International Journal of Wi reless Inform ation Networks, Vol. 4, No. 1, 1997
F u t u re Mobile Communications: Evolution or Revolution Hamid
Aghvami 1
Two different approaches towards meeting the full Third Generation Mobile System (TGMS) requirements are being discussed extensively in Europe. One is migration from the GSM-90 0 DCS180 0 PCS-190 0 network infrastructure to TGMS (the evolutionary approach) and the other is based on the design of a new system fully integrated with B-ISDN (the revolutionary approach). This paper examines the pros and cons of these two approaches and proposes an alternative that consolidates the two approaches into a single phased one.
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KEY W ORD S: M obile communications; network infrastructure.
FPLMTS has been studied within ITU-R since the mid80s. FPLMTS has recently been renamed as IMT-2000 (International Mobile Telecommunications operating at 20 00 MHz). TGMS is intended to provide a wide range of mobile services with up to 2 Mb s to the users. MBS is aimed at providing a range of broadband services with transmission at up to 15 5 Mb s. The standardization of MBS has not yet been commenced and MBS is not the subject of this paper which discusses two different approaches towards meeting the full TGMS requirements. The main requirements of TGMSs are identi® ed as:
1. INTRODUCTION Global Systems for Mobile Communications (GSM) is a Common European standard for digital cellular mobile communications introduced into Europe in 19 92. DCS-180 0 (Digital Cellular System operating at 180 0 MHz) and PCS-190 0 (Personal Cellular System operating at 190 0 MHz) are European and North American standards for PCN. Both systems are based on GSM technology but con® gured around low power handportable mobile terminals with smaller cell sizes. More than 150 operators worldwide have chosen GSM-based cellular systems for their networks. Currently, there are two system concepts for future mobile communications being developed and standardised in Europe. These are TGMS, refered to as Universal Mobile Telecommunications System (UMTS) in Europe and Future Public Land Mobile Telecommunications System (FPLMTS) worldwide, and the Mobile Broadband System (MBS). UMTS is being standardized by European Telecommunications Standards Institute (ETSI) through its various technical committee Special Mobile Groups (SMGs). SMG5 is responsible for the de® nition of UMTS and co-ordinations of its standardization processes in other SMGs within ETSI.
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· Supporting multi-rate services (voice, video, data, etc.) while maintaining high quality. · Operation in a multi-cell environment (macro, micro and pico cells) · Operation in a multi-operator environment (both public and private networks) · Maximum utilization of spectrum An extensive study has been carried out in Europe to de® ne the UMTS (European version of TGMS) concept and its requirements [1, 2]. The detailed UMTS initial requirements as speci® ed by ETSI SMG5 are given in Ref. [1], as: · Integration of residential, of® ce and cellular services into a single system with one user equipment.
1 Centre
for Telecommunications Research, King’s College London, Strand W C2R 2LS, UK.
