LTE System Interfaces 20110525 a 1.0

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Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.

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Security Level: Internal Use

LTE System Interfaces

2010-09

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page2

On completion of this course, you should be able

to:

Know the overall architecture of E-UTRAN, function

split between CN and RAN

Know the radio interface protocol stack and the

function of each layer

Know the physical layer functions and basic

procedures

Know S1/X2 interface protocol stack and the

functions of the interfaces.

Objectives


References

3GPP TS 《 36.211 》

3GPP TS 《 36.300 》

3GPP TS 《 36.410 》

3GPP TS 《 36.420 》


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


LTE/SAE Architecture

SGSN

GPRSGPRS

UMTSUMTS

E-UTRANE-UTRAN

cdma2000cdma2000

MME

HSS PCRF

Serving GW PDN GW

BTS BSC/PCU

NodeB RNC

eNodeB

S2b

S1-U

S6a

Gx

S5/8

Gb

Iu

S1-MMES12

S3

S4S11

SGi

S9S10

User planeControl plane

BTS

Internet

CorporateInternet

Operator ServiceNetwork

EPS (Evolved Packet System)

S6d

PDSNBSC

A10/A11

MME: Mobility management entity

PCRF: Policy and Charging Rules Function


Functional Split between E-UTRAN and EPC

internet

eNB

RB Control

Connection Mobility Cont.

eNB MeasurementConfiguration & Provision

Dynamic Resource Allocation (Scheduler)

PDCP

PHY

MME

S-GW

S1MAC

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

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

S1 S

1

X2

X2X2E-UTRAN


General protocol model for E-UTRAN interfaces

General principle for S1/X2 is that the layers and planes are

logically independent of each other. Therefore, as and when

required, the standardization body can easily alter protocol

stacks and planes to fit future requirements.

Application Protocol

Transport Network

Layer

Physical Layer

Signalling Bearer(s)

Transport User

Network Plane

Control Plane User Plane

Transport User

Network Plane

Radio Network

Layer

Data Bearer(s)


Control plane protocol stacks

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


User plane protocol stacks

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


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


Radio interface protocol stack

LTE does not have BMC entity

All types of RB need PDCP processing

NAS

relay

S1 Uu Uu S1


RRC services and functions


RRC services and functions Broadcast of System Information related to NAS and AS

Mobility functions including:

UE measurement reporting and control of the reporting for mobility;

UE cell selection and reselection and control of cell selection and

reselection;

Context transfer at handover.

Establishment, maintenance and release of an RRC connection

between the UE and E-UTRAN including:

Allocation of temporary identifiers between UE and E-UTRAN;

Configuration of signaling radio bearer(s) for RRC connection:

Security functions including key management;

Establishment, configuration, maintenance and release of point to

point Radio Bearers;


RRC protocol states & state transitions

LTE supports 2 RRC states: RRC_IDLE and

RRC_CONNECTED

RRC_IDLE:

PLMN selection;

Broadcast of system information;

Paging;

Cell re-selection mobility;

No RRC context stored in the eNB

RRC_CONNECTED

UE has an E-UTRAN-RRC

connection;

E-UTRAN knows the cell which

the UE belongs to;

Network can transmit and/or

receive data to/from UE;

Neighbor cell measurements;


Relation between RRC state and NAS states

EPS Mobility Management (EMM) state includes: EMM-DEREGISTERED

EMMREGISTERED

EPS Connection Management (ECM) state includes: ECM-IDLE

ECM-CONNECTED


E-UTRAN identities

E-UTRAN Cell Global Identifier (ECGI): used to identify cells

globally.

The ECGI is constructed from the MCC (Mobile Country Code), MNC

(Mobile Network Code) and the ECI (E-UTRAN Cell Identifier).

ECI: used to identify cells within a PLMN.

ECI has a length of 28 bits and contains the eNB Identifier.

Global eNB Identifier: used to identify eNBs globally.

The Global eNB Identifier is constructed from the MCC (Mobile Country

Code), MNC (Mobile Network Code) and the eNB-Id (eNB Identifier).

eNB Identifier: used to identify eNBs within a PLMN.

The eNB Id is contained within the E-UTRAN Cell Identifier


Segm.ARQ etc

Multiplexing UE1

Segm.ARQ etc

...

HARQ

Multiplexing UEn

HARQ

BCCH PCCH

Scheduling / Priority Handling

Logical Channels

Transport Channels

MAC

RLCSegm.

ARQ etcSegm.

