LTE System Principle

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

LTE system principle

2010-09

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

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Upon completion of this course, you will be able

to ：

Know the backgrounds of evolution

Know system architecture of LTE

Know key features of LTE

Objectives


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3GPP TS 《36.401》

3GPP TS 《36.101》

3GPP TS 《36.211》

Page 3

References


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1. Overview

2. LTE system architecture

3. LTE key features

Contents

Page 4


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1. Overview


3. LTE key features

Contents

Page 5


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Mobile communications standards landscape


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3GPP is working on two approaches for 3G evolution: the LTE

and the HSPA Evolution

HSPA Evolution is aimed to be backward compatible while LTE do

not need to be backward compatible with WCDMA and HSPA

By the end of 2007, 3GPP R8 is released as the first specs of LTE

Page 7

3GPP Releases

GSM

9.6kbit/s

GPRS

171.2kbit/s

EDGE

473.6kbit/s

UMTS

2Mbit/s

HSDPA

14.4Mbit/s

HSUPA

5.76Mbit/s

HSPA+

28.8Mbit/s

42Mbit/s

LTE

+300Mbit/s

Phase 1

Phase 2+

(Release 97)

Release 99

Release 99

Release 5

Release 6

Release 7/8

Release 8

Release 9/10

LTE

Advanced


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Copyright @ 2010 Huawei Technologies Co.,Ltd. All rights reserved Page 8

LTE will be the Single Global Standard

FDD LTE

TDD LTE

UMTS

CDMA

TD-SCDMA

GSM

WiMAX

700M

800M

850M

900M

1500M

1700M

1800M

1900M

2100M

2300M

2600M

……

LTE will be the natural migration choice for mobile operators.

84Mbps

/10MHz

21Mbps

/5MHz

42Mbps

/5MHz

64QAM 64QAM

2x2

MIMO

DC

64QAM

2x2

MIM

O 2x2

MIMO

28Mbps

/5MHz

Spectral Efficiency

Title

64QAM

>1.2Gbps

/80MHz

64QAM

300Mbps

/20MHz

OFDM OFDM

4x4

MIMO

New

Key

Tech.

4x4

MIMO

Relay

2x2

MIMO

64QAM

OFD

M

150Mbps

/20MHz


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SDR Facilitating Smooth Evolution

Page

Technolog

y

800M 900M 1800M 2100M 2.6G

GSM

UMTS

LTE

GSM+UMTS

GSM+LTE

LTE

mRRU MRFU

SDR SDR

SDR SDR

GSM

2600MHz LTE

2100MHz UMTS

1800MHz GSM

900MHz

800MHz

2010 2011 2012

LTE

LTE

LTE

LTE UMTS

GSM

Spectrum refarming starts from

900M/1800M, which can be utilized

for LTE deployment.

SDR technology supports flexible and

smooth transition from 2G/3G to LTE.

Spectrum for LTE Smooth Transition to LTE


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Reduced delays, in terms of both connection establishment (less then

100ms) and transmission latency (less then 10ms)

Increased user data rates: (Peak data-rate requirements are 100

Mbit/s and 50 Mbit/s for downlink and uplink respectively, when

operating in 20MHz spectrum allocation)

Improved spectral efficiency

Seamless mobility, including between different radio-access

technologies

Supporting flexible spectrum allocation (1.4, 3, 5, 10, 15 and 20 MHz)

to meet the complicated spectrum situation requirement

Simplified network architecture

Reasonable power consumption for the mobile terminal.

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LTE requirements and targets


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The LTE downlink transmission scheme is based on downlink

OFDMA and uplink SC-FDMA

LTE adopts shared-channel transmission, in which the time-

frequency resource is dynamically shared between users. This is

similar to the approach taken in HSDPA

Fast hybrid ARQ with soft combining is used in LTE

MIMO is supported by LTE, basically this is Spatial multiplexing

which can increase data rate prominently

LTE supports flexible spectrum allocation in terms of duplex

arrangement which support both FDD and TDD and bandwidth

allocations which ranges 1.4, 3, 5, 10, 15 and 20 MHz

Support SON

Page 11

LTE technical features


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LTE is designed to operate in these frequency bands：

2.1GHz, 1.9GHz, 1.7GHz, 2.6GHz, 900 MHz, 800 MHz, 450 MHz,

etc , refer to 36.101 for details.

