LTE Fundamentals, Channels, Architecture and Call Flow

5/28/2018 LTE Fundamentals, Channels, Architecture and Call Flow

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LTE/EPC Fundamentals


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2

Agenda

LTE Overview

LTE/EPC Network Architecture

LTE/EPC Network Elements

LTE/EPC Mobility & Session Management

LTE/EPC Procedure

LTE/EPS overview


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3

Agenda

Air Interface Protocols

LTE Radio Channels

Transport Channels and Procedure

LTE Physical Channels and Procedure

LTE Radio Resource Management

MIMO for LTE


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LTE Overview


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5

Cellular Generations

There are different generations as far as mobile communication is concerned:

First Generation (1G)

Second Generation (2G)

2.5 Generation (2.5G)

Third Generation (3G)

E3G (4G)

Fifth Generation(5G)


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6

History and Future of Wireless

data rates

< 1 Gbps

mobility

GSM/IS95

AMPS

WCDMA/cdma2000HSPA LTE

802.11a/b/g

802.16a/d 802.16e

< 100 Mbps< 50 Mbps< 10 Mbps< 1 Mbps< 200 kbps

time

2010200520001990

HIGH

LOW

2G

3G 3G Enhacements 3G Evolution

802.11 802.11nWLAN Family

WiMAX Family

1G


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3GPP Releases & Features


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Main LTE Requirements

Peak data ratesof uplink/downlink 50/100 Mbps

Reduced Latency:

Enables round trip time


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What is new in LTE?

New radio transmission schemes:

OFDMA in downlink

SC-FDMA in uplink

MIMO Multiple Antenna Technology

New radio protocol architecture:

Complexity reduction

Focus on shared channel operation, no dedicated channels anymore

New network architecture: flat architecture:

More functionality in the base station (eNodeB)

Focus on packet switched domain


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What is new in LTE?

Important for Radio Planning: Frequency Reuse 1

No need for Frequency Planning

Importance of interference control

No need to define neighbour lists in LTE

LTE requires Physical Layer Cell Identity planning (504 physical layer cell IDs organised

into 168 groups of 3)

Additional areas need to be planned like PRACH parameters, PUCCH and PDCCHcapacity and UL Demodulation Reference Signal


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Reasons for changes

Time

Traffic

volume

New technology, interfaces,

protocols

Simple low-cost architecture,

seamless transition from old

technologies (smooth coexistence)

Quick time2market for new

chipsets

OFDM, MIMO, large

bandwidth, scalable PHY/RRM

Cooperation with chipset

vendors

Flat LTE/SAE, co-location and

migration concept


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Evolution Path to LTE

Operator migration paths to LTE

>90 % of world radio access market migrating to LTE

Enabling flat broadband architecture

TD-SCDMAGSM /

(E)GPRS

LTE

CDMA

I-HSPA

WCDMA /

HSPA

TD-LTE


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LTE/EPC Network Architecture


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LTE/SAE Key FeaturesEUTRAN

Evolved NodeB No RNC is provided anymore

The evolved Node Bs take over all radio management functionality.

This will make radio management faster and hopefully the network architecture simpler

IP transport layer EUTRAN exclusively uses IP as transport layer

UL/DL resource scheduling In UMTS physical resources are either shared or dedicated

Evolved Node B handles all physical resource via a scheduler and assigns themdynamically to users and channels

This provides greater flexibility than the older system


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LTE/SAE Key FeaturesEUTRAN

QoS awareness

The scheduler must handle and distinguish different quality of service classes

Otherwise real time services would not be possible via EUTRAN

The system provides the possibility for differentiated service

Self configuration

Currently under investigation

Possibility to let Evolved Node Bs configure themselves

It will not completely substitute the manual configuration and optimization.


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Evolution of Network Architecture


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Evolution of Network Architecture

GGSN

SGSN

RNC

Node B

(NB)

Direct tunnel

GGSN

SGSN

HSPA R7 HSPA R7 LTE R8

Node B + RNC

Functionality

Evolved

Node B

(eNB)

GGSN

SGSN

RNC

Node B

(NB)

HSPA R6

LTE

SAE GW

MME/SGSN


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LTE Network Architecture Evolution

Node B RNC SGSN GGSN

Internet

3GPP Rel 6 / HSPA

User plane

Control PlaneOriginal 3G architecture.

2 nodes in the RAN.

2 nodes in the PS Core Network.

Every Node introduces additional delay.

Common path for User plane and Control plane data.

Air interface based on WCDMA.RAN interfaces based on ATM.

Option for Iu-PS interface to be based on IP


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Direct tunnel

3GPP Rel 7 / HSPA

Internet

Node B RNC

SGSN

GGSN

User plane

Control Plane

Separated path for Control Plane and User Plane data in the PS Core Network.

Direct GTP tunnel from the GGSN to the RNC for User plane data: simplifies the CoreNetwork and reduces signaling.

First step towards a flat network Architecture.

30% core network OPEX and CAPEX savings with Direct Tunnel.

The SGSN still controls traffic plane handling, performs session and mobility management,and manages paging.

Still 2 nodes in the RAN.


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Direct tunnel

3GPP Rel 7 / Internet HSPA

Internet

Node B

SGSN

GGSN

Node B

(RNC Funct.)User plane

Control Plane

I-HSPA introduces the first true flat architecture to WCDMA.

Standardized in 3GPP Release 7 as Direct Tunnel with collapsed RNC.

Most part of the RNC functionalities are moved to the Node B.

Direct Tunnels runs now from the GGSN to the Node B.

Solution for cost-efficient broadband wireless access.

Improves the delay performance (less node in RAN).

Deployable with existing WCDMA base stations.

Transmission savings


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Direct tunnel

3GPP Rel 8 / LTE

Internet

Evolved Node B

MME

SAE GW

LTE takes the same Flat architecture from Internet HSPA.

Air interface based on OFDMA.

All-IP network.

New spectrum allocation (i.e 2600 MHz band)

Possibility to reuse spectrum (i.e. 900 MHZ)

User plane

Control Plane


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LTE Network Architecture Evolution - Summary

Node B RNC SGSN GGSNInternet

3GPP Rel 6 / HSPA

Direct tunnel

3GPP Rel 7 / HSPA

Internet

Node B RNC

SGSN

GGSN

Direct tunnel

3GPP Rel 7 / Internet HSPA

Internet

Node B

SGSN

GGSN

Node B

(RNC Funct.)

Direct tunnel

3GPP Rel 8 / LTE

Internet

Evolved Node B

MME

SAE GW


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Terminology

EPS

EPCEPC - Evolved Packet Core

eUTRAN eUTRAN - Evolved UTRAN

EPSEvolved Packet System

SAE - System Architecture Evolution

LTE - Long Term Evolution

IP Network
http://www.sonyericsson.com/spg.jsp?cc=gb&lc=en&ver=4000&template=pp1_loader&php=php1_10238&zone=pp&lm=pp1&pid=10238http://www.sonyericsson.com/spg.jsp?cc=se&lc=sv&ver=4000&template=pp1_loader&php=php1_10409&zone=pp&lm=pp1&pid=10409


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TerminologyInterfaces----Logical view

EPC

S1S1 S1

X2 X2

eNodeBeNodeB eNodeB


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LTE/SAE Network Architecture

GGSN => Packet Gateway

SGSN => Mobility server

BSC

RNC

SGSN/ MME

GGSN/ P/S-GW

GSM, WCDMA

IP networks

LTE

SAE

MME = Mobility Management Entity

P/S-GW = PDN/Serving gateway


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Overall EPS Architecture

Basic EPS entities & interfaces


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LTE/EPC Network Elements


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LTE/SAE Network Architecture Subsystems

LTE/SAE architecture is driven by the goal to optimize the system for packet

data transfer.

