[Type text]
TABLE OF CONTENTSExecutive Summary ..........................................................................................
EXECUTIVE SUMMARYLTE networks are being rolled out at an increasing speed, while at the same time the existing HSPAnetwork...
1. INTRODUCTION1.1 SCOPEThis white paper will highlight some of the key aspects and architecture options available for agg...
ubiquitous in major cities throughout Latin America and is setting the stage for future deployments of LTEin 2012 and beyo...
According to research from In-Stat, LTE mobile broadband technology is set for a surge in growth overthe next four years. ...
2. MULTICARRIER AND MULTI-RADIO NETWORK EVOLUTION2.1 SPECTRUM AND DEPLOYMENT ASPECTSMobile operators are being driven to p...
The efficiency of LTE is greater in the wider channel widths (2 x 10 MHz and greater). And 5 MHz HSPAchannels combined wit...
2.2 HSPA EVOLUTION FROM MULTIPLE CARRIERS TO MULTICARRIERTraditionally in the HSPA technology evolution the possibility fo...
6                            Figure 2: PDCP-RLC-MAC-PHY layer mapping on DownlinkTo allow multiple carriers operation in d...
Similar to DC-HSDPA, multiple carriers operation was introduced in the uplink in Rel-9 as DC-HSUPA,and the peak data rate ...
Table 2: 3GPP-defined 4-Carrier HSDPA band combinations with all carriers within a band adjacent to each other   4C-HSDPA ...
Release 11                                                                                    336 Mbps                    ...
2.3 LTE EVOLUTION FROM MULTIPLE CARRIERS TO CARRIER AGGREGATIONTraditionally in the LTE technology evolution the possibili...
7                           Figure 6: PDCP-RLC-MAC-PHY layer mapping on downlinkFrom the higher layer perspective, each co...
Figure 7: Regular DL resource assignment           Figure 8: DL resource assignment with cross-carrier controlWhile Releas...
2.4 HSPA AND LTE INTERWORKINGDuring the roll-out of the LTE, it is vital to be able to use the HSPA system to provide cove...
When the UE is in connected mode in LTE, it can be moved to HSPA by means of an inter-RAT handoveror inter-RAT redirection...
2.5 HSPA+LTE CARRIER AGGREGATIONThe previous sections capture the work done in the HSPA and LTE evolution from single carr...
3. BENEFITS AND USE CASES OF HSPA+LTE AGGREGATION3.1 BENEFITS OF HSPA+LTE AGGREGATIONAs discussed in sections 1 and 2, at ...
Figure 12 illustrates downlink data rates in a single UE scenario, where before re-farming both HSPA andLTE have 10MHz ban...
4. HSPA+LTE AGGREGATION SYSTEM ARCHITECTURE CONSIDERATIONSThe most critical architectural design choice for HSPA+LTE aggre...
Table 6: A high level summary of the different architecture approachses for HSPA+LTE aggregation Split/Merger             ...
4.1 SERVICE OR CORE NETWORK LEVEL SPLIT/MERGERWhile carrier aggregation is usually seen as a RAN functionality, in theory ...
Both alternatives would however require pure dual-radio with simultaneous dual-transmission which leads(at least) to the f...
4.2 HSPA RAN LEVEL SPLIT/MERGERAnother alternative is to place the data split/merger point in HSPA RAN in which case the d...
Introducing the data split/merger at NodeB level (Figure 17) would limit most of the changes to basestation level which co...
Here, the most appealing alternative would be to reuse the PDCP, RLC and MAC-d protocols from HSPA.With this approach, the...
4.3 LTE RAN LEVEL SPLIT/MERGERIn this alternative data is divided between LTE and HSPA radio in eNodeB (as illustrated in ...
implies that NodeB and eNodeB should either be co-located or integrated into one multi-radio BTS. Thisis however not that ...
5. PRACTICAL IMPLEMENTATION ASPECTS OF HSPA+LTE AGGREGATION5.1 BASE STATION RADIO IMPLEMENTATION ASPECTSFigure 21 shows a ...
5.2 DEVICE RADIO IMPLEMENTATION ASPECTSFigure 22 shows a very simplified block-diagram of a UE capable of receiving simult...
Figure 23 shows a very simplified block-diagram of a UE capable of transmitting on two frequency bands,but not simultaneou...
5.3 IMPLEMENTATION ASPECTS OTHER THAN RADIO PROCESSINGDifferent architecture options discussed in section 4 set different ...
6. CONCLUSIONHSPA+ and LTE are the overwhelming mobile broadband technologies of choice for operators throughoutthe world....
ABBREVIATIONS3GPP       3rd Generation Partnership Project4C-HSDPA   4-Carrier HSDPA8C-HSDPA   8-Carrier HSDPAA/N        A...
NACK    Negative ACKO&M     Operation and MaintenanceOEM     Original Equipment ManufacturerPA      Power AmplifierPCC    ...
ACKNOWLEDGEMENTSThe mission of 4G Americas is to promote, facilitate and advocate for the deployment and adoption of the3G...
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Getting further integration between HSPA and LTE with carrier aggregation

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LTE networks are expanded and upgraded with the more advanced HSPA+ features in order to cater to the ever-increasing appetite for wireless data. Due to the major investments in the HSPA+ infrastructure and the vast and rapidly increasing HSPA+ based mobile broadband device penetration the two networks can be foreseen to coexist in parallel for years to come. The evolution of both HSPA+ and LTE standards has introduced aggregation of carriers for higher data rates, better load balancing and increased spectrum utilization, and since the dawn of LTE, the standard support for radio level interworking for HSPA and LTE radios has been included. A natural continuation of such development is to tighten the interworking even further and introduce similar aggregation of carriers between the two radio access technologies.

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Transcript of "Getting further integration between HSPA and LTE with carrier aggregation"

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  2. 2. TABLE OF CONTENTSExecutive Summary ...................................................................................................................................... 2 1. Introduction .............................................................................................................................................. 3  1.1 Scope .................................................................................................................................................. 3  1.2 HSPA+ and LTE network deployment projections .............................................................................. 3 2. Multicarrier and multi-radio network evolution ......................................................................................... 6  2.1 Spectrum and deployment aspects ..................................................................................................... 6  2.2 HSPA evolution from multiple carriers to multicarrier .......................................................................... 8  2.3 LTE Evolution from multiple carriers to carrier aggregation .............................................................. 13  2.4 HSPA and LTE interworking.............................................................................................................. 16  2.5 HSPA+LTE carrier aggregation ......................................................................................................... 18 3. Benefits and use cases of HSPA+LTE aggregation .............................................................................. 19  3.1 Benefits of HSPA+LTE aggregation .................................................................................................. 19  3.2 Example USE cases for HSPA+LTE Aggregation ............................................................................ 20 4. HSPA+LTE aggregation system architecture considerations ................................................................ 21  4.1 Service or core network level split/merger ........................................................................................ 23  4.2 HSPA RAN level split/merger ............................................................................................................ 25  4.3 LTE RAN level split/merger ............................................................................................................... 28 5. Practical implementation aspects of HSPA+LTE aggregation............................................................... 30  5.1 Base station Radio implementation aspects ..................................................................................... 30  5.2 Device Radio implementation aspects .............................................................................................. 31  5.3 Implementation aspects other than radio processing........................................................................ 33 6. Conclusion ............................................................................................................................................. 34 Abbreviations .............................................................................................................................................. 35 Acknowledgements ..................................................................................................................................... 37  1 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  3. 