Transmission bandwidth could be:

Channel bandwidth BWChannel [MHz] 1.4 3 5 10 15 20

Transmission bandwidth configuration NRB 6 15 25 50 75 100

Transmission

Bandwidth [RB]

Transmission Bandwidth Configuration [RB]

Channel Bandwidth [MHz]

Res

ou

rce

blo

ck

Ch

an

nel e

dg

e

Ch

an

nel e

dg

e

DC carrier (downlink only)Active Resource Blocks Page 12

LTE frequency bands


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LTE Release 8 Bands Band Duplex FDL_low

(MHz)

FDL_high

(MHz)

NOffs-DL NDL FUL_low

(MHz)

FUL_high

(MHz)

NOffs-UL NUL

1 FDD 2110 2170 0 0-599 1920 1980 18000 18000-18599

2 FDD 1930 1990 600 600-1199 1850 1910 18600 18600-19199

3 FDD 1805 1880 1200 1200-1949 1710 1785 19200 19200-19949

4 FDD 2110 2155 1950 1950-2399 1710 1755 19950 19950-20399

5 FDD 869 894 2400 2400-2649 824 849 20400 20400-20649

6 FDD 875 885 2650 2650-2749 830 840 20650 20650-20749

7 FDD 2620 2690 2750 2750-3449 2500 2570 20750 20750-21449

8 FDD 925 960 3450 3450-3799 880 915 21450 21450-21799

9 FDD 1844.9 1879.9 3800 3800-4149 1749.9 1784.9 21800 21800-22149

10 FDD 2110 2170 4150 4150-4749 1710 1770 22150 22150-22749

11 FDD 1475.9 1500.9 4750 4750-4999 1427.9 1452.9 22750 22750-22999

12 FDD 728 746 5000 5000-5179 698 716 23000 23000-23179

13 FDD 746 756 5180 5180-5279 777 787 23180 23180-23279

14 FDD 758 768 5280 5280-5379 788 798 23280 23280-23379

17 FDD 734 746 5730 5730-5849 704 716 23730 23730-23849

33 TDD 1900 1920 26000 36000-36199 1900 1920 36000 36000-36199

34 TDD 2010 2025 26200 36200-36349 2010 2025 36200 36200-36349

35 TDD 1850 1910 26350 36350-36949 1850 1910 36350 36350-36949

36 TDD 1930 1990 26950 36950-37549 1930 1990 36950 36950-37549

37 TDD 1910 1930 27550 37550-37749 1910 1930 37550 37550-37749

38 TDD 2570 2620 27750 37750-38249 2570 2620 37750 37750-38249

39 TDD 1880 1920 28250 38250-38649 1880 1920 38250 38250-38649

40 TDD 2300 2400 28650 38650-39649 2300 2400 38650 38650-39649

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1. Overview


3. LTE key features

Contents

Page 14


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LTE System architecture

LTE: simplified IP flat architecture

Less equipment node and easier deployment

Less transmission delay and easier O&M

S1 and X2 interfaces are based on a full IP transport stack

eNB

MME / S-GW MME / S-GW

eNB

eNBS1 S1

S1 S1

X2

X2X2

E-UTRAN

UMTS LTE

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LTE-SAE System architecture

SAE

Control plane

User plane

Operator's

IP ServiceSGi

Rx

UE

S-GW P-GW

PCRF

Gx

S5

MME

HSS

S1-U

S11

S6a

LTE

S1-MME

LTE

-UuX2 S1-U

S1-MME

eNodeB

eNodeB

Gxc

An evolved core network, the Evolved Packet Core is at the same time

developed, which generally is called System Architecture Evolution.

