White paper: LTE Release 12

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The work on the next evolutionary step of LTE, Release 12, started recently. Important areas to further improve in Release 12 are capacity, user quality and energy efficiency in macro deployments by adding support for enhanced multi-antenna transmission and advanced receivers,
and by introducing a new lean carrier type.

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White paper: LTE Release 12

  1. 1. ericsson White paper284 23-3189 Uen | January 2013LTE Release 12– taking another step toward theNetworked SocietyThe evolution of LTE is key to the realization of Ericsson’s vision of a Networked Society. Thisvision means that, in the future, anything that benefits from being connected will be connected– from parking meters and house alarms to cars and trash cans. However, the Networked Society also comes with a number of new requirements on connectivity.The next release of LTE Release 12 – will play a key role in ensuring that the networks can delivera high-quality user experience in the future.
  2. 2. LTE RELEASE 12AND BEYONDThere are three main challenges that need to be addressed by future wireless communicationsystems to enable a truly Networked Society, where information can be accessed and data sharedanywhere and anytime, by anyone and anything. These are:>> A massive growth in the number of connected devices.>> A massive growth in traffic volume.>> An increasingly wide range of applications with varying requirements and characteristics.For these challenges to be addressed properly, it is necessary for LTE radio-access technology(RAT) to evolve further. This evolution will take place mainly within the following areas:>> General enhancements applicable to a wide range of scenarios and use cases.>> Enhancements specifically targeting small-cell/local-area deployments.>> Enhancements specifically targeting new use cases, such as machine-type communication (MTC) and national security and public safety services (NSPS).The further evolution of LTE – LTE Release 12 and beyond – is sometimes referred to as LTE-B.Work on Release 12 has now started within3GPP [1]. Further evolution of LTEBACKGROUND – Release 12 and beyondThe deployment of 4G mobile-broadbandsystems based on 3GPP LTE RAT is nowprogressing on a large scale [2], with 55 LTE LTE-A LTE-Bmillion users as of November 2012 andclose to 1.6 billion users anticipated in 2018[3]. Current commercial LTE deploymentsare based on 3GPP Release 8 and Release9 – that is, the first releases of the LTEtechnical specifications. Rel 8 Rel 9 Rel 10 Rel 11 Rel 12 Rel 13 The first major step in the evolution of Figure 1: The evolution of LTE beyond LTE-A.LTE – sometimes also referred to as LTE-Advanced or LTE-A – occurred as part of3GPP Release 10, which was finalized in2010. Release 10 extended and enhanced LTE RAT in several dimensions. For example, thepossibility was created for transmission bandwidth beyond 20MHz and improved spectrumflexibility through carrier aggregation, and enhanced multi-antenna transmission based on anextended and more flexible reference-signal structure. Another extension was the introduction ofrelaying functionality – that is, the possibility of using LTE radio access not only for the access(network-to-terminal) link but also as a solution for wireless backhauling. The 3GPP is currently in the concluding stage of LTE Release 11. In addition to further refiningsome of the features introduced in Release 10, Release 11 includes basic functionality forcoordinated multipoint (CoMP) transmission and reception, as well as enhanced support forheterogeneous deployments. The latter refers to the deployment of low-power network nodesunder the coverage of on overlaid layer of macro nodes. In June 2012, a 3GPP RAN workshop about the Release 12 scope took place in order to preparethe next evolution step of LTE. At that meeting requirements and potential technologies wereidentified. [4]KEY CHALLENGESWhile they are currently dominant, the number of human-centric communication devices will besurpassed tenfold by “communicating machines” in the future [5], including surveillance cameras,smart-home and smart-grid devices, and connected sensors. Wireless communication systemsLTE Release 12 • LTE RELEASE 12 AND BEYOND 2
