ABSTRACTThe WCDMA air interface was initially

designed to support a wide variety of serviceswith different QoS requirements having a maxi-mum bit rate of 2 Mb/s. In order to satisfy thefuture service and application needs severaltechnical enhancements are being studied andstandardized for WCDMA in 3GPP. Even withevolved WCDMA, there is a need for anotherpublic wireless access solution to cover thedemand for data-intensive applications andenable smooth online access to corporate dataservices in hot spots. This need could be fulfilledby WLAN together with a high-data-rate cellularWCDMA system. WLAN offers an interestingpossibility for cellular operators to offer addi-tional capacity and higher bandwidths for endusers without sacrificing the capacity of cellularusers. The evolved WCDMA air interface willprovide better performance and higher bit ratesthan basic WCDMA, based on first releases ofthe specifications. Eventually, evolution may notbe the answer to all the needs, and some revolu-tionary concepts need to be considered. Howev-er, before some future wireless system can beregarded as belonging to 4G it must possesscapabilities that by far exceed those of 3G sys-tems like WCDMA. Judging from an applicationand services point of view, one distinguishingfactor between 3G and 4G will still be the datarate. We could define that 4G should support atleast 100 Mb/s peak data rates in full-mobilitywide area coverage and 1 Gb/s in low-mobilitylocal area coverage. Other possible characteris-tics of 4G need to be further studied.

INTRODUCTION

Wideband code-division multiple access(WCDMA) was initially proposed and engineeredwith a vision that already has shown its future-proofness. WCDMA was designed to be a high-performance system able to support futureapplications requiring simultaneous transmissionof several bitstreams that require individual quali-ty of service (QoS). The original design choiceseems to be well aligned with the future, where allapplications and services can be carried over IPnetworks using IP protocols. This trend favors newapplications where mobile users have several par-allel ongoing sessions based on one or several

applications. At the same time WCDMA is alreadydeveloping beyond original 3G technology targets,far outperforming any other wireless technology.Furthermore, the possibility to complementWCDMA coverage and capacity wireless LAN(WLAN) solutions will be discussed briefly. Eventhough WCDMA is exceeding its initial capabilitytargets, there is still a need for a quantum leap inair interface development in the longer term. Thequantum leap can be seen as the fourth genera-tion (4G). What this quantum leap is and when itcould happen will be briefly discussed.

WCDMA EVOLUTIONBACKGROUND: DEVELOPMENT FROM 2G TO 3G

Before going into technical solutions in 3G evolu-tion, it is most essential to understand the needfor such evolution and essential differences fromwhat the original 3G WCDMA system can offer.

It is important to realize that most oftenwhen different generations are discussed (e.g.,2G and 3G), people are referring to majorchanges in air interface standards. This actuallyis a good approach, because both core networkand applications are developing at their ownspeeds, and we cannot really see clear differ-ences between “generations” anymore.

Looking back to 2G Global System for MobileCommunications (GSM) evolution and first 3GWCDMA systems, some essential differences canbe seen in the air interface implementation. As anexample, one key WCDMA feature has been sup-port of multiple simultaneous services with differ-ent QoS parameters. Another key developmenthas been in data rates, where original GSM couldnot efficiently support many user needs (e.g.,email downloading). However, GSM capabilitieshave evolved to being close to original WCDMAtargets when WCDMA is launched.

These kinds of new system characteristics,such as support of simultaneous services orincreased data rate, first need to be understoodbefore the technical solutions are decided.

DEVELOPMENT OBJECTIVES:WCDMA FOR 3G EVOLUTION

The development of 3G will follow a few keytrends, and the evolution following these trendswill continue as long as the physical limitationsor backward compatibility requirements do not

IEEE Wireless Communications • April 200214 1070-9916/02/$17.00 © 2002 IEEE

WCDMA AND WLAN FOR 3G AND BEYONDHARRI HONKASALO, KARI PEHKONEN, MARKKU T. NIEMI, AND ANNE T. LEINO

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The WCDMA airinterface was initiallydesigned to supporta wide variety ofservices withdifferent QoSrequirements havingmaximum bit rate of2 Mb/s. In order tosatisfy the futureservice andapplication needsseveral technicalenhancements arebeing studied andstandardized forWCDMA in 3GPP.

