lte-advanced

Nokia Siemens Networks LTE-Advanced The advanced LTE toolbox

for more efficient delivery of better user experience

Technical White Paper

2 LTE-Advanced white paper

Table of contents

1. Overview 3 1.1 LTE-Advanced, the evolution of LTE 3 1.2 Status of LTE-A (as of January 2011) 3

2. Drivers 4

3. The LTE-A toolbox 5 3.1 Overview 5 3.2 Carrier Aggregation 5 3.3 Advanced MIMO schemes 7 3.4 Coordinated multipoint transmission 9

and reception 3.5 Relay Nodes 10 3.6 Heterogeneous Networks 11 3.7 Self Organizing Network and network 12

architecture evolution with LTE-A 3.8 Outlook 13

4. Summary 15

2

3LTE-Advanced white paper

1. Overview

base technology of LTE which provides highest efficiency and a smooth evolution in the deployment of the existing LTE ecosystem towards LTE-A. It allows operators to deploy larger bands than 20MHz in particular by carrier aggregation, while also enabling an advanced toolbox with advanced MIMO schemes and totally new features like Relaying. Moreover, it is fully backwards compatible with the earlier LTE releases, implying that legacy devices can operate in LTE-A networks but may not necessarily benefit from all the new features of LTE-A. Thanks to these advanced features, LTE makes its transition to a true 4G technology, in accordance with the requirements of ITU for IMT-Advanced.

This paper introduces the advanced toolbox of LTE-A, including information on new technologies, features and enhancements to existing technologies, as well as discusses the benefits that LTE-A provides to operators and end-users.

1.2 Status of LTE-A (as of January 2011)

LTE has been specified in 3GPP Releases 8 and 9. The LTE standard has been stable and backwards compatible since March 2008, while

1.1 LTE-Advanced, the evolution of LTE

The introduction of LTE was driven by the industrys quest for a more efficient technology that could help deliver ever faster mobile broadband services. In comparison with basic HSPA networks, LTE delivered this enhancement by offering the state of the art combination of new air interface base technology (OFDMA/SC-FDMA), greater flexibility for utilizing spectrum like for example support of 20MHz bands and TD-LTE for using unpaired spectrum, as well as a toolbox to support further enhancements like MIMO and Higher Order Modulation. In fact, a similar toolbox has been applied to HSPA for facilitating a seamless evolution to HSPA+.

At the same time, we continue to witness exponential growth in mobile broadband traffic; thereby necessitating further enhancement in the overall efficiency, with a view to deliver faster mobile broadband services to a constantly increasing user base. LTE-Advanced abbreviated as LTE- A has primarily been conceptualized to address both the aforementioned demands.

LTE-A marks the evolution of LTE; it continues to deploy the air interface

initial trials and commercial networks have given ample proof of the fact that LTE delivers superior mobile broadband user experience in real deployments. LTE has been a commercial success, going by its adoption rate, that has exceeded any other mobile network technology. By the end of 2010, more than 120 operators were committed to rolling out commercial LTE networks.

One of the main drivers of the technical enhancements and timetable for LTE-A development has been IMT-Advanced. ITU initiated the IMT-Advanced process to define the requirements for the next generation of Radio Interface Technologies (RIT) that were released in a circular letter in early 2008. Meeting the IMT-Advanced requirements has been the goal that 3GPP has to achieve and standardization in 3GPP has progressed well. The first LTE-Advanced specifications are expected to be frozen in early 2011 while evaluations conducted by 3GPP contributors and external parties have demonstrated that LTE-A meets all the IMT-Advanced requirements. As a consequence, ITU-R has already approved LTE-Advanced as IMT-Advanced RIT or true 4G system in November 2010. The first LTE-A 3GPP standard compliant products are expected to enter the markets from 2012 onwards.

3


Looking ahead, the exponential growth in data traffic is expected to continue on the same lines owing to certain key drivers: Increased adoption of mobile

broadband Enhancedcoverage(spreading

across more locations) Increaseinusageintensity Greateravailability&choicesin

terms of devices (smart devices, phones, pads, booklets, netbooks...)

