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Advanced Radio Interface TechnologIes for 4G SysTems
Overview
Date: Monday, July 16th 2012 Raphael Visoz - OrangeITU-R WP5D Workshop “Research Views on IMT Technology Evolution”
Advanced Radio Interface TechnologIes for 4G SysTems 1
Advanced Radio Interface TechnologIes for 4G SysTems
Outline
ARTIST4G drivers Objectives and concepts Management structure Some Results Conclusion
2
Advanced Radio Interface TechnologIes for 4G SysTems
ARTIST4G Drivers
Customers• Have new devices and greedy usages (iPhone, video, web 2.0)• Won’t pay for the traffic increase they generate• Expect an even more uniform Quality of Service
The market• Has limited investments capabilities (operators and vendors)• Must capitalize on existing infrastructures: LTE (backward
compatibility)
3
Advanced Radio Interface TechnologIes for 4G SysTems
Objectives and Concepts
Increase the average performance for the benefit of cell-edge users
• In limiting the interferences, especially at the cell-edge
• Or via densification at low cost
4
Advanced Radio Interface TechnologIes for 4G SysTems
Main Research Directions WP1: Interference avoidance
• avoiding interference e.g. through coordination among different non co-located transmission points and designing the generated radio signals accordingly
WP2: Interference exploitation• resources allocation algorithms allowing for efficient
interference cancellation, with a two-step approach– Investigation of interference cancelling receiver algorithms
– Design of higher-layer allocation schemes and control signaling
WP3: Advanced relays• Providing ubiquitous user experience: advanced relays need
to provide capacity on top of coverage (current relays in LTE-A are designed for coverage extension)
Limiting Interference
Densification
6
Advanced Radio Interface TechnologIes for 4G SysTems
Transversal Supporting Activities WP4: Impact of innovations on the RAN
architecture• Proposed RAN innovations may enforce additional requirements
on backhaul networks: innovations need to be classified– No cooperation through the RAN– Cooperation with control-plane exchange– Cooperation with user-plane exchange
WP5: Evaluating innovations• Agreed procedures have to be settled to allow fair comparison of
innovations– Scenarios, metrics and methodologies– A main KPI is needed to measure uniformity of performances
WP6: Live testing of innovations• Several test beds available to experiment the most promising
innovations
7
Advanced Radio Interface TechnologIes for 4G SysTems
Field Trials in Dresden- 16 Base Stations interconnected via microwaves links- Real time transmissions over the air
8
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced receiver proof of concept
Performance and Complexity trade-off are first evaluated before implementation into real production chain
Complexity and energy consumption are evaluated on CEA’s Network on Chip platform
Many field trial campaigns have been performed to evaluate advanced receivers performance gain with recorded radio channel samples.
9
Advanced Radio Interface TechnologIes for 4G SysTems
Some Results 3D beamforming evaluations A Working CoMP framework Advanced relaying techniques
• Moving relays, multi-hop relays, Improved backhaul performances
Interference cancellation receivers• Innovative receivers algorithms • Performance prediction methodologies for iterative receivers• Flexible interference concepts: adapt resource allocation to the
receivers interference cancellation capabilities
10
Advanced Radio Interface TechnologIes for 4G SysTems
3D-Beamforming
This concept is not part of LTE R10
11
Conventional fixed down-tilt causes interference
Objective: exploit also elevation dimension dynamically
Ground breaking innovation
LTE-A ARTIST4G
Simultaneous gains for both spectral efficiency (about 15 – 20%) andcell edge throughput (up to 50%)
Coordination gain and vertical BF gain (3D BF) are almost additive Exact vertical downtilt adaptation is approximated reasonably with 2 or 3 fixed
downtilts 3D beamforming already became part of ALUD product strategy
Advanced Radio Interface TechnologIes for 4G SysTems
Coordinated Multi-Point (CoMP)
Study item stopped in R10
Not included in LTE R10• Technology not mature
enough
Study Item R11• No convincing results
12
Enlarged cluster of coordinated cells (e.g., 9 cells)
Better inter-cluster interference management (with 3D beam-forming)
Overlapping clusters (cover shift) in different frequency subbands
User centric scheduling (choose best cover shift per user)
Improved feedback in terms of efficiency and robustness by use of channel predictors
LTE-A ARTIST4G
Spectral efficiency up to 6..7 bit/s/Hz/cell about 100% CoMP gains
Advanced Radio Interface TechnologIes for 4G SysTems
Interference Cancellation Full orthogonality provides interference avoidance
• But known to be suboptimal in terms of capacity
Cancelling interference at Rx increases the capacity through resource re-use
• But interference is not always easy to estimate
Controlling and structuring the interference conditional on advanced receiver processing opens ways to optimize the spectral efficiency
WP2 focused on non linear receivers using iterative processing (turbo principle)
• various functions in the receiver collaborate (e.g. channel estimator, detector and decoder) to better estimate the transmitted information
13
New physical layer abstraction for turbo-sic receivers enabling CLO (proven with measurements)9dB gains on colliding reference signals in Almost Blank Sub-frames used by pico cells.
