LTE Release 12 and Beyond

NSN White paper February 2014

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CONTENTS

1. Introduction 3

2. Technology enablers coming with Release 12 4 2.1 Small cell enhancements 4 2.2 Carrier aggregation enhancements 6 2.3 Macro cell enhancements 7 2.4 Machine-Type Communications (MTC) 8 2.5 3GPP-WLAN radio level interworking 9 2.6 LTE Unlicensed 10 2.7 Network Assistend Interference

Cancellations and Suppression (NAICS)11

2.8 Further enhancements 11

3. Summary 13

4. Further reading 15

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1. IntroductionLiving up to what LTE promised, commercial LTE deployments have shown that LTE networks can deliver peak data rates of up to 150 Mbps and average data rates of tens of Mbps as well as latencies below 20 milliseconds. The next step in LTE evolution has already been made, with LTE-Advanced pushing peak data rates beyond 1 Gbps and enhancing multi-band and multi-antenna operation that is compatible with existing deployments. The first LTE-A feature being commercial deployed e.g. in Korea is carrier aggregation.

The continuing demand for ever more capacity is driven largely by video usage. As outlined by Nokia Solutions and Networks (NSN) in its Vision 2020, a 1,000 fold increase in network capacity requires increases in all dimensions:

As the media-intense lifestyle is set to penetrate all social environments, another issue is end users’ continually rising expectations of throughput and service - by 2020, a typical user will consume 1 Gbyte of data per day. Finally, operators need to secure their share of the mobile broadband market by improving their operational efficiency and network robustness, developing new business opportunities, extending their spectrum and by protecting their investment.

LTE Release 12 and beyond will provide the initial enablers of meeting these challenging demands as well as a smooth way towards 4G / 5G era.

ASA

Smart Scheduler New bands

Carrier Aggregation

HetNet management

Advanced macros

Flexible small cells

MIMO & adv. receiver

eCoMP

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2. Technology enablers coming with Release 12

Release 12 enhancements focus on four areas of Capacity, Coverage, Coordination (between cells), and Cost. Improvements in these areas are based on using several technology enablers: small cell enhancements, macro cell enhancements and Machine-Type Communications (MTC). These enablers are described in this paper.

Customer experience, capacity and coverage will be improved with small cell enhancements, based on inter-site Carrier Aggregation, LTE-WLAN integration and macro cell enhancements. Small cell enhancements are also known as enhanced local access.

Improvements in capacity and a more robust network performance are achieved by 3D Beamforming/MIMO (Multiple Input Multiple Output), advanced user equipment (UE) receivers and evolved Coordinated Multipoint (CoMP) techniques, as well as through Self-Organizing Networks for small cell deployments.

Finally, new spectrum footprint and new business will be opened up by optimizing the system for Machine-Type Communications, as well as by, for example, using LTE for public safety.

Small cell enhancements

Carrier Aggregation enhancements

Macro cell enhancements

Machine-Type Communications

SON, WLAN integration, public safety

1 GB per day per user everywhere

1000x capacity increase

New business, new spectrum footprint

Efficiency and robustness

Capacity

Coverage

Coordination

Cost

Figure 1: The Focus (a.k.a. The Four Cs), the Enablers, the Benefits

2.1 Small cell enhancementsThe increasing traffic load will require more cells and more capacity to cope with the expected throughput. Release 12 enhancements help small cell deployments in two main areas - reducing mobility signaling in high density cell deployments and improving user data rates by using macro cells and small cells together.

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The high number of small cells will increase signaling traffic in the core network as users move frequently from one small cell to another. This situation will be improved by separating the user plane and control plane functions in the Radio Access Network (RAN) architecture, that is, letting the macro layer manage the mobility while offloading high data traffic to the small cells.

Dual connectivity (Inter-site Carrier Aggregation) – i.e. carrier aggregation between sites – is an attractive solution for HetNets that do not have an ideal backhaul network. Dual connectivity allows mobility management to be maintained on the macro layer while aggregating small cells to provide extra user plane capacity, increasing the throughput. Inter-site carrier aggregation is one of NSN’s innovations in the small cell area. The concept optimizes performance by combining the benefits of macro cell coverage and small cell capacity. Based on increasing the bandwidth through carrier aggregation, inter-site carrier aggregation can provide a cell edge gain of 50%, even in loaded networks.

Figure 2 below describes how, in order to support dual connectivity, the radio protocols of the user plane are split between the Master eNB (MeNB, typically a macro cell) and the Secondary eNB (SeNB, typically a small cell). With such a protocol architecture, radio bearers carrying user data can either use resources of the macro cell only (depicted in grey), of the small cell only (depicted in light grey) or aggregate both (depicted in orange), depending on whether coverage, offload or throughput is to be favored.

