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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
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Page 2
References
3GPP TS 36.401 3GPP TS 36.101 3GPP TS 36.211
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Page 3
Contents1. Overview2. LTE system architecture
3. LTE key features
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Page 4
Contents1. Overview
2. LTE system architecture3. LTE key features
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Page 5
Mobile communications standards landscape
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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 @
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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.
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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
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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
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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
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Channel edge
Resource block
Active Resource Blocks
DC carrier (downlink only)
Page 12
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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Page 13
Carrier Frequency EARFCN CalculationFDL = FDL_low + 0.1(NDL - NOffs-DL)
eNBFUL = FUL_low + 0.1(NUL - NOffs-UL)
UE
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Page 14
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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Page 16
Contents1. Overview
2. LTE system architecture3. LTE key features
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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
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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
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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
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Page 20
Contents1. Overview
2. TE system architecture3. LTE key features
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Page 21
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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Page 22
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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Page 24
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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Page 25
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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Page 27
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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Page 28
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
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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
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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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Page 31
OFDM used in LTERadio ChannelTDD
eNBFDDRadio Channel UE
UE
OFDM (OFDMA)
eNB
OFDMUE
(SC-FDMA)
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Page 32
Orthogonal Frequency Division Multiple AccessPower TimeOFDMA Each user allocated a different resource which can vary in time and frequency.
Frequency
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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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Page 36
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
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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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Page 38
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
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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
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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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Page 41
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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Page 42
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
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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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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
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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 (