Tài liệu Điện thoại di động mạng lưới Radio P5 ppt

Networks Core TransportUIM: User Identification Module Services MBS CATV WAN LAN Application Network Domain Core Transports Domain Equipment Terminal UMTS B-ISDN ISDN S-PCN DECT Networks

Dramatic developments have been taking place in the mobile radio area allover the world during the last couple of decades Mobile communications isone of the fastest growing markets in the telecommunications area According

to projections, there will be a linear increase in the number of subscribers tothe major GSM networks operated in Europe by the end of the decade.The political environment in Europe is the main reason for the rapid devel-opment Without a free exchange of information, the concept of an internalmarket striving for a free flow of goods between EU states would be inconceiv-able This was the line of thinking behind the liberalization and deregulation

of the telecommunications industry, which promoted and accelerated tition and opened up the markets

compe-Another reason for this rapid development is the advances being made

in the microelectronics, microprocessor and transmission technology areas.These advances are enabling the use of ever smaller terminal equipment, withcomputing power previously only possible with mainframes, and with lowpower consumption—factors that have improved customer acceptance

In Europe the development of uniform standards, the introduction of pean-wide radio systems and the participation of industry in the standardiza-tion process through the establishment of ETSI have further contributed tothe widespread success of mobile communications

Euro-The chronological development of different kinds of mobile radio networkswhich conform to different user needs is presented in Figure 1.2 [23]

The systems that fall into the category of first-generation mobile nications systems in which mobility is only ensured within a specific networkarea are the different analogue cellular systems (e.g., C-Netz, NMT), cordlesssystems (CT1/CT2) and various national paging systems

commu-The second generation includes the digital systems such as GSM, DCS

1800, USDC, PDC, IS-95 and ERMES, which underwent further developmentand were expanded or were first introduced during the first half of the 1990s.Along with these public cellular systems that provide PSTN/ISDN ser-vices at a mobile terminal, there are other systems that fall into the second-generation or the transitional category between the second and third gen-erations, and cater specifically to mobile or moving applications These in-clude trunked radio (ETSI/TETRA, see Section 6.3), cordless communica-

∗ With the collaboration of Arndt Kadelka, Matthias Lott and Peter Seidenberg

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)

Networks Core Transport

UIM: User Identification Module

Services

MBS CATV WAN LAN

Application

Network Domain Core Transports Domain

Equipment

Terminal

UMTS B-ISDN ISDN S-PCN DECT

Networks Access

Access Network Domain

Figure 5.1: Global multimedia mobility architecture

tions (ETSI/DECT, see Chapter 9, and the Personal Handyphone System,PHS, see Chapter 11), local broadband communications (ETSI/HIPERLAN

1, see Section 13.1, IEEE 802.11, see Section 13.9), wireless ATM systems(ETSI/BRAN, see Section 12.1.5), mobile personal satellite radio (IRIDIUM,Globalstar, see Chapter 14) and other systems integrating aspects of thesesystems

Third-generation mobile radio systems, which use intelligent networks toincorporate public mobile radio services that previously were operated sep-arately, are already being developed today Under the designation GlobalMultimedia Mobility (GMM), ETSI is developing an architecture that definesmobile radio networks as the access networks to an integral transport plat-form that is based on broadband (B)-ISDN and provides mobility-supportedvalue-added services (see Figure 5.1) It is planned that these future standardmobile communications networks (UMTS and FPLMTS or IMT 2000), whichaim to support the services of the terrestrial broadband ISDN, will lead to

a universal worldwide public mobile radio system, which is expected to beoperational by the year 2003

The main characteristics of third-generation mobile radio systems are [1]:

5.1 UMTS (Universal Mobile Telecommunications System) 323

• Support of all features currently being offered by different systems

• Support of new services with high quality of service, the same as in thefixed network

• High capacity, which will support high market penetration

• High spectral efficiency

• Lightweight, small (pocket-sized) and inexpensive handheld equipmentfor mobile telephone use

