LTE System Interfaces

7/31/2019 LTE System Interfaces

1/66

www.huawei.com

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

Security Level: Internal Use

LTE System Interfaces

2010-09


2/66


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


3/66


Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page3

References

3GPP TS36.211

3GPP TS36.300

3GPP TS36.410

3GPP TS36.420


4/66Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page4

1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


5/66

Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page5

LTE/SAE Architecture

SGSN

GPRS

UMTS

E-UTRAN

cdma2000

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 plane

Control plane

BTS

Internet

Corporate

Internet

Operator Service

Network

EPS (Evolved Packet System)

S6d

PDSNBSC

A10/A11

MME: Mobility management entity

PCRF: Policy and Charging Rules Function


6/66


Functional Split between E-UTRAN and EPC

internet

eNB

RB Control

Connection Mobility Cont.

eNB Measurement

Configuration & Provision

Dynamic ResourceAllocation (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 MobilityHandling

NAS Security

P-GW

UE IP address

allocation

Packet Filtering

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

S1

S1

X2

X2X2

E-UTRAN


7/66


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.

ApplicationProtocol

TransportNetwork

Layer

Physical Layer

SignallingBearer(s)

TransportUser NetworkPlane

Control Plane User Plane

TransportUser NetworkPlane

RadioNetwork

Layer

DataBearer(s)


8/66


Control plane protocol stacks

SCTP

L2

L1

IP

L2

L1

IPSCTP

S1-MMEeNodeB MME

S1-APS1-AP

NAS

MAC

L1

RLC

PDCP

UE

RRC

MAC

L1

RLC

PDCP

RRC

LTE-Uu

NASRelay


9/66


10/66


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

Contents


11/66


Radio interface protocol stack

LTE does not have BMC entity

All types of RB need PDCP processing

NAS

relay

S1 UuUuS1


12/66


RRC services and functions


13/66


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;


14/66


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;


15/66


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


16/66


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


17/66


Segm.

ARQ etc

Multiplexing UE1

Segm.

ARQ etc...

HARQ

Multiplexing UEn

HARQ

BCCH PCCH

Scheduling / Priority Handling

Logical Channels

Transport Channels

MAC

RLCSegm.

ARQ etc

Segm.

ARQ etc

PDCP

ROHC 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)


18/66


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 Signaling

Control Plane

Encryption

Integrity Checking

User Plane

IP Header Compression

Encryption

Sequencing and Duplicate Detection


19/66


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


20/66


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

RLCMAC

PHY

PDCP

RRC

NAS Signaling

Channel Mapping and MultiplexingError Correction - HARQ

QoS Based Scheduling


21/66


Physical Layer

eNB

RLC

MAC

PHY

PDCP

RRC

NAS SignalingError Detection

FEC Encoding/DecodingRate Matching

Mapping of Physical ChannelsPower Weighting

Modulation and DemodulationFrequency and Time Synchronization

Radio MeasurementsMIMO ProcessingTransmit Diversity

Beamforming

RF Processing


22/66


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


23/66


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


24/66


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


25/66


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


26/66


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;


27/66


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

Ph i l l f TDD


28/66


Physical layer frame structure -TDD

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

0

Special

Subfram

e

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


29/66


Type 2 Radio Frame Switching Points

Configuration SwitchingPoint

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)


30/66


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 = 160

Ts (OFDM symbol #0) , TCP = 144

Ts (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 CyclicPrefix)

0 1 2 3 4 5 6

0 1 2 3 4 5

CP (Cyclic

Prefix)

Ts

Ts

Ph i l l f t t FDD(2/2)


31/66


Physical layer frame structure-FDD(2/2)

h l d f


32/66


LTE physical resource definition

Basic definitions

Resource element

Resource block

RB

scN

ULsymbNConfiguration

Normal cyclic prefix 12 7

Extended cyclic prefix 12 6

h i l l i


33/66


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 blockconcatenation

110 ,...,, Aaaa

110 ,...,, Bbbb

110 ,...,, rKrrr ccc

)(

1

)(1

)(0 ,...,,

iDr

ir

ir r

ddd

110 ,...,, rErrr eee

110 ,...,, Gfff

Transport blockCRC attachment

Code block segmentationCode block CRC attachment

Ph i l l i


34/66


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)

