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3G Long-term Evolution (LTE) andSystem Architecture Evolution (SAE)
Background
Evolved Packet System Architecture
LTE Radio Interface
Radio Resource Management
LTE-Advanced
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UMTS Networks 2Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
3GPP Evolution Background
Discussion started in Dec 2004 State of the art then:
The combination of HSDPA and E-DCH provides very efficient packet data
transmission capabilities, but UMTS should continue to be evolved to meet the everincreasing demand of new applications and user expectations.
10 years have passed since the initiation of the 3G programme and it is time toinitiate a new programme to evolve 3G which will lead to a 4G technology.
From the application/user perspectives, the UMTS evolution should target atsignificantly higher data rates and throughput, lower network latency,and support of always-on connectivity.
From the operator perspectives, an evolved UMTS will make business sense if it: Provide significantly improved power and bandwidth efficiencies Facilitate the convergence with other networks/technologies Reduce transport network cost Limit additional complexity
Evolved-UTRA is a packet only network there is no support of circuit switched
services (no MSC) Evolved-UTRA started on a clean state everything was up for discussion including
the system architecture and the split of functionality between RAN and CN Led to 3GPP Study Item (Study Phase: 2005 4Q2006)
3G Long-term Evolution (LTE) for new Radio Accessand System Architecture Evolution (SAE) for Evolved Network
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LTE Requirements and Performance Targets
High Peak Data Rates
100 Mbps DL (20 MHz, 2x2 MIMO)
50 Mbps UL (20 MHz, 1x2)
Improved Spectrum Efficiency
3-4x HSPA Rel6 in DL*
2-3x HSPA Rel6 in UL
1 bps/Hz broadcast
Improved Cell Edge Rates
2-3x HSPA Rel6 in DL*
2-3x HSPA Rel6 in UL
Full broadband coverage
Support Scalable BW
1.4, 3, 5, 10, 15, 20 MHz
Low Latency
< 5ms user plane (UE to RAN edge)
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UMTS Networks 4Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Key Features of LTE to Meet Requirements
Selection of OFDM for the air interface
Less receiver complexity
Robust to frequency selective fading and inter-symbol interference (ISI) Access to both time and frequency domain allows additional flexibility in
scheduling (including interference coordination)
Scalable OFDM makes it straightforward to extend to differenttransmission bandwidths
Integration of MIMO techniques
Pilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMOin the UL
Simplified network architecture
Reduction in number of logical nodes flatter architecture
Clean separation of user and control plane
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UMTS Networks 5Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
3GPP / LTE R7/R8 specifications timeline
After Study Phase: Two Lines in 3GPP
EVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO)
REVOLUTION towards LTE/SAE (OFDM based)
Stage 2 (Principles) completed in March 07
Stage 3 (Specifications) completed in Dec 07
Test specifications completed in Dec 08
RAN 32 March 06
WI agreed, conceptsapproved
LTERAN 35 March 07
Stage 2 TechnicalSpecs
RAN 37 Sept 07
Stage 3 TechnicalSpecs- L1 & L2
Corrections Phase(2008 andbeyond)
RAN 34 Dec 06
NEW WI (64/16 QAM)
RAN 35 Mar 07
WI Completion (inc 64QAM)
RAN 36 Jun 07
WI Completion 16QAM UL
RAN 37 Sept 07
WI Completion (performance)
2006 2007 2008
R7 HSPA+
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
RAN 38 Dec 07Stage 3 Technical
Specs L3
RAN 42 Dec 08
Test Specs
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UMTS Networks 6Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Terminology: LTE + SAE = EPS
From set of requirements it was clear that evolution work would be requiredfor both, the radio access network as well as the core network
LTE would not be backward compatible with UMTS/ HSPA !
RAN working groups would focus on the air interface and radio accessnetwork aspects
System Architecture (SA) working groups would develop the EvolvedPacket Core (EPC)
Note on terminology
In the RAN working groups term Evolved UMTS Terrestrial RadioAccess Network (E-UTRAN) and Long Term Evolution (LTE) areused interchangeably.
In the SA working groups the term System Architecture Evolution
(SAE) was used to signify the broad framework for the architecture For some time the term LTE/SAE was used to describe the new evolved
system, but now this has become known as the Evolved PacketSystem (EPS)
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Network Simplification: From 3GPP to 3GPP LTE
3GPP architecture
4 functional entities on thecontrol plane and user plane
3 standardized user plane &control plane interfaces
3GPP LTE architecture
2 functional entities on the
user plane: eNodeB and S-GW SGSN control plane functions S-GW & MME
Less interfaces, somefunctions will disappear
4 layers into 2 layers
Evolve GGSN integratedS-GW
Moving SGSN functionalities toS-GW.
RNC evolutions to RRM on aIP distributed network for
enhancing mobilitymanagement.
