HSDPA demystiﬁed Simplifying core networks WLAN and ...download.iop.org/we/we_01_38.pdf · ISSUE...

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J U N E / J U LY 2 0 0 5

HSDPA demystified Simplifying core networks WLAN and cellular unite

Measuring voice quality where it counts

http://wireless.iop.org

http://www.ti.com/3g

U P F R O N T 6

N E W S 7

L E A D E R 8

A N A LY S I S 11Testing: First impressions are crucialOptimization: Coverage benefits from definitionHealth & Safety: Landlords must take responsibility

O P I N I O N 17Mark PaxmanThe industry must beware of stealth IP, which could unravel the tightest standard.

H S D PA 18HSDPA introduces new level of complexity to 3GHSDPA brings significant changes to the W-CDMAair interface. Marta Iglesias makes sense of the myriad new channels and protocols.

M U LT I M O D E 2 3Multimode terminals link cellular and WLAN servicesCreating a terminal that can roam effortlessly betweencellular and WLAN networks is a challengingproposition for both hardware and software.

C O R E N E T W O R K S 2 7Networks are dying a death of complexityAging hardware and inaccessible customer data are stalling the roll-out of new wireless services. But there’s a simpler approach that puts the subscriber at the centre of the network.

D R I V E T E S T I N G 2 9Voice quality must be measured where it countsDespite spending large sums of money on networktesting, operators are failing to measure the quality of service experienced by subscribers.

P R O D U C T S 3 2Handset components Infrastructure

T H E F U T U R E 3 4CMOS brings Moore’s Law to RFSilicon Laboratories’ vice-president of wirelessproducts Dan Rabinovitsj explains why he ispassionate about CMOS RF.

3C O N T E N T S

JUNE/JULY 2005ISSUE 39

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Standardized servers reduce complexity. p27.

What does ‘coverage’ actually mean? p14.

Ericsson and ZTE team up on TD-SCDMA. p6.

On the cover:Voice quality shouldbe tested in the field,where it reallymatters to users.p29.


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6 U P F R O N T

J u n e / J u l y 2 0 0 5 wire less. iop.org w i r e l e s s e u r o p e

Analog Devices and DatangMobile have completed a refer-ence design for handsets that sup-port TD-SCDMA – the Chinese3G standard. Although neitherChina, nor any other country, hasissued TD-SCDMA licences,momentum is growing in thecommercialization of handset andinfrastructure equipment.

Datang’s vice president SunYuwang suggested that the refer-ence design will speed the grantingof TD-SCDMA licences “by help-ing to eliminate the obstacle ofinsufficient handset availability.”

Analog’s Doug Grant told

Wireless Europe he is “as confi-dent as you can be that TD-SCDMA will be used [in China].Interest in TD-SCDMA is grow-ing among handset makers.” Hebelieves China’s version of lowchip rate TD-SCDMA, “couldbe used in unpaired spectrum inother parts of the world, but itmust succeed in China first”.

Called DTivy, the referencedesign is based on hardware fromUS-based chipmaker AnalogDevices and software fromChina’s Datang Mobile. Datangis a key developer and proponentof TD-SCDMA technology.

Analog and Datang boost TD-SCDMA

Analog Devices’s Doug Grant is confidentabout the future of TD-SCDMA.

ZTE and Ericsson have joinedforces to supply TD-SCDMAinfrastructure equipment for theChinese market. Ericsson willoffer China-based ZTE’s TD-SCDMA base transceiver station(or node-b) as part of its radioaccess network. The two compa-nies will also participate in TD-SCDMA trials in China.

Mats Olsson, president ofEricsson Greater China, said theagreement will make the com-pany “very well positioned to cap-ture the huge opportunitiespresented by China’s fast-growingmobile market”. Xie Daxiong,general manager of ZTE’s mobiledivision said that thanks to theEricsson deal, “ZTE has all thenecessary resources in place topromote our TD-SCDMA solu-tions for the world”.

The partnership coincideswith ZTE’s launch of a range ofcommercial TD-SCDMA infra-structure equipment. In additionto the node-b, ZTE has alsolaunched TD-SCDMA core-network equipment and a radionetwork controller. TD-SCDMAis a 3G standard that is expectedto be licensed for use in China.

In a separate move, Ericssonwill establish a TD-SCDMAresearch and development centrein Nanjing, China. The centre isexpected to employ 50 researchstaff. Dan Redin, Ericsson’s chieftechnology officer for GreaterChina, described the develop-ment as “one more step forwardin addressing the specific needsof the local market”.

This sudden flurry of TD-SCDMA activity by Ericsson

suggests that the Swedish equip-ment maker believes that Chinawill grant wide-scale licences forTD-SCDMA when it issues 3Glicences sometime in the future.

In-building systemssales will experiencesteady growthThe installation of in-buildingcellular infrastructure will “expe-rience stable and steady growthover the next five years”, saidLance Wilson of ABI Research.However, he cautioned that theindustry should not expect dou-ble-digit growth in this sector,which will track the overallexpansion of the 3G market.

“In-building wireless isabsolutely mandatory for data,”said Wilson, explaining thatdemands for data services willincrease throughout 2005, whichhe described as “the year for 3G”.

Wilson, who is director ofwireless research at the US-basedanalyst firm, told Wireless Europethat both picocellular basestations and distributed antennasystems from larger base stationswill be used to provide in-build-ing coverage. “Larger deploy-ments will likely contain bothpicocells and distributed anten-nas systems. Large picocell-onlysystems are difficult to designand manage. Picocells make mostsense in smaller spaces where IPbackhaul is available.”

Wilson described in-buildingdeployments as a “very impres-sive challenge” and observed thatonly about 10% of new buildingsare being designed to ease thedeployment of in-building wire-less. Architects must reduce theamount of metal used in ceilingsand insist on non-metal cableducts compatible with leaky-cable antenna systems, he said.

Slow progress in the developmentof handsets will delay the wide-scale launch of HSDPA servicesuntil mid-2006, claims a reportfrom Informa Telecoms andMedia. In its HSDPA StatusUpdate, the UK-based analystfirm predicts that HSDPA use inthe remainder of 2005 will belimited to data-card users.

Informa’s senior research analystJohn Everington said that the lackof HSDPA handsets will be “anexact repeat” of the delays experi-enced in the launch of UMTSservices, which were caused byhandset shortages in 2003.

The update predicts that theUS-based Cingular will be thefirst operator to launch commer-

cial HSDPA services in late 2005.Japan’s NTT DoCoMo and UK-based O2 are also expected topioneer HSDPA services. A suc-cessful launch by Cingular wouldrepresent a significant shift in theglobal pattern of technologyinnovation, which has tradition-ally been led by Asian andEuropean operators.

Report warns lack of handsets will delay HSDPA take-up

ZTE and Ericsson partnership supplies TD-SCDMA equipment

Ericsson hopes to benefit from ZTE’sexpertise in building TD-SCDMA equipment.

Picocellular equipment such as ip.access’snanoBTS base station will play animportant role in in-building coverage.


7N E W S


The Open Base StationArchitecture Initiative (OBSAI)has integrated WiMAX capabil-ities into its RP3 specificationfor the baseband-to-RF inter-face. WiMAX is a wirelessbroadband standard that couldbe deployed in both wide- andlocal-area scenarios.

Peter Kenington, OBSAI’sTechnical Chair, told WirelessEurope that the WiMAX com-munity was initially planning todevelop its own standard, butinstead opted to join forces withOBSAI to avoid a proliferationof standards.

According to Kenington, onlythe baseband-to-RF interfaceneed be defined for WiMAX,because in a typical WiMAXbase station only one low-costmodule will be required in addi-

tion to the RF equipment.The interface would allow the

development of both multimodecellular/WiMAX base stations aswell as stand-alone WiMAXequipment. In addition toWiMAX, the OBSAI standardsalso cover the GSM/GPRS/EDGE, CDMA and W-CDMAstandards.

The organization has alsoreleased compliance-test docu-mentation, which covers all ofthe essential modules and inter-faces in the current OBSAI spec-ifications.

According to Kenington,equipment vendors can eitherperform the tests themselves oruse a testing house. The resultsare then scrutinized by OBSAI,which will issue certificates ofapproval.

Europe’s largest shopping mall ishome to one of the continent’slatest shared 2G/3G in-buildinginfrastructure systems. DundrumTown Centre on the outskirts ofDublin, Ireland, has been fittedwith a distributed antenna sys-tem comprising 69 antennas,more than 100 couplers andalmost 5 km of cable. The instal-lation includes a main equip-ment room, housing the 2G and3G base-station equipment usedby the three operators. VodafoneIreland and O2 offer both 2G

and 3G services, while MeteorMobile Communications oper-ates 2G services only.

The main equipment room at DundrumTown Centre, which houses 2G and 3Gbase stations from three operators.

Ireland gets shared in-building 3G system

Ericsson plans to close the head-quarters of its Mobile SystemsCDMA unit in San Diego,California. The closure will occurin the next nine months andabout 250 staff will be made

redundant. Activities currentlyperformed in San Diego will betransferred to other Ericssonfacilities. The move is part of anongoing effort by Ericsson tostreamline its CDMA activities.

Ericsson cuts CDMA operations

OBSAI integrates WiMAX standard intobase-station interface specification

http://www.imst.com

http://www.microcrystal.com/


8 L E A D E R


While the cellular industry obsesses over boosting data ratesand cramming as much functionality into tiny phones aspossible, solutions to basic challenges such as ensuring coverageand voice quality can remain elusive. On page 14 John Berryexplains why coverage is the most poorly defined term in thecellular industry. He then provides a comprehensive definitionthat involves a dozen or so spatial and temporal parameters.While this might seem extreme, Berry explains that anydefinition of coverage must consider the RF nature of theenvironment, any restrictions to the movement of thesubscriber, and whether the user is moving or not.

Most subscribers see coverage and voice quality assynonymous – and Robin Burton believes that operators arefailing to measure the quality of service experienced by theircustomers. On page 29 he argues that operators are too reliantupon labour-intensive drive tests that employ expensiveequipment and generate copious amounts of data. Instead, hebelieves that the quality of service experienced by customers isbetter measured using a greater number of lower-cost unitsdeployed in commercial vehicles such as buses, taxis anddelivery vans. Burton claims that these provide simplenetwork information in real-time, allowing operators tomonitor the development of potential problems and solvethem before service is disrupted.

