1 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Status på LTE-AStandardisering og teknologi
Præsenteret af Troels B. SørensenSektionen for Radio Access Teknologi (RATE), Aalborg UniversitetIDA-TTS Konference, 4. december, 2012
2 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012Matti Kiiski, 1 July 2011
3 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Standardization
ITU-R – International Telecommunication Union - Radiocommunication (sector)IMT-A – International Mobile Telecommunications - AdvancedE-UTRAN – Evolved UMTS Terrestrial Radio Access NetworkUMTS – Universal Mobile Telecommunications System3GPP – 3rd Generation Partnership ProgramLTE – Long Term EvolutioneNB – evolved Node BUE – User Equipment
4 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Requirements
• The 3GPP LTE evolution to meet/exceed the ITU-R IMT-Advanced capabilities of a 1Gbps (4G) system– Peak data rates of 100 Mbit/s for high and 1 Gbit/s for low mobility– Peak spectral efficiencies 15bps/Hz downlink (4×4 MIMO) and 7.5bps/Hz uplink
(2×4 MIMO)– Bandwidth scalability up to 40MHz, and preferably to 100MHz– User plane latency 10ms and 100ms for control (idle to active)
• 3GPP set its own requirements for LTE-Advanced as detailed in 3GPP TR 36.913, including– Increased spectral efficiencies (improved efficiency over LTE)
Average targets increased 30% for downlink and 40% for uplink Peak extended to 8×8 MIMO downlink and 4×4 MIMO uplink
– Meeting 3GPP operator requirements for the evolution of E-UTRASelf-Organizing Networks (SON)
– Backwards compatibility requirementsA Release 8 E-UTRA terminal can work in an Advanced E-UTRAN, An Advanced E-UTRA terminal can work in an Release 8 E-UTRAN
5 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Technology Components
Carrier Aggregation
MIMO
Cooperative Systems
Relaying
8x 4x
Backward compatible
to LTE
Mobility
Heterogeneous Networks
1st LTE field trialBerlin, 11/2007
Smooth Migrationto LTE-A
Key ingredients
Carrier1 Carrier2 Carrier3 … Carrier5
up to 100 MHz
These fulfill the ITU requirements for 3-sector macro
LTE standardization is not driven only by
IMT-Advanced!
6 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Standardization – 3GPP Releases
2008 2009 2010 2011
LTE-AStudy Items
Rel. 10
LTE-A
LTE-AWork Items
“The 18 months cycle” for releases -
and market (terminal) introduction
First LTE-A release …
PAST
2012 2013 2014 2015
Rel. 11
LTE-A
?Rel. 12… and the
next almost here
NOW
7 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Standardisation - Specifications
• The core of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) specifications relates to the 36 series of the 3GPP specifications– http://www.3gpp.org/specification-numbering (overview of the 3GPP
specification numbering)
Specifications and responsible Radio
Access Network (RAN) Working Group
After “LTE for UMTS”, Wiley 2011
LTE and LTE-A in Rel. 10 and beyond specifications
RF: 36.101 - 36.104, 36.133 (RAN4)
L2/L3: 36.321 – 36.323, 36.331, 36.304/306
(RAN2)
L1: 36.211 - 36.214(RAN1)
X2: 36.421 - 36.424(RAN3)
S1: 36.411 - 36.414(RAN3)
Packet coreAir interface
eNBS1
X2
UE
8 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Technology ComponentsCA, MIMO, HetNet (eICIC), CoMP, Relays
9 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Carrier Aggregation (CA)BW – BandwidthRRC – Radio Ressource Control (layer or signalling)PDCCH – Physical Downlink Control CHannelPUCCH – Physical Uplink Control CHannelCQI – Channel Quality IndicatorFDD – Frequency Division DuplexDL – DownlinkUL – UplinkCC – Component CarrierPCell/SCell – Primary and Secondary CellCRS – Common Reference SignalPSS/SSS – Primary and Secondary Synchronization SignalOFDM – Orthogonal Frequency Division Multiplexing
CCE – Common Control ElementBCCH – Broadcast Control CHannelRRC – Radio Ressource Control (signalling)CQI – Channel Quality IndicatorNACK/ACK – Negative AcknowledgeCSI – Channel State InformationPRB – Physical Resource Block
10 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Carrier Aggregation (CA)
• High peak data rates achieved even with fragmented spectrum (important practical aspect)
• Backwards compatibility requirements with Release 8 LTE is achieved with carrier aggregation by combining up to N = 5 Release 8 component carriers to form N x LTE bandwidth, for example 5 x 20 MHz = 100 MHz
• LTE terminals receive/transmit on one component carrier, whereas LTE-Advanced terminals may receive/transmit on multiple component carriers simultaneously
Both contiguous and non-contiguous CA is supported offering improved spectrum flexibility (e.g. for
refarming).