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1068-9605 97 0100-0001$12.50 0
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1997 Plenum Publishing Corporation
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Ag hv am i Table I. Examples of UM TS Teleservi ces
Teleservi ce
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Speech telephony terrestrial Voice band data Program sound High quality audio Video telephony Short messages paging
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Electronic mail Telefax (G4) Broadcast multicast Public voice announce Public A N announce Unrestricted digital data Data base access Teleshopping Electronic Newspaper Remote control services Location and navigation Telewriting
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Throughput (kbps) 8± 32 2.4± 64 128 940 64± 384 1.2± 9.6 (1.2± 2.4 typ) 1.2± 64 64 1.2± 9.6 (2.4 typ) 8± 32 1.2± 9.6 (2.4 typ) 64± 1920 2.4± 768 2.4± 768 2.4± 2000 1.2± 9.6 64 32± 64
· Speech quality comparable to current ® xed network · Service capability up to Multimedia · Separation of service provision and network operation · UMTS user number independent of network or service provider · Capacity and capability to serve over 50% of population · Seamless and global radio coverage achievable · Radio bearer services up to 14 4 Kbps and further to 2 Mbps for various services · Radio resource ¯ exibility to allow for competition within a frequency band · High frequency spectrum ef® ciency · Creation of direct satellite access · Use of a new frequency band · Low cost of services and terminals Examples of UMTS teleservices and supplementary services are also identi® ed [1, 2] and are given in Tables 1 and 2. Table 1 shows examples of UMTS service types identied so far. It ranges from speech, image, video and data transmission at variab le bit rates up to 14 4 Kb/s. The support of higher bit rate data services (up to 2 Mb s) for a limited radio environment are also anticipated. Table 2 shows examples of UMTS supplementary services identi® ed for UMTS, so far. It is clear that TGMS designers and planners are
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Residual Error Rate
Delay (ms)
10E-4 10E-6 10E-6 10E-5 10E-7 10E-6
40 200 200 200 40± 90 100
10E-6 10E-6 10E-6 10E-4 10E-6 10E-6 10E-6 10E-6 -7 10E-6 10E-6 10E-6 10E-6
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100 100 100 90 100 100 200+ 90 200 100 100 90
Table II. Examples of UM TS Supplementary Services Number identi® cation Call offering (call transfer, call forwardin g etc.) Call completio n (call waiting, call hold etc.) Closed user group Private numbering plan Charging User-to-user signalling Call restriction (barring of incoming or outgoing calls)
faced with a formidable task in providing such a wide range of services and in meeting their quality requirements. In the following sections, we look at two different approaches towards TGMS concept and discuss how can these two approaches can be consolidated into one compromise approach.
2. EVOLU TIONA RY APPRO ACH This approach is based on migration from the GSM-900 DCS-180 0 PCS-190 0 network infrastructure to TGMS. The philosophy behind the evolutionary approach is that, by the end of this year, there will be more than 150 committed GSM-based cellular operators worldwide and, by the time TGMS is operational, there will be a substantial worldwide infrastructure of GSM90 0 DCS-180 0 PCS-190 0 networks. It is therefore real-
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F u t ure Mobile Communicat ions: Evolution or Revolution istic and cost effective to build upon this huge investment by choosing an evolutionary path to TGMS rather than a revolutionary one [3]. The success of this approach depends on the capability and ¯ exibility of the GSM infrastructure to support multi-mode air interfaces and also, to interwork with a range of public networks. Figure 1 shows the three elements of the evolved GSM infrastructure. In this approach, the GSM infrastructure must support as many existing and future air interfaces as possible and also interwork with a range of public networks and other mobile networks. Changing the radio interface in a GSM network has a direct impact on the Radio Resource Management functions and to a lesser extent on the Mobility Management and Connection Management functions. The GSM protocols at A-bis and A interfaces (A-bis interface is the interface between a base transceiver and its base station controller and A interface is the interface between a base station controller and its mobile services switching center) are based on message-oriented transactions [4]. A large number of these are used by Mobility Management and Connection Management but a number remain which could be used to support other radio interfaces, such as CDMA. Already, some GSM manufacturers and operators are investigating the possibility of supporting dual-mode GSM DECT, GSM IS-95 and also GSM Satellite using the GSM infrastructure (at A interface). This is the ® rst step towards this approach. Regarding interworking with the range of public networks shown in Fig. 1, more Interworking Functions (IWF) are needed at the Mobile Services Switching Centre (MSC) to take care of the differences between the protocols and transmission rates in GSM on the one hand and those in the ® xed networks. It also requires new switches at MSC capable of handling packet transmissions.
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Fig. 1. Evolutionary approach based on GSM infrastructure.
3 The advantages of this evolutionary approach are: · It facilitates a smooth market driven introduction of TGMS services and migration of mobile services and users into a new system. · The network operators can use their existing infrastructures, bene® t from their huge investment in GSM-900 DCS-180 0 PCS-190 0 and as a result reduce their initial investment.
