lte system principle 20110525 a 1.0

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LTE system principle

2010-09

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

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


3GPP TS 《 36.401 》

3GPP TS 《 36.101 》

3GPP TS 《 36.211 》

References


1. Overview

2. LTE system architecture

3. LTE key features

Contents


Mobile communications standards landscape


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

3GPP Releases

GSM9.6kbit/s

Phase 1

GPRS171.2kbit/s

Phase 2+(Release 97)

EDGE473.6kbit/s

Release 99

UMTS2Mbit/s

Release 99

HSDPA14.4Mbit/s

Release 5

HSUPA5.76Mbit/s

Release 6

HSPA+28.8Mbit/s42Mbit/s

Release 7/8

LTE+300Mbit/s

Release 8

Release 9/10LTE Advanced


LTE will be the Single Global Standard

FDD LTEFDD LTE

TDD LTETDD LTE

UMTSUMTS

CDMACDMA

TD-SCDMATD-SCDMA

GSMGSM

WiMAXWiMAX

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

64QAM64QAM

2x2MIMO

DC

64QAM

2x2MIM

O2x2

MIMO

28Mbps/5MHz

Spectral Efficiency

Title

64QAM

>1.2Gbps/80MHz

64QAM

300Mbps/20MHz

OFDM OFDM

4x4MIMO

New Key Tech.

4x4MIMO

Relay

2x2MIMO

64QAM

OFDM

150Mbps

/20MHz


SDR Facilitating Smooth Evolution

Technology

800M

900M 1800M

2100M

2.6G

GSM

UMTS

LTE

GSM+UMTS

GSM+LTE

LTE

mRRU MRFU

SDRSDR

SDR SDR

GSM

2600MHzLTE

2100MHzUMTS

1800MHz GSM

900MHz

800MHz

2010 2011 2012

LTE

LTE

LTE

LTEUMTSGSM

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


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.

LTE requirements and targets


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

LTE technical features


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

TransmissionBandwidth [RB]

Transmission Bandwidth Configuration [RB]

Channel Bandwidth [MHz]

Reso

urce b

lock

Ch

ann

el edg

e

Ch

ann

el edg

e

DC carrier (downlink only)Active Resource Blocks

LTE frequency bands


LTE Release 8 BandsBand 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


eNB

UE

Carrier Frequency EARFCN Calculation

FDL = FDL_low + 0.1(NDL - NOffs-DL)

FUL = FUL_low + 0.1(NUL - NOffs-UL)


Example

Frequency

Uplink Downlink

100kHz Raster

2127.4MHz1937.4MHz

FDL = FDL_low + 0.1(NDL - NOffs-DL)

(FDL - FDL_low)

0.1+ NOffs-DL

(2127.4 - 2110)

0.1+ 0

NDL =

NDL = = 174


Huawei mirror site for 3GPP specifications.

http://szxmir01-in.huawei.com/www.3gpp.org/www.3gpp.org

The specification document for LTE is 36 series, inherits

the structure of UTRAN 25 series:

36.1xx series is about the physical layer general aspect

36.2xx series is about radio interface physical layer

36.3xx series is about the radio interface layer 2 and 3

36.4xx series is about the terrestrial interfaces (S1, X2 )

LTE standardization and specifications


1. Overview

2. LTE system architecture

3. LTE key features

Contents


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

X2 E-UTRAN

UMTS LTE


LTE-SAE System architecture

SAE

Control plane

User plane

Operator'sIP Service

SGi

Rx

UE

S-GW P-GW

PCRF

Gx

S5

MME

HSS

S1-U

S11

S6a

LTE

S1-MME

LTE-Uu

X2 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


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

E-UTRAN functions


1. Overview

2. TE system architecture

3. LTE key features

Contents


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.

Basic principles of OFDM

Frequency

Guard Band

ChannelBandwidth

Subcarrier

Frequency

ChannelBandwidth


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.

Why use OFDM?


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

OFDM implementation by IFFT/FFT

Coded Bits

IFFTSerial

toParallel

SubcarrierModulation

RF

Inverse Fast FourierTransform

Complex Waveform

Coded Bits

Parallelto

SerialFFT

SubcarrierDemodulation

Receiver

Fast FourierTransform


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


Cyclic-prefix insertion


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


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


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

Advantage of OFDM


Peak to Average Power Ratio

Amplitude

Time

OFDM Symbol

PAPR (Peak to Average Power Ratio) Issue

Peak

Average

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.


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.

SC-FDMA in uplink

Time Domain

CP Insertion

Subcarrier Mapping

Frequency Domain

DFTSymbols

Time Domain

IDFT

0000

000


eNB

UE

OFDM used in LTE

OFDM

(OFDMA)

OFDM

(SC-FDMA)

eNB

UE

Radio Channel

FDD Radio Channel

UE

TDD


Frequency

Power Time

Orthogonal Frequency Division Multiple Access

OFDMAEach user allocated a different resource which can vary in time and frequency.