Part of RNC mobility functionbeing moved to S-GW &eNodeB
GGSN
SGSN
RNC
NodeB
ASGW
eNodeB
MMF
GGSN
SGSN
RNC
NodeB
Control plane User plane
ASGW
eNodeB
MMF
S-GW
eNodeB
MME
Control plane User plane
S-GW: Serving GatewayMME: Mobility Management Entity
eNodeB: Evolved NodeB
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Evolved UTRAN Architecture
eNB
eNB
eNB
MME/S-GW MME/S-GW
X2
EPC
E-UT
RAN
S1
S1
S1S1
S1
S1
X2
X2
EPC = Evolved Packet Core
Key elements of networkarchitecture
No more RNC
RNC layers/functionalitiesmoves in eNB
X2 interface for seamlessmobility (i.e. data/ contextforwarding) and interferencemanagement
Note: Standard only defineslogical structure/ Nodes !
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EPS Architecture Functional description of the Nodes
internet
eNB
RB Control
Connection Mobility Cont.
eNB Measurement
Configuration & Provision
Dynamic Resource
Allocation (Scheduler)
PDCP
PHY
MME
S-GW
S1
MAC
Inter Cell RRM
Radio Admission Control
RLC
E-UTRAN EPC
RRC
Mobility
Anchoring
EPS Bearer Control
Idle State Mobility
Handling
NAS Security
P-GW
UE IP address
allocation
Packet Filtering
eNodeB contains all radioaccess functions
Admission Control
Scheduling of UL & DLdata
Scheduling andtransmission of paging andsystem broadcast
IP header compression
Outer ARQ (RLC)
Serving Gateway
Local mobility anchor for inter-eNB handovers
Mobility anchor for inter-3GPP handovers
Idle mode DL packet buffering
Lawful interception
Packet routing and forwarding
PDN Gateway
UE IP address allocation
Mobility anchor between 3GPP and non-3GPPaccess
Connectivity to Packet Data Network
MME control plane functions
Idle mode UE reachability
Tracking area list management
S-GW/P-GW selection
Inter core network node signalingfor mobility bw. 2G/3G and LTE
NAS signaling
Authentication
Bearer management functions
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EPS Architecture Control Plane Layout over S1
eNB
PHY
UE
PHY
MAC
RLC
MAC
MME
RLC
NAS NAS
RRC RRC
PDCP PDCP
UE eNode-B MME
RRC sub-layer performs:
Broadcasting
Paging
Connection Mgt Radio bearer control
Mobility functions
UE measurement reporting & control
PDCP sub-layer performs:
Integrity protection & ciphering
NAS sub-layer performs:
Authentication
Security control
Idle mode mobility handling
Idle mode paging origination
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EPS Architecture User Plane Layout over S1
UE eNode-B MME
eNB
PHY
UE
PHY
MAC
RLC
MAC
PDCPPDCP
RLC
S-Gateway
RLC sub-layer performs:
Transferring upper layer PDUs
In-sequence delivery of PDUs
Error correction through ARQ Duplicate detection
Flow control
Segmentation/ Concatenation of SDUs
PDCP sub-layer performs:
Header compression
Ciphering
MAC sub-layer performs:
Scheduling
Error correction through HARQ Priority handling across UEs & logical
channels
Multiplexing/de-multiplexing of RLC
radio bearers into/from PhCHs on TrCHs
Physical sub-layer performs:
DL: OFDMA, UL: SC-FDMA
FEC
UL power control
Multi-stream transmission & reception (i.e. MIMO)
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EPS Architecture Interworking for 3GPP and non-3GPP Access
Home Subscriber Server (HSS) is the subscription data repository for permanent userdata (subscriber profile).
Policy Charging Rules Function (PCRF) provides the policy and charging control (PCC)rules for controlling the QoS as well as charging the user, accordingly.
S3 interface connects MME directly to SGSN for signaling to support mobility across LTEand UTRAN/GERAN; S4 allows direction of user plane between LTE and GERAN/ UTRAN(uses GTP)
GERAN
UTRAN
E-UTRAN
SGSN
MME
non-3GPP Access
Serving GW PDN GW
S1-U
S1-MME S11
S3
S4
S5
Internet
EPS Core
S12
SGi
HSS
S6a
S10
PCRF
Gx
Gxc
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LTE Key Radio Features (Release 8)
Multiple access scheme
DL: OFDMA with CP
UL: Single Carrier FDMA (SC-FDMA) with CP Adaptive modulation and coding
DL modulations: QPSK, 16QAM, and 64QAM
UL modulations: QPSK, 16QAM, and 64QAM (optional for UE)
Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders,
and a contention-free internal interleaver. ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer.
Advanced MIMO spatial multiplexing techniques
(2 or 4)x(2 or 4) downlink and 1x(2 or 4) uplink supported.
Multi-layer transmission with up to four streams.
Multi-user MIMO also supported.
Implicit support for interference coordination
Support for both FDD and TDD
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LTE Frequency Bands
LTE will support all band classes currently specified for UMTS as well asadditional bands
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OFDM Basics Overlapping Orthogonal
OFDM: Orthogonal Frequency Division Multiplexing
OFDMA: Orthogonal Frequency Division Multiple-Access
FDM/ FDMA is nothing new: carriers are separated sufficiently in frequencyso that there is minimal overlap to prevent cross-talk.
