– taking another step toward the Networked SocietyThe evolution of LTE is key to the realization of Ericsson’s vision of a Networked Society. This vision 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 deliver a high-quality user experience in the future.

ericsson White paper284 23-3189 Uen | January 2013

LTE Release 12

LTE RELEasE 12 • LTE RELEasE 12 aND BEYOND 2

There are three main challenges that need to be addressed by future wireless communication systems to enable a truly Networked Society, where information can be accessed and data shared anywhere 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 within 3GPP [1].

BACKGROUNDThe deployment of 4G mobile-broadband systems based on 3GPP LTE RAT is now progressing on a large scale [2], with 55 million users as of November 2012 and close to 1.6 billion users anticipated in 2018 [3]. Current commercial LTE deployments are based on 3GPP Release 8 and Release 9 – that is, the first releases of the LTE technical specifications.

The first major step in the evolution of LTE – sometimes also referred to as LTE-Advanced or LTE-A – occurred as part of 3GPP Release 10, which was finalized in 2010. Release 10 extended and enhanced LTE RAT in several dimensions. For example, the possibility was created for transmission bandwidth beyond 20MHz and improved spectrum flexibility through carrier aggregation, and enhanced multi-antenna transmission based on an extended and more flexible reference-signal structure. Another extension was the introduction of relaying 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 refining some of the features introduced in Release 10, Release 11 includes basic functionality for coordinated multipoint (CoMP) transmission and reception, as well as enhanced support for heterogeneous deployments. The latter refers to the deployment of low-power network nodes under 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 prepare the next evolution step of LTE. At that meeting requirements and potential technologies were identified. [4]

KEY CHALLENGESWhile they are currently dominant, the number of human-centric communication devices will be surpassed tenfold by “communicating machines” in the future [5], including surveillance cameras, smart-home and smart-grid devices, and connected sensors. Wireless communication systems

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LTE LTE-A LTE-B

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Further evolution of LTE– Release 12 and beyondFurther evolution of LTE– Release 12 and beyond

Figure 1: The evolution of LTE beyond LTE-A.

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must be able to handle such a large number of connected devices in an efficient way.

The traffic of wireless communication systems has grown dramatically over the past 10 years and there is no indication this growth will slow down. There are predictions that overall traffic demands will increase in the order of a thousand times within the next 10 years. Continued growth in the use of mobile broadband will be the main reason for this increase, but it will be further fuelled by new traffic due to the mass introduction of communication machines. Handling this traffic growth in an affordable and sustainable way will be a further challenge for future wireless communication systems.

The range of applications, with corresponding requirements and characteristics, that need to be covered by future wireless communication systems will expand tremendously. Mobile broadband will remain a core application, and future wireless communication systems must be able to offer mobile-broadband services with user data rates in the multi-Gbps range 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 further use cases and applications with a wide range of new requirements and characteristics in areas such as device cost and energy consumption, latency and reliability.

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Figure 2: Key challenges to be addressed by future wireless

communication systems including the evolution of LTE.

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Highly efficient wide-area deployments of macro base stations will continue to be the core of future wireless communication systems, providing extensive coverage and also partly serving as backhaul for more local access. Thus, a key aim for the future evolution of LTE is to further enhance 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 of always-on signals. The enhancements are general in the sense that benefits are expected not only 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 since its first release, with further enhancements introduced in later releases. Release 10 extended downlink spatial multiplexing up to eight layers and introduced uplink spatial multiplexing up to four layers.

When it comes to CoMP technologies, which are primarily designed to reduce inter-cell interference, uplink CoMP is to a large extent not related to specification but simply a question of 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 technologies that we foresee for LTE Release 12 and beyond:

Enhancements to CSI from terminals to the network can improve the performance of existing multiple-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 space and frequency domains. It allows even more advanced transmission schemes, integrating precoding 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 Antenna Systems (AAS). AAS are where radio-frequency components, such as power amplifiers and transceivers are integrated with an array of antenna elements. This kind of implementation offers several advantages over current implementations, with passive antennas being connected to transceivers through feeder cables. Not only are cable losses reduced, leading to better performance and reduced energy consumption, but installation also becomes easier and the required 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 compared with today. AAS may be an enabler for concepts where the elevation domain can be further utilized with antennas of a similar form-factor compared with conventional sector antennas. A wide range of approaches are possible, and the performance depends on the deployment scenario, 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 solutions with relaxed backhaul requirements.