ScramblingModulation

Mapper

Layer

MapperPrecoding

Resource

Element

Mapper

OFDM

Signal

Generation

Resource

Element

Mapper

OFDM

Signal

Generation

ScramblingModulation

Mapper

Codewords LayersAntenna

Ports

Synchronization signals


35/66



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

procedure. The particular sequences which are transmitted for the PSS andSSS 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.

d i f


36/66

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

72Subcarriers

PSS (PrimarySynchronizationSequence)

SSS(SecondarySynchronizationSequence)

62Subcarri

ers



37/66



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)

DownlinkSyn

chronizationS

ignals

eNB

UE

Where:

NID = 3NID + NID

NID = 0,..167NID = 0, 1, or 2

Ph i l C ll Id titi


38/66


Physical Cell Identities

eNB

eNB

eNB

PSS - One of 3 Identities

SSS - One of 168

Group Identities

504 Unique Cell

Identities

l


39/66


PSS Correlation

Subframe

Correlation

PSS0

PSS1

PSS2

SSS C l i


40/66


SSS Correlation

Subframe

SSS

SSS

Cyclic Shift based

on Cell ID and

Subframe (0 or 5)

Device can identify

Cell ID and frame

timing

E l f SSS I di


41/66


Example of SSS Indices

N 1ID m0 m1 N

1ID m0 m1 N

1ID m0 m1 N

1ID 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


42/66


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 ofslots 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


43/66


Cell Search

0 1 2 3 4 5 6 7 8 9

Frame - 10ms

5MHz (25ResourceBlocks)

PSS

SSS

PBCH

Downlink Reference signals


44/66



Cell-specific downlink reference signals

The reference signal is used to make channel estimation and carry out downlinkcoherent 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 = 0

R

R

R

R

R

R

R

R

Physical Cell ID = 8

RS position is basedon Physical Cell ID

(Physical Cell ID mod

6)

eNB eNB



45/66



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

Downlink Physical channels


46/66



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

PBCH-physical broadcast channel


47/66


MIB

System

Bandwidth

CRC

Channel Coding

Rate Matching

Scrambling

ModulationLayer Mapping

Precoding

Mapping to REs

10ms Frame

PBCH

PBCH physical broadcast channel



48/66



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



49/66



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.



50/66



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


51/66


p

72 center RE

Control channelCFI/PHI/PDCCH

Sync channel PBCH

User 1 PDSCH User 2 PDSCH


52/66

Uplink Reference signals


53/66


p g

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


54/66


p g

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 RRCsignalling

Uplink Physical channels


55/66


p y

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.



56/66


p y 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


57/66


PLMN/Cell

Selection

Downlink Synchronization

Complete

Power On Cell SearchRACH

Process

Uplink SynchronizationComplete

Send

Preamble

Identify RACHPreambles

Identify

PRACH

Format

Receive

Response

No

Decode

Response

Yes

Send RRC

Connection

Request

MAC

Connection

Resolution

SRB

Established



58/66


Contention-based random access procedure

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

network transmitting a timing advancecommand 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 theterminal has not yet been assigned a C-RNTI, the temporary identityfrom the second step is promoted to the C-RNTI, Terminals which donot find a match between the identity are considered failed

LTE channel mapping


59/66


pp g

Contents


60/66


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

S1 Interface architectureS1 f ti


61/66


EPCEUTRAN

eNode

B

S1-U

S1-MME

S-GTW

MME

eNode

B

S-GTW

MME

S1 functions:

S1 UE context management function:

Establishment/release SAE bearer context, security context, UE S1 signalingconnection 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


62/66


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

Contents


63/66


1. Overview

2. Radio interface

3. S1 interface

4. X2 interface

X2 Interface architecture


64/66

Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.Page64

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


65/66


eNB eNB

X2

IP

Layer 2

Layer 1

SCTP

X2AP

Control Plane

IP

Layer 2

Layer 1

UDP

GTP-U

User Plane


66/66

Thank you

www.huawei.com

Documents

LTE System Interfaces