TE C H N O L O G I E S F O R 4G MO B I L E CO M M U N I C AT I O N S

IEEE Wireless Communications • April 2002 15

force the development to move from evolutionto revolution. The key trends include:• Voice services will also stay important in fore-

seeable future, which means that capacityoptimization for voice services will continue.

• Together with increasing use of IP-based appli-cations, the importance of data as well assimultaneous voice and data will increase.

• Increased need for data means that efficiencyof data services needs to be improved as wellas delay, and average and peak user data rates.

• When more and more attractive multimediaterminals emerge in the markets, the usage ofsuch terminals will spread from office, homes,and airports to roads, and finally everywhere.This means that high-quality high-data-rateapplications will be needed everywhere.

• When the volume of data increases, the costper transmitted bit needs to decrease in orderto make new services and applications afford-able for everybody.The data rate trends are summarized in Fig.

1. The other current trend in Fig. 1 indicatesthat in the 3G evolution path very high datarates are achieved in hot spots with WLANrather than cellular-based standards.

WCDMA EVOLUTION ANSWERS TOEXPECTED TRENDS

The WCDMA evolution view from release 99 andrelease 4 (March 2001) to beyond 3G can be seenin three phases. The three phases are described indetail below. In Third Generation Project Part-nership (3GPP) standardization phase 1 is alreadyin progress; the other two phases try to highlightfuture potentials, but such development has yet tobe seen in 3GPP standardization.

Phase 1: High-Speed Downlink Packet Access — In thefirst phase, the peak data rate and throughput ofWCDMA downlink for best effort data will begreatly enhanced when compared to release 99.In March 2000, a feasibility study on high-speeddownlink packet access (HSDPA) was approvedby 3GPP [1]. The study report was released aspart of release 4, and the specification phase ofHSDPA was completed in release 5 at the endof 2001 [2].

The feasibility study focused on defining ahigh-speed downlink shared channel (HS-DSCH)that inherits many of the features of the DSCHdefined in release 99. The main proposed techni-cal enhancements of HS-DSCH include [2]:• Adaptive modulation and coding (AMC)• Fast hybrid automatic repeat request (FHARQ)• Fast cell selection (FCS)

AMC is a radio link adaptation techniquewhere the modulation order and channel codingmethod are varied according to the quality ofthe received signal [2, 3]. AMC is somewhat sen-sitive to measurement errors and delays; there-fore, FHARQ has been proposed to provideimplicit link adaptation to instantaneous channelconditions [2–4].

FCS has also been proposed to potentiallydecrease interference and increase the capacityof the system. Using FCS, the mobile terminalindicates the best cell to serve it on the downlinkthrough uplink signaling. Thus, while multiple

cells may be members of the active set, only onetransmits at any time [2, 3].

As a result the peak data rate of HS-DSCHwill be about 10 Mb/s; based on preliminary simu-lation results the throughput of a cell/sector willbe roughly doubled when compared to release 99.It is anticipated that not all of the proposed tech-nical enhancements will be standardized in phase1 (i.e., release 5). Release 5 will include somevery basic solutions like AMC and FHARQ.

Also, from the time-division duplex (TDD)development viewpoint, high data rates can beseen as a necessity. Especially when we thinkabout usage of TDD in the office environment,being competitive with frequency-division duplex(FDD) mode and other indoor solutions is cru-cial. Thus, HSDPA for TDD mode in release 5will include some basic technical improvements.

Among the interesting research topics aremultiple-input multiple-output (MIMO) diversitytechniques, which are also studied as part ofHSDPA [2, 5]. They can potentially improve sys-tem performance quite considerably, as shown inFig. 2, which depicts the channel capacity basedon [6] for different Tx/Rx antenna configura-tions. Due to implementation complexity theymay become reality a little bit later than theother techniques proposed for HS-DSCH.Therefore, from a timing perspective, MIMOtechniques could be more relevant for phase 2or 3 of WCDMA evolution.

Although HSDPA is raised here, 3GPP release5 work includes and will include many other workitems that contribute to 3G development.

Phase 2: Uplink High-Speed Data, High-Speed Access forTDD — Although the main emphasis in air inter-face optimization can be seen in the area ofdownlink high-data-rate support, the uplink alsoneeds attention. Enhanced data rates in theuplink will benefit the end user (e.g., in file

� Figure 1. Data rate trends.

