LTE System Principle 20110525 a 1.0

2010-09

Security Level: Internal Use

LTE system principle

www.huawei.com

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

Objectives

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

2010 Huawei Technologies Co.,Ltd. Co., Ltd.All Allrights rightsreserved reserved. Copyright @

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References

3GPP TS 36.401 3GPP TS 36.101 3GPP TS 36.211


Page 3

Contents1. Overview2. LTE system architecture

3. LTE key features


Page 4

Contents1. Overview

2. LTE system architecture3. LTE key features


Page 5

Mobile communications standards landscape


3GPP Releases

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 LTEPhase 2+ (Release 97) GPRS 171.2kbit/s Release 99 UMTS 2Mbit/s Release 6 HSUPA 5.76Mbit/s Release 8 LTE +300Mbit/s

Release 9/10 LTE Advanced GSM 9.6kbit/s Phase 1 EDGE 473.6kbit/s Release 99 HSDPA 14.4Mbit/s Release 5 HSPA+ 28.8Mbit/s 42Mbit/s Release 7/8


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LTE will be the Single Global StandardGSM700M 800M 850M 900M 1500M 1700M 1800M 1900M 2100M 2300M 2600M

>1.2Gbps /80MHz

Spectral EfficiencyTitleNew Key Tech.

UMTS150Mbps /20MHz

300Mbps /20MHz

FDD LTE

Relay

CDMA42Mbps /5MHz

84Mbps /10MHz2x2 MIMO

4x4 MIMO

4x4 MIMO

DC

TD-SCDMA21Mbps /5MHz

28Mbps /5MHz 2x2MIMO

WiMAX

2x2 64QAM MIMO

2x2 MIM O 64QAM

OFD M 64QAM

OFDM

OFDM

TDD LTE

64QAM

64QAM

64QAM

LTE will be the natural migration choice for mobile operators. 2010 Huawei Technologies Co.,Ltd. Co., Ltd.All Allrights rightsreserved reserved. Copyright @

Page 8

SDR Facilitating Smooth Evolution Spectrum for LTE2600MHz LTE

Smooth Transition to LTEGSM+UMTSLTE

2100MHz

UMTS

SDR

SDR

GSM1800MHz 900MHz 800MHz 2010

LTEmRRU MRFU

GSMGSM UMTS

LTE

LTE LTE

SDR2012

SDR

2011

GSM+LTE

Technolog y GSM UMTS LTE

800M

900M

1800M

2100M

2.6G

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.


LTE requirements and targets

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 100Mbit/s and 50 Mbit/s for downlink and uplink respectively, when operating in 20MHz spectrum allocation)

Improved spectral efficiencySeamless 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.Page 10


LTE technical features

The LTE downlink transmission scheme is based on downlink OFDMA and uplink SC-FDMA LTE adopts shared-channel transmission, in which the timefrequency 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 SONPage 11


LTE frequency bands

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] Transmission bandwidth configuration NRB 1.4 6 3 15 5 25 10 50 15 75 20 100

Channel Bandwidth [MHz] Transmission Bandwidth Configuration [RB] Transmission Bandwidth [RB]

Channel edge


Channel edge

Resource block

Active Resource Blocks

DC carrier (downlink only)

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LTE Release 8 BandsBand Duplex FDL_low (MHz) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD 2110 1930 1805 2110 869 875 2620 925 1844.9 2110 1475.9 728 746 758 FDL_high (MHz) 2170 1990 1880 2155 894 885 2690 960 1879.9 2170 1500.9 746 756 768 0 600 1200 1950 2400 2650 2750 3450 3800 4150 4750 5000 5180 5280 0-599 600-1199 1200-1949 1950-2399 2400-2649 2650-2749 2750-3449 3450-3799 3800-4149 4150-4749 4750-4999 5000-5179 5180-5279 5280-5379 NOffs-DL NDL FUL_low (MHz) 1920 1850 1710 1710 824 830 2500 880 1749.9 1710 1427.9 698 777 788 FUL_high (MHz) 1980 1910 1785 1755 849 840 2570 915 1784.9 1770 1452.9 716 787 798 18000 18600 19200 19950 20400 20650 20750 21450 21800 22150 22750 23000 23180 23280 18000-18599 18600-19199 19200-19949 19950-20399 20400-20649 20650-20749 20750-21449 21450-21799 21800-22149 22150-22749 22750-22999 23000-23179 23180-23279 23280-23379 NOffs-UL NUL