Core networks could also benefit from a simpler approach toquality assurance. Paul Magelli believes that complexproprietary architectures prevent operators from fullyexploiting customer data (see page 27). While this was not asignificant issue when voice services dominated the airwaves,the lack of standardized core-network hardware is preventingoperators from rolling out innovative data services.

It is becoming increasingly likely that data services of thefuture will be delivered to mobile handsets using several radiointerfaces – including cellular, WiFi and even WiMAX. On page23 Leo Ivrissimtzis outlines the hardware and software challengesinvolved in creating handsets that operate on both GSM/EDGE/W-CDMA and WLAN networks. Beyond the problemof reducing the power requirements of the WLAN transceiver,Ivrissimtzis also identifies quality-of-service assurance as a keychallenge in the operation of multimode services.

HSDPA sooner, not later Perhaps even more complex than cellular/WLAN integration,the introduction of HSDPA introduces a perplexing array ofnew communications channels and protocols toW-CDMA (seepage 18). While HSDPA represents anything but a move backto basics, the industry is united in the desire to launch the3.5G technology sooner rather than later. As well as increasingdata rates in the downlink, HSDPA could also give a boost tothe US cellular industry, which traditionally lags behind Asiaand Europe. Indeed, analyst John Everington predicts that theUS network Cingular will be the first to launch commercialHSDPA services later this year (see page 6).

Hamish Johnston, Editor

Back to basicsE D I T O R I A L

India seeks global harmony for 3GIndia’s telecoms regulator TRAI has called for the country to remaincommitted to allocating the 2 GHz band to 3G services as defined by theIMT-2000 international framework for spectrum allocation. In a recent set ofrecommendations, TRAI also stated that the 1.9 GHz band would remainreserved for defence use. This spectrum is often referred to as the PCS bandand is used by CDMA services. TRAI has recommended that CDMA servicesbe accommodated in the 2 GHz band, but it admits that this might result ininterference problems. TRAI has also recommended that additional spectrumbe allocated to CDMA operators in the 800 MHz band. The regulator indicatedthat it will consider the merits of spectrum trading at a later date.

Flomerics buys Hungary’s MicReDUK-based Flomerics has bought MicReD, a Hungarian company that producessystems to determine the thermal properties of integrated circuits. MicReD’smain product is the T3Ster system that is often used in conjunction withFlomerics’ thermal analysis software. The two companies have previouslycollaborated in a European Commission research project to develop transientthermal models of chip packages. According to Flomerics’ research managerJohn Parry: “The T3Ster embodies the knowledge and technology gained inthe project to automate the measurement procedure and enable thermalmodels to be generated directly from the measurements.” T3Tter is used byseveral leading wireless technology companies including Nokia, Samsung,Philips, Infineon and ST Microelectronics.

QinetiQ leads interference consortiumA consortium of companies led by QinetiQ has won a £500 000 (7725 000)one-year contract to develop a demonstration system for performingautomatic radio interference monitoring. Funding is provided by the UKtelecoms regulator Ofcom. The consortium also includes TRL Technology,which specializes in high-performance intercept receivers, and the network-planning firm Arup Communications. According to Rhod Scott of QinetiQ’sSpectrum Solutions division, the system will be delivered by the end of 2005.Initial plans for the system involve a network of interconnected receivers infixed locations that would provide continuous monitoring of radio signals. Thelong-term goal of the project is to deploy the boxes in large numbers toensure that interfering radio signals can be detected with sufficient accuracyto identify the source of the interference.

Andrew expands manufacturing in China

Andrew has increased its manufacturing capabilities in Suzhou, China. Thefacility, which produces base-station antennas, has been expanded by 40%.US-based Andrew has also increased its Chinese engineering-designworkforce to support the development of 3G technologies – including TD-SCDMA, which is a Chinese 3G standard. Andrew currently manufactures itsDecibel range of base-station antennas in China.

N E W S I N B R I E F


http://www.andrew.com

http://www.vectron.com

1 1A N A LY S I S


Lance Hiley explains why conformancetesting of handsets is crucial to thesuccess of new mobile services.Annual sales of mobile phones grew by 30%in 2004 to 674 million units, according to theanalyst firm Gartner. This impressive growthlooks set to continue as industry leaders suchas Nokia, Orange, Vodafone, O2 andMotorola invest heavily in developing thewireless applications of tomorrow. A key partof this effort is aimed at ensuring that newwireless data services work properly from dayone across an expanding range of handsets.

While network operators clamber for therapid development of phones with higherdownload speeds and more storage space,handset makers must strive to deliver themost reliable and cost-efficient products onthe market. The testing stage of the handsetdevelopment process is crucial to achievingthese often conflicting goals. Indeed, it isduring the testing phase that handset mak-ers can ensure that their extensive spendingon research and development will result inthe launch of a successful product.

The expertise of test-equipment vendors isnow being sought at a much earlier point inthe development process, because confor-mance testing has become a vital part of thehandset-launch strategy. Conformance testingconfirms that a new product meets therequirements of a standard or specification.There are many types of conformance testing,including testing for performance, robustness,behaviour, functions and interoperability.

Short messaging and multimedia messag-ing services (SMS and MMS respectively)provide excellent examples of how quality-of-service at the time of launch affects theconsumer up-take of a new communicationtool. SMS has been one of the most successfulproduct rollouts of the last decade. In 2004the Yankee Group announced that SMS userswill grow from fewer than 17 million users in2002 to nearly 70 million in 2007, a penetra-

tion of 40% among wireless users in five yearsin the US alone. To further illustrate the suc-cess of SMS, English-speaking users sent anincredible 25 billion SMS messages in 2004.

Interoperability issuesWhile the real push to commercialize SMSbegan after most technical problems wereworked out of the system, efforts to promoteMMS have been hampered by interoperabil-ity issues since its arrival. As a result, sub-scribers have been reluctant to embrace thistechnology. While 47.5 million peopleowned MMS handsets in 2004, only 11.3million actually used the MMS functionality,according to the Mobile Data Association.Despite this relatively slow uptake, MMS isexpected to gain revenues of $161 billion by2009 and will ultimately replace SMS as themost commonly used non-voice mobile

communication tool. However, MMS suc-cess may only come as a result of consumersbeing part of the testing and developmentprocess, which could reflect badly on theindustry as a whole.

An independent programme of standardsto ensure global interoperability of 2G and3G mobile wireless handsets has been createdby the Global Certification Forum (GCF), apartnership involving network operators andhandset manufacturers. The GCF hasrecently set technical testing standards thatmanufacturers must meet before they canmarket handsets with MMS capability.While the GCF cannot provide an overnightsolution, in time these standards will solvespecific interoperability problems that arestalling MMS uptake.

Test vendors have released testing suitesthat comply with these GCF standards. With

First impressions arecrucial in handset testing

T E S T I N G

A phone of the future from Nokia: Handset manufacturers, equipment vendors and test-equipment suppliers must worktogether to ensure that 3G services work the first time.

NOKI

A


1 2 A N A LY S I S


these procedures in place, the handsetsshould be available to allow operators to meetthe 2009 revenue projections.

As technologies become increasingly com-plicated and difficult to implement, and asconsumer expectations continue to rise, theneed for more stringent standards and testingis becoming even more important. Many inthe industry argue that fierce competitionhas driven operators to launch data servicesbefore they were ready. For example, whenthe first UMTS operators launched theirhandsets to the market in 2003, the serviceworked – but not as well as consumerswanted. A reasonable conclusion is that 3Gwas launched too early, which reduced con-sumer confidence in the service.

More usersDespite these problems, W-CDMA usersincreased by more than 500% in 2004. InJapan, 20% of NTT DoCoMo subscribersuse its 3G FOMA network and the operatorexpects to sell more than 20 million high-speed data handsets this year. User uptakeand revenues gained from 3G will continueto rise, but growth could have been faster ifthe launch had been met with universally

positive press and consumer support. Moving one step further, much has been

discussed regarding the high-speed downlinkpacket access (HSDPA) enhancement to theW-CDMA air interface. HSDPA promisesdata transmission rates of up to 10 Mbit/swith the downlink. Operators have beenworking with equipment vendors and test-solution providers for more than two years toensure that there are technology and test sys-tems in place to support a successful launchof HSDPA in 2006.

HSDPA will be followed by the launch ofhigh-speed uplink packet access (HSUPA),which should deliver uplink data rates of upto 5.8 Mbit/s. When HSUPA becomes real-ity, the increased uplink data rates will allowmobile phones to be used in even more cre-ative ways than today.

There is no doubt that operators havelearned a valuable lesson from successes andfailures of previous technology launches:when subscribers first use a service, it is cru-cial that it must work to the highest stan-dards. Operators have responded to thischallenge by working more closely with thetesting houses, which in turn are now offeringconsolidated testing products. For example,Anite has recently launch its SAT-A hardwareplatform, which runs tests for GSM, GPRS,EDGE, W-CDMA and HSDPA.

HSDPA is the next major technologicaladvancement to be launched to consumers,and already the signs are encouraging, withtesting companies working for over two yearsto ensure a successful launch on purely tech-nological terms. Marketing the benefits toconsumers should be a relatively simple taskin comparison, considering all the prepara-tion that has gone into the developmentcycle. It seems handset manufacturers andoperators have now realized that the mobilesector is no different to many other walks oflife – first impressions last.

Lance Hiley is marketing director at AniteTelecoms.

Participating companies include: IPv6 Forum, Telenor R&D, BT, Teliasonera, Cable & Wireless, O2, Fraunhofer Institute FOKUS.

Participating companies include: UMTS Forum, Teliasonera Mobile Networks, TELE.RING, WCDMA HSDPA, Nokia, Omnitele/Finnet.

Key topics: • When to launch HSDPA • How to launch HSDPA services effectively • What is the value-add of HSDPA? • HSDPA enabled phone terminals/handsets

The aim of this international, director-level conference is to explorein detail the migration to, and the integration of, IMS with legacyarchitecture in the core network. Further, this conference will focus on the opportunity to collaboratively create, combine, provision, andmarket multiple real-time, VAS using Session Initiation Protocol (SIP).

HSDPA is expected to offer data speeds up to 10 times faster than UMTS.This conference will discuss and explore the strategic and technical issuessurrounding HSDPA to enable operators to make the right decisions.

