3G Long-Term Evolution (LTE) and System Architecture ...€¦ · – LTE-Advanced with increased performance targets – Application of new scenarios (MTC) and novel concepts (D2D)

3G Long-Term Evolution (LTE) andSystem Architecture Evolution (SAE)

• Intro• Architecture• Air Interface• Bearers and QoS• Call Handling Procedures• Mobility Handling• LTE-Advanced

Separate sessions on • LTE Radio• LTE Applications & Services• SON

Cellular Communication Systems 2Andreas Mitschele-Thiel, Jens Mueckenheim November 18

3GPP Evolution – Background

• 3G Long-Term Evolution (LTE) is the advancement of UMTS with the following targets:– Significant increase of the data rates: mobile broadband– Simplification of the network architecture– Reduction of the signaling effort esp. for activation/ deactivation

• Work in 3GPP started in Dec 2004– LTE is not backward compatible to UMTS HSPA– LTE is a packet only network – there is no support of circuit switched

services (no MSC)– LTE started on a clean state – everything was up for discussion including

the system architecture and the split of functionality between RAN and CN

• Since 2010, LTE has been further enhanced– LTE-Advanced with increased performance targets– Application of new scenarios (MTC) and novel concepts (D2D)


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

3–4x HSPA Rel.6 in DL*

2–3x HSPA Rel.6 in UL

1 bps/Hz broadcast

Improved Cell Edge Rates

2–3x HSPA Rel.6 in DL*

2–3x 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

* Assumes 2x2 in DL for LTE,

but 1x2 for HSPA Rel.6


Key Features of LTE to Meet Requirements

• Selection of OFDM for the air interface– Less receiver complexity– Robust to frequency selective fading and inter-symbol interference (ISI)– Access to both time and frequency domain allows additional flexibility in

scheduling (including interference coordination)– Scalable OFDM makes it straightforward to extend to different

transmission bandwidths

• Integration of MIMO techniques– Pilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMO

in the UL

• Simplified network architecture– All IP architecture– Reduction in number of logical nodes → flatter architecture– Clean separation between user and control plane


LTE/SAE ReleasesRelease 8 2008 Q4 First LTE release. All-IP Network (SAE). New OFDMA, FDE and MIMO based radio

interface.

Release 9 2009 Q4 SAES Enhancements, WiMAX and LTE/UMTS Interoperability. LTE HeNB.

Release 10 2011 Q1 LTE Advanced fulfilling IMT Advanced 4G requirements. Backwards compatible withrelease 8 (LTE).

Release 11 2012 Q3 Advanced IP Interconnection of Services. Service layer interconnection betweennational operators/carriers as well as third party application providers. Heterogeneous networks (HetNet) improvements, Coordinated Multi-Point operation(CoMP). In-device Co-existence (IDC).

Release 12 2015 Q1 Enhanced Small Cells (higher order modulation, dual connectivity, cell discovery, selfconfiguration), Carrier Aggregation (2 uplink carriers, 3 downlink carriers, FDD/TDD carrier aggregation), MIMO (3D channel modeling, elevation beamforming, massive MIMO), New and Enhanced Services (cost and range of MTC, D2D communication, eMBMS enhancements)

Release 13 2016 Q1 LTE in unlicensed, LTE enhancements for Machine-Type Communication. Elevation Beamforming/Full-Dimension MIMO, Indoor positioning. LTE-Advanced Pro.

Release 14 2017 Q2 Energy Efficiency, Location Services (LCS), Mission Critical Data over LTE, Mission Critical Video over LTE, Flexible Mobile Service Steering (FMSS), Multimedia Broadcast Supplement for Public Warning System (MBSP), enhancement for TV service, massive Internet of Things, Cell Broadcast Service (CBS)

Release 15 Planned for Sept 2018

First "New Radio" (NR) release. Support for 5G Vehicle-to-x service, IP Multimedia Core Network Subsystem (IMS), Future Railway Mobile Communication System

https://en.wikipedia.org/wiki/3GPP_Long_Term_Evolutionhttps://en.wikipedia.org/wiki/OFDMAhttps://en.wikipedia.org/wiki/Frequency-domain_equalizationhttps://en.wikipedia.org/wiki/MIMOhttps://en.wikipedia.org/wiki/WiMAXhttps://en.wikipedia.org/wiki/Universal_mobile_telecommunications_systemhttps://en.wikipedia.org/wiki/3GPP_Long_Term_Evolutionhttps://en.wikipedia.org/wiki/Home_eNode_Bhttps://en.wikipedia.org/wiki/LTE_Advancedhttps://en.wikipedia.org/wiki/IMT_Advancedhttps://en.wikipedia.org/wiki/4Ghttps://en.wikipedia.org/wiki/Interconnectionhttps://en.wikipedia.org/wiki/Service_layerhttps://en.wikipedia.org/wiki/LTE-Uhttps://en.wikipedia.org/wiki/LTE-Advanced_Pro


How to navigate in 3GPP documents?

Overview on 3GPP document series: http://www.3gpp.org/specifications/specification-numbering

• 22 series: Service aspects• 23 series: Technical realization

– TS 23.203: Policy and Charging Control Architecture – TS 23.401: GPRS enhancements for E-UTRAN access– TS 23.501: Systems Architecture for the 5G System

• 24 series: Signaling protocols – user to network– TS 24.301 NAS protocol for EPS (MM, SM procedures)

• 29 series: Signaling protocols - intra-fixed-network– TS 29.171-173: Location Services

• 33 series: Security• 36 series: LTE radio aspects

– TS 36.300: E-UTRAN – Overall description; Stage 2– TS 36.331: Radio Resource Control (RRC); protocol specification

• 38: 5G radio aspects

http://www.3gpp.org/specifications/specification-numbering

LTE/SAE Network Architecture

• Evolved UTRAN (E-UTRAN)• Evolved Node B

• Evolved Packet System (EPS)• MME, S-GW, P-GW, HSS, PCRF

• EPS Protocol Architecture and Interfaces


Evolved UTRAN (E-UTRAN) Architecture

• Key elements of radio network architecture– No more RNC – RNC functionalities moved to

evolved-NodeB (eNB)– Termination of radio access in

eNB– X2 interface for seamless

mobility (i.e. data/context forwarding) and load management among eNBs

• Note: Standard only defines logical structure/nodes !