• High security, comparable to that of the fixed network

High demands are being placed on the third-generation systems, e.g.:

• Services (voice and data, teleservices, bearer services, supplementaryservices)

• Different bit rates (low bit rates for voice; data rates up to 2 Mbit/s)

• Variable bit rates and packet-oriented services

• Use of different sized cells (macro, micro, pico) for indoor and outdoorapplications, with seamless handover between indoor and outdoor basestations

• Operation in non-synchronous base station subsystems

• Advanced mobility characteristics (UPT, see Chapter 15; roaming, dover, etc.)

han-• Flexible frequency management

• Flexible management of radio resources

Telecommunications System)

In Europe work continues to be carried out on the development of a generation mobile radio system called UMTS (Universal Mobile Telecommuni-cations System) in the EU programmes RACE (1989–1994) (Research and De-velopment in Advanced Communications Technologies in Europe) and ACTS(1995–1998) (Advanced Communication Technologies and Services) in coop-eration with ETSI Work on UMTS is also being done in COST (EuropeanCooperation in the Field of Scientific and Technical Research) projects [20].The technical subcommittee (STC) SMG 5 at ETSI has been given theresponsibility for producing the UMTS standard Other SMG subcommit-tees that are currently still working on the GSM 2+ standard will eventually

third-become involved in the standardization of UMTS, e.g., SMG 2 SMG 5 willthen take over the creation of the UMTS standard and the coordination ofthe standardization activities There is also the UMTS Forum, comprisingthe European signatories to the UMTS–Memorandum of Understanding ofthe Introduction of UMTS defined in 1996.

The main tasks of SMG 5 are [2, 15]:

• Study and definition of services, system architecture, the air interfaceand the network interfaces for UMTS

• Generation of basic technical documentation for UMTS

• Coordination of ETSI and of SMG regarding UMTS

• Cooperation and coordination with the ITU for the definition of a wide standard on the basis of UMTS/FPLMTS/IMT 2000

world-• Cooperation with European research programmes

The aim of the UMTS concept is to provide users with a handheld terminalthat will cover all areas of application—at home, in the office, en route bycar, in a train, in an aircraft and as a pedestrian UMTS will therefore offer

a common air interface that will cover all fields of application and have theflexibility to integrate worldwide the different mobile communications systemsavailable today, such as mobile telephone and telepoint, trunked radio, dataradio, and satellite radio systems, into one system

What will play an important role in UMTS is the concept of intelligentnetworks (IN) that will provide call charging and mobility management for thelocalization and routing of calls across networks operated by different serviceproviders and operators UMTS will be the first system to offer mobile usersroaming during an existing connection, with handover between networks withdifferent applications and different operators [17]

UMTS will offer transmission capacity comparable to ISDN for servicessuch as video telephony and wideband connections, and will support the ser-vice concept Universal Personal Telecommunications (UPT) [4]; see Chap-ter 15 With UMTS it will be possible to transmit voice, text, data andimages over one connection, and subscribers will be assigned a personal tele-phone number that will allow them to be reached anytime, anywhere in theworld

The first series of standards for UMTS has been completed in March 1999.The projection is that UMTS, which according to Appendix D will use thefrequency band between 1.885 and 2.2 GHz, will be introduced around 2003.However, the UMTS Forum has a preference for the frequencies indicated

in Figure 5.2, staggered timewise as shown, and is promoting the refarming

of bands previously used for other purposes (see Appendix D) and workingtowards including asymmetrical bands along with the symmetrical ones Theplanned frequency allocations to IMT 2000/UMTS are shown in Figure 5.3