For further information on either of these two events please contact Sumreen Rizvi on: Tel: +44 (0) 20 7647 2336 Email: [email protected]

IMS Implementation andService Creation Forum

HSDPA Network Deploymentand Services Forum London, UK14th-16th September,

London, UK 7th-9th September 2005

conferences

HSDPA and HSUPA willallow mobile phones to beused in even morecreative ways than today



http://www.cmu.rohde-schwarz.com

1 4 A N A LY S I S


By John Berry“Coverage” is a trendy word that has enteredtoday’s parlance at many different levels.While everyone from teenagers to radio engi-neers use it, few really understand its mean-ing. Indeed, coverage is probably the mostpoorly defined term used in the cellular com-munications industry.

At the most basic level, a user is covered ifhe or she can access cellular services for sometime and at several different locations.However, a more precise definition requiresfurther assumptions to be made. For exam-ple, the nature of the service must be definedand there must be a precise definition of howthe equipment is being used. The need toestablish service in the uplink, downlink orboth must be also be specified.

Location and timeAs a starting point in the definition of cov-erage, the exact location of the user must bespecified along with where the service is to bederived and at what time the service isneeded. Restrictions on the user’s behaviour,such as their movement being limited to rail-way lines or roads, must be considered. Amap and pen is the best way to documentthis parameter.

At the RF level, the signal in the environsof a user is a 3D standing wave with a mini-mum value of some 30 dB below the median.The nature of the standing wave changes asthe environment around the user changes.The user may also move through the stand-ing wave and experience a change in thereceived signal with location.

This location variability must beaccounted for in both analogue systems andin static digital systems. This can be done bydefining the percentage probability that auser deriving service is present in any shortsector measuring 100 wavelengths or so. Thisdefines the “percentage of locations” or“availability” parameter.

When a user is moving while connectedto a digital network, the error-correction fly-wheel prevents loss of service until the signaldrop-out becomes excessive and total lossoccurs. This slightly more complex statedemands a different specification of thereceiver threshold at which total loss occurs,

effectively yielding 100% availability. Thismeans that coverage for static and mobileusers is specified differently.

The percentage of short sectors where theservice availability threshold is exceeded canbe determined by assigning a one to everyshort sector where the service can be derivedfor more than the desired availability and azero when it cannot. This figure is the “per-centage coverage”.

For example, an operator may want tocover 98% of all major roads within a coun-try. Defining coverage to a given availability,over a given area of ground, is a near-idealdefinition. In many networks, however, it isdistinctly possible to achieve, say, 98% cover-age while having very large areas with no ser-vice. To complete the specification it is wiseto define a maximum size for any such areas.

Time percentageRadio signals propagate through a mediumthat varies with time. Luckily, in networkswhere the path length is a few kilometres,this change is small, resulting in a small vari-ance. Where paths are obstructed or trans-

horizon, this variation increases and a timepercentage must be determined for whichservice should exist.

Finally, network planners must be awarethat there will be a discrepancy – both posi-tive and negative – between the planned cov-erage and what is actually achieved. Plannersmust therefore consider the certainty towhich planned and actual coverage agree.This certainty covers the errors involved inthe prediction process and allows the plannerto quote a certainty of achieving a given cov-erage at a specified location.

Comprehensive definitionAll of these parameters can then be puttogether to create a comprehensive definitionof coverage. For example, coverage could bedefined as: “Achieving 95% availability inshort sectors of 100 m along a bus route for90% of the time for static users. The systemshall cover 97% of each and every bus routeacross the city. There shall be no bus routewhere a route length of more than 200 m iswithout the stated availability. There shall bea 90% certainty of achieving this coveragewhen the network is actually installed.”

This comprehensive statement provides agood definition of the term “coverage”.While other factors such as man-made noise,delay spread in wide-band systems and inter-ference could degrade the coverage, this def-inition allows coverage to be tested andperformance proven.

John Berry is managing director of ATDI’sUK operations.

O P T I M I Z A T I O N

Coverage benefitsfrom comprehensivedefinition

A pen is the best way to map the role that roads and railways play in the definition of cellular network coverage.

Network planners must beaware that there will be adiscrepancy between theplanned coverage andwhat is actually achieved


http://www.spirentcom.com/3Gtest

1 6 A N A LY S I S


By Mike KennettHealth and safety guidelines for macro-cellular sites are relatively clear and areadhered to by the cellular industry. However,WLAN infrastructure is cheap and simple toinstall and “operators” are often individualtenants with little or no radio experience.Audits by the network design company CDShave revealed many instances where access-point (AP) antennas are installed in inappro-priate locations and set to radiate atunnecessarily high power levels. These con-tribute to the total RF exposure levels aris-ing from the combination of all radio systemsin an environment. As a result they must bemanaged via a holistic radio strategy in lightof the relevant exposure guidelines.

The International Committee on Non-Ionizing Radiation Protection (ICNIRP) isresponsible for providing guidance andadvice on the health hazards of non-ionizingradiation exposure. It is an independent non-governmental scientific organization createdby the World Health Organisation and theInternational Labour Office.

Restrictions and levelsIn 1998 ICNIRP examined the availableresearch and published its Basic Restrictionsin terms of the specific absorption rate(SAR), which is the amount of energyabsorbed by tissue. At sufficient distancesfrom the antenna these basic restrictions canbe translated into Reference Levels, which areexpressed in terms of electric-field strength.ICNIRP provides both occupational andpublic limits and these apply to all radiatingsources including cellular, WLAN, privatemobile radio, and broadcast services. Theselevels are such that any antenna will have anexclusion zone around it where the ICNIRPlimits are exceeded.

While the ICNIRP recommendations arenot binding, they have been adopted bymany jurisdictions – including the EuropeanCouncil in its 1999 Recommendation (1999/519/EC) on the limitation of exposure of thepublic to electromagnetic fields in the0–300 GHz range. Nevertheless there are stillvariations across Europe. In France andGermany, for example, compliance with1999/519/EC has been mandatory since2002. In Italy, reference levels are morerestrictive than the ICNIPR guidelines.

In the UK, the Independent Expert Groupon Mobile Phones (IEGMP) recommendedin 2000 that the ICNIRP guidelines for pub-

lic exposure be adopted in the UK. As aresult, the UK’s mobile phone industry hasvoluntarily adopted ICNIRP guidelines forpublic exposure to RF fields.

While the ICNIRP levels are not a specificlegal requirement in the UK, the occupa-tional exposure guidelines were included inthe European Union’s EMF Physical AgentsDirective in 2004. This is expected to beincorporated into UK law in April 2008.

The National Radiological ProtectionBoard (NRPB) – which recently merged withthe Health Protection Agency – provides sci-entific advice to the UK government on radi-ation matters. It published new advice onlimiting public exposure to electromagneticfields in 2004, following an extensive reviewof the science and a public consultation.

The NRPB recognized that “it is likely thatthe number of picocells within buildings willsubstantially increase”, and that “it is impor-tant that as the networks develop, there is aneed for clarity in terms of legal responsibili-ties and regulations in relation to the installa-tion of microcells and picocells”.

CDS has expanded the body of knowledgein this field in several ways. It has workedwith the UK regulator Ofcom to improve itssurvey methodology for RF-exposure quo-tients, and with the Department of Health indesigning and installing equipment for RF-exposure experiments.

Protecting the publicThe UK’s Mobile Operators’ Association wasquick to respond to the Stewart Report, issu-ing guidelines on signage and barriers formacro sites, for example. However, warningsigns and physical barriers are not suitable forindoor public areas such as shopping centresor airports, and in such places it is best prac-tice to ensure that antennas are touch-safe.

This means that the ICNIRP public-exclusion zone is contained entirely withinthe antenna radome. Because of the proxim-ity of the radome to active elements forindoor antennas, direct measurement of SARis often the only reliable method of deter-mining whether an antenna is touch-safe atthe proposed input power.

Despite the current lack of specific legisla-tion, the landlord has a duty to ensure thatthe property is not inherently dangerous forthe intended use. In practice, this means thatlandlords (rather than tenants or networkoperators) must assess the RF health-and-safety risk due to in-building deployments.While mobile operators are familiar with RFH&S risks in outdoor and indoor environ-ments, other parties such as tenants deploy-ing WLAN systems are likely to have littleawareness of the risks.

At CDS we recommend that landlordsactively manage their airspace, both to mini-mize RF H&S risks and WLAN interferencerisk. WLAN systems are small and often hardto spot, so surveys and monitoring equip-ment may be required to identify unautho-rized systems. This then permits thelandlords and their tenants to benefit fullyfrom the wide range of services that can beprovided over wireless systems of all types.

Mike Kennett is Senior Strategy Consultant atCDS (Cellular Design Services) Ltd.

H E A LT H A N D S A F E T Y

Landlords must take responsibility for in-building safety

Landlords must ensure that RF health-and-safety surveysof their premises are performed to ensure that electric-field strength levels are within the appropriate limits.

While mobile operatorsare familiar with risks,other parties deployingWLAN systems are likelyto have little awareness


1 7O P I N I O N


M A R K P A X M A NThe industry must beware of stealth IP, which couldunravel the tightest standard.

Most modern standards contain embedded intellectual property (IP), somanufacturers must obtain the appropriate licences before they can produce compliantproducts. For decades, standards bodies have struggled to balance the rights of the IPowners with the need to promote standards and make them easy to implement.

Members of a standards body usually agree to a compulsory licensing obligation tolicense all relevant IP on fair, reasonable and non-discriminatory (FRAND) terms.This prevents the standard from being rendered unusable – or blocked – by IPholders that refuse to license.

Unfortunately, FRAND can’t always protect a new standard. It is becomingincreasingly common for standards bodies to incorporate “stealth” IP owned by non-members. This is often accidental, because it is difficult to vet each idea proposed fora standard to see if it infringes any IP.

Recently the Open Mobile Alliance (OMA) had a close call with stealth patents. TheAlliance has standardized a digital rights management (DRM) scheme and published

the specifications, which are likely to be widelyadopted by cellular network operators andequipment manufacturers. Members of OMAwho contributed to the standard agreed toFRAND terms. But some of the key IP was notowned by OMA members. Companies such asPhilips, Matsushita, ContentGuard and Intertrustclaim fundamental IP in the way DRM works,but did not participate in the standards building.These non-members would be well within theirrights to refuse to license critical IP, which wouldblock the standard.