EPC = Evolved Packet Core

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1 S1

S1 S1

X2

X2

X2

E-UTRAN

EPC


Evolved Node B

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

eNodeB (eNB) provides all radio access functions

– Radio Resource Management (RRC, dynamic scheduling)

– Routing of User Plane data towards Serving Gateway

– Scheduling and transmission of paging and broadcast messages

– IP header compression and user plane ciphering

– Measurements and measurement reporting configuration

– Selection of a MME at UE attachment, when not given by UE


Evolved Packet System (EPS) Architecture

• EPS comprises EPC, E-UTRAN and UE• E-UTRAN, i.e. eNB performs radio access functions• EPC provides connectivity & performs mobility & user management functions

– separation between C Plane and U Plane in EPC

E-UTRAN

MME

Serving GW PDN GWS1-U

S1-MME S11

S5

Internet

Evolved Packet Core (EPC)

SGi

HSSS6a

S10

PCRF

GxGxc

Control planeUser plane


Mobility Management Entity (MME)

– UE Reachability in ECM-Idle/RCC-Idle state– Tracking area management– NAS signaling/security, AS security control– Authentication & authorization– S-GW/P-GW selection– MME selection for HO with MME change, SGSN selection for HO to 3G/2G– Inter-EPC signaling for mobility between 3GPP access networks– Bearer management functions including dedicated bearer establishment

E-UTRAN

MME

Serving GWS1-U

S1-MME S11

HSSS6a

S10


Serving and PDN Gateways

Serving Gateway (S-GW)– Serves EPC (U Plane) - E-UTRAN interface (S1-U interface) – Local mobility anchor for inter-eNB as well as inter-3GPP handovers– Packet routing and forwarding– Idle mode (ECM_IDLE) DL packet buffering and triggering of network-

based service request procedure– Accounting on user and QCI granularity for inter-operator charging– UL and DL charging per UE, PDN, and QCI– Lawful Interception

PDN Gateway (P-GW)– Serves SGi interface towards PDN – UE IP address allocation– Mobility anchor for internetworking with non-3GPP networks– DL packet filtering and assignment to EPS bearers (QoS) based on TFTs– QoS enforcement and flow based-charging according to rules from PCRF

(Policy and Charging Enforcement Function – PCEF)– Lawful Interception


Home Subscriber Server (HSS)

– User subscription repository for permanent user data (subscriber profiles including MSISDN, IMSI, keys, user capabilities, etc.)

– Dynamic user data esp. current location– Combines functionality of HLR and AuC

E-UTRAN

MME

Serving GW PDN GWS1-U

S1-MME S11

S5

Internet

EPS Core

SGi

HSSS6a

S10

PCRF

GxGxc


PCRF – Policy Control and Charging Rules Function

Key Functionalities:• fundamental entity to manage flow-

specific traffic differentiation and QoS provisioning

• maps QoS requirements of individual services (SDF – beyond EPS) to an individual flow (EPS bearer – inside EPS)

• Subscriber-specific and service-specific selection of Access Point Name (APN) and APN-specific policy control, e.g. IMS for voice

• ensures proper charging for use of QoS enabled services (time-, volume- or event-based)

• instructs and authorizes the P-GW (PCEF – Policy and Charging Enforcement Function) about QoS authorization (QCI and throughput)

PCRF• controls QoS and charging of

EPS bearers• provides policy and charging

control (PCC) rules

See TS 23.203 for details

Serving GW PDN GWS5

InternetSGi

PCRF

GxGxc

PCEF


EPS Protocol Architecture (U Plane)

Serving GW PDN GW

S5/S8

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

LTE-Uu: radio interface (UE - eNB)GPRS Tunneling Protocol for the user plane (GTP-U): • tunnels user data between eNodeB and the S-GW as well as between the S-

GW and the P-GW


EPS Protocol Architecture (C 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

Non-Access Stratum Signaling (NAS): • supports mobility management functionality and user plane bearer activation,

modification and deactivation • ciphering and integrity protection of NAS signaling

S1 Application Protocol (S1-AP): Signaling Application Layer between eNBand MME


• S1 Interface is the reference point between eNodeB and EPC• Two types of S1 Interface

– C Plane: S1-MME between eNodeB and MME– U Plane: S1-U between eNodeB and S-GW

Legend– S1 Application Protocol (S1-AP): Application Layer Protocol between the eNodeB

and the MME– Streaming Control Transfer Protocol for the control plane (SCTP): guaranteed

delivery of signaling messages between MME and eNodeB (S1); defined in RFC 4960– GPRS Tunneling Protocol for the user plane (GTP-U): tunnels user data between

eNodeB and S-GW

S1 Interface (eNB - EPC)

UDP

L2

L1

IP

L2

L1

IP

UDP

S1-UeNodeB S-GW

GTP-U GTP-U

SCTP

L2

L1

IP

L2

L1

IP

SCTP

S1-MMEeNodeB MME

S1-AP S1-AP


X2 Interface (eNB - eNB)

• The X2 Interface is defined between two eNodeBs– U Plane: X2-U used for data forwarding– C Plane: X2-C used for HO support and load management

Legend:– X2 Application Protocol (X2-AP): Application Layer Protocol between the

eNodeBs

– Streaming Control Transfer Protocol for the control plane (SCTP):guarantees delivery of signaling messages between the eNodeB (X2)

– GPRS Tunneling Protocol for the user plane (GTP-U): tunnels user data between the eNodeB

X2-U interface X2-C interface


S5/S8 Interface (S-GW - P-GW)

• S5 and S8 interfaces provide user plane tunneling and tunnel management between the S-GW and the P-GW– S5 to connect S-GW to (non-collocated) P-GW of same operator– S8 to connect S-GW in visited PLMN to a P-GW in Home-PLMN

Legend– GPRS Tunnelling Protocol for the control plane (GTP-C): tunnels signalling

messages between S-GW and P-GW– GPRS Tunneling Protocol for the user plane (GTP-U): tunnels user data

between S-GW and P-GW– Proxy Mobile IP (PMIP): transports signalling messages between S-GW and

P-GW; PMIPv6 is defined in RFC 5213

S5/S8 interface via GTP

UDP

L2

L1

IP

L2

L1

IP

UDP

S5 or S8S-GW P-GW

GTP-U/C GTP-U/C

S5/S8 interface via PMIP

S5 or S8Serving GW PDN GW

IPv4/IPv6

L2

L1

PMIPv6

IPv4/IPv6

L2

L1

PMIPv6

Air Interface Protocol Architecture

• LTE Protocol Architecture• LTE Channels• Services and Functions


LTE Protocol Architecture - Overview

eNB

PHY

UE

PHY

MAC

RLC

MAC

MME

RLC

NAS NAS

RRC RRC

PDCP PDCP

eNB

PHY

UE

PHY

MAC

RLC

MAC

PDCPPDCP

RLC

S-Gateway

C Plane

U Plane


LTE Protocol Architecture – U Plane Overview

UE eNodeB MME

eNB

PHY

UE

PHY

MAC

RLC

MAC

PDCPPDCP

RLC

S-GatewayRLC 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 to transport channelsSchedulingError correction through HARQPriority handling across UEs & logical channels

Physical sub-layer performs: ModulationCoding (FEC)UL power controlMulti-stream transmission & reception (MIMO)


LTE Protocol Architecture – C Plane Overview

eNB

PHY

UE

PHY

MAC

RLC

MAC

MME

RLC

NAS NAS

RRC RRC

PDCP PDCP

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 control Idle mode mobility handling/ paging origination


Physical Layer Resource Scheduling and Allocation

Basic unit of allocation is called a Resource Block (RB)12 subcarriers in frequency (= 180 kHz) 1 timeslot in time (= 0.5 ms, = 7 OFDM symbols)Multiple resource blocks can be allocated to a user in a given subframe

The total number of RBs available depends on the operating bandwidth

12 sub-carriers(180 kHz)

