LTE System Principle Overview: Architecture and Key Features

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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.
Copyright @ 2010 Huawei Technologies Co.,Ltd. All rights reserved Page 2
 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》
Page 3
References

1. Overview
2. LTE system architecture
3. LTE key features
Contents
Page 4

1. Overview
3. LTE key features
Contents
Page 5

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
Page 7
3GPP Releases
GS
M
9.6kbit/s
Phase 1
GP
R
S
171.2kbit/s
Phase 2+
(Release 97)
E
DGE
473.6kbit/s
Release 99
UMTS
2Mbit/s
Release 99
HS
DP
A
14.4Mbit/s
Release 5
HS
UP
A
5.76Mbit/s
Release 6
HS
P
A+
28.8Mbit/s
42Mbit/s
Release 7/8
LTE
+300Mbit/s
Release 8
Release 9/10
LTE Advanced

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

SDR Facilitating Smooth Evolution
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

 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.
Page 10
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
Page 11
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
Transmission
Bandwidth [RB]
Transmission Bandwidth Configuration [RB]
Channel Bandwidth [MHz]
Resource
block
Channel
edge
Channel
edge
DC carrier (downlink only)
Active Resource Blocks
Page 12
LTE frequency bands

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
Page 13

eNB
UE
Carrier Frequency EARFCN
Calculation
FDL = FDL_low + 0.1(NDL - NOffs-DL)
FUL = FUL_low + 0.1(NUL - NOffs-UL)
Page 14

Example
Frequency
Uplink Downlink
100kHz Raster
2127.4MHz
1937.4MHz
FDL = FDL_low + 0.1(NDL - NOffs-DL)
(FDL - FDL_low)
0.1
+ NOffs-DL
(2127.4 - 2110)
0.1
+ 0
NDL =
NDL = = 174
Page 15

 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 )
Page 16
LTE standardization and specifications

1. Overview
3. LTE key features
Contents
Page 17

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
eNB
S1
S1
S
1
S
1
X2
X
2
X
2
E-UTRAN
UMTS LTE
Page 18

LTE-SAE System architecture
SAE
Control plane
User plane
Operator's
IP 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
Page 20
E-UTRAN functions

1. Overview
2. TE system architecture
3. LTE key features
Contents
Page 21

 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.
Page 22
Basic principles of OFDM
Frequency
Guard Band
Channel
Bandwidth
Subcarrier
Frequency
Channel
Bandwidth

 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.
Page 23
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
Page 24
OFDM implementation by IFFT/FFT
Coded
Bits
IF
F
T
S
erial
to
P
arallel
S
ubcarrier
Modulation
R
F
Inverse F
ast
F
ourier
Transform
Complex
Waveform
C
oded
Bits
P
arallel
to
S
erial
F
F
T
S
ubcarrier
Demodulation
R
eceiver
F
ast F
ourier
Transform

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
Page 25

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
Page 27

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
Page 28

 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
Page 29
Advantage of OFDM

Peak to Average Power Ratio
Amplitude
Time
OFDM
S
ymbol
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.
Page 30

 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.
Page 31
SC-FDMA in uplink
Time Domain
CP
Insertion
S
ubcarrier
Mapping
Frequency Domain
DFT
S
ymbols
Time Domain
IDFT
0
0
0
0
0
0
0

eNB
UE
OFDM used in LTE
OFDM
(OFDMA)
OFDM
(SC-FDMA)
eNB
UE
Radio
Channel
FDD Radio
Channel
UE
TDD
Page 32

Frequency
Power
Time
Orthogonal Frequency Division Multiple
Access
OFDMA
Each user allocated a
different resource
which can vary in
time and frequency.
Page 33

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 34
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
OF
DM S
ymbols (= 7 for Normal CP
)
2
1 3 4 5 6
Nsymb
DL
160 144 144 144 144 144 144
2048 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
Page 35

OFDM Symbol Mapping
Time
Frequency
Amplitude
OFDM
Symbol
Cyclic
Prefix
Modulated
OFDM
Symbol
OFDMA
E
ach user allocated a
different resource
which can vary in
time and frequency.
Page 36

 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
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
Page 38

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
Page 39

 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
Page 40

UL Virtual MIMO
Features
Benefits
 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.
Page 41

2x2 MIMO
eNodeB UE 1
1x2 SIMO
eNode
B
UE 1
Throughput
(Mbps)
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
Throughput
(Mbps)
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
Page 42

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 43

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential 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

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
Page 45

 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 46
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)

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
Page 47
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

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 48

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
Value
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 49

LTE System Principle Overview: Architecture and Key Features

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