4G: The Future Mobile TechnologyMohsin Jamil l, Shahan Parwaiz Shaikh2, Mohsin Shahzad 3, Qasim Awais4

lNational University of Science & Technology,Pakistan, 2Nanyang Technological University, Singapore.3University of Sheffield, United KingdomAWah Engineering College, Pakistan.

mj2p07@soton.ac.uk, shahan@pmail.ntu.edu.sg, qasimawais@gmail.com, mohsin1416@yahoo.com

Abstract: With the rapid growth of user demands, andthe limitations of third generation (3G) mobilecommunication systems, it is expected that fourthgeneration (4G) mobile systems are likely to reach theconsumer market in another 4-5 years. 4G systems areexpected to become a platform capable of providingincreased bandwidth, higher data rates, and greaterinteroperability across communication protocols, and userfriendly, innovative, and secure applications. This systemwill primarily focus on seamlessly integrating the existingsystems like GSM, wireless LAN, and Bluetooth. Thispaper describes modulation scheme, different technologies,and network architectures that support 4G mobile systems.Challenges and some applications will also be presented. Atlast recommendations will be followed by conclusion.

I. INTRODUCTION

First generation (1 G) mobile systems, introduce in early1980's, initiated commercial mobile voice services. 1G mobilesystem offered voice and low speed data transmission and wasoperated in circuit switched mode. These 1G network systemsuse Frequency Division Multiple Access (FDMA) schemes andoperate in the 450 and 800MHz frequency bands. The majorproblems of 1G mobile system were internetworking betweendifferent networks and the quality was far from the standardoffered by wire line telephony. These shortcomings wereovercome with the advent of the Second Generation (2G)mobile systems. By using digital technology instead of analogone, 2G systems such as Global System for MobileCommunications (GSM) increased the number of supportedusers within a cell and enhanced voice quality significantly. Inits original form, the GSM in the 900, 1800 and 1900MHzfrequency bands uses a Time Division Code Multiple Access(TDMA) schemes for circuit mode transmission of digitizedspeech and digital data at up to 9.6kb/s. Since itscommercialization in 1990's, GSM has been currentlyupgraded, by the introduction of High Speech Circuit SwitchedData (HSCSD), General Packet Radio Services (GPRS), andEnhanced Data rates for GSM Evolution (EDGE), EnhancedCircuit Switched Data (ECSD) and Enhanced GPRS (EGPRS).

20's success story prompted the development of 2.50 and(30) mobile systems. Universal Mobile TelecommunicationsSystem (UMTS) standards were also developed to yield highervoice capacity and higher-speed data using a wideband carrier(5.2 MHz). The introduction of UMTS, based on WidebandCode Division Multiple Access (WCOMA) technology is afurther step towards the increasing demand of high data rates.

In the 30, circuit mode speech and data as well as packet modedata transmission are possible with UMTS. Furthermore,higher data rates were designed to provide new innovativeservices, like mobile videophone, video streaming, and voiceover IP. Moreover, wider coverage was promised with the helpof macro, micro, and pico cells. 30 technology supports 144Kbps data rate, with high speed movement (vehicles), 384Kbps (on campus) & 2 Mbps for stationary (in building).

Even before 30 networks are fully launched and utilized,various study groups are considering the shape of the nextgeneration of cellular technology, so called 40. There is nosingle global vision for 40 as yet, but the next generation ofnetwork is likely to be all IP-based. In 40 the radio interfaceswill support up to approximately 100 Mbps for high mobilityand up to approximately 1 Obps for low mobility such asnomadic/local wireless access. 40 networks will also featureIP interoperability for seamless mobile Internet access. 30 isbased on a wide-area concept applying circuit and packetswitching for transmission with limited access technology,such as WCOMA, CDMA and TD-SOMA. However, the 40standard will base on broadband IP-based, entirely applyingpacket switching method of transmission with seamlesslyaccess convergence. 4G mobile system will include all systemsfrom various networks~ from public to private~ from operator­driven broadband networks to personal areas: and from cell ularto ad hoc networks.

Table 1 presents a short history of mobile technologies.

II. LIMITATIONS OF 30/NEED FOR 4G

It has been observed that after every 10 years a new mobilegeneration comes up with new capabilities and functionalities.As the roll out took around 10 years for 2G, a similar periodwill apply to 30 which has started deploying since 2001 andby the year 2010 it will be the time to deploy 40 [1] networksand with this assumption the work on 40 has been started sinceyear 2000. However 3G systems have some limitations whichare stated as:

• 30 can support multimedia internet type services at highdata rates up to 384kb/s for moving up to 2Mb/s in limitedcoverage area. [1]

• In 30, extension to higher data rate is difficult withCOMA due to excessive interference between the servicesand users.