Bandwidth (MHz) 1.4 3.0 5.0 10.0 15.0 20.0

Number of available resource blocks

6 15 25 50 75 100


Physical Layer Services – Transport Channels

• Shared Channel SCH (UL & DL)– Carries majority of data and control traffic– Adaptive modulation and coding (AMC) & Hybrid ARQ (HARQ)– Possibility to use beamforming– Controlled by eNodeB scheduler

• Broadcast Channel BCH (DL)– Broadcast of system information (MIB)– Fixed transport format, broadcast over entire cell

• Paging Channel PCH (DL)– Notification of UEs– Support of DRX, broadcast over entire cell– Mapped to PDSCH

• Random Access Channel RACH (UL):– Provides indication of UE request– Collision-based channel


Physical Layer Model: DL-SCH

CRC

RB mapping

Coding + RM

Data modulation

CRC

Resource mapping

Coding + RM

QPSK, 16QAM, 64QAMData modulation

HARQ

MA

C s

ched

uler

N Transport blocks( dynamicsize S1 ..., SN)

Node B

Redundancyfordata detection

Redundancyforerror detection

Multi- antennaprocessing

Resource/powerassignment

Modulationscheme

version

Antennamapping

HARQ info

ACK/NACK

Channel- stateinformation, etc.

Antenna mapping

CRC

RB mapping

Coding + RM

Data modulation

CRC

Resource demapping

Decoding + RM

Data demodulation

HARQ

UE

HARQ info

ACK/NACK

Antenna demapping

Errorindications

CRC

RB mapping

Coding + RM

Data modulation

CRC

Resource mapping

Coding + RM

QPSK, 16QAM, 64QAMData modulation

HARQ

MA

C s

ched

uler

N Transport blocks( dynamicsize S1 ..., SN)

Node B

Redundancyfordata detection

Redundancyforerror detection

Multi- antennaprocessing


Modulationscheme

version

Antennamapping

HARQ info

ACK/NACK

Channel- stateinformation, etc.

Antenna mapping

CRC

RB mapping

Coding + RM

Data modulation

CRC

Resource demapping

Decoding + RM

Data demodulation

HARQ

UE

HARQ info

ACK/NACK

Antenna demapping

Errorindications

RedundancyRedundancy


Physical Layer Model: UL-SCH

CRC

RB mapping

Coding + RM

Data modulation

Interl.

CRC

Resource demapping

Decoding + RM

Data demodulation

Deinterleaving

MA

C s

ched

uler

Node B

Resourceassignment

Modulationscheme

Redundancyversion

Antennamapping

HARQ info

ACK/NACK

Antenna demapping

CRC

RB mapping

Coding + RM

Data modulation

Interl.

CRC

Resource mapping

Coding + RM

Data modulation

Interleaving

HARQ

UE

HARQ info

Antenna mapping

Errorindications


Modulationscheme

Antennamapping

HARQ

Upl

ink

tran

smis

sion

con

trol

Channel- state information, etc.

CRC

RB mapping

Coding + RM

Data modulation

Interl.

CRC

Resource demapping

Decoding + RM

Data demodulation

Deinterleaving

MA

C s

ched

uler

Node B

Resourceassignment

Modulationscheme

Redundancyversion

Antennamapping

HARQ info

ACK/NACK

Antenna demapping

CRC

RB mapping

Coding + RM

Data modulation

Interl.

CRC

Resource mapping

Coding + RM

Data modulation

Interleaving

HARQ

UE

HARQ info

Antenna mapping

Errorindications


Modulationscheme

Antennamapping

HARQ

Upl

ink

tran

smis

sion

con

trol

Channel- state information, etc.

Redundancyversion

Redundancyversion


Layer 2 – Structure (DL)

Segm.ARQ etc

Multiplexing UE1

Segm.ARQ etc...

HARQ

Multiplexing UEn

HARQ

BCCH PCCH

Logical Channels

Transport Channels

MAC

RLC Segm.ARQ etcSegm.

ARQ etc

PDCPROHC ROHC ROHC ROHC

Radio Bearers

Security Security Security Security

...CCCH

MCCHMTCH

Unicast Scheduling / Priority Handling

Multiplexing

MBMS Scheduling

Segm. Segm.

DL structure – eNodeB side


Layer 2 – Structure (UL)

Multiplexing

...

HARQ

Scheduling / Priority Handling

Transport Channels

MAC

RLC

PDCP

Segm.ARQ etc

Segm.ARQ etc

Logical Channels

ROHC ROHC

Radio Bearers

Security Security

CCCH

UL structure – UE side


MAC Sublayer

• Services – Logical Channels– Dedicated Traffic Channel DTCH (UL & DL): user data– Dedicated Control Channel DCCH (UL & DL): control data (SRB1 & 2)– Common Control Channel CCCH: control data (SRB0)– Broadcast Control Channel BCCH: broadcast of cell information– Paging Control Channel PCCH: notification of UEs

• Functions– Mapping between logical channels and transport channels– Multiplexing/ demultiplexing of MAC SDUs belonging to one or different

logical channels into/from transport blocks (TB) delivered to/ from the physical layer on transport channels

– Scheduling information reporting– Error correction through HARQ– Priority handling between logical channels of one UE– Priority handling between UEs by means of dynamic scheduling– Transport format selection– Padding


Mapping between DL Channels

PCH: paging channel

BCH: broadcast channel

DL-SCH: DL shared channel

PDSCH: physical DL shared channel

PDCCH: physical DL control channel

PHICH: physical HARQ indication channel

PCFICH: physical control format indication channel

PBCH: Physical broadcast channel

BCCHPCCH CCCH DCCH DTCH MCCH MTCH

BCHPCH DL-SCH MCH

DownlinkLogical channels

DownlinkTransport channels

DownlinkPhysical Channels

PDSCH PDCCHPBCH PHICHPCFICH PMCH


Mapping between UL Channels

CCCH DCCH DTCH

RACH UL-SCH

UplinkLogical channels

UplinkTransport channels

UplinkPhysical Channels

PUSCH PUCCHPRACH

RACH: random access channel

UL-SCH: UL shared channel

PUSCH: physical UL shared channel

PUCCH: physical UL control channel

PRACH: physical random access channel


RLC Sublayer

• Services– TM (transparent mode) data transfer: no modification– UM (unacknowledged mode) data transfer: error indication only– AM (acknowledged mode) data transfer: error correction

• Functions– Transfer of upper layer PDUs– Error correction through ARQ (only for AM data transfer)– Concatenation, segmentation and reassembly of RLC SDUs (only

for UM and AM data transfer)– Re-segmentation of RLC data PDUs (only for AM data transfer)– Reordering of RLC data PDUs (only for UM and AM data transfer)– Duplicate detection (only for UM and AM data transfer)– RLC SDU discard (only for UM and AM data transfer)– RLC re-establishment– Protocol error correction (only for AM data transfer)


RLC Model for AM

Transmissionbuffer

Segmentation &Concatenation

Add RLC header

Retransmission buffer

RLC control

Routing

Receptionbuffer & HARQ

reordering

SDU reassembly

DCCH/DTCH DCCH/DTCH

AM-SAP

Remove RLC header

RLC Acknowledged Mode Entity


PDCP Sublayer

• Functions on U Plane– Transfer of user data– Ciphering and deciphering– Robust header compression and decompression: ROHC– In-sequence delivery of upper layer PDUs at PDCP re-

establishment procedure for RLC AM– Duplicate detection of lower layer SDUs at PDCP re-

establishment procedure for RLC AM– Retransmission of PDCP SDUs after handover (RLC AM only)– Timer-based SDU discard in uplink

• Functions on C Plane– Transfer of control plane data– Ciphering and Integrity Protection


Data Flow through Layer 2

RLC header

RLC PDU

......

n n+1 n+2 n+3RLC SDU

RLC header

PDCP SDUPDCP header

PDCP PDU

MAC Control element 1

...