Machine-to-machinecommunicationsstepping alongside human users

A detailed analysis reveals that data traffic is distributed in an uneven way. Eventually mobile broadband networks need to evolve in a manner which goes beyond the conventional approach of applying one standard remedy to the capacity squeeze. Also, the laws of physics imply that conventional mobile broadband networks are approaching the theoretically achievable spectral efficiency, which in turn implies the costs per bit/Hz. Consequently the need for higher bandwidths and higher efficiency can only be answered by

combining several tools optimized for specific network scenarios.

This is the prime reason for using the term toolbox in this paper. LTE-A defines a large set of tools focused on enhancing the mobile broadband user experience, as well as reducing the costs per bit.

Figure 1: Evolution of data speeds for stationary and mobile use cases

2. Drivers

Mobility

4


3.1 Overview

LTE (as specified in 3GPP Releases 8 and 9) has been optimized for conventional wide area deployment, based on macro base stations and for dual receiver and single transmit antenna single band terminals. Talking specifically about this basic use case, LTE-A does not really provide significant performance improvements since no new technologies have been found to make this feasible. Instead, the focus has shifted to developing new features and technologies to extend the capabilities of LTE, as well as supporting new ways of deploying and operating networks ensuring optimal distribution of services. New technologies of LTE-A include enhancements in uplink and downlink multi-antenna (MIMO) technologies, coordinated multi-cell transmission and reception (CoMP), bandwidth extension with carrier aggregation (CA), relay nodes (RN) and heterogeneous network deployments (Hetnet).

The new technology components of LTE-A spell a host of benefits for the CSP community: enabling performance improvements in peak data rates, average spectrum efficiency, cell edge performance, coverage, new ways of cost reduction in the process of deploying and operating networks with small base stations, and with cells without fixed transport connections.

3.2 Carrier Aggregation

Carrier Aggregation allows for combining up to five LTE Release 8 compatible carriers with the aim of increasing transmission bandwidth, and for enhancing data rates for end-users. It enables operators to provide high throughput without wide contiguous frequency band allocations, and ensures statistical multiplexing gain by distributing the traffic dynamically over multiple carriers. With Carrier Aggregation, operators can take asymmetrical bands into use

with FDD since there can be uplink or downlink only frequency bands.

Carrier Aggregation can provide bandwidths with a maximum range of 100 MHz. Even higher bandwidths could easily be supported by the concept, but the need has not been identified yet. Aggregated carriers can be adjacent or non-adjacent even at different frequency bands, so basically all the frequency allocations can be used. There are a lot of permutations and combinations, and some of them are a bit more difficult to implement due to interference problems caused e.g. by intermodulation products of transmitted signals on different frequency bands. Therefore, only intra-band carrier aggregation is supported in uplink in LTE Release 10, while a higher range of band combinations will be supported in later releases. Carrier aggregation provides almost as high spectrum efficiency and peak rates as single wideband allocation. In some heterogeneous deployment scenarios, the performance can be even better since flexible frequency reuse can be arranged between local area nodes to provide better inter-cell interference coordination.

Figure 2: LTE-A support both: enhancing the LTE macro network and enabling the efficient introduction of small cells

3. The LTE-A toolbox

Matti Kiiski, 21 January 2011

LTE-Advanced

Enable efficient use of small cells

Enhance macro network performance Enables focused capacity enhancement with small cellsby interference coordination

Enables focused coverage extensions with small cells by self-backhaul

Peak data rate scalingwith antenna pathsfor urban gridand small cells

Capacity and celledge performanceenhancements byactive interference cancelation

Peak data rate and throughput scaling with aggregated bandwidth

Carrier Aggregation

Carrier1

Heterogeneous networks

Coordinated Multipoint

MIMO 4x8x

Carrier4

up to 100 MHz

Carrier2 Carrier3

Relaying

5


Carrier Aggregation supports cross component carrier scheduling, implying that the control channel at one carrier can be used to allocate resources at another carrier for user data transmission. It can be used to provide both frequency diversity and interference coordination in frequency domain at the same time, underlining its significance as a powerful technology for effective utilization of radio resources. Carrier

Aggregations capability to improve single user throughput depends on the number of users in a cell. The number of users is directly proportional to the overall statistical multiplexing gain even on a single carrier, so scheduling high number of users over multiple carriers provides only marginal gain. However, if the number of users is low, scheduling over multiple carriers provides significant throughput gain since all radio resources can be

allocated to the user(s) with the most favorable radio conditions. Gain in uplink is lower than in downlink, since the UE can not always utilize multi-carrier transmission due to limited transmit power.