ARQ etc

PDCPROHC ROHC ROHC ROHC

Radio Bearers

Security Security Security Security

...

Layer 2 in overall Layer 2 is split into the following sublayers:

Medium Access Control (MAC), Radio Link Control

(RLC) and Packet Data Convergence Protocol (PDCP)


PDCP Sublayer

The main services and functions of the PDCP sublayer

Header compression and decompression for user plane data.

Security functions:

ciphering and deciphering;

integrity protection and verification

eNB

RLC

MAC

PHY

PDCP

RRC

NAS SignalingControl Plane

EncryptionIntegrity Checking

User PlaneIP Header Compression

EncryptionSequencing and Duplicate Detection


RLC Sublayer

The main services and functions of the RLC sublayer include:

Transfer of upper layer PDUs supporting AM, UM and TM

Error Correction through ARQ (CRC check provided by the physical

layer)

Concatenation of SDUs for the same radio bearer;

Duplicate Detection;

Segmentation;

SDU discard;;

eNB

RLC

MAC

PHY

PDCP

RRC

NAS Signaling

TM (Transparent Mode)UM (Unacknowledged Mode)

AM (Acknowledged Mode)Segmentation and Re-Assembly

ConcatenationError Correction


MAC Sublayer The main services and functions of the MAC sublayer include:

Mapping between logical channels and transport channels;

Multiplexing/demultiplexing of RLC PDUs belonging to one or

different radio bearers into/from transport blocks (TB) delivered

to/from the physical layer;

Priority handling between logical channels of one UE;

Priority handling between UEs;

Error correction through HARQ;

Padding;

Transport format selection;

eNB

RLC

MAC

PHY

PDCP

RRC

NAS Signaling

Channel Mapping and Multiplexing Error Correction - HARQQoS Based Scheduling


Physical Layer

eNB

RLC

MAC

PHY

PDCP

RRC

NAS SignalingError Detection

FEC Encoding/Decoding Rate Matching

Mapping of Physical ChannelsPower Weighting

Modulation and DemodulationFrequency and Time Synchronization

Radio MeasurementsMIMO ProcessingTransmit Diversity

BeamformingRF Processing


LTE channel mapping-downlink

DL-SCH

Physical Layer

MAC Layer

RLC Layer

PDCP Layer

RRC Layer

PhysicalChannels

TransportChannels

LogicalChannels

PDSCH

PDCCH

PHICHPCFIC

HPBCH

BCH PCH

BCCH PCCH CCCH DCCH DTCH

TM TM TM UM/AM UM/AM

Ciphering

Integrity

Ciphering

ROHC

RRC

ESM EMM IPNAS Layer


LTE channel mapping-uplink

Physical Layer

MAC Layer

RLC Layer

PDCP Layer

RRC Layer

PhysicalChannels

TransportChannels

LogicalChannels

PUSCH

PUCCH

PRACH

RACH

CCCH

TM UM/AM UM/AM

Ciphering

Integrity

Ciphering

ROHC

RRC

ESM EMM IPNAS Layer

UL-SCH

DCCH DTCH


Transport channels

Downlink:

Broadcast Channel (BCH)

fixed, pre-defined transport format;

Downlink Shared Channel (DL-SCH)

support for HARQ

support for dynamic link adaptation by varying the modulation,

coding and transmit power;

possibility to use beam forming;

support for both dynamic and semi-static resource allocation;

support for UE DRX to enable UE power saving;

support for MBMS transmission


Transport channels

Downlink:

Paging Channel (PCH)

support for UE DRX to enable UE power saving

mapped to physical resources which can be used

dynamically also for traffic/other control channels

Multicast Channel (MCH)

support for MBSFN combining of MBMS transmission on

multiple cells


Transport channels

Uplink:

Uplink Shared Channel (UL-SCH)

possibility to use beam forming

support for dynamic link adaptation by varying the transmit

power and potentially modulation and coding;

support for HARQ;

support for both dynamic and semi-static resource

allocation.

