Download - Part1 - Techno
12/12/08 2LTE Part 1 - DIAM
LTE - Content
Overview
Overall architecture
E-UTRAN in-depth Architecture
Radio protocol
Transport
Security
QoS
Mobility Idle Mode
Connected Mode
Impacts Access Network
Other (GERAN, Terminals, services, Voice continuity…)
12/12/08 3LTE Part 1 - DIAM
Terminology SAE (System Architecture Evolution) and LTE (Long Term Evolution) terms should no longer
be used
The following should be preferred (as in 3GPP standard documents): E-UTRAN – Evolved UTRAN
EPC – Evolved Packet Core
EPS – Evolved Packet System, i.e. [ E-UTRAN + EPC ]
Standard state
Work item initiated in 2005 in 3GPP, first stage 2 document in 2006
RAN ASN1 protocols to be frozen in Sept 2008
CT protocols completion is expected Dec 2008 (Common IMS is a big part of R8)
SA groups still have a lot to do: O&M, billing, …
LTE - Overview
No mature commercial grade product before 2011/2012
12/12/08 4LTE Part 1 - DIAM
Throughput
Downlink peak data rate of 100Mb/s within 20 MHz (2 receive antennas at terminal)
Uplink peak data rate of 50Mb/s within 20MHz (1 transmit antenna at terminal)
Latency
Less than 5ms latency from the E-UTRAN Access GW and the terminal
State transition
The transition from Idle to an Active state shall be less than 100ms (excluding time for paging)
The transition between Active and Standby states shall be less than 50ms
LTE – Expectations (as in 3GPP TS 25.913)
Camped(idle)
Active(Cell_DCH)
Dormant(Cell_PCH)
Less than 100 msec
Less than 50 msec
12/12/08 5LTE Part 1 - DIAM
Is LTE a 4G standard ?
IMT-Advanced (4G) activities have already started in ITU-R (Circular Letter under discussion)
From a 3GPP perspective, 4G will most probably be a "LTE phase 2"
4G expectations voiced in the press:
1Gb/s peak over 100MHz bandwidth
Scalable bandwidth
All IP
Always-On
Advanced MIMO
…
LTE - Overview
PROPOSALSPROPOSALS
EVALUATIONEVALUATIONRevision of proposalsRevision of proposals
CONSENSUS BUILDINGCONSENSUS BUILDINGinside & outside of ITUinside & outside of ITU / / Revision of proposalsRevision of proposals
20082008 20092009#23 #24 #25 #26 #27 #28
Circular Letter forIMT-Advanced
20072007#21 #22
Evaluation criteria and methodology based
on the requirements (IMT.EVAL)
#29
Requirements related totechnical system
performance (IMT.TECH)
ServicesRecommendation
(IMT.SERV)
IMT
-Ad
van
ce
dW
OR
KS
HO
P
IMT.RADIO
20102010#30 #31
IMT.RSPEC
preliminarypreliminaryEVALUATIONEVALUATION
ITU-R 8F meetings
:
Jan. May Feb. June Oct. Feb. June Oct. Feb. June Oct.
"4G" sounds like an "evolved LTE"
12/12/08 6LTE Part 1 - DIAM
The MME (Mobility Management Entity) supports the control signalling Session setup, location management, authentication, bearer management
The S-GW is a 3G/2G mobility anchor point
The PDN-GW plays the same role as the GGSN (IP allocation, Policy enforcement, …)
The "S-GW + PDN-GW" collapsed deployment looks like the "One Tunnel" solution
LTE - Overall architecture
SGi
S12
S3
S1-MME
PCRF
S7
S6a
HSS
Operator’s IP Services (e.g. IMS, PSS etc.)
Rx+
S10
UE
UTRAN
GERANSGSN
“LTE-Uu”
E-UTRAN
MME
S11
S5ServingGateway
PDNGateway
S1-U
S4
12/12/08 7LTE Part 1 - DIAM
eNodeB is the only E-UTRAN node Radio resource allocation, radio protocol implementation, radio mobility support, physical layer support, …
A flavor of I-HSPA… but not quite the same (X2 is not Iur)
S1 is a UMTS/Iu equivalent S1-flex is possible from day-1
Supports: SAE bearer management, radio mobility management, …
X2 is a kind of UMTS/Iur equivalent X2 user data traffic load is much lower than Iur (no soft handover)
X2 is actually a meshed interface – full eNB connectivity is however not needed
Supports: Radio mobility management, user data forwarding, load information sharing
Is X2 an optional interface ??