If carriers are at different frequency bands they have different propagation losses and different interfering systems which affect achievable data rates, transmit power and usage of resources, e.g. far-off UE could be better served with a low frequency carrier and near cell center UE with a high frequency carrier. Inter-band Carrier Aggregation provides more flexibility to utilize fragmented spectrum allocations but one must take UE capabilities into account. There must be enough (but not all) inter-band capable UE before the feature can improve network performance.

Studies have been conducted on the benefits of extension carriers, e.g. without common control channels, to have lower control channel overhead and better efficiency, but the improvements seem quite marginal for the scenarios evaluated in LTE Release 10. Future releases might include extension carrier for specific use cases, e.g. energy efficient machine-to-machine communication.

Figure 3: Carrier Aggregation improves average cell throughput both in uplink and downlink due to more efficient utilization of radio resources, i.e. by statistical multiplexingMatti Kiiski, 21 January 2011

3GPP macro #1 with 2x20MHz

2x2 SU-MIMO for DL, 1x2 for UL

Dynamic traffic with Poisson arrival and finite buffer

Rel-8 UE case (one CC per UE) and LTE-A UE case (2-CCs per UE)

1 dB power back-off assumed for UL with Txon two CCs

Uplink

Offered Load [Mbps]

Ave

rage

UE

thro

ughp

ut [M

bps]

Ave

rage

UE

thro

ughp

ut [M

bps]

0 5 10 15 20 25 300

10

20

30

40

Downlink

Offered Load [Mbps]

0

50

100

150

200

10 20 30 40 50 60 70

LTE Rel-8LTE Rel-10

6


3.3 Advanced MIMO schemes

Multi-antenna or MIMO (Multiple Input, Multiple Output) technology is based on transmitting and receiving with multiple antennas and utilizing uncorrelated communication channels when radio signals propagate through the physical environment. If there is enough isolation between the communication channels, then multiple data transmissions can share the same frequency resources. If the multiple transmissions are for a single user, then the technology is called Single-User MIMO (SU-MIMO), for multiple users Multi-User MIMO (MU-MIMO).

The better the system can utilize these communication channels for multiple transmissions, the higher is the capacity that the system can provide. MIMO performance is subject to a large number of parameters: the number of transmitter and receiver antennas, reference signals and algorithms for channel estimation, feedback of channel estimation data from the receiver to the transmitter and spatial encoding methods. Consequently a comprehensive design is crucial to provide optimum system performance.

Transmission peak date rates depend on the number of antennas on the transmitter and the receiver, the used bandwidth and the configuration of radio parameters like the resource allocation for control channels. The maximum peak data rates vs. the number of transmitter and receiver antennas can be seen in Fig. 5 for 40 MHz band allocation for both, the downlink and the uplink.

LTE Releases 8 and 9 support multi-antenna (MIMO) technology with up to four transmit and receiver antennas in downlink, but only single antenna transmission in uplink. Release 10 extends the MIMO support for eight transmit and receiver antennas in downlink and introduces uplink MIMO by supporting up to four transmit and eight receiver antennas.

Figure 5: Carrier Aggregation and MIMO provide high peak data rates bounded by allocated bandwidth and the number of transmit and receiver antennas


# of UEantennas

# of eNBantennas

Downlink [Mbps] Uplink [Mbps]

1 2 4 8

1

2

4

8

304

161305

152

- 2x20 MHz Carrier Aggregation and 64QAM with 9/10 code rate

555610

1102


Offered Load [Mbps]Offered Load [Mbps]

Ave

rage

UE

thro

ughp

ut [M

bps]

Cov

erag

e [M

bps]

30

25

20

15

10

5

010 20 30 5040

Marginal Avg. TP loss in Rel8 by assigning cell center UEs on 2.1GHz carrier

Coverage gain in Rel8 by assigning cell edge UEs on 800MHz carrier

10 20 30 5040

Carrier Aggregation of 800 and 2100MHz: Rel-8: case3, RRRel-8: case3, SmartRel-10: case3

Rel-8: 3km ISD, RRRel-8: 3km ISD, SmartRel-10: 3km ISD

80

70

60

50

40

30

20

10

0

Figure 4: Inter-band Carrier Aggregation enables to benefit from different propagation characteristic of different frequency bands

7


Release 10 has enhanced the reference signal design with user specific reference symbols for signal demodulation and common reference symbols for feedback purposes in downlink and more orthogonal reference signal structure in uplink. The enhanced design enables better performance when the number of antenna branches is high.

