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  • 1. T E C H N O L O G I E S F O R 4G M O B I L E C O M M U N I C AT I O N S WCDMA AND WLAN FOR 3G AND BEYOND HARRI HONKASALO, KARI PEHKONEN, MARKKU T. NIEMI, AND ANNE T. LEINO NOKIA ABSTRACT applications. At the same time WCDMA is already Wide area coverage GSM (MAP) developing beyond original 3G technology targets, HSCS The WCDMA air interface was initially far outperforming any other wireless technology. 15.2 kb/s 1 designed to support a wide variety of services Furthermore, the possibility to complement 30 kHz with different QoS requirements having a maxi- WCDMA coverage and capacity wireless LAN TDMA (IS-41) CDPD mum bit rate of 2 Mb/s. In order to satisfy the (WLAN) solutions will be discussed briefly. Even 43.2 kb/s future service and application needs several though WCDMA is exceeding its initial capability technical enhancements are being studied and targets, there is still a need for a quantum leap in PDC/PDC-P standardized for WCDMA in 3GPP. Even with air interface development in the longer term. The evolved WCDMA, there is a need for another quantum leap can be seen as the fourth genera- 14.4 kb/s public wireless access solution to cover the tion (4G). What this quantum leap is and when it cdmaOne demand for data-intensive applications and could happen will be briefly discussed. (IS-41) enable smooth online access to corporate data 76.8 kb/s services in hot spots. This need could be fulfilled WCDMA EVOLUTION al by WLAN together with a high-data-rate cellular The WCDMA air WCDMA system. WLAN offers an interesting BACKGROUND: DEVELOPMENT FROM 2G TO 3G possibility for cellular operators to offer addi- Before going into technical solutions in 3G evolu- interface was initially tional capacity and higher bandwidths for end tion, it is most essential to understand the need users without sacrificing the capacity of cellular for such evolution and essential differences from designed to support users. The evolved WCDMA air interface will what the original 3G WCDMA system can offer. provide better performance and higher bit rates It is important to realize that most often a wide variety of than basic WCDMA, based on first releases of when different generations are discussed (e.g., the specifications. Eventually, evolution may not 2G and 3G), people are referring to major services with be the answer to all the needs, and some revolu- changes in air interface standards. This actually tionary concepts need to be considered. Howev- is a good approach, because both core network different QoS er, before some future wireless system can be and applications are developing at their own regarded as belonging to 4G it must possess speeds, and we cannot really see clear differ- requirements having capabilities that by far exceed those of 3G sys- ences between “generations” anymore. tems like WCDMA. Judging from an application Looking back to 2G Global System for Mobile maximum bit rate of and services point of view, one distinguishing Communications (GSM) evolution and first 3G factor between 3G and 4G will still be the data WCDMA systems, some essential differences can 2 Mb/s. In order to rate. We could define that 4G should support at be seen in the air interface implementation. As an least 100 Mb/s peak data rates in full-mobility example, one key WCDMA feature has been sup- satisfy the future wide area coverage and 1 Gb/s in low-mobility port of multiple simultaneous services with differ- local area coverage. Other possible characteris- ent QoS parameters. Another key development service and tics of 4G need to be further studied. has been in data rates, where original GSM could not efficiently support many user needs (e.g., application needs INTRODUCTION email downloading). However, GSM capabilities have evolved to being close to original WCDMA several technical Wideband code-division multiple access targets when WCDMA is launched. (WCDMA) was initially proposed and engineered These kinds of new system characteristics, enhancements are with a vision that already has shown its future- such as support of simultaneous services or proofness. WCDMA was designed to be a high- increased data rate, first need to be understood being studied and performance system able to support future before the technical solutions are decided. applications requiring simultaneous transmission standardized for of several bitstreams that require individual quali- DEVELOPMENT OBJECTIVES: ty of service (QoS). The original design choice WCDMA FOR 3G EVOLUTION WCDMA in 3GPP. seems to be well aligned with the future, where all applications and services can be carried over IP The development of 3G will follow a few key networks using IP protocols. This trend favors new trends, and the evolution following these trends applications where mobile users have several par- will continue as long as the physical limitations allel ongoing sessions based on one or several or backward compatibility requirements do not 14 1070-9916/02/$17.00 © 2002 IEEE IEEE Wireless Communications • April 2002