17

FDD

734

746

5730

5730-5849

704

716

23730

23730-23849

33 34 35 36 37 38 39 40

TDD TDD TDD TDD TDD TDD TDD TDD

1900 2010 1850 1930 1910 2570 1880 2300

1920 2025 1910 1990 1930 2620 1920 2400

26000 26200 26350 26950 27550 27750 28250 28650

36000-36199 36200-36349 36350-36949 36950-37549 37550-37749 37750-38249 38250-38649 38650-39649

1900 2010 1850 1930 1910 2570 1880 2300

1920 2025 1910 1990 1930 2620 1920 2400

36000 36200 36350 36950 37550 37750 38250 38650

36000-36199 36200-36349 36350-36949 36950-37549 37550-37749 37750-38249 38250-38649 38650-39649


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Carrier Frequency EARFCN CalculationFDL = FDL_low + 0.1(NDL - NOffs-DL)

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

UE


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Example100kHz Raster Uplink Downlink

1937.4MHz

2127.4MHz

Frequency

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

(2127.4 - 2110) NDL = + 0 = 174 0.1


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LTE standardization and specifications

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 )


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Contents1. Overview

2. LTE system architecture3. LTE key features


Page 17

LTE System architectureUMTS LTE

MME / S-GW

MME / S-GW

X2eNB eNB

S1

eNB

LTE: simplified IP flat architecture

Less equipment node and easier deployment

Less transmission delay and easier O&MS1 and X2 interfaces are based on a full IP transport stackPage 18


X2

S1S1X2

S1E-UTRAN

LTE-SAE System architecture

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 domainHSS eNodeB MME S1-MME S6a Gxc S11 Rx Gx PCRF Control plane User plane

LTE -Uu

X2

S1-U

S1-MME eNodeB S1-U

S5

SGi P-GW

Operator's IP Service

S-GW

UE

LTE

SAEPage 19


E-UTRAN functions

Transfer of user data Radio channel ciphering and deciphering

Inter-cell interference coordination

Connection setup and releaseLoad Balancing Distribution function for NAS messages

Integrity protection Header compression Mobility control functions Handover Paging Positioning

NAS node selection function Synchronization

Radio access network sharingMBMS function


Page 20

Contents1. Overview

2. TE system architecture3. LTE key features


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Basic principles of OFDM

Transmission by means of OFDM can be seen as a kind of multicarrier transmission.

Due to the fact that two modulated OFDM subcarriers are mutually

orthogonal, multiple signals could be transmitted in parallel over thesame radio link, the overall data rate can be increased up to M times.Guard Band Subcarrier

Frequency Channel Bandwidth

Frequency Channel Bandwidth


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Why use OFDM?

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 greaterchance 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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OFDM implementation by IFFT/FFT

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 SubcarrierModulation Inverse Fast Fourier Transform

Coded Bits

Serial to Parallel

IFFT

RF

Complex Waveform

Subcarrier Demodulation Fast Fourier Transform Parallel to Serial

Receiver

FFT

Coded Bits


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LTE Channel and FFT SizesChannel FFT Size Bandwidth 1.4MHz 3MHz 5MHz 10MHz 15MHz 20MHz 128 256 512 15kHz 1024 1536 2048 15.36MHz 23.04MHz 30.72MHz Subcarrier Sampling Rate Bandwidth 1.92MHz 3.84MHz 7.68MHz


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Cyclic-prefix insertion


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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 blocklength 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 atime-dispersive channel, as long as the span of the time dispersion is shorter than the cyclic-prefix length.


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Downlink CP ParametersConfiguration Normal Cyclic Prefix Extended Cyclic Prefix f = 15kHz CP Length (Ts) 160 for slot 0 144 for slot 1, 2, 6 f = 15kHz f = 7.5kHz 512 for slot 0, 1, 5 1024 for 0, 1, 2 Time ~ 5.208s ~ 4.688s ~16.67s ~ 33.33 s Delay Spread ~ 1.562km ~ 1.406km ~ 5km ~ 10km


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Advantage of OFDM

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 spectrumPage 29


Peak to Average Power RatioPAPR (Peak to Average Power Ratio) IssueAmplitude OFDM Symbol

Peak Averag eTime

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.Page 30


SC-FDMA in uplink

SC-FDMA, which has much in common with OFDMA, such as multicarrier 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.Time Domain Frequency Domain Time Domain0 0 0 0 IDFT

DFT Symbols

Subcarrier Mapping

CP Insertion

0 0 0


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OFDM used in LTERadio ChannelTDD

eNBFDDRadio Channel UE

UE

OFDM (OFDMA)

eNB

OFDMUE

(SC-FDMA)


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Orthogonal Frequency Division Multiple AccessPower TimeOFDMA Each user allocated a different resource which can vary in time and frequency.