Primary and Secondary Cells
(Component Carriers - CC)
11 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
CA Band Combinations
• Initial focus is on CA for two band combinations, specific to different regions of the world– Radio frequency aspects are being handled per case and in a release independent
manner
• Current RF specification work has beenprioritized to focus on downlink CA– CA for uplink is more complicated and
will be standardized based on the DL CA combinations
SpuriousHarmonicsBroadband noise
Band 20: 791 – 821 MHz (DL) | 832 – 862 MHz (UL) Band 7: 2500 – 2570 MHz (UL) | 2620 – 2690 MHz (DL)
Band 3 + 7(FDD)
Band 20 + 7(FDD)
Band 3: 1710 – 1785 MHz (UL) | 1805 – 1880 MHz (DL) Band 7: 2500 – 2570 MHz (UL) | 2620 – 2690 MHz (DL)
Need for (maximum) power reduction of
4-6dB
12 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
CA Gain Mechanisms
• Multi-carrier scheduling allows for: – more bandwidth per user (peak data rate) and better use of high frequency bands
(coverage)– load balancing/ressource sharing and frequency domain scheduling across carriers
Segm.ARQ etc
Multiplexing UE1
Segm.ARQ etc...
Scheduling / Priority Handling
Logical Channels
Transport Channels
MAC
RLC Segm.ARQ etc
Segm.ARQ etc
PDCPROHC ROHC ROHC ROHC
Radio Bearers
Security Security Security Security
...
HARQ HARQ...
Multiplexing UEn
HARQ HARQ...
CC1 CCx... CC1 CCy...
Independent HARQ per CC. Thus, HARQ retransmissions
shall be send on the same CC as the corresponding original
transmission
There is one PDCP and RLC per Radio Bearer. Not visible from
RLC on how many CCs the PHY layer transmission is conducted.
Separate transport channel per CC
Dynamic Layer-2 packet scheduling accross multiple CCs
supported
13 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
CA Signalling
• Each CC provides reference (CRS) and synchronisation signals (PSS/SSS), as well as system broadcast information (BCCH) specific to that carrier– only PCell however carries radio ressource control (RRC) signalling - for bearer setup, CA
configuration, mobility measurements, handover, …– individual SCells can be activated
/deactived with MAC controlelement to save terminal power – within 7ms
• Added capacity in control channels for multi-carrier to support more CQI requests, ACK/NACK and CSI reporting, power headroom signalling .. and somesimplifications to reduce terminal complexity at the same time– reduced need for DPCCH decoding on SCells (e.g. CCE blind decoding on PCell only),
control signalling in uplink PCell PUCCH only– Cross-carrier scheduling capability of special importance to heterogeneous network
operation
TTI with 2 slots of 0.5 ms (14 OFDM symbols)
Freq
uenc
y
Time
PRB
OFDM SymbolPDCCH
14 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Multiple Input Multiple Output (MIMO)SISO – Single Input Single Output (antenna system) MU-MIMO – Multi-User MIMOSU-MIMO – SIngle User MIMOPMI – Precoding Matrix IndicatorDM-RS – Demodulation Reference SignalCSI-RS – Channel State Information – Reference SignalURS – UE specific Reference SignalOCC – Orthogonal Cover CodesSRS – Sounding Reference SignalCM – Cubic MetricSC – Single CarrierCQI – Channel Quality Indicator