OFDM: still FDM but carriers can actually be orthogonal (no cross-talk)while actually overlapping, if specially designed saved bandwidth !
conventional FDM
frequency
OFDM
frequency
saved bandwidth
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OFDM Basics Waveforms
Frequency domain: overlapping sincfunctions
Referred to as subcarriers
Typically quite narrow, e.g. 15 kHz
Time domain: simple gated sinusoidfunctions
For orthogonality: each symbol hasan integer number of cycles overthe symbol time
fundamental frequency f0 = 1/T Other sinusoids with fk= k f0
4 5 6 7 8 9
x 105
-0.2
0
0.2
0.4
0.6
0.8
1
freq
Df = 1/T
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
time
T = symbol time
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OFDM Basics The Full OFDM Transceiver
Modulating the symbols onto subcarriers can be done verry efficiently inbaseband using the FFT algorithm
Serial toParallel
.
.
.
IFFT
bit
stream ..
.
Parallelto Serial
D/A
A/D
Serial to
Parallel
.
.
.FFT
.
.
.
OFDM Transmitter
OFDM Receiver
Parallel
to Serial
addCP
RFTx
RF
Rx
remove
CP
Encoding +Interleaving
+ Modulation
Demod +De-interleave
+ Decode
Estimated
bit stream
Channel estimation& compensation
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OFDM Basics Cyclic Prefix
ISI (between OFDM symbols) eliminated almost completely by inserting aguard time
Within an OFDM symbol, the data symbols modulated onto thesubcarriers are only orthogonal if there are an integer number ofsinusoidal cycles within the receiver window
Filling the guard time with a cyclic prefix (CP) ensures orthogonality ofsubcarriers even in the presence of multipath elimination of same cellinterference
CP Useful OFDM symbol time
OFDM symbol
CP Useful OFDM symbol time
OFDM symbol
CP Useful OFDM symbol time
OFDM symbol
OFDM Symbol OFDM Symbol OFDM Symbol
TG TG
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OFDM Basics Choosing the Symbol Time for LTE
Two competing factors in determining the right OFDM symbol time:
CP length should be longer than worst case multipath delay spread, and the OFDM
symbol time should be much larger than CP length to avoid significantoverhead from the CP
On the other hand, the OFDM symbol time should be much smaller than theshortest expected coherence time of the channel to avoid channel variabilitywithin the symbol time
LTE is designed to operate in delay spreads up to ~5 s and for speeds up to 350 km/h(1.2 ms coherence time @ 2.6 GHz). As such, the following was decided:
CP length = 4.7 s
OFDM symbol time = 66.6 s(= 1/20 the worst case coherence time)
Df = 15 kHz
CP
~4.7 s ~66.7 s
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Scalable OFDM for Different Operating Bandwidths
With Scalable OFDM, the subcarrier spacingstays fixed at 15 kHz (hence symbol time isfixed to 66.6 s) regardless of the operating
bandwidth (1.4 MHz, 3 MHz, 5 MHz, 10 MHz,15 MHz, 20 MHz)
The total number of subcarriers is varied inorder to operate in different bandwidths
This is done by specifying different FFT
sizes (i.e. 512 point FFT for 5 MHz, 2048point FFT for 20 MHz)
Influence of delay spread, Doppler due to usermobility, timing accuracy, etc. remain the sameas the system bandwidth is changed robust
design
common channels
10 MHz bandwidth
20 MHz bandwidth
5 MHz bandwidth
1.4 MHz bandwidth
3 MHz bandwidth
centre frequency
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LTE Downlink Frame Format
Subframe length is 1 ms consists of two 0.5 ms slots
7 OFDM symbols per 0.5 ms slot 14 OFDM symbols per 1ms subframe
In UL center SC-FDMA symbol used for the data demodulation referencesignal (DM-RS)
slot = 0.5ms slot = 0.5ms
subframe = 1.0ms
OFDM symbol
Radio frame = 10ms
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Multiple Antenna Techniques Supported in LTE
SU-MIMO Multiple data streams sent to the same user
(max. 2 codewords) Significant throughput gains for UEs in high
SINR conditions
MU-MIMO or Beamforming Different data streams sent to different users
using the same time-frequency resources Improves throughput even in low SINRconditions (cell-edge)
Works even for single antenna mobiles
Transmit diversity (TxDiv) Improves reliability on a single data stream Fall back scheme if channel conditions do
not allow SM Useful to improve reliability on common
control channels
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MIMO Support is Different in Downlink and Uplink
Downlink
Supports SU-MIMO, MU-MIMO, TxDiv
Uplink Initial release of LTE does only support MU-MIMO with a single transmit
antenna at the UE Desire to avoid multiple power amplifiers at UE
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LTE Duplexing Modes
LTE supports both Frequency Division Duplex (FDD) and Time DivisionDuplex (TDD) to provide flexible operation in a variety of spectrumallocations around the world.
Unlike UMTS TDD there is a high commonality between LTE TDD & LTE FDD
Slot length (0.5 ms) and subframe length (1 ms) is the same than LTEFDD with the same numerology (OFDM symbol times, CP length, FFT
sizes, sample rates, etc.)