3. EXECUTIVE SUMMARYLTE networks are being rolled out at an increasing speed, while at the same time the existing HSPAnetworks are expanded and upgraded with the more advanced HSPA+ features in order to cater to theever-increasing appetite for wireless data. Due to the major investments in the HSPA+ infrastructure andthe vast and rapidly increasing HSPA+ based mobile broadband device penetration the two networks canbe foreseen to coexist in parallel for years to come.The evolution of both HSPA+ and LTE standards has introduced aggregation of carriers for higher datarates, better load balancing and increased spectrum utilization, and since the dawn of LTE, the standardsupport for radio level interworking for HSPA and LTE radios has been included. A natural continuation ofsuch development is to tighten the interworking even further and introduce similar aggregation of carriersbetween the two radio access technologies.The HSPA+LTE aggregation allows for transmitting data to one user simultaneously using both the HSPAand the LTE radios for maximal utilization of the available spectrum and the deployed equipment. This isconsidered beneficial especially in the environment where the spectrum that needs to be shared betweenthe two radio access technologies is not abundant, and the deployed HSPA and LTE capacities and userdata rates suffer from spectrum crunch. One example of such deployment is the 900 MHz for HSPA andthe 800 MHz for LTE which are both seen attractive bands for building the coverage due to the lowfrequency but also suffer from very limited spectrum availability. With aggregation of the two bands it ispossible to provide the high data rates expected from the LTE services while at the same time maintaincoverage for the HSPA devices.The same gain mechanisms that have been seen beneficial for Multicarrier HSDPA as well as LTECarrier Aggregation can be benefited from by aggregating HSPA with LTE. At low or medium load,HSPA+LTE aggregation is able to take advantage of the unused resources leading to significant data rateincreases both at the cell edge and the cell center for the carrier aggregation capable devices. In addition,the carrier aggregation enables fast (millisecond level) load balancing across the carriers thus improvingthe data rates of all users.A number of possible network architectures can be foreseen for HSPA+LTE aggregation, and are brieflytouched upon in this white paper. Most promising architecture options are seen with co-located multiradiobase stations with the base station (NodeB + eNodeB) acting as the data aggregation point, andsimultaneously maintaining the existing network architecture for the devices connecting to the networkwith one radio system at a time only. This architecture can utilize some of the already deployed RFhardware in the base station, while new baseband functionality managing the data flow is required. Onthe device side, receiver radio architectures capable of multiband carrier aggregation should be suitablealso for HSPA+LTE aggregation.While Dual-Cell HSDPA is already in commercial operation, and higher levels of HSPA carrieraggregation as well as LTE carrier aggregation are part of 3GPP specifications existing today,HSPA+LTE aggregation is currently not standardized. Although conceptually straightforward and buildingon already standardized concepts, HSPA+LTE aggregation is a major feature, with a standardizationeffort comparable to that of LTE carrier aggregation. 2 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  4. 4. 1. INTRODUCTION1.1 SCOPEThis white paper will highlight some of the key aspects and architecture options available for aggregatingHSPA and LTE carriers. Individually within both the HSPA and the LTE evolution, downlink and uplinkcarrier aggregation as well as co-site and inter-site aggregation have been considered. For both radioaccess technologies, the co-site aggregation has been standardized first and inter-site aggregation iscurrently being worked on.The HSPA+LTE aggregation is a potential 3GPP Release 12 topic, and at the time of writing, there is yetno official commitment or ongoing work related to any Release 12 items ongoing in the standards body.Hence the contents of this white paper can be seen more as visionary and exploratory than describing afeature already existing, or being worked on in the standard.1.2 HSPA+ AND LTE NETWORK DEPLOYMENT PROJECTIONSHSPA, HSPA+ AND LTE DEPLOYMENTS AS OF JUNE 2012  HSPA: 473 commercial networks in 180 countries  HSPA+: 227 commercial networks in 109 countries  LTE: 91 commercial networks in 47 countries  LTE: 335 operator Commitments worldwide  LTE: Over 130 commercial networks expected by year end 20124G AMERICAS WHITE PAPER “THE EVOLUTION OF HSPA” – OCTOBER 2011Whereas, LTE has tremendous momentum in the marketplace and it is clearly the next generationOFDMA based technology of choice for operators gaining new spectrum, HSPA will continue to be aleader in mobile broadband subscriptions for the next five to ten years. Some forecasts put HSPA at over3.5 billion subscribers by the end of 2016, almost five times as many LTE subscribers predicted. Clearly,operators with HSPA and LTE infrastructure and users with HSPA and LTE multi-mode devices will becommonplace. With the continued deployment of LTE throughout the world, and the existing ubiquitouscoverage of HSPA in the world, HSPA+ will continue to be enhanced through the 3GPP standardsprocess to provide a seamless solution for operators as they upgrade their networks.High-Speed Packet Access (HSPA) systems are now commonplace across Latin America and operatorsare looking to get full benefit from this technology as it evolves to HSPA+. Although the future is LTE, theregion is a good example of how 3G networks can take the customer all the way to the cusp of that newera. Progress made since 3GPP Release 7 has allowed HSPA+ to benefit from the techniques used inthe elaboration of LTE to ensure that both support smart phones, tablets and PCs as user needs grow.The 4G Americas white paper “The Evolution of HSPA” predicts that future enhancements in 3GPPRelease 11 should allow HSPA+ to deliver up to 336 Mbps. Talking about the paper, Erasmo Rojas, of4G Americas says, “HSPA+, with its continuously evolving and growing ecosystem, is becoming 3 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  5. 5. ubiquitous in major cities throughout Latin America and is setting the stage for future deployments of LTEin 2012 and beyond as operators gain access to new spectrum assets”.HSPA+ IN EMERGING MARKETSEmerging markets operators will hold off on LTE deployments in favor of upgrading their 3G networks toHSPA+. This technology provides spectral efficiency and headline data speeds similar to currentimplementations of LTE for the price of a software upgrade in most cases. Short-term, the HSPA+ecosystem will be better developed than that of LTE, especially in handsets, meaning there will be plentyof lower-cost devices better suited to price-sensitive emerging markets consumers.(RCR Wireless, 2012 Predictions: Emerging markets operators will invest more in HSPA+ than LTE,Posted on 19 January 2012 by Wally Swain, SVP of Emerging Markets, Yankee Group.)LTE IN THE US (JUNE 2012)AT&Ts 4G LTE network was live in 41 markets as of June 21, 2012 and covered 74 million POPS. Thecarrier expects to cover 150 million POPS by year end 2012 and complete its LTE network by the end of2013. If youre an AT&T customer in a city or town that doesnt have LTE yet, your 4G network is HSPA+.T-Mobile will launch 4G LTE in 2013 in 1700/2100 MHz spectrum. T-Mobile’s nationwide HSPA+network covers 220 million people in 230 markets as of June 2012. They plan to launch 4G HSPA+service in the 1900 MHz band in a large number of markets by the end of the year.Verizon’s LTE network was available in 304 cities as of June 21, 2012, covering more than 200 millionAmericans; coverage is expected to surpass its existing 3G footprint by end-2013. More than 260 millioncustomers in 400 markets will be able to access 4G LTE by the end of the year.Sprint customers in Baltimore, Kansas City, Dallas, San Antonio, Houston and Atlanta are slated toreceive 4G LTE service by mid-2012. The company hopes to cover 123 million POPS with LTE by the end of2012, and 250 million by the end of 2013.Clearwire is planning to launch LTE in TDD spectrum in 31 cities in the first half of 2013.HSPA+ AND LTE GROWTHThere are a number of reports that support the growth for HSPA+ and LTE network deployments,including research from ABI Research, which predicts that there will be 80 million super-fast LTE mobilebroadband lines across the world by 2013. The preferred frequencies for 4G LTE broadband services arethe 700 MHz and 2.6 GHz bands, although the 1.8 GHz and 2.5 GHz bands have been utilized incountries such as Poland and Singapore. In the UK, network operators will have the opportunity to deployLTE networks using the 800 MHz and 2.6 GHz spectrum bands, but British consumers still face a lengthywait for access to the technology.1In the Americas, LTE was first deployed in the Americas at 700 MHz and followed soon by the AWSspectrum band 1700/2100 MHz. In Latin America, HSPA+ and LTE is deployed in the 700, 1700/2100,1900 and 2600 MHz spectrum bands. It is possible that the AWS 1700/2100 MHz spectrum band will bea common LTE spectrum band in North, Central and South America.1 ABI Research predicts LTE mobile broadband lines will hit 80m by 2013. ABI Research, 24 October, 2011. 4 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  6. 