  3. 3. must be able to handle such a large numberof connected devices in an efficient way. Massive growth in Massive growth in Wide range of The traffic of wireless communication Connected devices Traffic volume Requirements andsystems has grown dramatically over the characteristicspast 10 years and there is no indication this Massive amount of Further expansion of Multi-Gbps in specificgrowth will slow down. There are predictions communicating machines mobile broadband scenariosthat overall traffic demands will increase in Additional users andthe order of a thousand times within the increased usage Tens of Mbps almost + everywherenext 10 years. Continued growth in the use New use cases due toof mobile broadband will be the main communicating machines New requirements andreason for this increase, but it will be further characteristics due tofuelled by new traffic due to the mass communication machinesintroduction of communication machines.Handling this traffic growth in an affordable “50 billion devices” “1000”x in 10 yearsand sustainable way will be a furtherchallenge for future wireless communication Figure 2: Key challenges to be addressed by future wirelesssystems. communication systems including the evolution of LTE. The range of applications, withcorresponding requirements andcharacteristics, that need to be covered by future wireless communication systems will expandtremendously. Mobile broadband will remain a core application, and future wireless communicationsystems must be able to offer mobile-broadband services with user data rates in the multi-Gbpsrange locally, and in the tens-of-Mbps range almost everywhere else. In addition, the mass-introduction of communicating machines in the emerging Networked Society, will lead to furtheruse cases and applications with a wide range of new requirements and characteristics in areassuch as device cost and energy consumption, latency and reliability.LTE Release 12 • LTE RELEASE 12 AND BEYOND 3
  4. 4. GeneralenhancementsHighly efficient wide-area deployments of macro base stations will continue to be the core offuture wireless communication systems, providing extensive coverage and also partly servingas backhaul for more local access. Thus, a key aim for the future evolution of LTE is to furtherenhance and expand the capabilities in macro deployments. Examples of this include further enhancements to multiple-antenna and CoMP technologies,as well as advanced terminal receivers and a new carrier type with reduced transmission ofalways-on signals. The enhancements are general in the sense that benefits are expected notonly for macro deployments, but also for deployments with low-power nodes.Further enhanced multi-antenna transmissionDifferent types of multi-antenna transmission technologies have been integral to LTE RAT sinceits first release, with further enhancements introduced in later releases. Release 10 extendeddownlink spatial multiplexing up to eight layers and introduced uplink spatial multiplexing up tofour layers. When it comes to CoMP technologies, which are primarily designed to reduce inter-cellinterference, uplink CoMP is to a large extent not related to specification but simply a questionof implementation. Downlink CoMP on the other hand, requires a larger specification effort, primarily in the area ,of channel-state information (CSI) to be fed back from the device to the network. For this purpose,a multi-point CSI feedback framework has been introduced in Release 11. The following are areas of further extensions of the multiple-antenna and CoMP technologiesthat we foresee for LTE Release 12 and beyond: Enhancements to CSI from terminals to the network can improve the performance of existingmultiple-antenna technologies for up to eight antenna ports on the transmitter (network) side.For closed-loop spatial multiplexing technologies, one example is finer resolution in the spaceand frequency domains. It allows even more advanced transmission schemes, integratingprecoding with fast radio resource management, such as scheduling and link adaptation. Updates to base-station requirement specifications to better fit also the use of Active AntennaSystems (AAS). AAS are where radio-frequency components, such as power amplifiers andtransceivers are integrated with an array of antenna elements. This kind of implementation offersseveral advantages over current implementations, with passive antennas being connected totransceivers through feeder cables. Not only are cable losses reduced, leading to betterperformance and reduced energy consumption, but installation also becomes easier and therequired space for equipment decreases. Enhanced support for elevation beamforming with vertically stacked antenna sub-elements,as well as, potentially beamforming with a substantially larger number of antenna ports comparedwith today. AAS may be an enabler for concepts where the elevation domain can be furtherutilized with antennas of a similar form-factor compared with conventional sector antennas. Awide range of approaches are possible, and the performance depends on the deploymentscenario, including radio-channel and propagation characteristics. Evolution of CoMP including enhancements with respect to channel-state information feedback ,from the terminals, and, more importantly, to broaden the practical applicability of CoMP solutionswith relaxed backhaul requirements.Further advanced terminal receiversIn the first release of LTE, advanced receivers with at least two antennas at the device side wererequired to handle the interference between spatially multiplexed streams. This release alsoprovided the means to support both linear receivers and non-linear interference-cancellingreceivers. In Release 11, performance requirements for linear inter-cell-interference rejection have beendefined. In parallel, more advanced receivers with partial inter-cell-interference cancellation andmitigation of cell-specific reference signals, for example, are being defined. The primary motivationLTE Release 12 • General enhancements 4