No circuit switched components New approach in the inter-connection between radio access network and core

network

IMS/PDN

EPC

eUTRAN

LTE-UE


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EPS Architecture - Subsystems

LTE or EUTRAN SAE or EPC


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LTE/SAE Network Elements

LTE-UE

Evolved UTRAN (E-UTRAN)

MME S10

S6a

Serving

Gateway

S1-U

S11

PDN

Gateway

PDN

Evolved Packet Core (EPC)

S1-MME PCRF

S7

Rx+

SGiS5/S8

Evolved

Node B

(eNB)

cell

X2

LTE-Uu

HSS

MME: Mobility Management Entity

PCRF:Policy & Charging Rule Function

SAE

Gateway


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Evolved Node B (eNB)

RNC is not a part of E-UTRAN

Completely removed from the architecture

eNB is the only one entity in E-UTRAN eNB main functions:

Serving cell (or several cells)

Provisioning of radio interface to UEs (eUu)

Physical layer (PHY) and Radio Resource Management (RRM)

Exchange of crucial cell-specific data to other base stations (eNBs) eNB

RNC

eNB

X2

RRM(bearer control, mobility control, scheduling, etc.)

ROHC (Robust Header Compression)

MME selection when no info provided from UE

User Plane data forwarding to SAE-GW

Transmission of messages coming from MME

(i.e. broadcast, paging, NAS)

Ciphering and integrity protection for the air interface

Collection and evaluation of the measurements


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X2 interface

Newly introduced E-UTRAN interface

Inter eNB interface

X2 main functions: Provisioning of inter eNB direct connection

Handover (HO) coordination without EPC involvement

Data packets buffered or coming from SAE-GW to the source

eNB are forwarded to the target eNB

Improved HO performance (e.g. delay, packet loss ratio)

Load balancing Exchange of Load Indicator (LI) messages between eNBs to

adjust RRM parameters and/or manage Inter Cell Interference

Cancellation (ICIC)

X2 interface is not required

Inter eNB HO can be managed by MME

Source eNB target eNB tunnel is established using MME

eNB

eNB

X2

eNB

X2

X2

( )


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Evolved

Node B

(eNB)

MME

Serving

Gateway

S1-U

S1-MME

S11

HSS

S6a

MME Functions

Non-Access-Stratum (NAS)

Security (Authentication,

integrity Protection)

Idle State Mobility Handling

Tracking Area updates

Radio Security Control

Trigger and distribution of

Paging Messages to eNB

Roaming Control (S6a interfaceto HSS)

Inter-CN Node Signaling

(S10 interface), allows efficient

inter-MME tracking area updates

and attaches

Signalling coordination for

SAE Bearer Setup/Release

Subscriber attach/detach

Control plane NE in EPC

Mobility Management Entity (MME)

It is a pure signaling entity inside the EPC.

SAE uses tracking areas to track the position of idle UEs. The basicprinciple is identical to location or routing areas from 2G/3G.

MME handles attaches and detaches to the SAE system, as well astracking area updates

Therefore it possesses an interface towards the HSS (homesubscriber server) which stores the subscription relevant informationand the currently assigned MME in its permanent data base.

A second functionality of the MME is the signaling coordination tosetup transport bearers (SAE bearers) through the EPC for a UE.

MMEs can be interconnected via the S10 interface


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Evolved

Node B

(eNB)

MME

Serving SAE

Gateway

S1-U

S1-MME

S5/S8

PDN

Gateway

S11

S6a

Serving SAE Gateway

The serving gateway is a network element that manages the userdata path (SAE bearers) within EPC.

It therefore connects via the S1-U interface towards eNB andreceives uplink packet data from here and transmits downlinkpacket data on it.

Thus the serving gateway is some kind of distribution and packetdata anchoring function within EPC.

It relays the packet data within EPC via the S5/S8 interface to orfrom the PDN gateway.

A serving gateway is controlled by one or more MMEs via S11interface.

Local mobility anchor point:

Switching the user plane path to a

new eNB in case of Handover

Idle Mode Packet Buffering and

notification to MME

Packet Routing/Forwardingbetween eNB, PDN GW and SGSN

Lawful Interception support

Serving Gateway Functions

Mobility anchoring for inter-3GPP

mobility. This is sometimes referred

to as the 3GPP Anchor function

k k ( ) SA G


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Packet Data Network (PDN) SAE Gateway

The PDN gateway provides the connection between EPC and anumber of external data networks.

Thus it is comparable to GGSN in 2G/3G networks.

A major functionality provided by a PDN gateway is the QoScoordination between the external PDN and EPC.

Therefore the PDN gateway can be connected via S7 to a PCRF(Policy and Charging Rule Function).

MME

Serving

Gateway

S5/S8

PDN SAE

Gateway

PDNSGi

PCRF

S7 Rx+

S11

S6a

Policy Enforcement (PCEF)

Per User based Packet Filtering (i.e.

deep packet inspection)

Charging & Lawful Interception support

PDN Gateway Functions

IP Address Allocation for UE

Packet Routing/Forwarding betweenServing GW and external Data Network

Mobility anchor for mobility between

3GPP access systems and non-3GPP

access systems. This is sometimes

referred to as the SAE Anchor function

Packet screening (firewall functionality)

P li d Ch i R l F i (PCRF)


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Policy and Charging Rule Function (PCRF)

The PCRF major functionality is the Quality of Service (QoS)coordination between the external PDN and EPC.

Therefore the PCRF is connected via Rx+ interface to theexternal Data network (PDN)

This function can be used to check and modify the QoSassociated with a SAE bearer setup from SAE or to request thesetup of a SAE bearer from the PDN.

This QoS management resembles the policy and chargingcontrol framework introduced for IMS with UMTS release 6.

MME

Serving

Gateway

S5/S8

PDN SAE

Gateway

PDNSGi

PCRF

S7 Rx+

S11

S6a

Charging Policy: determines how

packets should be accounted

QoS policy negotiation with PDN

PCRF: Policy & Charging Rule Function

H S b ib S (HSS)


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Home Subscriber Server (HSS)

The HSS is already introduced by UMTS release 5.

With LTE/SAE the HSS will get additionally data persubscriber for SAE mobility and service handling.

Some changes in the database as well as in the HSSprotocol (DIAMETER) will be necessary to enable HSS forLTE/SAE.

The HSS can be accessed by the MME via S6a interface.

Permanent and central subscriber

database

HSS Functions

Stores mobility and service data for

every subscriber

MME

HSS

S6a

Contains the Authentication Center

(AuC) functionality.

LTE R di I t f d th X2 I t f


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LTE Radio Interface and the X2 Interface

LTE-Uu

Air interface of EUTRAN

Based on OFDMA in downlink and SC-FDMA inuplink

FDD and TDD duplex methods

Scalable bandwidth 1.4MHz to currently 20 MHz

Data rates up to 100 Mbps in DL

MIMO (Multiple Input Multiple Output) is a major

component although optional.

X2

Inter eNB interface

Handover coordination without involving the EPC

X2AP: special signalling protocol

During HO, Source eNB can use the X2 interface toforward downlink packets still buffered or arrivingfrom the serving gateway to the target eNB.

This will avoid loss of a huge amount of packetsduring inter-eNB handover.

(E)-RRC User PDUs User PDUs

PDCP (ROHC = RFC 3095)

..

RLC

MAC

LTE-L1 (FDD/TDD-OFDMA/SC-FDMA)

TS 36.300

eNB

LTE-Uu

eNB

X2

User PDUs

GTP-U

UDP

IPL1/L2

TS 36.424

X2-UP

(User Plane)

X2-CP

(Control Plane)

X2-AP

SCTP

IPL1/L2TS 36.421

TS 36.422

TS 36.423

TS 36.421

TS 36.420[currently also in TS 36.30020]

X2 H d


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X2 Handover

EUTRAN & EPC t d ith S1 fl


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1

2

3

EUTRAN & EPC connected with S1-flex

Several cases

eNB 1Single S1-MME

Single S1-U

eNB 2 Single S1-MME

Multiple S1-US1Flex-U

eNB 3 Multiple S1-ME

S1Flex Single S1-U


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LTE/EPC Mobility & Session Management

LTE/SAE Mobility Areas


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Two areas are defined for handling of mobility in LTE/SAE:

The Cell

identified by the Cell Identity. The format is not standardized yet.

Tracking Area (TA)

It is the successor of location and routing areas from 2G/3G.When a UE is attached to the network, the MME will know the UEs position on

tracking area level.

In case the UE has to be paged, this will be done in the full tracking area.

Tracking areas are identified by a Tracking Area Identity (TAI).