Uplink MIMO provides significantly higher peak rates and improved spectrum efficiency in uplink direction. SU-MIMO provides mainly increased data rates in lightly loaded networks for high-end multi-transmitter UE, whereas MU-MIMO can offer significant improvement of spectrum efficiency even with single transmitter UE. This can boost network capacity at

low costs and is depicted in Fig. 6 and 7. The LTE-A system can operate in both SU and MU-MIMO modes at the same time using dynamic user specific MIMO transmission configuration.

Downlink MIMO has already been included in LTE Release 8. The LTE Release 8 codebook and reference symbol design was found to be quite optimum for two and four transmit antennas (2x2, 2x4 and 4x4 antenna configurations), but the channel state information feedback from UE to eNB could have been more accurate. This limitation is overcome by the new reference symbol design of Release 10, which is also more effective when the number of transmit antennas is higher. Based on the studies and numerous contributions in 3GPP, it can be safely concluded that the higher the number of antennas, the higher is the gain that Release 10 MIMO provides in downlink. With two eNB and two UE antennas, Release 10 downlink MIMO provides no improvements over Release 8 in SU-MIMO mode but small performance improvements have been gained in MU-MIMO mode. In most cases it is best to operate two TX antenna eNBs in Release 8 SU-MIMO mode. When eNB has four transmit

Figure 6: an example how uplink MU-MIMO improves system performance with different TX/RX antenna configurations


Ideal: Perfect knowledge of interference assumed at the receiverRealistic: Only have estimate of interference power available at the receiver.

100%100%

113%108% 133%

121% 147%136%2.02

1.57

2.171.77

2.442.75

2.092.30

Capacity - Correlated

Aver

age

SE [b

ps/H

z/ce

ll]

1x4 no MIMO 1x4 MU-MIMO Rel-8 1x4 MU-MIMO Rel-10 2x4 MU dual

4.00

3.00

2.00

1.00

0.00

Ideal MMSE/SIC Realistic MMSE/SIC

113%

107%123%

112%

122%

117%

100%

100%

0.075

0.049

0.080

0.0550.060

0.084 0.088

0.060

Coverage - Correlated

Cel

l-edg

e us

er S

E [b

ps/H

z/us

er]

1x4 no MIMO 1x4 MU-MIMO Rel-8 1x4 MU-MIMO Rel-10 2x4 MU dual


0.000

0.025

0.050

0.075

0.100

0.125

Figure 7: an example how uplink SU-MIMO improves system performance with different TX/RX antenna configurations


Ideal: Perfect knowledge of interference assumed at the receiverRealistic: Only have estimate of interference power available at the receiver.

100% 127%116%

180%198%

1.251.45 1.35

2.252.47


Ave

rage

SE

[bps

/Hz/

cell]

1x2 no MIMO 2x2 SU-MIMO 1x4 no MIMO 4x4 SU-MIMO

4.00

3.00

2.00

1.00

0.00


148%

162%

2.021.57

2x4 SU-MIMO

100%

1.06 173%

1.84

194%

2.06

100% 133%123%

183%199%

0.0440.055

0.045

0.081 0.088


Cel

l-edg

e us

er S

E [b

ps/H

z/us

er]

1x2 no MIMO 2x2 SU-MIMO 1x4 no MIMO 4x4 SU-MIMO

0.100

0.075

0.050

0.025

0.000


146%

169%

0.075

0.049

2x4 SU-MIMO

100%

0.034 155%

0.052190%

0.064

8


antennas, Release 10 downlink MIMO gain is more than 20% over Release 8 and with eight transmit antennas a bit higher. Reference symbol overhead effects on system performance are significant with four and eight transmit antennas. Therefore the selection of MIMO operating modes and system parameters for both Release 8 and 10 UE is a critical network optimization task.