R/R/E/LCID sub-header

MAC header

R/R/E/LCIDsub-header

... R/R/E/LCID/F/L sub-header

R/R/E/LCID padding sub-header

MAC Control element 2 MAC SDU MAC SDU

Padding (opt)

MAC PDU

PDCP SDU: IP packet (compressed/ uncompr.)PDCP header: 1 or 2 bytes

MAC control elements:• UL: MAC reports• DL: Timing advance• Control Information

All PDUs are byte-aligned

RLC header:• Sequence number• Segmentation/

concatenation information


RRC Layer

• Services– Broadcast of common control information– Notification of UEs in RRC_IDLE, e.g. about an arriving call– Transfer of dedicated control information, i.e. information for one

specific UE

• Functions– Broadcast of system information:

Including NAS common information Information for UEs in RRC_IDLE state, e.g. cell (re-)selection

parameters, neighbouring cell information Information for UEs in RRC_CONNECTED state, e.g. common

channel configuration information


RRC Layer (contd.)

• Functions (contd.)– RRC connection control:

Paging Establishment, modification & release of RRC connection Initial security activation RRC connection mobility Establishment, modification & release of radio bearers carrying user

data (DRBs) Radio configuration control QoS control Recovery from radio link failure

– Inter-RAT mobility including e.g. security activation, transfer of RRC context information

– Measurement configuration and reporting– Generic protocol error handling


RRC States

RRC States incl. Inter-RAT mobility (3GPP only)

Connection establishment/release

UMTS LTE GSM/GPRS


Tracking Area

BCCHTAI 1

BCCHTAI 1

BCCHTAI 1

BCCHTAI 1

BCCHTAI 1

BCCHTAI 2

BCCHTAI 2

BCCHTAI 2

BCCHTAI 2

BCCHTAI 2

BCCHTAI 2

BCCHTAI 3

BCCHTAI 3

BCCHTAI 3

BCCHTAI 3

Tracking Area 1

Tracking Area 2 Tracking Area 3

• Tracking Area Identifier (TAI) sent over Broadcast Channel BCCH• Tracking Areas can be shared by multiple MMEs• An UE may be allocated to multiple tracking areas• Different from UMTS, no hierarchy in the paging area!

Bearers, States and Identifiers

• EPS Bearers and Radio Bearers• RRC, ECM & EMM States• UE Identifiers


EPS Bearer Service Architecture – Overview

P-GWS-GW PeerEntity

UE eNB

EPS Bearer

Radio Bearer S1 Bearer

End-to-end Service

External Bearer

Radio S5/S8

Internet

S1

E-UTRAN EPC

Gi

E-RAB S5/S8 Bearer

3GPP: TS 23.203 Policy and Charging Control Architecture


Radio Bearer: SRB vs. DRB

• A radio bearer is a RLC connection between UE and eNodeB– Radio Bearers provide the data transfer over the air interface

• Signaling Radio Bearers (SRB) are used to transfer RRC and NAS control messages between UE and eNodeB– SRB0: RRC messages over CCCH– SRB1: RRC and NAS (when no security) messages over DCCH– SRB2: NAS messages (when security established) over DCCH

• Data Radio Bearer (DRB) transports packets of an EPS bearer between UE and eNodeB– One-to-one mapping between this data radio bearer and the EPS

bearer/E-RAB– Each DRB has its own handling policy (QoS, priority, handling

during HO)


EPS Bearer: Default vs. Dedicated

• EPS Bearer: logical association between UE and P-GW– Aggregates one or several service data flows (SDF)– Consists of three elements: Radio Bearer, S1 Bearer, S5/S8

Bearer– Each bearer has its own QoS attributes (e.g. GBR/MBR)

• Default EPS Bearer– First connection, established during initial attach to a PDN– Remains established during lifetime of PDN connection– There can be multiple default bearers to different PDN (having a

unique IP address)• Dedicated EPS Bearers

– Additional EPS bearers established to the P-GW– Multiple bearer connections with dedicated QoS policies

• All EPS bearers of an UE are handled by the same S-GW


LTE RRC States

• No RRC connection, no context in eNodeB (but EPS bearers are retained)

• UE controls mobility through cell selection

• UE acquires system information from broadcast channel

• UE monitors paging channel to detect incoming calls

• UE-specific paging DRX cycle controlled by upper layers

• RRC connection and context in eNodeB

• Network controlled mobility• Transfer of unicast and broadcast

data to and from UE• UE monitors control channels

associated with the shared data channels

• UE provides channel quality and feedback information

• Connected mode DRX can be configured by eNodeB according to UE activity level

RRC_IDLE RRC_ConnectedRelease RRC connection

Establish RRC connection


EPS Connection Management States (ECM)

• No signaling connection between UE and core network (no S1-U/ S1-MME)

• No RRC connection (i.e. RRC_IDLE)

• UE performs cell selection and tracking area updates (TAU)

• Signaling connection established between UE and MME, consists of two components– RRC connection– S1-MME connection

• UE location is known to accuracy of Cell-ID

• Mobility via handoverprocedure

ECM_IDLE ECM_ConnectedSignaling connection released

Signaling connection established


EPS Mobility Management States (EMM)

• EMM context does not hold valid location or routing information for UE

• UE is not reachable by MME as UE location is not known

• UE successfully registers with MME with Attach procedure or Tracking Area Update (TAU)– Setup EPS security context

• UE location known (at least) with accuracy of tracking area

• MME can page UE• UE maintains at least one PDN

connection (default EPS bearer)