6. According to research from In-Stat, LTE mobile broadband technology is set for a surge in growth overthe next four years. Between now and 2015, the number of people signed up for the next-generationservice will increase by 3,400 percent, the market intelligence firm claimed.2 In-Stat attributed this rapidrise in subscriptions to consumer desire to connect to the Internet while on the move at any time of dayand using a variety of devices, such as smartphones and tablet PCs. More than half of all infrastructurerollouts from network operators are now based on LTE, the organization revealed, sparking a decline in2G usage from 2012 onwards.3As LTE is gaining traction throughout the industry, it is also getting an increasingly larger chunk ofnetwork operator budgets. A recent report from IHS iSuppli indicates that spending on LTE infrastructureworldwide is set to more than triple from $8.7 billion in 2012 to $24.3 billion in 20134. IHS iSuppli furtherstated that there will be about 200 LTE networks operating commercially or being deployed around theworld by next year, about 40 more than were in place in 2010.Research from In-Stat claims that tablets will have the highest 3G/4G attach rate among all cellular-enabled portable and computing devices with 78 percent of tablets shipping with a 3G/4G modem by2015. The research firm suggests that this trend represents an opportunity for mobile operators to movebeyond the maturing handset market and into connecting emerging wireless device markets, like e-readers and tablets. A senior analyst at In-Stat predicts that by 2015, 65 percent of e-readers worldwidewill ship with an embedded 3G/4G modem.”5 The research firm also notes that approximately 16 millionportable and computing devices shipped with 3G/4G cellular connectivity in 2010 and that over 50percent of all 3G/4G tablets in 2015 will have LTE WAN connectivity.Finally, 4G Americas research shows 473 HSPA operators, of which 227 have deployed HSPA+. As ofJune 2012, there were 91 commercial deployments of LTE in 47 countries, with 335 total operatorcommitments to the technology.2 LTE mobile broadband set for 3,400% growth by 2015. (In-Stat, June 2011)3 LTE mobile broadband set for 3,400% growth by 2015. (In-Stat, June 2011)4 Fresh Research forecasts spending surge (IHS iSuppli, February 2012)5 78% of tablets shipped in 2015 will have 3G/4G modem By eGov Innovation Editors | May 23, 2011 5 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  7. 7. 2. MULTICARRIER AND MULTI-RADIO NETWORK EVOLUTION2.1 SPECTRUM AND DEPLOYMENT ASPECTSMobile operators are being driven to pursue carrier aggregation techniques by both technology andoperational realities. Ever rising traffic volumes are motivating service providers towards technologies thatexploit spectrum resources in the most efficient and economical manner. Spectrum holdings locatedacross several frequency bands, and the coexistence of deployments based on diverse accesstechnologies such as HSPA and LTE over long periods of time also incentive the use of carrieraggregation techniques.Broadly speaking, carrier aggregation technologies provide benefits such as the following  Maximize the total peak data rate and throughput performance by combining peak capacities and throughput performance available at different frequencies  Provide a higher and more consistent quality of service to customers as a result of load-balancing across frequencies and systems. A customer encountering congestion in one band and one system can seamlessly access unused capacity available at another frequency or system  Mitigate the relative inefficiencies that may be inherent in wireless deployments in non-contiguous or narrow (5 MHz or less) channel bandwidths, often spread across different spectrum bandsThe universe of potential frequencies that could potentially exploit carrier aggregation techniques is large.Most obviously, these include frequencies being used for IMT systems today. In the future, this shouldexpand to include spectrum being contemplated for IMT-Advanced systems, as well as spectrum thatmay be “re-farmed” from GSM use toward more advanced technologies or other spectrum unlocked or“re-farmed” for WWAN usage. In the former category are spectrum bands common across manycountries such as “digital dividend” spectrum (700 or 800 MHz depending on the ITU Region) and 2500(also known as the 2600) MHz bands, as well as AWS (1700/2100 MHz) in the Americas (ITU Region 2).GSM spectrum that may be repurposed includes widely deployed bands such as the cellular and SMRbands (at 800-850 MHz) and 1900 MHz in the Americas, and 900 and 1800 MHz in other areas of theglobe.Currently deployed spectrum bands differ widely in terms of contiguous bandwidth and in channelizationschemes. Further, service providers hold much more paired than unpaired bandwidth. Compoundingmatters, bands allocated to mobile broadband are diversifying. All of these factors conspire to presentgrowing challenges to equipment vendors and device OEMs developing multi-frequency (and increasinglymultimode products). Mobile handheld devices present especially keen issues related to battery sizelimitations, screen size, weigh, and constrained interiors into which more and more RF components mustbe squeezed to accommodate increasing numbers of frequencies. .HSPA systems can only be deployed with carriers with nominal bandwidth of 5 MHz or multiples thereof(up to 40 MHz with 8 aggregated 5 MHz carriers) and only in paired mode, while LTE technology isspecified for deployment in both unpaired and paired channels, and in a wide range of different channelwidths from 1.4 MHz through 3, 5, 10 and 15 MHz options up to the maximum channel width of 20 MHztoday, to 40 and even 100 MHz (as contemplated in LTE-Advanced with up to 5 aggregated 20 MHzcarriers). 6 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  8. 8. The efficiency of LTE is greater in the wider channel widths (2 x 10 MHz and greater). And 5 MHz HSPAchannels combined with existing HSPA carrier aggregation and other technological advances can deliverperformance that is competitive with today’s LTE systems. HSPA systems will continue to be maintainedfor many years, as momentum behind LTE technology continually ramps up. Consequently, serviceproviders will increasing be operating mixes of HSPA and LTE networks, across multiple bands. Thisreality suggests that operators and vendors should seriously consider the potential gains that may be hadby combining the performance of existing systems via techniques such as HSPA+LTE carrier aggregationtechniques.There is some commonality of frequencies within ITU regions, and to some extent between regions. Ingeneral, commonality exists to greater extent between ITU Regions 1 and 3 than between these tworegions and Region 2 (Americas). One exception is the 2500/2600 MHz band, which is on a path toachieve widespread global use with the increasing adoption of the ITU Option 1 (2x70 MHz pairedspectrum and a mid-band of 50 MHz unpaired spectrum).In summary, there are a number of factors heightening the importance of carrier aggregationdevelopments, including the potential benefits of HSPA/LTE carrier aggregation. These include  Overlapping deployments of HSPA and LTE that will persist through the end of the decade, if not beyond.  The need to maintain and enhance existing networks, both for service continuity to the installed base of device as well as to maximize returns on investment  Varying technology features (bandwidth flexibility or limitations, channelization scheme, duplex options)  Spectrum scheduled to be auctioned, as well as additional spectrum being pursued globally (i.e., post WRC-12) or regionally, which should be deployed in the most optimal way given existing network investments, capabilities, and limitations. 7 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  9. 9. 2.2 HSPA EVOLUTION FROM MULTIPLE CARRIERS TO MULTICARRIERTraditionally in the HSPA technology evolution the possibility for aggregating two 5 MHz HSDPA cellstogether has been called Dual-Cell HSDPA (or DC-HSDPA), and further evolution where more than twocells can be aggregated has been dubbed N-cell or N-carrier HSDPA, where the number N refers to thenumber of 5 MHz HSDPA carriers aggregated together. Commonly the multiple HSDPA carrieraggregation options are often referred to as Multicarrier HSDPA. Rel‐7 Rel‐8 Rel‐9 Rel‐10 Rel‐11 Rel‐12 DB DC‐HSDPA HSPA+ DC‐HSDPA 4C‐HSDPA 8C‐HSDPA … DC‐HSUPA 2007 2008 2009 2010 2011 2012 2013 Rel‐7 Rel‐8 Rel‐9 Rel‐10 Rel‐11 ASN.1 ASN.1 ASN.1 ASN.1 ASN.1 Freeze Freeze Freeze Freeze Freeze Figure 1: HSPA multicarrier evolution in 3GPP standard releasesThe concept of multiple carriers operation for HSPA was first introduced in Rel-8 as Dual-Cell HSDPA,with the scope of increasing coverage for high data rates in deployments where multiple carriers areavailable. DC-HSDPA operation is applied to two adjacent 5 MHz carriers and by scheduling HSDPAtransmissions on both carriers simultaneously, allows doubling the peak data rate from a single HSPA+carrier’s 21 Mbps to 42 Mbps with 64QAM when MIMO is not used. DC-HSDPA users can be scheduledon either of the two carriers, and either carrier can be configured as the primary serving cell, therebybenefiting an efficient load balancing between carriers. The two HS-DSCH transport blocks are processedindependently, including the HARQ retransmissions. Rel-9 further extended the DC-HSDPA operation tobe possible simultaneously with MIMO. 3GPP specifications define DC-HSDPA requirements for all thesame frequency bands that have been defined for single carrier operation.Combining multiple carriers to Multicarrier HSDPA for a UE is performed only on the MAC-hs in the NodeB, and there is a single RLC and PDCP layer just as with the single carrier operation, and practically theonly difference in the RNC user plane when comparing to single carrier HSDPA is higher user throughput.At the MAC-hs layer in the Node B, each aggregated carrier has its own independent Hybrid AutomaticRepeat reQuest (HARQ) entity. From a UE perspective, characteristics of each carrier procedures areunchanged with respect to basic single carrier HSDPA operation. Figure 2 shows the multicarriermapping on downlink. 8 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  10. 10. 