UL/ DL switching pointsdesigned to allow co-existance with UMTS-TDD
(TD-CDMA, TD-SCDMA)
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UMTS Networks 28Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
LTE Half-Duplex FDD
In addition to FDD & TDD, LTE supports also Half-Duplex FDD (HD-FDD)
HD-FDD is like FDD, only the UE cannot transmit and receive at the sametime
Note, that the eNodeB can still transmit and receive at the same time todifferent UEs; half-duplex is enforced by the eNodeB scheduler
Reasons for HD-FDD
Handsets are cheaper, as no duplexer is required
More commonality between TDD and HD-FDD than compared to fullduplex FDD
Certain FDD spectrum allocations have small duplex space; HD-FDD leadsto duplex desense in UE
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UMTS Networks 29Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
LTE Downlink
The LTE downlink uses scalable OFDMA
Fixed subcarrier spacing of 15 kHz for unicast
Symbol time fixed at T = 1/15 kHz = 66.67 s
Different UEs are assigned different sets of subcarriers so that theyremain orthogonal to each other (except MU-MIMO)
Serial toParallel
.
.
.
IFFT
bitstream .
.
.
Parallelto Serial
addCP
Encoding +Interleaving+ Modulation
20 MHz: 2048 pt IFFT10 MHz: 1024 pt IFFT5 MHz: 512 pt IFFT
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UMTS Networks 30Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Physical Channels to Support LTE Downlink
eNodeB
Carries DL traffic
DL resource allocation
HARQ feedback for DL
CQI reporting
MIMO reporting
Time span of PDCCH
Carries basic systembroadcast information
Allows mobile to get timing andfrequency sync with the cell
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UMTS Networks 31Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Mapping between DL Logical, Transport and Physical Channels
LTE makes heavy use of sharedchannels common control,
paging, and part of broadcastinformation carried on PDSCHPCCH: paging control channel
BCCH: broadcast control channel
CCCH: common control channel
DCCH: dedicated control channel
DTCH: dedicated traffic channel
PCH: paging channel
BCH: broadcast channel
DL-SCH: DL shared channel
BCCHPCCH CCCH DCCH DTCH MCCH MTCH
BCHPCH DL-SCH MCH
Downlink
Logical channels
Downlink
Transport channels
Downlink
Physical ChannelsPDSCH PDCCHPBCH PHICHPCFICH PMCH
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UMTS Networks 32Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
LTE Uplink Transmission Scheme (1/2)
To facilitate efficient power amplifier design in the UE, 3GPP chose singlecarrier frequency domain multiple access (SC-FDMA) in favor of OFDMA
for uplink multiple access.
SC-FDMA results in better PAPR
Reduced PA back-off improved coverage
SC-FDMA is still an orthogonalmultiple access scheme
UEs are orthogonal in frequency
Synchronous in the time domainthrough the use of timing advance(TA) signaling
Only need to be synchronouswithin a fraction of the CP length
0.52 ms timing advance resolution
Node B
UE C
UE B
UE A
UE A Transmit Timing
UE B Transmit Timing
UE C Transmit Timing
a
b
g
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UMTS Networks 33Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
LTE Uplink Transmission Scheme (2/2)
SC-FDMA implemented using an OFDMA front-end and a DFT pre-coder, thisis referred to as either DFT-pre-coded OFDMA or DFT-spread OFDMA (DFT-SOFDMA)
Advantage is that numerology (subcarrier spacing, symbol times, FFTsizes, etc.) can be shared between uplink and downlink
Can still allocate variable bandwidth in units of 12 sub-carriers
Each modulation symbol sees a wider bandwidth
+1-1-1+1-1-1-1+1+1+1-1
DFT pre-coding
Serial toParallel IFFT
bit
stream ..
.
Parallelto Serial
addCP
Encoding +Interleaving+ Modulation
.
. DFT.
.
.
.