The OMA had a lucky escape this time. Thekey players in DRM had already responded to a “call for IP in DRM” issued byMPEG LA, the licensing authority originally developed to handle MPEG-2licensing. MPEG LA has a sound commercial ethos and has developed a “one stopshop” licensing programme for this key DRM IP. There is now a heated debate aboutwhat fee or royalty MPEG LA should charge for a licence – but this is all part of thenormal commercial process as MPEG LA seeks a reasonable return on its members’investment without stifling the DRM market.

Stealth IP will become increasingly common as standards bodies incorporate morediverse technologies. At the same time, standardization wars between differentindustry factions will increase the chances that one company will refuse to license itsIP, in order to block a rival standard in which it hasn’t invested.

The only way to solve this is for standards bodies and end users – primarilymanufacturers and network operators – to get involved in IP analysis sooner ratherthan later. This will prevent an expensive and labour-intensive standardization effortfrom being undone by a single blocking patent.

Mark Paxman is a managing consultant at PA Consulting’s Wireless Technology Group.He can be contacted at [email protected].

Stealth IP willbecome increasinglycommon asstandards bodiesincorporate morediverse technologies

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1 8 H S D P A


HSDPA brings significant changes to the W-CDMAair interface. Marta Iglesias makes sense of themyriad new channels and protocols.

The highspeed downlink packet access (HSDPA) enhancementto W-CDMA enables higher downlink data rates and greaterbase station capacity. Indeed, the incorporation of HSDPA inRelease 5 of the 3GPP W-CDMA specification is the most sig-nificant change on the RF side since Release 99.

HSDPA makes several changes to the W-CDMA radio inter-face, which mainly affect the physical, transport and MAC layers.As well as a new high-speed shared downlink channel that usescode multiplexing combined with time multiplexing, HSDPAbrings a shorter radio frame and the use of quadrature ampli-tude modulation (16QAM). New downlink and uplink controlchannels are also introduced to support the high-speed downlinktransmission. More importantly, the medium-access control(MAC) scheduling function is moved to the base station, and fastlink adaptation using adaptive modulation and coding (AMC)and hybrid automatic-repeat-request (HARQ) is used.

The HSDPA radio frame is a subframe within the W-CDMAarchitecture. It is 2 ms in length, which is equivalent to threecurrent W-CDMA slots. There are five HSDPA subframes in a10 ms W-CDMA frame. User data transmissions can beassigned to one or more physical channels for a shorter duration,thus allowing the network to readjust its resource allocation.

New channelsA new transport channel, the high-speed downlink shared chan-nel (HS-DSCH) is added to the downlink, as well as two newphysical channels: the high-speed physical downlink sharedchannel (HS-PDSCH) carries the payload data, and the high-speed shared control channel (HS-SCCH) carries the user-equip-ment (UE) identity and channel parameters of the associatedHS-PDSCH. HSDPA also adds one uplink physical channel, thehigh-speed dedicated physical control channel (HS-DPCCH).

The layer-2 (the MAC layer) can map existing logical channels(DCCH and DTCH) onto the high-speed transport channel(HS-DSCH). Layer 1 (the physical layer) in turn maps the trans-port channel (HS-DSCH) onto up to 15 physical channels(HS-PDSCH). Layer 1 also creates the HS-SCCH andHS-DPCCH to control and assist with HS-DSCH transmission.

The HS-DSCH evolved from the downlink shared channel(DSCH), which was introduced in W-CDMA Release 99. Toobtain higher data rates and greater spectral efficiency, the fastpower control and variable spreading factor of the DSCH arereplaced in Release 5 by short packet size, multicode operation,and techniques such as AMC and HARQ on the HS-DSCH.

The coding blocks for the HS-DSCH are shown in figure 1.

The channel coding is based on the Release 99 1/3 turboencoder and is always 1/3 rate (for every bit that goes into thecoder, three bits come out). The effective code rate varies, how-ever, depending on the parameters applied during the two-stageHARQ rate-matching process. The bits output by the channelcoder are punctured to match the total number of bits of theHS-PDSCH set – to which the HS-DSCH is mapped. TheHARQ function is controlled by the redundancy version (RV)parameter. The exact set of bits at the output depends on thenumber of input bits, the number of output bits and the RVparameter. When more than one HS-PDSCH is used, physicalchannel segmentation is used to divide the bits among the dif-ferent physical channels.

Like W-CDMA, HSDPA uses quadrature phase shift keying(QPSK) modulation. However, when radio conditions are verygood, 16 quadrature amplitude modulation (16QAM) is used toincrease data rates in the downlink. Constellation rearrange-ment can be performed for 16QAM during retransmissions.

In HS-DSCH channel coding, the first rate-matching stagematches the number of input bits to a virtual incremental redun-dancy (IR) buffer. The second rate-matching stage matches theresulting number of bits to the number of physical channel bitsavailable in the HS-PDSCH set during the transmission timeinterval (TTI). This stage is controlled by the RV parameter.

The number of HS-PDSCHs and the modulation formatdefine the number of physical channel bits after RV selection.The turbo-encoding code rate is fixed at 1/3, but the effectivecode rate is the combination of turbo-encoding and the rate-matching stages. The effective code rate for any HS-DSCH con-figuration thus can be calculated if the transport block size, thenumber of HS-PDSCHs and the modulation format are known.

With HS-SCCH, the first slot carries critical information forHS-PDSCH reception, such as the channelization code-set andthe modulation scheme. After receiving the first slot, the UE hasjust one time slot for decoding the information and preparing toreceive the HS-PDSCH.

The number of HS-PDSCHs (or code channels) that maponto a single HS-DSCH can vary dynamically between 1 and15. Orthogonal variable spreading factor (OVSF) codes areused. The number of multicodes and the corresponding offsetfor the HS-PDSCHs mapped from a given HS-DSCH are sig-nalled on the HS-SCCH. The multicodes (P) at offset (O) areallocated as follows: Cch, 16, O … Cch, 16, O+P–1. The secondand third slots carry the HS-DSCH channel coding informa-tion, such as the transport block size, HARQ information, theRV and constellation versions, and the new data indicator. Thedata of the three slots are covered with the 16-bit UE identity.

The HS-DPCCH carries uplink feedback signalling related tothe downlink HS-DSCH transmission. These signals comprisethe HARQ acknowledgment (HARQ-ACK) and channel-

HSDPA introduces new le


1 9H S D P A

quality indication (CQI). Each 2 ms subframe – like those of thedownlink physical channels – consists of three slots, each slotof 2560 chips. The HARQ-ACK is carried in the first slot of theHS-DPCCH subframe, and the CQI in the second and thirdslots. There is at most one HS-DPCCH on each radio link.The HS-DPCCH can exist only in association with aW-CDMA uplink DPCCH.

Different pathsTwo different paths are used for HARQ-ACK and CQI cod-ing. The HARQ-ACK information (1 bit) is coded to 10 bits,with ACK coded as 1, and NACK coded as 0. The CQI infor-mation is coded using a (20,5) code. The coded bits are mappeddirectly to the HS-DPCCH. The feedback cycle of the CQI canbe set as a network parameter in predefined steps from 2 ms toinfinity (disabled). Note that an active HS-DPCCH may haveslots in which no HARQ-ACK or CQI information is trans-mitted. The HS-DPCCH is thus a bursty channel.

Link adaptation is used to improve data throughput. Adaptivemodulation and coding (AMC) matches the modulation-codingscheme to the instantaneous channel conditions for each usertransmission. The power of the transmitted signal is held con-stant over a subframe interval, and the modulation and codingformat are changed to match the quality of the received signal orthe channel conditions. In this scenario, users close to the base-station are typically assigned higher-order modulation schemeswith higher code rates. The modulation-order and code rate will

decrease as the distance from the base station increases. In HSDPA, the UE reports the channel conditions to the base

station via the uplink channel CQI. The CQI value can be 0 to30, with a value of 0 indicating “out-of-range”. Each CQI valuecorresponds to a certain transport block size, number ofHS-PDSCHs, and modulation format for a certain UE category.

These parameters are used by the base station in combina-tion with other parameters to determine the appropriateHS-DSCH configuration (transport block size, number ofHS-PDSCHs, etc). For example, the largest transport blocksize is 27 952 bits, which corresponds to the highest data rateof 13.976 Mbit/s. This data rate is obtained by using 16QAM,an effective code rate of 0.9714, and 15 HS-PDSCHs. This datarate is only theoretical, since it requires ideal channel conditionsthat can only be achieved in a laboratory environment.

Hybrid automatic repeat request (HARQ) combines feed-forward error correction (FEC) and ARQ methods that saveinformation from previous failed attempts for use in futuredecoding. HARQ is an implicit link-adaptation technique and– unlike AMC – it uses link-layer acknowledgments (ACK/NACK) for re-transmission decisions. As a result, AMC pro-vides the coarse data-rate selection, while HARQ provides finedata-rate adjustment based on channel conditions.

For a re-transmission, HARQ uses the same transport-blocksize – and thus the same number of information bits – as wereused in the initial transmission. However, it may use a differentmodulation scheme, channelization-code set or transmission


evel of complexity to 3GCRC attachment

bit scrambling

code block segmentation

channel coding

physical layer HARQ functionality

physical channel segmentation

HS-DSCH interleaving

constellation re-arrangement for 16QAM

physical channel mapping

physical channel #1 physical channel #P

original data

rate 1/3coded data

1st ratematching

2nd ratematching

RV = 0

2nd TX

3rd TX

1st TX

RV = 2

RV = 5Reff = 4/5

Reff. = 4/5

Reff. = 4/5

eff. rate = 2/5 IR buffer size = 10 bits/process

Reff. = 4/5 = 0.8

Reff. = 2/5 = 0.4

Reff. = 4/15 = 0.27

1st decode attempt NACK

2nd decode attempt NACK

3rd decode attempt ACK

Fig. 1. Coding blocks for the HS-DSCH. Fig. 2. How the IR scheme works. For simplicity, an IR buffer of 10 bits per process and a single process are assumed.


2 0 H S D P A

power. As a result, the number of channel bits available for a re-transmission may differ from that of the initial transmission.Channel bits are transmitted over the air. And if the number ofchannel bits is the same, the channel-bit set may be different.