6 Figure 2: PDCP-RLC-MAC-PHY layer mapping on DownlinkTo allow multiple carriers operation in deployment scenarios when adjacent bands are not available,Dual-Band DC-HSDPA was introduced in Rel-9. The primary and secondary serving carriers reside indifferent bands, and the uplink transmission can be configured in either one of the two bands. Theintroduction of DB DC-HSDPA can be regarded as taking the evolution from multiple single carrier cellsystems to multicarrier systems to include also the aggregation of non-contiguous spectrum bands. Thecapability of scheduling transmissions over multiple carriers of different bands provides an efficientutilization of the spectrum resources resulting in a substantial increase in cell capacity. In Rel-9 only threeband combinations were allowed, and other band combinations have been added at a later stage whileretaining the same functionalities as in Rel-9 specifications and can be implemented in Rel-9 networksand devices in a release independent manner. Currently defined band-combinations DB DC-HSDPA arelisted in Table 1. Table 1: 3GPP-defined Dual-Band Dual-Cell HSDPA band combinations Dual Band DC-HSDPA Band A Band B 3GPP release Configuration 1 I (2100 MHz) VIII (900 MHz) Rel-9 2 II (1900 MHz) IV (1.7/2.1 GHz) Rel-9 3 I (2100 MHz) V (850 MHz) Rel-9 4 I (2100 MHz) XI (1500 MHz) Rel-10 5 II (1900 MHz) V (850 MHz) Rel-106 Figure adapted from 3GPP TS36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description”, V10.7.0 9 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  11. 11. Similar to DC-HSDPA, multiple carriers operation was introduced in the uplink in Rel-9 as DC-HSUPA,and the peak data rate doubled to 23 Mbps with 16QAM. DC-HSUPA users transmit two E-DCH transportblocks, one on each uplink carrier, and each transmission is done independently according to theprinciples used for the non-serving cells. The two carriers belong to the same sector of a serving NodeB,and the serving NodeB can activate/deactivate the secondary carrier dynamically. DC-HSUPA can onlybe used with DC-HSDPA because control signaling for the secondary UL carrier is carried over thesecondary DL carrier. DC-HSDPA can instead be activated regardless if the uplink uses single or dualcarrier(s). 3GPP specifications define DC-HSUPA requirements for all the same frequency bands thathave been defined for single carrier operation. 8C‐HSDPA 8 x 5 MHz Rel‐11 40 MHz 4C‐HSDPA, Rel‐10 4 x 5 MHz Non‐contig. single‐band, Rel‐11 20 MHz Dual‐Cell HSDPA, Rel‐8 2 x 5 MHz Dual‐Band, Rel‐9 10 MHz Single carrier HSDPA 5 MHz up to Rel‐7 5 MHz Figure 3: Aggregating more and more carriers to increase the total transmit bandwidthDriven by an increasing demand for high data rates, multicarrier operation in the DL has evolved with theintroduction of 4 carriers and 8 carriers in Rel-10 and Rel-11, respectively. The additional flexibilityprovided by the larger number of carriers improves the load balancing through the dynamic configurationof the serving cell of each multicarrier user. As is the case with DC-HSDPA, also with 4C-HSDPA and 8C-HSDPA, all secondary carriers can be dynamically activated/deactivated by the serving NodeB throughHS-SCCH orders. Depending on the type of traffic, the deactivation of all carriers in a frequency band canbe useful for UE power savings.With the 4C-HSDPA feature, four HSDPA transmissions can be scheduled simultaneously over fourcarriers that do not need to be adjacent and can reside on different bands, featuring a peak data rate of168 Mbps when configured with 2x2 MIMO and 64QAM. Similar to DC-HSDPA, each transmission isdone independently and all secondary serving carriers can be activated/deactivated in a dynamic fashionby the serving NodeB. The uplink signaling, as in DC-HSDPA, is carried over a single carrier, and thefeedback channel has been redesigned to include the information for all four DL transmissions. The bandcombinations for 4C-HSDPA include up to two frequency bands, and up to three carriers can bescheduled in the same band. All supported band combinations up to Release 10 require configuringadjacent carriers within each aggregated band to facilitate the UE receiver implementation. As for DB DC-HSDPA, other band combinations can be added at a later stage. Currently defined band-combinations for4C-HSDPA where carriers on a band are adjacent to each other are listed in Table 2. 10 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  12. 12. Table 2: 3GPP-defined 4-Carrier HSDPA band combinations with all carriers within a band adjacent to each other 4C-HSDPA Band A Band B Carrier 3GPP release Configuration combination I-3 I (2100 MHz) N/A 3 Rel-10 II-3 II (1900 MHz) N/A 3 Rel-11 II-4 4 Rel-11 I-2 – VIII-1 I (2100 MHz) VIII (900 MHz) 2+1 Rel-10 I-3 – VIII-1 3+1 Rel-10 I-2 – VIII-2 2+2 Rel-11 I-1 – V-2 I (2100 MHz) V (850 MHz) 1+2 Rel-10 I-2 – V-1 2+1 Rel-10 I-2 – V-2 2+2 Rel-11 II-1 – IV-2 II (1900 MHz) IV (1.7/2.1) 1+2 Rel-10 II-2 – IV-1 2+1 Rel-10 II-2 – IV-2 2+2 Rel-10 II-1 – V-2 II (1900 MHz) V (850 MHz) 1+2 Rel-113GPP Rel-11 further extended the supported cases for 4C-HSDPA to include single-band non-adjacentcarrier configurations. In these cases all carriers of a 4C-HSDPA configuration reside in the samefrequency band, but in two non-adjacent blocks. The carriers within each block are adjacent to eachother, but there is a gap between the two blocks. Currently defined band-block combinations for the non-contiguous single-band 4C-HSDPA are listed in Table 3. Table 3: 3GPP-defined 4-Carrier HSDPA single band non-adjacent carrier combinations Single-band non- Carrier Gap between adjacent 4C-HSDPA Band 3GPP release combination band blocks Configuration I – 1-5-1 1+1 5 MHz Rel-11 I – 1-5-2 I (2100 MHz) 1+2 5 MHz Rel-11 I – 1-10-3 1+3 10 MHz Rel-11 IV – 1-5-1 1+1 5 MHz Rel-11 IV – 1-10-2 1+2 10 MHz Rel-11 IV – 2-15-2 IV (1.7/2.1 GHz) 2+2 15 MHz Rel-11 IV – 2-20-1 2+1 20 MHz Rel-11 IV – 2-25-2 2+2 25 MHz Rel-11The introduction of 8C-HSDPA is a further extension of the multicarrier operation with eight carriers.Similar to the four carrier feature, in 8C-HSDPA the transmissions are independent. The carriers do notneed to be adjacent and can reside on different frequency bands. The activation/deactivation of thesecondary carriers is done by the serving NodeB through physical layer signaling. The uplink signaling iscarried over a single carrier. The first band combination for 8C-HSDPA to be introduced in 3GPP is 8adjacent carriers on band I (2100 MHz). 11 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  13. 13. Release 11 336 Mbps Release 10 40 MHz, 2x2 MIMO 168 Mbps 20 MHz, 4x4 MIMO Release 9 20 MHz Release 8 84 Mbps 2x2 MIMO Release 7 42 MbpsRelease 5 10 MHz 28 Mbps 2x2 MIMO 14 Mbps 10 MHz 5 MHz No MIMO 5 MHz 2x2 MIMO No MIMO Figure 4: HSDPA peak data rate evolution in 3GPP standard releases 12 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  14. 14. 2.3 LTE EVOLUTION FROM MULTIPLE CARRIERS TO CARRIER AGGREGATIONTraditionally in the LTE technology evolution the possibility for aggregating multiple LTE cells togetherhas been called “LTE Carrier Aggregation” rather than e.g. Multicell or Multicarrier LTE.LTE Release 8 and 9 supports single carrier operation with variable bandwidth from 1.4 MHz through 3,5, 10 and 15 MHz up to the maximum of 20 MHz. In order to provide support for operation beyond 20MHz on downlink and uplink, carrier aggregation was introduced as a part of LTE-Advanced Release-10(shown in Figure 5).Release-10 carrier aggregation supports the following features:  Peak data rates of 1 Gbps on downlink and 500 Mbps on uplink.  Up to five carriers can be aggregated, where each carrier is called a “component carrier”.  Each component carrier can have any of the bandwidths supported in LTE Rel-8 (1.4, 3, 5, 10, 15 and 20 MHz). As a result, LTE carrier aggregation can support operation on transmission bandwidths of up to 100 MHz by aggregating five 20 MHz carriers.  Each component carrier is fully backward compatible to Release-8/9. This backward compatibility to Release 8/9 allows the technologies developed for LTE Release-8/9 to be fully reused in Release-10. It also allows the coexistence of Release 8 and 9 UEs together with Release-10 UEs, which is very important for seamless system transition from Release 8 and 9 to Release 10.  A carrier aggregation capable UE can simultaneously receive and transmit in one or multiple component carriers. Figure 5: LTE/LTE-A multicarrier evolution in 3GPP standard releasesCarrier aggregation for LTE is performed on the MAC and PHY layers only, and there is a single RLC andPDCP layer for all aggregated component carriers. At the MAC layer, each component carrier has its ownindependent Hybrid Automatic Repeat reQuest (HARQ) entity and physical layer. From a UE perspective,characteristics of the HARQ procedures for each component carrier are unchanged with respect toRelease-8/9. Figure 6 shows the CC mapping on DL. 13 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  15. 15. 7 Figure 6: PDCP-RLC-MAC-PHY layer mapping on downlinkFrom the higher layer perspective, each component carrier appears as a separate cell with its physicalcell identifier. Therefore, it appears that a carrier aggregation UE is connected to multiple cells. Amongthe multiple cells the UE is connected to, one particular cell is denoted as “primary serving cell”, whileother cells (up to four) are denoted as “secondary serving cells”. Primary serving cell plays a unique andessential role with respect to security, upper layer system information, and some lower layer functions,while secondary serving cells are configured to primarily provide additional resources for UE to transmitand receive data. Another difference between primary and secondary serving cell is that primary servingcell can only be changed via RRC (re)configuration, while secondary serving cells, once configured viaRRC signaling, can be activated or deactivated by MAC signaling without additional RRC signaling. Thisfeature enables very fast activation and deactivation of secondary serving cells.One salient feature of LTE carrier aggregation is “cross-carrier assignment”, where DL scheduling or ULgrant information of one component carrier can be carried via the PDCCH of another component carrier.Specifically, a PDCCH on one component carrier can schedule data transmissions on another componentcarrier by including a 3-bit Carrier Indicator Field (CIF) in the grant message to indicate the targetcomponent carrier. This is especially useful when secondary serving cell cannot be used to conveycontrol information reliably. As an example, Figure 7 illustrates the regular DL assignment without cross-carrier assignment, while Figure 8 shows DL assignment with cross-carrier assignment, where PDCCH ofcomponent carrier 2 is used to schedule not only component carrier 2, but also component carrier 1 and3.7 Figure adapted from 3GPP TS36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description”, V10.7.0 14 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  16. 