Whereas the limitingfactor with wireline networks is the network infrastructure that has to be cre-ated, the capacity of radio networks is determined by the frequency spectrumavailable a
Trang 1Introduction
During the first half of this century, the transmission of human voice throughthe telephone was the dominant means of communication next to telegraphy.Radio-supported mobile communication has constantly grown in importanceduring the last few decades and particularly the last few years to technicaladvances in transmission and switching technology as well as in microelec-tronics Table 1.1 presents an overview of the chronological development ofmobile radio systems
In contrast to wireline networks, mobile radio networks that comply withthe wish for geographically unrestricted communication can be used anywherewhere it is not economic or possible to install cabling Whereas the limitingfactor with wireline networks is the network infrastructure that has to be cre-ated, the capacity of radio networks is determined by the frequency spectrumavailable and the physical attributes of radio waves in the earth’s atmosphere.The development of radio systems is influenced considerably by the scarcity
of an important resource—frequencies For instance, spectral efficiency can beimproved through the digitalization of speech and the use of source and chan-nel coding Existing analogue radio systems are therefore being replaced moreand more by digital mobile radio networks Modern digital techniques used
in modulation, coding and equalization enable bandwidth-efficient sion and offer better interference behaviour and lower susceptibility to noisethan analogue-modulated signals Digital voice and data can be processedand stored before being transmitted
transmis-This allows the use of multiplexing methods such as TDM (Time-DivisionMultiplexing), FDM (Frequency-Division Multiplexing) and CDM (Code-Division Multiplexing) that enable services to be provided to many users.For example, with TDM a large number of users in a specific frequency band-width are able to exchange information without extremely high selectivity
of the receiver This means that fewer steep-edged filters and resonating ements are needed, thereby resulting in a cost reduction, whereas modemstransmit in burst mode and therefore are more costly Digital modulationtechniques often produce a higher level of transmission quality and are alsomore compatible with existing digital fixed networks
el-Mobile communication today is available from a broad spectrum of logical and service-specific forms The aim of this book is to provide the readerwith an overview of the digital communications networks that have been in-troduced over the last few years, along with the services these networks offer
techno-Mobile Radio Networks: Networking and Protocols Bernhard H Walke
Copyright © 1999 John Wiley & Sons Ltd ISBNs: 0-471-97595-8 (Hardback); 0-470-84193-1 (Electronic)
Trang 2Mobile terrestrial system standards
Mobile satellite system standards
Phone System RC2000(F) Radio Communication C450 (D,P) Cellular
TACS (UK) Total Access nication System
Commu-Inmarsat-C
Communication DCS 1800 Digital Cellular System
at 1800 MHz
Inmarsat-B Inmarsat-M Inmarsat- Paging
System
Iridium, Aries, Odyssey, Globalstar, Ellipso
Telecommunication System FPLMTS Future Public Land Mobile Telecommunication System
Wireless ATM
and their protocols Special emphasis is given to systems in Europe that arecurrently being used, are being standardized or whose introduction is immi-nent
Deregulation and liberalization of the telecommunications market, alongwith the various agreements on standardization, are having a major effect
on the development of mobile radio systems Detailed specifications are essary in order to achieve compatibility between the products of differentsystem and terminal suppliers International and European standards bod-ies are defining mobile radio systems that can be used and operated acrosscountry boundaries This will enable users to be reachable wherever they areroaming and will result in the cost-effective production of terminals per unit,thereby opening up the market to different types of customers The mostimportant standards organizations active in the mobile radio area are covered
nec-in Appendix B
Physical connections over a radio channel are far more complex than those
in a fixed network Some of the main characteristics of radio transmission aretherefore presented in Chapter 2
Trang 66 1 Introduction
Figure 1.3: Distribution of analogue cellular systems in Europe
The concept of cordless communication systems summarizes services and
tele-phones, the cable between the telephone terminal and the handset was merelyreplaced by a radio path that allows a radio connection of up to 300 m/50 m(outdoors/indoors); see Chapter 9
Wireless local area networks take into account the growing demand to avoidcabling of workstation computers; see Chapter 12, whereas mobile satelliteradio systems provide global communication and accessibility; see Chapter 14.The mobile communications market is currently developing at a rapid pace,and it is anticipated that the next few years will bring a dramatic growth inthe number of users and an increased demand for quality As a result, thestandardization bodies are already developing new standards with the aim ofproviding a universal, service-integrated mobile telecommunications system inthe near future; see Chapter 5