.Subcarriermapping
h l h l l k
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UMTS Networks 34Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Physical Channels to Support LTE Uplink
eNodeB
Random access for initialaccess and UL timing
alignment
UL scheduling grant
Carries UL Traffic
UL scheduling request fortime synchronized IEs
HARQ feedback for UL
Allows channel stateinformation to beobtained by eNB
M i b UL L i l T d Ph i l Ch l
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UMTS Networks 35Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Mapping between UL Logical, Transport and Physical Channels
CCCH DCCH DTCH
RACH UL-SCH
Uplink
Logical channels
Uplink
Transport channels
Uplink
Physical ChannelsPUSCH PUCCHPRACH
CCCH: common control channel
DCCH: dedicated control channel
DTCH: dedicated traffic channel
RACH: random access channel
UL-SCH: UL shared channel
PUSCH: physical UL shared channel
PUCCH: physical UL control channelPRACH: physical random access channel
D li k P k R t
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UMTS Networks 36Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Downlink Peak Rates
bandwidth
# of parallel streams supported
1 2 4
1.4 MHz 5.4 MBps 10.4 MBps 19.6 MBps
3 MHz 13.5 MBps 25.9 MBps 50 MBps
5 MHz 22.5 MBps 43.2 MBps 81.6 MBps
10 MHz 45 MBps 86.4 MBps 163.2 MBps
15 MHz 67.5 MBps 129.6 MBps 244.8 MBps
20 MHz 90 MBps 172.8 MBps 326.4 MBps
assumptions: 64QAM, code rate = 1, 1OFDM symbol for L1/L2, ignores subframes with P-BCH, SCH
U li k P k R t
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UMTS Networks 37Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Uplink Peak Rates
bandwidth
Highest Modulation
16 QAM 64QAM
1.4 MHz 2.9 MBps 4.3 MBps
3 MHz 6.9 MBps 10.4 MBps
5 MHz 11.5 MBps 17.3 MBps
10 MHz 27.6 MBps 41.5 MBps
15 MHz 41.5 MBps 62.2 MBps
20 MHz 55.3 MBps 82.9 MBps
assumptions: code rate = 1, 2PRBs reserved for PUCCH (1 for 1.4MHz), no SRS, ignores subframes with PRACH,takes into account highest prime-factor restriction
LTE R l 8 U E i t C t i
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UMTS Networks 39Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
LTE Release 8 User Equipment Categories
Category 1 2 3 4 5
Peak rate
Mbps
DL 10 50 100 150 300
UL 5 25 50 50 75
Capability for physical functionalities
RF bandwidth 20MHz
Modulation DL QPSK, 16QAM, 64QAM
UL QPSK, 16QAM QPSK,
16QAM,
64QAM
Multi-antenna
2 Rx diversity Assumed in performance requirements.
2x2 MIMO Not
supported
Mandatory
4x4 MIMO Not supported Mandatory
S h d li d R All ti (1/2)
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UMTS Networks 40Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Scheduling and Resource Allocation (1/2)
Basic unit of allocation is called a Resource Block (RB)
12 subcarriers in frequency (= 180 kHz)
1 timeslot in time (= 0.5 ms, = 7 OFDM symbols) Multiple resource blocks can be allocated to a user in a given subframe
The total number of RBs available depends on the operating bandwidth
12 sub-carriers
(180 kHz)
Bandwidth (MHz) 1.4 3.0 5.0 10.0 15.0 20.0
Number of availableresource blocks
6 15 25 50 75 100
Sched ling and Reso ce Allocation (2/2)
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UMTS Networks 41Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Scheduling and Resource Allocation (2/2)
LTE uses a scheduled, shared channel on both the uplink (UL-SCH) and thedownlink (DL-SCH)
Normally, there is no concept of an autonomous transmission; alltransmissions in both uplink and downlink must be explicitly scheduled
LTE allows "semi-persistent" (periodical) allocation of resources, e.g. for VoIP
14 OFDM symbols
12
subcarriers
Slot =0.5ms
Slot =0.5ms
UE A
UE B
UE C
Time
Frequen
cy
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UMTS Networks 42Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012
Uplink Power Control
Open-loop power control is the baselineuplink power control method in LTE
(compensation for path loss and fading) Open-loop PC is needed to constrain the
dynamic range between signals received fromdifferent UEs
Unlike CDMA, there is no in-cell interference tocombat; rather, fading is exploited by ratecontrol
Transmit power per PRBTxPSD(dBm) = aPL(dB) + P0nominal(dBm)
PLdB: pathloss, estimated from DL referencesignal
P0nominal (dBm) = nominal (dB) + Itot (dBm) Sum of SINR target
nominaland total interference
Itot sent on BCH
Fractional compensation factora 1 (PUSCH) only a fraction of the path loss is compensated
Additionally, (slow) closed loop PC can beused
June 2010 LTE Training
Page 42
TargetSINR
Target SINR on PUSCH is now a function ofthe UEs path loss:
SINR(dBm) = nominal (dB) + (1a)PL(dB)
Interference Coordination with Flexible Frequency Reuse
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Interference Coordination with Flexible Frequency Reuse
Cell edge users with frequency reuse > 1,
eNB transmits with higher power
Improved SINR conditions
Cell centre users can use whole frequency band
eNB transmits with reduced power
Less interference to other cells
Flexible frequency reuse realized throughintelligent scheduling and power allocation
a
b
g
a
b
g
a
b
g
a
b
g
a
b
g
a
b
g
a
b
g
a
b
g
a
b
g
ab
g
a
b
g
a
b
g
a
b
g
ab
g
Cell edge
Reuse > 1
Cell centre
Reuse = 1
Scheduler can place restriction on whichPRBs can be used in which sectors
Achieves frequency reuse > 1
Reduced inter-cell interference leads toimproved SINR, especially at cell-edge
Reduction in available transmissionbandwidth leads to poor overall spectralefficiency
0 1 2 3 4 5 6 7 8 9 10 11
Sectora Sectorb Sectorg
F1 F2 F3
Full Transmission Bandwidth
Random Access Procedure
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Random-Access Procedure
RACH only used for Random Access Preamble
Response/ Data are sent over SCH
Non-contention based RA to improve access time, e.g. for HO
UE eNB
RA Preamble assignment0
Random Access Preamble 1
Random Access Response2
UE eNB
Random Access Preamble1
Random Access Response 2
Scheduled Transmission3
Contention Resolution 4
Contention based RA Non-Contention based RA
LTE Handover
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LTE Handover
LTE uses UE-assisted network controlled handover
UE reports measurements; network decides when handover and to whichcell
Relies on UE to detect neighbor cells no need to maintain andbroadcast neighbor lists
Allows "plug-and-play" capability; saves BCH resources
For search and measurement of inter-frequency neighboring cells onlycarrier frequency need to be indicated
X2 interface used for handover preparation and forwarding of user data Target eNB prepares handover by sending required information to UE
transparently through source eNB as part of the Handover RequestAcknowledge message
New configuration information needed from system broadcast
Accelerates handover as UE does not need to read BCH on target cell Buffered and new data is transferred from source to target eNB until path
switch prevents data loss
UE uses contention-free random access to accelerate handover
LTE Handover: Preparation Phase
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LTE Handover: Preparation Phase
UEUESource
eNBSource
eNB
Measurement Control
TargeteNB
TargeteNB MMEMME sGWsGW
Packet Data Packet Data
UL allocation
Measurement Reports
HO decision
Admission Control
HO Request
HO Request Ack
DL allocation
RRC Connection Reconfig.