To minimize the number of additional re-transmissionrequests, HARQ uses one of two “soft-combining” schemes toensure proper message decoding. Chase combining (CC)involves sending an identical version of an erroneously detectedpacket. Received copies are combined by the decoder prior todecoding. Incremental redundancy (IR) involves sending a dif-ferent set of bits incrementally to be combined with the origi-nal set, thus increasing the amount of redundant data and thelikelihood of recovering from errors introduced on the air.

Incremental redundancyFigure 2 illustrates how the IR scheme works. For simplicity,an IR buffer size of 10 bits per process and a single process areassumed in this example. The original data (4 bits) correspondto the data block after the CRC has been added. The data areencoded at the 1/3 rate, and are punctured as part of the firstrate-matching stage. At this stage, the output bits are matched tothe IR buffer size, which is 10 bits in this case.

The second rate-matching stage is redundancy version selec-tion, which punctures the data again. The data can be punc-tured into different data sets, each corresponding to a differentRV. In figure 2 they are represented by red, green and orange.Only one of these data sets will be sent in any given transmission.

The five red bits (RV = 0) are sent over-the-air (OTA), result-ing in an effective code rate of 4/5. For every original data bit,1+1/4 bits are transmitted OTA. The data arrives at the UE, isdemodulated, padded with dummy bits and stuffed into the IRbuffer. The data are then decoded, with some possibility of error,to provide the four blue bits. This block is checked against theCRC and, if it is found to be in error, it is stored and a NACK issent to request a re-transmission.

When the re-transmission is sent, it employs a different RV orpuncture scheme, and sends the five green bits OTA. At the UE,the green bits are recombined with the original transmission’sred bits to provide an effective code rate of 2/5. For every databit there are 2 +1/2 bits available for decoding, which increasesthe likelihood of success. However, when the results are checkedagainst the CRC, if the block is still in error, the re-transmis-sion process begins again.

Yet another RV or puncture scheme is used, appearing nowas the orange bits that are sent OTA and recombined at the UEwith the red and green bits from the first and second transmis-sion. Note that the new RV provides additional redundant data,even if some or all of the encoded bits are repetitions of encodedbits sent earlier. After the third transmission, the effective coderate is 4/15 – for every data bit there are now 3 + 3/4 bits. Thedata is at last correctly decoded and an ACK is sent back. If theblock were still in error, a NACK would be sent and still moreRVs could be transmitted, depending on the maximum numberof transmissions allowed for a block. In the case of 16QAM for-mats, the different RVs may correspond not only to differentpuncturing schemes, but also to different constellation versions.

HSDPA does not re-transmit a data block until it receives anACK or NACK for that data. Five subframes are needed to

receive the ACK/NACK for a transmitted data block. Since theACK/NACK is required before data transmission for a specificprocess can continue, the minimum interval between TTIs mustbe at least six subframes for a single HARQ process. Multipleindependent HARQ processes can be run in parallel to mini-mize the time between transmission of the data block and recep-tion of the ACK/NACK response. Six HARQ processes runningsimultaneously will completely fill every subframe with data toa specific UE.

User equipment must support a minimum inter-TTI inter-val of one subframe (capable of receiving data every subframe),two (capable of receiving data every other subframe), or three(capable of receiving data every third subframe). Which mini-mum interval value they can support depends on theHS-DSCH category, described in table 1. Note that UE inCategories 11 and 12 support QPSK only.

As well as the channel coding and physical and transport layerchanges, HSDPA moves the packet-scheduling functionalityfrom the network controller to the MAC layer in the basestation, which allows for fast link adaptation. The packet sched-uling algorithm takes into account the radio channel conditionsand the amount of data to be transmitted to the different users.Throughput gains can be maximized by serving the UE that isexperiencing the best radio channel conditions, but obviouslysome degree of fairness in scheduling is required. In addition,there are other factors that could be considered by the schedulingalgorithm, including quality of service. The actual throughputwill depend heavily on the packet-scheduling algorithm used.

Marta Iglesias is at Agilent Technologies Agilent TechnologiesWireless Business Unit.


HS-DSCH Max. no. Min. Max. no. bits of an Total no.category HS-DSCH inter-TTI HS-DSCH transport of soft(FDD) codes interval block received in channel

received an HS-DSCH TTI bits

Category 1 5 3 7298 19 200

Category 2 5 3 7298 28 800

Category 3 5 2 7298 28 800

Category 4 5 2 7298 38 400

Category 5 5 1 7298 57 600

Category 6 5 1 7298 67 200

Category 7 10 1 14 411 115 200

Category 8 10 1 14 411 134 400

Category 9 15 1 20 251 172 800

Category 10 15 1 27 952 172 800

Category 11* 5 2 3630 14 400

Category 12* 5 1 3630 28 800

*User equipment of categories 11 and 12 support QPSK only

1. HS-DSCH categories


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Creating a terminal that can roam effortlesslybetween cellular and WLAN networks is achallenging proposition. Leo Ivrissimtzis chartsthe way forward in hardware and software.Multimode terminals will provide a seamless connection to het-erogeneous radio-access networks based on cellular and wirelesslocal area network (WLAN) technologies. Users will benefit fromaccess to high data rates in home, office and public-hotspotWLAN deployments as well as the high mobility and ubiqui-tous coverage of cellular networks – albeit at lower data rates.

Indeed, multimode devices could even access both networkssimultaneously – for example using WLAN for data and cellularfor voice. WLAN access could be initiated by the user or it couldoccur automatically when the terminal detects an appropriatenetwork. Advanced session mobility management techniquesand the use of Unlicensed Mobile Access (UMA) technologywill further support roaming and data/voice handovers betweenWLAN and UMTS/EDGE/GSM networks.

Integrating UMTS, GSM and WLAN networks is a challeng-ing proposition. UMTS and WLAN have differing capabilitieswhen it comes to ensuring quality-of-service (QoS). For example,UMTS already supports QoS for well-defined service classes,while the IEEE 802.11e (draft) standard introduces QoS such asvoice-call prioritization. While WLAN addresses mobility at thelocal-area network (LAN) level, mobility between heterogeneousnetworks must be addressed by specifications such as UMA or3GPP Release 6 GAN; the latter addresses roaming betweenUMTS and generic access networks (GANs). Plus, specific usagescenarios and handover practices require further consideration.

Most multimode handsets will be used in a home, office andhotspot scenario, in which the operator will offer high-speedWLAN data services in conjunction with UMTS. There arethree main service models that could be implemented. TheWLAN and UMTS could be used for data and voice communi-cations respectively and the terminal would be capable of main-taining both connections simultaneously. In the second scenario,UMTS data services are augmented by WLAN – either simulta-neously or during idle periods of UMTS operation. Finally,UMTS and WLAN can be used independently for data andvoice services, with WLAN supplementing the cellular networkwhere coverage is patchy. In each case, the flow of data packetsis redirected to the appropriate network in a manner commen-surate with the operator’s mobility management capabilities.

Examples of multimode terminal hardware and softwarearchitectures are shown in figure 1. This architecture can be real-

ized in commercial terminals with an integration effort thatfocuses on reducing both power and cost, while complying withthe appropriate standards.

The hardware design comprises a layer-one (L1) processorfor each MAC interface and a dual-microprocessor system forcommunications and applications. The L1 processor and digi-tal signal processor (DSP) subsystems are augmented with frameschedulers and a Viterbi co-processor for EDGE/GPRS/GSMor a rake receiver for W-CDMA. These subsystems performphysical layer control and DSP functions including acquisi-tion, tracking, demodulation/decoding in the receive path andformatting/encoding in the transmission path.

The communications processor is a dedicated host for theUMTS-EDGE/GPRS/GSM protocol stack. It processes layertwo and three (L2 and L3) protocols and performs system-control functions such as power management, clocking andmemory. The application processor becomes a separate entityto support user applications such as the user interface, multi-media, and data storage devices.

The front-end comprises the RF subsystem and also performsthe analogue-to-digital and digital-to-analogue signal conver-sions of the analogue baseband signals. The level of integration ofthe front-end depends mainly on specific network requirements.

2 3M U L T I M O D E


Multimode terminals linkcellular and WLAN services

ARMcommunications uP

memory

external memory

DSP core (L1 uP)scheduler

host interfacecontrol memory

DSP core (L1 uP)scheduler

host interfacecontrol memory

MAC acceleratorMAC processorhost interface

control memory

ARMapplications uP

memory

A/D–D/Asignal

conversion

A/D–D/Asignal

conversion

A/D–D/Asignal

conversion

RF transceiverWLAN

RF transceiverGSM/EDGE

RF transceiverW-CDMAfro

nt-e

nd s

witc

hing

/dup

lexin

g

PMU

bluetoothGPSIrDAMMI

application layer

hardware

transportnetwork

physical

IP/TCP/UDPUSIM/SIMMM/GMM

CC SC SM GSSNDCPRSVP LMMIP/TCP/UDP802.2 LLC

802.11 MAC

802.11 PHY

UMARRC RRC

MAC

RR/GRR

RLC/MAC

LLC

3G L1EGPRS L1

PPPPPP

RLCdata link

Fig. 1. Hardware (a) and software (b) architectures for a multimode terminal.

(a)

(b)


2 4 M U L T I M O D E

The transceiver circuitry can be reduced in certain cases – forexample if UMTS compressed mode need only be supported –if packet data transfer via the WLAN is accommodated in idleslots or frames of the GSM TDMA multiframe structure; or ifonly one network is used at a time.

The implementation of the software protocol stack is depictedin figure 1 with respect to the Open System Interconnection(OSI) model. The stack supports both the WLAN and com-pressed-mode GSM/W-CDMA radio interfaces. The IEEE802.11 L2 comprises the MAC and 802.2 logical link control(LLC) entities, which along with the physical layer constitutethe terminal driver. The UMTS and EDGE/GPRS/GSM L1/L2protocol stacks are separate entities.

In addition to the PHY/MAC layers, the EDGE/GPRS/GSMpart of the device driver incorporates protocols below the IPlayer. These include the logical link control in L2, which pro-vides the link between the terminal, SGSN and the subnetworkdependent convergence protocol (SNDCP). The SNDCPresides in L3 and connects high-level data protocols with theLLC. The control plane includes protocols such as theRRC/RR/GRR of L3 for radio resource control and GMM/SMfor mobility and session management. The data protocol suitecan also include RSVP for QoS signalling and resource reserva-tion and a local WLAN mobility management protocol.

