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LTE Training Document

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Index1. Introduction

2. LTE Key feature

3. LTE Network Elements(Architecture)

4. LTE Network Interfaces

5. LTE-Channel

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3G LTE evolution

Although there are major step changes between LTE and its 3G predecessors, it is nevertheless

looked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of

radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities with theearlier forms of 3G architecture and there is scope for much re-use.

LTE can be seen for provide a further evolution of functionality, increased speeds and general

improved performance.

LTE Introduction

WCDMA

(UMTS)

HSPA

HSDPA / HSUPA

HSPA+ LTE

Max downlink speed

bps

384 k 14 M 28 M 100M

Max uplink speed

bps

128 k 5.7 M 11 M 50 M

Latency

round trip time

approx

150 ms 100 ms 50ms (max) ~10 ms

3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8

Approx years of initial

roll out

2003 / 4 2005 / 6 HSDPA

2007 / 8 HSUPA

2008 / 9 2009 / 10

Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA

In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. There is also no

basic provision for voice, although this can be carried as VoIP.

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3GPP LTE technologies

LTE has introduced a number of new technologies when compared to the previous cellular

systems. They enable LTE to be able to operate more efficiently with respect to the use ofspectrum, and also to provide the much higher data rates that are being required.

OFDM (Orthogonal Frequency Division Multiplex): OFDM technology has been

incorporated into LTE because it enables high data bandwidths to be transmitted efficiently

while still providing a high degree of resilience to reflections and interference. The accessschemes differ between the uplink and downlink: OFDMA (Orthogonal Frequency Division

Multiple Access is used in the downlink; while SC-FDMA(Single Carrier - Frequency Division

Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to

average power ratio is small and the more constant power enables high RF power amplifier

efficiency in the mobile handsets - an important factor for battery power equipment.

MIMO (Multiple Input Multiple Output): One of the main problems that previous

telecommunications systems has encountered is that of multiple signals arising from the

many reflections that are encountered. By using MIMO, these additional signal paths can be

used to advantage and are able to be used to increase the throughput.

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When using MIMO, it is necessary to use multiple antennas to enable the different paths

to be distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices canbe used. While it is relatively easy to add further antennas to a base station, the same is

not true of mobile handsets, where the dimensions of the user equipment limit the

number of antennas which should be place at least a half wavelength apart.

Architecture Evolution: With the very high data rate and low latency requirements for

3G LTE, it is necessary to evolve the system architecture to enable the improved

performance to be achieved. One change is that a number of the functions previously

handled by the core network have been transferred out to the periphery. Essentially this

provides a much "flatter" form of network architecture. In this way latency times can be

reduced and data can be routed more directly to its destination.

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LTE specification overview

It is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there

are a number of differences between the operation of the uplink and downlink, these naturally

differ in the performance they can offer.

PARAMETER DETAILS

Peak downlink speed

64QAM

(Mbps)

100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)

Peak uplink speeds

(Mbps)

50 (QPSK), 57 (16QAM), 86 (64QAM)

Data type All packet switched data (voice and data). No circuit

switched.

Channel bandwidths

(MHz)

1.4, 3, 5, 10, 15, 20

Duplex schemes FDD and TDD

Mobility 0 - 15 km/h (optimised),

15 - 120 km/h (high performance)

Latency Idle to active less than 100ms

Small packets ~10 ms

Spectral efficiency Downlink: 3 - 4 times Rel 6 HSDPA

Uplink: 2 -3 x Rel 6 HSUPA

Access schemes OFDMA (Downlink)

SC-FDMA (Uplink)

Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)

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LTE Key Features

Evolved NodeB (eNB)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 layerEUTRAN exclusively uses IP as transport layer

UL/DL resource scheduling

In UMTS physical resources are either shared or dedicatedEvolved 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 Network Architecture

LTE-UE

Evolved UTRAN (E-UTRAN)

MME S10

S6a

Serving

Gateway

S1-U

S11

PDN

Gateway

Evolved Packet Core (EPC)

S1-MME

S5/S8

Evolved

Node B

(eNB)

cell

X2

LTE-Uu

HSS

MME: Mobility Management Entity

LTE

Gateway

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Inter-cell RRM: HO, load balancing between cells

Radio Bearer Control: setup, modifications and

release of Radio Resources

Connection Mgt. Control: UE State Mgmt. MME-UE

Connection

Radio Admission Control

eNode B Measurements

Collection and evaluation

Dynamic Resource

Allocation (Scheduler)

eNB Functions

IP Header Compression/ de-compression

Access Layer Security: ciphering and integrity

protection on the radio interface

MME Selection at Attach of the UE

User Data Routing to the LTE GW.

