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Introduction to Third Generation Communications (3G) Technology
Wideband Code Division Multiple Access
www.3gpp.org
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Outline
• Background
• Key concepts
– Code multiplexing
– Spreading
• Introduction to Wideband Code Division Multiple Access (WCDMA)
• WCDMA Performance Enhancements
– High Speed Packet Access (HSDPA/HSUPA)
– Advanced features for HSDPA
Background
• Why new radio access system
• Frequency Allocations
• Standardization
• WCDMA background and evolution
• Evolution of Mobile standards
• Current WCDMA markets
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Why new radio access system
• Need for universal standard (Universal Mobile Telecommunication System)
• Support for packet data services
– IP data in core network
– Wireless IP
• New services in mobile multimedia need faster data transmission and flexible utilization of the spectrum
• FDMA and TDMA are not efficient enough
– TDMA wastes time resources
– FDMA wastes frequency resources
• CDMA can exploit the whole bandwidth constantly
• Wideband CDMA was selected for a radio access system for UMTS (1997)
– (Actually the superiority of OFDM was not fully understood by then)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Frequency allocations for UMTS
• Frequency plans of Europe, Japan and Korea are harmonized
• US plan is incompatible, the spectrum reserved for 3G elsewhere is
currently used for the US 2G standards
• IMT-2000 band in Europe:
– FDD 2x60MHz
Expected air interfaces and spectrums, source: “WCDMA for UMTS”
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Standardization
• WCDMA was studied in various research programs in the industry and
universities
• WCDMA was chosen besides ETSI also in other forums like ARIB
(Japan) as 3G technology in late 1997/early 1998.
• During 1998 parallel work proceeded in ETSI and ARIB (mainly), with
commonalities but also differences
– Work was also on-going in USA and Korea
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Standardization
• At end of 1998 different standardization organizations got together and created 3GPP, 3rd Generation Partnership Project.
– 5 Founding members: ETSI, ARIB+TTC (Japan), TTA (Korea), T1P1 (USA)
– CWTS (China) joined later.
• Different companies are members through their respective standardization organization.
ETSI Members
ETSI
ARIB Members
ARIB
TTA Members
TTA
T1P1 Members
T1P1
TTC Members
TTC
CWTS Members
CWTS
3GPP
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA Background and Evolution
• First major milestone was Release „99, 12/99– Full set of specifications by 3GPP
– Targeted mainly on access part of the network
• Release 4, 03/01 – Core network was extended
– markets jumped over Rel 4
• Release 5, 03/02– High Speed Downlink Packet Access (HSDPA)
• Release 6, end of 04/beginning of 05– High Speed Uplink Packet Access (HSUPA)
• Release 7, 06/07– Continuous Packet connectivity (improvement for e.g. VoIP), advanced features for HSDPA
(MIMO, higher order modulation)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA Background and Evolution
2000 2002 2004 2006 2007200520032001
3GPP Rel -99
12/99
3GPP Rel 4
03/01
3GPP Rel 5
(HSDPA)
03/02
3GPP Rel 6
(HSUPA)
2H/04
3GPP Rel 7
HSPA+
06/07Further Releases
JapanEurope
(pre-commercial)Europe
(commercial)
HSDPA
(commercial)HSUPA
(commercial)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Evolution of Mobile standards
EDGE
GPRSGSM
HSCSD
cdmaOne(IS-95)
WCDMA FDD
HSDPA/HSUPA
cdma2000
TD-SCDMA TDD LCR
cdma20001XEV - DO
cdma20001XEV - DV
TD-CDMATDD HCR
HSDPA/HSUPA
LTE
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA markets• Graph of the technologies adopted by the wireless users worldwide:
• Over 3.5 billion wireless users worldwide
• GSM+WCDMA share currently over 88 % (www.umts-forum.org)
• CDMA share is decreasing every year
GSM (80.9%)
CDMA (12%)
WCDMA (4.6%)
iDEN (0.9%)
PDC (0.8%)
US TDMA (0.8%)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA markets
• Over 200 million WCDMA subscribers globally (04/08) (www.umts-forum.org)
– 10 % HSDPA/HSUPA users
• Number of subscribers is constantly increasing
Millio
n s
ub
scri
bers
Key concepts
• CDMA
• Spread Spectrum
• Direct Sequence spreading
• Spreading and Processing gain
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Multiple Access Schemes
