Addressing Carrier Aggregation Challenges Using Multiplexer Solutions

WHITE PAPERAddressing Carrier AggregationChallenges Using Multiplexer SolutionsExecutive SummaryMobile network operators worldwide are deploying carrier aggregation (CA), which enables them to provide faster dataservices by bonding two or more blocks of spectrum into a wider channel. With CA, mobile devices communicate onmultiple LTE bands simultaneously, but this creates a challenge: how to avoid interference between the bands(cross-isolation) while minimizing insertion loss to maintain good reception and battery life. Multiplexers provide anelegant solution – and in many cases, the only practical solution – for CA combinations that use closely spaced bands.Multiplexers integrate all the filters required for multiple aggregated bands, providing isolation between and withinbands while allowing them to connect to the antenna at the same time. Carefully matched bulk acoustic wave (BAW)and temperature compensated-surface acoustic wave (TC-SAW) filters are essential to meet system requirements.Multiplexers will become increasingly important as operators aggregate three or more bands. Additional benefits ofmultiplexers include space savings, simplified design and reduced cost.January 2016 Subject to change without notice1 of 6www.qorvo.com

WHITE PAPER: Addressing Carrier Aggregation Challenges Using Multiplexer SolutionsIntroductionThe Challenges ofCarrier AggregationWorldwide demand for fastermobile data services is drivingmobile network providers to rapidlydeploy CA, a key feature of 4GLTE-Advanced that enablesoperators to provide higher datarates by bonding two or more blocksof spectrum into a wider channel.Figure 1 illustrates the globalmomentum of CA deployments,with 88 LTE-Advanced systems in45 countries commercially launchedby July 2015 and another 22 indevelopment. Current deploymentsare based on specifications (3GPPRelease 10/11/12) that allow thecombination of up to five blocks ofspectrum called component carriers(CCs), each between 1.4 and20 MHz wide and with a maximum of100 MHz of aggregated bandwidth.CA requires specific categories ofmodem in communicating devices,such as Category 4 (20 MHzaggregated bandwidth, 150 Mbps)and Category 6 (40 MHz, 300 Mbps).Most early CA deploymentscombined only two CCs. But manynetwork operators will quickly addcombinations of three or more bandsas they seek to offer still faster dataservices and maximize utilization offragmented spectrum allocations. Ingeneral, three or more CCs arerequired to provide more than40 MHz bandwidth and deliverspeeds greater than around300 Mbps. Operators in Korea andother countries are alreadyaggregating three CCs; four-CCaggregations are expected in 2016,with five-CC aggregations in 2017and six-CC aggregations likely by2018. Looking further into the future,3GPP is working on specificationsthat are expected to support asmany as 32 CCs, with much fasterdata rates.As shown in Figure 2, operators canaggregate CCs in different LTEbands (inter-band CA) or within thesame band (intra-band); CCs may becontiguous (occupying adjacentspectrum) or non-contiguous.Figure 2. Options for aggregating CCs.Top: intra-band contiguous.Middle: intra-band non-contiguous.Bottom: inter-band non-contiguous.Figure 1. Global LTE-Advanced carrier aggregation deployments.Global networks using Category 6 and Category 4 modems,which support up to 300 Mbps and 150 Mbps respectively.Source: Global mobile Suppliers Association (GSA).January 2016 Subject to change without notice2 of 6www.qorvo.com