Precoding – ”Antennevægtning af TX-antenner”
15 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
MIMO
• The targeted data rates of LTE-A can only be achieved by using advanced Multiple Input Multiple Output (MIMO) antenna techniques
• Primarily an evolution of LTE MIMO ...– Transmit Diversity/Beamforming (Open/Closed Loop)– Spatial Multiplexing (Open Loop)– Precoded Spatial Multiplexing (Closed Loop)
• .. except for – Increased MIMO constellations– Uplink Single-User MIMO (SU-MIMO)– Flexible Multi-User Scheduling in both downlink and uplink
SISO2x2 MIMO4x4 MIMO8x8 MIMO
SISO2x2 MIMO4x4 MIMO
Downlink Uplink
Tx
1
2
NT
1
2
NR
Rx
feedback
DiversitygainCoherent
gainMultiplexing
gain
16 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Downlink MIMO
eNB
CQI, PMI
MIMO UE4
UE3
MIMO UE2
MIMO UE1
Data Stream 1
Data Stream 2
Data Stream 1
Data Stream 2
Data
MU-MIMOTransmit Diversity
/Beamforming
SU-MIMO
CQI, PMI, RIDynamic
switching based onoptimised feedback
CQI, PMI, RI ”Double codebook”for 8 TX antennas
”New” UE specific reference signal (URS) for demodulation:
Includes precoding information for flexibleMU-MIMO operation
(pairing per ressource)
New reference signals ”replacing”Common Reference Signal (CRS):
Sparse CSI-RS for feedback generation reduces overhead
17 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Uplink MIMO
eNB
UE3
UE2
UE1
Data Stream 1
Data Stream 2
DataVirtual (MU)-MIMO Transmit diversity
MIMO UE4Data Stream 1
Data Stream 2
SU-MIMOWideband (Closed
Loop) Precoding whichis Cubic Metric (CM)
preserving
Aperiodic and dynamic SRS reference signal transmisson:
Enhances the use of SRS ressources
New Orthogonal Cover Code (OCC) on top of demodulation reference signal (DM-RS):Allows separation of partially overlapping
transmissions for flexible MU-MIMO operation
18 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Reference signals (DL)
OFDM symbols
Sub
carri
ers
”The Devil is in the details!”
Sparse CSI-RS, sent only when in fact needed (overlapped with data transmissions) to reduce overhead
for large MIMO constellationsSupport for 2, 4 and 8 TX antennas
URS (DM-RS) sent withprecoding, hence no need to signal precoder separately
Allows decoupling in spatial and frequency
domain scheduling
In uplink, the same scheduling flexibility is introduced using OCC
19 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Performance
QAM – Quadrature Amplitude ModulationUL/DL – Uplink and Downlink
20 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
UE Categories• In addition to the existing 5 categories in rel. 8 (LTE), three new
terminal categories added in rel. 10 specifications
• Peak data rates can be achieved in different combinations from CA and MIMO capabilities
Class 4 --- Class 6 Class 7 Class 8150/50 Mbps 300/50 Mbps 300/100 Mbps 3000/1500
MbpsPeak rate DL/UL
64QAMModulation DL 64QAM 64QAM 64QAM
16QAMModulation UL 64QAM 16QAM 16QAM
2x2MIMO DL 8x8 with CA2x2 with CA*4x4 without CA
2x2 with CA*4x4 without CA
NoMIMO UL 4x4 with CANo 2x2
Downlink 4x4 MIMO: 15bps/Hz
Uplink 2x2, MIMO (64QAM): 7.5bps/HzCell edge
efficiency is about 1% of
peak!