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced Relays
The relay standardized in LTE-A has the full eNB functionalities
• can be seen as an eNodeB with a wireless backhaul operating in LTE spectrum
Expected benefits• Reduced cost: no backhaul, low-cost
device• Easy and quick to deploy (no
backhaul, small, low-power)
Foreseen main scenario: coverage enhancement
14
Advanced relays need to provide capacity in addition to coverage
CA on the relay backhaul
Adaptive HARQ
Distributed coding
Multi-hop relays
Moving relays
LTE-A features ARTIST4G innovations
CA on backhaul link gains:+20% in 5%-ile throughputs+11% in throughput Jain’s index
Advanced Radio Interface TechnologIes for 4G SysTems
Conclusion
15
A mid term oriented research project• 20% of short term innovations• 60% of mid-term innovations• 20% of long term innovations
Some innovations already discussed in 3GPP Project finished since June 2012 More than 100 publications, ~20 deliverables All results available (for free) online at:
http://ict-artist4g.eu
Advanced Radio Interface TechnologIes for 4G SysTems
Introduction ARTIST4G’s goal: improvement of user experience ubiquity LTE-A Rel. 10 is the baseline system ARTIST4G WP1: design of interference avoidance schemes for improving
user experience ubiquity
We have defined different requirements on the architecture• CP_COOP: only control is exchanged between nodes for the sake of cooperation• UP_COOP: control+data are exchanged between nodes• HETNET: New architecture enabler are need for the sake of cooperation
We are targeting• Short term deployments: No modification of LTE Rel 10• Medium term deployments: New mechanisms and architecture solutions based
on LTE Rel 10• Long term deployments: New deployments optimized for CoMP
Advanced Radio Interface TechnologIes for 4G SysTems
Introduction 3D beamforming and
coordinated schedullingfor CP_COOP systems
• Short and Medium term solutions
• Improvement of the cell edge throughput
Joint transmission with interference shaping (UP_COOP)
• Long term innovation• Improvement of the
spectral efficiency and user experience ubiquity
Massive deployment of small cells (HETNET)
• Improvement of the network capacity
Advanced Radio Interface TechnologIes for 4G SysTems
eNB
Low inter-cell interferenceon each of the resources represented bydifferent colors:
eNB
Low inter-cell interferenceon each of the resources represented bydifferent colors:
Advanced 3D Beamforming (1/3)
Advanced Radio Interface TechnologIes for 4G SysTems
• Today:beamforming and MIMO schemes with fixed vertical antenna pattern
• Impact on signal strength according to UE location
• Constant inter-cell interference independent of served UE location
• Advanced 3D Beamforming:• additional degree of freedom for Tx signal
optimization and interference reduction
• Exploitation of dynamic vertical beamsteering per radio resource
• Serve each UE with individual Tx antenna pattern
• Verification of 3D beamforming• Field measurements in real deployment
scenarios
D1.2
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
Methods and implementation options Implicit coordination
fixed resource allocation according tocell areas
Distributed horizontal and vertical beam coordination Resource allocation to UEs
depending on dynamic feedbackand exchange of adjacent cellworst case interference PMIsamong base stations
Multiple fixed downtilts vs. exact steering
Advanced 3D Beamforming (2/3)
serving cell
its cooperation set
site
information exchangeinformation exchange
serving cell
its cooperation set
site
information exchangeinformation exchange
= 9° = 13° = 17°3 DT areas:
Multiple fixed downtilts
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
Impact & applicability Advanced 3D beamforming shows clear benefits over the conventional
one fixed downtilt solution, even without coordination.
