Part1 - Techno

12/12/08 1-

Part 1 - Technology

Pierre Lescuyer

DIAM

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…)


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


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


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"


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


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


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


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



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


(x4.2)

LTE2 x 2 TX diversity10 MHz bandwidth / Reuse 1


(x4.3)

LTE4 x 2 MU-SDMA10 MHz bandwidth / Reuse 1


(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)


(x1.0)

LTE1 x 2 RX diversity10 MHz bandwidth


(x2.6)

LTEInterference coordination10 MHz bandwidth


(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…

Part1 - Techno

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