In addition to higher layer related enhancements, Release 12 improves also physical layer capabilities in small cell environment. Introduction of 256 QAM (quadrature amplitude modulation) in downlink enhances the spectrum efficiency for UEs experiencing favorable channel conditions. Another improvement area is to reduce transition time for dormant cell on/off with enhanced small cell discovery. This provides improved opportunities for energy saving and allows further reduction of Cell-Specific Reference Signals (CRS) interference in varying traffic load conditions.

MeNB

PDCP

RLC

SeNB

RLC

S1

X2

RLC

MAC MAC

S1

PDCP

RLC

PDCP

Figure 2: Dual connectivity

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Higher peak data rate

150 Mbps

150 Mbps 450 Mbps

20 MHz 150 Mbps

20 MHz

20 MHz

2.2 Carrier aggregation enhancementsThe work on enhancing the carrier aggregation capabilities in Release 12 will enable the use of FDD/TDD carrier aggregation. The Release 10 based carrier aggregation allows to aggregate FDD carriers for intra or inter-band case and respectively TDD carriers for intra or inter-band case. But Release 12 will enable aggregating also co-located FDD and TDD carriers to a single UE, as shown in Figure 3. As part of the small cell enhancements the aggregation will be further extended to support aggregation between sites, thus enabling inter-site carrier aggregation between the macro and small cell sites.

The work on the RF and performance requirements is enabling also support for downlink carrier aggregation with 3 downlink carriers, up to 60 MHz of total spectrum being aggregated. This will enable data rates of up to 450 Mbps being supported, as illustrated in Figure 4.

As part of the Release 12 work also the use of non-backwards compatible New Carrier Type (NCT) was also considered but concluded that the obtainable small gains did not justify the resulting market fragmentation.

Figure 3. FDD/TDD aggregation

FDD TDD

Figure 4. Aggregating 3 downlink carriers with carrier aggregation.

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2.3 Macro cell enhancementsWith exponential growth in network traffic, future networks need to continue to evolve both in macro and small cells. There are opportunities to enhance the network capacity and coverage of current LTE macro cell deployment significantly by exploiting multi-antennas, advanced receivers, network architectures and new spectrum. Macro cell enhancements are attractive for operators because they allow further exploiting of the existing base station sites and transport infrastructure.

Base stations such as the NSN’s Flexi Multiradio 10 Base Station establish high capacity macro cells with the potential to double the spectral efficiency of existing LTE macro networks. The target is to support LTE and LTE-Advanced technology in the 700-2600 MHz bands, tight coordination with small cells, for example in the 3.5 GHz band, and combinations of the following features:

• Large number of transmit and receive antennas: more than four transmit and receive antennas

• Active Antenna Systems (AAS) where antenna and RF are built together

• AAS with vertical sectorization and user specific elevation beamforming/3-D MIMO

• Advanced uplink receivers

• Enhanced Cooperative Multipoint Transmission and Reception (eCoMP)

• Advanced radio network architecture including on-site resource pooling

• High capacity backhaul

• Authorized Shared Access (ASA) to gain access to more IMT spectrum

By increasing the number of transmit and receive antennas at the base stations from two to four and then to eight, a significant gain in network capacity can be achieved. This gain can be further enhanced by using advanced receiver and single-user and multi-user MIMO schemes (SU/MU MIMO) based on dedicated demodulation reference signals.

Using active antennas where the RF components are integrated into the antenna and performing vertical sectorization or sector specific elevation beamforming (using two fixed beams per sector) can give significant improvements in sector capacity compared to a single beam system. Building upon vertical sectorization, Release 12 will be developing two techniques namely a) UE-specific elevation beamforming that adds UE specific vertical beamsteering to existing azimuth-only closed loop SU/MU MIMO methods and b) 3D-MIMO techniques that simultaneously exploit both the azimuth and the elevation dimensions of the multipath channel on a user-specific basis. These techniques are expected to give significant improvements in both the cell edge and sector capacity.

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Next in line for deployment are centralized solutions like cluster level on-site resource pooling using high capacity and low latency fiber backhaul (Centralized RAN) where a baseband pool serves the macro site and underlay remote radio heads. Such a radio network architecture allows for further improvements in radio performance.

Following the study of centralized scheduling with non-ideal backhaul, work is being done also for the enhanced CoMP focusing on the scenario where benefits were identified, namely the case between a macro and small cell. In such a scenario and a macro cell may coordinated the scheduler for the small cells in the same coverage area.

Last but not least, networks evolve by exploiting Authorized Shared Access / Licensed Shared Access – a new and complementary way of authorizing spectrum use in addition to exclusive licensed spectrum – which leads to higher spectrum availability and predictable QoS in the shared spectrum, thereby increasing the number of subscribers and the capacity of the network.