  • 2. force the development to move from evolution to revolution. The key trends include: • Voice services will also stay important in fore- seeable future, which means that capacity optimization for voice services will continue. Vehicular • Together with increasing use of IP-based appli- cations, the importance of data as well as simultaneous voice and data will increase. • Increased need for data means that efficiency Mobility WCD of data services needs to be improved as well cdma as delay, and average and peak user data rates. MA • When more and more attractive multimedia 2000 relea terminals emerge in the markets, the usage of such terminals will spread from office, homes, 1X, se 4 and airports to roads, and finally everywhere. Pedestrian HS EDGE This means that high-quality high-data-rate DP A applications will be needed everywhere. = evo • When the volume of data increases, the cost W re CD per transmitted bit needs to decrease in order lea M se A lved 2 to make new services and applications afford- 5 WLAN able for everybody. Stationary G The data rate trends are summarized in Fig. 1. The other current trend in Fig. 1 indicates 0.1 1 10 100 that in the 3G evolution path very high data rates are achieved in hot spots with WLAN Data rate (Mb/s) rather than cellular-based standards. I Figure 1. Data rate trends. WCDMA EVOLUTION ANSWERS TO EXPECTED TRENDS cells may be members of the active set, only one The WCDMA evolution view from release 99 and transmits at any time [2, 3]. release 4 (March 2001) to beyond 3G can be seen As a result the peak data rate of HS-DSCH in three phases. The three phases are described in will be about 10 Mb/s; based on preliminary simu- detail below. In Third Generation Project Part- lation results the throughput of a cell/sector will nership (3GPP) standardization phase 1 is already be roughly doubled when compared to release 99. in progress; the other two phases try to highlight It is anticipated that not all of the proposed tech- future potentials, but such development has yet to nical enhancements will be standardized in phase be seen in 3GPP standardization. 1 (i.e., release 5). Release 5 will include some very basic solutions like AMC and FHARQ. Phase 1: High-Speed Downlink Packet Access — In the Also, from the time-division duplex (TDD) first phase, the peak data rate and throughput of development viewpoint, high data rates can be WCDMA downlink for best effort data will be seen as a necessity. Especially when we think greatly enhanced when compared to release 99. about usage of TDD in the office environment, In March 2000, a feasibility study on high-speed being competitive with frequency-division duplex downlink packet access (HSDPA) was approved (FDD) mode and other indoor solutions is cru- by 3GPP [1]. The study report was released as cial. Thus, HSDPA for TDD mode in release 5 part of release 4, and the specification phase of will include some basic technical improvements. HSDPA was completed in release 5 at the end Among the interesting research topics are of 2001 [2]. multiple-input multiple-output (MIMO) diversity The feasibility study focused on defining a techniques, which are also studied as part of high-speed downlink shared channel (HS-DSCH) HSDPA [2, 5]. They can potentially improve sys- that inherits many of the features of the DSCH tem performance quite considerably, as shown in defined in release 99. The main proposed techni- Fig. 2, which depicts the channel capacity based cal enhancements of HS-DSCH include [2]: on [6] for different Tx/Rx antenna configura- • Adaptive modulation and coding (AMC) tions. Due to implementation complexity they • Fast hybrid automatic repeat request (FHARQ) may become reality a little bit later than the • Fast cell selection (FCS) other techniques proposed for HS-DSCH. AMC is a radio link adaptation technique Therefore, from a timing perspective, MIMO where the modulation order and channel coding techniques could be more relevant for phase 2 method are varied according to the quality of or 3 of WCDMA evolution. the received signal [2, 3]. AMC is somewhat sen- Although HSDPA is raised here, 3GPP release sitive to measurement errors and delays; there- 5 work includes and will include many other work fore, FHARQ has been proposed to provide items that contribute to 3G development. implicit link adaptation to instantaneous channel conditions [2–4]. Phase 2: Uplink High-Speed Data, High-Speed Access for FCS has also been proposed to potentially TDD — Although the main emphasis in air inter- decrease interference and increase the capacity face optimization can be seen in the area of of the system. Using FCS, the mobile terminal downlink high-data-rate support, the uplink also indicates the best cell to serve it on the downlink needs attention. Enhanced data rates in the through uplink signaling. Thus, while multiple uplink will benefit the end user (e.g., in file IEEE Wireless Communications • April 2002 15