Random Access Channel(s) (RACH)

limited control information;

collision risk;


Physical layer frame structure -FDD

Type 1, applicable to FDD

The downlink OFDM sub-carrier spacing is f = 15 kHz, a reduced

sub-carrier spacing f = 7.5 kHz is only for MBMS-dedicated cell

Slot (0.5ms)

Radio Frame Tf = 307200 x Ts = 10ms

Subframe (1ms)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Ts = 1/(15000x2048) = 32.552083ns

Tslot = 15360 x Ts


Physical layer frame structure -TDD

Type 2 Radio Frame Tf = 307200 x Ts = 10ms

0

Special Subframe

2 3 4 5 7 8 9

DwPTS (Downlink Pilot Time Slot)

GP (Guard Period)

UpPTS (Uplink Pilot Time Slot)

Page 28

• Type 2, applicable to TDD


Type 2 Radio Frame Switching Points

Configuration Switching Point Periodicity

Subframe Number

0 1 2 3 4 5 6 7 8 9

0 5ms D S U U U D S U U U

1 5ms D S U U D D S U U D

2 5ms D S U D D D S U D D

3 10ms D S U U U D D D D D

4 10ms D S U U D D D D D D

5 10ms D S U D D D D D D D

6 5ms D S U U U D S U U D

Page 29


Physical layer frame structure-FDD(1/2)

In the case of 15 kHz sub-carrier spacing there are two cyclic-prefix lengths,

corresponding to seven and six OFDM symbols per slot respectively

Normal cyclic prefix:

TCP = 160Ts (OFDM symbol #0) , TCP = 144Ts (OFDM symbol #1 to #6)

Extended cyclic prefix: TCP-e = 512Ts (OFDM symbol #0 to OFDM symbol #5)

In case of 7.5 kHz sub-carrier spacing, there is only a single cyclic prefix

length TCP-low = 1024Ts, corresponding to 3 OFDM symbols per slot.

Radio Frame = 10ms

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

7 OFDMSymbols (Normal

Cyclic Prefix)

6 OFDM Symbols (Extended Cyclic

Prefix)

0 1 2 3 4 5 6

0 1 2 3 4 5

CP (Cyclic Prefix)

Ts

Ts


Physical layer frame structure-FDD(2/2)


LTE physical resource definition Basic definitions Resource element

Resource block

RBscN

ULsymbNConfiguration

Normal cyclic prefix 12 7

Extended cyclic prefix 12 6


Physical layer processing

Bit level processing:

Transport block from MAC layer

24 bit CRC is the baseline

Channel coding: Turbo coding Channel coding

Rate matching

Code block concatenation

110 ,...,, Aaaa

110 ,...,, Bbbb

110 ,...,, rKrrr ccc

)(

1)(

1)(

0 ,...,, iDr

ir

ir r

ddd

110 ,...,, rErrr eee

110 ,...,, Gfff

Transport block CRC attachment

Code block segmentationCode block CRC attachment


Physical layer processing

Symbol level processing:

The scrambling stage is applied to all downlink physical channels,

and serves the purpose of interference rejection

Modulation: QPSK, 16QAM, and 64QAM (64 QAM optional in UE)

Scrambling Modulation

Mapper

Layer Mapper

Precoding

Resource Element Mapper

OFDM Signal

Generation

Resource Element Mapper

OFDM Signal

Generation

Scrambling Modulation

Mapper

Codewords LayersAntenna

Ports


Synchronization signals The primary and secondary synchronization signals are used in the cell

search procedure. The particular sequences which are transmitted for the

PSS and SSS in a given cell are used to indicate the physical layer cell

identity to the UE

The synchronization signals are always transmitted on the 62 centre sub

carriers and specified symbols.

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page36Page36

PSS and SSS Location for FDD

0 1 2 3 4 5 6

Bandwidth

0 1 2 3 4 5

Bandwidth

Normal CP

Extended CP

Radio Frame

Slots 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Repeated in slots 0 and 10

72 Subcarriers

PSS (Primary Synchronization Sequence)

SSS (Secondary Synchronization Sequence)

62 Subcarri

ers


Synchronization signals There are 504 unique physical layer cell identities in LTE, grouped

into 168 groups of three identities.

The three identities in a group would usually be assigned to cells

under the control of the same eNodeB. Three PSS sequences are

used to indicate the cell identity within the group.

168 SSS sequences are used to indicate the identity of the group.

cell (1) (2)

(1)

(2)

Downlink Synchronization Signals

eNB

UEWhere:

NID = 3NID + NID

NID = 0,…..167NID = 0, 1, or 2


Physical Cell Identities

eNB

eNB

eNB

PSS - One of 3 Identities

SSS - One of 168 Group Identities

504 Unique Cell Identities


PSS Correlation

Subframe

Correlation

PSS0

PSS1

PSS2


SSS Correlation

Subframe

SSS

SSS

Cyclic Shift based on Cell ID and Subframe (0 or 5)

Device can identify Cell ID and frame timing


Example of SSS Indices

N 1ID m0 m1 N 1

ID m0 m1 N 1ID m0 m1 N 1

ID m0 m1 N 1ID m0 m1

0 0 1 34 4 6 68 9 12 102 15 19 136 22 27

1 1 2 35 5 7 69 10 13 103 16 20 137 23 28

2 2 3 36 6 8 70 11 14 104 17 21 138 24 29

3 3 4 37 7 9 71 12 15 105 18 22 139 25 30

. . . . .