2.4 Machine-Type CommunicationsThe number of embedded machine-to-machine modems is expected to increase substantially in the future. While the urban area today can have up to 5,000-10,000 subscribers per base station. The growth of machine-to-machine could see up to 100,000 connected devices per base station, setting new requirements for the mobile network.

In addition to the already specified MTC support in 3GPP, the following areas of optimization are expected to be covered in Release 12:

UE-specific elevation beamforming/3D-MIMO

Figure 5: UE-specific 3D-MIMO

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• Network load optimizations will continue: MTC-specific signaling and connectivity optimizations ensure that a very large number of connected devices can be supported by the LTE radio, with small data amounts are delivered efficiently.

• The low cost MTC device studies are completed. Based on these, 3GPP is defining a new UE category which is cost optimized for MTC operations. 3GPP studies showed that for the RF part, with the UE using only a single receive antenna and half-duplex operation, significant saving can be achieved. On the baseband side, significant saving can be achieved from single receive antenna, bandwidth reduction, and peak data rate reduction. The studies indicated that with the peak data rate reduction, bandwidth reduction and single receiver chain together modem cost saving of approximately 60% could be obtained.

Some MTC UEs are installed in the extreme coverage scenario and might have characteristics such as very low data rate and greater delay tolerance. Release 12 solutions will provide a relative LTE coverage improvement – corresponding to 15 dB for FDD – for UEs operating delay tolerant MTC applications with respect to their respective nominal coverage. This is achieved by means of various techniques such as further repetition, power boosting and simplification of certain control channel functionalities.

2.5 3GPP-WLAN radio level interworking3GPP has made a RAN level study on the mechanisms for enabling enhancements for the radio level 3GPP-WLAN interworking.

Current ANDSF (Access network discovery and selection function) based methods for access network selection and traffic routing do not consider neither RAN network conditions nor take e.g. WLAN load conditions into account. The mere presence of a WLAN network allowed by ANDSF rules along with acceptable radio signal strength is used to divert traffic from 3GPP RAN network to a WLAN network.

RAN level assistance for 3GPP-WLAN interworking is targeted for the situation where typical WLAN selections are not enough (i.e. legacy device behavior is not sufficient) to achieve sufficient load balancing between cellular and WLAN, ensuring the Quality of Experience of the user, etc. The reason for load balancing or traffic steering may be due to dynamic load situation in both WLAN and 3GPP radio access networks. With today’s solutions, load is not considered as part of the WLAN selection process. The intention of load balancing is to steer by the eNB initiative the UE traffic to use either the operator controlled WLAN or the RAN, depending on the dynamic needs. Only RAN has a comprehensive overview of its load situations and resource allocation strategies.

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As part of Release 12 the intention is to specify mechanism for 3GPP/WLAN access network selection and traffic steering. The introduced solution supports deployments with and without ANDSF and co-existence of ANDSF with RAN rules when both are deployed.

In the defined mechanism the RAN assistance parameters are transferred via system broadcast and/or dedicated signaling. In the network without enhanced ANDSF deployment or with UE without ANDSF support these RAN assistance parameters are used within RAN rules defined within RAN WG specifications. In the networks with ANDSF support and with ANDSF capable UEs the RAN assistance parameters are used as part of the ANDSF policies.

2.6 LTE UnlicensedA new study area emerging in 3GPP is the use of LTE for unlicensed (LTE-U) spectrum. Such a solution would complement LTE operation especially in the public hotspot or enterprise type of environment, as shown in Figure 6. This would allow the operator to benefit from the local extra capacity from the unlicensed spectrum without having to use alternative technologies with special interworking and admission control arrangements. The solutions are foreseen not to be standalone but always being used with aggregation to the licensed band LTE operation.

Public indoor cells Home cells to rely on Wi-Fi (or femto)

Coordinated with macro/micro cells

Outdoor hot spot

Figure 6. LTE-U application environment.

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2.7 Network Assistend Interference Cancellations and Suppression (NAICS)

Co-channel interference is the dominant limiting factor for achieving higher capacity in cellular networks. In addition to various interference coordination schemes, interference aware receivers attempting to mitigate co-channel interference have show promising performance gain compared to receivers considering co-channel interference as AWGN (Additive white Gaussian noise).

Specifying interference rejection combining (IRC) receiver UE performance requirements in Release 11 was the first step towards increasing the receiver role in the system design.

The first steps have been taken also with non-linear interference cancellation receivers. Release 11 specified UE performance requirements for CRS interference mitigation for heterogeneous deployments where co-channel interference from CRS dominates but is negligible from data assuming that data resource element muting is in use.