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Tracking Areas

S-eNBTAI3

TAI3 TAI3TAI3

TAI3TAI3

TAI3

MME

HSS

eNB

TAI2

TAI2TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI1

TAI1TAI1

TAI1

TAI1eNB 1 2

MME

3

Cell Identity

Tracking Area

Tracking Areas Overlapping


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Tracking Areas Overlapping

S-eNBTAI3

TAI3TAI3

TAI3

TAI3TAI3

TAI3

MME

HSS

eNB

TAI2

TAI2 TAI2TAI2

TAI2

TAI2

TAI2

TAI2

TAI1-2TAI1

TAI1

TAI1 eNB 1 2

MME

3

Cell Identity

1.- Tracking areas are allowed to overlap:

one cell can belong to multiple trackingareas

TAI1-2

2.- UE is told by the network to be in several

tracking areas simultaneously.Gain: when the UE enters a new cell, it checkswhich tracking areas the new cell is part of. Ifthis TA is on UEs TA list, then no tracking areaupdate is necessary.

Tracking Areas: Use of S1 flex Interface


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Tracking Areas: Use of S1-flex Interface

TAI1-2

S-eNBTAI2

TAI2TAI2

TAI3

TAI3TAI3TAI3

MME

HSS

eNB

TAI2

TAI2TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI1

TAI1

TAI1

eNB

S-MME

TAI1-2 MME

Pooling:several MME

handle the

same

tracking area

Cell Identity

321

1 2 3

UE Identifications


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UE Identifications

IMSI: International Mobile Subscriber Identity

S-TMSI: SAE Temporary Mobile Subscriber Identity

C-RNTI: Cell Radio Network Temporary Identity

S1-AP UE ID: S1 Application Protocol User Equipment Identity

UE Identifications: IMSI


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UE Identifications: IMSI

IMSI:International Mobile Subscriber Identity.

Used in SAE to uniquely identify a subscriber world-wide.

Its structure is kept in form of MCC+MNC+MSIN:MCC: mobile country code

MNC: mobile network codeMSIN: mobile subscriber identification number

A subscriber can use the same IMSI for 2G, 3G and SAE access.

MME uses the IMSI to locate the HSS holding the subscribers permanentregistration data for tracking area updates and attaches.

IMSI

MCC MNC MSIN

3 digits 2 digits 10 digits

UE Identification: S TMSI


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UE Identification: S-TMSI

S-TMSI:

SAE Temporary Mobile Subscriber Identity

Itis dynamically allocated by the serving MME (S-MME).

Its main purpose is to avoid usage of IMSI on air.

Internally the allocating MME can translate S-TMSI into IMSI and vice versa.

Whether the S-TMSI is unique per MME.

In case the S1flex interface option is used, then the eNB must select the right MME for

a UE. This is done by using some bits of the S-TMSI to identify the serving MME of the

UE. This identifier might be a unique MME ID or a form of MME color code. Under

investigation

S-TMSI

MME-ID or

MME color code

32 bits

UE Identifications: C RNTI


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UE Identifications: C-RNTI

C-RNTI:

Cell Radio Network Temporary Identity

C-RNTI is allocated by the eNB serving a UE when it is in active mode(RRC_CONNECTED)

This is a temporary identity for the user only valid within the serving cell of

the UE.

It is exclusively used for radio management procedures.

X-RNTI identifications under investigation.

UE Identifications Summary


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UE Identifications Summary

IMSI International Mobile Subscriber Identity

S-TMSI S-Temporary Mobile Subscriber Identity

C-RNTI Cell Radio Network Temporary Identity

S-MME Serving MME

S-eNB Serving E-Node B

TAI Tracking Area Identity (MCC+MNC+TAC)

S-TMSI

MME-ID or

MME color code

C-RNTI

eNB S1-AP UE-ID | MME S1-AP UE-ID

MCC

IMSI

MNC MSIN

S-eNBTAI2

TAI2TAI2

TAI3

TAI3TAI3

TAI3

MME

HSS

eNB

TAI2

TAI2TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI1

TAI1TAI1

TAI1

TAI1

eNB

1 2

S-MME

32

Cell IdentityMME Identity

3

1

Terminology for 3G & LTE: Connection & Mobility Management


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Terminology for 3G & LTE: Connection & Mobility Management

3G LTEConnection Management

GPRS Attached EMM Registered

PDP Context EPS Bearer

Radio Access Bearer Radio Bearer + S1 Bearer

Mobility Management

Location Area Not Relevant (no CS core)

Routing Area Tracking Area

Handovers (DCH) and Cell

reselections (PCH) when RRC

connected

Handover when RRC

connected

RNC hides mobility from corenetwork

Core Network sees everyhandover

LTE Mobility & Connection States


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LTE Mobility & Connection States

There are two sets of states defined for the UE based on the information held by

the MME.

These are:

- EPS* Mobility Management (EMM) states

- EPS* Connection Management (ECM) states

*EPS: Evolved Packet System

EPS Mobility Management (EMM) states


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EMM-DEREGISTERED:

In this state the MME holds no valid location information about the UE

MME may keep some UE context when the UE moves to this state (e.g. to avoid the needfor Authentication and Key Agreement (AKA) during every attach procedure)

Successful Attach and Tracking Area Update (TAU) procedures lead to transition to EMM-

REGISTERED

EMM-REGISTERED:In this state the MME holds location information for the UE at least to the accuracy of a

tracking area

In this state the UE performs TAU procedures, responds to paging messages and performs

the service request procedure if there is uplink data to be sent.



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EMM

deregistered

EMM

registered

Attach

Detach

EPS Connection Management (ECM) and LTE Radio Resource Control


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States

UE and MME enter ECM-CONNECTED state when the signalling connection is established

between UE and MME

UE and E-UTRAN enter RRC-CONNECTED state when the signalling connection is

established between UE and E-UTRAN

RRC IdleRRC

Connected

ECM IdleECM

Connected

EPS Connection Management (ECM) states


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EPS Connection Management (ECM) states

ECM-IDLE:

In this state there is no NAS signalling connection between the UE and the network andthere is no context for the UE held in the E-UTRAN.

The location of the UE is known to within the accuracy of a tracking area

Mobility is managed by tracking area updates.

ECM-CONNECTED:

In this state there is a signalling connection between the UE and the MME which is

provided in the form of a Radio Resource Control (RRC) connection between the UE and the

E-UTRAN and an S1 connection for the UE between the E-UTRAN and the MME.

The location of the UE is known to within the accuracy of a cell.Mobility is managed by handovers.

RRC States


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RRC States

RRC_IDLE: No signalling connection between the UE and the E-UTRAN, i.e. PLMN

Selection.

UE Receives system information and listens for Paging. Mobility based on Cell Re-selection performed by UE. No RRC context stored in the eNB. RACH procedure used on RRC connection establishment

RRC_CONNECTED: UE has an E-UTRAN RRC connection. UE has context in E-UTRAN (C-RNTI allocated). E-UTRAN knows the cell which the UE belongs to. Network can transmit and/or receive data to/from UE. Mobility based on handovers UE reports neighbour cell measurements

EPS Connection Management


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EPS Connection Management

ECM Connected= RRC Connected + S1 Connection

eNB

MME

UE

RRC Connection S1 Connection

ECM Connected

EMM & ECM States Transitions


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EMM & ECM States Transitions

EMM_Deregistered

ECM_Idle

Power On

Registration (Attach)

EMM_Registered

ECM_Connected

Allocate C-RNTI, S_TMSI

Allocate IP addresses

Authentication

Establish security context

Release RRC connection

Release C-RNTI

Configure DRX for paging

EMM_Registered

ECM_Idle

Release due to

Inactivity

Establish RRC Connection

Allocate C-RNTI

New TrafficDeregistration (Detach)

Change PLMN

Release C-RNTI, S-TMSI

Release IP addresses

Timeout of Periodic TA

Update

Release S-TMSI

Release IP addresses

EMM & ECM States Summary


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EMM & ECM States Summary

EMM_Deregistered

ECM_Idle

Network Context:

no context exists

Allocated IDs:

IMSI

UE Position:

unknown tonetwork

Mobility:

PLMN/cell

selection

UE Radio Activity:none

EMM_Registered

ECM_Connected

Network Context:

all info for ongoing

transmission/recepti

on

Allocated IDs:

IMSI, S-TMSI per

TAI1 or several IP

addresses

C-RNTI

UE Position:

known on cell level

Mobility:

NW controlled

handover

EMM_Registered

ECM_Idle

Network Context:

security keys

enable fast

transition to

ECM_CONNECTED

Allocated IDs:IMSI, S-TMSI per

TAI

1or several IP

addresses

UE Position:

known on TA level

(TA list)

Mobility:

cell reselection

LTE/SAE Bearer


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/

The main function of every mobile radio telecommunication network is to

provide subscribers with transport bearers for their user data.

