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Ericsson Review: HSPA evolution for future mobile-broadband needs


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As HSPA evolution continues to address the needs of changing user behavior, new techniques develop and become standardized. This article covers some of the more interesting techniques and concepts under study that will provide network operators with the flexibility, capacity and coverage needed to carry voice and data into the future, ensuring HSPA evolution and good user experience.

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Ericsson Review: HSPA evolution for future mobile-broadband needs

  1. 1. The communications technology journal since 1924 2013 • 9 HSPA evolution for future mobile-broadband needs August 28, 2013
  2. 2. HSPA evolution for future mobile-broadband needs As HSPA continues to evolve, addressing the needs of changing user behavior, new techniques develop and become standardized. These techniques provide network operators with the flexibility, capacity and coverage needed to carry voice and data into the future. achievedbysecuring: capacity–tohandlegrowingsmart- phonetrafficcost-efficiently; flexibility–tomanagethewiderangeof trafficpatternsefficiently;and coverage–toensuregoodvoiceandapp userexperienceeverywhere. Appcoverage For smartphone applications, like social networking and video stream- ing, to function correctly, access to the data network and a network that can deliver a defined minimum lev- el of performance is needed. The rela- tionship between the performance requirements (in terms of data speed and response time) of an application and the actual performance delivered by the network for that user at their location at a given time determines howwelltheuserperceivestheperfor- manceoftheapplication. The term app coverage denotes the level of network performance need- ed to provide subscribers with a sat- isfactory user experience for a given application. In the past, the task of dimensioning networks was simpler, as calculations were based on deliv- ering target levels of voice coverage and providing a minimum data rate. Today’s applications, however, have widely varying performance require- ments. As a result, dimensioning a network has become a more dynam- ic process and one that needs to take these varying performance require- mentsintoconsideration,forappsthat arecurrentlypopularwithsubscribers. Footprint Illustrated in Figure 2, at the end of 2012, 55 percent of the world’s replacingvoice-centricfeaturephones. For less than USD 100, consumers can purchase highly capable WCDMA/ HSPA-enabledsmartphoneswithdual- core processors and dual-band oper- ation that support data rates up to 14.4Mbps.Thisprice-to-­sophistication ratio has turned the smartphone into an affordable mass-market product, and has accelerated the increase in smartphonesubscriptions–­estimated to rise from 1.2 billion at the end of 2012to4.5billionby20181 . Ericsson ConsumerLab studied a group of people to assess how they perceived network quality and what issues they encountered when using their smartphones. The study identi- fiedtwokeyfactorsthatareessentialto theperceivedvalueofasmartphone:a fastandreliableconnectiontothedata network,andgoodcoverage2 . These findings highlight an impor- tant goal for operators: to provide all network users with high-speed data services and good-quality voice ­services everywhere. This can be NIKLAS JOHANSSON, LINDA BRUS, ERIK LARSSON, BILLY HOGAN AND PETER VON WRYCZA BOX A Terms and abbreviations CELL_FACH Cell forward access channel CPC Continuous Packet Connectivity DPCH Dedicated Physical Channel EUL Enhanced Uplink HS-DSCH High-Speed Downlink Shared Channel HSDPA High-speed Downlink Packet Access HSPA High-speed Packet Access HSUPA High-speed Uplink Packet Access LPN low-power node M2M machine-to-machine MBB mobile broadband MIMO multiple-input multiple-output ROT rise-over-thermal SRB Signaling Radio Bearer UL uplink URA_PCH UTRAN registration area paging channel UTRAN Universal Terrestrial Radio Access Network WCDMA Wideband Code Division Multiple Access Mobile broadband (MBB), providing high-speed internet access from more or less anywhere, is becoming a reality for an increasing proportion of the world’s population. There are several factors fuelling the need for high-performance MBB networks, not the least, the growing number of mobile internet connections. As Figure 1 illustrates, global mobile subscriptions (excluding M2M) are predicted to grow to 9.1 billion by the end of 2018. Nearly 80 percent of mobile subscriptions will be MBB ones1 , indicating that MBB will be the primary service for most operators in the coming years. Impactofaffordablesmartphones To a large extent, the rapid growth of MBB can be attributed to the wide- spread availability of low-cost MBB- capable smartphones, which are 2 ERICSSON REVIEW • AUGUST 28, 2013 Smarter networks