5.1 UMTS (Universal Mobile Telecommunications System) 325

300-500 MHz

UMTS Core Band

2025 MHz 2000

MSS

MSS

IMT-2000 UMTS IMT-2000

PCS IMT-2000

MSS MSS

MSS IMT-2000

UMTS MSS GSM 1800

Figure 5.3: Spectrum Allocation

Originally it was planned to specify one air interface only able to cover allthe different services and applications aimed at From the decision made inJanuary 1998 (see Section 5.7.5), it is now clear that at least two air interfaceswill be specified—one based on paired bands with frequency division duplexing(FDD) transmission, and another air interface operating in a single band withtime division duplexing (TDD) transmission

Both standards will use DS-CDMA for radio transmission and channelaccess, and are addressed as FDD-CDMA and TDD-CDMA systems respec-tively From the viewpoint of intellectual property right (IPR), there are stillthose in Europe proposing to stay with F/TDMA as the basis for UMTS and

to make no use of CDMA, since QUALCOMM is the owner of some CDMAkey patents but is not willing to license their use under the so-called fair rules

established by ETSI In fact, the EDGE proposal (see Section 3.11) submitted

by Ericsson to ITU-R is capable of providing wideband services compatible

to GSM 2+

The main driving force towards UMTS at present comes from ers aiming to introduce new products into the market and operators aiming toget under the label UMTS access to more bandwidth for voice services only.Mobile data was still only a few percent of business in 1998 The EuropeanCommission has issued guidelines for the licensing of UMTS bands to opera-tors demanding that 50 % of the services offered should be data services formultimedia applications

manufactur-The demand for more bandwidth can of course easily be covered by ing UMTS frequency bands to be used by GSM networks, and does not needthe introduction of a new air interface

Telephone System); IMT 2000 (International Mobile Communications at 2000 MHz)

In 1985 the CCIR (see Annex B.1.2) set up a working group, the Task Group8/1 (previously IWP 8/13), for the purpose of specifiying all the requirementsand system parameters for a future public land mobile telecommunicationsystem (FPLMTS) The following requirements for an FPLMTS were drawn

up by the working group [5, 13, 19]:

• Small, lightweight handheld equipment

• Worldwide use of terminal equipment, i.e., uniform frequencies wide

world-• Integration of different mobile radio systems and international roaming

• Integration into the fixed telephone networks (ISDN compatibility)

• Integration of mobile satellite radio

• Use of terminal equipment on land, in the air and at sea

As with the UMTS, the aim with the FPLMTS is to integrate all existingservices (mobile telephony, cordless telephony, paging, trunked radio, etc.)into one service Many of the aspects of FPLMTS are the same as those ofUMTS; however, since the ITU activities are globally based, there are somedifferences between the two systems For example, FPLMTS defines severalair interfaces for dealing with the different requirements of densely populatedareas (e.g., in Europe) versus sparsely populated areas (third world countries)[22]:

5.3 Services for UMTS and IMT 2000 327

• R1: radio interface between mobile station (MS) and base station (BS)

• R2: radio interface between personal station (PS) and personal basestation

• R3: radio interface between satellite base station and mobile earth tion (MES)

sta-• R4: additional air interface for paging FPLMTS terminals

The plan is to use FPLMTS as a temporary or permanent substitute forfixed networks in developing countries and in rural areas where it is not eco-nomically feasible to set up fixed networks

At W(A)RC 1992 a spectrum of 230 MHz in the frequency bands 1885–

2025 MHz and 2110–2200 MHz was allocated to the FPLMTS system wide These frequency bands were not exclusively reserved for FPLMTS, andcan also be used in other systems So in Europe, for example, the lower part ofthe allocated frequency band is occupied by GSM 1800 and the DECT system.The UMTS Forum is now requesting that 500 MHz starting from 1900 MHz

world-be reserved for symmetrical and asymmetrical connections (see Figure 5.2).The earliest date being envisaged for the operation of FPLMTS is sometimebetween 2000 and 2005, the same as for UMTS Since about 1995, FPLMTShas often been referred to as IMT 2000, but both designations refer to thesame system operating around 2000 MHz

