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NEC’s proposals for LTE AdvancedNEC’s proposals for LTE Advanced

NEC Corporation

7th, 8th April 2008

3GPP RAN IMT-Advanced Workshop

REV-080022REV-080022

© NEC Corporation 2007 2

IntroductionIn REV-080021, NEC’s view on requirements of LTE Advanced have been

shown

Following technical features are focused here to meet part of these requirements

Proposal 1 : Adaptive Uplink Multiple Access To be optimized for wider system bandwidth To achieve good trade-off between cell throughput and cell coverage

Proposal 2 : Advanced SON solutions for radio optimization To reduce the human oriented manual operations for lowering Cost of

Ownership (CAPEX and also OPEX) To allow “Always on RAN performance monitoring” for maintaining better

RAN performance Proposal 3 : Advanced RRM solutions for full scale femto deployments

To reduce the impact on macro-femto and femto-femto interference.


LTE-Advanced Feature Proposal 1: Adaptive Uplink Multiple Access


Background

In LTE Advanced, system bandwidth can be much wider than that in LTE (ex. 100MHz for DL and 50MHz for UL in maximum)

Higher frequency selectivity

Severer power limited condition

Under these conditions, system should be optimized with considering the trade-off between cell throughput and cell coverage

　　 Proposal: Adaptive uplink multiple accessDFT-s-OFDM with Spectrum Division ControlAdaptive selection of DFT-s-OFDM and OFDM

f f

Proposal 1

UE UE


DFT-s-OFDM with SDC

• DFT-s-OFDM can generate both single carrier signal and multi-carrier signal

• LTE adopts single carrier generation only currently to achieve the lowest PAPR Restriction in resource allocation

Cell throughput can be maximized by controlling SD (Spectrum Division) considering trade-off between PAPR and resource allocation flexibility

+CP

f

f

SC-FDMA(SD=1)

　 MC-FDMA(SD=4)

IFFTDFTData Sub-carriermapping

Sub-carriermapping

Proposal 1


• PAPR increases gradually as SD (Spectrum Division) is getting larger.

• We can find UE-specific SD to satisfy different PAPR requirement.

PAPR of DFT-s-OFDM with SDC

DFT-s-OFDM

OFDM

f

f

SD=4

SD=2

QPSK

f

SD=1 （ SC-FDMA ）

Proposal 1


DFT-s-OFDM with UE-specific SDC

• Spectrum Division (SD): Number of discontinuous resource block (RB) groups

• UE-specific SD: CQI-based SD for different UE– High throughput of cell-center users– Low PAPR of cell-edge users

f

f

SC-FDMA

DFT-s-OFDM w/ SDC

SD

CQI Level

4

2

1

UE3 UE2 UE1

Low PAPR

Flexible resource allocation

Proposal 1

UE1UE2

UE3


Adaptive selection of DFT-s-OFDM / OFDMBase Station selects DFT-s-OFDM or OFDM depending on the cell size For Macro cell: DFT-s-OFDM (Wide coverage with low PAPR) For Micro/Femto cell: OFDM (Higher Peak Rate with MIMO)

Additional use of OFDM in cell center of Macro cell gives extra gain ⇒ UE specific(Hybrid)use of DFT-s-OFDM and OFDM could be applicable

Femto/Micro Cell:OFDM

Macro Cell:DFT-s-OFDM

On either cell specific or UE specific,tradeoff in Complexity and Throughput must be considered

Cell Specific

UE Specific(Hybrid)

Femto/Micro Cell:OFDM

Macro Cell:DFT-s-OFDM / OFDM

Proposal 1

OFDM

DFT-s-OFDM


SummaryThe followings have been proposed for LTE+ uplink access scheme to

achieve good trade-off between cell throughput and cell coverage

DFT-s-OFDM with SDC (Spectrum Division Control)Throughput optimization by CQI-based Spectrum Division for different

UELower SD for power limited UEs to achieve lower PAPRHigher SD for non-power limited UEs to achieve higher scheduling

flexibility

Adaptive selection between DFT-s-OFDM and OFDMCell specific selection

OFDM for small cell to maximize MIMO gainDFT-s-OFDM for large cell to maximize coverage