EMM_DeregisteredDetach

Attach

EMM_Registered


Relation between EMM and ECM States

EMM-Deregistered EMM-Registered

ECM-Idle

RRC-Idle

ECM-Idle

RRC-Idle

A B

Power is turned off for a long

time

Power On Power On

PLMN/Cell Selection

PLMN/Cell Selection

Attach

Attach

ECM-Connected

RRC-Connected

ECM-Idle

RRC-Idle

C D

Handover Cell Reselection

• UE Inactivity Detection• TAU Accept

• New Traffic• TAU Request

UE Power Off

• Detach• Attach Reject• TAU Reject• UE Power Off

Adapted from www.netmanias.com


EPS Bearer and Signaling Connections in EMM-registered State

RRC Connection

Data Radio Bearer

S5 GTP-C

S1 Bearer S5 Bearer

S11 GTP-CCon

trol

Pla

ne

Dat

a P

lan

e

State C:• EMM-Registered • ECM-Connected• RRC-Connected

S1 signalingConnection

ECM Connection

EPS Bearer

UE eNB S-GW P-GW

MME


EPS Bearer and Signaling Connections in EMM-registered State

RRC Connection

Data Radio Bearer

S5 GTP-C

S1 Bearer S5 Bearer

S11 GTP-CCon

trol

Pla

ne

Dat

a P

lan

e

S1 signalingConnection

EPS Bearer

MME

UE eNB S-GW P-GW

State D:• EMM-Registered • ECM-Idle• RRC-Idle

ECM Connection


EMM, ECM and RRC States

Layer State Entity Description

EMM EMM-Deregistered

UE, MME

• UE is not attached to any LTE network • MME does not know the current location of the UE, but may have

tracking area (TA) information last reported by the UE

EMM-Registered

UE,MME

• UE has been attached to the LTE network• IP address has been assigned to the UE • EPS bearer has been established • MME knows the current location of the UE with an accuracy of a

cell or, at least, a tracking area

ECM ECM-Idle UE, MME

• No NAS signalling connection (ECM connection) established yet • UE has not been assigned physical resources, i.e. radio resources

(SRB/DRB) and network resources (S1 bearer/S1 signallingconnection) yet

ECM-Connected

UE, MME

• NAS signalling connection (ECM connection) is established• UE has been assigned physical resources, i.e. radio resources

(SRB/CRB) and network resources (S1 bearer/S1 signallingconnection)

RRC RRC-Idle UE, eNB • No RRC connection is established yet

RRC-Connected

UE, eNB • RRC connection has been established


EMM, ECM and RRC States – User View

Case State User Experiences (Examples)

AEMM-Deregistered+ ECM-Idle + RRC-Idle

• When a UE is switched on for the first time after subscription• When a UE is switched on after staying turned off for a long time• No UE context is present in the LTE network

B

EMM-Deregistered+ ECM-Idle + RRC-Idle

• When a UE is switched on within a certain period of time after being turned off

• When ECM connection is lost during communication due to radio link failure

• Some UE context from the last attach can still be stored in the network (e.g. to avoid running an AKA procedure during every Attach procedure)

CEMM-Registered+ ECM-Connected + RRC-Connected

• UE is attached to the network (an MME) and is using services (e.g. Internet, VoIP, Live TV)

• Mobility handled by handover procedures

DEMM-Registered+ ECM-Idle + RRC-Idle

• UE is attached to the network (an MME), but not using any service• Mobility handled by cell reselection procedures


UE Location Information in Network Elements

Case State UE eNB S-GW P-GW MME HSS PCRF SPR

AEMM-Deregistered+ ECM-Idle+ RRC-Idle

- - - - - - - -

BEMM-Deregistered+ ECM-Idle+ RRC-Idle

- - - - TAI oflast TAU

MME - -

CEMM-Registered+ ECM-Connected+ RRC-Connected

- Cell/eNB

Cell/eNB

Cell/eNB

Cell/eNB

MME -

DEMM-Registered+ ECM-Idle+ RRC-Idle

- - TAI oflast TAU

TAI oflast TAU

TAI oflast TAU

MME -


UE Identifiers

• IMSI: International Mobile Subscriber Identity– Assigned by service provider, stored on SIM-card

• TMSI: Temporary Mobile Subscriber Identity– Assigned temporarily by the control nodes

• IMEI: International Mobile Equipment Identity– Unique identity for each mobile assigned by manufacturer

• MSISDN: Mobile Subscriber ISDN number– Telephone number assigned by service provider


UE Identifiers

• GUTI: Global Unique Temporary Identity– UE Identity without revealing the mobile or the user– GUTI has two parts

Globally Unique MME Identifier (GUMMEI) identifies the MME, assigned by service provider

M-TMSI identifies UE within the MME, assigned by MME

• The UE can attach to the network using either IMSI or GUTI

GUTI

GUMMEI M-TMSI

MME ID48 bits 32 bits

MCC MNC MME Group ID MMECode


UE Identifiers

• RNTI: Radio Network Temporary Identifier– Used by eNB to temporary address the UEs (MAC)

• There exist a variety of different RNTIs– Cell RNTI (C-RNTI): unique identification used for identifying RRC

connection and scheduling– Paging RNTI (P-RNTI)– Random Access RNTI (RA-RNTI)– System Information RNTI (SI-RNTI)– Transmit Power Control RNTI (TPC-RNTI)– MBMS RNTI (M-RNTI, Rel.-9)


UE IDs maintained in Network Elements

GUTI (Globally Unique Temporary UE Identity) replaces TMSI to uniquely identify the UE and theused MME

Case State UE eNB S-GW P-GW MME HSS PCRF SPR

AEMM-Deregistered+ ECM-Idle+ RRC-Idle

IMSI - - - - IMSI - IMSI

BEMM-Deregistered+ ECM-Idle+ RRC-Idle

IMSI,GUTI

- - - IMSI, GUTI IMSI - IMSI

C

EMM-Registered+ ECM-Connected+ RRC-Connected

IMSI, GUTI, UE IP addr, C_RNTI

C-RNTI, eNB/MME UE S1AP

ID, Old/NeweNB UE X2AP ID

IMSI IMSI, UE IP addr

IMSI, GUTI, UE IP addr,

eNB/MME UE S1AP ID


IMSI

DEMM-Registered+ ECM-Idle+ RRC-Idle

IMSI, GUTI, UE IP addr

- IMSI IMSI, UE IP addr

IMSI, GUTI, UE IP addr


IMSI

Quality of Service

• QoS Parameters• QoS Bearers• QoS Architecture


QoS Architecture (U Plane) - Overview

P-GWS-GW PeerEntity

UE eNB

EPS Bearer

Radio Bearer S1 Bearer

End-to-end Service

External Bearer

Radio S5/S8

Internet

S1

E-UTRAN EPC

Gi

E-RAB S5/S8 Bearer

3GPP: TS 23.203 Policy and Charging Control Architecture


Implementation of QoS

- QoS involves functions in - C plane (connection management) and - U plane (forwarding and policing)

- QoS requires end-to-end considerations of all involved network entities as QoS can only be as good as its weakest element

- QoS is a cross-layer issue involves basically all layers- Application layer: identification of service and classification,

source coding- Transport layer: Retransmission policy – latency and reliability- Network, data link and PHY layer: provisioning of needed

resources (transport and processing), forwarding and scheduling over physical resources (including, modulation, channel coding, PRB scheduling, diversity and redundancy strategy)


Options that influence QoS

QoS requirements and influencing factors

- throughput ⇒depends on amount of resources allocated

- error rate/reliability ⇒depends on robustness of transmission (modulation and coding,

TX power/SINR, redundancy, transmission diversity, etc.)

- latency⇒depends on scheduling strategy, processing delay, error

rate/retransmission rate, system load

=> See AMCN course for details on QoS in general


QoS Class Identifier (QCIs)

QCI Resource Type PriorityPacket Delay

Budget

Packet Error LossRate

Example Services

1 2 100 ms 10-2 Conversational Voice

2 GBR 4 150 ms 10-3 Conversational Video (Live Streaming)

3 3 50 ms 10-3 Real Time Gaming

4 5 300 ms 10-6Non-Conversational Video (Buffered Streaming)

5 1 100 ms 10-6 IMS Signalling

6 6 300 ms 10-6Video (Buffered Streaming)TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.)