  • 3. standards (IEEE 802.11a and HIPERLAN/2), will 30 offer bandwidths up to 54 Mb/s [7, 8]. In the past, WLANs have been mostly used as a wireless replacement for wired LANs in the 25 office environment. Recently, mobile business professionals have increasingly been looking for an efficient way to 20 access corporate information systems and databases remotely through the Internet back- 2 8 bone. However, the high bandwidth demands of 8 2 2 4 15 typical office applications (e.g., large email 4 2 attachment downloading) often calls for very fast 2 2 transmission capacity. Furthermore, certain hot 10 spots like airports and railway stations are natu- 2 1 ral places to use the services. However, in these 1 2 places the time available for information down- 5 load is typically fairly limited. 1 1 In light of the above there is a clear need for a public wireless access solution that could cover 0 the demand for data-intensive applications and 0 5 10 15 20 25 enable smooth online access to corporate data services in hot spots. Together with high-data-rate cellular access, I Figure 2. Channel capacity vs. number of antennas. WLAN has the potential to fulfill end user demands in hot spot environments. WLAN offers an interesting possibility for cellular operators to transmission or when such office applications as offer additional capacity and higher bandwidths NetMeeting are used). Also, an optimized uplink for end users without sacrificing the capacity of can be designed to support lower terminal out- cellular users, since WLANs operate on unli- put powers. censed frequency bands. Furthermore, solutions Additionally, in phase 2 further improve- exist that enable operators to utilize the existing ments of HSDPA for both FDD and TDD cellular infrastructure investments and well estab- modes will be seen. This could include the above lished roaming agreements for WLAN network mentioned FCS and MIMO techniques if subscriber management and billing. proven, performance and implementation points The TDD component of the Universal Mobile of view, feasible and useful. Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) is also opti- Phase 3: Capacity Improvements in Uplink and Downlink, mized for hot spot usage on unpaired TDD bands. and Further Data Rate Enhancement — Some of the On one hand, the achievable end user data rates foreseen air interface technologies become are lower than in WLAN systems; on the other mature in a timeframe that may be unacceptable hand, the achievable cell sizes are larger. In addi- for the proposed phases 1 and 2 of WCDMA tion, the cost savings in dual mode between development. It is obvious, however, that further WCDMA FDD and TDD are significant, and may enhancement will be introduced in later phases. support implementation of TDD in areas where As the demand for very high data rates grows, dual mode with WCDMA is seen as essential. we can expect the need to further enhance WCDMA data rates up to significantly above 10 DEVELOPMENT IN ITU Mb/s. Increase of spreading bandwidth in new frequency allocations could be one answer to the Also, the International Telecommunication technology challenge. Union (ITU) is working on systems beyond 3G. So far the work has concentrated on looking at Standardization Timeframe — Phase 1 of WCDMA the objectives for “beyond 3G systems.” One evolution was completed in 2001. important aspect is that new spectrum is also For later phases no approved workplan exist. needed before beyond 3G systems can be fully The approximate schedule for phase 2 could deployed. This development is covered in [9]. align with following phases of 3GPP releases (e.g., mid-2003 could be the right timeframe). BEYOND 3G: 4G Phase 3 could again take place a couple of years after phase 2, depending on market As mentioned earlier, services, applications, and demand and spectrum availability. even the core network are evolving at high speeds, and distinguishing different generations is not OTHER TRENDS really possible anymore. The evolution, and some- times revolution, is a very significant trend, but in The other major trend is the development of this article 4G is seen as a revolution of the air picocell and personal area network technologies interface rather than a new phase of evolution. (e.g., WLAN and Bluetooth) for office, public, The other major trend is that access methods will and home indoor solutions. be less tightly coupled to the network. This also Current WLAN products are able to provide confuses generational thinking (Fig. 4). bandwidths up to 11 Mb/s. The next-generation After a certain point, evolution is not no longer wireless LAN products, based on recently approved an answer to air interface development, and revo- 16 IEEE Wireless Communications • April 2002