In circuit switched networks users get a fixed assigned portion of the networks

bandwidth.

In packet networks users get a bearer with a certain quality of service (QoS)

ranging from fixed guaranteed bandwidth down to best effort services without anyguarantee.

LTE/SAE is a packet oriented system

LTE/SAE

Bearer

PDN GW

UE

SAE Bearer Architecture


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SAE Bearerspans the complete network, from UE over EUTRAN and EPS up to the

connector of the external PDN.

The SAE bearer is associated with a quality of service (QoS) usually expressed by a label

or QoS Class Identifier (QCI).

cell

S1-U

LTE-Uu

S5PDN

Sgi

eNB Serving

Gateway

PDN

Gateway

End-to-End Service

SAE Bearer Service (EPS Bearer)External Bearer

Service

SAE Radio Bearer Service (SAE RB) SAE Access Bearer Service

Physical Radio Bearer Service S1 Physical Bearer Service

E-UTRAN EPC PDN

S5/S8 Bearer Service

SAE Bearer Establishment


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It can be establish by MME or P-GW

MME:

This happens typically during the attach procedure of an UE. Depending on theinformation coming from HSS, the MME will set up an initial SAE bearer, also known

as the default SAE bearer. This SAE bearer provides the initial connectivity of the UE

with its external data network.

PDN Gateway:

The external data network can request the setup of a SAE bearer by issuing thisrequest via PCRF to the PDN gateway. This request will include the quality of service

granted to the new bearer.

cell

S1-U

UE

S5PDN

Sgi

eNB

Serving

Gateway

PDN

Gateway

SAE Bearer Service (EPS Bearer)External Bearer

Service

MME

S1-MME

S11

QoS Class Indentifier (QCI) Table in 3GPP


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77

Q (Q )

GBR1

Guarantee Delay budget Loss rate ApplicationQCI

GBR

100 ms 1e-2 VoIP

2

GBR

150 ms 1e-3 Video call

3

GBR

300 ms 1e-6 Streaming

4

Non-GBR 100 ms 1e-6 IMS signalling5

Non-GBR 100 ms 1e-3 Interactive gaming6

Non-GBR 300 ms 1e-6TCP protocols :

browsing, email, filedownload

7

Non-GBR 300 ms 1e-68

Non-GBR 300 ms 1e-69

Priority

2

4

5

1

7

6

8

9

50 ms 1e-3 Real time gaming3

Operators can define more QCIs

Several bearers can be aggregated together if they have the same QCI


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LTE/EPC Procedures

Attach


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80

MMEHSS

PCRF

UE eNB new

MME

Serving

Gateway

(SGW)

PDN

Gateway

Attach Request

S-TMSI/IMSI,old TAI, IP address allocation

Authentication Request

Authentication Response

Update Location

Authentication Vector Request (IMSI)

Insert Subscriber Data

IMSI, subscription data = default APN, tracking area restrictions,

Insert Subscriber Data Ack

Update Location Ack

EMM_Deregistered

Authentication Vector Respond

RRC_Connected

ECM_Connected

Attach cont.


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81

Update Bearer Response

Update Bearer Request

IP/TEID of eNB for S1u

Attach Complete

IP/TEID of eNB for S1u

RB Est. Resp.

Includes Attach Complete

Create Def. Bearer Req.

MMEHSS

PCRF

UE eNB new

MME

Serving

Gateway

(SGW)

PDN

Gateway

S-TMSI, security info,

PDN address, ,IP/TEID

of SGW-S1u (only for eNB)

Create Def. Bearer Rsp.

IP/TEID of SGW-S1u,

PDN address, QoS,

Create Def. Bearer Rsp.

PDN address, IP/TEID of PDN GW,

QoS according PCRF

select SAE GW

Create Default Bearer Request

IMSI, RAT type, default QoS, PDN address info

IMSI, , IP/TEID of SGW-S5

Attach Accept

RB Est. Req.

Includes Attach Accept

UL/DL Packet Data via Default EPS Bearer

PCRF Interaction

EMM_Registered

ECM_Connected

S1 Release


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After attach UE is in EMM Registered state.

The default Bearer has been allocated (RRC connected + ECM connected) even it maynot transmit or receive data

If there is a longer period of inactivity by this UE, then we should free these admissioncontrol resources (RRC idle + ECM idle)

The trigger for this procedure can come from eNB or from MME.

RRC Connection Release

MME

S1 Release Request

causeUpdate Bearer Request

release of eNB S1u resources


Serving

Gateway

(SGW)

PDN

Gateway

S1 Release Command

cause

S1 Release Complete

RRC Connection Release Ack

EMM_Registered

ECM_Connected

S1 Signalling Connection ReleaseEMM_Registered

ECM_Idle

Detach


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83

Can be triggered by UE or by MME.

During the detach procedure all SAE bearers with their associated tunnels andradio bearers will be deleted.

MME

NAS: Detach Accepted

Delete Bearer Request

Delete Bearer Response

EMM-Registered

Serving

Gateway

(SGW)

PDN

Gateway

NAS Detach Request

switch off flag Delete Bearer Request


PCRF

S1 Signalling Connection Release

RRC_Connected

ECM_Connected

EMM-Deregistered

RRC_Connected + ECM Idle

Note: Detach procedure initiated by UE.

Detach


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84

Note: Detach procedure initiated by MME.

MME

NAS: Detach Accepted



EMM-Registered

Serving

Gateway

(SGW)

PDN

Gateway

NAS Detach Requestswitch off flag



PCRF

S1 Signalling Connection Release

RRC_Connected

ECM_Connected

EMM-Deregistered

RRC_Connected + ECM Idle

Service Request


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85

From time to time a UE must switch from ECM_Idle to ECM_connected

The reasons for this might be UL data is available, UL signaling is pending (e.g.tracking area update, detach) or a paging from the network was received.

MMEServing

Gateway

(SGW)

PDN

Gateway

Paging

S-TMSI, TAI/TAI-list

Service Request

DL Packet DataDL Packet NotificationPaging

S-TMSI

S-TMSI, TAI, service type

Authentication Request

authentication challenge

Authentication Response

Authentication response

RRC_Idle+ ECM_Idle

ECM_Connected

RRC_Connected

Service Request


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86

MME

Initial Context Setup Req.


eNB-S1 IP/TEID


Serving

Gateway(SGW)

PDN

Gateway

SGW-S1 IP/TEID, QoSRB Establishment Req.

RB Establishment Rsp.

Initial Context Setup Rsp.

eNB-S1 IP/TEID, ..

Tracking Area Update (TAU)


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87

Tracking area (TA) is similar to Location/Routing area in 2G/3G .

Tracking Area Identity = MCC (Mobile Country Code), MNC (Mobile NetworkCode) and TAC (Tracking Area Code).

When UE is in ECM-Idle, MME knows UE location with Tracking Area accuracy.