  5. 5. for such advanced receivers in Release 12 is to enhance the support for offloading in heterogeneousdeployments, using even larger cell-selection offsets than is possible with existing receiveralgorithms. At the same time, such receivers are also expected to provide user-data-rate benefitsin macro deployments at typical low to medium loads. Advanced receivers, for further mitigation of intra and inter-cell interference coming from controland data transmission, are a natural evolution of the current ones available. Advanced receivers for user experience are an important area for LTE Release 12 since theyimprove system performance.New carrier typeHigh network energy efficiency is becoming increasingly important in wireless communication.One reason is that energy cost in many cases is a significant part of overall opex for an operator,a part that is expected to grow further in the future with increasing energy prices.Another reason is that reduced energy consumption may open up for new deployment scenarios:for example, solar-powered base stations with reasonably sized solar panels in areas with noaccess to the electrical grid. This is of particular interest for the further spread of mobile-broadbandservices in rural areas, especially in the developing world. Network energy efficiency is to a large extent an implementation issue. However, specificfeatures of the LTE technical specifications may improve energy efficiency. This is especially truefor higher-power macro sites, where a substantial part of the energy consumption of the cell siteis directly or indirectly caused by the power amplifier. The energy consumption of the power amplifiers currently available is far from proportional tothe power-amplifier output power. On the contrary, the power amplifier consumes a non-negligibleamount of energy even at low output power, for example when only limited control signaling isbeing transmitted within an “empty” cell. Minimizing the transmission activity of such “always-on” signals is essential, as it allows basestations to turn off transmission circuitry when there is no data to transmit. Eliminating unnecessarytransmissions also reduces interference, leading to improved data rates at low to medium loadin both homogeneous as well as heterogeneous deployments. A new carrier type is considered for Release 12 to address these issues. Part of the designhas already taken place within 3GPP with transmission of cell-specific reference signals being ,removed in four out of five sub frames. Network energy consumption can be further improvedby enhancements to idle-mode support.LTE Release 12 • General enhancements 5
  6. 6. Small-cell andlocal-areadeploymentNetwork densification – increasing the number of network nodes, and thereby bringing themphysically closer to the user terminals – is key to improving traffic capacity and extending theachievable user-data rates of a wireless communication system. In addition to straightforward densification of a macro deployment, network densification canbe achieved by the deployment of complementary low-power nodes under the coverage of anexisting macro-node layer. In such a heterogeneous deployment, the low-power nodes providevery high traffic capacity and very high userthroughput locally, for example in indoorand outdoor hotspot positions. Meanwhile,the macro layer ensures service availabilityand QoE over the entire coverage area. Inother words, the layer containing the low-power nodes can also be referred to asproviding local-area access, in contrast tothe wide-area-covering macro layer. The installation of low-power nodes aswell as heterogeneous deployments hasbeen possible since the first release of LTE.Additional features – extending thecapabilities to operate in heterogeneous Figure 3: Dual connectivity – simultaneous connection to the macro and low-power layer.deployments – were added to the LTEspecifications as part of Releases 10 and11. More specifically, these releasesintroduced additional tools to handle inter-layer interference in heterogeneous deployments. During the further evolution of LTE – Release 12 and beyond – this trend will continue. Thismeans further enhancements related to low-power nodes and heterogeneous deployments willbe considered under the umbrella of “small-cell enhancements” activities [6]. Some of these activities will focus on achieving an even higher degree of interworking betweenthe macro and low-power layers, including different forms of macro assistance to the low-powerlayer and dual-layer connectivity. As outlined in Figure 3, dual connectivity implies that the devicehas simultaneous connections to both macro and low-power layers. Dual connectivity may imply: Control and data separation where, for instance, the control signaling for mobility is provided via the macro layer at the same time as high-speed