Design considerationsThe integration of WLAN into terminals based on existingUMTS/EDGE/GPRS core architectures involves four funda-mental design considerations. These are: hardware integration;the host interface; standards compliance; and power consump-tion. Handset designers will adopt different strategies to balancethe desire to offer new features and high versatility with the needto minimize cost, size and power consumption. However, anyintegration can readily be executed based on qualified, com-mercially available hardware and software building blocks.

Individual hardware integration strategies are dependent pri-marily on how the terminal will be used and the availability ofintegrated WLAN/cellular transceivers. Early multimode termi-nals are likely to employ discrete architectures with separatetransceivers for each mode of operation. By contrast, later state-of-the-art designs will be optimized in terms of cost, integra-tion and power consumption. These terminals will comprisesingle-chip transceivers, a single- or dual-package multi-processor, cellular baseband and power management unit, aWLAN DSP/MAC device with host interface control, periph-erals for power amplification and filtering, and modules for thesupport of different multimedia features.

The host interface connects the WLAN DSP/MAC controllerto the host application processor. It should be of sufficient band-width to accommodate established data rates and have a stan-dard interface – such as USB or SPI – at both ends.

Standard compliance applies to both 3GPP specifications forcellular (3GPP TS 51.010/34.121) and WLAN standards (IEEE802.11 and its extensions). In addition, the terminal conformancerequirements should cover extended multimode user cases, suchas simultaneous operation in WLAN and cellular modes andtheir implications in terms of electromagnetic compatibility.

Minimal power consumption and maximal battery life are key

requirements for portable equipment. These needs introducesubstantial design constraints and have an impact on productdefinition and quality. The power consumption of a cellularphone must be considered in both traffic mode and idle mode.These requirements can be simulated and determined by con-sidering three factors, which apply to both the cellular andWLAN subsystems.

The first is the baseband and power management IC design– including the process technology used and the voltage regula-tion and efficiency. The second factor is the RF transceiver andcomponent specification and design – including power ampli-fier efficiency. The third factor involves how the L1/stack isdesigned for power efficient implementation of standardrequirements and management of core engine blocks and theradio. Examples include powering-down blocks that are not inuse during idle periods or clocking-down and entering sleepperiods when medium access is not required.

For cellular operation – particularly, during sleep and standbymodes or a voice call – peak and average power consumption aredetermined using the IC performance specifications and sys-tem parameters such as activity factors for subsystem blocks.Power requirements during packet transmission and receptionare largely dependent upon data rates and the multislot config-uration and coding schemes supported by the system.

The power demands of the WLAN submodule is a functionof the operational mode: sleep, listen, receive or transmit. Themajority of system blocks are powered off in the sleep mode,while during the listen mode the terminal listens for traffic,although it does not pass any data to the host processor. In thereceive and transmit modes, the terminal actively sends andaccepts packet data. Determining power consumption subject todifferent usage scenarios – such as searching, associated and idle,and TCP uplink/downlink – can be achieved by defining aweighted average of the different operational states.

From an analysis of power requirements of cellular terminals,two main considerations regarding integration of WLAN capa-bilities in the terminal are apparent. Firstly, the current consumedin WLAN search or idle modes results in a significant negativeimpact on the overall standby time expectations, when comparedto conventional mobile phones. As a result, significant effort isrequired to enhance power-saving modes in the WLAN subsystem.

Secondly, although the communications processor master con-trol can preclude the simultaneous operation of both radios, peakcurrent consumption must also be monitored and moderated viathe master control. This is particularly relevant when a voicecall at high power levels is supported by the cellular subsystem.

The integration of WLAN functionality within existing dual-mode cellular terminal architectures will allow seamless useraccess to the high data rates offered by WLAN in hotspot andhome deployments. The cellular network can be used for voicecalls or lower data rate transfers, either simultaneously or outsidethe WLAN coverage. The network infrastructure, as well asbuilding hardware and software blocks, are available and can bereadily used. Areas for careful consideration and analysis includeusage models to understand and manage the requirements ofhandover techniques and power consumption.

Leo Ivrissimtzis is Senior Systems Engineer at Agere Systems.



http://www.emblazemobile.com

Cellular operators are facing increasing competitive pressuresand their chief technical officers (CTOs) have the unenviabletask of reducing the cost and complexity of their core net-works, while improving the quality of service (QoS), reducingservice deployment time and increasing network resilience. Inaddition, any new network architecture must be scalable forfuture growth and to support the ongoing evolution towardsconverged networks and services.

Before looking for a way forward, CTOs must consider howtheir complex GSM networks have developed and why thingsmust change. For more than 15 years, operators seeking toaccommodate new subscribers, launch new services, or developnew market sectors, had little choice but to invest in more andmore hard-wired proprietary equipment.

Indeed, it is not uncommon to find 40 or more distincthome location registers (HLRs) in a network serving 15 millionsubscribers. Replacement costs for this proprietary hardwarecan be huge – many hundreds of thousands of euros for a boxthat supports 1 million subscribers, plus all of the professionalservices required to install it. This expense is compoundedwhenever a new service – such as prepay, number portability,location or voicemail – is introduced.

Hardware faultsProprietary infrastructure has no in-built redundancies in theevent of a major hardware fault or site problem. For example,a HLR is co-located with a single standby, which takes over incase of failure. The configuration of the standby – cold, warmor hot standby mode – determines the level of service disrup-tion. However, if there is a catastrophic failure at a site, bothof the paired HLRs will fail and cause a service outage.

As a result, operators have been forced to buy additionalhardware to replicate existing systems, which further increasesits complexity and cost. Managing architectures is a complex

and costly process and the hardware lacks the level of resiliencerequired in today’s environment.

Indeed, most CTOs agree that hardware-based, legacy tech-nology is no longer up to the job. Older technology buries vitalsubscriber data under myriad applications and is inflexible,proprietary, outdated and cannot scale. Finally, legacy systemsare hard-wired to delivery primarily voice services, and there-fore are unsuitable at the most elementary level for providingmodern data services.

RevolutionFortunately, this is changing in a process similar to the revolu-tion that has occurred in the information-technology (IT)industry over the last 20 years. In this sector, mainframe com-puters were replaced by standardized and non-specialized hard-ware and software platforms, which greatly reduced the costand increased the performance of the technology. This funda-mental shift changed the way that businesses use IT and accel-erated the pace of innovation.

This positive trend is finally affecting one of the last bas-tions of proprietary hardware infrastructure: telecoms core net-works. Standardization is being driven by the desire to convergetelecoms services, networks and technologies. The ultimate aimis seamless mobility, whereby a particular service will follow theuser – moving from home to the car, car to work, work tomeeting and so on. Today, this is technically difficult to achieveon a complex network connected to myriad devices using sev-eral different wireless and wireline link technologies.

The plethora of standards in today’s wireless world reflectsthe trend towards converged networks. The increasing roll-outof WLAN hotspots is testament to this desire to fuse the wire-less and wired worlds. With WiFi and WiMAX already avail-able, and ultra-wideband and 4G on the horizon, the pace ofchange will quicken.

2 7C O R E N E T W O R K S


Networks aredying a deathof complexityAging hardware and inaccessible customer dataare stalling the roll-out of new wireless services. Paul Magelli argues for a simpler approach thatputs the subscriber at the centre of the network.

Cellular operators must dispense with proprietary core-network architecturesand deploy standardized hardware such as these servers.


2 8 C O R E N E T W O R K S

IP Multimedia Subsystem (IMS) technology will play animportant role in delivering converged services across fixed andmobile networks. IMS allows operators to build an open IP-based service infrastructure that will ease the deployment of newmultimedia communication services. Consequently, IMS isviewed as the stepping-stone to seamless mobility in an IP world.

However, before operators can profit from offering seamlessIP services, they must perform a crucial task – the consolida-tion and mobilization of subscriber data. True convergence isnot just a seamless link between connectivity technologies. Atits most fundamental level, convergence must involve the cre-ation and management of a single, comprehensive profile ofeach subscriber.

Managing customer dataThe effective management of customer data is a hallmark ofany successful business, yet for the past 15 years GSM opera-tors have been denied easy access to information regardingtheir own subscribers. The data are often hidden within pro-prietary hardware systems and gaining access involves expensivenegotiations with equipment suppliers and lengthy technicalprocedures. Bluntly put, operators often have to pay theirequipment suppliers in order to retrieve their own customerinformation in order to update records or market new services.

These data are often described as being in “silos” – referringto the fact that the data are held within specific parts of the

network and are not accessi-ble by most other parts.Conventional hardware-basedarchitectures separate sub-scriber data on many systemsacross the network, makingaccess almost impossible with-out the assistance of an equip-ment manufacturer or systemsintegrator. Data are effectivelylocked under layers of

switches, applications and services, making subscriber infor-mation inaccessible, inconsistent and fragmented.

It would be a fundamental error if operators were to retainthis silo architecture for next-generation services. Indeed, thefate of both fixed and mobile operators is inextricably linked totheir ability to support services from a single data repository.Such an environment would allow a subscriber to have multi-ple identities to support the delivery of a range of services.These identities must be tied together to create a single, coher-ent user profile.

The development of subscriber-centric networks will forceoperators to rethink and simplify their core-network architec-tures. Add to this the business realities of a maturing mobilemarket. The industry has already moved from the “wild west”days of relentless subscriber growth, to a greater emphasis onaverage revenue per user (ARPU). More recently, operators areeager to maximize the average margin per user (AMPU), whichis focusing attention on the cost of servicing individual cus-tomers, rather than the cost of deploying technologies. Themove to a subscriber-based environment significantly reducesoperational expenditure as maintenance and support costs fallthrough the elimination of data silos.

Open softwareSilo architectures are best eliminated using an open software-based approach. A resilient, scalable and high-performanceplatform that offers a common subscriber profile can supporta complete suite of mobility applications including the homesubscriber server (HSS), home location server (HLR), prepay,authentication, equipment identify (EIR) and many others.