. . . . 167 2 9

33 3 5 67 8 11 101 14 18 135 21 26


Cell search procedure The first step of cell search is to do matched filtering between the

received signal and the sequences specified for the primary

synchronization signal, When the output of the matched filter

reaches its maximum, the terminal is likely to have found timing

on a 5 ms basis, and the identity within the cell-identity group.

The second step is to detects the cell-identity group, by observing

pairs of slots where the secondary synchronization signal is

transmitted, since each combination (s1, s2) in subframe zero

and five represents one of the cell identity groups uniquely

In the case of the initial synchronization, in addition to the

detection of synchronization signals, the UE proceeds to decode

the Physical Broadcast CHannel (PBCH), from which critical

system information is obtained.


Cell Search

0 1 2 3 4 5 6 7 8 9

Frame - 10ms

5MHz (25 Resource Blocks)

PSS

SSS

PBCH


Downlink Reference signals Cell-specific downlink reference signals

The reference signal is used to make channel estimation and carry out

downlink coherent detection and demodulation

The RS sequence also carries unambiguously one of the 504 different

cell identities

Cell-specific reference symbol arrangement in the case of normal CP

length for one antenna port:

R

R

R

R

R

R

R

R

Physical Cell ID = 0R

R

R

R

R

R

R

R

Physical Cell ID = 8

RS position is based on Physical Cell ID

(Physical Cell ID mod 6)

eNB eNB


Downlink Reference signals Cell-specific downlink reference signals in case of 2 and 4 antenna port


Downlink Physical channels

Physical broadcast channel (PBCH)

P-BCH transmitted only in the centred frequency, BW is 72

subcarriers

P-BCH use QPSK

P-BCH occupy symbol 7,8,9,10 of the centred 6RB

P-BCH is used to carry BCH for system information broadcast Only MIB (Master Information Block) which consists of a limited number of

the most frequently transmitted parameters essential for initial access to

the cell is carried on PBCH

Other System Information Blocks (SIBs) which, at the physical layer, are

multiplexed together with uncast data are transmitted on the Downlink

Shared Channel


MIB

Sys

tem

B

andw

idthCRC

Channel CodingRate Matching

ScramblingModulation

Layer MappingPrecoding

Mapping to REs

10ms Frame

PBCH

PBCH-physical broadcast channel



Physical downlink shared channel (PDSCH)

PDSCH is used to carry DL-SCH, PCH and BCH

User data, broadcast system information which is not carried

on the PBCH, and paging messages may be transmitted on

PDSCH

Physical multicast channel (PMCH)

PMCH is used to carry MCH for MBMS service



Physical control format indicator channel (PCFICH)

Carries information about the number of OFDM symbols used

for transmission of PDCCHs in a subframe.

Three different CFI values are used in the first version of LTE.

In order to make the CFI sufficiently robust each codeword is

32 bits in length. These 32 bits are mapped to 16 resource

elements using QPSK modulation

In order to achieve frequency diversity, the 16 resource

elements carrying the PCFICH are distributed across the

frequency domain. This is done according to a predefined

pattern in the first OFDM symbol in each downlink subframe.



Physical downlink control channel (PDCCH) Informs the UE about the resource allocation of PCH and DL-

SCH, and Hybrid ARQ information related to DL-SCH

Carries the uplink scheduling grant

Multiple PDCCHs can be transmitted in a subframe

The set of OFDM symbols possible to use for PDCCH in a

subframe is the first n OFDM symbols where n 3

Physical Hybrid ARQ Indicator Channel (PHICH) Carries Hybrid ARQ ACK/NAKs in response to uplink

transmissions.