data connectivity is provided via the low- power layer. A separation between downlink and uplink, where downlink and uplink connectivity is provided via different layers. Diversity for control signaling, where Radio Resource Control (RRC) signaling may be provided via multiple links, further enhancing mobility performance.Macro assistance including dual connectivity may provide several benefits: Enhanced support for mobility – by maintaining the mobility anchor point in the macro layer, as described above, it is possible to maintain seamless mobility between macro and low-power layers, as well as between low-power nodes. Low overhead transmissions from the low-power layer – by transmitting only information required for individual user experience, it is possible to avoid overhead coming from supporting idle-mode mobility within the local-area layer, for example.LTE Release 12 • small-cell and local-area deployment 6
  7. 7. Energy-efficient load balancing – by turning off the low-power nodes when there is no ongoing data transmission, it is possible to reduce the energy consumption of the low-power layer. Per-link optimization – by being able to select the termination point for uplink and downlink separately, the node selection can be optimized for each link.Integration of Wi-Fi with LTEComplementing a cellular system with theoption of Wi-Fi access can be used to Limited Fiberfurther boost the overall traffic capacity and backhaulservice level. Interworking and integration between LTE xDSL (e.g. 10/2Mbps) HS/LTE/and Wi-Fi is currently supported at the core- Wi-Finetwork level. However, as public Wi-Fideployments managed by operators Wi-Fibecome more common, operators will Loaddemand 3GPP Wi-Fi integration on a radio-access-network level. This will allow forbetter overall radio-resource management, 5Mbps 50Mbpsprovide improved overall mobile-broadbandperformance, and allow operators tomaintain a more seamless user experience. LTE HS Wi-Fi Wi-Fi access selection currently dependsvery much on the device implementation.This means that in typical implementations, Figure 4: LTE/Wi-Fi integration.the device selects Wi-Fi when it is available.Examples of when it would be beneficial forthe user experience to remain in a 3GPP mobile system include situations when the Wi-Fi radioquality is worse than the LTE quality and when the Wi-Fi backhaul is congested. Different devices may also have different implementations, leading to different user experiences.From the operator’s point of view, it would be good to have more control of the access selectionto be able to provide a more uniform experience. With the integration of Wi-Fi on the RAN levels there is a focus on providing operators withmore control over Wi-Fi access selection. This control may be gained through network-centricmobility mechanisms (for example, direct handover command or redirection to Wi-Fi), or by device-centric mechanisms (for example, more careful specification of the access-selection algorithm inthe terminal).LTE Release 12 • small-cell and local-area deployment 7
  8. 8. New use casesMachine-type communicationThe world is developing into a Networked Society, where all kinds of devices interact and shareinformation. This means phenomenal growth in terms of communicating devices and traffic volumesin a variety of fields, such as transport and logistics, smart power grids and e-health.To prepare for this scenario, 3GPP has identified MTC as an important area for future enhancementsand extensions of the LTE RAT. Although LTE is already capable of handling a wide range of MTC scenarios, the aim is toimprove matters even further: Allowing for very low-cost MTC device types. Allowing for very low device energy consumption to ensure long battery life for relevant MTC applications. Providing extended coverage options for MTC services in challenging locations. Handling a very large number of devices per cell.To address the possibility for really low-cost MTC devices, the following are of particular interest:the possibility for device-side half-duplex operation, reduced requirements on maximum supportedpeak data-rate requirements and reduced requirements on maximum supported bandwidths (lessthan 20MHz). To enable extended battery life, the energy consumption that results from every data transferperformed by a device needs to be reduced to a minimum. For devices that transmit datainfrequently, energy consumption can be reduced significantly by longer cycles for discontinuousreception (DRX). In addition, for infrequent transmissions of small amounts of user data, signaling procedures,for instance, for radio-bearer establishment, are sometimes more expensive to carry out from anenergy-consumption perspective than the data transfer itself. For that reason, simplifying theprocedures for the infrequent transfer of small amounts of data can provide significant benefitsin terms of energy consumption for MTC devices. In some use cases, MTC devices may be placed in locations where LTE coverage is not availablewith existing network deployments. This may