Transmission of Paging Message coming from MME

Transmission of Broadcast Info (System info, MBMS)

Evolved

Node B

(eNB)cell

LTE-Uu

LTE-UE

It is the only network element defined as partof EUTRAN.

It replaces the old Node B / RNC combinationfrom 3G.

It terminates the complete radio interfaceincluding physical layer.

It provides all radio management functions

An eNB can handle several cells.

To enable efficient inter-cell radio

management for cells not attached to the sameeNB, there is a inter-eNB interface X2 specified.It will allow to coordinate inter-eNB handoverswithout direct involvement of EPC during thisprocess.

Evolved Node B (eNB)

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Evolved

Node B

(eNB)

MME

Serving

Gateway

S1-U

S1-MME

S11

HSS

S6a

MME Functions

Non-Access-Stratum (NAS)

Signalling

Idle State Mobility Handling

Tracking Area updates

Security (Authentication,

Ciphering, Integrity protection)

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

Signaling coordination for

LTE Bearer Setup/Release & HO

Subscriber attach/detach

Control plane NE in EPC

Mobility Management Entity (MME)

It is a pure signaling entity inside the EPC.LTE uses tracking areas to track the position of idle UEs. Thebasic principle is identical to location or routing areas from

2G/3G.MME handles attaches and detaches to the LTE system, aswell as tracking area updates

Therefore it possesses an interface towards the HSS (homesubscriber server) which stores the subscription relevantinformation and the currently assigned MME in its permanent

data base.A second functionality of the MME is the signalingcoordination to setup transport bearers (LTE bearers) throughthe EPC for a UE.

MMEs can be interconnected via the S10 interface

It generates and allocates temporary ids for UEs

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Evolved

Node B

(eNB)

MME

Serving

Gateway

S1-U

S1-MME

S5/S8

PDN

Gateway

S11

S6a

Serving Gateway

The serving gateway is a network element that manages

the user data path ( bearers) within EPC.It therefore connects via the S1-U interface towards eNBand receives uplink packet data from here and transmitsdownlink packet data on it.

Thus the serving gateway is some kind of distribution andpacket data anchoring function within EPC.

It relays the packet data within EPC via the S5/S8 interfaceto or from the PDN gateway.

A serving gateway is controlled by one or more MMEs viaS11 interface.

At a given time, the UE is connected to the EPC via a singleServing-GW

Packet Buffering and notification to

MME for UEs in Idle Mode

Packet Routing/Forwarding

between 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

Local Mobility Anchor Point:

Switching the User plane to a new

eNB in case of Handover

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Packet Data Network (PDN) Gateway

The PDN gateway provides the connection betweenEPC and a number of external data networks.Thus it is comparable to GGSN in 2G/3G networks.

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

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

If a UE is connected simultaneously to several PDNs thismay involved connections to more than one PDN-GW

MME

Serving

Gateway

S5/S8

PDN LTE

Gateway

S11

S6a

PolicyEnforcement (PCEF)

Per User based Packet Filtering (i.e.

deep packet inspection)

Charging Support

PDN Gateway Functions

IP Address Allocation for UE

Packet Routing/Forwarding between

Serving 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 LTE Anchor function

Packet screening (firewall functionality)

Lawful Interception support

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Home Subscriber Server (HSS)

The HSS is already introduced by UMTS release 5.

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

Some changes in the database as well as in the HSSprotocol (DIAMETER) will be necessary to enable HSSfor LTE/LTE.

The HSS can be accessed by the MME via S6ainterface.

Permanent and central subscriber

database

HSS Functions

Stores mobility and service data for

every subscriber

MME

HSS

S6a

Contains the Authentication Center

(AuC) functionality.