ETSI has published a preliminary list of services [10] that are to be supported

by UMTS and are based on the ITU-R/CCIR recommendations for FPLMTSand the specifications of various European research projects of the RACE 2programme These UMTS-supported services are described below

– 3.1, 5 and 7 kHz audio transmission

– Alternative voice or transparent data transmission with user datarates of 8, 16, 32 and 64 kbit/s

(so-Interactive services fall into the category of conversational services, messageservices or interrogation services Conversational services are implementedthrough end-to-end connections, which can be either symmetrical bidirec-tional, asymmetrical bidirectional or unidirectional Message services offercommunication between users that is not time transparent Interrogation ser-vices are used for the inquiry and receipt of centrally stored data.

With distribution services information can be transmitted continuouslyfrom one central location to any number of users, with the users unable toinfluence the start or the end of a transmission Another distribution serviceoffers users the possibility of influencing the start of the information trans-mission

Asynchronous Transfer Mode (ATM) was specified by ETSI as the mission technology for these B-ISDN services in the fixed (core) networks Inorder to derive requirements for the radio interface from the bearer servicesbeing supported, ETSI, in accordance with the functional descriptions of B-ISDN and the ATM adaptation layer (AAL) (see Section 12.2.4), divided thebearer services into four classes [11] These four classes of bearer servicesdiffer from each other in their time responses, bit rates and types of con-nection Maximum bit ratio, maximum bit-error probability and maximumdelay time are specified within each class of bearer service for the differentcommunication scenarios

trans-5.3.2 Teleservices

The teleservices to be supported by UMTS are divided into three classes [10]:

1 Teleservices that already exist in the fixed network in accordance withITU-T/CCITT recommendations of the E, F and I series:

• Telephony:

– Voice

– Inband facsimile

(tele-fax groups 2 and 3)– Inband data trans-

mission (using modem)

• Teleconferencing:

– Multiparty, added valueservices

– Group calls– Acknowleged group calls– Multiple calls

5.3 Services for UMTS and IMT 2000 329

2 UMTS teleservices and applications, e.g.:

• Audio and video

• Teleaction services (e.g.,remote control)

• Mobility services (e.g.,

to use more than one of these media at the same time Multimedia allowsthe transmission of more than one type of information, e.g., video andaudio information No further specifications exist yet for this service[10]

In the standardization of supplementary services a differentiation has cipally been made between traditional non-interactive PSTN/ISDN servicesand personalized interactive supplementary services The service provider hasthe option of making these services accessible to user groups or to individualusers The following classes of supplementary services have been proposed inaccordance with the GSM and ISDN standards:

prin-Number identification, e.g., abbreviated dialling, protection against able calls, calling party identification

undesir-Call offering, e.g., call forwarding

Call termination, e.g., call holding

Multiparty communication, e.g., conference call

Group communication, e.g., communication in closed user groups

Billing, e.g., credit balance

Additional information, e.g., user-to-user signalling

Call rejection, e.g., blocking all incoming calls

A list of different service attributes is available in [10]

Bandwidth-on-Demand This offers an efficient use of resources for servicesthat have heavily varying requirements for transmission bandwidth, such

as short-message services and video Furthermore it allows users theindependent option of selecting between a higher bandwidth for a max-imum quality of service or a lower bandwidth for more favourable costs

• Maximum bit-error ratio based on channel decoding

• Maximum delay allowed in data transmission

The net bit rate is the product of the average number of bits that have to

be transmitted within a certain period of time

The delay parameter describes how long a waiting time is allowed in thetransmission of these bits For example, a voice service requires a small delaywhereas a packet-data transmission has minimal requirements for the delaytimes of individual packets However, data transfer requires a considerablylower bit-error ratio than a voice service, because the redundancy of the voicecodec can be fully utilized A higher coding factor is needed for achieving a

5.3 Services for UMTS and IMT 2000 331

Table 5.1: Quality of service parameters

The usage level parameter describes how often a connection is being used

to transmit data For example, the usage level of a voice service is less than0.5 because a user is generally either listening or speaking