L1/L2signaling
L3 signaling
User data
HO decision is made by source eNB based on UE measurement report
Target eNB prepares HO by sending relevant info to UE through source eNB as part
of HO request ACK command, so that UE does not need to read target cell BCCH
SN Status Transfer
LTE Handover: Execution Phase
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LTE Handover: Execution Phase
UEUESource
eNBSource
eNB
TargeteNB
TargeteNB MMEMME sGWsGW
Detach from old cell,sync with new cell
Deliver buffered packets and forwardnew packets to target eNB
DL data forwarding via X2
Synchronisation
UL allocation and Timing Advance
RRC Connection Reconfig. Complete
L1/L2signaling
L3 signaling
User dataBuffer packets from
source eNB
Packet Data
Packet Data
RACH is used here only so target eNB can estimate UE timing and provide timing
advance for synchronization; RACH timing agreements ensure UE does not need to
read target cell P-BCH to obtain SFN (radio frame timing from SCH is sufficient to
know PRACH locations)
UL Packet Data
LTE Handover: Completion Phase
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LTE Handover: Completion Phase
UEUESource
eNB
TargeteNB
TargeteNB MMEMME sGWsGW
DL Packet Data
Path switch req
User plane update req
Switch DL path
User plane update responsePath switch req ACK
Release resources
Packet Data Packet Data
L1/L2signaling
L3 signaling
User data
DL data forwarding
Flush DL buffer,continue deliveringin-transit packets
End Marker
Release resources
Packet Data
End Marker
LTE Handover: Illustration of Interruption Period
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LTE Handover: Illustration of Interruption Period
UL
U-plane active
U-plane active
UEUESource
eNBSource
eNBTargeteNB
TargeteNB
UL
U-plane active
U-plane active
UEs stops
Rx/Tx on the old cell
DL sync
+ RACH (no contention)+ Timing Adv
+ UL Resource Req andGrant
ACK
HO Request
HO Confirm
Handover
Latency(approx 55 ms)
approx20 ms
MeasurementReport
HO Command
HO Complete
HandoverInterruption
(approx35 ms)
Handover Preparation
Tracking Area
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Tracking Area
BCCH
TAI 1
BCCH
TAI 1
BCCH
TAI 1
BCCHTAI 1
BCCH
TAI 1
BCCH
TAI 2
BCCH
TAI 2
BCCHTAI 2
BCCH
TAI 2
BCCH
TAI 2
BCCH
TAI 2
BCCH
TAI 3
BCCHTAI 3
BCCH
TAI 3
BCCH
TAI 3
Tracking Area 1
Tracking Area 2Tracking Area 3
Tracking Area Identifier (TAI) sent over Broadcast Channel BCCH
Tracking Areas can be shared by multiple MMEs
One UE can be allocated to multiple tracking areas
EPS Bearer Service Architecture
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EPS Bearer Service Architecture
P-GWS-GW Peer
Entity
UE eNB
EPS Bearer
Radio Bearer S1 Bearer
End-to-end Service
External Bearer
Radio S5/S8
Internet
S1
E-UTRAN EPC
Gi
E-RAB S5/S8 Bearer
LTE RRC States
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LTE RRC States
No RRC connection, no context ineNodeB (but EPS bearers are retained)
UE controls mobility through cellselection
UE specific paging DRX cycle controlledby upper layers
UE acquires system information frombroadcast channel
UE monitors paging channel to detectincoming calls
RRC connection and context in eNodeB
Network controlled mobility Transfer of unicast and broadcast data
to and from UE
UE monitors control channelsassociated with the shared datachannels
UE provides channel quality andfeedback information
Connected mode DRX can beconfigured by eNodeB according to UEactivity level
RRC_IDLE RRC_Connected
Release RRC connection
Establish RRC connection
EPS Connection Management States
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EPS Connection Management States
No signaling connection between UEand core network (no S1-U/ S1-MME)
No RRC connection (i.e. RRC_IDLE)
UE performs cell selection and trackingarea updates (TAU)
Signaling connection establishedbetween UE and MME, consists of twocomponents
RRC connection
S1-MME connection
UE location is known to accuracy of
Cell-ID Mobility via handover procedure
ECM_IDLE ECM_Connected
Signaling connection released
Signaling connection established
EPS Mobility Management States
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EPS Mobility Management States
EMM context holds no valid location orrouting information for UE
UE is not reachable by MME as UElocation is not known
UE successfully registers with MME withAttach procedure or Tracking AreaUpdate (TAU)
