3G Long-Term Evolution (LTE) andSystem Architecture Evolution (SAE)
BackgroundSystem ArchitectureRadio InterfaceRadio Resource ManagementLTE-Advanced
Cellular Communication Systems 2Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
3GPP Evolution Background
3G Long-Term Evolution (LTE) is the advancement of UMTS with the followingtargets:
Significant increase of the data rates: mobile broadbandSimplification of the network architectureReduction of the signaling effort esp. for activation/ deactivation
Work in 3GPP started in Dec 2004LTE is not backward compatible to UMTS HSPA.LTE is a packet only network there is no support of circuit switchedservices (no MSC).LTE started on a clean state everything was up for discussion includingthe system architecture and the split of functionality between RAN and CN.
Since 2010, LTE has been further enhancedLTE-Advanced with increased performance targetsApplication of new scenarios (MTC) and novel concepts (D2D)
Cellular Communication Systems 3Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
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
34x HSPA Rel.6 in DL*
23x HSPA Rel.6 in UL
1 bps/Hz broadcast
Improved Cell Edge Rates
23x HSPA Rel.6 in DL*
23x HSPA Rel.6 in UL
Full broadband coverage
Support Scalable BW
1.4, 3, 5, 10, 15, 20 MHz
Low Latency
< 5 ms user plane (UE to RAN edge)
< 100 ms camped to active
< 50 ms dormant to active
Packet Domain Only
High VoIP capacity
Simplified network architecture
* Assumes2x2 in DLfor LTE,
but 1x2 forHSPA Rel.6
Cellular Communication Systems 4Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
Key Features of LTE to Meet Requirements
Selection of OFDM for the air interfaceLess receiver complexityRobust to frequency selective fading and inter-symbol interference (ISI)Access to both time and frequency domain allows additional flexibility inscheduling (including interference coordination)Scalable OFDM makes it straightforward to extend to differenttransmission bandwidths
Integration of MIMO techniquesPilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMOin the UL
Simplified network architectureReduction in number of logical nodes flatter architectureClean separation between user and control plane
Cellular Communication Systems 5Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
Network Simplification: From 3GPP to 3GPP LTE
3GPP architecture4 functional entities on thecontrol plane and user plane3 standardized user plane &control plane interfaces
3GPP LTE architecture2 functional entities on theuser plane: eNodeB and S-GWSGSN control plane functions
MMELess interfaces, somefunctions disappeared
4 layers into 2 layersEvolved GGSN integratedP-GWMoved SGSN functionalities toS-GWEvolutions to RRM on an IPdistributed network forenhancing mobilitymanagementPart of RNC mobility functionmoved to MME & eNodeB
GGSN
SGSN
RNC
NodeB
ASGW
eNodeB
MMFGGSN
SGSN
RNC
NodeB
Control plane User plane
ASGW
eNodeB
MMF
S/P-GW
eNodeB
MME
Control plane User plane
S/P-GW: Serving/PDN GatewayMME: Mobility Management Entity
eNodeB: Evolved NodeB
Cellular Communication Systems 6Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
Evolved UTRAN Architecture
eNB
eNB
eNB
MME/S-GW MME/S-GW
X2
EPCE-U
TRAN
S1
S1
S1S1
S1S1
X2
X2
EPC = Evolved Packet Core
Key elements of networkarchitectureNo more RNCRNC layers/functionalitiesmostly moved in eNBX2 interface for seamlessmobility (i.e. data/context forwarding) andinterferencemanagement
Note: Standard onlydefines logical structure/Nodes !
Cellular Communication Systems 7Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
EPS Architecture Functional description of the Nodes
eNodeB contains allradio access functionsRadio ResourceManagementScheduling of UL & DLdataScheduling and trans-mission of paging andsystem broadcastIP header compression& encryption
Serving GatewayLocal mobility anchor for inter-eNB handoversMobility anchor for inter-3GPP handoversIdle mode DL packet bufferingLawful interceptionPacket routing and forwarding
PDN GatewayConnectivity to Packet Data NetworkMobility anchor between 3GPP and non-3GPP accessUE IP address allocation
MME control plane functionsIdle mode UE reachabilityTracking area list managementS-GW/P-GW selectionInter core network node signalingfor mobility bw. 2G/3G and LTENAS signalingAuthenticationBearer management functions
Cellular Communication Systems 8Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
EPS Architecture User Plane Layout over S1
UE eNodeB MME
S-Gateway
RLC sub-layer performs:Transfer of upper layer PDUsError correction through ARQReordering of RLC data PDUsDuplicate detectionFlow controlSegmentation/ Concatenation of SDUs
PDCP sub-layer performs:Header compressionCiphering
MAC sub-layer performs:Mapping of logical channels totransport channelsSchedulingError correction through HARQPriority handling across UEs & logicalchannels
Physical sub-layer performs:ModulationCoding (FEC)UL power controlMulti-stream transmission &reception (MIMO)
Cellular Communication Systems 9Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
EPS Architecture Control Plane Layout over S1
UE eNodeB MME
RRC sub-layer performs:BroadcastingPagingRRC Connection ManagementRadio bearer controlMobility functionsUE measurement reporting & control
PDCP sub-layer performs:Integrity protection & ciphering
NAS sub-layer performs:AuthenticationSecurity controlIdle mode mobility handling/paging origination
Cellular Communication Systems 10Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
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 GWS1-U
S1-MME S11
S3
S4
S5
Internet
EPS Core
S12
SGi
HSSS6a
S10
PCRF
GxGxc
Cellular Communication Systems 11Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
LTE Key Radio Features (Release 8)
Multiple access schemeDL: OFDMA with CPUL: Single Carrier FDMA (SC-FDMA) with CP
Adaptive modulation and codingDL modulations: QPSK, 16QAM, and 64QAMUL 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 coordinationSupport for both FDD and TDD
Cellular Communication Systems 12Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
LTE Frequency Bands
LTE will support all band classes currently specified for UMTS as well asadditional bands
Cellular Communication Systems 13Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
OFDM Basics Overlapping Orthogonal
OFDM: Orthogonal Frequency Division MultiplexingOFDMA: Orthogonal Frequency Division Multiple-AccessFDM/ 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
Cellular Communication Systems 14Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
OFDM Basics Waveforms
Frequency domain: overlapping sincfunctions
Referred to as subcarriersTypically quite narrow, e.g. 15 kHz
Time domain: simple gated sinusoidfunctions
For orthogonality: each symbol hasan integer number of cycles overthe symbol timefundamental frequency f0 = 1/TOther sinusoids with fk = k f0
f = 1/T
freq.
time
T = symbol time
0 1 2 3 4 5 6-0.2
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1-1
-0.5
0
0.5
1
Cellular Communication Systems 15Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2017
OFDM Basics The Full OFDM Transceiver
Modulating the symbols onto subcarriers can be done very efficiently inbaseband using the FFT algorithm
SerialParallel
..
. IFFT
bitstream .
..
Parallelto Serial
D A
D ASerial toParallel
..
.FFT
..
.
OFDM Transmitter
OFDM Receiver
ParallelSerial
addCP
RFTx
RFRx
removeCP
Encoding +Interleaving+ Modulation
Demod +De-