A service is also defined by its symmetry This value determines whichbandwidth is required for a connection in one or the other direction The voiceservice is an example of a symmetrical service, because the same bandwidth isused for both speaking and listening Internet browsing (e.g., world wide web,WWW) is a typical example of an asymmetrical service, because it requiresconsiderably less bandwidth for requesting than for receiving data Table 5.1lists the characteristics of some of the services

5.3.6 Service-Specific Traffic Load

The effective service bandwidth can be calculated from the data of the vice parameters net bit rate, symmetry and coding factor [12] The servicebandwidth describes the bandwidth used to provide a particular service.The traffic generated by the use of a service is calculated by taking theaverage duration of this usage and the frequency of usage The effective call

ser-duration Tef f, which is calculated on the basis of the usage level N and theaverage call duration Tcall, is produced as

For the systems being planned, the frequency of usage of a service canonly be estimated It is measured in BHCA (busy hour call attempts), andindicates the average frequency of the usage of a service by a user during thepeak traffic hour

If it is known which portion of the overall usage of services is an ual service then it is possible to calculate the effective bandwidth needed by

individ-a user The shindivid-are of the service in the overindivid-all usindivid-age is then indicindivid-ated withthe penetration D The penetration varies with different operating environ-ments (see Section 5.5.1) The traffic produced by a user utilizing a service iscalculated in Equivalent Telephony Erlang (ETE) [12]:

transmis-to the form of symmetry For example, with the telephony services data istransmitted in both directions, whereas with the facsimile service it is mainly

in one direction

5.3.6.1 Voice Telephony

Voice telephony is a symmetrical service with a usage level of 0.5 or less Thenet bit rate of the voice codec is 16 kbit/s Since the requirements for biterror ratio are low, a coding factor of 1.75 is sufficient For the average callduration 120 s is assumed This equates to an effective service bandwidth of

56 kbit/s and an effective call duration of 60 s (see Table 5.2)

The estimated values for penetration D and for the frequency of calls during

a busy hour produce the ETE/user values shown in Table 5.3 for the voiceservice in different communications environments (see Section 5.5.1)

5.3.6.2 Video Telephony

Video telephony is a symmetric service and has a usage level of one, i.e.,transmission is always in both directions of a connection The effective servicebandwidth for the video telephony service is 384 kbit/s and the effective callduration 2 min (see Table 5.2)

The estimated values for the penetration D and for the BHCA produce theETE/user values in Table 5.4 for different communications environments

5.3 Services for UMTS and IMT 2000 333

Table 5.2: Service bandwidth and effective call duration of some services

Voice telephony Video telephony Fax service

Table 5.3: Calculation of traffic load for voice telephony

Table 5.4: Calculation of traffic load for video telephony

fac-The estimated values for penetration D and for BHCA produce theETE/user values in Table 5.5 for different communications environments.5.3.6.4 Resultant Overall Traffic Loads

The procedures presented in the sections above can be used to calculate thetraffic generated by a user in each of the services listed Table 5.6 gives thetotal traffic generated by a user in the different communications environments

Table 5.5: Calculation of traffic load for facsimile services

Table 5.6: Resulting total traffic loads

Business use indoors 4.10· 10−2 4.92· 10−2 180000 8.85· 103

Local high bit rate 4.10· 10−2 4.92· 10−2 108000 8.85· 103

(see Section 5.5.1) If a specific user density is assumed for each tions environment [10] then it is always possible to arrive at a value for thetraffic load

communica-This traffic load describes in ETEs the traffic originating from an area.The requirement for frequency spectrum can be calculated if an assumption

is made on the efficiency of the radio interface (see Section 5.4)