Both X2, S1 are based on SCTP/IP for the Control Plane – SCTP is inherited from UTRAN/IP
GTP/UDP/IP for the User Plane – same transport layers as EPC User plane
LTE – E-UTRAN architecture
eNB
MME / S-GW MME / S-GW
eNB
eNB
S1
S1
S1 S
1
X2
X2X2
E-UTRAN
12/12/08 8LTE Part 1 - DIAM
NAS (Non Access Stratum) refers to EMM (Evolved Mobility Management) – the evolution of GMM and SM GPRS protocols
Attach – detach – location management – service request
No more MM and CC protocols in NAS (because CS domain disappears)
LTE – end-to end Control plane
SCTP
L2
L1
IP
L2
L1
IP
SCTP
S1-MME eNodeB MME
S1-AP S1-AP
NAS
MAC
L1
RLC
PDCP
UE
RRC
MAC
L1
RLC
PDCP
RRC
LTE-Uu
NAS Relay
12/12/08 9LTE Part 1 - DIAM
Packet Core transport is still GTP based An IETF based PMIP UP solution is also proposed – as an alternative to GTP
LTE – end-to end User plane
Serving GW PDN GW
S5/S8a
GTP-U GTP-U
UDP/IP UDP/IP
L2
Relay
L2
L1 L1
PDCP
RLC
MAC
L1
IP
Application
UDP/IP
L2
L1
GTP-U
IP
SGi S1-U LTE-Uu
eNodeB
RLC UDP/IP
L2
PDCP GTP-U
Relay
MAC
L1 L1
UE
Same principles as in UTRANThe location and hierarchy of radio protocols is preserved
12/12/08 10LTE Part 1 - DIAM
Usual 3-level channel modelling - as in UMTS
But simplified model (less channel types for user data transport)
Logical channel – what is transmitted (data, control / broadcast / paging , …)BCCH – broadcast PCCH – paging
CCCH – common control
MCCH – multicast control DCCH – dedicated control
DTCH – dedicated traffic MTCH – multicast traffic
Transport channel – how it is transmitted (channel coding, modulation type, …)BCH – broadcast PCH – paging
MCH – multicast RACH – random access
DL-SCH – downlink shared UL-SCH – uplink shared
Physical channel – the real radio physical channelPBCH – broadcast PRACH – paging
PMCH – multicast
PDSCH – downlink shared data PUSCH – uplink shared data
PDCCH – downlink control PUCCH – uplink control
LTE – Radio channels
12/12/08 11LTE Part 1 - DIAM
LTE – Radio channels
PCCH BCCH CCCH DCCH DTCH MCCH MTCHLogical Channels
Transport Channels
PhysicalChannels
PCH BCH RACHMCH
PBCH PDSCHPUSCH
DL-SCH
PMCHPDSCH PDSCH
DL-SCH UL-SCH
PRACH
BCH PCH FACHRACH
BCCH DCCH CCCHPCCH
DCH
DTCH
Transport Channels
Logical Channels
CTCH
HS-DSCHE-DCH
MSCHMCCH MTCH
Very straightforward channel mapping
UTRAN toolbox complexity
12/12/08 12LTE Part 1 - DIAM
•2G was TDMA/FDMA
•3G had to be CDMA
•3G+ and 4G are/will be OFDM based
•OFDM already used in DAB, DVB, ADSL, 802.11g, 802.16
•LTE uses OFDMA for downlink / SC-OFDM for uplink / and MIMO Scalable OFDM (from 1,25MHz to 20 MHz)
QPSK / 16QAM / 64QAM modulations for both UL and DL
Channel coding (1/3 turbo & convolutional coding)
0,5 ms slot and 1 ms TTI (means short interleaving and transmission delay)
LTE – Physical layer
…
S u b -c a r r ie rsF F T
T im e
S y m b o ls
5 M H z B a n d w id th
G u a rd I n te rv a ls
…
F r e q u e n c y
12/12/08 13LTE Part 1 - DIAM
Allocated radio resources are time and frequency multiplexed
Cell are characterized by: Fc (central Frequency)
NRB (number of resource block) – 6 possible values
In this picture NRB = 25 Cell Channel Bandwidth = 5MHz
Transmission Bandwidth Configuration [NRB]
Channel Bandwidth [MHz]
Resource block12 x 15KHz carriers = 180KHz
Channel edge
DC carrier (downlink only)
Time
. . .