  3. 3. population was covered by WCDMA/ HSPA, a figure that is set to rise to 85 percent by the end of 20181 . Today, many developed markets are nearing the 100 percent population coverage mark3 . This widespread deployment, togetherwithsupportforthebroadest rangeofdevices,makesWCDMA/HSPA the primary radio-access technology to handle the bulk of MBB and smart- phonetrafficforyearstocome. Since its initial release, the 3GPP WCDMA standard has, and continues to,evolveextensively.Today,WCDMA/ HSPA is a best-in-class voice solution withexceptionalvoiceaccessibilityand retainability. It offers high call reten- tionaswellasbeinganexcellentaccess technologyforMBB,asitdelivershigh data rates and high cell-edge through- put – all of which enable good user experienceacrosstheentirenetwork. ThecontinuedevolutionofWCDMA/ HSPAinReleases11and12includessev- eral key features that aim to increase network flexibility and capacity to meet growing smartphone traffic and securevoiceandappcoverage. Evolutionoftrafficpatterns Applications have varying demands and behaviors when it comes to when and how much data they transmit. Some apps transmit a large amount of data continuously for substantial periods of time and some transmit small packets at intervals that can range from a few seconds to minutes orevenlonger.Applicationshavevary- ing demands, typically sending lots of data in bursts, interspersed with peri- ods of inactivity when they send little ornodataatall. Rapid handling of individual user requests, enabled by high instanta- neous data rates, improves overall net- work performance as control-channel overhead is reduced and capacity for other traffic becomes available soon- er. So, if a network can fulfill requests speedily, all users will experience the benefits of reduced latency and faster round-triptimes. Web browsing on a smartphone is a classicexampleofaburstyapplication, bothforuplinkanddownlinkcommu- nication.Whenasmartphonerequests the components of a web page from the network (in the uplink) they are transferredinbursts(inthedownlink), andthedeviceacknowledgesreceiptof the content (in the uplink). As a result, uplink and downlink performance becomes tightly connected and there- fore better uplink performance has a positive effect on downlink data rates aswellasoverallsystemthroughput. Forwebbrowsing,theinstantaneous downlinkspeedformobileusersneeds tobemuchhigheronaveragethanthe uplinkspeed.However,thenumberof services requiring higher data rates in the uplink, such as video calling and cloud synching of smartphone data, is ontherise. As user behavior changes, traffic-­ volumepatternsalsochange,andmea- surements show it is becoming more commonforuplinklevelstobeon FIGURE 1 Mobile and MBB subscriptions (2009-2018)1 Mobile subscriptions Mobile broadband 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 0 2,000 1,000 3,000 4,000 6,000 5,000 8,000 7,000 9,000 10,000 Subscriptions/lines (million) FIGURE 2 Population coverage by technology (2012-2018) 100 80 60 40 20 2012 2018 2012 2018 2012 2018 0 %populationcoverage (Source: Ericsson1 ) 85% 90% ~55% 85% ~10% ~60% GSM/EDGE WCDMA/HSPA LTE 3 ERICSSON REVIEW • AUGUST 28, 2013
  4. 4. par with downlink levels, and in some cases even outweigh the down- link traffic. Consequently, continuing to develop data rates to secure uplink- heavyservicesiskeytoimprovingover- alluserperformance. Highperformancenetworks Thestandardapproachusedtocreatea high-performance network with wide coverage and high capacity is to first improve the macro layer, then ­densify it by deploying additional macro base stations, and finally add low power nodes (LPNs) in strategic places, such astraffichotspots,thatcanoffloadthe ­macronetwork. Each step addresses specific perfor- mance targets and applies to different population densities, from urban to rural – as illustrated in Figure 3. The evolution of WCDMA/HSPA includes a number of features that target macro layer improvement and how deploy- ments where LPNs have been added canbeenhanced. Improvingtheuplink Featuresinthe3GPPspecificationhave recentlyachievedsubstantialimprove- ment of uplink capabilities. Features such as uplink multi-carrier, higher- order modulation with MIMO, EUL in CELL_FACH state, and Continuous Packet Connectivity (CPC) have multi- plied the peak rate (up to 34Mbps per carrierinRelease11)andincreasedthe number of simultaneous users a net- workcansupportalmostfivefold. Given the high uplink capabilities already supported by the standard, thenextdevelopment(Release12)will enable and extend the use of these capabilities to as many network users aspossible. Themaximumalloweduplinkinter- ference level in a cell, also known as maximum rise-over-thermal (ROT), is a highly important quantifier in WCDMAnetworks.Thisisbecausethe maximum allowed interference level has a direct impact on the peak data ratesthatthecellcandeliver. Typically, macro cells are dimen- sioned with an average ROT of around 7dB, which enables UL data rates of 5.7Mbps (supported by most commer- cial smartphones), and secures voice and data coverage for cell-edge users. FIGURE 3 Where to improve, densify and add Improve Densify Add Improve Densify Improve Dense urban Urban Suburban Rural Area traffic density FIGURE 4 Relationship between maximum interference and peak rate UL ROT Rate Y X Y = Maximum interference handled by the network X = Maximum uplink data rate that can be achieved Legend 4 ERICSSON REVIEW • AUGUST 28, 2013 Smarter networks