This section presents the UMTS Forum assessments on the frequency trum required for UMTS [12] They are based on estimates of market pene-tration, future user density, service characteristics and characteristics of theradio interface

spec-In determining the bandwidth needs the UMTS Forum makes its tions based on the breakdown of different categories of service shown in Fig-ure 5.4 In addition, assumptions are made on anticipated user numbers inrelationship to the communications environment The figures for the year

assump-2010 are given in Table 5.7

The service characteristics compiled in Table 5.8 are also taken into count, with a 16 kbit/s voice codec assumed The voice service is a symmet-

ac-5.4 Frequency Spectrum for UMTS 335

Figure 5.4: Anticipated service spectrum for UMTS

Table 5.7: User density in the year 2010

rical service with the same transmission rates on the uplink and the link Simple message services are those services that are similar to the SMS(Short-Message Service) in GSM The asymmetric multimedia services (MM)represent typical Internet services (WWW using the http protocol), whereasthe interactive multimedia service represents a symmetrical connection such

down-as is required for video conferencing

Together with the ratio of the average number of active users to the overallnumber, measured during the busy hour (see Table 5.9), the bandwidth re-quirements for UMTS can be calculated from the information supplied in theservice characteristics and user density (see Table 5.10)

The projected bandwidth requirements for each service for the years 2005and 2010 are presented in Figure 5.5

The maximum requirement for bandwidth projected for the year 2010 is

554 MHz for traffic bands and 28 MHz for guard bands The basic standardsfor UMTS have been completed in March 1999, and UMTS itself is expected

to be introduced in about 2003 The UMTS Forum has a preference forthe frequencies given in Figure 5.2, staggered timewise as shown, with bands

Table 5.8: Overview of service characteristics

previously used for other purposes set aside for refarming, and is aiming tohave asymmetrical as well as symmetrical bands

The need for frequency spectrum in individual countries can vary ing on population density and economic development The UMTS Forum isinitially planning the use of a so-called core band Since UMTS is being inter-preted as a third-generation system within the IMT 2000 family, either part

depend-or all of the cdepend-ore band is to be available fdepend-or UMTS/IMT 2000 wdepend-orldwide Thisband is therefore earmarked for mobile applications The 1900–1980 MHz and2010–2015 MHz as well as the 2110–2170 MHz bands are being provided forterrestrial applications The 1980–2010 MHz and 2170–2200 MHz bands are

to be used for satellite-supported applications

for a defined quality of service within a specific frequency band in a definedgeographically restricted area [11] Finally, the radio interface is measured onthe basis of how cost-efficiently a bearer service can be provided Along withthe efficient use of the frequency band, this includes a consideration of thetechnical difficulty involved in implementing the proposed concepts.

Sometimes it can take more than a radio interface to provide the requiredrange of services for all possible environments In this case the different in-terfaces should be as similar as possible

Mobile data terminals play a big role in the development of a radio interface,because it is assumed that they will constitute the most commonly used type ofdata terminal The radio interface should allow the cost-effective developmentand production of small and lightweight portable terminals that, with littleeffort, offer a large range and long operating times Basically these factors aredetermined by transmitter power, radio resource management and signallingrequirements

Another prerequisite of the radio interface is that it enables the networkinfrastructure to be set up and maintained as well as developed and producedcost-effectively The possibility of maintaining very small and very large cellsshould be considered in this context

The radio interface should also be flexible enough so that different levels

of coverage can be realized Along with wide-area coverage, it should also bepossible to supply coverage to regionally restricted areas

The radio interface is defined by the bearer services that are to be provided(see Section 5.3) It should ensure that future teleservices and supplementaryservices and new techniques for improving quality of service can be introduced

In principle, the network capacity should be adequate to provide differentlevels of quality of service Therefore any evaluation of proposals for a radiointerface must take into account the different multiple-access procedures withtheir specific transmission delays and interference characteristics as well asthe performance of the proposed handover and power control protocols

5.5 Demands on the Radio Interface 339

Table 5.11: Different communications environments [11]

outdoors

bit rate

mobile BS

Table 5.12: Relative speeds [km/h]

tain amount of data loss, whereas the data service requires a high level ofprotection against bit errors but accepts a slower handover speed.