UE specific selection- Higher gain than cell specific one is expected, but actual gain

should be investigated- Increase of complexity by introducing UE specific adaptation should

be carefully investigated

Proposal 1

© NEC Corporation 2007 10NEC Confidential

LTE-Advanced Feature Proposal 2: Advanced SON solutions

for radio optimization = SONv2


Introduction: Self-X Radio Access Network

• Self-X RAN == More Intelligent RAN– Self Organizing based on PnP behavior– Self Optimizing based on always on monitoring– Self Coordinating based on distributed decision– Self Healing based on detection/reporting– …

• Why Self X Technologies?– Reduce the human oriented manual operations.

• Lowering Cost of Ownership (CAPEX and also OPEX)

– “Always on RAN performance monitoring”• Maintaining better RAN performance

Proposal 2


SON related Agreements in Release 8 Global Cell ID and Automatic Neighbor Search

Building up neighboring cell list ANR mechanism allows detection of missing neighbour relation

=> automatic optimization of the neighboring cell list

eNB measurements RACH access, DL/UL throughputs, RB utilizations

UE measurements Detected cells, Global cell ID

SON features in Release 8 provide a good starting point and more SON features are needed for LTE advanced systems.

LTE advanced should focus not only on L1 speed but also more advanced SON mechanisms

Release 8 SON FeaturesProposal 2


Example 1: Self-deployment of eNodeBs

• More autonomous deployment becomes obviously more interesting – Without planning of radio parameters– Also useful study item for home NodeB deployment

• Start with minimal coverage and gradually increase cell size• Radio scanning to find unused resources• Negotiation with neighbor cells about spectrum resource usage

Resource negotiations

Proposal 2


Example 2: Self Neighbor Scanning HeNB

• Operator will have many thousands/millions of home eNB.– Human operation based configuration of each hEB is not economical.

• Home eNB frequently scan – All neighbors of own or other PLMN ID

• heNB capable of scanning neighboring macro cells/frequencies

– All neighbors of other RAT• heNB capable of scanning neighboring UMTS/WIMAX cells

– Scan results are sent to the central server

Proposal 2


Example 3: Self Coordinating Interference Management

time

frequency

Slots that are not to be used for high power transmission in blue cell

• To coordinate scheduling in interfering cells, – Alt1: Semi-static restrictions for users close to cell borders

• Self coordination between cells set by rules • Agreed in Release 8 as HII

– Alt2: Short time-scale coordination • Very high speed of coordination for re-optimization based on load in different cells

X2 based Standardized RRMProcedures

Proposal 2


Example 4: HO Parameterization Optimization

• Handover parameter optimization triggered by “performance problems”

• Optimization of individual neighbor-to-neighbor parameters– E.g. HO hysterisis control

• Slow optimization loop – Cautiously change parameter to avoid user perceivable degradation– Evaluate results through performance monitoring

Reporting of Radio Link Failure with Location

Proposal 2


Example 5: UE Measured Performance Reporting

• Real performance based UE’s reporting of poor user experiences – For example, very low throughput reporting (below 64kbps at location X,Y)

• Problem analysis– Drawing the real performance map over X days or Y weeks.

• RAN parameters– Antenna tilt, TX power, Scheduler parameters, …

• Slow optimization loop – Cautiously change RAN parameters to avoid user perceivable degradation

Reporting of Very Low Throughputwith Location Info

Proposal 2


Example 6: Common Channel Self Optimization

RACH, PCH, BCH Power optimizations• Instead of drive tests: slow optimization based on UE reports

– received signal strength, channel quality, neighbor signal strength

– Ideally also location of UE

• Cautious adjustment of power in one cell, monitoring of effects– search optimal settings, e.g. gradient descent

Proposal 2


Example 7: Reduction of Energy Consumption by RAN

• Partial or complete eNB power down during low load, e.g. at night

• Stored profiles used to reconfigure radio parameters for the new topology

• Wake up based on timers or external triggers

• Question: would operators be interested in solutions that close down an eNB?