This approach eliminates the silos, reduces the number ofnetwork elements and removes data inconsistencies. By migrat-ing all subscriber data from multiple and complex networkapplications into a single, manageable directory at the heart ofthe network, mobile operators can radically reduce the size andcomplexity of the network itself. Simplicity is the end productand the benefits are clear and proven: reduced whole-life costby between five and ten times; reduced in-service deploymenttime to less than five days; and the ability to develop anddeliver new services in eight weeks.

IMS will create a phenomenally competitive environmentwith fixed and mobile operators jostling to own the customer.The winners will be those operators that can make the funda-mental shift in both philosophy and underlying core-networkarchitecture.

Paul Magelli is chief executive of Apertio.


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“We test everything that we can test. The one thing that wedon’t test, however, is the only thing that counts – the customer’sexperience. The reason that we don’t do that is because, frankly,it is just too expensive to do in any meaningful way.” Thislament from a senior representative of a cellular network opera-tor reflects the fact that the point of delivery is the only placewhere quality has any real meaning for the mobile-phone user.

The cellular communications industry has been unable tomanage this quality in any meaningful way. This is not for wantof effort on the part of the industry, as many quality measure-ments are taken every day. Rather, the problem lies in the choiceof measurements and how they are made.

Quality has become an important area of competitionbetween operators. Recent surveys have reported that more than30% of subscribers cite quality of service as their top issue and10% of users say that they will change networks because of poorquality. Indeed, this latter figure would probably be higher ifsubscribers believed that there was a higher-quality network tomove to. Quality is even more important when usage is consid-ered, rather than simply subscriber numbers. Heavy users –typically corporate customers – are even more likely to churn ifthey see a chance of better quality.

Churn as indicatorIn a maturing market with few new subscribers left to recruit,churn is becoming an important performance indicator, withoperators seeking to retain existing subscribers, while attractingtheir competitor’s customers.

When voice-call quality drops to the point that one or bothparties cannot follow the conversation, the connection is ter-

minated by a user. If the call was important, the subscribermight switch to a fixed-line phone, but if the conversation wascasual, the call will likely be abandoned. Either way the cus-tomer becomes dissatisfied and the network operator loses rev-enue. However, as far as the network is concerned the call wassuccessful because it was terminated by a user.

Fixed-line network operators have focused their QoS activitieson the core network because this is where the greatest variabil-ity was to be found. Much effort went into improving the over-all quality of the core and, as a result, most fixed-line calls areclear and of high quality.

Radio access networkIn cellular networks the radio access network (RAN) is thegreatest cause of service variability because its characteristicscan change rapidly with both geography and time. Although thequality of the RAN is a crucial parameter, it is often not a quan-tity that is determined in a meaningful way.

Above all, any measurement of quality must reflect the cus-tomer’s perception of the service provided. Most operatorsemploy mean opinion score (MOS) measures – or somethingsimilar – to determine the quality of voice calls. These mea-surements are based upon the perception of quality by thehuman ear and use a scoring system of 0–5. For data and otherservices, quality measurements are based upon transmissionspeed and related parameters. The availability of specific net-work services must also be measured. These criteria are sensiblebecause they reflect the customer’s experience. They can beunderstood by everyone including the network engineer, cus-tomer, marketing director and chief executive.

2 9D R I V E T E S T I N G


Despite spending large sums of money on network testing, operators are failing to measure the quality of service experienced by subscribers. Robin Burton offers a solution.

“I can’t hear you”: Cellular operators struggle to measure the quality of their services where it really matters – at the point of service delivery.

Voice quality must bemeasured where it counts


3 0 D R I V E T E S T I N G

Today, most network operators survey their network for qual-ity using MOS and other measures that reflect the customer’sexperience. Often, a relatively small number of measurementsare taken, which means that any conclusions are based on a sta-tistically insignificant number of measurements. Parts of thenetwork are often missed altogether and important periods ofthe day, such as rush hour, are not adequately surveyed.

Most surveys simply deliver a snapshot service quality at specificlocations, at particular points in time. Long-term trends are oftenmissed and seasonal variations and the effects of special events maybe missed. It certainly means that the process cannot be relied onto provide an early warning of a developing network problem.

Key testThe key test for any measurement system is whether it providesthe information that allows the operator to take decisive action.The answer to that, for most operators’ systems today is, at best,“some of the time”.

Voice quality is traditionally measured by drive testing, whichinvolves teams of network engineers. Sophisticated test phonesare driven around the network while measurements are made.This process yields prodigious amounts of data, which provideinsight into how network problems can be resolved and how thenetwork could be improved.

This is a costly process involving expensive equipment andhighly skilled people. This technique is therefore used sparingly

with an emphasis on problem areas in the network. The numberof readings made is relatively small and, usually, the exercise iscarried out in reaction to customer complaints, rather than as apro-active and ongoing exercise.

A better approach is to automate the process and monitorthe user experience continuously, wherever and whenever sub-scribers are using their phones. This involves the use of largenumbers of highly integrated mobile test units controlled by aback-office server.

These test units are sufficiently small and rugged to be placedon taxis, buses, delivery vehicles and the operator’s own vehicles.Equally important, they are sufficiently low in cost to bedeployed in large numbers. They can – and do – operate 24hours a day for 365 days a year and offer the possibility of gath-ering data in nearly every nook and cranny of the network.Units can also be deployed in fixed positions – to monitor thequality on the premises of important corporate customers, at thehome of a key customer’s chief executive or in the executivelounge of an airport.

Data monitoringOnce these data are collected, it is crucial that they are processedand presented as high-quality information. Data that are gath-ered continuously are best presented in a real-time manner. Thisallows the operator to monitor the development of potentialproblems, and often deal with them before they degrade the cus-tomer’s experience.

The information must also support decision making at severaldifferent levels within the operator. Therefore it must be acces-sible to chief executives, accountants and marketing directorsas well as engineers. Operators must be alerted to exceptions inservice quality to identify areas that need action – rather thanhaving to wade through masses of figures corresponding to nor-mal behaviour in order to identify faults.

This new model for quality assurance is not a replacement fordrive testing, because it will always be necessary to look closely atthe network infrastructure to resolve engineering issues.However, this new model is the only way to measure quality atthe point of delivery – which is where it really counts.

Robin Burton is head of marketing at Sensustech.


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http://www.eumw2005.com

3 2 P R O D U C T S

Transmit module simplifiesGSM/GPRS designThe highly integrated AWT6202PowerPlexer transmit module for GSM/GPRS handsets is new from Anadigics. Themodule comprises an InGaP power amplifier(PA), a pHEMT antenna switch, harmonicfilters and CMOS power control circuitry.

According to Anadigics, the moduleachieves 45% efficiency in the 900 MHzband, equivalent to 57% PA efficiency. Itprovides 40% efficiency in the 1800 MHzband, equivalent to 52% PA efficiency. Themodule occupies 6 × 6 mm board space andis protected from electrostatic discharges ofup to 15 kV.www.anadig ics.com

Platform for GPRS and EDGE Said to include all the hardware andsoftware components required for high-performance wireless phones with advancedmultimedia functionality, the MP-Eplatform is new from Infineon. Theplatform can be used to design GPRS/EDGE phones that support advanced dataservices including video streaming, videorecording and playback. Described as a truethree-chip solution, the platform comprisesbaseband, power management and RFtransceiver devices and occupies less than1250 mm2 on a printed circuit board.

In addition to GSM and GPRS, theplatform supports EDGE with EGPRS class12. The EDGE coding schemes MCS 1–9can achieve data rates up to 236 kbit/s. Theplatform also includes Infineon’s ApplicationProgramming Object-Oriented ExtendableInterface (APOXI), which facilitates thereuse of applications over several productgenerations. An open application protocolinterface (API) is said to ease the integrationof third-party applications. The MP-Eplatform is supplied with a protocol stackand application framework.www.inf ineon.com

PA module breaks size barrierSaid to reduce printed-circuit board spacerequirements by more than 40% comparedto current technologies, the MMM6015power amplifier module is new fromFreescale Semiconductor. The GSM/GPRSmodule performs power amplification,power control, low-pass filtering andantenna switching functions. According toFreescale, the module can also be used tocreate handsets with longer battery life.

The MMM6015 is intended for use inquad-, tri- and dual-band GSM handsets inthe 850, 900, 1800 and 1900 MHz bands.The module also meets requirements relatedto the reduction of hazardous materials inconsumer electronics.

Integrating low-pass harmonic filters andtransmit and receive switches, the moduleoccupies an area of 6 × 8 mm and is 1.15 mmin height. Anti-saturation technology isemployed to prevent switching transientswhen the battery voltage drops. Low-bandcurrent limiting prevents battery collapseunder extreme conditions.www.freescale.com

PA integrates power detectorClaimed to be the world’s smallest linearpower amplifier (PA) module to include anon-chip power detector, the RF5198 is newfrom RF Micro Devices. Designed for usein W-CDMA handsets, the module offersboth high power and high efficiency whileoperating in the 1920–1980 MHz band.

According to RF Micro Devices, the on-chip integration of power detectortechnology allows the module to reducedesign complexity, thereby streamlining thehandset development process. The modulemeasures 3 × 3 × 0.9 mm and has a 50 Ωinput and output ports. The module ismatched internally to obtain optimumpower, efficiency and linearity.

Manufactured on an advanced third-generation GaAs HBT process, the modulefeatures a digital control line that minimizesthe quiescent current. www.rfmd.com

PA combines InGaP and CMOSTriQuint Semiconductor has released aGSM/EDGE power amplifier (PA) modulethat is said to lead the market in efficiencyand RF performance for linear EDGEoperation. The TQM7M5001 is describedas an extremely small multimode poweramplifier module measuring 7 × 7 ×1.1 mm.

Optimized for high EDGE efficiency and

E2 power-class operation, the device alsooffers high GSM/GPRS efficiency. TwoEDGE quiescent current states are providedto minimize power consumption duringbacked-off operation. In EDGE mode thecontrol voltage input is disabled,eliminating the need for a constant voltageduring operation.

The module combines a highly integratedand rugged InGaP power amplifier die witha CMOS controller. The latter implements afully integrated closed-loop power controlwithin the module for GSM operation. Thiseliminates the need for any external couplers,power detectors and current sensors, whilestill assuring the correct output power level.www.tr iquint .com

WLAN front-end is for cellularClaimed to be the industry’s first completelyintegrated WLAN RF front-end modulesoptimized for cellular handsets, theRangeCharger SE2551A and SE2557Amodules are new from SiGe Semiconductor.Offering high performance, integration andlow current consumption, the modulesensure that cellular handset manufacturerscan support WLAN capability withoutimpacting handset form factor, cellularperformance, or battery life.