One 0,5 ms slot = 7 OFDM symbols per 15KHz OFDM sub-carrier
NRB Channel Bandwidth
6 1,4 MHz
15 3 MHz
25 5 MHz
50 10 MHz
75 15 MHz
100 20 MHz
LTE – Physical layer
12/12/08 14LTE Part 1 - DIAM
MAC (Medium Access Control / 3GPP 36.321)
Looks like a all-in-one-box HSPA MAC
Reduced numbers of transport channels Priority handling – between users and channels of one user
Multiplexing / de-multiplexing of MAC-SDU into MAC-PDU
HARQ based error correction
Logical to transport channel mapping
UE DRX support on PDCCH
LTE – MAC Radio protocol
NEW
BCCHPCCH CCCH DCCH DTCH MCCH MTCH
BCHPCH DL-SCH MCH
DownlinkLogical channels
DownlinkTransport channels
CCCH DCCH DTCH
UL-SCHRACH
UplinkLogical channels
UplinkTransport channels
UE shall monitor PDCCH
On Duration
DRX Cycle
Opportunity for DRX
12/12/08 15LTE Part 1 - DIAM
RLC (Radio Link Control / 3GPP 36.322)
Principles and features are very similar to UMTS
LTE-RLC is defined as a very generic Layer 2 protocol
The classical 3 modes of operation: TM (Transparent) – does nothing except peer-to-peer transmission (for BCCH, PCCH)
UM (Unacknowledged) – segmentation, concatenation, re-ordering, loss detection
AM (Acknowledged) – like UM + transmission window and ARQ based error correction
LTE – RLC Radio protocol
RLC header
RLC PDU
......
n n+1 n+2 n+3RLC SDU
12/12/08 16LTE Part 1 - DIAM
PDCP (Packet Data Convergence Protocol / 3GPP 36.323): RoHC defined as a basis for "IP and above" overhead compression (applies to RTP/TCP/UDP/IP)
New RoHC V2 framework and profiles have been taken into account (more robust / less complex)
user data ciphering (refers to user data as well as application level signalling – SIP/SDP/RTCP)
control plane integrity protection (refers to NAS and RRC signalling)
LTE – PDCP Radio protocol
Radio Interface (Uu)
UE/E-UTRAN E-UTRAN/UE
Transmitting PDCP entity
Ciphering
Header Compression (u-plane only)
Receiving PDCP entity
Sequence numbering
Integrity Protection (c-plane only)
Add PDCP header
Header Decompression (u-plane only)
Deciphering
Remove PDCP Header
Re-ordering (u-plane only)
Integrity Protection (c-plane only)
Packets associated to a PDCP SDU
Packets associated to a PDCP SDU
Packets not
associated to a P
DC
P S
DU
Packets not
associated to a P
DC
P S
DU
NEW
12/12/08 17LTE Part 1 - DIAM
RRC (Radio Resource Control / 3GPP 36.331): Same features as in UTRAN (Broadcast / Paging / Connection mgt / Resource mgt / Radio mobility mgt / …)
A very simplified two-state RRC machine
• Because there is only one type of transport channel for user data
• And also because MAC DRX mode helps to reduce signalling and save battery when inactive
LTE – RRC Radio protocol
Handover
CELL_PCH
URA_PCH
CELL_DCH
UTRA_Idle
E-UTRA RRC_CONNECTED
E-UTRA RRC_IDLE
GSM_Idle/GPRS Packet_Idle
GPRS Packet transfer mode
GSM_Connected
Handover
Reselection Reselection
Reselection
Connection establishment/release
Connection establishment/release
Connection establishment/release
CCO, Reselection
CCO with NACC
CELL_FACH
CCO, Reselection
NEW
12/12/08 18LTE Part 1 - DIAM
LTE – QoS
One EPS Bearer = one PDP Context
One EPS bearer = Radio bearer +
S1 Bearer +
S5/S8 bearer
Serving GW PDN GWeNB
Radio Bearer S5/S8 Bearer
Application / Service Layer
DL Service Data Flows
S1 Bearer
UE
UL Service Data Flows
Serving GW PDN GW
Application / Service Layer
UE
EPS Bearer
Some rewording …
but same UMTS underlying concepts
12/12/08 19LTE Part 1 - DIAM
LTE – QoS•The main difference with UMTS/R99 is about QoS representation