* Carrier aggregation of two 20MHz carriers
21 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Cell Performance• From simulations, average LTE-A cell spectral efficiencies exceed ITU
requirements
• Much of the gain can be achieved already with LTE rel. 8 (e.g. Multi-User MIMO), but additional MIMO capability and flexibility in scheduling gives additional gain for LTE-A rel. 10
– Downlink: UE specific reference signals (URS, or DM-RS), dynamic switching SU/MU-MIMO and optimised double codebook feedback for 8 TX antennas
– Uplink: SU-MIMO operation, orthogonal cover codes on DM-RS, dynamic aperiodic SRS transmission
2.6bps/Hz
2x2 MIMO
3.4bps/Hz
4x2 MIMO
4.7bps/Hz
4x4 MIMO1.4
bps/Hz1x2 MIMO
2.3bps/Hz
2x4 MIMO
DownlinkUplink
“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 2012
22 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
LTE-A Capability
LTE 50MHz FDD6GB/sub/month
LTE-A 50MHz FDD10GB/sub/month
LTE-A 50MHz FDDHetNet
54GB/sub/month
Heterogeneous Networks with small and large cells are essential to cell-edge improvements! – secondarily CoMP
LTE-A 50MHz FDDNetwork upgrade15GB/sub/month
LTE-A 100MHz FDDHetNet
107GB/sub/month
?
“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 2012
23 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Heterogeneous Networks (HetNet)
ABS – Almost Blank SubframeHeNB – Home eNBCSG = Closed Subscriber GroupEIRP = Equivalent Isotropic Radiated PowerHeNB = Home base stationRE = Range ExtensioneICIC = Enhanced ICICHII = High Interference IndicationICIC = Inter-Cell Interference CoordinationOI = Overload IndicationRNTP = Relative Narrow band Transmit PowerSON = Self Optimizing Network
24 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
The Combined Benefit of Wide & Local Area
Macro
Micro
Pico, Femto
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 Access
Points
Wide Area sites
Medium area sites
Local area
Local area
Local area
Local area
WLAN
WLANWLAN
Medium area sites
Local area
WLAN
WLAN
Benefits of Multi-Layer Deployment• Coverage improvement from local area cells
in edge or shadowed regions• Capacity increase from more transmission
points in a given area
Tradeoffs involved with Multi-Layer• Co-channel deployment needs no additional
spectrum but creates interference between the layers and within the same layer >> this interference needs to be controlled for QoS
25 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
HetNet Co-Channel Interference
Pico eNB:Tx power: 30 dBmAntenna gain: 5 dBiEIRP: 35 dBm
Macro eNB:Tx power: 46 dBmAntenna gain: 14 dBiEIRP: 60 dBm
Macro eNB
CSG HeNB:Tx power: 20 dBmAntenna gain: 0 dBiEIRP: 20 dBm
Dominancearea of HeNB
Coverage area of pico without RE
Extendedcoverage area of
pico with RE
Coverage area of macro
26 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
LTE Multi-Cell Coordination via X2Cell ACell B
µ-cell B
µ-cell A1
No X2 betweenmacro and
HeNBs(rel.10 includes
X2 betweenHeNBs for some
cases)• Each 3GPP releases has added few new features:
– Release 8Mobility Management (Handover)ICIC (RNTP, HII, OI)SON Management
– Release 9SON enhancementsLoad balancingEnergy Saving
– Release 10TDM eICIC
27 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
TDM eICIC PrincipleAlmost blanksub-frame (ABS)Sub-frame withnormal transmission
Macro-layer
Pico-layer
HeNB-layer
Pico-nodes can schedule UEs withlarger RE, if not interfered from non-
allowed CSG HeNB(s)
Macro-eNBs and Pico-eNBs can schedulealso users that are close to non-allowed CSG
HeNB(s), but not pico-UEs with larger RE.
Pico-UEswith
largerRE,
close to CSG
HeNB(s) are
schedulable (as well as
pico-UEswithout
RE).