The modules are based on SiGe’sestablished and highly integrated 2.4 GHzRF front-end architecture. Supplied in a6 × 5 × 1.4 mm package, the devicesincorporate a linear three-stage poweramplifier, power detector, digital enablecircuitry, transmit and receive filtering and areceive balun. A differential receive outputis a key feature of the SE2551A, while theSE2557A has a single-ended receive output.

Both modules support the simultaneoustransmission and reception of WLAN andcellular signals. Operating in 802.11g mode,the devices consume 120 mA, minimizingthe impact of WLAN on battery life.www.sige.com


HANDSET COMPONENTS

http://www.anadigics.com

http://www.infineon.com

http://www.freescale.com

http://www.rfmd.com

http://www.sige.com

http://www.triquint.com


3 3P R O D U C T S

SMA connectors are quick Compel Electronics has released a series ofSMA male connectors with a proprietarypush–pull coupling device compatible withstandard SMA female connectors. Compelsays the connectors allow for a simple andquick interconnection, while achieving theperformance of standard SMA connectors.

The male connectors can be implementedwithout the redesign or modification of thefemale interface. The connectors can beused in confined spaces because no specialtool is required to make the connection.Indeed, in areas where a high number ofinterconnections are required in a limitedspace, the male connectors can be used inconjunction with Compel’s new SMAfemale connectors with reduced flangedimensions. The coupling mechanismachieves a high retention force and electricalperformance of the connector adheres to theMIL-PRF-39012 standard. The connectorscan be used with both flexible and semi-rigid coaxial cables.www.compel . i t

Rake receiver employs FPGAsLattice Semiconductor has released areference design for a rake receiver thatemploys field-programmable gate array logic(FPGA) devices. Intended for use in basestations, the rake receiver counters thenegative effects of RF multipath. Thereference design is based on Lattice’sLatticeECP FPGAs, which combine anoptimized FPGA fabric with high-speed,dedicated on-chip DSP blocks.

The rake receiver operates at 61.44 MHzoperating frequency and has aninterpolation of two-times over-sampledinput data to 1/16 of a chip resolution. Thereceiver handles 16 control channels and 16data fingers. It can achieve the simultaneousgeneration of 16 scrambling codes at chiprate speeds and the simultaneous generationof 16 orthogonal variable spreading factor(OVSF) codes. The de-scrambling anddispreading of input signals with 16different delays is supported. Multiple de-scrambled, de-spread and channel-correctedsignals from a variable number of fingerscan be combined by the receiver.www.latt icesemi.com

BDAs bridge 2G indoor gapRadio Frequency Systems (RFS) hasunveiled a new range of medium- to low-power bidirectional amplifiers (BDAs). TheBDAs are designed for use in indoor 2G

installations and are available in 800, 900and dualband 900/1800 MHz models.According to RFS, the devices are compactand offer flexible “plug and play”installation options for extending the reachof RF distribution systems.

The single-band I-BDA800-1 andI-BDA900-1 models operate at 800 MHzand 900 MHz respectively. Both feature anominal gain of 40 dB and compositeoutput power levels of 13 dBm in the uplinkand 23 dBm in the downlink. These BDAshave an internal AC power supply and areoptimized for single- and multicarrier usefor CDMA at 800 MHz and GSM at900 MHz.

Dual-band 900/1800 MHz BDAs areavailable in two power ratings: the medium-power I-BDA900/1800-1 and the low-power I-BDA900/1800-2 have nominalgains of 30 dB and 20 dB respectively. www.rfswor ld.com

Integrated base stationtransceiver reduces costsOneBase Macroshelf combines productsand technologies from Andrew into a single,integrated base-station transceiver (BTS) RFsystem. Based on open standards such asCPRI or OBSAI – rather than a customdesign – the system allows OEMs topurchase the entire RF portion of a BTSfrom one supplier.

According to Andrew, OneBaseMacroshelf will allow OEMs to reduce thecost of their equipment as well as devote

more engineering resources towards thedevelopment of revenue-generatingintellectual property. Andrew claims thatthe system allows OEMs to retain fullcontrol of the BTS system specificationsbecause OneBase Macroshelf provides theRF portion of the system according to theOEM’s RF performance requirements.www.andrew.com

RF mixer simplifies base stationsA new active down-converting RF mixerfrom Linear Technology is claimed toreduce the cost and complexity of 3G basestations. The LT5527 features high-linearityand operates at frequencies between400 MHz and 3.7 GHz. At 1.9 GHz thedevice features an input third-orderintercept point (IIP3) value of 23.5 dBm, aconversion gain of 2.3 dB, and a 12.5 dBnoise figure.

The local oscillator (LO) and RF inputsare single-ended and have on-chip RFtransformers to ensure 50 Ω impedance.This reduces the number of externalmatching components required in thereceiver design. The LT5527 alsoincorporates a low-noise LO buffer, whichallows operation at a –3 dBm LO drivelevel. This eases RF isolation and minimizesthe need for external filtering.www.l inear.com

7/16 DIN loads operate to 3 GHzMECA introduces compact 2 W and 5 W7/16 DIN male coaxial loads for use in basestations and in-building wirelessdeployments. The rugged devices are said tooffer excellent performance across allwireless bands from DC to 3 GHz.

The 401-11 operates at an average powerof 2 W and a peak power of 250 W. It offersa voltage standing wave ratio (VSWR) of1.10:1 in the DC to 1.0 GHz range; 1.15:1at 1.0–2.0 GHz; and 1.20:1 at 2.0–3.0 GHz.The 405-11 has the same VSWR values butoperates at 5 W with 250 W peak power.www.e-meca.com


INFRASTRUCTURE

http://www.compel.it

http://www.latticesemi.com

http://www.rfsworld.com

http://www.andrew.com

http://www.linear.com

http://www.e-meca.com


3 4 T H E F U T U R E

Why do analogue RF in CMOS?Moving all the analogue RF circuitry to CMOSopens the door to further integration with dig-ital circuits. For years the industry believed thatRF applications could never fully take advan-tage of CMOS. Silicon Laboratories proved thiswrong in 1998 when we pioneered the integra-tion of voltage-controlled oscillators (VCOs)with phase-locked loops (PLLs) on a singlechip. This was a significant achievement and wetook the market by storm. Canned VCO mod-ules quickly became obsolete because ourCMOS components delivered higher perfor-mance, better yields, low power requirementsand improved settling times – all at a lower cost.

We took a radical approach to VCO integra-tion. Digital techniques were used to managethe integration of a high-performance VCOand a high-performance PLL synthesiser, while meeting theexacting standards of GSM/GPRS handset makers. Achievingthis in a standard CMOS process was a bonus because we couldguarantee that we could keep costs low, which is a fundamentalreason that we are working in CMOS.

As microprocessor production moves from the 90 nm to the65 nm node, digital chipmakers pipe-clean the process for usand drive the cost down. This allows us to put our RF chips intoprocess nodes that are much, much smaller than our competi-tors. Things get easier for RF circuits as the CMOS process nodegets smaller. One key point is that the 1/f noise is reduced asthe process shrinks. The other important point is that the FT[cut-off frequency] increases as the process shrinks, which givesus more margin for higher frequency operation.

How does the company approach multimode integration?Our goal is to simplify the overall architecture. We are the onlycompany doing this in high-volume production and we alreadyhave many of the required digital circuits on our transceiver.An important part of our strategy is to move some digital func-tionality from the baseband to the transceiver. While this makesthe transceiver more expensive, it reduces the overall system cost.

For example, we have an analogue-to-digital converter (ADC)in the receive path on our transceiver, which provides a digitalinterface to the baseband. This is a major advantage for multi-mode operation because it allows the transceiver to performthe down conversion and output a digital, rather than an ana-logue signal. As a result, the baseband no longer requires anADC or filters and other expensive analogue circuits.

While a digital interface does not necessarily minimize theamount of analogue circuitry, our design reduces the overall

cost. The same thing can be achieved on thetransmit side by eliminating some of the digi-tal-to-analogue converters (DACs), which fur-ther lowers the overall system cost. A digitalinterface definitely represents the future – andnot just for multimode, but also for more con-ventional handset designs.

Can this architecture support multiplemodulation schemes?Issues related to the various modulation schemesare complex, but the challenges can be over-come. If the digital interface is in the transmitpath, then the modulators must be on the trans-ceiver rather than on the baseband – a GMSKmodulator for GSM, 8PSK for EDGE, and var-ious modulators for UMTS and HSUPA.

The challenge is to manage this, and I believethis can be done. Another option – which may be even morecost effective – is for the modulator to remain on the baseband,from where it directly modulates a VCO on the transceiver.Modulation can be approached in different ways and there areno hard and fast rules as to where these boundaries will be.

Is higher integration on silicon always the best way to go?We think about this issue a lot and our general impression isthat integration on a monolithic piece of silicon always wins inthe end. Time after time, when a company releases an integratedmonolithic solution in CMOS, the rest of the industry follows.

I am a true believer in CMOS integration because it mini-mizes the cost associated with chip packaging, which is veryhigh when you have multiple dies. While innovative packagingstrategies like multichip modules can reduce costs, they are stop-gap measures compared to monolithic integration.

Is device integration changing the way phones are developed?The handset development process has changed considerably in thepast three to four years. In the past our customers maintained50:50 split in their hardware and software engineering pro-grammes – today it is 30% hardware and 70% software.The hard-ware has become easier because companies such as SiliconLaboratories have simplified RF design through greater integra-tion.This has had a real impact on the industry because companieswith very few RF engineering experts can still achieve excellentperformance with minimal revisions of the design of their PCBs.Integration on the silicon is allowing our customers to achieve sen-sitivities that they could only dream of a few years ago.

Interview by Hamish Johnston, editor of Wireless Europe.


CMOS brings Moore’s Law to RFSilicon Laboratories’ vice-president of wireless products Dan Rabinovitsj

explains why he is passionate about CMOS RF.

Dan Rabinovitsj: “Integration on amonolithic piece of silicon alwayswins in the end.”


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