An important point worth remembering is that the network should also support Release 8 and 9 UE which does not benefit from the Release 10 enhancements. The capacity gain from Release 10 downlink MIMO enhancements could even be negative since new reference symbols create overhead for all UE. However, these overheads can be decreased by decreasing the Release 8 and 9 specific reference symbols, but this would prevent non-LTE-A UE to operate in MIMO mode and thus lower their data rates.

Additionally, there would be negative effects on common control channel performance. Consequently, the timing of the introduction of the new features and the configuration of the system parameters are essential for an optimum performance of the LTE network.

3.4 Coordinated multipoint transmission and reception

Coordinated multipoint transmission and reception (CoMP) shows great potential to improve the cell edge performance and system capacity. However, the technology was not seen mature enough for including it in Release 10. The studied CoMP technologies are Coordinated Scheduling/Coordinated Beamforming (CS/CB), Joint Processing/Dynamic Cell Selection (JP/DCS) and Joint Processing/Joint Transmission (JP/JT). It has been demonstrated with

simulations and field tests that CoMP technologies have high potential from a single user point of view but there are open issues on the operation of large scale networks and the signalling between UE and network to characterize the radio environment for multi-site transmission. Signalling should provide enough information to enable high performance, but not at the cost of excessive overhead or additional energy and radio resource consumption.

The system performance gains of realistic CoMP deployments with an ideal channel state information (CSI) feedback is presented in Fig. 8 and 9. The critical system deployment issue is the communication between the cells. Intra-site CoMP deployment, in which the communication is between the sectors of a single eNB, is likely the most feasible system solution. CoMP studies in 3GPP continue in a Release 11 study item kicked off in December 2010 and will focus on finding practical

Downlink Uplink

CoMP Category

Intra-site 2TX (4TX)

Intra& Inter-site

Intra-site joint reception

Inter-site macro diversity

Inter-site joint reception

Cell Avg. 5% (10%) 20% 5% 6% 15%

Cell Edge 12% (20%) 21% 5% 8% 25%

SystemsimulationsDownlinkwithidealCSIfeedback,realisticCQIfeedback,realisticreferencesymboloverhead(10%)andidealinter-cell

communicationUplinkwithidealfeedback,idealinter-cellcommunication,idealcellselection,realisticMMSE/SICreceiverandrealisticclosedloop

power control2RXand2TXantennasineNB2RXand1TXantennasinUEGainoverRelease8SingleUserMIMOTypicalUrbanMicro,max.500minter-celldistance,10userspercell

Figure 8: JP/JT CoMP system performance gain in an urban environment with ideal CSI feedback and realistic system and receiver implementation

9


concepts with real performance benefits, taking into account implementation and interoperability issues of UE, eNBs and transport technologies.

3.5 Relay Nodes

Relay nodes enable the deployment of small cells at locations where conventional fixed line or microwave

backhaul is not possible or commercially viable. Relay nodes use the LTE-A air-interface for self-backhaul to a so-called Donor eNB. The gain from relay nodes is most pronounced in coverage limited scenarios, e.g. large donor cells, which serve multiple relay nodes. They in turn provide an expansion of the coverage, where needed, into buildings or other areas receiving poor signal from the macro cell directly.

LTE Release 8 supports simple amplify and forward relays (also called repeaters) that can be used for coverage extension. However, those do not use the radio resources efficiently. The enhanced relaying technology in LTE-A is based on self-backhauling base stations sharing features with (pico) base stations. For the user equipment the relay node is just a cell of the Donor eNB. The management of the network is straightforward. LTE Release 10 specifies a new interface Un between Donor eNB and Relay Node (RN), see Fig. 11. The new interface uses MBSFN (Multicast-Broadcast Single Frequency Network) subframes which were introduced in Release 8 already to hide the Un interface from UE operating on the same carrier and thus make it fully backward compatible: UE interprets Un transmission as MBSFN transmission for which they are not subscribed and simply ignore them. The so called Proxy S1/X2 concept forwards both S1 and X2 messages towards the RN transparently for the Core Network which sees a Relay Node as a sector of the Donor eNB as well. Thus relaying is also backwards compatible for both the MME and Serving Gateway which serve the UE.

