overview and basics of lte

Presenting the Future: LTE

3GPP Release 8

By

Chaitanya T K

Email:tkchaitanya@tataelxsi.Co.In

Discontent is the first step in the progress of a man or a nation.       -Oscar Wilde

Why LTE ?

Less number of components so less cost,low latency and complexity.

End user perspective: Support for high end multimedia services

High data rates fast downloading capabilities

Support for multicast and broadcast services

Low latency and high reliability Global roaming between different radio access technologies

Support for DVB-H

Network provider perspective: Scalable bandwidth results in high flexibility (1.4 –20mhz)

Easy upgrade from existing technologies High spectral efficiency (3-4 times HSPA)

High ARPU(average revenue per user) ALL IP network

Requirements

Simple architecture in terms of number of components, low cost ,latency and complexity.

Down->OFDMA (384 kbps), UP->SC-FDMA (86 kbps)

2 operating modes: FDD and TDD User plane latency (UE->BS) < 5ms and control plane <100ms (idle->active)

Seamless mobility (prepared handoff’s) QOS directly evolved from HSPA+ ALL IP network Spectrum utilization: 1.4 Mhz to 20 Mhz

Requirements

Frequency Bands

BW Comparison:

Block Diagram

Functionality of All the Components in LTE

eNobeB: Radio resource management: Radio bearer control,Radio admission control,Scheduling, radio resource allocation (UL and DL),paging message forwarding , ROHC (user plane encryption) and Ciphering (PDCP)

EPC and enB have a many-many mapping to support redundancy,load sharing and avoiding congestion.

MME: Mobility management Entity

Tracking and maintenance of UE position Inter MME handovers pre-ordained Inter 3GPP handovers AS (UE-enB) and NAS(UE-MME) security Controls NAS signaling Consults HSS on 6a then chooses SGW and PDNGW accordingly (establishes a bearer between UE and PDNGW)

S-GW:

Routing and forwarding user data to PGW through S5 (GTP/PMIP based)

Provides user plane tunneling and inter eNB handovers through s1u

Inter 3GPP mobility through s1a (SGW-SGSN)

Lawful interception and accounting

Provides local mobility

PDN GW:

It is UE’s default router Provides user plane mobility and inter 3GPP handoff by acting as HA

Allocates IP address during default EPS bearer setup

QOS is here in the DL Enforces DL data rate ensuring that user is not crossing the subscription levels

S7 to PCRF S5 to SWGW(GTP/PMIP/Both) Provides global mobility

HSS:Home Subscriber Service

Stores subscription info (User info,Authentication and authorization )

S6a interface to MME for ciphering and auth (Mutual auth and integrity check)

1 or more HSS as per the number of subscribers

PCRF

Policy control decision and flow based charging

Contacts IMS for dynamic QOS and charging related service through “rx reference point”

Controls service data flows and IP bearer

Redundancy

When the UE powers up and attaches to the network eNB performs a load balancing algorithm to choose MME from MME pool

Then similarly MME selects SGW from SGW pool

By the we can achieve high fault tolerance and low congestion

This can be implemented using MME identifiers (MMEC,MMEGI,MMEI and GUMMEI)

Protocol Stack

Radio Resource Control (RRC)

Medium Access Control(MAC)

Transport channels

Physical layer

Contr

ol

/ M

easure

ments

Layer 3

Logical channelsLayer 2

Layer 1

Layers Functionality:

PDCP sublayer (terminated in eNB on the network side) performs ROHC, ciphering and integrity protection;

MAC- Mapping between logical channels and transport channels;

Multiplexing/demultiplexing of RLC PDUs belonging to one or different radio bearers into/from transport blocks (TB) delivered to/from the physical layer on transport channels;

MAC (Contd…):

MAC: - Traffic volume measurement 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.

RLC sub layer: Transfer of upper layer PDUs supporting AM or UM;

TM data transfer; Error Correction through ARQ (CRC check provided by the physical layer, in other words no CRC needed at RLC level);

Segmentation according to the size of the TB: only if an RLC SDU does not fit entirely into the TB then the RLC SDU is segmented into variable sized RLC PDUs, which do not include any padding;

RLC (Contd…..)

Re-segmentation of PDUs that need to be retransmitted: if a retransmitted PDU does not fit entirely into the new TB used for retransmission then the RLC PDU is re-segmented;

The number of re-segmentations is not limited;

Concatenation of SDUs for the same radio bearer;

In-sequence delivery of upper layer PDUs except at HO;

Duplicate Detection; Protocol error detection and recovery;

SDU discard; Reset.

RLC (Contd…..)

RRC (terminated in eNB on the network side) performs the functions listed below:- Broadcast;- Paging;- RRC connection management;- RB control;- Mobility functions;- UE measurement reporting & control.

NAS control protocol (terminated at MME)

- EPS bearer management;- Authentication;- ECM-IDLE mobility handling;- Paging origination in ECM-IDLE;- Security control.

RRC and NAS:

RRC in detail:

Broadcast of System Information related to the non-access stratum (NAS);

Broadcast of System Information related to the access stratum (AS);

Paging; Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN including:

Allocation of temporary identifiers between UE and E-UTRAN;

Configuration of signalling radio bearer(s) for RRC connection: Low priority SRB and high priority SRB.

Security functions including key management; Establishment, configuration, maintenance and release of point to point Radio Bearers;

Mobility functions including: UE measurement reporting and control of the reporting for inter-cell and inter-RAT mobility;

Handover; UE cell selection and reselection and control of cell selection and reselection;

Context transfer at handover.