The philosophy of the SAE is to focus on the packet-switched domain,

and migrate away from the circuit-switched domain


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Transfer of user data

Radio channel ciphering

and deciphering

Integrity protection

Header compression

Mobility control functions

Handover

Paging

Positioning

Inter-cell interference coordination

Connection setup and release

Load Balancing

Distribution function for NAS

messages

NAS node selection function

Synchronization

Radio access network sharing

MBMS function

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E-UTRAN functions


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1. Overview

2. TE system architecture

3. LTE key features

Contents

Page 18


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Transmission by means of OFDM can be seen as a kind of multi-

carrier transmission.

Due to the fact that two modulated OFDM subcarriers are mutually

orthogonal, multiple signals could be transmitted in parallel over the

same radio link, the overall data rate can be increased up to M times.

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Basic principles of OFDM

Frequency

Guard Band

Channel

Bandwidth

Subcarrier

Frequency

Channel

Bandwidth


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Efficient use of radio spectrum includes placing modulated carriers as close

as possible without causing Inter-Carrier Interference (ICI)

In order to transmit high data rates, short symbol periods must be used, In

a multi-path environment, a shorter symbol period leads to a greater

chance for Inter-Symbol Interference (ISI).

Orthogonal Frequency Division Multiplexing (OFDM) addresses both of

these problems:

OFDM provides a technique allowing the bandwidths of modulated

carriers to overlap without interference (no ICI).

It also provides a high date rate with a long symbol duration, thus

helping to eliminate ISI.

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Why use OFDM?


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OFDM modulation implementation in LTE

Normally ,assume LTE sub carrier frequency f =1/Tu=15khz, and

IFFT bin size N=2048, the sampling rate is fs =1/Ts

=N ·f=30720000Hz

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OFDM implementation by IFFT/FFT

Coded

BitsIFFT

Serial

to

Parallel

Subcarrier

Modulation

RF

Inverse Fast

Fourier

Transform

Complex

Waveform

Coded

Bits

Parallel

to

Serial

FFT

Subcarrier

Demodulation

Receiver

Fast Fourier

Transform


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LTE Channel and FFT Sizes

Channel Bandwidth

FFT Size Subcarrier Bandwidth

Sampling Rate

1.4MHz 128

15kHz

1.92MHz

3MHz 256 3.84MHz

5MHz 512 7.68MHz

10MHz 1024 15.36MHz

15MHz 1536 23.04MHz

20MHz 2048 30.72MHz

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Cyclic-prefix insertion


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Time dispersion on the radio channel may cause ISI

To deal with this problem, cyclic-prefix insertion is typically used

in case of OFDM transmission

The last NCP samples of the IFFT output block of length N is copied

and inserted at the beginning of the block, increasing the block

length from N to N +NCP. At the receiver side, the corresponding

samples are discarded before OFDM demodulation

Subcarrier orthogonality will then be preserved also in case of a

time-dispersive channel, as long as the span of the time

dispersion is shorter than the cyclic-prefix length.

Cyclic-prefix insertion

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Downlink CP Parameters

Configuration CP Length (Ts) Time Delay Spread

Normal Cyclic

Prefix

∆f = 15kHz 160 for slot 0 ~ 5.208µs ~ 1.562km

144 for slot 1, 2, …6 ~ 4.688µs ~ 1.406km

Extended Cyclic

Prefix

∆f = 15kHz 512 for slot 0, 1, …5 ~16.67µs ~ 5km

∆f = 7.5kHz 1024 for 0, 1, 2 ~ 33.33 µs ~ 10km

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High spectrum efficiency - the bandwidth of each subcarrier would

be adjacent to its neighbors, so there would be no wasted spectrum

With multiple subcarriers transmitting in parallel, long symbol

duration is used, thus OFDMA is more tolerant to multi-path

environment and better entitled to eliminate ISI (inter symbol

interference)

Especially with a cyclic prefix, inter-symbol interference could be

minimized

OFDM is flexible in allocating power and rate optimally among

narrowband sub-carriers (scheduling)

Frequency diversity could be enabled due to the wide spectrum

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Advantage of OFDM


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Peak to Average Power Ratio

Amplitude

Time

OFDM

Symbol

PAPR (Peak to

Average Power Ratio)

Issue

Peak

Averag

e

The drawback of OFDM is the high peak-to-average ratio of the

transmitted signal, which greatly decrease the efficiency of the

linear amplifiers

This is especially critical for the uplink, due to the high

importance of low mobile-terminal power consumption and cost.