Advanced antenna systems suitable for implementation of advanced3D beamforming are available
3D beamforming already became part of ALUD product strategy Verification with field measurements
Field trials verified the basic characteristic of the vertical channel as assumed for the simulations
Advanced 3D Beamforming (3/3)
Key outcomes: Simultaneous gains for both spectral efficiency (about 15 – 20%) and
cell edge throughput (up to 50%) Coordination gain and vertical BF gain (3D BF) are almost additive Exact vertical downtilt adaptation is approximated reasonably
with 2 or 3 fixed downtilts
Advanced Radio Interface TechnologIes for 4G SysTems
User centric cooperation in clustered networks:
Enlarged cooperation areas (e.g. 9 cells) increase probability to contain e.g. 3 strongest cells within cooperation area
Partial reporting limits feedback overhead
Setup of overlapping cooperation areas in different frequency subbands cover shifts
Cooperation area edge UEs are scheduled into center of best fitting cover shift
User centric clustering for partial CoMP (1/3)(Tortoise)
Advanced Radio Interface TechnologIes for 4G SysTems D1.4
789 1
23456
789 1
23456
123
456 7
897
89 1234
56
123
456 7
89
With six cover shifts all UEs having their 3 strongest cells within 3 adjacent sites are being served user centric
cover shift 1
cover shift 2
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
Interference floor shaping – Tortoise concept Cell edge UEs suffer from low SNR as well as
strong interference floor generated by other cells
JP CoMP gains hidden in interference floor Cover shift concept provides novel options for IF
floor shaping Cooperation area (CA) cell individual
antenna tilting and power allocation
CA center/outbound wideband beams with low/strong tilt & strong/low Tx power
CA edge UEs scheduled into other cover shift
User centric clustering for partial CoMP (2/3)(Tortoise)
Tortoise like shape ofRx power over location
7° tilt / 46dBm
15° tilt 40dBm
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
Impact & applicability User centric clustering essential for generating real world CoMP gains
Partial CoMP combines a large penetration rate of user centric served users with limited feedback overhead
‘Tortoise’ interference floor shaping boosts performance and localizes thenetwork wide to a cooperation area limited optimization problem
Interaction with WP6:
WP6 field trials verified the basic principle of the Tortoise interference floor shaping technique
User centric clustering for partial CoMP (3/3)(Tortoise)
Key outcomes: Penetration rate for CoMP users of about 90% Interference floor suppression of about -20dB for about 70% of UEs In combination with other means spectral efficiency up to
6..7 bit/s/Hz/cell about 100% CoMP gains
Advanced Radio Interface TechnologIes for 4G SysTems
Statement: Most of the traffic is in indoor (home and offices)HeNB deployments improve the network capacity
HeNBs allows for offloading the in-home traffic HeNBs must bring high wireless performance Closed Subscriber Groups restricting the access to the HeNBs generate
interference issues in downlink The high number of HeNBs generates non-negligible levels of
interference on the macro network in uplink eNB/HeNB cooperation is limited by the architecture
Objectives: Interference avoidance mechanisms and architecture enablers for protecting the macro network while taking benefit from the huge offloading gain from a massive small cell deployment
Interference avoidance scheme for co-channeleNB/HeNB deployments
Advanced Radio Interface TechnologIes for 4G SysTems D1.4
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
Principle: Define a power setting strategy guarantees a target degradation in a High Interference Zone (HIRZ) around each HeNBNo eNB/HeNB cooperation is required
Based on measurements available at the HeNB onlyTarget short term deployments, no impact on the architecture
Key outcome: For an average 2b/s/Hz cell edge performance at the HeNBsNo degradation of the eNB cell edge performance for less than 125 HeNB/km²For 500 HeNBs/km² => Huge network capacity gain by offloading
35% degradation of the eNB cell-edge performance with fixed power
10% degradation only with the proposed power control strategy
Macro network protection in Downlink
Advanced Radio Interface TechnologIes for 4G SysTemsAdvanced Radio Interface TechnologIes for 4G SysTems
• Virtualization of the “Small Cell Network”(SCN) as a single interferer in uplink and a single radio neighbor
• Architecture enablers: Group PCI and Coordination Gateway
• Shaping of the interference distribution in a semi centralized fashion (one central unit per eNBcell)
• Measurements of the eNB from the small cells• Measurements of the SCN from the eNB• Optimization and broadcast of parameters to small
cells• Selection of parameters and computation of the
Ues power control oin each small cell• Excellent trade-off between eNB protection, small
cell performance, and small cell-UEs power consumption
Macro network protection in Uplink
Advanced Radio Interface TechnologIes for 4G SysTems
Conclusions We have shown three research axes of the ARTIST4G
project, based on interference avoidance The innovations that have been developed can be
associated with interference cancelation or used in the relays context
New architecture enablers have been developed in ARTIST4G WP4 for supporting these innovations• New cooperation interface for Joint Processing CoMP• Design of the cooperation protocols for Joint
Processing CoMP• Enablers for eNB/HeNB cooperation
Advanced Radio Interface TechnologIes for 4G SysTems
Paradigm “interference exploitation”: Don’t avoid
interference; instead make use of it through flexible interference control and advanced receivers
Advanced Receivers
Link to System Abstraction
System Level Concepts
Main Focus of Presentation
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced Receivers
Link to System Abstraction
System Level Concepts
Advanced Radio Interface TechnologIes for 4G SysTems
Iterative MMSE-Soft IC Iterative receiver with equalization and channel decoding step Basis for advanced receiver enhancements (like complexity reduction and
semi-blind channel estimation) in ARTIST4G System level analysis and link adaptation require easy and fast
performance prediction.