Proposal 2


Summary of Proposal 2: SONv2 for LTE Advanced

• 7 examples of SONv2 are presented that can reduce the cost of ownership of LTE advanced system.

• Clear work split between RAN and SA groups – i.e. RAN related parameters & mechanisms to be

handled by RAN groups.

Self　Deployable　Cell

HO　failure　reporting　with　location　info

Automatic　Common　Channel　Power　

Control

Very　low　throughput　reporting　with　location　

info.

Configurationprofiles

O&M

Measurement data

Always　on　RAN　performance　

monitoring　based　on　BTS　and　MS　reporting.

Proposal 2


LTE-Advanced Feature Proposal 3: Several Issues and Challenges

for the Future Full Scale Femto Deployment


Advantages in Femto cell deployment in a Radio Aspect

• Providing very high throughput for indoor users• Extending indoor coverage • Increasing radio capacity in an outdoor and indoor environment

Macro NodeB

Outdoor UE

Indoor UE

Macro NodeB Home

NodeB

Outdoor UE

Indoor UE

Before introducing femto Cells

After introducing femto Cells

0200400600800100012001400160018002000

0 400 800 1200 1600 2000システムスループット [kbps]

ユー

ザス

ルー

プッ

ト [kbps]

Indoor

1MbpsBefore introducing femto cells

Cell　ThroughputHSDPA　User　Throughput

After introducing femto cells

Outdoor

Example: User throughput of HSDPA (Category6) at 1 Mbps of cell throughput will increase by 1.3 and 2.3 times in an outdoor and indoor environment respectively.

Proposal 3


Macro NodeB

Femto NodeB

Macro UE

Femto UE

Desired signal

3. DL interference from Macro NodeB to Femto UE

1. DL interference from Femto NodeB

to Macro UE

4. UL interference from Femto UE to Macro

NodeB

2. UL interference from Macro UE to

Femto NodeB

5. DL interference from Femto NodeB to Femto UE in another femto cell

6. UL interference from Femto UE to Femto NodeB

in another femto cell

Desired signal

Interference Scenarios

The impact of interference will depend on the following:• Radio frequency (same as or different from that of macro NodeBs) • Maximum or CPICH transmission power of Home NodeB (fixed or adaptive)• Indoor environment condition• The number of Home NodeBs per macro cell• Access to Home NodeBs (open or closed)

There are 6 interference scenarios between macro and femto cells or among femto cells, which may minimize the femto cell advangtages.

Proposal 3


RF Selection

• Purpose:To avoid the mutual interference between femto cells and macro

or micro cells • Solution:

RF is selected for Home NodeBs based on CPICH RSCP measured at Home NodeBs and cell information such as HCS or CPICH Tx Power.

• If there is a RF whose CPICH RSCP is below a certain level, then a femto cell selects that RF

• Oherwise, a femto cell selects RF which has lowest HCS or largest CPICH Tx Power.

Macro Cell : RF1Micro Cell : RF2

Conventional: RF2 is selected because of lower CPICH RSCP, leading to increasing the interference.Proposal: RF1 is selected because of lower HCS, leading to avoiding the interference.

Assumptions at this example:-Femto cell is in a micro cell-CPICH RSCP: RF1 > RF2 -HCS: RF1 < RF2- (CPICH Tx Power: RF1 > RF2 )

Proposal 3


Technical challenges to solve the interference issues

• Home NodeBs are required to function as minimizing the interference in the self-organizing way.

• For example, the following technical solutions to minimize the interference between macro and femto cells ( from 1 to 4 at the previous page) can be considered. RF selection for femto cell Maximum or CPICH transmission power control of femto cell

considering indoor environment conditions

Proposal 3


Summary

• RF-related technical subjects and the interference mitigation scenarios for 3G Home NodeB are described.

• It is necessary to study techniques for minimizing the interference which can cause the degradation of indoor coverage or radio capacity of macro or femto cells.

Proposal 3


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