7 Non-GBR 7 100 ms 10-3Voice,Video (Live Streaming)Interactive Gaming

8 8 300 ms 10-6Video (Buffered Streaming)TCP-based (e.g., www, e-mail, chat, ftp, p2p file

9 9 sharing, progressive video, etc.)


Traffic Flow Template (TFT) and QoS Enforcement

Context• QCIs represent classes (or QoS types) of traffic• To provide a flow with a certain QoS, we need

– QCI, to specify handling wrt latency, error correction and data rate– Throughput (guaranteed and maximum bit rate – GBR & MBR) – TFT, to define rules to identify external flows and to map each flow

on specific EPS bearer (with QCI and throughput requirements)– ARP (Admission and Retention Policy) for overload handling

Purpose of TFT • Identify IP packet flows (SDFs) and map to EPS bearers• Mapping implemented at the edges of the network, i.e. UE and P-GW

Content of TFT (for traffic identification)• IP source and destination• Port numbers• ...


Important Terms and Ingredients for QoS

- QCI (QoS Class Identifier) – defines QoS requirements with exception of throughput

- ARP (Admission and Retention Policy) – defines priority of EPS bearer for admission and contention cases

- TFT (Traffic Flow Template) – defines mapping of SDFs on EPS bearer (formerly PDP context) – unit for QoS management- Data rate, latency, error rate/reliability

- SDF (Service Data Flow) – service-specific IP flow- EPS bearers (IP addresses, port numbers, protocol ID)- IP CAN (end-to-end bearer), i.e. an IP flow

- GBR: Guaranteed Bit Rate- MBR: Maximum Bit Rate- AMBR: Aggregated MBR - APN-AMBR: APN-specific MBR


Service Data Flow (SDF):- defines QCI, ARP, MBR and possibly GBR

EPS bearer- defines QCI, ARP, possibly GBR, MBR or UE-AMBR and APN-AMBR- may combine several SDFs to a single EPS bearer

EPS session:- comprises one or more SDFs (i.e. services) mapped to one or more EPS

bearers (default or dedicated bearer)

Source: www.netmanias.com

QoS Parameters for SDF and EPS Bearer


Enforcement of QoS

Main entities for QoS handling are the network edges, i.e.- P-GW for the DL- eNB and UE for the UL (eNB provides grants to the UE for UL transmission)


EPS bearers(inside EPS)

SDFs(outside EPS)

SDF-EPS mapping via TFTs


QoS Policing and Scheduling for DL


SDF-EPS mapping via TFTsPolicing DL Scheduling


QoS Policing and Scheduling for UL


SDF-EPS mapping via TFTsPolicing on UL provided grants

Provision of UL grants

Call Handling Procedures

• Basic procedures− Paging− RRC Connection Establishment− Dedicated S1 Establishment− E-RAB Setup/Release− RRC Re-establishment

• End-to-end procedures:− First Attach − Tracking Area Update


Call Handling: End-to-End ScenariosEnd-to-end scenarios (cf 3GPP 23.401)

eNB use cases Applicable eNB procedure blocks

Applicable 3GPP RRC, S1, X2 procedures

Attach MO Default E-RAB setup RRC Connection Establishment RRC: RRC Connection EstablishmentS1-AP: -

S1 Dedicated Establishment RRC: -S1-AP: Initial UE Message

NAS Transfer RRC: NAS Direct TransferS1-AP: NAS Transport

Initial Context Setup RRC: RRC Connection ReconfigurationS1-AP: Initial Context Setup

Detach S1 release (EPC triggered) S1 Release (EPC triggered) RRC: RRC Connection ReleaseS1-AP: UE Context Release

Tracking Area Update Connection establishment without E-RAB setup

RRC Connection establishment RRC: RRC Connection EstablishmentS1-AP: -

S1 Dedicated Establishment RRC: -S1-AP: Initial UE Message

NAS Transfer RRC: NAS Direct TransferS1-AP: NAS Transport

UE Release RRC: RRC Connection ReleaseS1-AP: UE Context Release

UE triggered Service Request MO Default E-RAB setup Same as “Attach”Network Triggered Service Request

MT Default E-RAB setup Paging + MO Default E-RAB Setup

Dedicated bearer activation (or UE requested bearer resource activation)

Dedicated E-RAB setup E-RAB Setup RRC: RRC Connection ReconfigurationS1-AP: E-RAB Setup

Dedicated bearer de-activation (or UE Requested Bearer Resource Release)

Dedicated E-RAB release E-RAB Release RRC: RRC Connection ReconfigurationS1-AP: E-RAB Release

S1 release (EPC triggered) S1 release (EPC triggered) S1 Release (EPC triggered) RRC: RRC Connection ReleaseS1-AP: UE Context Release

S1 release (ENB triggered) S1 release (ENB triggered) S1 Release Request (ENB triggered)S1 Release (EPC triggered)

RRC: RRC Connection ReleaseS1-AP: UE Context Release Request

UE Context Release


Paging

• Upon receiving an S1-AP PAGING message, the eNB determines the list of cells on which to page the UE from the “List of TAIs” provided by the S1-AP PAGING message

• For each cell on which the UE must be paged, the eNB will:– Compute the frame number and sub-frame number of the UE's paging

occasion (based on UE Identity Index Value, DRX paging cycle)– ASN1 encode the paging record for the given UE– Provide this data to the scheduler along with the DRX paging cycle

RRC: Paging

UE MME eNB

S1-AP: Paging


RRC Connection Establishment

• RRC Connection Establishment procedure establishes SRB1 between UE and eNB

UE eNB

RRCConnectionRequest

InitialUE-IdentityestablishmentCause

RRCConnectionSetupRadioResourceConfigDedicated

RRCConnectionSetupComplete

SelectedPLMN-Identity,

RegisteredMME

NAS-DedicatedInformation

CCCHSRB0RLC TM

CCCHSRB0RLC TM

DCCHSRB1RLC AM

UE RRC_connected

UE RRC_idleRandom Access


RRC Connection Establishment (cont.)

• RRC Connection Setup uses contention-based Random Access– RACH only used for indication of scheduling request– First data sent on assigned UL-SCH

• Establishment causes– Emergency– High Priority Access– Mobile Terminated (MT) Access– Mobile Originated (MO) Signaling– Mobile Originated Data

• In case of failure (RRC Connection Reject) UE will repeat RRC Connection Request message


Dedicated S1 Establishment

• Dedicated S1 Establishment procedure establishes the S1 dedicated connection to complement RRC connection

S1-AP: DL NAS TRANSPORT MME S1-AP UE Identity, eNB S1-AP UE identity

UL INFORMATION TRANSFER

DL INFORMATION TRANSFER

UE eNB MME

S1-AP: UL NAS TRANSPORT

S1-AP: INITIAL UE MESSAGEeNB S1-AP UE Identity

S1-AP: INITIAL CONTEXT SETUP RESPONSE

S1-AP: INITIAL CONTEXT SETUP REQUESTMME S1-AP UE Identity, eNB S1-AP UE identity

(Case 1) or (Case 2)

RRC Connection Establishment

AS Security ActivationE-RAB Setup


Dedicated S1 Establishment (contd.)