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced Receivers
Link to System Abstraction
System Level Concepts
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced L2S Modelling Keep track of the coded bit average mutual information (AMI)
circulating between the MUD and the bank of outer APP decoders Demapping and decoding understood as a joint process.
Measurements
• Transport Format• Transmit power• UE Positions
Measurement
UE1
UE2
IQ-B
aseb
and
Sam
ples
TUD ML Chain
SIC Receiver
FT ML Chain
Prediction
MeasuredBLER
PredictedBLER
Parameter Value Bandwidth 20 MHz FFT size 2048 Subcarriers for tx 1200 Sampling rate 30.72 MHz Subcarrier spacing 15 kHz Transmit Time Interval 1ms OFDM symbols/TTI 14 Subcarriers per PRB 12 Total available PRBs 100 Modulation Schemes QPSK, 16QAM, 64QAM
Effective SNR
BLE
R
Regime of InterestreferencePredicted from measurements
Measurement Results
Performance predictionmethodology shows reasonable accuracy for real world measurements
Abstraction algorithmcould be used for fastlink adaptation and in resource allocation algorithms
Recommended Deliverables: D2.3, D6.4
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced Receivers
Link to System Abstraction
System Level Concepts
Flexible Interference Control
UL CoMPScheduling
Advanced Radio Interface TechnologIes for 4G SysTems
Flexible Interference Control (FIC) Combine interference exploitation (receiver side) with
interference avoidance (transmitter side) in flexible ways.
A) avoid interference, where possible
B) Cope with remaining interference
Advanced Radio Interface TechnologIes for 4G SysTems
Flexible Interference Control Examples
Joint Transmission Interference Cancellation Receiver (JTICR)
• based on combination of Joint Transmission and successive interference cancellation receivers for a more efficient operation of the downlink
• two modes applied in different operational conditions, mainly associated with the operation in HetNet environments
Adaptive Resource Allocation Algorithms for Multiuser MIMO Systems with Iterative MMSE-IC Joint Decoding
• resource allocation algorithms taking advantage of Iterative MMSE-IC receivers at the base station to maximize capacity in Multiuser MIMO systems
Advanced Radio Interface TechnologIes for 4G SysTems
Flexible Interference ControlIn homogeneous networks, traffic is served by macro base stationsDeploying pico cells offers capacity gains by traffic offloadingAdvantages
– Better load balancing between macro and pico layer improves network capacity and user
How to achieve traffic offloading? Answer: Cell range expansion of the pico cell
– The UE should connect to the pico cell even if the macro cell is stronger
– Coverage area of the pico cell is artificially enlarged Cell range expansion
MacroPico Pico
Pico
SIR = 0 dB at cell edge of regular coverage area
SIR < 0 dB at cell edge of expanded coverage area
Advanced Radio Interface TechnologIes for 4G SysTems
Flexible Interference Control UEs in close proximity to CSG femto cells that it is not allowed to connect to
• strong interference from the CSG cell
Macro-pico deployments with UEs operating in cell range expansion• Nominally, a UE associates with a base station with strong DL SINR • With cell range expansion, a UE can associate with a low power eNB
Femto is the aggressor and macro the victim
Macro is the aggressor and pico the victim
MacroFemto Femto
MacroPico Pico
Advanced Radio Interface TechnologIes for 4G SysTems
eICIC (Rel-10)
1ms
12 sub
carrier o
f 15 kH
z each
RS antenna port 1 resource element
RS antenna port 2 resource element
Empty PDSCH resource element
Empty PDCCH/PHICH/PCFICH resource element
In Rel-10, almost blank subframes (ABS) have been introduced
In a ABS, no unicast PDSCH and PDCCH is transmitted
To ensure backward compatibility, following signals are transmitted
• CRS (pilot signal)• PSS/SSS (synchronization signals)• SIB1/MIB (broadcast information)
CRS/PSS/SSS/SIB1/MIB can still cause strong interference in certain PRBs/REs
Advanced Radio Interface TechnologIes for 4G SysTems
eICIC (Rel-10)
Interference coordination between aggressor cell and victim cell is done by means of a bitmap sent over X2 interface
• Each bit is mapped to a single subframe and indicates an ABS subframe• Based on the data traffic demand, the pattern can change each 40ms• Cell creating strong interference controls which resources can be used by the