Downlink resource allocation sample

72 center RE

Control channelCFI/PHI/PDCCH

Sync channel PBCH

User 1 PDSCH User 2 PDSCH


Uplink Reference signals Uplink Reference signal

Two types of uplink reference signals are supported:

Demodulation reference signal (DM RS), associated with transmission of

PUSCH or PUCCH, are primarily used for channel estimation for coherent

demodulation

Sounding reference signal (SRS), not associated with transmission of PUSCH

or PUCCH, primarily used for channel quality determination to enable

frequency-selective scheduling on the uplink

The uplink reference signals in LTE are based on Zadoff–Chu (ZC)

sequences, which satisfy these properties:

Good autocorrelation properties for accurate channel estimation.

Good cross-correlation properties between different RSs to reduce

interference from RSs transmitted on the same resources in other (or, in

some cases, the same) cells.


Uplink Reference signals

Demodulation reference signal (DM RS)

The DM RSs associated with uplink PUSCH data or PUCCH control

transmissions are primarily provided for channel estimation for

coherent demodulation, and are present in every transmitted uplink

slot.

The DM RSs of a given UE occupy the same bandwidth as its

PUSCH/PUCCH data transmission (same RBs)

The position of uplink reference signals in a slot:


Uplink Reference signals

Sounding reference signal (SRS)

The subframes in which SRS are transmitted by any UE within the cell

are indicated by cell-specific broadcast signalling

(‘srsSubframeConfiguration’)

The SRS transmissions are always in the last SC-FDMA symbol in the

configured subframes

The eNodeB in LTE may either request an individual SRS transmission

from a UE or configure a UE to transmit SRS periodically until

terminated

The specific SRS bandwidth to be used by a given UE is configured

through RRC signalling


Uplink Physical channels

Physical uplink shared channel (PUSCH)

carries data from the Uplink Shared Channel (UL-SCH) transport

channel

Physical uplink control channel (PUCCH)

Carries Hybrid ARQ ACK/NAKs in response to downlink

transmission;

Carries Scheduling Request (SR);

Carries CQI reports.


Uplink Physical channels Physical random access channel (PRACH)

Carries the random access preamble

One or several subframes is reserved for preamble transmission in a frame, and In the frequency domain, the random-access preamble has a bandwidth corresponding to six resource blocks

The physical layer random access burst consists of a cyclic prefix, a preamble, and a guard time to avoid interference

A fixed number (64) of preamble signatures is available


Initial Procedures

PLMN/Cell Selection

Downlink Synchronization Complete

Power On Cell SearchRACH

Process

Uplink Synchronization Complete

Send Preamble

Identify RACH Preambles

Identify PRACH Format

ReceiveResponse

No

Decode Response

Yes

Send RRC Connection

Request

MAC Connection Resolution

SRB Established


Uplink Physical channels Contention-based random access procedure

On request of higher layers which should provides: Random access channel parameters, a single preamble is transmitted using an random selected preamble sequence

network transmitting a timing advance command and assigns uplink resources to the terminal to be used in the third step

transmission of the mobile-terminal identity to the network, C-RNTI(LTE-CONNECTED) or a CN terminal identifier(IDLE)

contention-resolution message is transmitted on the DL-SCH, If the terminal has not yet been assigned a C-RNTI, the temporary identity from the second step is promoted to the C-RNTI, Terminals which do not find a match between the identity are considered failed


LTE channel mapping


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


EPC EUTRAN

eNode

B

“S1-U”

“S1-MME”

S-GTW

MME

eNode

B

S-GTW

MME

S1 Interface architecture S1 functions:

S1 UE context management function: Establishment/release SAE bearer context, security context, UE S1

signaling connection ID(s), etc.

SAE bearer management functions

GTP-U tunnels management function

S1 Signalling link management function

Intra-LTE handover

Inter-3GPP RAT handover

Paging function

Network sharing function

NAS node selection function

Security function


S1 Interface

eNB

IP

Layer 2

Layer 1

SCTP

S1AP

Control Plane

S1-MME

MME

IP

Layer 2

Layer 1

UDP

GTP-U

User Plane

eNB

S1-U

S-GW


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


X2 Interface architecture X2 functions:

Intra LTE-Access-System Mobility Support for UE in LTE_ACTIVE:

Context transfer from source eNB to target eNB;

Control of user plane tunnels between source eNB and target eNB;

Handover cancellation.

Load Management

Inter-cell Interference Coordination

Uplink Interference Load Management;

General X2 management and error handling functions:

Error indication.

Trace functions


X2 Interface

eNB eNB

X2

IP

Layer 2

Layer 1

SCTP

X2AP

Control Plane

IP

Layer 2

Layer 1

UDP

GTP-U

User Plane

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Documents

LTE System Interfaces 20110525 a 1.0