be the case, for example, for smart meters in thebasements of buildings. Options for coverage extensions can be achieved by technologies, suchas enhanced multi-antenna technologies (for example, beamforming), more robust transmissionmodes, as well as repetition and energy accumulation of signals. Because the number of connected machines is expected to grow significantly, mechanismsdesigned to handle a large number of devices within a single cell are needed. A load-controlscheme called enhanced access barring has been specified for Release 11 to avoid overload ofthe RAN due to many spontaneous access attempts. In general, signaling for every connected device can result in a very high control-plane load.For that reason, lightweight signaling procedures are desired to reduce the signaling load perdevice that is caused to the network.discovery and communicationSupport for direct device-to-device (D2D) discovery and/or communication as an integrated partof the wireless communication system is currently being considered for the further evolution ofLTE. The usage scenarios for D2D range from NSPS support (see below under the NSPS section)to more general proximity-based commercial services for devices close to each other. The first step of the 3GPP D2D activities will involve a focus on proximity-detection functionality– that is, the possibility of a terminal to search its surroundings and detect the presence of otherdevices nearby. The second step will entail examining the possibility for direct D2D communication. A key feature of LTE D2D communication, including proximity detection, is its integration intothe overall wireless access network. Whether communication occurs directly between devices orvia the infrastructure should be transparent to the user, and the network should be involved andassist in the D2D communication.LTE Release 12 • new use cases 8
  9. 9. National security and public safetyMany parties are interested in using the cellular systems to provide communication services forthe NSPS area. In 2012, the US government allocated dedicated spectrum to a newly formedNSPS operator (FirstNet) with the intention of delivering such services over an LTE network. Consequently, 3GPP has been asked tocomply with a full range of requirements forsupporting NSPS services over LTE networks.Even though LTE seems to already complywith most such requirements, a first analysisindicated that, from a radio accessperspective, D2D functionalities should beused for NSPS support in case of a lack ofnetwork coverage. From that perspective, the challenge is todevelop a common D2D framework to enableboth high-performance network-assisteddiscovery and communication (for commercialpurpose) and out-of-network-coverage D2Dfor NSPS support. The ability to reusecommon D2D technology for both commercial Proximity detection D2D communicationand NSPS applications is expected to reducecosts for NSPS-enabled devices by enabling Figure 5: Proximity detection and communication phase for D2D.better economies of scale.LTE Release 12 • new use cases 9
  10. 10. SUMMARY ANDCONCLUSIONSEricsson’s vision of the Networked Society, where everything that gains from being connectedwill be connected, will entail new requirements on connectivity. The evolution of LTE is the mostimportant step to ensure a high-quality wireless network for the future. The work on the next evolutionary step of LTE, Release 12, started recently. Important areasto further improve in Release 12 are capacity, user quality and energy efficiency in macrodeployments by adding support for enhanced multi-antenna transmission and advanced receivers,and by introducing a new lean carrier type. It is also crucial to improve capacity and user quality in local-area scenarios by making furtherenhancements to LTE small-cell deployments, as well as creating better possibilities for the closeintegration of LTE and Wi-Fi deployments. Finally, Release 12 should extend LTE to new use cases by introducing features to improve thesupport for MTC communication as well as NSPS services, including the support for D2Dcommunication. All in all, this will further solidify LTE as the dominating global wireless-access technology forthe future.LTE Release 12 • summary and conclusions 10
  11. 11. References1. www.3gpp.org/Release-122. http://www.amazon.com/4G-LTE-LTE-Advanced-Mobile-Broadband/dp/012385489X/ ref=dp_ob_image_bk/183-8826124-55613523. http://www.ericsson.com/ericsson-mobility-report4. http://www.3gpp.org/Future-Radio-in-3GPP-300-attend5. http://www.ericsson.com/thinkingahead/networked_society6. http://www.3gpp.org/ftp/Specs/archive/36_series/36.932/36932-c00.zipLTE Release 12 • references 11
  12. 12. GLOSSARYAAS Active Antenna SystemsCoMP coordinated multipointCSI channel-state informationD2D device-to-deviceDRX discontinuous receptionDSL digital subscriber lineHS high-speedMTC machine-type communicationNSPS national security and public safetyRAT radio-access technologyRRC Radio Resource ControlLTE Release 12 • glossary 12

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