victim cell to serve terminals in harsh interference conditions
MacroPico
Interference bitmap transmitted over X2 backhaul
Statically assigned almost blank subframe
Semi‐statically assigned almost blank subframe
Semi‐statically assigned regular subframe
X2 backhaul link
Advanced Radio Interface TechnologIes for 4G SysTems
Why IC Receivers are needed
Even in case of almost blank subframes at the aggressor nodes, the CRS/PSS/SSS/SIB1/MIB are still transmitted
This interference from aggressor node causes significant performance degradation to data and control channels of serving cell
• Therefore cancelling interference of CRS, PSS/SSS and PBCH is needed to enlarge cell range expansion
Interference cancelation algorithms for those signals/channels can be designed that achieve SIR = -18 dB
Advanced Radio Interface TechnologIes for 4G SysTems
Throughput Gains by CRS IC –Colliding RS (Rel-11)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 320
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
Serving cell C/I (dB)
Thro
ughp
ut (K
bps)
CollidingRS-TxMode3
CellID0-TxMode3CellID0-TxMode3-CellID96-TxMode3-16dBCellID0-TxMode3-CellID96-TxMode3-IC-16dB
CRS IC Gains for colliding RSin non-MBSFN ABS
9 dB Gain
Recommended Deliverables: D2.4, D2.5
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced Receivers
Link to System Abstraction
System Level Concepts
Flexible Interference Control
UL CoMP Scheduling
Advanced Radio Interface TechnologIes for 4G SysTems
Interference Exploitation – UL CoMP
Distributed Schedulers
Joint Detection
Array G
ain
Multiplex
ing Gain
Multi-User Diversity
Joint Scheduler
Backhaul
Advanced Radio Interface TechnologIes for 4G SysTems
Scheduling and Power Control for UL CoMP
Joint Scheduling:•Scheduler centrally assigns resources in all cells•Full CSI needed at scheduler
Cooperation Cluster
Backhaul
Joint Detection:•BSs exchange of rx-signals•Performance increase through interference exploitation
Joint SchedulerJoint Detection
• Single-antenna BSs• Single-antenna MTs• 2 user spatial multiplex (grouping)
dd-d00 d0
K Terminals (uniform distri.)
JD
Scenario
Advanced Radio Interface TechnologIes for 4G SysTems
Power Control
All Terminals transmit with the same power.
Fixed Power Single-Cell Multi-Cell
Pathloss to the nearest BS is compensated to achieve an average target SNR.
Pathloss to both BSs is compensated to achieve an average target SNR (involving receive power and noise at both BSs).
0 100 200 300 400 500-30
-25
-20
-15
-10
-5
0
5
Position (m)
Pow
er (d
Bm
)
Power vs. Position (SNRsingle=30dB)
Multi-cellSingle-cellFixed
0 100 200 300 400 5000
0.5
1
1.5
2
Position (m)P
ower
(mW
)
Power vs. Position (SNRsingle=30dB)
Multi-cellSingle-cellFixed
Advanced Radio Interface TechnologIes for 4G SysTems
Scheduling Algorithms
50 100 150 200 250 300 350 400 4500
1
2
3
4
5
6
Position (m) - (bin size 20m)
Ave
rage
Thr
ough
put (
bpcu
)
MultiSingleFixed
Proportional Fair
• Multi-Cell Power Control achieves good fairness (and higher throughput than for other algorithms)
• Fixed power control not as fair as Single/Multi
50 100 150 200 250 300 350 400 4500
1
2
3
4
5
6
Position (m) - (bin size 20m)
Ave
rage
Thr
ough
put (
bpcu
)
MultiSingleFixed
Max Rate
Advanced Radio Interface TechnologIes for 4G SysTems
Scheduling Algorithms
50 100 150 200 250 300 350 400 4500
1
2
3
4
5
6
Position (m) - (bin size 20m)
Ave
rage
Thr
ough
put (
bpcu
)
MultiSingleFixed
50 100 150 200 250 300 350 400 4500
1
2
3
4
5
6
Position (m) - (bin size 20m)
Ave
rage
Thr
ough
put (
bpcu
)
MultiSingleFixed
Max Fair Proportional Fair
• Similar fairness for all power controls • Overall higher throughputs• Fixed power control not as fair as
Single/Multi
Advanced Radio Interface TechnologIes for 4G SysTems
Throughput vs. Fairness
0.5 1 1.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Mean Throughput (bpcu)
Jain
´s In
dex
multi - max ratemulti - prop fairmulti - max fairsingle - max ratesingle - prop fairsingle - max fairfixed - max ratefixed - prop fairfixed - max fair
fair, spectrally inefficient
unfair, spectrally inefficient
fair, spectrally efficient
unfair, spectrally efficient
Recommended Deliverables: D2.5
Advanced Radio Interface TechnologIes for 4G SysTems
Conclusions Advanced receivers with interference cancellation capability allow to
overcome some of the limitations of current system without requiring changes to the standards.