16. Figure 7: Regular DL resource assignment Figure 8: DL resource assignment with cross-carrier controlWhile Release-10 air interface allows up to five component carriers, only limited inter-band carrieraggregation combinations are defined (Table 5), and only intra-band carrier aggregation with contiguouscomponent carriers for limited bands are defined (Table 4) as of Release-10. More band combinationsare being defined in Release-11 and beyond. Table 4 : Intra-band contiguous carrier aggregation operating bands8 E-UTRA E-UTRA Uplink (UL) operating band Downlink (DL) operating band Duplex CA Band Band BS receive / UE transmit BS transmit / UE receive Mode FUL_low – FUL_high FDL_low – FDL_high CA_1 1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD CA_40 40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD Table 5: Inter-band carrier aggregation operating bands8 E-UTRA E-UTRA Uplink (UL) operating band Downlink (DL) operating band Duplex CA Band Band BS receive / UE transmit BS transmit / UE receive Mode FUL_low – FUL_high FDL_low – FDL_high 1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz CA_1-5 FDD 5 824 MHz – 849 MHz 869 MHz – 894 MHz8 3GPP TS36.101 “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radiotransmission and reception”, V10.6.0 15 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  17. 17. 2.4 HSPA AND LTE INTERWORKINGDuring the roll-out of the LTE, it is vital to be able to use the HSPA system to provide coverage outsidethe LTE deployment. This is the main reason why the LTE standard includes mechanisms to transfer UEsfrom LTE to HSPA and back. The same philosophy was used during the 3G standardization, wherefallback to 2G was included from the start. In addition to the difference in coverage, LTE does not initiallysupport all services that WCDMA supports. The most prominent example is voice, where an LTE solutionis not readily available. Instead, fallback to WCDMA is the initial solution used by many operators.In the future, other inter-working scenarios will become interesting. One example is load sharing, wheretraffic can be steered to the least loaded RAT, leading to better performance. Here the service aspectshould also be taken into account, so that services that benefit most from the LTE would use LTE, whileless demanding services would use HSPA.In Idle mode, the RAT is autonomously selected by the UEs, based on broadcast information. The UEsthus performs cell reselection, based on measurements of the quality of the serving and target RATs. ForRelease-8 UEs, there is also the notion of priority: with each RAT, there is also an associated priority. Atypical use-case here is that a RAT is selected if its quality is good enough, and its priority is higher thanthat of the serving RAT. This makes it possible for idle UEs to start in HSPA, and autonomously reselectLTE when LTE coverage becomes available. As an alternative, each UE may individually be providedwith a dedicated priority which overrides the one in broadcast. HSPA LTE Idle Idle Reselect Connected Connected Connected URA_PCH CELL_PCH Redirect CELL_FACH CELL_DCH Handover Figure 9: The procedures for moving UEs between HSPA and LTE. 16 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  18. 18. When the UE is in connected mode in LTE, it can be moved to HSPA by means of an inter-RAT handoveror inter-RAT redirection procedures. An inter-RAT handover leads to a very short interrupt in thecommunication: in the order of tens of milliseconds. This is achieved through reservation of resources inthe target cell before the serving cell is released. Also, data is forwarded from the serving RAT to thetarget RAT. After the inter-RAT handover procedure, the UE ends up in the RRC state CELL_DCH inWCDMA and the UE immediately proceeds to update the routing area so that it can be reached in thenew RAT. The corresponding procedure can be used to move a UE in CELL_DCH in WCDMA to LTE.After the inter-RAT redirection procedure the UE ends up in the RRC idle mode and after finding thetarget cell proceeds to register to the WCDMA RAT with Cell Update procedure. The inter-RAT redirectionprocedure leads to significantly longer outage than the inter-RAT HO procedure: no data transmission ispossible until the routing area update has been performed. The outage is in the order of a few seconds.When an HSPA UE is in any of the RRC states CELL_FACH, CELL_PCH or URA_PCH, it performsnormal cell reselection. Here, if the UE reselects an LTE cell, the UE enters Idle mode and makes anaccess to LTE.In CELL_FACH, it is also possible to use inter-RAT redirection procedure. If the UE finds a cell where itwas directed, this procedure performs relatively well. However, when the UE fails to find a cell, it needs toestablish a connection to another cell, and this may take some time. In 3GPP Release 11, improvementsto this redirection procedure are being discussed that will minimize the interrupt in case the redirection isunsuccessful. The transitions are depicted in Figure 9.The Operation and Maintenance (O&M) and Self Optimizing Network (SON) is another important aspectof interworking of HSPA and LTE radios. The O&M/SON management principle is shown in Figure 10.The same framework used to operate joint HSPA and LTE network deployments is naturally applicablealso for the HSPA+LTE aggregating network. Depending on which radio aggregation architecture isconsidered, different O&M/SON improvements benefiting from tighter radio integration could be foreseen,although this aspect of the HSPA+LTE aggregation is not considered further in this paper. Figure 10: SON umbrella for joint LTE and HSPA deployment 17 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  19. 19. 2.5 HSPA+LTE CARRIER AGGREGATIONThe previous sections capture the work done in the HSPA and LTE evolution from single carrier operationto supporting bandwidths up to 40 MHz with Multicarrier HSPA and 100 MHz with LTE carrieraggregation, as well as summarize the different HSPA and LTE interworking cases already considered inthe 3GPP standards. Furthermore, the expectation is for the industry to move more towards multi-standard radios in base stations, small cells, baseband hotels with fiber-connected remote radio heads.When in addition considering a multimode device equipped with both HSPA and LTE receivers andspectrum-limited deployments where commercial situation requires operating both HSPA and LTEnetworks, the desire to be able to aggregate carriers of the two radio access technologies whentransmitting to a single user starts to look like a natural next step to work on.When thinking of the evolution of multicarrier HSPA as well as LTE carrier aggregation, there seems to bea common trend in both to  Support both downlink and uplink carrier aggregation  Initially support aggregating carriers of one base station site, and only later on investigate the possibilities of aggregating cells of multiple base station sites.Similarly, when considering HSPA+LTE aggregation, one can think of both downlink and uplink as well asco-site and inter-site aggregation of the two technologies, but for the same reasons leading to beingdownlink-centric and emphasizing downlink aggregation, the main focus of the HSPA+LTE aggregation,at least initially, can be expected to be on intra-site aggregation of downlink carriers. LTE LTE Carrier LTE evolution aggregation Load balancing, Re-selections, HSPA + LTE Simultaneous Handovers, voice continuity, reception of co-siting aggregation HSPA + LTE HSPA Carrier HSPA HSPA evolution aggregation Rel-5…Rel-9 Rel-7…Rel-11 …and beyondFigure 11: 3GPP standard evolution of LTE carrier aggregation, HSPA carrier aggregation and HSPA+LTE interworking 18 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  20. 20. 3. BENEFITS AND USE CASES OF HSPA+LTE AGGREGATION3.1 BENEFITS OF HSPA+LTE AGGREGATIONAs discussed in sections 1 and 2, at least the initial focus of the HSPA+LTE aggregation is seen to be onaggregating co-sited downlink carriers. Respectively, the discussion of the benefits in this section isconsidering co-sited downlink carriers.HSPA+LTE aggregation utilizes same mechanisms as the intra-RAT carrier aggregation schemesdescribed in section 2 and is thus expected to bring similar data rate gains:  Data rates of carrier aggregation UEs boosted by utilizing unused resources from overlapping cell(s) operating on different carrier(s)  Data rates of all UEs improved by fast (TTI level) load balancingSimilar to the intra-RAT carrier aggregation, the gains are highest at low/medium load and they benefitboth the cell edge and the cell center UEs. At high load with multiple active UEs per cell it is possible toperform load balancing handovers to balance the load and thus aggregation of carriers is less beneficial.However, statistics from today’s mature HSPA networks have shown that due to the burstyness of thedata traffic there is often only one active UE per cell with data in the RAN buffers (even though theremight be several UEs connected to the cell). In such case load balancing handovers are not helpful andpart of the resources remain unused. Also if the data bursts are very short, the load balancing handoverscan be rather inefficient due to the handover delays and overheads. In such scenarios carrier aggregationclearly outperforms load balancing handovers and HSPA+LTE aggregation simply brings the samebenefits to inter-RAT domain. In uplink the aggregation (both in intra- and inter-RAT domain) is howeverless appealing due to UL coverage and UE power consumption limitations.In addition to the data rate gains, HSPA+LTE aggregation allows more relaxed re-farming strategies forHSPA spectrum; HSPA+LTE aggregation capable UEs can enjoy improved data rates by utilizingefficiently both LTE and HSPA spectrum without reducing the data rates of the HSPA UEs.Figure 12: Average downlink data rate before and after refarming of one HSPA carrier (assuming low-to-medium systemloading, 10MHz LTE and 2x5MHz HSPA before refarming) 19 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  21. 