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SC-FDMA, which has much in common with OFDMA, such as multi-

carrier technology and guard interval protected symbol, but much

higher power amplifier efficiency (lower PAPR) is adopt in uplink.

SC-FDMA is just the DFT-S-OFDM, which can be seen as an OFDM

system with a DFT pre-coding. The localized RB distribution makes

each user occupy consecutive part of the whole bandwidth, which

looks like a single carrier.

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SC-FDMA in uplink

Time Domain

CP

Insertion

Subcarrier

Mapping

Frequency Domain

DFTSymbols

Time Domain

IDFT

0

0

0

0

0

0

0


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eNB

UE

OFDM used in LTE

OFDM

(OFDMA)

OFDM

(SC-FDMA)

eNB

UE

Radio

Channel

FDD Radio

Channel

UE

TDD

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Frequency

PowerTime

Orthogonal Frequency Division Multiple

Access

OFDMA

Each user allocated a

different resource

which can vary in time

and frequency.

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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

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OFDMA used in LTE.

DL: OFDMA (Orthogonal Frequency Division Multiple Access)

Anti multi-path interference

Anti frequency selective fading

Higher spectrum efficiency

Easy to cooperate with MIMO for higher

throughput

Flexible multi-users scheduling

UL: SC-FDMA (Single Carrier - FDMA)

Save terminal’s cost & power consumption

Lower PAPR modulation technology: DFT-S-OFDM,

which is similar to OFDM

Higher spectral efficiency compare with traditional

single carrier technology.


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Downlink PRB Parameters

Configuration NSCRB NSymb

DL

Normal Cyclic Prefix ∆f = 15kHz 12

7

Extended Cyclic

Prefix ∆f = 15kHz 6

∆f = 7.5kHz 24 3

0

OFDM Symbols (= 7 for Normal CP)

21 3 4 5 6

NsymbDL

16014

4

14

4

14

4

14

4

14

4

14

42048 2048 2048 2048 2048 2048 2048

Larger first CP when

Normal CP is configured

E.g. NCP = 144,

TCP= 144 x Ts = 4.6875µs

• Normal CP Configuration

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OFDM Symbol Mapping

Time

Frequency

Amplitude

OFDM

Symbol

Cyclic

Prefix

Modulated

OFDM

Symbol

OFDMA

Each user allocated a

different resource

which can vary in time

and frequency.

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Basically LTE uses shared-channel transmission, similar to HSDPA,

the time-frequency resource is dynamically shared between users

LTE can take channel variations into account not only in the time

domain, as HSPA, but also in the frequency domain

For LTE, scheduling decisions can be taken as often as once every

1 ms and the granularity in the frequency domain is 180 kHz

Page 34

Channel-dependent scheduling


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Multi-Antenna Technique — MIMO

Fundamentals of MIMO:

The data to be sent will be divided into multiple concurrent data streams.

The data streams are simultaneously transmitted from multiple antennas

through the spatial dimensions, through different radio channels, and

received by multiple antennas.

And then can be restored to the original data according to the spatial

signature of each data stream.

Receive diversity:

SIMO

Transmit diversity:

MISO

Multi-antenna reception

and transmission: MIMO

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2x2 MIMO

eNodeB

UE 1

1x2 SIMO

eNodeB

UE 1

Th

roug

hp

ut

(Mb

ps)

28.34%

18.15%

ISD:500m

Speed:3km/h

13.88

16.4

9.42

12.09

12.36

14.23

15.12%

MIMO

SIMO xx.xx%: Gain

ISD:500m

Speed:30km/h

ISD:1732m

Speed:30km/h

Th

roug

hp

ut

(Mb

ps)