Release 12 enhancements to intra-cell and inter-cell interference mitigation at the receiver side are achieved by increasing the degree of knowledge about interfering transmissions with possible assistance in the network. Network assistance enables usage of more advanced receiver (including non-linear receivers) and improves the performance compared to Release 11 IRC that does not require any transmission assistance in the network.

A specific intra-cell interference scenario part of Release 12 studies is SU-MIMO. Applying advanced receivers to mitigate inter-stream interference with SU-MIMO can be done without additional network assistance. It is enough to just define new UE performance requirements for this scenario.

2.8 Further enhancementsSelf Organizing Networks (SON) will play a key role in the efficient operation of dense small cells. Mass deployments will introduce new requirements in SON functions to ensure proper cell identity management and neighbor cell relations, as well as to enhance mobility robustness and load balancing in small cell coverage gaps. Additionally, intelligent solutions to easily switch small cell capacity layers to a power saving mode will be essential.

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LTE as the global 4G standard is also attracting the attention of public safety organizations and authorities, as a strong candidate to take their communication systems to a new level. To this end, LTE will be optimized to meet service requirements set by mission-critical group communication, including aspects like fast and efficient set-up of a low-delay communication path connecting any number of users possibly co-located, with the uncompromised robustness also at mobility familiar from today’s 3GPP systems.

Further enhancements to LTE TDD for uplink-downlink interference management and traffic adaptation (eIMTA) enable dynamic uplink-downlink reconfiguration according to instantaneous traffic statistics while maintaining backwards compatibility. The eIMTA feature improving TDD capabilities in Release 12 can provide significant performance benefits in small cells environment.

Furthermore, 3GPP will look for new opportunities to enhance LTE-HSPA integration and LTE-WLAN interworking as well as to enable device-to-device discovery and communication for commercial and public safety use.

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3. SummaryLTE evolution continues strongly in Release 12 and beyond by enhancing LTE and LTE-Advanced operation. In particular, LTE Release 12 addresses coordinated small cell deployments, macro cell enhancements, discovery in device-to-device communication, enhanced SON, flexible deployment and improved interference management in HetNets.

Release 12 features aim at boosting performance and at entering new areas and spectrum. The following two tables summarize the most promising Release 12 features:

Benefits from 3GPP Release 12 – Boost Performance

Rel12 Feature Benefit

Small Cell Enhancement based on Inter-site CA

• Optimized small cell mobility by reducing RAN to CN signaling• Improved data rates by using macro and small cells together• More flexible TDD spectrum use

UE-specific elevation beamforming/ 3D-MIMO

• Significantly enhanced macro cell capacity and coverage

Advanced receivers • Removing interference to increase UL and DL capacity

Enhanced Coordinated Multi-Point (eCoMP)

• Enhance coverage by exploiting coordination in case of non-ideal backhaul

Enhanced SON • Efficient operation of dense small cell deployments• Energy savings in small cell capacity layers

Benefits from 3GPP Release 12 – Expand to New Areas and New Spectrum

Rel12 Feature Benefit

LTE-WLAN integration • 10 Mbps minimum DL data rate• 1000x hot spot capacity in present decade

LTE-HSPA integration • Enhanced multi-technology support

Machine-Type Communication (MTC) • Get prepared for 50 Bn connected devices or 100.000 devices per cell

Public safety • Secure operator’s market share by expanding LTE footprint

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NSN is a leading contributor in 3GPP, driving LTE and LTE-Advanced standards. It is also shaping 5G through various activities, including participation in the EU FP7 collaborative project METIS and contribution to ITU-R IMT vision work.

LTE Rel-8 and Rel-9

2010+

2013+

2015+

2020+

LTE Advanced Rel-10 and Rel-11

LTE Advanced Evolution Rel-12 and Rel-13

5G

Figure 7: The radio evolution in the present decade

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4. Further reading• LTE-Advanced – The advanced LTE toolbox for more efficient delivery

of better user experience, NSN White Paper

• Deployment Strategies for Heterogeneous Networks, NSN White Paper

• Release 12 and beyond for C4 (Cost, Coverage, Coordination of small cells, and Capacity), NSN 3GPP presentation

• Looking ahead to 5G, NSN White Paper

• NSN Technology Vision

Nokia Solutions and Networks P.O. Box 1 FI-02022 Finland

Visiting address: Karaportti 3, ESPOO, Finland Switchboard +358 71 400 4000

Product code C401-00946-WP-201402-1-EN

©2014 Nokia Solutions and Networks. All rights reserved.

Public NSN is a trademark of Nokia Solutions and Networks. Nokia is a registered trademark of Nokia Corporation. Other product names mentioned in this document may be trademarks of their respective owners, and they are mentioned for identification purposes only.

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