The spectacular growth of the GSM-based cellular mobile radio networks,including networks based on the DCS 1800 standard, convey the impression
Trang 71.1 Existing and New Networks and Services 7
CITY RUF EURO SIGNAL
CT0
CT1
CT1+
ARTS IMTS
TACS
E TACS 900
NMT B
C450 RC 2000 RMTS
D AMPS CDMA? PDC GSM
D AMPS2 PCS 1900
PHS 1900 PCS 1800
DCS
UMTS IMT 2000
Europe
PLMN
NMT 450
Figure 1.4: Overview of worldwide standards for mobile radio systems
that the essential development needed in this area has been accomplishedthrough the introduction of these cellular mobile radio networks What oneforgets is that these networks have been designed as an “extension” of ISDN
to the mobile user, but only address the needs to a limited degree: instead
of two B-channels per user, only one with a considerably lower user datarate (13/6.5 kbit/s for voice and 9.6 kbit/s for data) is available Likewisethe ISDN-D channel has only been reproduced to a point: an X.25 packet
connection (2.048 Mbit/s) available with ISDN does not exist The situation
is a similar one with competing systems in the USA and Japan (see Table 1.3and Figure 1.4)
A number of concepts of GSM 900/DCS 1800 systems will have to be oped further in order to head off the competitive pressure of other conceptsfor cellular networks (UMTS, IMT 2000, Spread Spectrum CDMA) and toprovide better support to mobile image and data services The anticipateddemand for ISDN-compatible mobile data services (64 kbit/s) is pressuring
Trang 11devel-1.1 Existing and New Networks and Services 11
Trang 1212 1 Introduction
Deregulation in Europe ends the monopoly on voice services of the incumbentoperator, and is resulting in the expansion of former corporate networks bynew network operators in competition with the respective incumbent (some ofthem also using lines leased from the incumbent), who are providing services
to large customers and (eventually) all conveniently located corporate andprivate customers This expansion is being accompanied by the developmentand establishment of local cellular radio networks that use point-to-multipointradio relay or fixed radio user connections (see Figure 10.6), offer ISDN-basedand primary rate multiplex interfaces and can be used as access networks (Ra-dio in the Local Loop, RLL) to fixed networks of the incumbent’s competitors.GSM and DCS 1800 only have limited application in this area because
of their noticeably lower transmission rates compared with ISDN In channel operation DECT can offer ISDN interfaces; the appropriate standardswere drawn up by ETSI/RES 03 in 1996 Radios in the local loop networksare closely related to the systems described in Sections 1.1.1 and 1.1.2 butrequire further development to enable them to make better use of frequenciesand operate more cost-effectively
multi-Along with cellular networks that provide sectorial or radial coverage inthe proximity of a base station, chains of base stations (DECT relay) andtree-like arrangements of radio links, starting from the fixed network ac-cess point, are also expected to bridge the “last mile” between fixed net-works and customers in the local network area The same frequency bandused by cellular systems (e.g., with DECT) or public radio relay bands (e.g.,2.6/3.4/10/17/23/27/38 GHz) will be used
All the systems described above will place considerable and, in some cases,new demands on radio network planning, on the procedures for dynamic chan-nel allocation and on hierarchical cell structures, for which flexible solutionswill have to be sought In all probability, RLL technology will be developedand tested in Great Britain, and will then expand to the rest of Europe, withappropriate export opportunities to other continents
Wireless LAN, ETSI/HIPERLAN/1)
There is a considerable demand today for the wireless connection of (movable)workstation computers to provide flexibility in how and where equipment isinstalled in order to use standard Internet applications, which today are oftenaccessed over a local area network (LAN) Standardization has just producedsolutions that constitute the first fast step in this direction So-called single-hop solutions are currently possible; these tend to require the connection of
a base station to a fixed network (e.g., LAN) for each office room served
at the frequencies 2.4/5.3/40/60 GHz Further development is possible andnecessary to reduce the cabling required
Trang 131.1 Existing and New Networks and Services 13
Since these networks permit data transfer rates comparable to LANs ically up to 20 Mbit/s), they are more suitable for replacing LANs and lessappropriate for supporting new multimedia services These new services placereal-time demands on a transmission system that in principle cannot be sup-ported by the Internet, or at least not until considerable further developmenthas been carried out in this area Movable workstations along with mobileterminals can be supported In addition to radio, media such as infrared andvisible light are also being considered for wireless LANs Terminal mobility(or movability) is placing new demands on Internet protocols