Figure 9: CS/CB CoMP system performance gain in an urban environment with ideal CSI feedback and realistic system and receiver implementation

Downlink Uplink

CoMP Category Intra-site CS/CB Inter-site CS/CB Inter-site CS

Cell Avg. 13% 14% -

Cell Edge 13% 13% 15%

SystemsimulationsDownlinkwithidealCSIfeedback,realisticCQIfeedback,

realistic reference symbol overhead (10%), ideal inter-cell communication and MRC receiverUplinkwithidealfeedback,idealinter-cellcommunications,

ideal cell selection, realistic MMSE/SIC receiver and realistic closed loop power control4RXand4TXantennasineNBwith/2antennaspacing2RXand1TXantennasinUEGainoverRelease8Beamforming(1CRS,1DRS,singlestream)3GPPCase13D,500minter-celldistance,10userspercell

uplinkdownlink

-100%0%

100%200%300%400%500%600%

ISD 500m ISD 1732m ISD 500m ISD 1732m5%-ti

le T

hrou

ghpu

t gai

n

1 relay4 relays10 relays

uplinkdownlink

0%

20%

40%

60%

80%

100%

120%

ISD 500m ISD 1732m ISD 500m ISD 1732m

Cel

l Thr

ough

put g

ain

Figure 10: System performance gain of Relay Node deployment of one, four and ten Relay Nodes per a macro-cell

10


3.6 Heterogeneous Networks

The term Heterogeneous Networks does not necessarily refer to a specific technology or feature as such, but is instead used to describe networks that have both wide area and local area (small cell) deployments. In many expected deployment scenarios, heterogeneous networks spread accross multiple radio access technologies. Autonomous or automated interference coordination and handover optimization in such hierarchical network architectures are key aspects of heterogeneous networks. Other coordination technologies like self-configuration and self-optimization have been covered under Self Organized/Optimized Networks (SON) and Minimized Drive Testing (MDT) related study and work items since Release 8.

LTE Release 8 inter-cell interference coordination (ICIC) methods are mainly targeted at improving radio resource utilization of cell edge users. LTE Release 8 specifies eNB

measurements, signalling principles and messages for inter-cell interference coordination (ICIC) over X2 interface (direct eNB eNB interface to support mobility). The eNB interference reduction algorithms are considered vendor-specific implementation issues. Benefits from these Release 8 technologies are yet to be proven, since advanced packet scheduling methods have been demonstrated to provide equal

or better performance in wide area deployments. Since X2 interface is typically not available with Home eNBs (HeNBs) and distribution of the interference is different in local area deployments, new methods and evaluation cases for ICIC have been included in LTE Release 10.

Local area base stations and access points are deployed and in many cases operated by end users directly without

User Equipment

App.

TCP/UDP

IP

PDCPRLCMAC

PHY

Relay

GTP-uUDP

PDCPRLCMAC

PHY

PDCPRLCMAC

PHY

IP

Donor eNB(+Home eNB GW)

GTP-uUDP

PDCPRLCMAC

L2

IP

GTP-uUDP

IP

L1PHY

IP

GTP-u

UDP

IP

L2

L1

S-GW/P-GW(serving the UE)

Figure 11: Protocol architecture for Relay Nodes

Figure 12: Heterogeneous network deployment

Share will grow in future 10 100 m, < 500 mW

Share of sites growing 100 300 m 1 5 W

Majority of cell sites today > 300 m > 5 W output power

License exempt growing & Secondary services emerging 10-100 m < 100 mW

Wide Area sites

Medium area sites

Local area

Local area

Local area

Local area

Medium area sites

Local area

WLAN

WLANWLAN

WLAN

WLAN

11


Requires strict time-synchronization between Macro & HeNBsMacro-layer

One sub-frame

Sub-frames withnormal transmission

Almost blank sub-frame (ABS)

Macro CSG Femto case

Victim = Macro UE drownedby femto interference

only CRS is transmittedHeNB-layer

Figure 13: Inter-cell interference reduction with Almost blank sub-frames of TDM eICIC

network planning by an operator. These local area nodes create interference with each other and wide area base stations may also translate into degraded system performance like lower throughput and an increase of call drops. As such, automated management methods are required to remove the need for manual maintenance of a large number of local area base stations, as well as to prevent excessive inter-cell interference that could degrade the performance of the wide area base stations and other local area nodes.