• Upon reception of RRC Connection Setup Complete, the eNB will:– Perform MME selection if needed– Allocate an eNB UE identity that will be sent to the MME– Send S1-AP INITIAL UE MESSAGE towards the selected MME

• Case 1: UE not authenticated– Exchange of NAS-messages for authentication– MME S1-AP UE identity received in S1-AP DL NAS TRANSPORT

message• Case 2: UE authenticated (e.g. after case 1)

– Initial Context Setup procedure to establish the first E-RAB(s)– eNB will initiate security activation over the radio interface prior

to establishment of SRB2 and/or DRBs– eNB stores “UE Radio Capability” IE either from S1-AP message

or by using RRC UE capability transfer procedure– MME S1-AP UE identity received in S1-AP INITIAL UE CONTEXT

SETUP REQUEST message


Dedicated E-RAB setup

• Dedicated E-RAB setup procedure establishes new E-RAB(s) after Initial Context Setup– eNB will manage new E-RAB establishment similarly to SRB2 and

DRB(s) establishment in Initial Context Setup case.

UE eNB MME

S1AP E-RAB SETUP REQUESTeNB S1-AP UE Identity

MME S1-AP UE IdentityE-RAB to be Setup List

S1AP E-RAB SETUP RESPONSEMME S1-AP UE IdentityeNB S1-AP UE IdentityE-RAB Setup List

RRCConnectionReconfiguration

nas-DedicatedInformationList

RadioResourceConfigDedicated (DRB(s))

RRCConnectionReconfigurationComplete


E-RAB Release

• E-RAB Release procedure is used to release one or several E-RABs– Initiated by MME– When initiated by eNB: S1-AP E-RAB RELEASE INDICATION sent

to MME

UE eNB MME

S1AP E-RAB RELEASE COMMANDeNB S1-AP UE Identity

MME S1-AP UE IdentityE-RAB to be Released List

S1AP E-RAB RELEASE RESPONSEMME S1-AP UE IdentityeNB S1-AP UE IdentityE-RAB Release List

RRCConnectionReconfiguration

nas-DedicatedInformationList

RadioResourceConfigDedicated (DRB(s))

RRCConnectionReconfigurationComplete


UE Context Release

• UE Context Release procedure releases all E-RABs for an UE, including S1-U bearers, Radio bearers and the S1-MME signaling connection for the UE– Initiated by MME– When initiated by eNB: S1-AP UE CONTEXT RELEASE REQUEST

message sent before to MME

UE eNB MME

RRCConnectionRelease

S1AP UE CONTEXT RELEASE COMMANDeNB S1-AP UE Identity

MME S1-AP UE IdentityCause

S1AP UE CONTEXT RELEASE COMPLETEMME S1-AP UE IdentityeNB S1-AP UE Identity


RRC Connection Re-establishment

• Re-establishment procedure is triggered in the following cases:– UE detects a L1/ L2 failure– RRC Connection Reconfiguration procedure fails– Mobility procedure fails

• eNB re-establishes the RRC connection– Re-establishment of MAC, RLC and PDCP for SRBs and DRB– Re-establishment of SRB1– RRC Connection Reconfiguration used afterwards to re-establish SRB2

and DRB(s)

RRCConnectionReestablishmentRequest

UE eNB

RRCConnectionReestablishment

RRCConnectionReestablishmentComplete


Initial Attach Procedure

UE eNB MME SGW PGW PCRF HSS/EIR

Attach Request

RRC Connection Est.

Authentication/ Security

Update Location

Create Session Req.

IP-CAN Session Est.

Create Session Resp.

Create Session Req.


Attach Complete

UL Data

DL Data

Modify Bearer

Initial Context Setup/ Attach Accept

DL Data


Tracking Area Update with MME/S-GW Change

UE eNB New MME New S-GW Old MME P-GW HSS

TAU Request

RRC Connection Est.

Authentication/ Security


TAU Complete

Context Retrieval

Context Ack

Create Session Req.

Modify Bearer

Update Location

Cancel Location

Update Location Ack

TAU Accept

Old S-GW

Delete Session

LTE Mobility

• Handover Principle, UE Measurements• LTE-Handover over X2, S1• Inter-RAT Handover to UTRAN


LTE Handover

• LTE uses UE-assisted network-controlled handover– UE reports measurements; network decides when to handover and to

which cell– Relies on UE to detect neighbor cells → no need to maintain and

broadcast neighbor lists Allows "plug-and-play" capability; saves BCH resources

– For search and measurement of inter-frequency neighboring cells only carrier frequencies need to be indicated

• X2 interface used for handover preparation and forwarding of user data– Target eNB prepares handover by sending required information to UE

transparently through source eNB as part of the Handover Request Acknowledge message New configuration information needed from system broadcast Accelerates handover as UE does not need to read BCCH on target cell

– Buffered and new data are transferred from source to target eNB until path switch → prevents data loss

– UE uses non-contention based random access to accelerate handover


UE Measurements

• In LTE the UE measurements are mainly used for HO purpose

• Measurement quantities depend on the RAT to measure– LTE (intra-/ inter-frequency)

Reference Signal Received Power (RSRP) Reference Signal Received Quality (RSRQ)

– UMTS (FDD) Carrier Received Signal Strength Indicator (RSSI) CPiCH Received Signal Code Power (RSCP) CPiCH Ec/I0

– GSM Carrier Received Signal Strength Indicator (RSSI)

• eNB scheduler shall provide transmission gaps to allow inter-frequency and inter-RAT measurements


UE Measurement Model

• The measurement model consists of the following parts

• Measurement filtering:

𝐹𝐹𝑛𝑛 = 1 − 𝑎𝑎 ⋅ 𝐹𝐹𝑛𝑛−1 + 𝑎𝑎 ⋅ 𝑀𝑀𝑛𝑛Filter coefficient: 𝑎𝑎 = 2− ⁄𝑘𝑘 4, 𝑘𝑘 = 0 … 19sample rate at point B: 200msec

• Reporting criteria– Measurement triggers for event-based reporting: handover– Periodical reporting: e.g. tracing

Layer 1 filtering

Layer 3 filtering

Evaluation of reporting

criteria

A D B C

C'

RRC configures parameters

RRC configures parameters


Handover Measurement Events

• Intra-LTE measurement events (intra- and inter-frequency)– A1: Serving cell better than threshold– A2: Serving cell worse than threshold– A3: Neighbor cell with offset better than serving cell– A4: Neighbor cell better than threshold– A5: Serving cell worse than threshold #1, neighbor cell better

than threshold #2

• Inter-RAT measurement events– B1: Inter-RAT neighbor cell better than threshold– B2: Serving cell worse than threshold #1, Inter-RAT neighbor cell

better than threshold #2

• To reduce signaling amount, hysteresis and time-to-trigger might be applied


X2 Handover: Preparation Phase

UEUESource eNB

Source eNB

Measurement Control

Target eNB

Target eNB MMEMME sGWS-GW

Packet Data Packet Data

UL allocation

Measurement Reports

HO decision

Admission Control

HO Request

HO Request AckDL allocation

RRC Connection Reconfig.

