P921 d2 brochure

Project P921-PF

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Guidelines for the designof UMTS Access Networks Deliverable 2

GoalsThe main target of this work was todevelop recommendations and guide-lines for UMTS network design andimplementation. These guidelines andrecommendations are to support plan-ners and operators in designing andimplementing efficient UMTS networks.

Project P921

One of the fundamental characteristics ofCDMA systems implemented in UMTS is thatthe coverage range is intrinsically linked to thecapacity of the system: the more traffic iscarried by a cell, the smaller the coverage areaof the cell becomes. This phenomenon isknown as “cell breathing“, which shows theservice area of one base station with differenttraffic loads in the system. This dynamicbehaviour makes cell planning and networkdimensioning a very complex process.

Services, applications andQuality of ServiceUMTS is going to support a variety of servicesand applications, using both circuit and pack-et switched access. In the framework ofEURESCOM project P921 three kinds ofapplications have been selected for Quality ofService analysis: audio retrieval, MPEG-4 videodownload applications, and IP-based appli-

obtained by means of a link level simulator tocorrupt the application bit stream and toevaluate the degradation of the quality due tothe radio interface.

The results of the tests have shown a strongimpact of the UTRA interface on the Quality of

Cell coveragein UMTS

Application testing

SubjectiveTesting

ApplicationLink LevelSimulator

UTRAcharacter-

isation

Applicationperformance

Errorpatterns

QoS

cations (web browsing, ftp). The objective ofthe quality test was to assess the impact ofthe UTRA (UMTS Terrestrial Radio Access)interface on the selected applications. The testmethod applied was to use the error patterns

Service. For example, real time streamingof high quality music over UMTS requires ahighly protected channel, at least when theapplication is not using any error resiliencetools.

Cell breathing: left lower, right higher cell traffic

Traditional static prediction methods are notappropriate. Therefore simulation and statis-tical modelling techniques have to be used.However, the system is very complex, with somany interactions, that the simulation hasbeen split into two parts:

Link level, considering the effects of the radiochannel on individual bits transmitted in asingle communication. System level, considering a number of cellsand mobiles, based on output parametersfrom individual link simulations produced atlink level.

UTRAN characterisationUTRAN, the UMTS Terrestrial Radio AccessNetwork, operates in two modes, the UTRAFDD and the UTRA TDD mode. The UTRANlink level simulation results of P921 are givenfor the voice service, circuit switched dataservice (LCD, Long Constrained Delay) and forpacket switched data service (UDD Uncon-strained Delay Data) over the ETSI / ITUpropagation channels (vehicular A/B, outdoorto indoor A/B). The simulations includerealistic algorithms for closed loop powercontrol and pilot assisted channel estimation.For the up-link channel, the antenna diversitytechnique has been implemented by doublingthe Rake receiver structure and using an equalgain combiner before decoding. Voice servicewas simulated at 8 kbits/s, and LCD and UDDservices at 64, 144 and 384 kbits/s.

Link budgetand cell sizes

Resulting system working point for the 8 kbit/s voice serviceas a function of mobile speed and number of users per slot(downlink – Vehicular A channel)

8 usersper slot

4 usersper slot

Mobile speed [km/h]

System working point [Eb/No @ BER = 0,1 %]

The link budget is calculated by the followingprocedure:1. Uplink path loss evaluation 2. Downlink power level evaluation at cell

border 3. Downlink EIRP value evaluation per traffic

channel (Effective Isotropic Radiated Power– i.e. how much power you would be trans-mitting if transmitting in a perfect sphere)

4. Downlink power evaluation per trafficchannel

5. Downlink path loss evaluation

On the basis of the radio link results the UMTS(FDD component based on W-CDMA access)link budget has been evaluated for the case ofan urban environment. The cell radius of theUMTS system has been compared with theone of GSM 1800. The figure presents resultsfrom link level simulations: The coverage rangeof UMTS services in the urban environment as

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1 userper slot

a function of average power of the mobile sta-tion and offered service (70 % cell load). TheUMTS cell radius is compared to the cell radiusof a GSM 1800 system. It is worth noting thatin the GSM 1800 case the cell radius is notrelated to the system load. The results showthat, in the case of a voice service, the UMTS

cell radius is greater than the one of GSM1800. In contrast to this, the coverage in UMTSis smaller than in GSM 1800 systems for theother services.