• To ensure connection ubiquity together with highbandwidth and mobility, the network architecture must beheterogeneous rather than homogeneous.

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TABLE ISHORT HISTORY OF MOBILE TECHNOLOGIES

Technology IG 2G 3G 4G

Design Began 1970 1980 1990 2000Implementation 1981 1991 2001 2010Services Analog Digital Higher Higher

voice voice. capacity, capacity,short data rates Completelymessage up to IP- oriented.

2Mbps multimedia.data tohundredsof megabits

Standards AMPS, TDMA, WCDMA. SingleTACS. COMA, CDMA2000 standardNMT. GSMetc.

Data Rate NA 14.4 2 Mbps >200 Mbpskbps

Multiplexing FDMA TDMA. COMA OFDMCOMA

Core Network PSTN PSTN Packet Internetnetwork

Legend:AMPS = Advanced mobile phone serviceCDMA = Code division multiple accessFDMA = Frequency division multiple accessGSM = Global system for mobile communicationNMT = Nordic mobile telephoneOFDM = Orthogonal frequency division multiplexingPSTN = Pubic switched telephone networkTACS = Total access communicationsTDMA = Time division multipleWCDMA = Wideband CDMA

• It is difficult to provide full range of multi-rate serviceswith different QoS and performance requirements due tothe constraints imposed on the core network by the airinterface standard, e.g. 3G is not a fully integrated system.

• The bandwidth available in the 3G mobile systems will besaturated and there are limitations on the combination offrequency and time division duplex modes.

• Multi-modes appliances have to implement softwareconfigurable hardware architectures.

• Limitation of spectrum and its allocation.• Difficult to roam across distinct service environment in

different frequency bands.

When the 3G was launched, it was assumed that it wouldbecome popular among the users but this didn't happen.Network operators were forced to reduce their expectations.Despite the work is going on the higher-speed 3G mobilenetworks, the main reasons for the leap towards 4G are:

• As compare to 3G, 4G will provide rich multimediacontents. The downloading speed of 4G system willexceeds 100 Mbps, which is about 260 times greater than3G wireless networks.

• Because of single global standard, the roaming betweenthe different networks will be possible. Many services canbe access by the users from the same mobile terminal

• The 3G mobile network is based on primarily a wide-areaconcept. In 4G system, utilizing both wireless LAN andcellular design the users will be connected to a high-speednetwork anywhere, anytime.

• In near future, there will be a great demand for high datarates and bandwidth. The 4G technology, would offerhigh-bandwidth services with the transmission speeds ofmore than 20 Mbps within the reach of LAN "hotspots",which are installed everywhere in offices, homes, mallsand airport lounges. The 2G networks for voice and lowspeed coverage can be used by the users if they are awayfrom these hotspots.

• The 4G mobile networks systems will be cheaper than 3G.This is because they can be built on the existing networksand there will be no need for the operators to completelychange their equipments nor will they be required extraspectrum.

• The problem of handling increasing numbers of users anddiversity of services can be solved by the 4G system as itwas based on IP layer technology.

III. FEATURES OF 4G

A. User Friendliness and User PersonalizationThe combination of user friendliness and user

personalization appears to be the winning concept when we tryto encourage people to move towards a new technology, whichis a time taking process and involves a great deal of effort fromthe operator's side. In user friendliness the interaction betweenthe applications and users can be minimized and simplifies. Inuser personalization, the users can configure the mobileterminal and chose services according to their preferences.

B. Terminal Heterogeneity and Network Heterogeneity4G provides not only higher data rates but also a clear and

valuable advantage in people's everyday life, with thecombination of terminal heterogeneity and networkheterogeneity. Terminal heterogeneity refers to the differenttypes of terminals in terms of display size, energyconsumption, portability/weight, complexity, etc. Networkheterogeneity is related to the increasing heterogeneity ofwireless networks due to the large number of accesstechnologies available (e.g., UMTS, WiMAX, Wi-Fi, andBluetooth).

C. Other possible features ofthe 4G systems are• Support interactive multimedia, voice, video, wireless

internet and other broadband services.• High speed, high capacity and low cost per bit.• Global roaming and inter-working between different

access technologies; both horizontal (intra-system) andvertical (intersystem) handover.

• Better scheduling and call admission control techniques.

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• A common platform to complement other servicesconnection through a common, flexible, seamless, IP­based core network.

• Enabling person to person, person to machine, andmachine to machine communications.

• Can handle pre-existing 30 systems along with otherwireless technologies.