(typ-Consequently, there is a considerable need for research and development
to evaluate and improve the mobile Internet protocol (mobile IP ) to be usedwith wireless systems It should be mentioned here that in the future Internetprotocols will increasingly be used from terminals to fixed and mobile radionetworks The work being carried out on mobile IP is also important for themobile radio networks discussed in Sections 1.1.1–1.1.3 (and to those whichfollow)
This area of application has recently been of special interest, and could beready for the introduction of wireless communications systems, because exist-ing wireline networks are usually proprietary solutions and users are demand-ing open communication architectures A major upheaval is imminent thatcould also create opportunities for open radio-based systems Certain indus-trial environments have special requirements for transmission techniques andprotocols that are not easily or readily accommodated by the systems thatexist in the other areas described in Sections 1.1.1–1.1.7
What will be characteristic of the new wireless communications systems
in process control is that standard PCs and LAN technology, supplemented
by wireless systems, will displace the current solutions based on programmed controllers (SPC) connected by so-called field-bus systems
The MoU UMTS (Memorandum of Understanding for the Introduction ofUMTS ) group promotes a revolutionary (non-evolutionary) approach to thefurther development of current systems, and their integration into existingsystems and networks is desirable, even if the technical implementation will
be costly The critical factor with current mobile communications systems isthe bit rate, which is not sufficient for the new applications of the future andshould be allocated flexibly as required UMTS was regarded by some peopleless as a totally new system but more as a further development of GSM Thecurrent development is deviating to some extent from that view in that atleast the radio interface will be designed newly, but a number of services kept
as they are (see Chapter 5)
Trang 1414 1 Introduction
Owing to the increasing introduction and growing use of broadband servicesover fibre optic networks based on ATM transmission technology (broadbandISDN) with transmission rates of 34 (E3), 155, 622 and 2400 Mbit/s, a broad-band option is required for connecting movable or mobile terminals, similar
to GSM/DCS 1800 to connect to the narrowband ISDN The current state
of technology enables the implementation of radio-supported, cellular mobilebroadband systems with 25 Mbit/s user data rates In contrast to the systemsmentioned in Section 1.1.4, these are real-time wireless ATM systems based
on ATM cell transmission that logically are most comparable to DECT lated to ISDN) As soon as ATM networks (with real-time capability) directlyconnect terminals, many of the Internet protocols that were developed forheterogeneous, error-prone non-real-time-capable networks and services willhave to be rethought
(re-It will take several more years of effort to resolve the problems that arisewhen wireless broadband systems are introduced in all the areas already men-tioned in Section 1.1.1 ETSI/BRAN has been developing W-ATM standardsfor RLL, radio LANs and cellular systems since 1996 The ATM Forum hasbeen developing protocols for mobility management in ATM networks alsosince 1996 (see Chapter 12) Carrier frequencies of 5.3/17/40/60 GHz arebeing planned because of the large frequency bandwidth required
Geostationary satellites are preferred for providing coverage to slowly movingstations (ships) because of the large receiving antennas required owing to highsignal attenuation Various groups of companies are planning global mobileradio networks on the basis of low (700–1700 km height, LEO, Low Earth Or-bit ) and medium–high (10000 km height, ICO, Intermediate Circular Orbit )flying satellites (see Tables 1.6 and 1.7) The aim is to guarantee radio cov-erage at 1.6 GHz for hand-portable satellite receivers (300 g) Although thesesystems are primarily geared to providing coverage to rural and suburbanareas, it is evident that plans exist to provide wide-area coverage with highcapacity, including areas that are also well supplied by ground-based cellularnetworks This means that, in addition to the efforts involved in the devel-opment and evaluation of these systems, issues concerning the cooperationwith terrestrial mobile radio and fixed networks will also have to be resolved.Handover procedures in hierarchical cell structures, from picocells to satelliteumbrella cells, will have to be developed (see Section 1.1.1)
In addition to the switching functions on board satellites for the connection
of mobile stations to a suitable ground base station, other problems still need
to be resolved, such as routing between mobile satellites and the control of theradio links between the satellites The IRIDIUM system is a first example ofthis Satellite networks, like terrestrial mobile radio networks, will endeavour