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The disadvantages are: · The system will not be able to support the range of services and their quality requirements expected from TGMS. · The system will not be able to support the mobility requirements (e.g. fast handover) and easily support multi-operator environments. · Integration with B-ISDN will be dif® cult but not impossible.
3. REVOLU TIONA RY APPRO ACH In this approach, a new system fully integrated with B-ISDN will be implemented. The philosophy behind this approach is that, to produce the most ef® cient design of TGMS without risking the introduction of unnecessary performance trade-offs, the present standards need to be disregarded and replaced by a new standard that allows for the development of new air and network interfaces. This approach also allows the in¯ uencing and incorporation of emerging B-ISDN and IN standards, so increasing the likelihood of producing a uniform approach which is a step towards world-wide acceptance of TGMS [ 2]. This approach is the MONET project choice for UMTS. This approach is referred to as an ª evolutionary approachº within the MONET project, because, as far as the backbone network is concerned, it is evolution rather than revolution. However, as far as the access network and radio interface (both new) are concerned, the approach could be referred to as a revolutionary one. The Mobile Network (MONET) project was one of eight mobile related projects (Project Lines) of the European Commission RACE programme (Phase II) in Europe. The mobile Project Lines aimed at system integration and the building of prototypes of new services and applications for UMTS. The MONET project studied the network aspect of UMTS. Within the project, a possible generic UMTS network architecture based on a functional model supporting both personal and ter-
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minal mobility in a wide range of environments was identi® ed. Adapting this approach, TGMS will have three main parts: Access Network, Services and Mobility Provision and B-ISDN Backbone Network as illustrated in Fig. 2 [ 3]. The B-ISDN backbone network contains no TGMS speci® c functions. Functions for call handling, transfer of user data and switching are implemented by the Service and Mobility Provision part. Functions for radio resource management are implemented in the Access Network. In this scenario, TGMS will be considered as the mobile access to B-ISDN and its users as roaming B-ISDN users. Protocols, call processing and non-call processing functions of B-ISDN can be used for TGMS. For more details, the readers are referred to Ref. [2]. The advantages of this approach are identi® ed as [2] : · The need for a separate overlay network of TGMS can be avoided by exploiting the infrastructure of B-ISDN · Duplication of common functionality such as call handling, user data transfer and switching can be avoided · Certain B-ISDN protocols can be used for TGMS with minimal interworking · Integration of infrastructures of B-ISDN and TGMS reduces implementation cost for both, as well as operational costs
Fig. 2. Revolutio nary approach: The three main parts of a TGMS network.
The disadvantages are: · Current network operators cannot exploit their existing network during the introduction phase of TGMS. · B-ISDN will not be available in many countries during the introduction of TGMS.
4. ALTER NAT IVE APPRO ACH A more practical and realistic approach is to consolidate the above two approaches into one by using them in different time scales as shown in Fig. 3. This approach will have three phases: Phase 1 will run up to 20 03± 20 05 based on the migration approach and continue into the second phase (Phase 2). There has already been some progress made in phase 1 of this approach. They are: GSM phase 2 and phase 2+standards, PCS-190 0 with its enhanced speed coder and dual mode GMS DECT and GSM satellite handsets (developed but not yet commercially available). The most important development in this phase is GSM phase 2+ which now being de® ned by SMG2 of ETSI. Some of the features being considered to enhance GSM services and applications are:
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General Packet Radio Service (GPRS)Ð A packet switched transmission mode which is intended to support frequent transmission of small volume and infrequent transmission of medium volume (but not packetized speech). It will support point-to-point Connectionless (CL), point-to-point ConnectionOriented (CO) and point-to-multipoint services. High Speed Circuit Switched Data (HSCSD)Ð A high speed circuit switched mode capable of transmitting
Fig. 3. Time scales for an alternative approach.