WHITE PAPER: Addressing Carrier Aggregation Challenges Using Multiplexer SolutionsRF FilteringChallengesWith CA, each device transmitsand/or receives on more than oneCC simultaneously. This createsnew radio frequency (RF) filteringchallenges for mobile devices dueto the need for cross-isolation:preventing interferencebetween CCs.To enable simultaneouscommunication on multiple CCs,the device’s RF front end mustsupport multiple open, paralleltransmit and receive paths betweenthe transceiver and the antenna(s).Each pathway must be sufficientlyisolated from the others. Thisisolation can be achieved using RFfilters, and/or by allocating eachaggregated band to a differentantenna. Smartphone industrial formfactors are constrained by severalconsumer-driven requirements suchas height, functionality, screen sizeand battery life, which may make itprohibitive to add more antennas.Manufacturers therefore strive tomaximize the number of bands perantenna as much as possible withinthe practical limits of performance.aggregated bands. At the same time,each filter must minimize insertionloss of the transmitted signal in orderto maintain good reception andminimize power consumption.Cross-isolation is easiest to achievewhen aggregating widely separatedbands, such as the aggregation of ahigh-frequency band ( 2300 MHz)with a low-frequency band( 960 MHz). An example of awidely-spaced band combination isB7 B20, which is used in severalEuropean countries. When bandsare widely separated, adequateisolation may be provided by adiplexer (a simple frequency splitter).For example, a diplexer could beused to separate high-band andlow-band signals and direct themalong existing high-band andlow-band pathways within the phone.Cross-isolation is much morechallenging when aggregating bandsthat are closer together, such ascombinations of multiplemid-frequency (1428-2200 MHz)bands. Many of the widely usedCA combinations will fall into thiscategory: current examples includeB1 B3 and B25 B66 (seeTable 1).Achieving cross-isolation using RFfilters requires that filters attenuatethe out-of-band signals for each CCsufficiently to avoid loading the otherBand Combination MultiplexerSeparate Antenna Primary Region of UseB1 B3xChina, Korea, EuropeB25 B66xNorth AmericaB3 B7xxEurope, Middle East& AfricaB1 B3 B7xxKoreaB3 B7 B20xxB39 B41xEurope, Middle East& AfricaChinaB1 B3 B8xJapanThe Value of MultiplexerSolutionsMultiplexers provide an elegantsolution – and in many cases, theonly practical solution – for CAcombinations that use closelyspaced bands. Multiplexers integrateinto a single component all thetransmit and receive filters for theaggregated CCs, providing therequired isolation while allowingmultiple CCs to connect to theantenna at the same time. The filtersmust be carefully co-designed andmatched to achieve the requiredperformance. Without using amultiplexer, it may be impossibleto meet demanding systemrequirements for in-band isolationand cross-isolation, together withlow insertion loss and low currentconsumption.The complex performancerequirements for multiplexers can beillustrated by comparing the isolationrequirements when communicatingon a single band (i.e. without CA)to the requirements whencommunicating on multiplebands (with CA).Without CA: For communication ona single FDD-LTE band, the primarychallenge is in-band isolation:preventing interference between thetransmit and receive frequencies ofthe same band. The transmit filtermust sufficiently attenuate thetransmitted signal at the receivefrequency output, to avoiddesensitizing the receiver. In-bandisolation is typically achievedby using two bandpass filters,corresponding to the transmit andreceive frequencies. These filters areoften combined into a single devicecalled a duplexer.Table 1. Carrier aggregation band combinations that require multiplexers.January 2016 Subject to change without notice3 of 6www.qorvo.com

WHITE PAPER: Addressing Carrier Aggregation Challenges Using Multiplexer Solutions Figure 4. Performance of Qorvo multiplexer using BAW filters (right) TC-SAW/SAW filters (left).The BAW multiplexer delivers lower insertion loss across the B1 receive frequency range,with less variation over temperature, resulting in improved receive sensitivity.With CA: When using CA tocommunicate on multiple FDD-LTEbands, the isolation challengesbecome far more complex. There aremany more possible interactions,because of the requirement forcross-isolation between each of thebands as well as isolation withineach band. A multiplexer designed toallow aggregation of n bands mustinclude 2n filters (one filter for eachtransmit frequency and one for eachreceive frequency), and it mustensure adequate isolation betweeneach of the transmit and receivefrequencies. The number of requiredSingle FilterDuplexerisolations increases very rapidly withthe number of aggregated bands.Considering all the possibleinteractions, there are eightisolations required in a quadplexer(used for aggregating two bands)versus two in a duplexer. For ahexaplexer (six filters for threebands), the situation is even morecomplex with 18 possible isolations.To achieve these isolations whilemeeting system requirements for lowinsertion loss, the filters must bedesigned together and carefullymatched. For mid-band and higherfrequencies, BAW filters areMultiplexer (QUAD)Multiplexer (HEXA)essential to provide the requiredcombination of steep skirts to avoidinterference between closely spacedbands, consistent performance overa wide temperature range and lowinsertion loss. Some combinations oflow-frequency bands may requireTC-SAW filters: an example might beB26 B12.A well designed multiplexer providesadditional benefits to mobile deviceengineers because of the high levelof integration. Combining multiplefilters into a single componenttypically requires 60% less PCBspace than using discrete filters;such space savings becomesincreasingly important as morefeatures and bands are packedinto each generation of smartphones.The integration also reduces theoverall number of components ineach smartphone, which simplifiesdesign, reduces cost and acceleratestime to market for devicemanufacturers.Figure 3. Comparing single filters, duplexers and multiplexers.January 2016 Subject to change without notice4 of 6www.qorvo.com