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IEEE Wireless Communications • April 200216

transmission or when such office applications asNetMeeting are used). Also, an optimized uplinkcan be designed to support lower terminal out-put powers.

Additionally, in phase 2 further improve-ments of HSDPA for both FDD and TDDmodes will be seen. This could include the abovementioned FCS and MIMO techniques ifproven, performance and implementation pointsof view, feasible and useful.

Phase 3: Capacity Improvements in Uplink and Downlink,and Further Data Rate Enhancement — Some of theforeseen air interface technologies becomemature in a timeframe that may be unacceptablefor the proposed phases 1 and 2 of WCDMAdevelopment. It is obvious, however, that furtherenhancement will be introduced in later phases.

As the demand for very high data rates grows,we can expect the need to further enhanceWCDMA data rates up to significantly above 10Mb/s. Increase of spreading bandwidth in newfrequency allocations could be one answer to thetechnology challenge.

Standardization Timeframe — Phase 1 of WCDMAevolution was completed in 2001.

For later phases no approved workplan exist.The approximate schedule for phase 2 couldalign with following phases of 3GPP releases(e.g., mid-2003 could be the right timeframe).

Phase 3 could again take place a couple ofyears after phase 2, depending on marketdemand and spectrum availability.

OTHER TRENDS

The other major trend is the development ofpicocell and personal area network technologies(e.g., WLAN and Bluetooth) for office, public,and home indoor solutions.

Current WLAN products are able to providebandwidths up to 11 Mb/s. The next-generationwireless LAN products, based on recently approved

standards (IEEE 802.11a and HIPERLAN/2), willoffer bandwidths up to 54 Mb/s [7, 8].

In the past, WLANs have been mostly usedas a wireless replacement for wired LANs in theoffice environment.

Recently, mobile business professionals haveincreasingly been looking for an efficient way toaccess corporate information systems anddatabases remotely through the Internet back-bone. However, the high bandwidth demands oftypical office applications (e.g., large emailattachment downloading) often calls for very fasttransmission capacity. Furthermore, certain hotspots like airports and railway stations are natu-ral places to use the services. However, in theseplaces the time available for information down-load is typically fairly limited.

In light of the above there is a clear need fora public wireless access solution that could coverthe demand for data-intensive applications andenable smooth online access to corporate dataservices in hot spots.

Together with high-data-rate cellular access,WLAN has the potential to fulfill end userdemands in hot spot environments. WLAN offersan interesting possibility for cellular operators tooffer additional capacity and higher bandwidthsfor end users without sacrificing the capacity ofcellular users, since WLANs operate on unli-censed frequency bands. Furthermore, solutionsexist that enable operators to utilize the existingcellular infrastructure investments and well estab-lished roaming agreements for WLAN networksubscriber management and billing.

The TDD component of the Universal MobileTelecommunications System (UMTS) TerrestrialRadio Access Network (UTRAN) is also opti-mized for hot spot usage on unpaired TDD bands.On one hand, the achievable end user data ratesare lower than in WLAN systems; on the otherhand, the achievable cell sizes are larger. In addi-tion, the cost savings in dual mode betweenWCDMA FDD and TDD are significant, and maysupport implementation of TDD in areas wheredual mode with WCDMA is seen as essential.

DEVELOPMENT IN ITUAlso, the International TelecommunicationUnion (ITU) is working on systems beyond 3G.So far the work has concentrated on looking atthe objectives for “beyond 3G systems.” Oneimportant aspect is that new spectrum is alsoneeded before beyond 3G systems can be fullydeployed. This development is covered in [9].

BEYOND 3G: 4GAs mentioned earlier, services, applications, andeven the core network are evolving at high speeds,and distinguishing different generations is notreally possible anymore. The evolution, and some-times revolution, is a very significant trend, but inthis article 4G is seen as a revolution of the airinterface rather than a new phase of evolution.The other major trend is that access methods willbe less tightly coupled to the network. This alsoconfuses generational thinking (Fig. 4).

After a certain point, evolution is not no longeran answer to air interface development, and revo-

� Figure 2. Channel capacity vs. number of antennas.