•EPS QoS definition looks closer to initial GPRS parameter set than R99 UMTS toolbox
•Notion of label or QCI (Quality Class Identifier) to limit the number of combinations
Decreases implementation complexity
Allows same network behaviour across different manufacturers
R97/98 PDP attributes R99 PDP attributes EPS bearer attributes
Delay classTraffic class
Bearer typeTraffic handling priority
Reliability class
SDU error ratio
L2PLRResidual bit error ratio
Delivery of erroneous SDU
Peak throughput classMax bit rate for uplink
MBRMax bit rate for downlink
Precedence class ARP ARP
Mean Throughput Not applicable Not applicable
Not applicable Max SDU size Not applicable
Reordering required Delivery order Delivery order
Not applicable Transfer delay L2PDB
Not applicable Guaranteed bit rate GBR
Not applicable Not applicable AMBR
QCI value L2 Packet Delay Budget
L2 Packet Loss Rate
Example Services
1 (GBR) < 50 ms High (e.g.10-1) Realtime Gaming
2 (GBR) 50 ms (80 ms) Medium (e.g.10-2) VoIMS
3 (GBR) 250 ms Low (e.g.10-3) Streaming4 (non-GBR) Low (~50 ms) e.g. 10-6 IMS signalling
5 (non-GBR) Low (~50ms) e.g. 10-3 Interactive Gaming
6 (non-GBR) Medium(~250ms) e.g. 10-4 TCP interactive
7 (non-GBR) Medium(~250ms) e.g. 10-6 Preferred TCP bulk data8 (non-GBR) High (~500ms) n.a. Best effort TCP bulk data
QCI examples (will eventually become normative)
QoS attributes mapping
NEW
12/12/08 20LTE Part 1 - DIAM
Authentication and Security still makes use of SIM/UICC cards (to maintain backward compatibility)
All security mechanisms are fed by keys derived from K – secret key shared by the subscriber and the network
Same features as in UMTS: Signalling integrity protection
User data and control ciphering
Mutual network – subscriber authentication
But … 2G/GSM SIM access is prevented (64 bit key length is not seen as secure enough)
New key hierarchy to protect each information flows:
LTE – Security
USIM / AuC
UE / MME
UE / ASME
KASME
K
KUPenc
KeNBKNASint
UE / HSS
UE / eNB
KNASenc
CK, IK
KRRCint KRRCenc
NEW
12/12/08 21LTE Part 1 - DIAM
All 3 types of information flows are protected User plane (ciphering in eNodeB)
RRC Control plane (protected by eNodeB)
NAS signalling (protected by MME)
Network Domain Security (NDS) is applied to each interface (S1, X2, …) Security protection is ensured by IPsec/ESP
Key exchange is performed through IKE
LTE – Security
KNASenc
KNASint
KRRCint
KRRCenc
KUPenc S-GW
MME
eNodeB
RRC
NEW
Algorithms
UIA1/UEA1 (Kasumi) Possibly not for E-UTRAN
UIA2/UEA2 (SNOW) Maintained
AES based algo TBD as an alternative to SNOW
12/12/08 22LTE Part 1 - DIAM
•In LTE IDLE mode, the terminal location is known at the TA level (Tracking Area)
•The UTRAN Registration Area (URA) disappears
•TA is the LTE equivalent of LA and RA – a subscriber localization area for Core Network use
•Notion of "multi TA registration" so as to limit the amount of "TA update" procedures
•Re/selection criteria is RSRP based and very similar to UTRAN (25.304)
RSRP is the equivalent to UTRAN CPICH RSCP
LTE – Mobility in Idle mode
RA1 RA2 RA3
LA1 LA2
RA4
LA3
RA5
URA1 URA2 URA3
RA(s) handled by one 3G_SGSN
LA(s) handled by one 3G_MSC/VLR
CellLA RA
LA(s) and RA(s) handled by one UMSC
URA
The 3G/UTRAN location management system The LTE vision
This terminal is registered in TA1, 2 and 3
Reference signal received power (RSRP): the linear average over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals within the considered measurement frequency bandwidth.