UMTS speech

GSM 1800

Average power of the mobile station [dBm]

Cell radius [km]

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1,5

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Link-level simulation results

UMTS LCD384(Long ConstrainedDelay 384kb/s)

UMTS UDD480(UnconstrainedDelay Data 480kb/s)

The UMTS Radio Access Network is builtaround two new nodes and three new inter-faces (see the figure). The Node B is effec-tively a UMTS “base station“, while a RadioNetwork Controller (RNC) is comparable witha GSM Base Station Controller (BSC). Each

RNC is connected to the Core Network (bothpacket and circuit domains) by the Iu inter-face; RNCs are connected together with theIur interface. Each Node B is connected to anRNC by the Iub interface.There are some fun-damental limits on the numbers of cells andRNCs that can be supported, due to the way

UTRAN architecturethat cells and RNCs are identified – normallyby the number of bits in the identities, butsometimes hidden elsewhere in the protocoldefinitions. There is currently no restriction ofthe numbers of Nodes B in a Radio NetworkSubsystem (RNS) or PLMN.

UTRAN architectureAccording to standardisation the limits are asfollows:■ Maximum number of Cells in a PLMN

26,435,456 ■ Maximum number of RNCs in a PLMN

4,096■ Maximum number of Cells in an RNS

65,536■ Maximum number of Nodes B in an RNS

No limit defined in the standards■ Maximum number of Cells in a Node B

No limit currently defined in the standards

In practice, the maximum numbers supportedby the vendors will vary and are likely to belower than the absolute limit stated here.

Node B Node B

RNC

RNS

Iub

Iu

Node B Node B

RNC

RNS

Iub

Iu

Infrastructure sharingGiven the limited number of sites for new basestations, and the cost of errecting new masts,site sharing between 3G and GSM is likely tobe of importance, especially for existing

operators. In contrast to the mechanicalissues, there should be no problem with theco-location of W-CDMA and GSM900/1800sites. It should be possible to share the sameheadframe between GSM and UMTS, assum-ing there is sufficient space for the additional

antennas and feeders, and assuming thatthe structure is capable of withstanding theadditional wind load. This has to be deter-mined on a case by case basis.

Hierarchical cell structuresUMTS, as GSM, supports the deployment ofmicro cells within macro cells to provideincreased capacity in traffic hot spots andcoverage where previously none has existed.However, there is some concern that thelimited dynamic range of the terminal power as

specified in UMTS will result in a minimumobtainable cell radius, which is accentuatedwhen good line of sight is achieved. There isalso some doubt about the suitability of thecurrently specified soft handover mechanismfor use in contiguous micro-cellular coverageareas. Therefore it could be that micro cellscannot be designed to perform optimally until

equipment designed to a later release of thestandards is available. These issues requirefurther investigation. There are two options forthe choice of carrier for micro cells:■ Same carrier for micro/macro cells■ Different carriers for micro/macro cells

The UTRAN will support six sectored sites,which could maximise coverage and capacityof UMTS sites. The basic principle is that byusing six narrow beam antennas, the coveragearea of a cell will be extended due to theincreased forward gain, and the capacity willbe double that of a three-sectored cell. Theuse of six sectors can lead to an increase inthe coverage area that is served by multiplecells (i.e. the soft handover region), depend-ing on the local propagation conditions andthe antenna pattern. The two figures show theoverlap between the antenna patterns. Thisdoes not match the soft handover regions, butit shows, how the overlap can increase, givencertain antenna beamwidths.