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LTE UE Categories

Qualcomm first chipset has 50 Mbps downlink and 25 Mbps uplink

All categories support 20 MHz

64QAM mandatory in downlink, but not in uplink (except Class 5)

2x2 MIMO mandatory in other classes except Class 1

Class 1 Class 2 Class 3 Class 4 Class 5

10/5 Mbps 50/25 Mbps 100/50 Mbps 150/50 Mbps 300/75 MbpsPeak rate DL/UL

20 MHzRF bandwidth 20 MHz 20 MHz 20 MHz 20 MHz64QAMModulation DL 64QAM 64QAM 64QAM 64QAM

16QAMModulation UL 16QAM 64QAM16QAM 16QAM

YesRx diversity Yes YesYes Yes

1-4 txBTS tx diversity

OptionalMIMO DL 2x2 4x42x2 2x2

1-4 tx 1-4 tx 1-4 tx 1-4 tx

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LTE-Channel

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Upper Layers

RLC

MAC

PHY

Logical channels

Transport channels

BCCH

CCCH

PCCH

MTCH

MCCH

BCH

PCH

DL-SCH

RACH

UL-SCH

PBCH

PDSCH

PHICH

PDCCH

PCFICH

PMCH

PUCCH

PRACH

PUSCH

MCH

CCCH

DCCH

DTCH

ULDL

Air interface

DCCH

DTCH

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Physical channels: These are transmission channels that carry user data and control

messages.

Transport channels: The physical layer transport channels offer information transferto Medium Access Control (MAC) and higher layers.

Logical channels: Provide services for the Medium Access Control (MAC) layer within

the LTE protocol structure.

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Logical channels

BCCHBroadcast Control CH

System information sent to all UEs

PCCHPaging Control CH

Paging information when addressing UE

CCCHCommon Control CH

Access information during call establishment

DCCHDedicated Control CH

User specific signaling and control

DTCHDedicated Traffic CH

User data

MCCHMulticast Control CH Signaling for multi-cast

MTCHMulticast Traffic CH

Multicast data

LTE Channels

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Transport channels

BCHBroadcast CH

Transport for BCCH

PCHPaging CH

Transport for PCH

DL-SCHDownlink Shared CH

Transport of user data and signaling. Used by

many logical channels

MCHMulticast channel

Used for multicast transmission

UL-SCHUplink Shared CH

Transport for user data and signaling

RACHRandom Access CH

Used for UEs accessing the network

LTE Channels

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Physical Channel

PDSCHPhysical DL Shared CH Uni-cast transmission and paging

PBCHPhysical Broadcast CH Broadcast information necessary for accessing the network

PMCHPhysical Multicast Channel Data and signaling for multicast

PDCCHPhysical Downlink Control CH Carries mainly scheduling information

PHICHPhysical Hybrid ARQ Indicator Reports status of Hybrid ARQ

PCIFICPhysical Control Format Indicator Information required by UE so that PDSCH can be

demodulated (format of PDSCH)

PUSCHPhysical Uplink Shared Channel Uplink user data and signaling

PUCCHPhysical Uplink Control Channel Reports Hybrid ARQ acknowledgements

PRACHPhysical Random Access Channel Used for random access

LTE Channels

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Radio Resource Control (RRC) States

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From a mobility perspective, the UE can be in one of three states.

LTE_DETACHED

LTE_IDLE

LTE_ACTIVE

LTE_DETACHED

LTE_ACTIVE

LTE_IDLE

OFF

Power Up

Registration De-registration

Inactivity New Traffic

Timeout of

Tracking Area

Update/PLMNChange

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UE States

LTE_DETACHED

Power On

Registration (Attach)

LTE_ACTIVE

Allocate C-RNTI, S_TMSI

Allocate IP addresses

Authentication

Establish security context

Release RRC connection

Release C-RNTI

Configure DRX for paging

LTE_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

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LTE_DETACHEDstate is typically a transitory state in which the UE is powered-on but is in

the process of searching and registering with the network.

LTE_ACTIVEstate, the UE is registered with the network and has an RRC connection with

the eNB. In LTE_ACTIVE state, the network knows the cell to which the UE belongs and

can transmit/receive data from the UE.

LTE_IDLE state is a power-conservation state for the UE, where typically the UE is not

transmitting or receiving packets. In LTE_IDLE state, no context about the UE is stored in

the eNB. In this state, the location of the UE is only known at the MME and only at the

granularity of a tracking area (TA) that consists of multiple eNBs. The MME knows the TA

in which the UE last registered and paging is necessary to locate the UE to a cell.

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Thanks