  • 4. Evolution of 3G 200 kHz Wide area coverage GSM (MAP) GPRS EDGE EDGE Ph.2 HSCS GERAN 15.2 kb/s 170 kb/s 473 kb/s 473 kb/s 30 kHz Real-time IP TDMA (IS-41) Future CDPD 5 MHz WCDMA TDD 2 Mb/s wireless 43.2 kb/s High-speed WCDMA WCDMA downlink FDD HSPA packet access PDC/PDC-P 10 Mb/s 2 Mb/s 14.4 kb/s T-SCDMA 1.25 MHz cdmaOne cdma2000- 1XEV - DO, phase 2.4 Mb/s (IS-41) 1X 1XEV - DV, phase 5.4 Mb/s 76.8 kb/s 307. kb/s Local HiperLAN2 Harmonized WLAN 54 Mb/s HL2- 802.11b IEEE 802.11a IEEE 802.11a standard 11 Mb/s 54 Mb/s 2000 2001 2002 2003 2010-> I Figure 3. The path toward 4G from a radio perspective. The time axis shows the estimated launch times of the actual systems. lutionary concepts must also be considered. Fig- ure 3 illustrates the evolution of 2G/3G cellular and WLAN standards and the revolutionary step LAN toward future wireless systems. GSM evolution will continue in parallel with WCDMA. In the WLAN United States, cdma2000-1X will be followed by Intranet Bluetooth 1XeV-DO (high-bit-rate data only) and 1XeV- DV (high-bit-rate data and voice) standards. xDSL Looking at development in the Internet and applications, it is clear that the complexity of the ISDN transferred content is rapidly increasing and will Internet POTS increase further in the future. Generally it can be said that the more bandwidth is available, the TDMA more bandwidth applications will consume. In order to justify the need for a new air GSM interface, targets need to be set high enough to GPRS ensure that the system will be able to serve us 2G/3G long into the future. A reasonable approach CDMA would be to aim at 100 Mb/s full-mobility wide WCDMA area coverage and 1 Gb/s low-mobility local area coverage with a next-generation cellular system in about 2010 in standards fora. Also, the future I Figure 4. Coupling of air interface technologies to the network. application and service requirements will bring new requirements to the air interface and new emphasis on air interface design. One such issue, The demand for even higher data rates and which already strongly impacts 3G evolution, is potential need for wider bandwidths in cellular the need to support IP and IP-based multimedia. evolution raise even further questions on spec- If both technology and spectrum to meet such trum needs. However, before this need can be requirements cannot be found, the whole discus- defined, a much better idea/vision of the next sion of 4G may become obsolete. generation will be needed. For example, if WLAN is combined with WCDMA, the additional spec- SPECTRUM ISSUES trum is already the current WLAN spectrum, and something more is needed to justify even higher WRC2000 already identified new spectrum for spectrum requirements. There are many discus- IMT-2000 systems. The ITU identifications at 2 sions ongoing, for example, about reallocating GHz frequency range can be seen in Fig. 5. In addi- analog TV bands for mobile systems. On the tion to 2 GHz identifications, WRC2000 also iden- other hand, administrations seem to prefer more tified parts of the 806–960 MHz band that already flexible air interfaces where globally harmonized have primary mobile allocations to IMT-2000. spectrum would not be needed. IEEE Wireless Communications • April 2002 17
  • 5. [5] G. J. Foschini and M. J. Gans, “On Limits of Wireless Communication in a Fading Environment when Using ITU identifications Multiple Antennas,” Wireless Pers. Commun., vol. 6, no. 3, Mar. 1998, pp. 311–35. [6] E. Telatar, “Capacity of Multi-Antenna Gaussian Chan- S5AAA S5388 S5388 S5AAA 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- 1700 1750 1800 1850 1900 1950 2000 2050 2100 2150 2200 2500 2550 2600 2650 MHz formance Radio Local Area Network (HIPERLAN) Type 2; Requirements and Architectures for Wireless Broadband Access,” TR 101 031 (1999-01), v. 1.1.1. ETSI, 1999. I Figure 5. ITU spectrum identification: S5.388 are the WARC ’92 identifica- [8] ETSI, “Broadband Radio Access Networks (BRAN); High Performance Radio Local Area Network (HIPERLAN) tions, and S5.AAA are the additional WRC 2000 identifications. Type 2. ETSI Technical Specification, Physical Layer,” v.1.2.2, 2001. [9] D. McFarlane, “Enhancing the Capabilities of 3G Sys- CONCLUSIONS tems,” IEEE Int’l. Conf. 3G Wireless and Beyond, 30 May–2 June, 2001, San Francisco, CA. The WCDMA air interface is seen to develop far beyond its initial capabilities to satisfy future BIOGRAPHIES service and application needs. HARRI HONKASALO received his M.S. from Helsinki University of WLAN systems are seen to complement Technology in 1986. In 1985 he joined Nokia. From 1985 to 1993 he held various research and product development WCDMA-based cellular evolution in hot spots positions in Nokia Mobile Phones in Finland and the United in development beyond 3G. The other technolo- Kingdom, working on GSM and PDC terminals and standard- gy to be considered for hot spot coverage is ization. In 1994–1995 he was with Nokia Research Center in UTRAN TDD mode, which is well harmonized Finland, responsible for research activities on GSM stan- dards, and in 1996–1997 he was with Nokia Research Center with WCDMA FDD and in such a way facili- in the United States, responsible for research activities on IS- tates cost-efficient dual mode terminal design. 