The evaluation cases for heterogeneous network deployments have been included in LTE Release 10. There are multiple technologies that can be used for the interference coordination based on LTE Release 8 specification, e.g. HeNB power control and escape carrier or using Carrier Aggregation of LTE Release 10. LTE Release 10 includes one new interference coordination technology based on coordinated muting of the

transmission of overlapping cells. This technology is called TDM eICIC (Time Domain enhanced Inter-Cell Interference Coordination) and its basic principle is described in Fig. 13. Part of the transmitted signal is muted by sending Almost Blank Sub-frames, that allows other eNBs to transmit with lower inter-cell interference.

TDM eICIC needs time synchronization between the macro and femto layers, a pre-condition that could be difficult to guarantee with respect to HeNBs deployed by the users. Simpler frequency domain methods are then more likely to be used in case the operators frequency and deployment plans allow.

Later releases are likely to introduce new cost efficient small cell interference coordination and rejection technologies, since cost effective small cell deployment offers the most promising way to increase the capacity of mobile broadband networks in a focused way.

3.7 Self Organizing Network and network architecture evolution with LTE-A

LTE development is not only focusing on air interface performance enhancements. Cost of deployment and operation can be decreased with self organizing and optimization (SON) technologies. Automatic Neighbour Relation (ANR) and Minimization Drive Test (MDT) technologies have been developed to enable automatic configuration, optimization of handovers, as well as other radio resource management parameters. Moreover, other SON technologies are also in the process of being developed, e.g. for automated fault recovery and energy saving for complex deployments.

Some deployment concepts and network architectures are common for HSPA and LTE: Home base stations are a way to provide reliable and

12


Optical transport availability

Multiple power amplifiers in UE

4-8 antennas in UE

More spectrum

Multiband UE and BTS capability

Heterogeneous networks

Multi-antenna BTS site

Baseband processing capability

Low cost small BTS

LTE-A

Relays

Carrier aggregation

MIMO enhancements

CoMP

secure mobile broadband services in home and office environments. Local Break Out solutions (LIPA and SIPTO) decrease cost of transport and enable lower end-to-end latency for distributed services. Given the fact that a majority of mobile broadband networks fall under the domain of multi-radio networks, common solutions for HSPA+ and LTE-Advanced translate into lower cost for operators and seamless service experience for end users.

3.8 Outlook

Development of LTE-Advanced will continue in future 3GPP releases. Multi-hop and moving relays could increase efficiency in providing broadband services in high-speed trains and interference cancellation receivers will improve air interface capacity. Decreasing power consumption of the network and the user equipment enables the usage of battery powered devices for machine-to-machine applications wide bandwidth demand. LTE-A already has means for flexible spectrum management, self-configuration and multilayer deployments. Once the spectrum regulation defines the framework for usage of cognitive radio resource management methods, adoption of these methods can be easily adopted in LTE-A.

In real-world network deployments, the described LTE-A system features are closely related to network element implementation for the complete base station sites, including transport. Without a compact multi-antenna site solution, multiple antenna system technologies cannot be cost effective. Multi-site CoMP technologies need fast connectivity between base stations and remote radio heads which can be provided by modern optical transport solutions and open interface specifications. Carrier aggregation provides higher system bandwidths which need wide bandwidth high efficiency power amplifiers in base stations and terminals. There are various multi-system multi-band combinations which need tight control of spurious emissions and good receiver blocking performance.

The new features of LTE-A increase spectrum efficiency and cell edge performance, thus the bits per Hz ratio increases. This means that the probability of multi-stream transmission, higher order modulation and lower coding rates increases, with the consequence that the modulation accuracy of the transmitters also needs to improve in order to have sufficiently low inter-symbol interference. Power amplifiers, duplex filters, transmitters analogue and digital parts etc. have to be in a good balance and tightly integrated. One example of these

dependencies is the case where the power amplifier of the eNB gets into saturation with the consequence that the quality of signal deteriorates to an extent that higher order modulation can not be supported anymore. In that case the introduction of LTE-A features would not provide the expected system performance gain. Such balancing considerations are most relevant in the hot zones of the network, where additional bandwidth will be needed first.