The protocols of the UMTS radio interface are to fulfil the following ments [11]:

require-• Support a broad spectrum of services and operating environments

• Conform with the ISO/OSI model

• Develop maximum communality among different radio interfaces acrossthe protocol stack

• Provide efficient exchange of information between entities

• Support different multiple-access procedures, in particular CDMA,TDMA, FDMA and hybrid methods

• Consider new types of radio technologies, such as packet-data sion, dynamic adaptation of the interface parameters, soft handovers

transmis-• Support service-specific response times through the protocols

• Carry out signalling over the radio interface

• Provide parameterizable protocols to allow new characteristics of theradio interface to be implemented through modification of the protocolparameters

The protocol stack for the radio interface for UMTS should also includeprotocols of the so-called UMTS adaptation layer, which should be imbeddedabove the network layer This adaptation layer should map the teleservices tothe UMTS bearer services Since this functionality depends on the respectivebearer service, a separate protocol stack must be available for the adaptationlayer for each bearer service

UMTS has two different air interfaces, both of which rely on wideband mission with a bandwidth of 4.4–5 MHz per frequency channel A charac-teristic of mobile radio channels is that they are time-selective as well asfrequency-selective A statistical change to the channel parameters causes thereceived signal to experience fading at certain time intervals, which in turncauses transmission errors, thereby necessitating the use of effective channelcoding procedures Frequency-selectivity causes strong linear distortion of

trans-5.6 Basics of the UMTS Radio Interfaces 341

the receive signal, which must be offset by equalizers The effects of selectivity increase as the bandwidth narrows, whereas those of frequency-selectivity decrease because the bandwidth of a signal is inversely proportional

time-to the symbol duration

A compromise must therefore be found between coding and equalizing quirements, i.e., between bandwidth and symbol rate, when radio interfacesare designed Furthermore, appropriate procedures for multiple access andprotocols for power control and handover must be developed The high datarates demanded by the third generation of mobile radio systems require largebandwidths up to 2 Mbit/s Thus the effectiveness of these proposals is alsodetermined by how efficiently low transmission rates, e.g., for the voice ser-vice, are integrated Services with different rates in different environmentsshould be realized with the same radio interface

re-Depending on the duplexing method (FDD or TDD), two different multipleaccess schemes are defined as shown in Figures 5.9 and 5.12 Both operatingmodes have a common structure in the frequency and time domain, with acarrier spacing between 4.4 MHz and 5.0 MHz and a frame duration of 10 ms.Each frame is split into 16 slots, each 0.652 ms in length A super-framecorresponds to 72 consecutive frames The physical channels are subdividedinto dedicated physical (DPCH) and common physical (CPCH) channels

Code-Division-Multiple-Access (CDMA) is based on a separation of mission channels through codes A characteristic of this technique is that thenarrowband radio signal is transmitted in a wide frequency spectrum in whichthe narrowband signal is spread to a wideband signal through one code of a(pseudo) orthogonal codes family

trans-Each user of the radio communications system is assigned an appropriatespreading code, which is used to spread the signal spectrum being transmittedinto a multiple of its original bandwidth The signals obtained in this way arethen sent by the transmitters simultaneously in the same frequency band.The coding instructions used by the transmitters must be selected in such

a way that the interference experienced by the receivers is minimal despitethe simultaneous transmission The use of an orthogonal Pseudo-noise code(PN code) for carrier modulation of the information being transmitted meetsthis requirement; see Section 2.6.4

The receiver, which must know the spreading rules applied by the mitter, searches for the wideband signal according to the bit pattern of the

trans-PN sequence of the transmitter By setting up the autocorrelation function(ACF), the receiver is able to synchronize with the coding channel of thetransmitter and despread the signal to its original bandwidth The respectivesignals of the other transmitters whose codes do not agree with the selected

PN sequence are not despread back to the original bandwidth, and