  5. 5. High data rates, such as 11Mbps (avail- ablesincerelease7)and34Mbps(avail- ablesincerelease11)requireROTlevels greaterthan10dBand20dBrespective- ly.Figure 4illustratestherelationship betweenROTandpeakdatarate. The maximum uplink interference level permissible is determined by a number of factors including the den- sity of the network, the capability of thenetworktohandleinterference(for example with advanced techniques suchasInterferenceSuppression),and the capabilities of the devices in the network,includingbothsmartphones andlegacyfeaturephones. The Lean Carrier solution, intro- duced in Release 12, is an additional capability that helps operators meet the needs of high-data-rate users. This multi-carrier solution is built on the Release 9 HSUPA dual-carrier one that is currently being implemented in commercial smartphones. The dual- carrier solution allows two carriers, primaryandsecondary,tobeassigned to a user. By doing this, the traffic gen- eratedbytheusercanbeallocatedina flexible way between the two carriers, while at the same time doubling the maximumpeakrateachievable. TheLeanCarriersolutionoptimizes thesecondarycarrierforfastandflexi- blehandlingofmultiplehigh-data-rate users, through more efficient grant- ingandlowercostperbit.Thesolution is designed to support multiple bursty data users in a cell transmitting at the highestpeakrateswithoutcausingany uplinkinterferenceamongthemselves ortolegacyusers.Tomaximizeenergy efficiency, the Lean Carrier solution should cost nothing in system or ter- minal resources on the secondary car- rieruntiltheuserstartstosenddata. LeanCarriercanbeflexiblydeployed accordingtotheneedsofthenetwork. For example, the maximum ROT on a user’s secondary (lean) carrier can be configured to support any available uplink peak data rate, while the maxi- mum ROT on a user’s primary carrier can be configured to secure cell-edge coverage for signaling, random access andlegacy(voice)users. Rateadaptationisanothertechnolo- gyunderstudythatresultsinincreased network capacity for some common traffic scenarios, such as areas where subscribers are a mix of high and low-rate users or areas where there are only high-rate users. High uplinkdataratesrequiremorepow- er. Maintaining a fixed data rate at thedesiredqualitytargetinanenvi- ronment where interference lev- els vary greatly can result in large fluctuations in received power. To avoidsuchfluctuations,theconcept of rate adaptation can be applied. High-rate users are assigned with a fixedreceived-powerbudget,andas interferencelevelschange,bitrates areadaptedtomaintainthedesired quality target, while not exceeding theallowedpowerbudget.Inshort, as illustrated in Figure 5, the bit rate is adapted to received power, andnotthepowertotherate. Limitingfluctuationsinreceived power for high-rate users is good for overall system capacity because these high-rate users can transmit more efficiently, and other users in thesystem,includinglow-rateones such as voice users, consume less powerwhenpowerlevelsarestable andpredictable. Maintaining a device in connect- ed mode for as long as possible is anothertechniquethatcanbeused to improve performance of the uplink. Smartphone users want to be able to rapidly access the network from a state of inactivity. Maintaining a device in a connected-mode state, such as CELL_FACH or URA_PCH, for aslongaspossibleisonewayofachiev- ing this – access to the network from these states is much faster than from the IDLE state. In recent releases, con- nectedmodehasbeenmademoreeffi- cientfromabatteryandresourcepoint ofviewthroughtheintroductionoffea- turessuchasCPC,fractionalDPCHand SRB on HS-DSCH. As a consequence it is now feasible to maintain inactive devicesinthesestatesforlonger. As the number of smartphone users increases, networks need flexi- ble mechanisms to maintain high sys- tem throughput, even during periods of extremely heavy load. Allowing the networktocontrolthenumberofcon- currently active users, as well as the number of random accesses, is one suchmechanism. Improvements that enable high throughput under heavy load, and allowuserstobenefitfromlowerlaten- cy in connected mode, while enabling service-differentiated admission deci- sions and control over the number of simultaneous users, have been pro- posedforRelease12. Expandingvoiceandappcoverage Good coverage is crucial for positive smartphone user experience and cus- tomerloyalty2 ,whichforoperators FIGURE 5 Rate adaptation results in predictable interference levels Baseline: Fixed rate variable power Received power DATA Control DATA Control Time Rate adaptation: Fixed received power and variable rate 5 ERICSSON REVIEW • AUGUST 28, 2013
