT

WCDMA,

CDMA

2000

Single

Standard

Data

Bandwidt

h

1.9 kbps 14.4 kbps 384 Kbps 2 Mbps 200 Mbps

Multiplex

ing

FDMA TDMA,CDM

A

TDMA,CD

MA

CDMA CDMA/ultra

WCDMA/OF

DM?

Core

network

PTSN PTSN PTSN,

Packetnetwork

Packet

network

Internet

Basic Idea of Orthogonal Frequency Division Multiplexing

(OFDM):

If you take a signal and send it over multiple low-rate carriers instead of a

single high-rate carrier, the longer symbol periods lessen or eliminate inter-symbol-

interference (ISI) problems. The added benefit of the high data rate is then made

possible when the multiple carriers (numbering in the hundreds or even thousands) are


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modulated with higher-order symbol mapping, such as 8PSK or 16QAM. More bits

are then forced through the air in each symbol period.

Here is a little more detailed description of OFDM

Modulation: A mapping of the information on changes in the carrier phase, frequencyor amplitude or combination.

Multiplexing: Method of sharing a bandwidth with other independent data channels.

OFDM is a combination of both modulation and multiplexing. Multiplexing generally

refers to independent signals, those produced by different sources. So it is a question

of how to share the spectrum with these users. In OFDM the question of multiplexing

is applied to independent signals but these independent signals are the subset of the

main signal. In OFDM first the signal itself is split into independent channels,modulated by data and then re-multiplexed to create the OFDM carrier.

OFDM is a special case of Frequency Division multiplex (FDM).As an analogy, a

FDM channel is a flow out of a faucet, in contrast the OFDM signal is like a shower.

In a faucet all water comes in a big stream and cannot be subdivided. OFDM is made

up of a lot of little streams.

Fig.8-(a) A Regular-FDM single carrier-A Whole bunch of Water coming all in one

stream.(b) Orthogonal-FDM-same amount of water coming from a lot of small

streams

Think about what the advantage might be of one over the other? One obvious one is

that if my put my thumb over the faucet hole, I can stop the water but I cannot do the

same for the shower. So although both do the same thing, they respond differently to

interference. Thus more bits are then forced through the air in each symbol period.

Thus this is main considerationOFDM not only provides clear advantages for

physical layer performance, but also a frame work for improving layer to layer

performance by proposing an additional degree of freedom. It is possible to exploit the

time domain the space domain and the frequency domain and even the code domain to

optimize radio channel usage. It ensures very robust transmission in multi-path

environments with reduced receiver complexity


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Fig.9: OFDM Principles

As shown in the fig.5 the signal is split into orthogonal sub carriers, on each of which

the signal is narrowband (a few KHz) and therefore immune to multipath effects,Provided a guard interval is guarded between each OFDM symbol. OFDM also

provides a frequency diversity gain increasing the physical layer performance. It is

also compatible with other enhancement technologies, such as smart antenna and

MIMO.

OFDM can also be as a multiple access technology (Orthogonal Frequency

Division Multiple Access; OFDMA). In this case, each OFDM symbol can transmit

information to/from several users using a different set of subcarriers (sub channels).

This not only provides additional flexibility for resource allocation (increasing thecapacity), but also enables cross-layer optimization of radio link usage.

OFDM Characteristics:

High peak-to-average power levels.

Preservation of orthogonality in severe multi-path.

Efficient FFT based receiver structures.

Enables efficient TX and RX diversity.

Adaptive antenna arrays without joint Equalization. Support for adaptive modulation by sub carrier.

Frequency Diversity.

Robust against narrow-band interference.

Efficient for simulcasting.

Variable/Dynamic Bandwidth.

Used for highest speed Applications.

Supports dynamic packet Access.


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