Flexible interference control (tuning between interference avoidance and coping with interference) opens up a new design space that allows systems to adjust to the radio propagation conditions in a more fine grained way.
IC important component for traffic offloading in LTE HetNets (62% gains for 1MB file download at 30
New abstraction methodologies were provided that allow to make use of these added degrees of freedom for system analysis and design (proven with measurements)
UL CoMP is a promising means to exploit interference across cell borders. Scheduling and Power Control have large impact on system efficiency and fairness.
Advanced Radio Interface TechnologIes for 4G SysTems
Introduction ARTIST4G work on relay concepts beyond the scope of the actual
standardisation work LTE-Advanced Relays are for coverage WP3 is looking for capacity improvements and ways for introducing
advanced relays into the LTE technology roadmap ARTIST4G aims for ubiquitous user experience
• Advanced Relays needed to provide capacity on top of coverage• Improve average throughput• Improve ubiquity (more uniform QoS) (cell-edge)
WP3 work is based on features of LTE-A and related research to optimise
• CoMP • Carrier aggregation, with in- and outband operation • Channel Coding• Scheduling• Interference Management• Various types of relays
Advanced Radio Interface TechnologIes for 4G SysTems
Type-1 relay nodes Non-transparent RNs
• UEs see them as eNBs
They have their own cell ID, synchronization and control channels
RNs attach to a Donor eNB (DeNB)• RN acts like a UE while attaching to DeNB
Have been standardized by 3GPP• Several issues still need to be addressed
Advanced Radio Interface TechnologIes for 4G SysTems
Challenges for type-1 relay nodes
Resource partitioning between backhaul and access network (two-hop)
Backhaul optimization to avoid bottlenecks• Multi-carrier relaying with carrier aggregation
Multi-hop deployments Inter-cell interference coordination (ICIC)
Advanced Radio Interface TechnologIes for 4G SysTems
Resource Partitioning (RP) between backhaul and macro-access links
In-band Relays (RN tx-rx segregation in time):• In MBSFN frames: DeNB transmits to macro UEs and to the backhaul link• In non-MBSFN frames: DeNB transmits only to macro UEs and RN transmits to
relay UEs.
Out-band Relays (RN tx-rx segregation in frequency):• On primary carrier: DeNB transmits to macro UEs and to the backhaul link• On secondary carrier: DeNB transmits only to macro UEs and RN transmits to
relay UEs.