Tracking Area Update (1/2)


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88

MMEHSS

eNB new

MMEMME

old

MME

new

Serving

Gateway

(SGW)

PDN

Gateway

Tracking Area Update Request

Context RequestS-TMSI/IMSI,old TAI, PDN (IP) address allocation

S-TMSI/IMSI,old TAI

Context Response

mobility/context data

Create Bearer Request

IMSI, bearer contexts

Context Acknowledge

S-TMSI/IMSI,old TAI


new SGW-S5 IP/TEID

Create Bearer Response

new SGW-S1 IP/TEID


PDN GW IP/TEID

old

Serving

Gateway

(SGW)UEEMM_Registered

RRC_Idle + ECM_Idle

RRC_Connected

ECM_Connected

Authentication / Security

Tracking Area Update cont


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89

MMEHSS

eNB new

MME MME

old

MME

new

Serving

Gateway

(SGW)

PDN

Gateway

Update Location

new MME identity, IMSI,

IMSI, cancellation type = update

Cancel Location Ack


TEID


Cancel Location

old

Serving

Gateway

(SGW)

Update Location Ack

Tracking Area Update Accept

new S-TMSI, TA/TA-list

Tracking Area Update Complete

EMM_Registered

RRC_Idle + ECM_Idle

Handover Procedure


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90

SAE GW

MME

SourceeNB

TargeteNB

SAE GW

MME

SAE GW

MME

SAE GW

MME

= Data in radio

= Signalling in radio

= GTP tunnel

= GTP signalling

= S1 signalling

= X2 signalling

Before handoverHandover

preparationRadio handover

Late path

switching

Note: Inter eNB Handover with X2 Interface and without CN Relocation

User plane switching in Handover


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91

Automatic Neighbor Relations


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92

1--UE reports neighbor cell signal including Physical Cell ID

1

24

3

2--Request for Global Cell ID reporting

3--UE reads Global Cell ID from BCH

4--UE reports Global Cell ID


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LTE Air Interface

LTE Design Performance Targets


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94

Scalable transmission bandwidth(up to 20 MHz)

Improved Spectrum Efficiency Downlink (DL) spectrum efficiency should be 2-4 times Release 6 HSDPA.

Downlink target assumes 2x2 MIMO for E-UTRA and single Tx antenna with Type 1

receiver HSDPA.

Uplink (UL) spectrum efficiency should be 2-3 times Release 6 HSUPA.

Uplink target assumes 1 Tx antenna and 2 Rx antennas for both E-UTRA and Release 6

HSUPA.

Coverage

Good performance up to 5 km

Slight degradation from 5 km to 30 km (up to 100 km not precluded)

Mobility

Optimized for low mobile speed (< 15 km/h)

Maintained mobility support up to 350 km/h (possibly up to 500 km/h)

LTE Design Performance Targets


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95

Advanced transmission schemes, multiple-antenna technologies

Inter-working with existing 3G and non-3GPP systems Interruption time of real-time or non-real-time service handover between E-UTRAN

and UTRAN/GERAN shall be less than 300 or 500 ms.

Air Interface Capabilities


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96

Bandwidth support

Flexible from 1.4 MHz to 20 MHz

Waveform

OFDM in Downlink

SC-FDM in Uplink

Duplexing mode

FDD: full-duplex (FD) and half-duplex (HD)

TDD

Modulation orders for data channels

Downlink: QPSK, 16-QAM, 64-QAM

Uplink: QPSK, 16-QAM, 64-QAM

MIMO support

Downlink: SU-MIMO and MU-MIMO (SDMA)

Uplink: SDMA


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Downlink Air Interface-OFDMA

Fast Fourier Transform


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99

Two characteristics define a signal:

Time domain:represents how long the symbol lasts on air

Frequency domain:represents the spectrum needed in terms of bandwidth

Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT) allow to

move between time and frequency domain representation and it is a fundamental

block in an OFDMA system

OFDM signals are generated using the IFFT

OFDM Basics


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100

Transmits hundreds or even thousands of separately modulated radio signals using

orthogonal subcarriersspread across a wideband channel

Orthogonality:

The peak (centrefrequency) of one

subcarrier

intercepts the

nulls of theneighbouring

subcarriers

15 kHzin LTE: fixed

Total transmission bandwidth

OFDM Basics


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101

Data is sent in parallel across the set of subcarriers, each subcarrier only transports

a part of the whole transmission

The throughput is the sum of the data rates of each individual (or used) subcarriers

while the power is distributed to all subcarriers

FFT (Fast Fourier Transform) is used to create the orthogonal subcarriers. The

number of subcarriers is determined by the FFT size (by the bandwidth)

In LTE, these subcarriers are separated 15kHZ

Power

frequency

bandwidth

Multi-Path Propagation and Inter-Symbol Interference


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102

Inter Symbol Interference

BTS

Time 0 Ts

+

Time 0 Tt Ts+Tt

Tt

Multi-Path Propagation and the Guard Period


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103

2

time

TSYMBOLTime Domain

1

3

time

TSYMBOL

time

TSYMBOL

Tg

1

2

3

Guard Period (GP)

Guard Period (GP)

Guard Period (GP)

Propagation delay exceeding the Guard Period


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104

Multipath causes Inter Symbol Interference (ISI) which affects the subcarrier

orthogonality due to phase distortion

Solution to avoid ISI is to introduce a Guard Period (Tg) after the pulse

Tg needs to be long enough to capture all the delayed multipath signals

To make use of that Tg (no transmission) Cyclic Prefix is transmitted

12

34

time

TSYMBOLTime Domain

time

time

Tg

1

2

3

time

4

Obviously when the

delay spread of the

multi-path

environment is

greater than the

guard period

duration (Tg), then

we encounter inter-

symbol interference

(ISI)

Cyclic Prefix (CP) and Guard Time


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105

Consists in copying the last part of a symbol shape for a duration of guard-time andattaching it in front of the symbol

CP needs to be longer than the channel multipath delay spread.

A receiver typically uses the high correlation between the Cyclic Prefix (CP) and the lastpart of the following symbol to locate the start of the symbol and begin then with

decoding

2 CP options in LTE:

Normal CP:for small cells or with short multipath delay spread

Extended CP:designed for use with large cells or those with long delay profiles

t

total symbol time T(s)

Guard Time

T(g)

CP

T(g)Useful symbol time

T(b)

Note: CP represents an overhead

resulting in symbol rate reduction.

Having a CP reduces the

bandwidth efficiency but the

benefits in terms of minimizing the

ISI compensate for it

Last part of the next

Symbols is used as

Cyclic Prefic (CP)CP ratio = T(g)/T(b)

Cyclic Prefix


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106

In multi-path propagation environments the delayed versions of the signal arrive

with a time offset, so that the start of the symbol of the earliest path falls in the

cyclic prefixes of the delayed symbols.

As the CP is simply a repetition of the end of the symbol this is not a inter-

symbol interference and can be easily compensated by the following decoding

based on discrete Fourier transform.

CP

Ts

Symbol

Detection

Interval

CP

CP

SYMBOL

SYMBOL

SYMBOL

1

2

3

1

2

3

Multi-Carrier Modulation


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107

One solution is to use multiple carriers in parallel (Subcarriers).

This allows to increase the bit rate, but keeping the advantages of smaller

carriers with simple inter-symbol interference handling via cyclic prefix and/orcyclic suffix.

frequency

Serial-to-Parallel

ConverterFast Data

011001011100101001011101

011 001 011 100 101 001 011 101

Slow Data

Subcarriers

Guard Bands

OFDMA Symbol


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108

OFDMA is an extension of OFDM technique to allow multiple user transmissions

and it is used in other systems like Wi-Fi, DVB and WiMAX

OFDMA Symbol is the Time period occupied by the modulation symbols on all

subcarriers. Represents all the data being transferred in parallelat a point in time

OFDM symbol duration including CP is aprox. 71.4

s (*) Long duration when compared with 3.69s for

GSM and 0.26s for WCDMA allowing a good

CP duration

Robust for mobile radio channel with the

use of guard internal/cyclic prefix

Symbol length without considering CP:

66.67s (1/15kHz)

Subcarrier types


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Data subcarriers: used for data transmission

Reference Signals:

used for channel quality and signal strength estimates.

They dont occupy a whole subcarrier but they are periodically embedded in the

stream of data being carried on a data subcarrier.

Null subcarriers (no transmission/power):

DC (centre) subcarrier: 0Hz offset from the channels centre frequency

Guard subcarriers: Separate top and bottom subcarriers from any adjacent channel

interference and also limit the amount of interference caused by the channel.

Guard band size has an impact on the data throughput of the channel.