28 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
HetNet is ”hot”
Considered Small Cell Scenarios & ObjectivesOngoing LTE Rel-12 Study Item3GPP TR 36.932
Ongoing LTE Rel-12 Study Item3GPP TR 36.932
Cases with dedicated carrier deployment
Cases with dedicated carrier deployment
Macro-assisted and standalone small cell
solutions
Macro-assisted and standalone small cell
solutions
Enhanced mobility for dense small cell
deployments
Enhanced mobility for dense small cell
deployments
Efficient small cell SON
Efficient small cell SON
Study of PHY and Architecture
enhancements
Study of PHY and Architecture
enhancements
Exploiting new carrier type (NCT)
Exploiting new carrier type (NCT)
Spectrum:e.g. 3.5 GHz for small cells
Spectrum:e.g. 3.5 GHz for small cells
Energy efficient solution
Energy efficient solution
Rel. 12 WI on HetNetMobility improvements
for LTE (rel. 11 SI)
Rel. 12 WI on NCT
Rel. 12 WI on CarrierBased HetNet ICIC for
LTE (rel. 11 WI)
Rel. 12 SI onSmall Cell
Enhancements
29 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Coordinated Multipoint (CoMP) Transmission and Reception
JP – Joint Processing
30 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Cell A
CoMP Principle
Cell A (Anchor Cell for the CoMP Cooperative Set)
Cell BCell C
• A 3-cell CoMP Cooperative/Transmission Set in downlink
Inter-cell CoMP signaling
31 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
CoMP Techniques
• Categories of CoMP
– Joint Processing (JP):Data is available at each cell in CoMP cooperating set (CSI and scheduling info, AND data shared among cooperating cells)
Joint Transmission: Transmission from multiple points (part of or entire CoMPcooperating set) at a time Dynamic cell selection: Transmission from one point at a time (within CoMPcooperating set)• A single point is the transmission point at every subframe; this transmission point can change
dynamically within the CoMP cooperating set
– Coordinated Scheduling/Beamforming (CS/CB):Data is only available at serving cell and transmitted from that point (CSI and scheduling info shared among cooperating cells)
The user scheduling/beamforming decisions are made with coordination among cells corresponding to the CoMP cooperating set
Alike ICIC but faster and including spatial
domain
32 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Relays
33 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Relays
• Relay nodes with LTE backhaul – inband or outband– for coverage extension/cell edge performance improvement– backwards compatible with rel. 8
Macro eNodeB
Relay Nodes
Micro BTS
Backhaul linkRelay looks like an additional sector of
the macro
Access linkRelay looks like an eNB
seen from the UE
Full eNB functionality
34 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Summary
35 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Summary• Bandwidth has been extended in rel. 10 (LTE-A) up to 100MHz by using backwards
compatible carrier aggregation– Two carrier downlink CA combinations have been specified and more will come,
including uplink CA combinations • Support for Multiple Input Multiple Output (MIMO) antennas has been extended in
rel. 10– Uplink SU-MIMO up to 4 × 4 for increasing uplink peak spectral efficiency (up to
15bps/Hz) and enhance average cell spectral efficiency– Support of up to 8x8 MIMO in downlink to increase peak spectral efficiency (up to
30bps/Hz) and average cell spectral efficiency– “The Devil is in the details” of the reference signals, which has allowed
improvements especially to Multi-User MIMO• Multi-layer interference management for Heterogeneous Networks using time-
domain enhanced ICIC (eICIC)• CoMP techniques are still under investigation but included in rel. 11 for downlink and
improved for uplink over what is already possible with LTE rel. 8• Transparent relay nodes with wireless LTE backhaul were introduced in rel. 10,
primarily for cell edge improvements• With these techniques, the target of reaching a peak data rates of more than 1Gbit/s
and significant improved average cell spectral efficiency in both UL and DL are achieved
36 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012
Literature
“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 1st
edition, September 2012, Edited by Harri Holma and Antti Toskala
“LTE for UMTS; Evolution to LTE-Advanced", John Wiley, 2nd
edition, March 2011, Edited by Harri Holma and Antti Toskala
“4G: LTE/LTE-Advanced for Mobile Broadband”, Academic Press, 2011, Edited by Erik Dahlman, Stefan Parkvall and Johan Skjold
“LTE-advanced and 4G wireless communications”, IEEE Communications Magazine, vol. 50, no. 2, February 2012