Following table 2 shows some physical parameters of 40technology.

TABLE 2POSSIBLE 4G PARAMETERS

Parameters 4G

Key Requirement Data and voice converged over IP

Network Architecture Wireless LAN and WAN

IP All IP (lPv6)

Frequency Band Higher frequency bands 2 - 8 GHz

Bandwidth5 - 20 MHz (might even go to 100

MHz or higher)

Data RateUp to 20 Mbps (might even reach 100

Mbps or more)

Access TechnologyMulti-carrier CDMA (MC-CDMA)or

OFDM(TDMA)

Forward Error CorrectionConcatenated codes

(FEC)

Switching Design Basis Packet

Mobile Top Speeds 200 km/hr

Deployment 2007-2010

Smarter Antennas, software multi-Component Design

band and wideband radios

Service type Multimedia Machine to Machine

IV. TECHNOLOGIES FOR 4G

A mix of concepts and technologies involves in the makingof 40 mobile communications. Some originate from 30, andare called evolutionary (e.g., evolutions of WCDMA andcdma2000). Other is revolutionary which involves newapproaches to wireless mobile. Following are some of thetechnologies considered for 40.

A. Orthogonalfrequency division multiplexing (OFDM)[J-2)When a high speed mobile is transmitting its signals in high

frequency band, it is affected severely from frequency selectivefading. OFDM is being developed to reduce this frequencyselective fading. OFDM is a combination of modulation andmultiplexing. OFDM is a multi-carrier transmission technique,which uses the similar technique as that of Frequency DivisionMultiplexing (FDM). Multiple messages can be sent in movinga single radio channel in OFDM using principles of FDM.OFDM uses the spectrum more efficiently by making all thesub-carriers orthogonal to one another, using fast fourier

transform (FFT) [3] to prevent interference between the closelyspaced sub-carriers, allowing an improved spectral efficiency.OFDM achieves multiple access capability usually by usingCDMA or TDMA. Since each carrier in an OFDM signal has avery narrow bandwidth (i.e. few kHz), the resulting symbolrate is low. Due to the orthogonal nature of the modulation,these multiple sub-carriers overlap in the frequency domain,but do not cause Inter-Carrier Interference (ICI). In OFDM, theguard band is reduced by the orthogonal packing of the sub­carriers, improving the spectral efficiency (figure 1).

8andw~

Fn: Fost fourier transform

Following are the parameters ofOFDM in 40 [5]

TABLE 3OFDM PARAMETERS IN 4G

User data rate 2.56 - 8.96 Mbps

Modulation QPSK,16QAM

Coding rate 1/2 - 7/8

Data subcarriers 512 (average) (128, 256,384 optional)

Pilot subcarriers 128 (average) (32, 64, 96 optional)

Symbol duration 200/ls

Guard interval 40/ls

Subcarrier spacing 6.25 kHz

3 dB bandwidth 4 MHz ( 1, 2, 3 MHz optional)

Channel Spacing 5 MHz (1.25 MHz optional)

Carrier frequency --2GHz

FFT size 1024

B. Multiple-input multiple-output (MIMO)SmartlMultiple antennas [1][4] can significantly increasesystems capacity and have intelligent functions as suppressionsof interference signals, auto-tracking of desired signals, anddigital beam-forming with adaptive space-time processingalgorithms. One smart-antenna system which shows promise in40 systems is MIMO (Multi-Input Multi-Output) [1][6], asshown in figure 2, particularly since the antenna systems atboth transmitter and receiver are usually a limiting factor whenattempting to support increased data rates.

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The idea behind MIMO is that the signals at transmit (TX)antennas end and at receive (RX) antennas end are "combined"so that both the quality (Bit Error Rate or BER) and the datarate (bits/sec) of the communication can be improved. Fromthis the both the network's quality of service and the operator'srevenues can be increased.

frequency (RF) signal from the antenna. The conversion fromanalog to digital (on receiving path) and from digital to analog(on the transmitting path) is performed by using the ADCIDACat the IF section. The base-band operations such as connectionsetup, equalization, frequency hopping, timing recovery, andcorrelation are performed at the base-band section.

Antenna

BasebandProcessing

---H---

Rx

RFFront-end

Fig. 3. Block Diagram ofa Generic Software Defined Radio

V. APPLICATIONS AND SERVICES

Generally, four categories of services or applications arebeing developed for use in the 4G wireless communications.They are as follows:

The development of multi-band, multi-standard, multi-moderadio systems using SDR technology is fostered by theavailability of smart antennas, wideband RF front-end,wideband ADCIDAC technologies and ever increasingprocessing capacity of DSPs and general-purposemicroprocessors. The main advantages of SDR are:

• Flexibility and reconfigurability: which allows dynamicconfiguration of the system by selecting the appropriatesoftware module to run.