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IEEE Wireless Communications • April 2002 17

lutionary concepts must also be considered. Fig-ure 3 illustrates the evolution of 2G/3G cellularand WLAN standards and the revolutionary steptoward future wireless systems. GSM evolutionwill continue in parallel with WCDMA. In theUnited States, cdma2000-1X will be followed by1XeV-DO (high-bit-rate data only) and 1XeV-DV (high-bit-rate data and voice) standards.

Looking at development in the Internet andapplications, it is clear that the complexity of thetransferred content is rapidly increasing and willincrease further in the future. Generally it canbe said that the more bandwidth is available, themore bandwidth applications will consume.

In order to justify the need for a new airinterface, targets need to be set high enough toensure that the system will be able to serve uslong into the future. A reasonable approachwould be to aim at 100 Mb/s full-mobility widearea coverage and 1 Gb/s low-mobility local areacoverage with a next-generation cellular systemin about 2010 in standards fora. Also, the futureapplication and service requirements will bringnew requirements to the air interface and newemphasis on air interface design. One such issue,which already strongly impacts 3G evolution, isthe need to support IP and IP-based multimedia.If both technology and spectrum to meet suchrequirements cannot be found, the whole discus-sion of 4G may become obsolete.

SPECTRUM ISSUES

WRC2000 already identified new spectrum forIMT-2000 systems. The ITU identifications at 2GHz frequency range can be seen in Fig. 5. In addi-tion to 2 GHz identifications, WRC2000 also iden-tified parts of the 806–960 MHz band that alreadyhave primary mobile allocations to IMT-2000.

The demand for even higher data rates andpotential need for wider bandwidths in cellularevolution raise even further questions on spec-trum needs. However, before this need can bedefined, a much better idea/vision of the nextgeneration will be needed. For example, if WLANis combined with WCDMA, the additional spec-trum is already the current WLAN spectrum, andsomething more is needed to justify even higherspectrum requirements. There are many discus-sions ongoing, for example, about reallocatinganalog TV bands for mobile systems. On theother hand, administrations seem to prefer moreflexible air interfaces where globally harmonizedspectrum would not be needed.

� Figure 3. The path toward 4G from a radio perspective. The time axis shows the estimated launch times of the actual systems.

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CONCLUSIONSThe WCDMA air interface is seen to developfar beyond its initial capabilities to satisfy futureservice and application needs.

WLAN systems are seen to complementWCDMA-based cellular evolution in hot spotsin development beyond 3G. The other technolo-gy to be considered for hot spot coverage isUTRAN TDD mode, which is well harmonizedwith WCDMA FDD and in such a way facili-tates cost-efficient dual mode terminal design.

When looking at development of services,applications, or core networks, developmentespecially in applications is much faster than tra-ditional generation thinking assumes. This devel-opment will happen in an evolutionary waywithout clear generations. That is why here weconsider quantum leaps in air interface develop-ment as different generations. The next suchquantum leap will lead us to 4G. This thinking iswell in line with development from 1G to 2Gand 3G. People clearly refer to air interfacestandards when referring to these generations.

4G needs to be something that 3G evolutioncannot do. Looking at the complexity of applica-tion contents and development of such contents,going toward even higher data rates and avail-ability of high data rates everywhere is a trend.Thus, one distinguishing factor between 3G and4G will be the data rates. We assume that 4Gshould support at least 100 Mb/s peak rates infull-mobility wide area coverage and 1 Gb/s inlow-mobility local area coverage. There will beother characteristics for 4G, but at this point intime the requirements for 4G need further stud-ies (including market studies).

ACKNOWLEDGMENTSThis article is based on previously publishedmaterial from 3Gwireless 2001 organized by Del-son Group (http://www.delson.org).

REFERENCES[1] Motorola, Work Item Description sheet for High Speed

Downlink Packet Access,” TSGR#7(00)0032, March13–15, 2000, Madrid, Spain, p. 3.

[2] 3GPP TSG-RAN WG2, “UTRAN High Speed DownlinkPacket Access (release 4),” TSG-R2 TR 25.950.

[3] “Nokia, Considerations on High-Speed Downlink PacketAccess (HSDPA),” TSGR1#14(00)0868, July 4–7, 2000,Oulu, Finland, p. 9.

[4] Nokia, Text proposal on HARQ for HSDPA TR,TSGR1#17(00)1369, 21–24, Nov., 2000, Stockholm,Sweden, p. 4.