Increasing the coverage area3 sectors – 900 beamwidth (left) compared to 6 sectors –600 beamwidth (right)

Iur

Project Members

Name Company Email

Josef Noll (Project Leader) Telenor [email protected] Harris BT [email protected]

Milan Jankovic Community of Yugoslav PTT [email protected]

Borislav Odadzic [email protected]

Armando Annunziato CSELT – Telecom Italia Group [email protected]

Enrico Buracchini [email protected]

Bruno Melis [email protected]

Anne-Gaële Acx France Télécom [email protected]

Jean-Francois Chaumet [email protected]

Nicolas Guerin [email protected]

Georgos Agapiou OTE [email protected]

Dimitrios Xenikos [email protected]

Amparo Sanmateu T-Nova [email protected]

Ignacio Berberabana Telefónica I+D [email protected]

Héctor González [email protected]

Fernando Martinez [email protected]

Jorge Montero [email protected]

Arild Jacobsen Telenor [email protected]

Tor Jansen [email protected]

Tore Arthur Worren [email protected]

Uwe Herzog (Project Supervisor) EURESCOM [email protected]

The Project team:

About P921EURESCOM Project P921-PF started on23 February 1999 with a planned duration of18 months. The total budget was 100 MM.Additional information can be obtained from:

http://www.eurescom.de/public/projects/P900-series/p921/P921.htm

Publications resulting from this work:

■ The number of services in a UMTS systemis substantially higher compared to GSM,which makes the network design morecomplex. Packet switched mode allows cost-effective transport of data, but requires QoScontrol. Some applications such as voice orreal-time video require throughput with aguaranteed data rate and maximum delay.Mobile communication applications have tobe designed according to the user mobility,the radio environment (user speed andcoverage radius), the application topology,and the user terminal requirements.Current applications content, e.g. JPEG,does not allow missing data.

■ UMTS radio interface has a strong impacton the QoS of applications, requiring anerror-resistant mechanism to obtain therequired QoS level. In a CDMA network

Conclusionscoverage is intrinsically linked to thecapacity of the system. Cells are breathing;the coverage range for voice varies between200 m and 1.4 km, depending on thenumber of users. Traditional static predic-tion methods for network planning are notapplicable.

■ Two link level simulators (W-CDMA and TD-CDMA) have been developed in the projectto evaluate the radio performance of UTRA.The main outcome of link level simulationsis the system working point, the minimumEb/No (ratio between energy per bit andnoise). Voice services have an almostconstant system working point with respectto the mobile speed in the range of 3-250 km/h. Data services (LCD & UDD)are more sensitive to the mobile speed andto the propagation environment. The link

performance of the TDD mode is more influ-enced by the mobile speed than the FDDmode. For the voice service, the UMTS cellradius is greater than the GSM 1800 one.Data services with data rates higher than384 kbit/s have a lower cell radius com-pared to GSM 1800.

■ The Project has reviewed available systemlevel simulators, and established scenariosfor system level simulations. A future pro-ject is envisaged to analyse these scenarios.

A more detailed version of this deliverable isavailable at:

http://www.eurescom.de/public/projects/P900-series/p921/P921.htm

1. D. Wake and R. E. Schuh, IEE ElectronicsLetters, vol. 36, no. 10, pp. 901-902, 2000.

2. D. Wake and R. E. Schuh, Technical Digest,International Topical Meeting on MicrowavePhotonics – MWP’99, Post deadline paper,Session F-12, pp. 9-12, ISBN 0-7803-5558-X, Melbourne, Australia, November 17 – 19,1999.

3. Ralf E. Schuh and David Wake, Proceedings,IEEE International Conference on ThirdGeneration Wireless Communications, IEEE3g Wireless'2000, San Francisco, SiliconValley, USA, ISSN No. 1529-2592 (2000),pp. 48 – 51, June 14 - 16, 2000

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EURESCOM GmbHSchloss-Wolfsbrunnenweg 35D-69118 Heidelberg, GermanyTel.: +49 6221 989 - 0 Fax: +49 6221 989 - 209http://www.eurescom.dee-mail: [email protected]

EURESCOM is the European institute for col-laborative research and strategic studies in allareas of telecommunications. Currently thereare 24 Operators from 23 European countriesparticipating in EURESCOM.

It acts as technical forum for sharing visionsand concepts, as an initiator of targeted activ-ities, and as facilitator for common under-takings on technical issues.

EURESCOM is open to any European NetworkOperator or Service Provider who may wishto join.

What is EURESCOM?

P921 d2 brochure

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