Frequency


Page 33

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 throughputFlexible multi-users scheduling

UL: SC-FDMA (Single Carrier - FDMA)

Save terminals 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 ParametersConfiguration Normal Cyclic Prefix Extended Cyclic Prefix f = 15kHz f = 15kHz f = 7.5kHz 12 6 24 3 NSCRB NSymbDL 7

Normal CP ConfigurationLarger first CP when Normal CP is configured Nsymb OFDM Symbols (= 7 for Normal CP) 0 160 2048 14 4 1 2048 14 4 2 2048 14 4 3 2048 14 4 4 2048 14 4 5 2048 14 4 6 2048DL

E.g. NCP = 144, TCP= 144 x Ts = 4.6875s


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OFDM Symbol MappingOFDMA Each user allocated a different resource which can vary in time and frequency.

Time Modulated OFDM Symbol Amplitude

Cyclic Prefix

Frequency OFDM Symbol


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Channel-dependent scheduling

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 37

Multi-Antenna Technique MIMOReceive diversity: SIMO Transmit diversity: MISO Multi-antenna reception and transmission: 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.


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MIMO ModesTransmission ModeMode 1 Mode 2 Mode 3 Mode 4

Transmission schemesingle-antenna port (port 0) transmit diversity open-loop space division multiplexing Closed-loop spatial multiplexing

ReferenceIt is compatible with single-antenna transmission It weakens the interference caused by channel fading and is applicable within low SINR environment It increases the peak rate and is applicable within high rate and SINR environment It is weighted according to the channel characteristics, increases the peak rate, and is applicable within low rate but high SINR environment

Mode 5Mode 6 Mode 7

Multi-user MIMOClosed-loop precoding with rank of 1 Beamforming, singleantenna port (port 5)

It improves cell throughputIt increases cell coverage It weakens interference and increases cell coverage

Mode 8

Dual-antenna port: Dualstream BF

It increases cell throughput

8 MIMO modes specified in 3GPP LTE standard


Page 39

Advantages of MIMO

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 afterspatial orthogonal channels are constructed.

Data Streaming

MIMO Channel


Page 40

UL Virtual MIMO

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

Features The uplink channels of paired users must be with good orthogonality to each other to prevent interference. Multi-users use the same timefrequency resource.


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MIMO--the Key to Improve Cell Throughput1x2 SIMOThroughput (Mbps) xx.xx%: Gain

eNodeB

UE 1

Macr oLLL T TT EEE

18.15%16.413.88 9.42

SIMO MIMO

28.34%12.09

15.12%14.23 12.36

2x2 MIMOeNodeB UE 1

ISD:500m Speed:3km/h

ISD:500m Speed:30km/ h

ISD:1732m Speed:30km/ h

xx.xx%: Gain

46.94%34.15

46.40%35.18

SIMO MIMO

Throughput (Mbps)

56.68%26.87 24.03 17.15

In typical urban area:15%~28% gain over SIMO @ Macro ~50% gain over SIMO @ Micro

Micro

23.24

Outdoor-to-Indoor Outdoor-to-Outdoor Outdoor-to-Outdoor Speed: 3km/h Speed: 3km/h Speed: 30km/h


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More Gains through Higher-order MIMODL 44 MIMO UL 24 MU-MIMO

eNodeB

UE 1 UE 1

eNodeB

UE 2

4x4 MIMO v.s. 2x2 MIMO: ~ 50% gain in average cell 23%~90% increasing in edge user throughput throughput

2x4 MU-MIMO v.s. 1x2 SIMO: 23%~90% increasing in edge ~50% gain in average celluser throughput throughputPage 43


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

Features Provide higher-data-rate services Significantly improve the system throughput

Improve users experience High-order modulation scheme used within excellent channel condition

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Page44

OFDM Signal Generation

Codewords

Layers

Antenna PortsResource Element Mapper

Scrambling

Modulation Mapper Layer Mapper

OFDM Signal Generation OFDM Signal Generation

PrecodingResource Element Mapper

Scrambling

Modulation Mapper


Page 45

Inter-cell interference coordination

By restricting the transmission power of parts of the spectrum in

one cell, the interference seen in the neighbouring cells in this partof the spectrum will be reduced, This part of the spectrum can then be used to provide higher data rates for users in the neighbouring cell2 2 7 6 1 1 6 5 5 9 7 4 8Power

4

Cell

1,4,7

Power Frequency

3 3 Cell 2,5,8Power Frequency

Cell

3,6,9Frequency

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 (

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LTE System Principle 20110525 a 1.0