[5] G. J. Foschini and M. J. Gans, “On Limits of WirelessCommunication in a Fading Environment when UsingMultiple Antennas,” Wireless Pers. Commun., vol. 6,no. 3, Mar. 1998, pp. 311–35.

[6] E. Telatar, “Capacity of Multi-Antenna Gaussian Chan-nels, Technical Memorandum,” Bell Labs, Lucent, Oct.1995, published in Euro. Trans. Telecommun., vol. 10,no. 6, Nov/Dec 1999, pp. 585–95.

[7] ETSI, “Broadband Radio Access Networks (BRAN); High Per-formance Radio Local Area Network (HIPERLAN) Type 2;Requirements and Architectures for Wireless BroadbandAccess,” TR 101 031 (1999-01), v. 1.1.1. ETSI, 1999.

[8] ETSI, “Broadband Radio Access Networks (BRAN); HighPerformance Radio Local Area Network (HIPERLAN)Type 2. ETSI Technical Specification, Physical Layer,”v.1.2.2, 2001.

[9] D. McFarlane, “Enhancing the Capabilities of 3G Sys-tems,” IEEE Int’l. Conf. 3G Wireless and Beyond, 30May–2 June, 2001, San Francisco, CA.

BIOGRAPHIESHARRI HONKASALO received his M.S. from Helsinki University ofTechnology in 1986. In 1985 he joined Nokia. From 1985 to1993 he held various research and product developmentpositions in Nokia Mobile Phones in Finland and the UnitedKingdom, working on GSM and PDC terminals and standard-ization. In 1994–1995 he was with Nokia Research Center inFinland, responsible for research activities on GSM stan-dards, and in 1996–1997 he was with Nokia Research Centerin the United States, responsible for research activities on IS-95 and cdma2000 standards. From 1998 to 2000 he washead of system research in Nokia Mobile Phones with globalresponsibility for system research activities. Since 2001 hehas been director of IPR for Nokia Corporation with globalresponsibility for standards-related IPR activities. He has pub-lished about 10 papers in international conferences andjournals, and holds 13 patent families covering differentareas of radio interfaces.

KARI PEHKONEN [M] (kari.pehkonen@nokia.com) received hisM.S., licentiate in technology, and doctor of technologydegrees from the University of Oulu in 1987, 1989, and1993, respectively. He joined the Computer TechnologyLaboratory of the Technical Research Centre of Finland in1987 and was involved in research on parallel program-ming and parallel computers. During 1989–1990 he was avisiting researcher at the Computer Vision Laboratory ofthe Center for Automation Research of the University ofMaryland, doing research on computer vision algorithms.Upon returning to Finland he continued with the TechnicalResearch Centre, studying further the algorithms developedduring his visit to the United States. Since 1993 he hasbeen with Nokia Mobile Phones, first as a research engi-neer and then holding various managerial positions withinthe company, doing research on WCDMA systems andstandardization. From 1998to 2001 he was with NokiaJapan, responsible for ARIB standardization activities. Sincethe beginning of 2001 he has been head of system researchat Nokia Mobile Phones with global responsibility for sys-tem research activities. He has published about 20 papersin international conferences and journals and holds 9patents covering different areas of radio interfaces. His cur-rent research interests include the system aspects of radioaccess networks with a special interest in L1 solutions.

ANNE-TUULIA LEINO received her M.S. degree from the Uni-versity of Technology, Espoo, in 1991. She joined theTelecommunications Administration Centre, Finland, in1991, working on spectrum topics related to the regulationof public mobile networks. She changed to Nokia Networksin 1997 to work as a spectrum expert covering frequencyarrangements related to IMT-2000 networks.

MARKKU NIEMI received his M.S. degree from Tampere Uni-versity of Technology in 1995. He joined Nokia MobilePhones in 1995 and currently is senior manager at NokiaMobile Phones responsible for WLAN standardization, reg-ulatory matters, and research cooperation. Prior to his cur-rent position he held various management positions insideNokia Mobile Phones. He has published about 10 papers ininternational conferences and journals, and holds severalpatent applications.

� Figure 5. ITU spectrum identification: S5.388 are the WARC ’92 identifica-tions, and S5.AAA are the additional WRC 2000 identifications.

S5388 S5AAAS5388S5AAA

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