95 and cdma2000 standards. From 1998 to 2000 he was When looking at development of services, head of system research in Nokia Mobile Phones with global applications, or core networks, development responsibility for system research activities. Since 2001 he has been director of IPR for Nokia Corporation with global especially in applications is much faster than tra- responsibility for standards-related IPR activities. He has pub- ditional generation thinking assumes. This devel- lished about 10 papers in international conferences and opment will happen in an evolutionary way journals, and holds 13 patent families covering different without clear generations. That is why here we areas of radio interfaces. consider quantum leaps in air interface develop- KARI PEHKONEN [M] (kari.pehkonen@nokia.com) received his ment as different generations. The next such M.S., licentiate in technology, and doctor of technology quantum leap will lead us to 4G. This thinking is degrees from the University of Oulu in 1987, 1989, and well in line with development from 1G to 2G 1993, respectively. He joined the Computer Technology Laboratory of the Technical Research Centre of Finland in and 3G. People clearly refer to air interface 1987 and was involved in research on parallel program- standards when referring to these generations. ming and parallel computers. During 1989–1990 he was a 4G needs to be something that 3G evolution visiting researcher at the Computer Vision Laboratory of cannot do. Looking at the complexity of applica- the Center for Automation Research of the University of Maryland, doing research on computer vision algorithms. tion contents and development of such contents, Upon returning to Finland he continued with the Technical going toward even higher data rates and avail- Research Centre, studying further the algorithms developed ability of high data rates everywhere is a trend. during his visit to the United States. Since 1993 he has Thus, one distinguishing factor between 3G and been with Nokia Mobile Phones, first as a research engi- neer and then holding various managerial positions within 4G will be the data rates. We assume that 4G the company, doing research on WCDMA systems and should support at least 100 Mb/s peak rates in standardization. From 1998to 2001 he was with Nokia full-mobility wide area coverage and 1 Gb/s in Japan, responsible for ARIB standardization activities. Since low-mobility local area coverage. There will be the beginning of 2001 he has been head of system research at Nokia Mobile Phones with global responsibility for sys- other characteristics for 4G, but at this point in tem research activities. He has published about 20 papers time the requirements for 4G need further stud- in international conferences and journals and holds 9 ies (including market studies). patents covering different areas of radio interfaces. His cur- rent research interests include the system aspects of radio ACKNOWLEDGMENTS access networks with a special interest in L1 solutions. This article is based on previously published ANNE-TUULIA LEINO received her M.S. degree from the Uni- material from 3Gwireless 2001 organized by Del- versity of Technology, Espoo, in 1991. She joined the son Group (http://www.delson.org). Telecommunications Administration Centre, Finland, in 1991, working on spectrum topics related to the regulation of public mobile networks. She changed to Nokia Networks REFERENCES in 1997 to work as a spectrum expert covering frequency [1] Motorola, Work Item Description sheet for High Speed arrangements related to IMT-2000 networks. Downlink Packet Access,” TSGR#7(00)0032, March 13–15, 2000, Madrid, Spain, p. 3. MARKKU NIEMI received his M.S. degree from Tampere Uni- [2] 3GPP TSG-RAN WG2, “UTRAN High Speed Downlink versity of Technology in 1995. He joined Nokia Mobile Packet Access (release 4),” TSG-R2 TR 25.950. Phones in 1995 and currently is senior manager at Nokia [3] “Nokia, Considerations on High-Speed Downlink Packet Mobile Phones responsible for WLAN standardization, reg- Access (HSDPA),” TSGR1#14(00)0868, July 4–7, 2000, ulatory matters, and research cooperation. Prior to his cur- Oulu, Finland, p. 9. rent position he held various management positions inside [4] Nokia, Text proposal on HARQ for HSDPA TR, Nokia Mobile Phones. He has published about 10 papers in TSGR1#17(00)1369, 21–24, Nov., 2000, Stockholm, international conferences and journals, and holds several Sweden, p. 4. patent applications. 18 IEEE Wireless Communications • April 2002