21. Figure 12 illustrates downlink data rates in a single UE scenario, where before re-farming both HSPA andLTE have 10MHz bandwidth. By re-farming of one HSPA carrier the data rates of LTE UEs can beboosted by ~50% but that happens at the cost of ~50% lower HSPA data rates. With HSPA+LTEaggregation it is possible to postpone the re-farming until HSPA penetration is very low, but at the sametime provide almost 100% higher data rate for the LTE UEs with HSPA+LTE carrier aggregationcapability.3.2 EXAMPLE USE CASES FOR HSPA+LTE AGGREGATIONNext some example use cases for HSPA+LTE aggregation are given;1. Aggregation of two low bands The increased penetration of HSPA capable UEs together with the GSM spectral efficiency improvements have made it possible for many European operators to start deploying HSPA at 900 MHz. At the same time some of the operators are starting to deploy LTE at 800 MHz with rather limited bandwidth. Both of these bands are appealing due to their better coverage compared to the other available frequency bands (such as the 2100 MHz for HSPA, 2600 MHz for LTE). The spectrum available at 800 MHz is however very limited and thus may not provide the data rates consumers are expecting from a 4G service. Furthermore it will be also difficult to re-farm the HSPA from 900 MHz band without sacrificing the HSPA coverage. HSPA+LTE aggregation can help to boost LTE data rates to the level of expectations also in the areas where only LTE at 800 MHz is available, and therefore motivating adaptation of LTE capable devices, while still maintaining the coverage for HSPA services.2. Limited LTE spectrum Some operators have access only to rather limited amount of spectrum to be used for LTE thus making it difficult to provide high data rate LTE services. One example of such case is a North American carrier announcing plans to transfer part of its’ HSPA+ services to PCS band (1900 MHz) thus freeing-up spectrum for future LTE deployments in AWS band (1700/2100 MHz). In this case aggregation of HSPA+LTE would provide significant data rate boost compared to the HSPA+ services.3. Intra-band aggregation Even though refarming of HSPA spectrum for LTE is not that relevant to most of the operators currently, in longer term also this will become a relevant use case (e.g. on 2100 MHz in Europe or on the above mentioned PCS band in US). As described in the previous section, the aggregation of HSPA and LTE enables more relaxed refarming by providing the needed additional capacity for LTE capable UEs while still maintaining the HSPA data rates. 20 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  22. 22. 4. HSPA+LTE AGGREGATION SYSTEM ARCHITECTURE CONSIDERATIONSThe most critical architectural design choice for HSPA+LTE aggregation is the choice of the networkelement where the single data stream is split to two independent downlink data streams to be send overthe two carriers; one going via HSPA radio interface and the other one via LTE radio interface. If uplinkaggregation is desired to be supported, this network element will serve also as merger point where theuplink data received from the two data streams is merged back to a single data stream.Figure 13 shows the main elements of the existing system architecture for E-UTRAN and UTRAN. Thereare five different levels of network elements where the data split/merge of HSPA+LTE aggregation mightpotentially take place; at Services, Core Network, LTE eNodeB, HSPA RNC, or HSPA NodeB level.Figure 13: Potential split/merger points of HSPA + LTE aggregation shown on top of current network architectureIn the next sections each of these potential split/merge points are analyzed in more detail. It is worth tonotice that no changes to the existing system architecture or protocols regarding the operation (HSPAonly or LTE only operation) are envisioned. Thus, the following architecture considerations focus purelyon the HSPA+LTE carrier aggregation operation. Table 6 summarizes some aspects of the differentarchitecture options. 21 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  23. 23. Table 6: A high level summary of the different architecture approachses for HSPA+LTE aggregation Split/Merger RAN aspects UE aspects Other aspects Point ‐ Simultaneous UL on bothService or Core ‐ Challenges in optimizing ‐ Minimal impact on RAN RATs requiredNetwork usage of resources ‐ Impact on battery ‐ RNC based scheduling ‐ No/minimal changes at slower than base station NodeB ‐ Deep reordering of based one ‐ Changes at RNC and packetsHSPA RNC eNB to support new ‐ Simultaneous UL on both ‐ Cannot benefit from the faster setups over LTE interface between eNB RATs may be required ‐ All traffic go through 3G and RNC CN ‐ Most changes limited to base station ‐ Very good performance ‐ No impact on core ‐ UL range reduction if due to fast scheduling network simultaneous HSPA/LTE and shallow reordering ‐ No or limited impact on UL ‐ Fast load balancingHSPA NodeB higher layers ‐ For HSPA UL only case, ‐ Cannot benefit from the HARQ timing may be an ‐ Changes to radio faster setups over LTE issue interface needed to ‐ All traffic go through 3G transport signaling and CN setup of radio interfaces ‐ Most changes limited to base station ‐ No impact on core network ‐ Very good performance ‐ UL range reduction if ‐ No or limited impact on due to fast schedulingLTE eNB higher layers simultaneous HSPA/LTE and shallow reordering UL ‐ Changes to radio ‐ Fast load balancing interface needed to transport of signaling and setup of radio interfaces 22 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  24. 24. 4.1 SERVICE OR CORE NETWORK LEVEL SPLIT/MERGERWhile carrier aggregation is usually seen as a RAN functionality, in theory the data path split/merge pointcould be located also above RAN either in services or core network level, as illustrated in Figure 14 andFigure 15. Figure 14: HSPA+LTE aggregation with split/merger at service levelHaving the split/merger at service level or CN level has the following advantage:  It can be introduced with a minimum impact on the RAN. In principle, no changes are required to the user plane processing; however to make it feasible in practice (i.e. to mitigate the disadvantages listed below), some changes in the UE will be required, and the network side of the RRC layers need to be aware of the dual-radio operation. Figure 15: HSPA+LTE aggregation with split/merger at core network level 23 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  25. 25. Both alternatives would however require pure dual-radio with simultaneous dual-transmission which leads(at least) to the following further requirements and drawbacks: o Double security, mobility context and CN protocol layers o UE total maximum TX power management and handling SAR requirements (e.g., UE TX power reduced by 3 dB in both systems) o Significant impact to UE battery life due to needing to operate multiple power amplifiers simultaneously o UE RF implementation issues such as inter-modulation, or interference to own receiver, due to two simultaneous transmissions o Challenging to optimise usage of HSPA or LTE resources, leading to that the full capacity gain cannot be achieved.In addition it appears that the RAN control plane processing could not stay agnostic to dual-radio userplane due to tight interworking of the HSPA and LTE. At least some level of coordination of the two RRCprotocol layers would be inevitable due to access and mobility management. 24 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  26. 26. 4.2 HSPA RAN LEVEL SPLIT/MERGERAnother alternative is to place the data split/merger point in HSPA RAN in which case the data needs tobe divided between LTE and HSPA radio either in RNC or in NodeB. In this architecture HSPA would bethe controlling RAT which decides how much data is to be transmitted over HSPA or LTE.The data split/merger at RNC level would suggest a new interface to be defined between RNC and LTEeNodeB, as shown in Figure 16.The advantages with having the aggregation point in the RNC are: No changes in the node B, and relatively small changes are required in the RNC and eNode B, No changes to the physical layer: the required standardization changes are limited to higher layers.The disadvantages are: The RNC scheduler will lead to suboptimum performance Deep reordering required in the UE, due to potentially very different delays in the two RATs Simultaneous uplink transmission on LTE and HSPA may be required. Figure 16: HSPA+LTE aggregation with split/merger at RNC 25 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  27. 