F u t ure Mobile Communicat ions: Evolution or Revolution
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data at up to 64 Kb s. It may be used for a wide variety of transparent and non-transparent tele-services by occupying multiple consecutive time-slots. Advanced Speech Call Items (ASCI)Ð This will introduce a number of new speech services such as: Voice broadcast service, group call service and priority call set-up service. Customised Applications for Mobile network Enhanced Logic (CAMEL)Ð Support for operator speci® c services when roaming. The function which will be introduced by CAMEL is that an operator will be able to offer the subscriber extra services in addition to GSM normal services even when the subscriber roams outside his home network. Data Compression based on V42 bisÐ V42 bis data compression will be included in the GSM standard. The V42 bis algorithm has the ability to compress normal text 2± 3 times. Packet Data on Signalling channels (PDS)Ð A circuit switched bearer service which uses signalling channels (SDCCH). Two type of data services have been identi® ed: Short Message Services and GPRS (1 timeslot) types with some improved capacity in comparison to existing SMS. In Phase 2, a new system will be introduced (revolutionary approach) which provides, in addition to conventional services, complementary services to those on offer by the existing operators, particularly video and high speed data. The new system could also be rolled out to areas of highest demand for new services ® rst (urban areas) and gradually expanded to areas of lower demand (rural areas). The new system subscribers could have dual mode terminals which enable them to access the evolved system too. As time passes, there will be natural migration of both services and customers to the new system. In this way, the second generation system operators will bene® t from their huge investment and also this approach facilitates a smooth market driven introduction of new services and migration of mobile services and users into the new system. By the end of the lifetime of the second generation systems, the new system will completely take over in the ® nal phase (Phase 3). 5. CONCLUSIONS The paper has addressed the two different approaches towards meeting full TGMS requirements, being discussed extensively in Europe. The advantages and disadvantages of the two approaches were given.
5 We also discussed an alternative approach which could easily consolidate the two approaches into one. The proposed scheme gains the advantages of the two distinct approaches without inheriting their disadvantages. This ensures the smooth introduction of market driven advanced TGMS services and applications and the existing second generation network operators could bene® t from their huge initial investments. This will easily satisfy the interests and concerns of opponents and supporters of the two approaches. RE FER EN CES 1. Juha Rapeli, ª UMTS targets, system concepts and standardisation,º IEEE Personal Com munications , Vol. 2, No. 1, pp. 20± 28, 19 95. 2. Proceeding s of RACE M obile Telecom munications Workshop, Amsterdam, May 17± 19, 19 94. 3. A. H. Aghvami, Future CDM A cellular, mobile, systems supporting multi-service operation , PIMRC’ 94 Proceedin gs, pp. 1276± 1279, 1994. 4. T. Haug, Overview of GSM : Philosophy and results, Internatio nal Journal of Wireless Informatio n Networks, Vol. 1, No. 1, pp. 6± 7, 1994.
P rofessor Ham id Aghvam i obtained his M Sc and PhD degrees from King’s College, The University of London, in 1978 and 1981, respectively. In April 1981 he joined the departmen t of Electronic and Electrical Engineering at King’s as a postdocto ral research associate. He worked on Digital and Microwave techniques projects sponsored by EPSRC. He joined the academic staff at King’s in 1984. In 1989 he was promoted to Reader and to professor in Telecommunications Engineering in 19 92. He is presently the Director of Centre for Telecommunications Research at King’s. Professor Aghvami carries out consulting work on Digital Radio Communication Systems for both British and International companies. He has published over 170 technical papers and lectures on Digital Radio Communications including GSM 90 0 DCS 1800 world-wide. He leads an active research team working on numerous mobile and personal communication system projects for third generation systems, these projects are supported both by the governmen t and industry. He is a distingui shed lecturer of the IEEE Communications Society. He has been member, Chairman, Vice-Chairman of the technical programme and organizing committees of a large number of international conferences. He is also the founder of International Conference on Personal Indoor and M obile Radio Communications. He is a Fellow member of the IEE and a senior member of the IEEE.
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