RRC in detail(Contd…):

Notification for MBMS services; Establishment, configuration, maintenance and release of Radio Bearers for MBMS services;

QoS management functions; UE measurement reporting and control of the reporting;

NAS direct message transfer to/from NAS from/to UE.

RRC in detail(Contd…):

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

X2 E-UTRAN

LTE Access Network Architecture

Functional Split between E-UTRAN and EPC

internet

eNB

RB Control

Connection Mobility Cont.

eNB MeasurementConfiguration & Provision

Dynamic Resource Allocation (Scheduler)

PDCP

PHY

MME

S-GW

S1MAC

Inter Cell RRM

Radio Admission Control

RLC

E-UTRAN EPC

RRC

Mobility Anchoring

EPS Bearer Control

Idle State Mobility Handling

NAS Security

P-GW

UE IP address allocation

Packet Filtering

RLC Layer

radio interface

lower layers(i.e. MAC sub layer and physical layer)

transmittingTM RLC entity

transmittingUM RLC entity

AM RLC entityreceiving

TM RLC entityreceiving

UM RLC entity

receivingTM RLC entity

receivingUM RLC entity

AM RLC entitytransmitting

TM RLC entitytransmitting

UM RLC entity

lower layers(i.e. MAC sub layer and physical layer)

upper layer (i.e. RRC layer or PDCP sub layer)

upper layer (i.e. RRC layer or PDCP sub layer)

eNB

UE

SAP betweenupper layers

logical channel

logical channel

SAP betweenupper layers

PDCP Functional Overview

Radio Interface (Uu)

UE/E-UTRAN E-UTRAN/UE

Transmitting PDCP entity

Ciphering

Header Compression (u-plane only)

Receiving PDCP entity

Sequence numbering

Integrity Protection (c-plane only)

Add PDCP header

Header Decompression (u-plane only)

Deciphering

Remove PDCP Header

Re-ordering (u-plane only)

Integrity Verification (c-plane only)

Packets associated to a PDCP SDU

Packets associated to a PDCP SDU

Packets not associated to a

PDCP SDU

Packets not associated to a

PDCP SDU

PDCP Sub layer

Radio BearersUE/E-UTRAN

PDCP sublayer

...

RLC sublayer

PDCP entiy

PDCP - PDU

RLC - SDU

C-SAP

PDCP-SAP PDCP-SAP

RLC UM-SAP RLC AM-SAP

...

PDCP entity PDCP entity

ARQ and HARQ

ARQ: ACK/NACK based scheme RLC mechanismHARQ: ACK/NACK based scheme MAC layer mechanism Buffers the corrupted packets and waits for the next packet, based on that 2 packets it decodes the original packet.

Implicit Link adaptation technique (Coarse Data rate selection)

Tx an encoded packet incrementally which saves BW

It reduces the amount of redundancy Synchronous in UL but Asynchronous in DL

Parallel Processes of HARQ are allowed in MAC layer

These 2 techniques along with the TCP retransmissions provide robust and reliable medium.

ARQ and HARQ (Contd...)

L2 Structure for Down Link

The PDCP, RLC and MAC layers together constitute L2.

L2 Structure for UP Link

ROHC (RFC 3095 and 5225)

Modes: Unidirectional Mode Bi-directional optimistic mode Bi-directional reliable mode States: Initialization & Refresh, First-Order Second-Order States

QOS:

There are 9 QOS classes categorized into BR and GBR with different priorities.

DSCP is also used here. Each class is represented by a Qos Class Identifier (QCI)

Classes are configured based on the latency, packet loss and data rate.

Applications requiring similar QOS are clubbed together as an SDF aggregate allocating a single EPS bearer for those 2 flows.

QOS Bearers

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

S5/S8 Bearer

Mobility States of a UE in LTE

A Typical Uninterrupted Hand

Off

Idle Mobility Management using Traffic Areas

Comparison b/w Release7and8:

PHY Layer Concepts: OFDMA Vs. SCFDMA

Time Domain Comparison:

Comparison Contd……

Channel Dependent Scheduling:

General Block Diagram:

Comparison b/w different schemes:

Framing:

Type 1 Frame Structure:

Type 2 Frame Structure:

Resource Grid:

BW/Resource Configuration:

Logical Channels in LTE

Transport Channels in LTE

Mapping of Logical to Transport Channels

Note: The mappings shown in dotted lines are still being studied by 3GPP.

LTE Vs WiMax: 2 Sibling Rivalries

2 different technologies so cannot compare.They do not compete in same market

Wimax is ready for deployment whereas LTE will be deployed mass in 2013.

LTE is superior to 802.16e when compared to speed, but 802.16m will achieve almost the same speeds as LTE.

For fixed and low roaming Wimax but for High Roaming-LTE.Alternatively LTE can be used for macro cellular coverage and Wimax for Micro cell coverage

Contd….

LTE release 8 supports interop between LTE and Wimax.

Also HSPA+ is highly used and also for most of the users it provides sufficient BW and data rate @ 14 Mbps

So the three technologies may co exist For Wimax we require new equipment but for LTE service providers can upgrade.

3 Current Hot Technologies:

Comparing all the Contemporary Technologies

Future

Release-9 (LTE advanced) is on the way, draft initialization will start in Dec-2008 and Dec-2009 1st draft release is expected.

LTE-advanced supports data rates of 1 gig/s

It also aims on improvising the pre-defined global roaming.

Its not that I am so smart , its just that I stay with problems longer

- Albert Einstein

Thank You