  6. 6. lower-rate speech codecs, where- as, four-way receiver diversity and advanced antennas can improve cov- erageforbothvoiceanddata. Uplinktransmitdiversitywasintro- duced in Release 11. This feature sup- ports terminals with two antennas to increase the reliability and coverage of uplink transmissions and decrease overall interference in the system. It works by allowing the device to use both antennas for transmission in an efficient way using beamforming. Figure 6 illustrates how the radio transmission becomes focused in a given direction, resulting in a reduc- tionininterferencebetweenthedevice and other nodes, and improving over- all­systemperformance. An additional mode within uplink transmitdiversityisantennaselection. Here, the antenna with the best radio propagation conditions is chosen for transmission. This is useful, for exam- ple, when one antenna is obstructed by the user’s hand. Uplink transmit diversity increases the coverage of all uplink traffic for voice calls and data transmissions. With Release 11, multi-flow HSDPA transmissions are supported. This allows two separate nodes to transmit to the same terminal, improving per- formanceforusersatthecelledgeand resultinginbetterappcoverage. In Release 12, simultaneous app data and voice call transmissions will become more efficient, and the time it takes to switch transmission time interval from 10ms to 2ms is consid- erably shorter. These improvements increasebothvoiceandappcoverage. Enhancingsmall-celldeployments The addition of small cells through deploying LPNs in a macro network – resulting in a heterogeneous network –isastrategicwaytoimprovecapacity, dataratesandcoverageinurbanareas. Typically, the deployment of LPNs is beneficialinhotspotswheredatausage is heavy, to bridge coverage holes cre- ated by complex radio environments, andinsomespecificdeploymentssuch asin-buildingsolutions. Figure 7 shows the performance gains in a heterogeneous-network deployment (described in Box B). Offloading to small cells not only FIGURE 7 System-level gains – for scenario described in Box B 1W 5W 0 50 Average Cell edge 100 150 200 250 300 User throughput gain (percent) BOX B   The system The scenario shown in Figure 7 is for bursty traffic. Four LPNs have been added to each macro base station in the network, and 50 percent of the users are located in traffic hotspots. The transmission power for the macro base station was 20W, and 1W and 5W LPNs were deployed. LPNs were deployed randomly and no LPN range expansion was used. Gains are given relative to a macro-only deployment. Offloading was 32 percent for 1W LPNs and 41 percent for 5W LPNs, where offloading is a measure of the percentage of traffic served by the LPN. FIGURE 6 Release 11 uplink transmit diversity beamforming translatesintosecuringvoicecoverage and delivering data-service coverage that meets the needs of current and futureapps. There are several ways to improve coverage for voice and data. One way is to use lower frequency bands, and refarmingthe900MHzspectrumfrom GSM, for example, provides a consid- erable coverage improvement when compared to 2GHz bands. Voice cover- agecanbesignificantlyextendedwith 6 ERICSSON REVIEW • AUGUST 28, 2013 Smarter networks
  7. 7. 1. Ericsson Mobility Report, June 2013, available at: 2. Ericsson ConsumerLab report, January 2013, Smartphone usage experience – the importance of network quality and its impact on user satisfaction, available at: network-quality-is-central-to-positive-smartphone-user-experiences-and- customer-loyalty_244129229_c 3. International Communications Market Report 2011, Ofcom, available at: http:// References FIGURE 8 LPN deployment scenarios LPN LPN LPN Macro LPNs deployed as separate cells on the same carrier RNC LPN LPN LPN Macro LPNs deployed as part of a combined cell on the same carrier RNC 7 ERICSSON REVIEW • AUGUST 28, 2013 provides increased capacity for han- dlingsmartphonetraffic,italsoresults inenhancedappcoverage. To maximize spectrum usage, the traditional macro base stations and LPNs share the same frequency, either with separate or shared cell identi- ties. These deployments, illustrated in Figure 8, are referred to as separate cellandcombinedcell. It is possible to operate both sepa- rate and combined-cell deployments based on functionality already imple- mentedinthe3GPPstandard,andsuch deployments have been shown to pro- videsubstantialperformancebenefits overmacro-onlydeployments. Today, combined cells tend to be deployed in specific scenarios, such as railroad,highwayandin-buildingenvi- ronments. Separate-cell deployments, on the other hand, are more generic andprovideacapacityincreaseinmore commonscenarios. In 