12/12/08 23LTE Part 1 - DIAM
LTE – Mobility in connected mode
1. The initial data path
2. The new data path via the target eNB
3. The "data forwarding path" (all unsent packets being buffered at source eNB are forwarded to the target eNB)
eNB
MME / S-GW MME / S-GW
eNB
eNB
S1
S1
S1 S
1
X2
X2X2
E-UTRAN
1
2
3•Looks like a GSM "external" handover
•No longer Access Anchor point (as there is no more SRNC)
•If X2 not present, forwarding can be done through S1
Can X2 be an option WRT handover QoE ?
Some remarks
Inter-eNodeB handover example
12/12/08 24LTE Part 1 - DIAM
Spectral efficiency
LTE = HSDPA x 4 in downlink
LTE = HSUPA x 3 in uplink
LTE - Performances
MetricAverage sector throughput
and spectral efficiency(x 3GPP Rel. 6)
3G UTRAN baseline - HSDPA(5MHz, 3GPP R6)
2.0 Mbps0.39 bps/Hz/sector
(x1.0)
LTE1 x 2 Single Antenna10 MHz bandwidth / Reuse 1
16.3 Mbps1.63 bps/Hz/sector
(x4.2)
LTE2 x 2 TX diversity10 MHz bandwidth / Reuse 1
16.7 Mbps1.67 bps/Hz/sector
(x4.3)
LTE4 x 2 MU-SDMA10 MHz bandwidth / Reuse 1
25.0 Mbps2.50 bps/Hz/sector
(x6.4)
4G expectations (as in ITU-R)100 Mbps / 1 Ggps
10 bps/Hz/sector
The tables below are simulation results presented in 3GPP (R1-071967 / R1-071968)
MetricAverage sector throughput
and spectral efficiency(x 3GPP Rel. 6)
3G UTRAN baseline - HSUPA(5MHz, 3GPP R6)
1.4 Mbps0.28 bps/Hz/sector
(x1.0)
LTE1 x 2 RX diversity10 MHz bandwidth
7.4 Mbps0.74 bps/Hz/sector
(x2.6)
LTEInterference coordination10 MHz bandwidth
8.4 Mbps0.84 bps/Hz/sector
(x3.0)
For the Downlink For the Uplink
12/12/08 25LTE Part 1 - DIAM
Frequency planning is now required – can possibly be self optimized (at least partially)
Can shape cell frequency occupancy depending on expected traffic (like in GSM) in number of 15KHz carriers
New antenna configuration (depends on which MIMO scheme is deployed)
Transport dimensioning evolution
LTE – Access Network impacts
All IP - at the user data and service level (no more CS domain)
All IP - at the transport level
All packet - at the radio level, mixing all kinds of traffic (RT and non-RT)
No more compressed mode (monitoring windows result from scheduling holes)
No more “soft handover”
No more “dedicated versus shared” channel arbitration – one unique LTE Radio UL/DL fat pipe
No more “dedicated channel reconfiguration” algorithms to tune
12/12/08 26LTE Part 1 - DIAM
OFDMA is a variant of TDMA/FDMA
A simple CDMA "reuse 1" is not possible (too many inter-Cell interferences)
3GPP solutions are currently being discussed Dynamic but semi-static configuration is still required SON (Self Optimized Network) remains one of the key LTE items
"Fractional Frequency Reuse" WiMAX-like deployment solutions seem to be preferred Allows single carrier deployment But can be very limiting at cell edge
LTE – Planning aspects
Users in inner part of the cell may be assigned the full spectrum.
Users at the outer part of the cell may only be assigned part of the full spectrum.