• Frequency Division Multiple Access (FDMA), different frequencies for different users– example Nordic Mobile Terminal (NMT) systems
• Time Division Multiple Access (TDMA), same frequency but different timeslots for different users, – example Global System for Mobile Communication (GSM)
– GSM also uses FDMA
• Code Division Multiple Access (CDMA), same frequency and time but users are separated from each other with orthogonal codes
Code
Frequency
Time
12
N…
TDMAFDMA CDMA
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Spread Spectrum
• Means that the transmission bandwidth is much larger than the information
bandwidth i.e. transmitted signal is spread to a wider bandwidth
– Bandwidth is not dependent on the information signal
• Benefits
– More secure communication
– Reduces the impact of interference (and jamming) due to processing gain
• Classification
– Direct Sequence (spreading with pseudo noise (PN) sequence)
– Frequency hopping (rapidly changing frequency)
– Time Hopping (large frequency, short transmission bursts)
• Direct Sequence is currently commercially most viable
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Spread Spectrum
• Where does spread spectrum come from
– First publications, late 40s
– First applications: Military from the 50s
– Rake receiver patent 1956
– Cellular applications proposed late 70s
– Investigations for cellular use 80s
– IS-95 standard 1993 (2G)
– 1997/1998 3G technology choice
– 2001/2002 Commercial launch of WCDMA technology
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Direct Sequence
• In direct sequence (DS) user bits are coded with unique binary
sequence i.e. with spreading/channelization code
– The bits of the spreading code are called chips
– Chip rate (W) is typically much higher than bit rate (R)
– Codes need to be in some respect orthogonal to each other (cocktail party
effect)
• Length of a spreading code code
– defines how many chips are used to spread a single information bit and thus
determines the end bit rate
– Shorter code equals to higher bit rate but better Signal to Interference and
Noise Ratio (SINR) is required
• Also the shorter the code, the fewer number of codes are available
– Different bit rates have different geographical areas covered based on the
interference levels
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Direct Sequence
• Transmission (Tx) side with DS
– Information signal is multiplied with spreading code => spread signal
• Receiving (Rx) side with DS
– Spread signal is multiplied with spreading code
– Multiplied signal (spread signal x code) is then integrated (i.e. summed
together)
• If the integration results in adequately high (or low) values, the signal is meant for
the receiver
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Direct Sequence
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Direct Sequence
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Spread Spectrum
Frequency
Despread narrowband signal
Spread wideband signal
W
R
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Frequency
Transmitted signalbefore spreading
Received signalbefore despreading
Interference for the part we are interested in
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Spread Spectrum
Frequency
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Po
we
r d
en
sit
y (
Wa
tts
/Hz)
Frequency
Received signalafter despreading butbefore filtering
Received signalafter despreading andafter filtering
Transmitted signal
Interference
Introduction to Wideband Code Division Multiple Access (WCDMA)
• Overview
• Codes in WCDMA
• QoS support
• Network Architecture
• Radio propagation and fading
• RAKE receiver
• Power Control in WCDMA
• Diversity
• Capacity and coverage
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA System
• WCDMA is the most common radio interface for UMTS systems
• Wide bandwidth, 3.84 Mcps (Megachips per second)
– Maps to 5 MHz due to pulse shaping and small guard bands between the
carriers
• Users share the same 5 MHz frequency band and time
– UL and DL have separate 5 MHz frequency bands
• High bit rates
– With Release ‟99 theoretically 2 Mbps both UL and DL
– 384 kbps highest implemented
• Fast power control (PC)
=> Reduces the impact of channel fading and minimizes the interference
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
WCDMA System
• Soft handover
– Improves coverage, decreases interference
• Robust and low complexity RAKE receiver
– Introduces multipath diversity