3GPP Release 12, small-cell range expansion techniques and control channel improvements are being introduced to enable further offload- ing of the macro network. Mobility performance enhancements for users moving at high speeds through small cell deployments are also being inves- tigatedby3GPP. When a macro cell in a combined- celldeploymentiscomplementedwith additionalLPNsclosetousers,thedata rateandnetworkcapacityisimproved. By allowing the network to reuse the same spreading codes in different parts of the combined cell, the cell’s capacity can be further increased – a techniquebeingstudiedinRelease12. Andasthereisnofundamentaluplink/ downlink imbalance in a combined cell, mobility signaling is robust, sig- naling load is reduced, and network managementissimplified. In summary, heterogeneous net- worksareessentialforhandlinggrow- ing smartphone traffic because they supportflexibledeploymentstrategies, increase the capacity of a given HSPA network,andextendvoiceandappcov- erage. The improvements standard- izedinRelease12willfurtherenhance theseproperties. Conclusions WCDMA/HSPA will be the main technology providing MBB for many years to come. Operators want WCDMA/HSPA networks that can guarantee excellent user experience throughout the whole network cover- age area for all types of current and future mobile devices. The prerequi- sitesfornetworksare: capacity–tohandlegrowingsmart- phonetrafficcost-efficiently; flexibility–tomanagethewiderangeof trafficpatternsefficiently;and coverage–toensuregoodvoiceandapp userexperienceeverywhere. HSPA evolution, through the capabili- tiesalreadyavailablein3GPPandthose under study in 3GPP Release 12, aims to fulfill these prerequisites. There are several ways to improve voice and app coverage. Enhancements to the uplink improve the ability to quick- ly and efficiently serve bursty traf- fic – improving user experience and increasing smartphone capacity. Small-cellimprovementswillincrease networkcapacityforsmartphonetraf- fic and further improve voice and app coverage. With all of these enhancements, WCDMA/HSPA, already the dominant MBB and best-in-class voice technolo- gy,hasastrongevolutionpathtomeet the future demands presented by the growth of MBB and highly capable smartphonesglobally.
  8. 8. Telefonaktiebolaget LM Ericsson SE-164 83 Stockholm, Sweden Phone: + 46 10 719 0000 Fax: +46 8 522 915 99 284 23-3201 | Uen ISSN 0014-0171 © Ericsson AB 2013 Niklas Johansson is a senior researcher at Ericsson Research. He joined Ericsson after receiving his M.Sc. in engineering physics and B.Sc. in business studies from Uppsala University in 2008. Since joining Ericsson, he has been involved in developing advanced receiver algorithms and multi-antenna transmission concepts. Currently, he is project manager for the Ericsson Research project that is developing concepts and features for 3GPP Release 12. Peter von Wrycza is a senior researcher at Ericsson Research, where he works with the development and standardization of HSPA. He received an M.Sc. (summa cum laude) in electrical engineering from the Royal Institute of Technology (KTH), Stockholm, Sweden, in 2005, and was an electrical engineering graduate student at Stanford University, Stanford, CA, in 2003-2005. In 2010, he received a Ph.D. in telecommunications from KTH. Erik Larsson joined Ericsson in 2005. Since then has held various positions at Ericsson Research, working with baseband algorithm design and concept development for HSPA. Today, he is a system engineer in the Technical Management group in the Product Development Unit WCDMA and Multi-Standard RAN and works with concept development and standardization of HSPA. He holds an M.Sc. in engineering physics (1999) and a Ph.D. in signal processing (2004), both from Uppsala University, Sweden. Billy Hogan joined Ericsson in 1995 and works in the Technical Management group in the Product Development Unit WCDMA and Multi-Standard RAN. He is a senior specialist in the area of enhanced uplink for HSPA. He works with the system design and performance of EUL features and algorithms in the RAN product, and with the strategic evolution of EUL to meet future needs. He is currently team leader of the EUL Enhancements team for 3GPP release 12. He holds a B.E. in electronic engineering from the National University of Ireland, Galway, and an M.Eng in electronic engineering from Dublin City University, Ireland. Linda Brus joined Ericsson in 2008. Since then, she has been working with system simulations, performance evaluations, and developing algorithms for WCDMA RAN. Today, she is a system engineer in the Technical Management group in the Product Development Unit WCDMA and Multi- Standard RAN, working with concept development for the RAN product and HSPA evolution. She holds a Ph.D. in electrical engineering, specializing in automatic control (2008) from Uppsala University, Sweden. 8 ERICSSON REVIEW • AUGUST 28, 2013 Smarter networks