1
2
3
4
5
6
7
12/12/08 27LTE Part 1 - DIAM
Geran impacts Use of SI2Quater and PSI3Quater to support E-UTRAN Neighbouring Cell List information
E-UTRAN cells are identified by Central Frequency and Physical Cell ID (to be confirmed)
Terminal impacts Single radio terminals for VCC is still a study item
SA2 decision to only support dual radio terminals in R8
Dual radio terminals are not seen as a viable solution (cost, battery, …)
Service impacts 2G only subscribers with LTE terminals cannot access EPS networks
Emergency calls on VoIP
Voice service continuity becomes critical. As of today, 3 solutions: VCC (Voice Call Continuity) based on "CS over PS access" T-Mobil initiated work item (as in 3GPP TS 23.879)
VCC based on an IMS solution (as in 3GPP TS 23.206)
CS Fallback (as in 3GPP TS 23.272)
LTE – Other impacts
12/12/08 28LTE Part 1 - DIAM
LTE Voice 1/3 – VCC (Voice Call Continuity)
The 23.206 VCC solution Relies on a network 3pc (3rd party call control): the DTF (Domain Transfer Function)
When in LTE, the call in anchored in IMS
When in 3G, the call is also anchored in IMS, via the CS domain and CS radio bearer path (seen as a CS
call from the terminal)
VCC UE#A
IMS+IP-BB
VMSC
IMS UE#B
S-CSCFMGCF
MGW
DTFSwitched End to End
CS Radio
IP-CAN
IMS+IP Leg
Remote Leg
(IMS+IP)
Control Plane
User Plane
CS Leg
Requires terminal adaptation (interworking between CS and PS domains)Requires VoIP to be fully supported (as well as supplementary services over IMS)
12/12/08 29LTE Part 1 - DIAM
LTE Voice 2/3 – VCC (Voice Call Continuity)
The 23.879 “CS over PS access” solution Objective is to allow “CS domain controlled voice calls over EPS” Legacy CS domain is preserved
Voice calls are anchored at the MSC level and Supplementary Services are preserved
When in EPS, the MSC is perceived as an Application Server
Changes at the MSC (MGW role)
Significant changes in terminal (CC/MM NAS is transported over TCP/IP and speech over RTP)A lot of work to do in 3GPP (3 alternatives are still being discussed)
UE
BTS/BSC
NodeB/RNC
eNodeBS-GW/PDN-
GW
eMSC/VLRSGi
MSC/VLR
A
ENc G
HSS
D
D
Z1
PCRFRx
Gx
Iu
MMEZ2
12/12/08 30LTE Part 1 - DIAM
LTE Voice 3/3 – CS Fallback
The 23.272 “CS fallback” solution Objective is to allow user redirection to 2G or 3G when a CS based service is requested
This applies to Voice calls as well as Supplementary Services
The terminal is simultaneously located in MME and VLR nodes
The terminal is redirected towards the 2G or 3G CS domain on Mobile Originating or Terminating call
Requires new interface and associated protocols on SGs interface between MME and MSC/VLRCan be seen as an equivalent to the Gs interface between SGSN and MSC
1. Attach Request
3. Derive VLR number
4. Location Update Request
5. Create SGs association
7. Location Update Accept
8. Attach Accept
UE MME HSS MSC/VLR
2. Attach as specified in TS 23.401
6. Location update in CS domain
12/12/08 31LTE Part 1 - DIAM
LTE is not a smooth upgrade (requires Core Network upgrade, IP transport upgrade)
LTE cannot be deployed until Voice service continuity solutions are made available (VCC, CS fallback…)
LTE deployment requires more than 10MHz, otherwise HSPA+ is enough (i.e. same spectral efficiency)
What is LTE needed for ?
For the High bit rates / High performances ?
For capacity reasons / capex reduction ?
For "home eNodeB" ?
For which services Can it be a data only layer / need to also support speech ?
Always-on is being generalized
LTE – possible scenario
12/12/08 32LTE Part 1 - DIAM
E-UTRAN standard is simpler than UTRAN
Less options in protocols, less channel combinations
Simpler architecture
The UTRAN "generic toolbox" spirit has evolved to more pragmatic considerations
However there are some key items to be looked at…
LTE is tight to SAE Core Network evolution
Interworking with legacy systems at the service level (e.g. VCC)
New constraints of OFDM deployment to be worked out (frequency planning, interference mitigation, …)
LTE – Some last words…