UE location known within tracking area
MME can page to UE
UE always has at least one PDN
connection
EMM_Deregistered
Detach
Attach
EMM_Registered
LTE Status
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LTE Status
LTE standard (Rel. 8) is stable
Rel. 8 frozen in 2Q2009
Since 2010, LTE has been deployed worldwide
Totally new infrastructure
First target was often to provide broadband coverage for fixed users
Currently, 111 LTE networks in 52 countries are in service (Nov. 2012)*
Implemented according to Release 8/9
Mostly FDD, but also some TDD networks Mobile packet data support with fallback to 3G/2G for CS voice service
Spectrum allocation in new frequency bands as well as existing 2G/3Gbands (refarming)
3GPP continues LTE development
Rel. 9: technical enhancements/ E-MBMS
Rel. 10/11: LTE-Advanced (cf. next slides)
*http://www.4gamericas.org -> Statistics
LTE-Advanced
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LTE Advanced
The evolution of LTE
Corresponding to LTE Release 10 and beyond
Motivation of LTE-Advanced
IMT-Advanced standardisation process in ITU-R
Additional IMT spectrum band identified in WRC07
Further evolution of LTE Release 8 and 9 to meet:
Requirements for IMT-Advanced of ITU-R
Future operator and end-user requirements
Work Item phaseStudy Item phase
First submiss ion
Final submissio n
LTE release 10 (LTE-Advanced)
2009 20102008
Proposals
Circular Letter
3GPP WS
IMT-Advanced
Specification
IMT-Advanc ed recommendation
Evaluation
3GPP
ITU
Evolution from IMT-2000 to IMT-Advanced
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Evolution from IMT 2000 to IMT Advanced
Interconnection
IMT-2000
Mobility
Low
High
1 10 100 1000Peak useful data rate (Mbit/s)
EnhancedIMT-2000
Enhancement
IMT-2000
Mobility
Low
High
1 10 100 1000
Area Wireless Acc ess
EnhancedIMT-2000
Enhancement
Digital Broadcast SystemsNomadic / Local Area Access Systems
New Nomadic / Loc al
IMT-Advanced w il l
encompass the
capabi l i t ies of p revious
systemsNew capabi l i t ies of
IMT-Advanced
New Mobi le
Access
5
7
System Performance Requirements
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Peak data rate
1 Gbps data rate will be achieved by 4-by-4 MIMO and transmissionbandwidth wider than approximately 70 MHz
Peak spectrum efficiency DL: Rel. 8 LTE satisfies IMT-Advanced requirement
UL: Need to double from Release 8 to satisfy IMT-Advanced requirement
Rel. 8 LTE LTE-Advanced IMT-Advanced
Peak data rate
DL 300 Mbps 1 Gbps
1 Gbps(*)
UL 75 Mbps 500 Mbps
Peak spectrum efficiency[bps/Hz]
DL 15 30 15
UL 3.75 15 6.75
*100 Mbps for high mobility and 1 Gbps for low mobility is one of the key features as written in
Circular Letter (CL)
y q
Technical Outline to Achieve LTE-Advanced Requirements
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q
Support wider bandwidth
Carrier aggregation to achieve wider bandwidth
Support of spectrum aggregation
Peak data rate, spectrum flexibility Advanced MIMO techniques
Extension to up to 8-layer transmission in downlink
Introduction of single-user MIMO up to 4-layer transmission in uplink
Peak data rate, capacity, cell-edge user throughput
Coordinated multipoint transmission and reception (CoMP) CoMP transmission in downlink
CoMP reception in uplink
Cell-edge user throughput, coverage, deployment flexibility
Relaying
Type 1 relays create a separate cell and appear as Rel. 8 LTE eNB toRel. 8 LTE UEs
Coverage, cost effective deployment
Further reduction of delay
AS/NAS parallel processing for reduction of C-Plane delay
Carrier Aggregation
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Frequency
System bandwidth,
e.g., 100 MHzCC, e.g., 20 MHz
UE capabilities
100-MHz case
40-MHz case
20-MHz case
(Rel. 8 LTE)
gg g
Wider bandwidth transmission using carrier aggregation
Entire system bandwidth up to, e.g., 100 MHz, comprises multiple basicfrequency blocks called component carriers (CCs)
Each CC is backward compatible with Rel. 8 LTE
Carrier aggregation supports both contiguous and non-contiguousspectrums, and asymmetric bandwidth for FDD
Advanced MIMO Techniques
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q
Extension up to 8-stream transmission forsingle-user (SU) MIMO in downlink
improve downlink peak spectrum
efficiency
Enhanced multi-user (MU) MIMO in
downlink Specify additional reference signals (RS)