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

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.


Downlink PRB Parameters

Configuration NSCRB NSymbDL

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

160 144 144 144 144 144 1442048 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


OFDM Symbol Mapping

Time

Frequency

Amplitude

OFDM Symbol

Cyclic Prefix

Modulated OFDM

Symbol

OFDMAEach user allocated a different resource which can vary in time and frequency.


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

Channel-dependent scheduling


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


MIMO Modes

8 MIMO modes specified in 3GPP LTE standard

Transmission Mode

Transmission scheme

Reference

Mode 1 single-antenna port (port 0)

It is compatible with single-antenna transmission

Mode 2 transmit diversity It weakens the interference caused by channel fading and is applicable within low SINR environment

Mode 3 open-loop space division multiplexing

It increases the peak rate and is applicable within high rate and SINR environment

Mode 4 Closed-loop spatial multiplexing

It is weighted according to the channel characteristics, increases the peak rate, and is applicable within low rate but high SINR environment

Mode 5 Multi-user MIMO It improves cell throughput

Mode 6 Closed-loop precoding with rank of 1

It increases cell coverage

Mode 7 Beamforming, single-antenna port (port 5)

It weakens interference and increases cell coverage

Mode 8 Dual-antenna port: Dual-stream BF

It increases cell throughput


Array gain: It increases the transmit power and can be used for

beamforming.

Diversity gain: It weakens the interference caused by channel fading.

Spatial multiplexing gain: It doubles the rate within the same bandwidth after

spatial orthogonal channels are constructed.

MIMO

Channel

Data

Streaming

Advantages of MIMO


UL Virtual MIMO

FeaturesFeaturesBenefitsBenefits

Improve the overall uplink cell throughput.Increase the UL spectrum efficiency.

The uplink channels of paired users

must be with good orthogonality to

each other to prevent interference.Multi-users use the same time-

frequency resource.


2x2 MIMOeNodeB UE 1

1x2 SIMOeNodeB UE 1

Th

rou

gh

pu

t (M

bp

s)

28.34%

18.15%

ISD:500mSpeed:3km/h

13.88

16.4

9.42

12.09

12.36

14.23

15.12%

MIMOSIMOxx.xx%:

Gain

ISD:500mSpeed:30km/h

ISD:1732mSpeed:30km/h

Th

rou

gh

pu

t (M

bp

s)

46.40%46.94%

Outdoor-to-Indoor

Speed: 3km/h

23.24

34.1556.68%

MIMOSIMOxx.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

LTE

LTE

LTE

Macro

Micro

MIMO--the Key to Improve Cell Throughput


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-MIMODL 4×4 MIMO


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Page44

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 Features


Antenna Ports

OFDM Signal Generation

Codewords

Scrambling

Scrambling

Modulation Mapper

Modulation Mapper

Layer Mapper

Precoding

Layers

Resource Element Mapper

Resource Element Mapper

OFDM Signal

Generation

OFDM Signal

Generation


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

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 2,5,8Power

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)


LTE Key Technologies － SON

Self-Optiz. & MaintenanceSelf-Optiz. & Maintenance

Network Performance Network Performance ImprovementImprovement

Network Planning & Network Planning & DesignDesign

Installation &Installation & Initial TuningInitial Tuning

Network Operation & Network Operation & MaintenanceMaintenance

Network Upgrade and Network Upgrade and evolutionevolution

Self-PlanningSelf-Planning Self-Config.Self-Config. Self-optimiz.Self-optimiz.

Deployment StageDeployment Stage

Operation & Maintenance StageOperation & Maintenance Stage

eNB 3

eNB 1

eNB 2

Self-Organising Network (SON) •SON effectively reduces human intervention in SON effectively reduces human intervention in deployment and operation stage. Thus, SON saves deployment and operation stage. Thus, SON saves both CAPEX & OPEX. both CAPEX & OPEX. •SON with ICIC : SON helps inter-cell interference SON with ICIC : SON helps inter-cell interference coordination to improve cell edge throughput and coordination to improve cell edge throughput and user experienceuser experience


SON Improving Operation Efficiency

Planning Phase

Deployment

Phase

Maintenance

Phase

Optimization

Phase

Inventory ManagementSleeping Cell detection Antenna Fault Detection Cell/interface/sub. trace

Automatic Network Planning

Automatic Config. PlanningAutomatic Parameter

Planning

Automatic PCI/TA Optimization Automatic Neighbor RelationInter-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


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

lu

e

eNodeB

EMS + DHCP

File Server

Config Config

Config

S/W

ConfigS/W

• More reliable

• Improve network KPI by HO optimization

• Plug & Play Installation

• Shorten deployment duration

Cell A Cell B Cell C

Cell CCell BCell A

Cell B

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lte system principle 20110525 a 1.0

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