FURtHER ADvANCED tERmiNAL RECEivERSIn the first release of LTE, advanced receivers with at least two antennas at the device side were required to handle the interference between spatially multiplexed streams. This release also provided the means to support both linear receivers and non-linear interference-cancelling receivers.

In Release 11, performance requirements for linear inter-cell-interference rejection have been defined.

In parallel, more advanced receivers with partial inter-cell-interference cancellation and mitigation of cell-specific reference signals, for example, are being defined. The primary motivation

General enhancements

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for such advanced receivers in Release 12 is to enhance the support for offloading in heterogeneous deployments, using even larger cell-selection offsets than is possible with existing receiver algorithms. At the same time, such receivers are also expected to provide user-data-rate benefits in macro deployments at typical low to medium loads.

Advanced receivers, for further mitigation of intra and inter-cell interference coming from control and 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 they improve 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 no access to the electrical grid. This is of particular interest for the further spread of mobile-broadband services in rural areas, especially in the developing world.

Network energy efficiency is to a large extent an implementation issue. However, specific features of the LTE technical specifications may improve energy efficiency. This is especially true for higher-power macro sites, where a substantial part of the energy consumption of the cell site is directly or indirectly caused by the power amplifier.

The energy consumption of the power amplifiers currently available is far from proportional to the power-amplifier output power. On the contrary, the power amplifier consumes a non-negligible amount of energy even at low output power, for example when only limited control signaling is being transmitted within an “empty” cell.

Minimizing the transmission activity of such “always-on” signals is essential, as it allows base stations to turn off transmission circuitry when there is no data to transmit. Eliminating unnecessary transmissions also reduces interference, leading to improved data rates at low to medium load in both homogeneous as well as heterogeneous deployments.

A new carrier type is considered for Release 12 to address these issues. Part of the design has 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 improved by enhancements to idle-mode support.

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Network densification – increasing the number of network nodes, and thereby bringing them physically closer to the user terminals – is key to improving traffic capacity and extending the achievable user-data rates of a wireless communication system.

In addition to straightforward densification of a macro deployment, network densification can be achieved by the deployment of complementary low-power nodes under the coverage of an existing macro-node layer. In such a heterogeneous deployment, the low-power nodes provide very high traffic capacity and very high user throughput locally, for example in indoor and outdoor hotspot positions. Meanwhile, the macro layer ensures service availability and QoE over the entire coverage area. In other words, the layer containing the low-power nodes can also be referred to as providing local-area access, in contrast to the wide-area-covering macro layer.

The installation of low-power nodes as well as heterogeneous deployments has been possible since the first release of LTE. Additional features – extending the capabilities to operate in heterogeneous deployments – were added to the LTE specifications as part of Releases 10 and 11. More specifically, these releases introduced additional tools to handle inter-layer interference in heterogeneous deployments.

During the further evolution of LTE – Release 12 and beyond – this trend will continue. This means further enhancements related to low-power nodes and heterogeneous deployments will be considered under the umbrella of “small-cell enhancements” activities [6].

Some of these activities will focus on achieving an even higher degree of interworking between the macro and low-power layers, including different forms of macro assistance to the low-power layer and dual-layer connectivity. As outlined in Figure 3, dual connectivity implies that the device has 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.

Small-cell and local-area deployment

Figure 3: Dual connectivity – simultaneous connection to the macro and low-power layer.

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> 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 the option of Wi-Fi access can be used to further boost the overall traffic capacity and service level.

Interworking and integration between LTE and Wi-Fi is currently supported at the core-network level. However, as public Wi-Fi deployments managed by operators become more common, operators will demand 3GPP Wi-Fi integration on a radio-access-network level. This will allow for better overall radio-resource management, provide improved overall mobile-broadband performance, and allow operators to maintain a more seamless user experience.

Wi-Fi access selection currently depends very much on the device implementation. This means that in typical implementations, the device selects Wi-Fi when it is available. Examples of when it would be beneficial for the user experience to remain in a 3GPP mobile system include situations when the Wi-Fi radio quality 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 selection to 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 with more control over Wi-Fi access selection. This control may be gained through network-centric mobility 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 in the terminal).