In both cases, we need RP between backhaul and macro access
Advanced Radio Interface TechnologIes for 4G SysTems
Resource Partitioning (RP) between backhaul and macro-access links
Proposals from Nomor:• Semi-static: Fair allocation of resources based on the number of users. • Dynamic: Fair allocation of resources to “uniformalize” the throughput per UE
Pros: Simple resource splitting, simple schedulers, works well in absence of QoS req Cons: Not an optimal solution especially for heterogeneous QoS constraints In real life scenarios, different applications with different QoS requirements co-exist
Advanced Radio Interface TechnologIes for 4G SysTems
QoS-aware scheduling proposalUnderlying principles
Jointly tackle the problem of resource partitioning and scheduling in a QoS-aware manner
In this presentation: a unified treatment of in-band and out-band relays Slots where macro-access and backhaul share resources:
• Use a QoS-aware scheduler by aggregating backhaul users as super users (one for each RN and each QoS type)
• The latency deadline for R-UEs needs to be split
Slots where only macro access is served at DeNB and relay-access at RNs• Scheduler at DeNB “as usual”• Scheduler at RNs need knowledge of already consumed delay budget• The latency dead line needs to be adjusted
Advanced Radio Interface TechnologIes for 4G SysTems
Simulation Results Relay enhanced scenario with heterogeneous traffic mix
• 3GPP case-1 (ISD 500m) with 2 RNs in macro-cell• 25UEs in total, some assigned to macro cell (called M-UEs) and
others assigned to RNs (called R-UEs)• Two types of user traffic with distinct bit rate and latency
requirements:– VoIP: 128kbps and latency deadline of 100ms– Video: 256kbps and latency deadline of 300ms
Measured the level of QoS satisfaction w.r.t. the achieved throughput and experienced packet delay
Percentage of QoS-satisfied users w .r.t. throughput and packet delay
0.020.040.060.080.0
100.0120.0
Video UEs VoIP UEs Video UEs VoIP UEs
Throughput Delay
Conventional
Proposed
Multi-Carrier RelayingMotivation:- Multi-carrier operation is necessary to
achieve IMT-A requirements- Baseline LTE relaying is single carrier
Proposed solutions:- Enable carrier aggregation on RN backhaul => higher capacity, bottleneck elimination- Utilize frequency domain ICIC => improved signal quality for RNs and UEs- Make dynamic carrier reconfiguration => resources on demand, higher flexibility, lower
power utilization
Allowed CAAllowed CAAllowed CAAllowed CANot allowed CANot allowed CA
Backhaul link is typically the
bottleneck
LTE Release 10 system configuration
Problems:- Performance of RN-attached UEs
limited by backhaul capacity- RN configuration is (semi-)static and
unable to follow dynamic conditions
Multi-Carrier Relaying Single carrier is often insufficient to support
traffic of RN backhaul (especially for multi-hop)
Carrier aggregation on RN backhaul provides:• Higher peak throughputs• Multi-carrier load diversity
Main gains:• +20% in 5%-ile throughputs• +11% in throughput Jain’s index
Carrier loadbalancing
Support for high traffic
High order carrier aggregation
High order carrier aggregation
Low order carrier aggregation
Low order carrier aggregation
Single carrier operation
Single carrier operation
Multi-Carrier Relaying Dynamic carrier reconfiguration:
• RN backhaul-access carrier reconfiguration for capacity balancing (bottleneck elimination)
• Dynamic deactivation of secondary RN access carriers in case of low traffic load (energy efficiency)
• Main gains:+6% capacity for RN UEs (+4% overall)-14% lower RN access carrier activity
Frequency domain ICIC:• Coordinated selection of RN backhaul and/or access
carriers to avoid interference• Iterative approach with several levels of decentralization
(centralized, distributed, autonomous)• Main gains: +14% capacity for RN UEs (+10% overall)
Advanced Radio Interface TechnologIes for 4G SysTems
Type-2 relay nodes Transparent RNs
• RNs just expand the cell of DeNB
They replicate the cell ID of DeNB Type-2 RNs can be used for capacity and QoS
enhancement• They implicitly forward information
Have received functional definition by 3GPP but yet part of the standards
Advanced Radio Interface TechnologIes for 4G SysTems
Challenges for type-2 relay nodes
How to best cooperate with eNB• Adaptive HARQ• Distributed coding between eNB and RNs
New transmission protocols enabling throughput enhancements
Advanced Radio Interface TechnologIes for 4G SysTems
Adaptive HARQHigh Low
Less More
Residual FER
Resources forretransmission
OptimalThroughputperformance
Apply adjustment of the retransmission bits, considering the tradeoff between FER and resource utilization.
In case of Type 2 relay without channel decoding, further ideas of how to optimize retransmission bits are necessary
Closed form solution for Mutual Information of relayed link
Advanced Radio Interface TechnologIes for 4G SysTems
Available Results/Analysis Possible gain of HARQ with memoryless Type 2
relay• Restricted to Chase combining• Inherent loss, SNR gain but no coding gain
SNR gain pays off the coding gain penalty for wide range of relay position
0 0.2 0.4 0.6 0.8 10.2
0.4
0.6
0.8
1
dSR
Nr/N
t
CC AFIR SourceCC Source
Advanced Radio Interface TechnologIes for 4G SysTems
Possible saving with 16QAM
Saving of up to 45 % of resources for retransmission
EF most promising
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced cooperative distributed turbo coding techniques coupled with cooperative HARQ (1/2)
Proposition of novel distributed HARQ protocols for cooperative transmissions, where source and relay cooperatively construct a turbo code (DTC).