27. Introducing the data split/merger at NodeB level (Figure 17) would limit most of the changes to basestation level which could be seen more desirable especially in the context of multi-radio base stations. Figure 17: HSPA+LTE aggregation with split/merger at NodeBWhile an aggregation in the RNC has the same main disadvantages as the CN/service layer solution, anaggregation in the node B has the possibility to avoid several of the drawbacks. Providing that the node B– eNode B interface has low enough latency, the following advantages may be achievable: Very good performance, due to fast scheduling and shallow reordering Possibility to use either HSPA uplink or LTE uplink or both for fast feedback No impact on core network nodes, and very limited if any impact to the existing RNC functionalities No or very limited impact to higher layersBoth HSPA and LTE uplink could be used simultaneously for fast feedback. This approach has theadvantage of requiring little or no layer 1 change. The drawback is that UL range is reduced due tosimultaneous transmission on both links. A single uplink may be desirable to avoid UL range reduction,though the approach has the following disadvantages: Standardization changes required to lower layers, in particular for the uplink layer 1 control signalling. This is true irrespective of which RAT is used for uplink transmission. LTE data would have to be routed via RNC which would violate the flat architecture design principle of LTE and lead to increased RNC load (the LTE UEs could be however still served using the existing LTE architecture without routing their traffic via RNC). 26 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  28. 28. Here, the most appealing alternative would be to reuse the PDCP, RLC and MAC-d protocols from HSPA.With this approach, the impact is limited to MAC in LTE. As the control plane and the data routing tohigher layers in this architecture would be managed by UTRAN, the HSPA uplink might be seen as mostnatural choice in case that single UL is desired. In this case, also the LTE feedback (HARQacknowledgements and CQI) would have to be transmitted via HSPA uplink which can be challengingdue to the shorter (1ms) TTI of LTE. This approach is depicted in Figure 18. Alternatively the uplinkcontrol and data could be mapped on the LTE. This approach might be more attractive from the controlsignalling perspective, but would require additional user plane modifications.Figure 18: Single uplink with data split/merger at NodeB. Most of the protocols are used as is: the main impact is seen inLTE MAC 27 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  29. 29. 4.3 LTE RAN LEVEL SPLIT/MERGERIn this alternative data is divided between LTE and HSPA radio in eNodeB (as illustrated in Figure 19),and LTE would be the controlling RAT.Even though eNodeB is in control of how the data is divided between HSPA and LTE radios, RNC can beexpected to stay in control of overall HSPA resources. This is possible e.g. by introducing additionalsignaling over Iub interface enabling RNC to provide limits how much HSPA resources NodeB is allowedto provide for HSPA+LTE carrier aggregation UEs at a given time. If there is no congestion, also moreresources can be temporarily allocated for HSPA+LTE aggregation. In general controlling the aggregationin base station level enables fast (TTI level) load balancing between HSPA and LTE, equivalent to theintra-RAT load balancing available to multicarrier deployments with Multicarrier HSDPA and LTE CarrierAggregation. Figure 19: HSPA+LTE aggregation with split/merger at eNodeBSince in HSPA the PDCP and RLC layers are located in RNC, the data split should take place at/belowLTE RLC layer. Using the LTE MAC could potentially lead to a more optimized performance and flexibility,but it would require rather dramatic modifications in the LTE MAC implementation, particularly in the UE,as major parts of the MAC-ehs would have to be ported to the LTE MAC to support HSDPA L1. If the datasplit is however performed in the RLC-MAC interface both the LTE and HSPA MAC (and L1) can be keptintact (if so desired) making this the most appealing alternative from the implementation complexity pointof view.As a consequence of the proposed architecture choices described above, the RLC, PDCP, and RRCprotocol layers of HSPA side would not be used for HSPA+LTE aggregation, instead only the LTE RLC,PDCP, and RRC would be utilized. Similarly, as S1 interface is terminated in LTE eNodeB, the GPRSpacket core protocols are not utilized, but core network functions are provided by EPC.As mentioned in Section 4.2, both HSPA and LTE uplink can be used simultaneously for fast feedback toavoid any layer 1 change, but this approach comes with a drawback of UL range reduction. Alternatively,if a single UL is used to maintain the UL range, the HSPA feedback (CQI, HARQ status) would have to bedelivered via LTE UL, as illustrated in Figure 20. The tight delay budget for delivering such feedback 28 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  30. 30. implies that NodeB and eNodeB should either be co-located or integrated into one multi-radio BTS. Thisis however not that strict requirement as co-location is in any case desirable to maximize the overlappingof the cell coverage areas, as well as to minimize the site costs. This approach is also well aligned withthe LTE-Advanced carrier aggregation frame work where single UL can provide feedback for multiple DLcarriers. Figure 20: Single uplink with data split/merger at eNodeBAs a summary, the solution with the split in the eNode B shares many of benefits of having the split in thenode B: o No impacts at core network or services level, and only minor impacts on RNC o Data split at BTS level enables fast load balancing o Single uplink via LTE UL possible thus maximizing the uplink rangeIn addition, using the eNode B as the aggregation point also means that o The LTE data flow would not have to travel via RNC o Allows to utilize the existing LTE CA frameworkQuite naturally, the solution also has these disadvantages: Standardization changes required to lower layers, in particular for the uplink layer 1 control signalling, if a single uplink is used for feedback of both HSPA and LTE. Since the RNC maintains the overall responsibility for the HSPA resources, the eNodeB cannot control all the resources in the node B, leading to somewhat degraded performance gains. 29 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  31. 31. 5. PRACTICAL IMPLEMENTATION ASPECTS OF HSPA+LTE AGGREGATION5.1 BASE STATION RADIO IMPLEMENTATION ASPECTSFigure 21 shows a very simplified block-diagram of a base station capable of transmitting on twofrequency bands with two transmit antennas common to the bands. The same transmit chain can inprinciple be able to transmit either LTE, HSPA, or even both LTE and HSPA carriers simultaneously onseparate carrier frequencies within the bandwidth of the transmitter, e.g. a 10 MHz transmitter couldsupport one 10 MHz LTE carrier or two adjacent 5 MHz HSPA carriers, and a 40 MHz transmitter couldsupport two adjacent 20 MHz carriers or 8 adjacent 5 MHz HSPA carriers, or even one 20 MHz LTEcarrier and next to it 4 adjacent 5 MHz HSPA carriers. PA Filter Filter Filter DAC Upconversion Base station transmit PA Filter Filter Filter DAC BB processing Band A PA Filter Filter Filter DAC Upconversion PA Filter Filter Filter DAC Band B Signal flow through base station transmit processing Figure 21: A simplified block diagram of a dual-band Tx diversity/MIMO base station transmit chainAs a concrete example, we can consider a co-sited HSPA and LTE deployment with one or several HSPAcarriers on PCS band and one LTE carrier on AWS band. Extending such deployment to supportHSPA+LTE aggregation would be directly able to utilize the RF hardware already in place. This can begeneralized to say that an existing co-sited deployment of HSPA and LTE RATs can be extended tosupport HSPA+LTE aggregation without any new requirements to the already deployed RF hardware.Note that new baseband functionality needs to be introduced.The architectures with data split point in the base station (HSPA Node B or LTE eNode B) would beeasiest to implement with a multi-standard radio base station, where both RATs are served by the samephysical entity. If the uplink is only limited to one or the other RAT, then a fast feedback loop would berequired from one RAT to the other to get the uplink channel state information and HARQ ACK/NACKfeedback across to the other RAT. These architectures assume either a high-speed, low latency interfacebetween two base stations, or more advantageously one multi-standard radio base station. 30 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  32. 32. 5.2 DEVICE RADIO IMPLEMENTATION ASPECTSFigure 22 shows a very simplified block-diagram of a UE capable of receiving simultaneously on twofrequency bands with two receive antennas common to the bands. If the two receivers are configurable tooperate in a Dual Band Multicarrier HSDPA configuration or Dual Band LTE Carrier Aggregationconfiguration then the two receivers are required to receive data at the same time as in the figure.Similarly, the UE of Figure 22 could represent a dual-mode UE capable of receiving LTE on band A andHSPA on band B but not vice versa, and if they UE is to be able to aggregate the data received on thetwo radio technologies, then the same logical architecture capable of dual-band LTE or HSPAaggregation can be used also in aggregating HSPA and LTE. One could say that the receiver capable ofaggregating carriers on two bands is as complex regardless of whether it is aggregating LTE and HSPAcarriers on both bands, or LTE carriers on one band and HSPA carriers on the other band. Amp Amp Filter Filter ADC Downconversion Amp Amp Filter Filter ADC BB processing UE receiver Band A Amp Amp Filter Filter ADC Downconversion Amp Amp Filter Filter ADC Band B Signal flow through UE receiver processing Figure 22: A simplified block diagram of a dual-band carrier aggregating Rx diversity/MIMO UE receiver chainA device supporting intra-band carrier aggregation could use a single wide band receiver rather than twonarrow band ones, e.g. a Dual Cell HSDPA UE can be expected to have one 10 MHz receiver rather thantwo 5 MHz receivers. If the aggregated carriers can be non-adjacent, then there may be a need to go tothe architecture similar to that used in inter-band carrier aggregation. 