Guard (no power)

DC (no

power)

data

Guard (no power)

OFDMA Parameters


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Channel bandwidth:Bandwidths ranging from 1.4 MHz to 20 MHz

Data subcarriers:They vary with the bandwidth

72 for 1.4MHz to 1200 for 20MHz

OFDMA Parameters


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111

Frame duration: 10ms created from slots and subframes

Subframe duration (TTI): 1 ms (composed of 2x0.5ms slots)

Subcarrier spacing: Fixed to 15kHz (7.5 kHz defined for MBMS)

Sampling Rate: Varies with the bandwidth but always factor ormultiple of 3.84 to ensure compatibility with WCDMA by using common clocking

Frame Duration

Subcarrier Spacing

Sampling Rate (MHz)

Data Subcarriers

Symbols/slot

CP length

1.4MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

10 ms

15 kHz

Normal CP=7, extended CP=6

Normal CP=4.69/5.12 sec, extended CP= 16.67sec

1.92 3.84 7.68 15.36 23.04 30.72

72 180 300 600 900 1200

10ms

Peak-to-Average Power Ratio in OFDMA


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112

The transmitted power is the sum of the powers of all the subcarriers

Due to large number of subcarriers, the peak to average power ratio (PAPR) tends

to have a large range

The higher the peaks, the greater the range of power levels over which the power

amplifier is required to work

Having a UE with such a PA that works over a big range of powers would be

expensive

Not best suited for use with mobile (battery-powered) devices

OFDM Wrap-up


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113

High spectral efficiency and little interference between channels

Robust in multi-path environments thanks to Cyclic Prefix

Frequency domain scheduling offer high potential for throughput gain

Severe High PAPR (Peak to Average Power Ratio)

Small subcarrier spacing makes it more sensitive to frequency offset (subcarriers may interfere

each others)

Pros:

Cons:

OFDMA Operation:

Total channel bandwidth

Transmitted frequency spectrum:

S/P IFFT CP

Modulation

mapping e.g.

QPSK

symbols

Transmitter structure Receiver structure

P/S FFTCP

Re-

moval

Modulation

mapping e.g.

QPSK

symbols


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Downlink Air Interface-SC-FDMA

SC-FDMA in Uplink


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115

Single Carrier Frequency Division Multiple Access: Transmission

technique used for Uplink

Variant of OFDM that reduces the PAPR: Combines the PAR of single-carrier system with the multipath resistance and

flexible subcarrier frequency allocation offered by OFDM

It can reduce the PAPR between 69dB compared to OFDMA

Reduced PAPR means lower RF hardware requirements (power

amplifier) SC-FDMA

OFDMA

SC-FDMA and OFDMA Comparison


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OFDMA transmits data in parallel across multiple subcarriers

SC-FDMA transmits data in series employing multiple subcarriers

In the example:

OFDMA: 6 modulation symbols (01,10,11,01,10 and 10) are transmitted per OFDMA

symbol, one on each subcarrier

SC-FDMA: 6 modulation symbols are transmitted per SC-FDMA symbol using all

subcarriers per modulation symbol. The duration of each modulation symbol is 1/6thof

the modulation symbol in OFDMA

OFDMA SC-FDMA

SC-FDMA and OFDMA Comparison


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SC-FDMA Operation


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118

The parallel transmission of multiple symbols in OFDMA creates high PAR

SC-FDMA avoids this by additional processing before the IFFT: modulation symbols

are presented to FFT. The output represents the frequency components of the

modulation symbols.

Subcarriers created by this process have a set amplitudethat should remain nearly

constant between one SC-FDMA symbol and the next for a given modulation

scheme which results in little difference between the peak power and the average

power radiated on a channel

Rx

Uplink Air Interface Technology-SC-FDMA


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119

User multiplexing in frequency domain, a user is allocated different bandwidths(multiples of 180kHz)

In OFDMA the user multiplexing is in sub-carrier domain: user is allocated Resource

Blocks

One user is always continuous in frequency

Smallest uplink bandwidth, 12 subcarriers: 180 kHz

same for OFDMA in downlink

Largest uplink bandwidth: 20 MHz

same for OFDMA in downlink

Terminals are required to be able to receive & transmit up to 20 MHz, depending on the

frequency band though


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Physical Layer


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Physical Layer Structure and Channels

Introduction

d h b b f l


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122

It provides the basic bit transmission functionality over air

LTE physical layer based on OFDMA downlink and SC-FDMA in uplink direction

This is the same for both FDD and TDD mode of operation

No need of RNC like functional element

Everything radio related can be terminated in the eNodeB

System is reuse 1, single frequency network operation is feasible

No frequency planning required

There are no dedicated physical (neither transport) channelsanymore, as all

resource mapping is dynamically driven by the scheduler

Frame Structure (FDD)

FDD F ( l ll d T 1 F ) i b h li k d


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FDD Frame structure (also called Type 1 Frame) is common to both uplink and

downlink.

Divided into 20 x 0.5ms slots

Structure has been designed to facilitate short round trip time

- Frame duration =10 ms (same as UMTS)

- FDD: 10 ms radio frame for UL and 10 ms radio frame for DL

- Radio frame includes 10 subframes- 1 Subframe represents a Transmission Time Interval (TTI)

- Each subframes includes two slots- 1 slot = 7 (normal CP) or 6 symbols (extended CP)

10 ms frame

0.5 ms slot

s0 s1 s2 s3 s4 s5 s6 s7s

18

s19..

SF0

1 ms sub-frame

SF1 SF2 SF9..

sy4sy0 sy1 sy2 sy3 sy5 sy6

0.5 ms slot

SF3SF1 SF2 SF3 SF9

SF: SubFrame

s: slot

Sy: symbol

Frame Structure (FDD)

LTE Ti D i i i d


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LTE Time Domain is organized as:

Frame (10 ms)

Subframe (1 ms) Slot (0.5 ms)

Symbol (duration depending on configuration)

Radio Frame has 2 structures:

Type 1 (FS1) for FDD DL/UL

Type 2 (FS2) for TDD FS1 is considered ithis presentation

Frequency Domain Organization

LTE DL/UL i i t f f l th l b i t d


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125

LTE DL/UL air interface waveforms use several orthogonal subcarriers to send

user traffic data, Reference Signals (Pilots), and Control Information.

f: Subcarrier spacing DC Subcarrier: Direct Current subcarrier at center of frequency band

Number of DL or UL Resource Blocks (groups of subcarriers)

Number of subcarriers within a Resource Block

Normal and Extended Cyclic Prefix


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126

Normal Cyclic Prefix

160 Ts 144 Ts

2048 Ts

Ts = 1/30720 ms

Cyclic Prefix

144 Ts 144 Ts 144 Ts 144 Ts 144 Ts

2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts

7 2048 Ts

+ 6 144 Ts

+ 1 160 Ts

15360 Ts = 0.5 ms

Main Body

512 Ts 512 Ts

2048 Ts

Ts = 1/30720 ms

Cyclic Prefix

512 Ts 512 Ts 512 Ts 512 Ts

2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts

6 2048 Ts

+ 6 512 Ts

15360 Ts = 0.5 ms

Main Body

Extended Cyclic Prefix

Resource Block

Ph i l R Bl k R Bl k (PRB RB)


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127

Physical Resource Block or Resource Block (PRB or RB):

12 subcarriers in frequency domain (180kHz) x 1 slot period in time domain (0.5ms)

Capacity allocation is based on Resource Blocks

Resource

Element

Note: Although 3GPP definition of RB refers to

0.5ms, in some cases it is possible to found that RBrefers to 12 subcarriers in frequency domain and

1ms in time domain. In particular, since the

scheduler in the eNodeB works on TTI basis (1ms)

RBs are considered to last 1ms in time domain. They

can also be known as scheduling resource blocks

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

Subcarrier 1

Subcarrier 12

180KHz

1 slot 1 slot

1 ms subframe

Resource Element

Theoretical minimum capacity allocation unit


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128

Theoretical minimum capacity allocation unit

Equivalent to one subcarrier x one symbol period

72 or 84 Resource Elements per Resource Block

Each Resource Element can accommodate 1 modulation symbol, e.g. 2 bits for

QPSK, 4 bits for 16QAM and 6 bits for 64 QAM

Modulation symbol rate per Resource Block is 144 ksps or 168 ksps

Case 1: Normal Cyclic Prefix Case 2: Extended Cyclic Prefix

7 symbols = 0.5 ms 6 symbols = 0.5 ms

12subcarriers=180kHz

Resource Element


Frequ

encyDomain


Time Domain Time Domain

Resource Grid Definition-Ul/DL

Resource Element (RE)


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129

Resource Element (RE)

One element in the time/frequency resource grid.