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Figure 4: LTE/Wi-Fi integration.

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mACHiNE-tYpE COmmUNiCAtiONThe world is developing into a Networked Society, where all kinds of devices interact and share information. This means phenomenal growth in terms of communicating devices and traffic volumes in 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 enhancements and extensions of the LTE RAT.

Although LTE is already capable of handling a wide range of MTC scenarios, the aim is to improve 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 supported peak data-rate requirements and reduced requirements on maximum supported bandwidths (less than 20MHz).

To enable extended battery life, the energy consumption that results from every data transfer performed by a device needs to be reduced to a minimum. For devices that transmit data infrequently, energy consumption can be reduced significantly by longer cycles for discontinuous reception (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 an energy-consumption perspective than the data transfer itself. For that reason, simplifying the procedures for the infrequent transfer of small amounts of data can provide significant benefits in terms of energy consumption for MTC devices.

In some use cases, MTC devices may be placed in locations where LTE coverage is not available with existing network deployments. This may be the case, for example, for smart meters in the basements of buildings. Options for coverage extensions can be achieved by technologies, such as enhanced multi-antenna technologies (for example, beamforming), more robust transmission modes, as well as repetition and energy accumulation of signals.

Because the number of connected machines is expected to grow significantly, mechanisms designed to handle a large number of devices within a single cell are needed. A load-control scheme called enhanced access barring has been specified for Release 11 to avoid overload of the 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 per device that is caused to the network.

DiSCOvERY AND COmmUNiCAtiONsupport for direct device-to-device (D2D) discovery and/or communication as an integrated part of the wireless communication system is currently being considered for the further evolution of LTE. 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 other devices 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 into the overall wireless access network. Whether communication occurs directly between devices or via the infrastructure should be transparent to the user, and the network should be involved and assist in the D2D communication.

New use cases

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NAtiONAL SECURitY AND pUBLiC SAFEtY Many parties are interested in using the cellular systems to provide communication services for the NSPS area. In 2012, the US government allocated dedicated spectrum to a newly formed NSPS operator (FirstNet) with the intention of delivering such services over an LTE network.

Consequently, 3GPP has been asked to comply with a full range of requirements for supporting NSPS services over LTE networks. Even though LTE seems to already comply with most such requirements, a first analysis indicated that, from a radio access perspective, D2D functionalities should be used for NSPS support in case of a lack of network coverage.

From that perspective, the challenge is to develop a common D2D framework to enable both high-performance network-assisted discovery and communication (for commercial purpose) and out-of-network-coverage D2D for NSPS support. The ability to reuse common D2D technology for both commercial and NSPS applications is expected to reduce costs for NSPS-enabled devices by enabling better economies of scale.

Proximity detectionProximity detection D2Dcommunication

D2Dcommunication

Figure 5: Proximity detection and communication phase for D2D.

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Ericsson’s vision of the Networked Society, where everything that gains from being connected will be connected, will entail new requirements on connectivity. The evolution of LTE is the most important 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 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.

It is also crucial to improve capacity and user quality in local-area scenarios by making further enhancements to LTE small-cell deployments, as well as creating better possibilities for the close integration of LTE and Wi-Fi deployments.

Finally, Release 12 should extend LTE to new use cases by introducing features to improve the support for mTc communication as well as NsPs services, including the support for D2D communication.

All in all, this will further solidify LTE as the dominating global wireless-access technology for the future.

SUMMARY AND CONCLUSIONS

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References1. www.3gpp.org/Release-12

2. http://www.amazon.com/4G-LTE-LTE-advanced-mobile-Broadband/dp/012385489X/ ref=dp_ob_image_bk/183-8826124-5561352

3. http://www.ericsson.com/ericsson-mobility-report

4. http://www.3gpp.org/Future-Radio-in-3GPP-300-attend

5. http://www.ericsson.com/thinkingahead/networked_society

6. http://www.3gpp.org/ftp/Specs/archive/36_series/36.932/36932-c00.zip

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GLOSSARYAAS Active Antenna SystemsComp coordinated multipointCSi channel-state informationD2D device-to-deviceDRX discontinuous receptionDSL digital subscriber lineHS high-speed mtC machine-type communication NSpS national security and public safetyRAt radio-access technologyRRC Radio Resource Control