31 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  33. 33. Figure 23 shows a very simplified block-diagram of a UE capable of transmitting on two frequency bands,but not simultaneously. Such dual-band (or multi-band) transmitter architectures are expected to be morecommonplace than those capable of using multiple transmitter chains simultaneously, e.g. a 10 MHztransmitter could be used for aggregating two adjacent 5 MHz HSUPA carriers for Dual Cell HSUPAconfiguration, or be able to transmit on one 10 MHz LTE carrier. It however is to be noted that thisarchitecture is not readily able to lend itself to transmitting on multiple frequency bands – a full dual-transmit chain architecture would be required for that. Band A BB processing PA Filter Filter Filter DAC PA Filter Filter upconversion Band B Signal flow through UE transmit processing Figure 23: A simplified block diagram of a dual-band UE transmitted chainFigure 24 shows a very simplified block-diagram of a UE capable of transmitting on two frequency bandssimultaneously, i.e. capable of uplink carrier aggregation on two bands. Such dual-band (or multi-band)transmitter able to lend itself to transmitting on multiple frequency bands and thus would be able tosupport also HSPA+LTE aggregation in the uplink. Band A PA Filter Filter Filter DAC BB processing upconversion PA Filter Filter Filter DAC upconversion Band B Signal flow through UE transmit processing Figure 24: A simplified block diagram of a uplink dual-band carrier aggregating UE transmitted chain 32 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  34. 34. 5.3 IMPLEMENTATION ASPECTS OTHER THAN RADIO PROCESSINGDifferent architecture options discussed in section 4 set different requirements for data processing andnode interfacing in the network. The architectures where the base station acts as the data managingentity the base station needs to be able to have a fast interface between the LTE and the HSPAprocessing in order to be able to split the downlink data flow over the two radios. Similarly in the uplinkdirection the base station needs to either route uplink data between the two processing entities (dualuplink), or forward the fast feedback from one side to the other (single uplink). At least for some of theoptions discussed in chapter 4, the RRC layers of the two RATs, LTE RRC in the base station and HSPARRC in the RNC, need to be aware of each other to some extent in order for the master RAT to be able toassign the UE with the resources of the other RAT. This implies some modifications to both eNodeB andRNC RRC layers, and introducing means for negotiating the resources assignable.The radio network centric architectures can be expected to avoid the need for the core network to beaware of the new UE type – again analogous to aggregating carriers of one RAT being visible to the corenetwork only by increased user data rates. The data split/aggregation in the core network obviouslymeans that the core would need to be able to support such functionality and the LTE core would need tobe able to interface with HSPA RAN or the HSPA core with the LTE RAN, and also indicate the radio thatthere is a new type of connection taking place.Similarly to the changes in the network side, the device needs a higher degree of integration betweenMAC and RRC layers of the two RATs than when aggregating HSPA or LTE carriers. The actual dataprocessing requirement would not differ from that of aggregating carriers within one RAT, but it wouldrequire two different types of protocol stacks to be able to run simultaneously and interface at the layerwhere the data aggregation/split is taking place.Operating both LTE and HSPA receivers simultaneously, can expected to increase device batteryconsumption, although this can be assumed to be no different to aggregating carriers in multiple bandswithin one RAT. Architectures with UE transmitting in the uplink on both LTE and HSPA simultaneouslycan be expected to have a more significant device battery consumption impact than that of the two RATreception, but again, the added power consumption can be expected to be comparable to what theaggregation of two uplink carriers on different frequency bands of one RAT would result with. 33 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  35. 35. 6. CONCLUSIONHSPA+ and LTE are the overwhelming mobile broadband technologies of choice for operators throughoutthe world. The evolution of both HSPA+ and LTE standards has introduced aggregation of carriers forhigher data rates, better load balancing and increased spectrum utilization, and since the dawn of LTE,the standard support for radio level interworking for HSPA and LTE radios has been included. A naturalcontinuation of such development is to tighten the interworking even further and introduce similaraggregation of carriers between the two radio access technologies.The same gain mechanisms that have been seen beneficial for Multicarrier HSDPA as well as LTECarrier Aggregation can be benefited from by aggregating HSPA with LTE. At low or medium load,HSPA+LTE aggregation is able to take advantage of the unused resources leading to significant data rateincreases both at the cell edge and the cell center for the carrier aggregation capable devices. In addition,the carrier aggregation enables fast (millisecond level) load balancing across the carriers thus improvingthe data rates of all users.A number of possible network architectures can be foreseen for HSPA+LTE aggregation, and are brieflytouched upon in this white paper. Most promising architecture options are seen with co-located multiradiobase stations with the base station (NodeB + eNodeB) acting as the data aggregation point, andsimultaneously maintaining the existing network architecture for the devices connecting to the networkwith one radio system at a time only. This architecture can utilize some of the already deployed RFhardware in the base station, whereas new baseband functionality managing the data flow will beneeded. On the device side receiver radio architectures capable of multiband carrier aggregation shouldbe suitable also for aggregated HSPA+LTE.While Dual-Cell HSDPA is already in commercial operation, and higher levels of HSPA carrieraggregation as well as LTE carrier aggregation are part of 3GPP specifications existing today,HSPA+LTE aggregation is currently not standardized. Although conceptually straightforward and buildingon already standardized concepts, HSPA+LTE aggregation is a major feature, with a standardizationeffort comparable to that of LTE carrier aggregation. 34 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  36. 36. ABBREVIATIONS3GPP 3rd Generation Partnership Project4C-HSDPA 4-Carrier HSDPA8C-HSDPA 8-Carrier HSDPAA/N ACK/NACKACK AcknowledgementADC Analog to Digital ConversionASN.1 Abstract Syntax Notation OneAWS Advanced Wireless SpectrumBB Base BandBTS Base Transceiver StationCA Carrier AggregationCC Component CarrierCDMA Code Division Multiple AccessCIF Carrier Indicator FieldCN Core NetworkCQI Channel Quality IndicationDAC Digital to Analog ConversionDB Dual BandDC-HSDPA Dual Cell HSDPADC-HSUPA Dual Cell HSUPADCH Dedicated ChannelDL DownlinkE-DCH Enhanced DCHE-UTRAN Evolved UTRANEPC Evolved Packet CoreFACH Forward Access CannelGPRS General Packet Radio ServiceGbps Gigabits per secondGSM Global System for Mobile CommunicationsHS-SCCH High Speed Shared Control ChannelHARQ Hybrid Automatic Repeat reQuestHSDPA High Speed Downlink Packet AccessHSPA High Speed Packet AccessHSUPA High Speed Uplink Packet AccessID IdentityITU International Telecommunication UnionL1 Layer oneLTE Long Term EvolutionLTE-A LTE AdvancedMAC Medium Access ControlMAC-d MAC dedicatedMAC-hs MAC high speedMAC-ehs MAC enhanced high speedMbps Megabits per secondMHz MegahertzMIMO Multiple Input Multiple Output 35 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  37. 37. NACK Negative ACKO&M Operation and MaintenanceOEM Original Equipment ManufacturerPA Power AmplifierPCC Primary Component CarrierPCell Primary Serving CellPCH Paging ChannelPCS Personal Communications ServicePDCCH Physical Downlink Control ChannelPDSCH Physical Downlink Shared ChannelPHY Physical [layer]PDCP Packet Data Convergence ProtocolQAM Quadrature Amplitude ModulationRAT Radio Access TechnologyRel ReleaseRF Radio FrequencyRLC Radio Link ControlRNC Radio Network ControllerROHC Robust Header CompressionRRC Radio Resource ControlSCC Secondary Component CarrierSCell Secondary Serving CellSIB System Information BlockSMR Specialized Mobile RadioSON Self Optimizing NetworkTTI Transmission Time IntervalTX TransmitUE User EquipmentUL UplinkUMTS Universal Mobile Telecommunications SystemURA UMTS Routing AreaUS United StatesUTRAN UMTS Terrestrial Radio Access NetworkWCDMA Wideband CDMAWRC World Radio Congress 36 4G Americas HSPA+LTE Carrier Aggregation – June 2012
  38. 38. ACKNOWLEDGEMENTSThe mission of 4G Americas is to promote, facilitate and advocate for the deployment and adoption of the3GPP family of technologies throughout the Americas. 4G Americas Board of Governor members includeAlcatel-Lucent, América Móvil, AT&T, Cable & Wireless, CommScope, Entel, Ericsson, Gemalto, HP,Huawei, Nokia Siemens Networks, Openwave, Powerwave, Qualcomm, Research In Motion (RIM),Rogers, T-Mobile USA and Telefónica.4G Americas would like to recognize the project leadership and important contributions of Karri Ranta-aho of Nokia Siemens Networks (NSN), as well as representatives from the other member companies on4G Americas’ Board of Governors who participated in the development of this white paper. 37 4G Americas HSPA+LTE Carrier Aggregation – June 2012

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