46.40% 46.94%

Outdoor-to-Indoor

Speed: 3km/h

23.24

34.15

56.68%

MIMO SIMO xx.xx%: Gain

24.03

35.18

17.15

26.87

Outdoor-to-Outdoor

Speed: 3km/h

Outdoor-to-Outdoor

Speed: 30km/h

In typical urban area:

15%~28% gain over SIMO @ Macro

~50% gain over SIMO @ Micro

L

T

E

L

T

E

L

T

E

Macr

o

Micro

MIMO--the Key to Improve Cell Throughput

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More Gains through Higher-order MIMO

23%~90% increasing in edge user

throughput

4x4 MIMO v.s. 2x2 MIMO:

~ 50% gain in average cell

throughput

23%~90% increasing in edge user

throughput

2x4 MU-MIMO v.s. 1x2 SIMO:

~50% gain in average cell

throughput

eNodeB

UE 1

UE 1

UE 2

eNodeB

UL 2×4 MU-MIMO DL 4×4 MIMO

Page 37


35pt

Font to be used by customers and

partners :

18pt

Font to be used by customers and

partners :

Page38

AMC & 64QAM

• AMC, Adaptive Modulation and Coding

Radio-link data rate is controlled by adjusting the modulation scheme and/or the

channel coding rate

Modulations: QPSK, 16QAM, and 64QAM

Turbo code

Provide higher-data-rate services

Significantly improve the system

throughput

Improve user’s experience

High-order modulation scheme used

within excellent channel condition

Features


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By restricting the transmission power of parts of the spectrum in

one cell, the interference seen in the neighbouring cells in this part

of the spectrum will be reduced, This part of the spectrum can then

be used to provide higher data rates for users in the neighbouring

cell

Page 39

Inter-cell interference coordination

2

3

6

5

7

4

2

3

5

9

1 1

4

7

8

6

Frequency

Cell 1,4,7 Power

Frequency

Cell 2,5,8 Power

Frequency

Cell 3,6,9

Power

Different subband allocated for different cell edge users among cells

Reducing the DL inter-cell interference among neighbor cells

30~50% throughput increased for cell edge users (<50% load)


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Page 40

LTE Key Technologies －SON

Self-Optiz. & Maintenance

Network Performance

Improvement Network Planning

& Design

Installation &

Initial Tuning

Network Operation &

Maintenance Network Upgrade

and evolution

Self-Planning Self-Config. Self-optimiz.

Deployment Stage

Operation & Maintenance Stage

eNB 3

eNB 1

eNB 2

Self-Organising Network (SON)

•SON effectively reduces human intervention in deployment and operation stage. Thus, SON saves both CAPEX & OPEX.

•SON with ICIC : SON helps inter-cell interference coordination to improve cell edge throughput and user experience


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SON Improving Operation Efficiency

Planning

Phase

Deploymen

t

Phase

Maintenance

Phase Optimization

Phase

Inventory Management

Sleeping Cell detection

Antenna Fault Detection

Cell/interface/sub. trace

Automatic Network Planning

Automatic Config. Planning

Automatic Parameter Planning

Automatic PCI/TA Optimization

Automatic Neighbor Relation

Inter-RAT ANR,MRO, System Load

Balance, RACH Optimization

Self- configuration (Plug & Play)

Auto Software Management

SON makes LTE network more efficient and solves new challenges when network architecture changes

Page 41


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Typical SON Features at Initial Stage

MLB: Mobility Load Balancing

ANR: Automatic Neighbor

Relation

Self-Config.: Quick Deployment

• Save cost & Improve exactness

• Avoid first HO failure due to missing neighbor

relation

New

• Optimizing cell reselection and handover

parameters

• Reduce call drop rate, handover failure rate,

• Reduce unnecessary redirection

MRO: Mobility Robust

Optimization

unnecessary HO Rate

HO successful rate

Va

lue

eNodeB

EMS + DHCP

File Server

Config Config

Config

S/W

Config S/W

• More reliable

• Improve network KPI by HO optimization

• Plug & Play Installation

• Shorten deployment duration

Cell A Cell B Cell C

Cell C Cell B Cell A

Cell B

Page 42

Thank you www.huawei.com

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LTE System Principle