Many of the new technologies introduced by LTE-A are based on complex algorithms, so more baseband processing capacity is needed in both the base stations and the terminals. Fig. 14 summarizes relations between the evolution of implementation technologies and LTE-A system technologies.

In fact, suppliers of LTE-A networks need to develop a core competency in terms of integrating a variety of products to support multiple modes to deploy the network. Network operation should be reliable and cost efficient, while maintaining optimum levels of customer satisfaction. In a majority of cases, there are other wireless and cellular technologies to inter-work and co-exist with. Therefore the supplier needs to have a good understanding of LTE-A, its preceding technologies, devices, services, along with end-user behaviour and expectations.

Figure 14: LTE-A new system technologies vs. implementation technologies

13


Spectrum efficiency

Spectrum utilization Savings in operation

Savings in deployment

UL MIMO

DL MIMO

CARelays

Multi-Layer

SON

Multi-Layer

LIPA/SIPTO

Relays

CA

Multi-RAT

UL MIMO

DL MIMOSON

LTE-A provides a powerful and versatile toolbox, which helps network operators to differentiate in mobile broadband user experience and to increase network efficiency. As the interdependencies between the tools

and the network implementation are complex, an experienced partner with a holistic view is needed to make the most of this toolbox. The text box above shows Nokia Siemens Networks long track record in LTE-A

research. Combined with its leading role in commercializing LTE, this makes Nokia Siemens Networks the partner of choice when planning and implementing LTE-A.

Figure 15: LTE-A toolbox reduces cost and improves performance

Nokia Siemens Networks track record in LTE-A related research 2003OFDMTDDdemonstration72Mbps(on20MHz,usingMultihop)

2004WorldsfirstOFDMdemonstrationof1Gb/sovertheair

(100MHz aggregated spectrum, MIMO) 2008WorldsfirstLTE-Arelaydemonstration

2009WorldsfirstLTE-AfieldtrialinBerlin

2010Relaytrialforenhancedindoornetworkperformance

2011WorldsfirstLTE-AdynamiccarrieraggregationdemonstrationoncommercialLTEBTS on a typical carrier combination

14


LTE-A enables a smooth and backward compatible evolution of LTE towards true 4G performance

LTE-Acomprisesofvarioustoolstoenhance mobile broadband user experience and network efficiency

Thereareseriousinterdependenciesbetween network implementation and the various tools of LTE-A, which require an experienced partner when planning and implementing LTE-A

NokiaSiemensNetworkshasalways been at the forefront of LTE-A research and development, with a strong focus on real operator opportunities in terms of efficiency and user experience

Figure 16: Radio performance gains of LTE-A system features

4. Summary

= clear gain

= moderate gain

Peak rate Average rate (capacity)

Cell edge rate (interference)

Coverage (noise limited)

Carrier aggregation ++ + ++ +

MIMO enhancements* ++(o)

++(+)

++(+) o

CoMP** o (+) (+) ++

Relays*** o o (+)+

(++) ++

Heterogeneous networks o ++ ++ +

* without increasing the number of antennas** not in LTE Release 10*** with multiple Relay Nodes per cell

15

www.nokiasiemensnetworks.com

Nokia Siemens NetworksP.O. Box 1FI-02022 NOKIA SIEMENS NETWORKSFinlandVisiting address:Karaportti 3, ESPOO, Finland

Switchboard +358 71 400 4000 (Finland)Switchboard +49 89 5159 01 (Germany)

Order-No: C401-00703-WP-201103-1-EN

Copyright 2011 Nokia Siemens Networks. All rights reserved.

Nokia is a registered trademark of Nokia Corporation, Siemens is a registered trademark of Siemens AG. The wave logo is a trademark of Nokia Siemens Networks Oy. Other company and product names mentioned in this document may be trademarks of their respective owners, and they are mentioned for identification purposes only.

This publication is issued to provide information only and is not to form part of any order or contract. The products and services described herein are subject to availability and change without notice.

lte-advanced

Documents

evolution of lte

advanced lte toolbox

advanced toolbox of

status of lte

lte standard

introduction of lte

lteadvanced abbreviated

commercial lte networks