Introduction of single-user (SU)-MIMO upto 4-stream transmission in uplink
Satisfy IMT requirement for uplink peak
spectrum efficiency
Max. 8 streams
Higher-order MIMO up
to 8 streams
Enhanced
MU-MIMO
CSI feedback
Max. 4 streams
SU-MIMO up to 4 streams
Coordinated Multipoint Transmission/ Reception (CoMP)
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p p ( )
Enhanced service provisioning, especiallyfor cell-edge users
CoMP transmission schemes in downlink
Joint processing (JP) from multiplegeographically separated points
Coordinated scheduling/beamforming(CS/CB) between cell sites
Similar for the uplink
Dynamic coordination in uplinkscheduling
Joint reception at multiple sites
Coherent combining or
dynamic cell selection
Joint transmission/dynamic cell selection
Coordinated scheduling/beamforming
Receiver signal processing at
central eNB (e.g., MRC, MMSEC)
Multipoint reception
Relaying
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eNB RNUE
Cell ID #x Cell ID #y
Higher node
y g
Type 1 relay
Relay node (RN) creates a separate cell distinct from the donor cell
UE receives/transmits control signals for scheduling and HARQ from/to RN
RN appears as a Rel. 8 LTE eNB to Rel. 8 LTE UEs
Deploy cells in the areas where wired backhaul is not available or very
expensive
Heterogenous Networks (HetNet)
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Network expansion due to varying traffic demand & RF environment Cell-splitting of traditional macro deployments is complex and iterative Indoor coverage and need for site acquisition add to the challenge
Future network deployments based on Heterogeneous Networks Deployment of Macro eNBs for initial coverage only Addition of Pico, HeNBs and Relays for capacity growth & better user experience
Improved in-building coverage and flexible site acquisition with low power base stations Relays provide coverage extension with no incremental backhaul expense
eICIC is introduced in LTE Rel-10 and further enhanced in Rel-11 Time domain interference management Cell range expansion Interference cancellation receiver in the terminal
LTE References
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Literature:
H. Holma/ A. Toskala (Ed.): LTE for UMTS - OFDMA and SC-FDMA Based RadioAccess, 2nd edition, Wiley 2011
E. Dahlman et al: 3G Evolution, HSPA and LTE for Mobile Broadband, 3rd edition,Academic Press 2011
S. Sesia et al:LTE, The UMTS Long Term Evolution: From Theory to Practice,Wiley 2011
T. Nakamura (RAN chairman): Proposal for Candidate Radio InterfaceTechnologies for IMT-Advanced Based on LTE Release 10 and Beyond LTE-Advanced), ITU-R WP 5D 3rd Workshop on IMT-Advanced, October 2009
Standards
TS 36.xxx series: RAN Aspects
TS 36.300 E-UTRAN; Overall description; Stage 2
TR 25.912Feasibility study for evolved Universal Terrestrial Radio Access (UTRA)and Universal Terrestrial Radio Access Network (UTRAN)
TR 25.814Physical layer aspect for evolved UTRA TR 23.8823GPP System Architecture Evolution: Report on Technical Options and
Conclusions
TR 36.912 Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)
TR 36.814 Further Advancements for E-UTRA - Physical Layer Aspects
Abbreviations
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CP Cyclic Prefix
DFT Discrete Fourier Transformation
DRX Discontinuous Reception
ECM EPS Connection Management
EMM EPS Mobility Management
eNodeB/eNB Evolved NodeB
EPC Evolved Packet Core
EPS Evolved Packet System
E-UTRAN Evolved UMTS Terrestrial Radio AccessNetwork
FDD Frequency-Division DuplexFDM Frequency-Division Multiplexing
FFT Fast Fourier Transformation
HD-FDD Half-Duplex FDD
HO Handover
HOM Higher Order Modulation
HSS Home Subscriber Server
IFFT Inverse FFT
ISI Inter-Symbol Interference
LTE Long Term Evolution
MIMO Multiple-Input Multiple-Output
MME Mobility Management Entity
MU Multi-User
OFDM Orthogonal Frequency-DivisionMultiplexing
OFDMA Orthogonal Frequency-Division
Multiple-AccessPCRF Policy & Charging Function
PDN Packet Data Network
P-GW PDN Gateway
RA Random Access
RB Resource Block
RRC Radio Resource Control
SAE System Architecture EvolutionSCH Shared Channel
S-GW Serving Gateway
SC-FDMA Single Carrier FDMA
SU Single User
TDD Time-Division Duplex
TA Timing Advance/ Tracking Area
TAI Tracking Area Indicator
TAU Tracking Area Update
UE User Equipment
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