L1/L2 signaling

L3 signaling

User data

• HO decision is made by source eNB based on UE measurement report• Target eNB prepares HO by sending relevant info to UE through source eNB as

part of HO request ACK command, so that UE does not need to read target cell BCH

SN Status Transfer


X2 Handover: Execution Phase

UEUESource eNB

Source eNB

Target eNB


Detach from old cell, sync with new cell

Deliver buffered packets and forward new packets to target eNB

DL data forwarding via X2

Synchronisation

UL allocation and Timing Advance

RRC Connection Reconfig. Complete

L1/L2 signaling

L3 signaling

User dataBuffer packets from source eNB

Packet Data

Packet Data

• RACH is used here only so target eNB can estimate UE timing and provide timing advance for synchronization; RACH timing agreements ensure UE does not need to read target cell P-BCH to obtain SFN (radio frame timing from SCH is sufficient to know PRACH locations)

UL Packet Data


X2 Handover: Completion Phase

UEUESource eNB

Source eNB

Target eNB


DL Packet Data

Path switch req

Modify bearer req.

Switch DL path

Path switch req ACKUE Context Release


L1/L2 signaling

L3 signaling

User data

DL data forwarding

Flush DL buffer, continue delivering in-

transit packets

End Marker

Release resources

Packet Data

End Marker

Modify bearer resp.


LTE Handover: Illustration of Interruption Period

UL

U- plane active

U- plane active

UEUESource eNB

Source eNB

Target eNB

Target eNB

UL

U- plane active

U- plane active

UEs stops Rx/Tx on the old cell

DL synchronisation+

Timing advance+

UL resource request/grant

DL sync+ RACH (no contention)

+ Timing Adv+ UL Resource Req

and Grant

ACK

HO Request

HO Confirm

HandoverLatency

(approx. 55 ms)Approx. 20 ms

Measurement Report

HO Command

HO Complete

HandoverInterruption

(approx. 35 ms)

Handover Preparation


S1 Handover

• S1 handover is performed, when there is no X2 connection between source and target eNodeB– Operator preference– No logical connectivity, e.g. HeNB

• Handover procedure is similar to X2 handover, except for– C Plane messages forwarded via MME– U Plane data forwarded via S-GW– increase in handover latency


S1 Handover Procedure

UEUESource eNB

Source eNB

Target eNB



Measurement Reports

HO decision

Admission Control

HO Required

HO Command

RRC Connection Reconfig.

L3 signaling

User data

ENB Status Transfer

HO Request

HO Request Ack

MME Status Transfer

Detach from old cell, sync with new cell

Path switch procedure/ UE Context Release in source eNB

DL data forwarding via S1

RRC Connection Reconfig. Complete

Packet Data

Packet Data UL Packet Data

HO Notify



References

• Literature– Holma, Toskala: LTE for UMTS – Evolution to LTE-Advanced, Wiley 2011– E. Dahlman, S. Parkvall, J. Sköld: 4G, LTE-Advanced Pro and the Road

to 5G, 3rd edition, Aademic Press, 2016– Sesia, Toufik, Baker: LTE - The UMTS Long Term Evolution: From

Theory to Practice, Wiley 2011– LTE EMM and ECM States: www.netmanias.com

– The LTE Network Architecture - strategic white paper – Alcatel-Lucent, 2009

• 3GPP standards (www.3gpp.org/specifications):– 36-series: LTE radio aspects– 36.300: E-UTRAN – Overall description; Stage 2– 36.213: Physical layer procedures– 36.321: Medium Access Control (MAC) protocol specification– 36.331: Radio Resource Control (RRC); protocol specification– 36.413: S1 Application Protocol (S1AP)– 36.423: X2 Application Protocol (X2AP)

http://www.netmanias.com/http://www.3gpp.org/specifications

3G Long-Term Evolution (LTE) and�System Architecture Evolution (SAE)3GPP Evolution – BackgroundLTE Requirements and Performance TargetsKey Features of LTE to Meet RequirementsLTE/SAE ReleasesHow to navigate in 3GPP documents?LTE/SAE Network ArchitectureEvolved UTRAN (E-UTRAN) ArchitectureEvolved Node BEvolved Packet System (EPS) Architecture Mobility Management Entity (MME)Serving and PDN GatewaysHome Subscriber Server (HSS) PCRF – Policy Control and Charging Rules FunctionEPS Protocol Architecture (U Plane)EPS Protocol Architecture (C Plane)S1 Interface (eNB - EPC)X2 Interface (eNB - eNB)S5/S8 Interface (S-GW - P-GW)Air Interface Protocol ArchitectureLTE Protocol Architecture - OverviewLTE Protocol Architecture – U Plane OverviewLTE Protocol Architecture – C Plane OverviewPhysical Layer Resource Scheduling and AllocationPhysical Layer Services – Transport ChannelsPhysical Layer Model: DL-SCHPhysical Layer Model: UL-SCHLayer 2 – Structure (DL)Layer 2 – Structure (UL)MAC SublayerMapping between DL ChannelsMapping between UL ChannelsRLC SublayerRLC Model for AMPDCP SublayerData Flow through Layer 2RRC LayerRRC Layer (contd.)RRC StatesTracking AreaBearers, States and IdentifiersEPS Bearer Service Architecture – Overview Radio Bearer: SRB vs. DRBEPS Bearer: Default vs. DedicatedLTE RRC StatesEPS Connection Management States (ECM)EPS Mobility Management States (EMM)Relation between EMM and ECM StatesEPS Bearer and Signaling Connections in EMM-registered StateEPS Bearer and Signaling Connections in EMM-registered StateEMM, ECM and RRC StatesEMM, ECM and RRC States – User ViewUE Location Information in Network ElementsUE IdentifiersUE IdentifiersUE IdentifiersUE IDs maintained in Network ElementsQuality of ServiceQoS Architecture (U Plane) - OverviewImplementation of QoSOptions that influence QoSQoS Class Identifier (QCIs)Traffic Flow Template (TFT) and QoS EnforcementImportant Terms and Ingredients for QoSQoS Parameters for SDF and EPS BearerEnforcement of QoSQoS Policing and Scheduling for DLQoS Policing and Scheduling for ULCall Handling ProceduresCall Handling: End-to-End ScenariosPagingRRC Connection EstablishmentRRC Connection Establishment (cont.)Dedicated S1 EstablishmentDedicated S1 Establishment (contd.)Dedicated E-RAB setupE-RAB ReleaseUE Context ReleaseRRC Connection Re-establishmentInitial Attach ProcedureTracking Area Update with MME/S-GW ChangeLTE MobilityLTE HandoverUE MeasurementsUE Measurement ModelHandover Measurement EventsX2 Handover: Preparation PhaseX2 Handover: Execution PhaseX2 Handover: Completion PhaseLTE Handover: Illustration of Interruption PeriodS1 HandoverS1 Handover ProcedureReferences

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3G Long-Term Evolution (LTE) and System Architecture ...€¦ · – LTE-Advanced with increased performance targets – Application of new scenarios (MTC) and novel concepts (D2D)