One subcarrier in one OFDM/LFDM symbol for DL/UL. Often used for Control channel

resource assignment.

Resource Block (RB)

Minimum scheduling size for DL/UL data channels

Physical Resource Block (PRB) [180 kHz x 0.5 ms]

Virtual Resource Block (VRB) [180 kHz x 0.5 ms in virtual frequency domain]

Localized VRB

Distributed VRB

Resource Block Group (RBG)

Group of Resource Blocks

Size of RBG depends on the system bandwidth in the cell

Modulation Schemes for LTE/EUTRAN

Each OFDM symbol even within a resource block can have a different


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130

Each OFDM symbol even within a resource block can have a differentmodulation scheme.

EUTRAN defines the following options: QPSK, 16QAM, 64QAM.

Not every physical channel will be allowed to use any modulation scheme:Control channels to be using mainly QPSK.

In general it is the scheduler that decides which form to use depending oncarrier quality feedback information from the UE.

b0 b1

QPSK

Im

Re10

11

00

01

b0 b1b2b3

16QAM

Im

Re

0000

1111

Im

Re

64QAM

b0 b1b2b3 b4 b5

LTE Frequency Variants in 3GPPFDD

T t l [MH ] U li k [MH ] D li k [MH ] E rope Japan Americas


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131

1

2

3

4

5

7

8

9

6

2x25

2x75

2x60

2x60

2x70

2x45

2x35

2x35

2x10

824-849

1710-1785

1850-1910

1920-1980

2500-2570

1710-1755

880-915

1749.9-1784.9

830-840

Total [MHz] Uplink [MHz]

869-894

1805-1880

1930-1990

2110-2170

2620-2690

2110-2155

925-960

1844.9-1879.9

875-885

Downlink [MHz]

10 2x60 1710-1770 2110-2170

11 2x25 1427.9-1452.9 1475.9-1500.9

1800

2600900

US AWS

UMTS core

US PCS

US 850

Japan 800

Japan 1700

Japan 1500

Extended AWS

Europe Japan Americas

788-798 758-768

777-787 746-756

UHF (TV)

US700

2x10

2x1013

12 2x18 698-716 728-746

14

790-820 832-862?2x30?xx

US700

US700

LTE Frequency Variants - TDD


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132

33

34

35

36

1x60

1x15

1x20

1x60

1850-1910

2010-2025

1900-1920

1930-1990

37

38

1x20

1x50

1910-1930

2570-2620

Total

Spectrum Frequency (MHz)

UMTS TDD1

UMTS TDD2

US PCS

US PCS

US PCS

Euro middle gap 2600

39

40

1x40

1x100

1880-1920

2300-2400

China TDD

2.3 TDD


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LTE Radio Interface LTE States


LTE DETACHED


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LTE_DETACHED

Used @ power up when the mobile terminal is not known to the network.

Before any further communication, the mobile terminal need to register with the

network using the random-access procedure.

LTE_ACTIVE

Mobile terminal is active with transmitting and receiving data.

IN_SYNC

Uplink is synchronized with eNodeB

OUT_SYNC

Uplink is not synchronized with eNodeB.

Mobile terminal needs to perform a random-access procedure to restore uplink

synchronization.


LTE IDLE


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LTE_IDLE

Low activity state to reduce battery consumption.

The only uplink transmission activity that may take place is random access to move

to LTE_ACTIVE.

In the downlink, the mobile terminal can periodically wake up in order to be paged

for incoming calls

The network knows at least the group of cells in which paging of the mobile

terminal is to be done.


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Downlink Physical Signals and Channels

Downlink Physical Signals and Channels

Downlink Physical Signals


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Downlink Physical Signals

Reference Signals

Synchronisation Signals

Downlink Physical Channels

Physical Broadcast Channel (PBCH)

Physical Downlink Shared Channel (PDSCH)

Physical Downlink Control Channel (PDCCH)

Physical Control Format Indicator Channel (PCFICH)

Physical Hybrid-ARQ Indicator Channel (PHICH)

Physical Multicast Channel (PMCH)

DL Physical Channels

PBCH:


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PBCH:

To broadcast the MIB (Master Information Block), RACH parameters

PDSCH:

Carries user data, paging data, SIBs (cell status, cell IDs, allowed services)

PMCH:

For multicast traffic as MBMS services

PHICH:

Carries H-ARQ Ack/Nack messages from eNB to UE in response to UL transmission

PCFICH:

Carries details of PDCCH format (e.g.# of symbols)

PDCCH:

Carries the DCI (DL control information): schedule uplink resources on the PUSCH or

downlink resources on the PDSCH. Alternatively, DCI transmits TPC commands for

UL

Note:There are no dedicated channels in LTE, neither in UL nor DL

DL Channelization Hierarchy


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PCCH BCCH CCCH DCCH DTCH MCCH MTCH

PCH BCH DL-SCH MCH

DL-RS SCH PCFICH PBCH PHICH PDSCH PDCCH PMCH

Dedicated & ControlCommon Control

Downlink

Logical Channels

Downlink

Transport Channels

DownlinkPhysical Channels

Paging

System

Broadcast

MBSFN

Reference Signals: OFDMA Channel Estimation

Channel estimation in LTE is based on reference signals (like CPICH functionality in


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140

g ( y

WCDMA)

Reference signals position in time domain is fixed (0 and 4 for Type 1 Frame)

whereas in frequency domain it depends on the Cell ID In case more than one antenna is used (e.g. MIMO) the Resource elements

allocated to reference signals on one antenna are DTX on the other antennas

Reference signals are modulated to identify the cell to which they belong.

Antenna 1 Antenna 2

sub

carriers

symbols 6 symbols

subcarriers

Synchronization Signals (PSS & SSS)

PSS and SSS Functions


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PSS and SSS Functions

Frequency and Time synchronization

Carrier frequency determination

OFDM symbol/subframe/frame timing determination

Physical Layer Cell ID determination

Determine 1 out of 504possibilities

PSS and SSS resource allocationTime: subframe0 and 5 of every Frame

Frequency: middle of bandwidth (6 RBs = 1.08 MHz)

Synchronization Signals (PSS & SSS)

Primary Synchronization Signals (PSS)


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y y g ( )

Assists subframe timing determination

Provides a unique Cell ID index (0, 1, or 2) within a Cell ID group

Secondary Synchronization Signals (SSS)

Assists frame timing determination

M-sequences with scrambling and different concatenation methods for SF0 and SF5)

Provides a unique Cell ID group number among 168 possible Cell ID groups

Synchronization Signals allocation (DL)

Synchronization signals:


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Transmitted during the 1stand 11thslots within a

radio frame

Occupy the central 62 Subcarriers (around the DC

subcarrier) to facilitate the cell search

5 Subcarriers above and 5 Subcarriers below the

synch. Signals are reserved and transmitted as DTx

Synchronisation Signal can indicate 504 (168 x 3)

CellID different values and from those one can

determine the location of cell specific reference

symbols


PBCH Function


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Carries the primary Broadcast Transport Channel

Carries the Master Information Block (MIB), which includes:

Overall DL transmission bandwidth

PHICH configuration in the cell

System Frame Number

Number of transmit antennas (implicit)

Transmitted in

Time: subframe 0 in every frame

4 OFDM symbols in the second slot of corresponding subframe

Frequency: middle 1.08 MHz (6 RBs)


TTI = 40 ms


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Transmitted in 4 bursts at a very low data rate

Same information is repeated in 4 subframes

Every 10 ms burst is self-decodable

CRC check uniquely determines the 40 ms PBCH TTI boundary

Last 2 bits of SFN is not transmitted

Physical Control Format Indicator Channel (PCFICH)

Carries the Control Format Indicator (CFI)


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( )

Signals the number of OFDM symbols of PDCCH:

1, 2, or 3 OFDM symbols for system bandwidth > 10 RBs

2, 3, or 4 OFDM symbols for system bandwidth > 6-10 RBs

Control and data do not occur in same OFDM symbol

Transmitted in:

Time: 1st OFDM symbol of all subframes

Frequency: spanning the entire system band4 REGs -> 16 REs

Mapping depends on Cell ID

PCFICH in Multiple Antenna configuration

1 Tx: PCFICH is transmitted as is

2Tx, 4Tx: PCFICH transmission uses Alamouti Code

Physical Downlink Control Channel (PDCCH)

Used for:


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DL/UL resource assignments

Multi-user Transmit Power Control (TPC) commands

Paging indicators

CCEs are the building blocks for transmitting PDCCH

1 CCE = 9 REGs (36 REs) = 72 bits

The control region consists of a set of CCEs, numbered

from 0 to N_CCE for each subframe

The control region is confined to 3 or 4 (maximum)

OFDM symbols per subframe (depending on system

bandwidth)

A PDCCH is an aggregation of contiguous CCEs

(1,2,4,8)

Necessary for different PDCCH formats and coding rate

protections

Effective supported PDCCH aggregation levels need to

result in code rate < 0.75

Physical Downlink Shared Channel (PDSCH)

Transmits DL packet data


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One Transport Block transmission per UEs code word per subframe

A common MCS per code word per UE across all allocated RBs

Independent MCS for two code words per UE

7 PDSCH Tx modes

Mapping to Resource Blocks (RBs)

Mapping for a particular transmit antenna port shall be in increasing order of:

First the frequency index,

Then the time index, starting with the first slot ina subframe.

Physical HARQ Indicator Channel (PHICH)

Used for ACK/NAK of UL-SCH transmissions


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Transmitted in:

Time

Normal duration: 1stOFDM symbol

Extended duration: Over 2 or 3 OFDM symbols

Frequency

Spanning all system bandwidth

Mapping depending on Cell ID

FDM multiplexed with other DL control channels

Support of CDM multiplexing of multiple PHICHs

DL Physical Channels Allocation

PBCH:


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Occupies the central 72 subcarriers across 4 symbols

Transmitted during second slot of each 10 ms radio frame on all

antennas

PCFICH:

Can be transmitted during the first 3 symbols of

each TTI

Occupies up to 16 RE per TTI

PHICH:

Normal CP: Tx during 1stsymbol of each TTI

Extended CP: Tx during first 3 symbols of each TTI

Each PHCIH group occupies 12 RE

PDCCH:

Occupies the RE left from PCFICH and PHICH within the first 3

symbols of each TTI

Minimum number of symbols are occupied. If PDCCH data is small

then it only occupies the 1st symbol

PDSCH:

Is allocated the RE not used by signals or other physical channels

RB

DL Reference Signals: 1 TxAntenna


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DL Reference Signals transmitted on 2 OFDM symbols every slot

6 subcarrier spacing

DL Reference Signals: 2 Tx Antenna


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DL Reference Signals: 4 Tx Antenna


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Overheads Normal CP Extended CP

1 TX Antenna 4.76% 5.56%

2 TX Antenna 9.52% 11.11%

4 TX Antenna 14.29% 15.87%

7Downlink TransmissionAn Example

Example of Frame Structure Type 1 (extended CP) transmission


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lDL Scheduled Operation Overview

1.UE reports CQI(Channel Quality Indicator),


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PMI(Precoding Matrix Index), and RI (Rank

Indicator) in PUCCH (or PUSCH if there is UL

traffic).

2.Scheduler at eNodeB dynamically allocates

resources to UE:UE readsPCFICH every

subframe to discover the number of OFDM

symbols occupied by PDCCH.UE readsPDCCH to discover Tx Modeand assigned

resources (PR BandMCS).

3.eNodeB sends user data in PDSCH.

4.UE attempts to decode the received packet

and sends ACK/NACK using PUCCH(or PUSCH

if there is UL traffic).

Uplink Physical Signals and Channels

Uplink Physical Signals


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Demodulation Signals:

Used for channel estimation in the eNodeB receiver to demodulate control and data

channels Located in the 4thsymbol (normal CP) of each slot and spans the same bandwidth as

the allocated uplink data

Sounding Reference Signals:

Provides uplink channel quality estimation as basis for the UL scheduling decisions -

> similar in use as the CQI in DL

Sent in different parts of the bandwidth where no uplink data transmission isavailable.

Not part of first NSNs implementations (UL channel aware scheduler in RL30)

Uplink Physical Channels

Physical Uplink Shared Channel (PUSCH) Physical Uplink Control Channel (PUCCH)

Physical Random Access Channel (PRACH)

UL Physical Channels

PUSCH: Physical Uplink Shared Channel


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Intended for the user data (carries traffic for multiple UEs)

PUCCH: Physical Uplink Control Channel

Carries H-ARQ Ack/Nack indications, uplink scheduling request, CQIs and MIMO

feedback

If control data is sent when traffic data is being transmitted, UE multiplexes both

streams together

If there is only control data to be sent the UE uses Resources Elements at the edges

of the channel with higher power PRACH: Physical Random Access Channel

For Random Access attempts. PDCCH indicates the Resource elements for PRACH

use

PBCH contains a list of allowed preambles (max. 64 per cell in Type 1 frame) and

the required length of the preamble

UL Channelization Hierarchy


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158

No dedicated transport channels: Focus on shared transport channels.

E-UTRA Uplink Reference Signals

Two types of E-UTRA/LTE Uplink Reference Signals:


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Demodulation reference signal

Associated with transmission of PUSCH or PUCCH

Purpose: Channel estimation for Uplink coherent demodulation/detection of the

Uplink control and data channels

Transmitted in time/frequency depending on the channel type (PUSCH/PUCCH),

format, and cyclic prefix type

Sounding reference signal

Not associated with transmission of PUSCH or PUCCH

Purpose: Uplink channel quality estimation feedback to the Uplink scheduler (for

Channel Dependent Scheduling) at the eNodeB

Transmitted in time/frequency depending on the SRS bandwidth and the SRS

bandwidth configuration (some rules apply if there is overlap with PUSCH andPUCCH)

OFDMA versus SC-FDMA


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Physical Uplink Shared Channel (PUSCH)


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Physical Uplink Control Channel (PUCCH)


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Sounding Reference Signals (SRS)

SRS shall be transmitted on the last symbol of the subframe.


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PUSCH:

The mapping to resource elements only considers those not

used for transmission of reference signals.

PUCCH Format 1 (SR) / 1a / 1b (HARQ-ACK):

When ACK/NAK and SRS are to be transmitted in SRS cell-

specific subframes:

If higher-layer parameter Simultaneous-AN-and-SRS is TRUE => Use

shortened PUCCH format.

Else UE shall not transmit SRS.

PUCCH Format 2 / 2a / 2b (CQI):

UE shall not transmit SRS whenever SRS and PUCCH 2 / 2a / 2b

coincide.

SRS multiplexing:

Done with CDM when there is one SRS bandwidth, and

FDM/CDM when there are multiple SRS bandwidths.

PRACH

The preamble format determines the length of the

Cyclic Prefix and Sequence


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Cyclic Prefix and Sequence.

FDD has 4 preamble formats (for different cell sizes).

16 PRACH configurations are possible.

Each configuration defines slot positions within a frame

(for different bandwidths).

Each random access preamble occupies a bandwidth

corresponding to 6 consecutive RBs.

is the starting RB for the PRACH.

PRACH6

-110RBs

6RBs

SequenceCP

Tcp Tseq FDD Specific RACH format


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MIMO

MIMO

MIMO stands for Multiple Input Multiple Output. It is a key technology to increase a channels capacity by using multiple transmitter


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y gy p y y g pand receiver antennas.

The propagation channel is the air interface, so that transmission antennas are

handled as input to the channel, whereas receiver antennas are the output of it. The very basic ideas behind MIMO have been established already 1970 , but have

not been used in radio communication until 1990. MIMO is currently used in 802.11n, 802.16d/e to increase the channel capacity.

Air Interface

Transmission antennas (inputs)

Reception antennas (outputs)


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THANK YOU

Documents

LTE Fundamentals, Channels, Architecture and Call Flow