• Interoperability: Using the SDR system, it is possible tointegrate other associated software functions into thesystem more easily.

• Connectivity: by uploading another software module, wecan enable the mobile terminals for using differentprotocols and standards.

SDR has some drawbacks like, it is impossible to have justone antenna and one low noise amplifier to serve the widerange of frequency bands. It can be done by using multipleanalog parts to work in different frequency bands but by doingthis the complexity and physical size of the terminal will beincreased. The other problem is that the available ADCs arenot fast enough. Finally, we have to use parallel DSP in orderto allow real-time execution of software implemented radiointerface functions.

Fig. 2. MIMO wireless system. The transmitter and receiver are equipped with

multiple antenna elements.

There are two different perspectives for MIMO systems.First, from the pure diversity point of view, one can enhancethe fading statistics of the received signal by the virtue ofmultiple available replicas being affected by the independentfading channels. The reliability of the communication link canbe improved, the outage probability can be decreased, and theeffects of multi-path fading can be reduced by sending thesame signal through parallel and independent fading channels[6]. The second approach is referred as spatial multiplexing[6]. In this approach the spectral efficiency can be increased bytransmitting different information streams on parallel spatialchannels associated with the transmit antennas. The receiverterminal should be equipped with at least same number ofreceive antennas as the number of parallel channels generatedby the transmitter in order to separate the individual streams.As the mobile terminals are getting smaller and smaller in sizeit is difficult to incorporate multiple antennas on them. Forsolving this issue, a new approach called cooperative MIMOrelaying (CMIMOR) or virtual antenna array (VAA)technology has been proposed. This approach appears to bevalid for implementing a MIMO system in mobile terminals.

c. Software defined radio (SDR)Due to the constant evolution of mobile communication

systems (2G, 3G, and 4G), the wireless industry is facingproblems in global roaming to provide different services to themobile subscribers. SDR technology promises to solve theseproblems by implementing the radio functionality as softwaremodules running on a generic hardware platform. Further,different standards can be presented in the radio systemthrough the implementation of multiple software modules.Through SDR the user's terminal can be operated in multi­mode fashion, adapting themselves to various network wirelessinterfaces [7]. The main purpose of SDR is to make a userterminal operate in different kinds of wireless networks,overcoming power, cost, size, and compatibility limitations.

SDR consists of three major functional blocks as shown inthe figure 3, namely front end (RF section), the IF section andthe base-band section. The RF section (also called RF front­end) is responsible for transmitting and receiving the radio

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challenges that researchers and developers of 4G are likely toface.

A. Multiple 4G definitions

Since the work has just begun on 4G mobile networks, thereis no well accepted or unique definition of 4G presented.Despite of huge research and years of discussion, there is noworldwide consensus on the definition of 4G. However someR&D companies, operators, and organizations are starting toidentify some common characteristics. There is a need forglobal 4G standard from users to service providers, tomanufactures.

B. Multimode user devices

As there will be wide range of applications provided bymultiple wireless networks, a terminal will be needed whichcan adapt to different wireless networks by reconfiguring itself.This will be done by a multimode terminal which eliminatesthe need to use multiple terminals (or multiple hardwarecomponents in a terminal). Multimode terminals can beimplemented using software defined radio approach. Figure 4illustrates the block diagram of an ideal software radio. Itconsists of two parts namely analog and digital. Analog part ofthe receiver have an antenna, a bandpass filter (BPF), and alow noise amplifier (LNA). The signal received in the digitalpart is first digitized by the analog/digital converter (ADC)after the analog processing. After ADC the DSP will processthe digitized signal in accordance with the wirelessenvironment.

C. Wireless System Selection

Using 4G mobile, the user can select any available wirelessnetworks for the required application. Because the using of asuitable network for a specific service as every network hasunique features, hence the right selection of network canensure the QoS required by each session. However, thechallenge is to correctly select the network for eachcommunication session since network availability changesfrom time to time. One of the solutions to this challenge is thatwhile making the network selection, the network resources andminimum QoS requirements should be considered [8].

D. Terminal Mobility

To get different types of wireless services at any time andanywhere, is known as terminal mobility. Terminal mobility ismust in 4G infrastructure because the 4G network will be a

Basebandnsp

Digital

ADC

Fig. 4. An ideal software defined radio

Analog

Entertainment services may include streaming audio,streaming video, chat, photo trading, and gaming. In the Asianwireless market, where preliminary iterations of 3G are beingdeployed, entertainment services are generating substantialrevenue.