Question to be solved:• How ACK/NACK feedback can be exploited to efficiently select which agent(s) of the
cooperation scheme has to retransmit when a packet decoding error is detected at relay(s) and/or at destination ?
Selection of the node that retransmits:• Check the quality not only of the relay to the destination channel, but also of the source to
the destination one, prior to chose the node that will retransmit.• Exploit the instantaneous mutual information knowledge at both UE and relay locations Intelligent ACK/NAK feedback with additional information is exploited in order to select the
node that retransmits.
From Turbo Codes (TC) to Distributed Turbo Codes (DTC)
CC
CCDecoder CC
Destination
Interleaver
Source
Information bits + Source coded bits
Relay
DTC
TC
CC1
Decoder CC1
Interleaver
Source
CC2
Decoder CC2
Interleaver
DeinterleaverInterleaver
info
infopcc1
pcc2
pcc1
pcc2
Asymmetric case +10dB, 4 Tx max
0,00
0,05
0,10
0,15
0,20
0,25
-13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6Es/N0 (dB)
Nor
mal
ised
Thr
ough
put
ReTx Both - partner info - perfect SR link
ReTx via outage - partner info - R, S, or R+S - perfect SR link
ReTx via outage - partner info - imm.stop - R,S,R+S - perfect S-R link
idem above but S-R @ 20dB
idem above but S-R @ 10dB
idem above but S-R @ 5dB
SS
RR
DD
SS
RR
DD
N1 retransmissions,(maximum: Nmax)
TCC at first, TCC or CC1/2 after
(Nmax- N1) retransmissions
ACK@R
Yes
No
SS
RR
DD
Yes
No
Go to next packet
ACK@D
ACK@DYes
No
ACK@DYes
No
Outageafter Nmax
?
Yes
No
TCC or CC1/2
CC1/2
Phase 1
Phase 2
Phase 3
Advanced Radio Interface TechnologIes for 4G SysTems
Advanced cooperative distributed turbo coding techniques coupled with cooperative HARQ (2/2)
Investigation of several HARQ schemes for cooperative networks:• Classical retransmission schemes where either both nodes retransmit the same
codeword or only one node with the highest average SNR retransmits. • Advanced schemes based on mutual information computation and outage check
Proposed strategies achieve interesting gain over classical retransmission schemes:
• The most promising schemes are “retransmission of both partner information” (lowest PER) and “retransmission of the partner information by one node via outage check” (highest link throughput).
Advanced Radio Interface TechnologIes for 4G SysTems
Adaptive resource allocation with interference mitigation for in-band relay nodes (1/2)
Proposition of novel frequency reuse schemes aiming at:• Interference mitigation• Throughput and fairness increase between macro and relay nodes• Taking into account the system load and the level of interference
Frequency adaptive allocation scheme based on:• Estimation for each type of traffic of the number of PRBs required for both
relayed and macro UEs• Allocation of the minimum number of PRBs in order to make sub-bands
orthogonals as much as possible between adjacent sectors
,
, 2RB M M M
RB R R R
N NN N
Nb MCS
1m
sp mNbBits m
Advanced Radio Interface TechnologIes for 4G SysTems
Adaptive resource allocation with interference mitigation for in-band relay nodes (2/2)
Adaptive frequency partitioning allows improvements w.r.t. FR1 scheme both in term of number of UEs with satisfied QoS and in term of Jain index.
2
2Jain index i ii i
x N x
Moving relay nodes
Advanced Radio Interface TechnologIes for 4G SysTems
RNs mounted on top of public transportation vehicles (buses, trains etc)• Consist of inter-connected outdoor and indoor antennas
Enhance performance of vehicular UEs whose number is greatly rising• Overcome vehicular penetration loss (VPL)• Facilitate handovers and manage mobility
A study item for 3GPP
Moving relay nodes for buses
Advanced Radio Interface TechnologIes for 4G SysTems
With moving relay nodes (MRNs), VPL can be reduced or even eliminated.
Users experience better signal reception and the system capacity can be increased.
Challenges for moving relay nodes
Advanced Radio Interface TechnologIes for 4G SysTems
Rate adaptation for backhaul links• Channel prediction can be employed
Handover issues• Guaranteeing no blocking and dropping for vehicular UEs
Interference coordination