Other main application of 4G is Tele-geoprocessing. It is acombination of Geographical Information Systems (GIS) andGlobal Positioning Systems (GPS), working in concert over ahigh-capacity wireless mobile system. Tele-geoprocessingover 4G networks will make it possible for the public safetycommunity to have wireless operational functionality andspecialized applications for everyday operations, as well as forcrisis management.

Virtual navigation is also an important application. A remotedatabase contains the graphical representation of streets,buildings, and physical characteristics of a large metropolitanarea. Blocks of this database are transmitted in rapid sequenceto a vehicle, where a rendering program permits the occupantsto visualize the environment ahead. They may also "virtually"see the internal layout of buildings to plan an emergencyrescue, or to plan to engage hostile elements hidden in thebuilding.

VI. CHALLENGES FOR THE 4G MOBILE SYSTEMS

4G systems means to integrate different networks, differentterminals and different services together seamlessly. The 4Gmobile networks are all-IP based network with heterogeneousconnectivity. It allows the users to use the wide range ofapplications provided by the different providers through theintegrated terminals, any time and anywhere. To migrate fromcurrent systems to the 4G systems, there would be numerousnumbers of challenges we have to face. Below are some of the

Communications services include short messaging service(SMS), e-mail, video conferencing, fax, and bulletin boards.Although some of these services are available in today'swireless systems, these services will be greatly enhanced infuture generations. Speed and reliability are the most notableenhancements planned for these services.

~ Organizational Services

Organizational services include personal digital assistant(POA) capabilities, currency exchange based on user location,and other personal management applications (e.g., calendars,call management, and address books).

~ Entertainment Services

A. Localized/Personalized Information ServicesInformation such as general news, location guides, mobile

commerce, and travel services will be provided by theLocalized/personalized information services and applications.Through this service roaming on other systems can beperformed for the user with single profile.

~ Communications Services

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heterogeneous network. In terminal mobility, there are twomain issues, location management and handoff management.In location management the mobile terminal is tracked andlocated by the system for possible connection. While on goingcommunications is maintained by the handoff managementwhen the terminal roams. In the 4G network systems, it is evenmore difficult to solve the handoff problem because two typesof handoff are involved, horizontal handoff and verticalhandoff. Figure 5 illustrates the horizontal and vertical handoff.Horizontal handoff is performed when the terminal roaming isin same wireless systems that is from one cell to another cell,while vertical handoff is done when the terminal movement isbetween two different wireless systems (e.g., from WLAN toGSM).

UMTScowrage

GSMcover.I

... Vertical ~ndoff --+ 'Horizontal handoff

Fig. 5. Vertical handoff and horizontal handoff [7]

VII. RECOMMENDATIONS

4G can be seen as a common, flexible and scalableconverging platform. Equivalently, 4G can be understood ascombination of many networks and access technologies.Integrating several networks and access technologies, to realizea pleasant mobile network would be one of the greatest initialchallenges of 4G. Some recommendations that are solved areas follows.• 4G definitions: There is no worldwide consensus on the

definition of the 4G, regardless of huge efforts and severalyears of discussions. A global definition of 4G is neededbefore its standardization starts.

• Seamless interconnectivity: 4G mobile network will be thenetwork of networks, then how these heterogeneousnetworks will work and how they will appear as the singlenetwork.

• User centric approach: The most logical approach to the4G development appears to be putting the user in thecenter of the scene, developing the new technology basedon the user demands and expectations. Failing to providethe user needs may leads to the failure of4G.

• New access architectures: In future mobile networks theremay be a need for the non conventional accessarchitectures to replace conventional ones in manycircumstances. More studies need to be conducted on theseapproaches.

• Spectrum issues: Designing a real wireless system withoutthe knowledge of frequency bands (spectrum) is verydifficult, in particular for multi-antenna based system suchas MIMO technology.

VIII. CONCLUSION

In this paper the overall vision of the 4G mobilecommunication systems was presented. Through discussion ithas been revealed that the future mobile network will providevery high data rate. We also discussed the technologies that arethe main building blocks of 4G which includes OFDM,MIMO, and SDR. It is difficult to predict which technologywill emerge in 4G cellular systems. However the multipleaccess techniques (OFDM) successfully come across channelimpairments and present a good complex implementation forsupporting the high wireless data rates. Therefore multi-carriersystems are forecast as being most applicable for the 4Gmobile networks implementation by many research groups andforums and as such these techniques are continued to mature.Some of the applications and services which are the key factorsin the success of 4G are also introduced and in the last some ofthe challenges of 4G mobile networks are briefly highlighted.

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