• Variable spreading factor
– Support for flexible bit rates
• Multiplexing of different services on a single physical connection
– Simultaneous support of services with different QoS requirements:
• real-time
– E.g. voice, video telephony
• streaming
– streaming video and audio
• interactive
– web-browsing
• background
– e-mail download
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Codes in WCDMA
• Channelization Codes (=short code)
– Codes from different branches of the code tree are orthogonal
– Length is dependent on the spreading factor
– Used for
• channel separation from the single source in downlink
• separation of data and control channels from each other in the uplink
– Same channelization codes in every cell / mobiles and therefore the additional
scrambling code is needed
• Scrambling codes (=long code)
– Very long (38400 chips = 10 ms =1 radio frame), many codes available
– Does not spread the signal
– Uplink: to separate different mobiles
– Downlink: to separate different cells
– The correlation between two codes (two mobiles/NodeBs) is low
• Not fully orthogonal
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
• New Radio Access network
needed mainly due to new
radio access technology
• Core Network (CN) is based
on GSM/GPRS
• Radio Network Controller
(RNC) corresponds roughly
to the Base Station
Controller (BSC) in GSM
• Node B corresponds
roughly to the Base Station
in GSM
– Term “Node B” is a relic from
the first 3GPP releases
RNC
NodeB
NodeB
NodeB
UE
CN
RNC
UE
Uu interface Iub interface
Iur interface
UTRAN
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
• Radio network controller (RNC)
– Owns and controls the radio resources in its domain
– Radio resource management (RRM) tasks include e.g. the following
• Mapping of QoS Parameters into the air interface
• Air interface scheduling
• Handover control
• Outer loop power control
• Call Admission Control
• Setting of initial powers and SIR targets
• Radio resource reservation
• Code allocation
• Load Control
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
• Node B
– Main function to convert the data flow between Uu and Iub interfaces
– Some RRM tasks:
• Measurements
• Inner loop power control
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Radio propagation and fading
• A transmitted radio signal goes
through several changes while
traveling via air interface to the
receiver
– reflections, diffractions, phase
shifts and attenuation
• Due to length difference of the
signal paths, multipath
components of the signal arrive
at different times to the receiver
and can be combined either
destructively or constructively
– Depends on the phases of the
multipath components
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Radio propagation and fading
• Example of the fast fading
channel of a function of time
• Opposite phases of two
random multipath components
arriving at the same time
cancel each other out
– Results in a fade
• Coherent phases are
combined constructively
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Diversity
• Transmitting on a single path only can lead to serious performance
degradation due to fading
• As fading is independent between different times and spaces it is reasonable
to use the available diversity of them to decrease the probability of a deep
fade
– The more there are paths to choose from, the less likely it is that all of them have a
poor energy level
• There exists different types of diversity which can be used to improve the
quality, e.g.:
– Multipath
• RAKE receiver exploits taps arriving at different times
– Macro
• Different Node Bs send the same information
– Site Selection Transmit Diversity (SSTD)
• Maintain a list of available base stations and choose the best one, from which the transmission
is received and tell the others not to transmit
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Diversity
– Time
• Same information is transmitted in different times
– Receive antenna
• Transmission is received with multiple antennas
• Power gain and diversity gain
– Transmit antenna
• Transmission is sent with multiple antennas
WCDMA evolution
•High Speed Downlink Packet Access (HSDPA)
•High Speed Uplink Packet Access (HSUPA)
•Advanced receivers with HSDPA
•Advanced HSDPA scheduling
•Femto cells with HSDPA
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
High Speed Downlink Packet Access (HSDPA)
• The High Speed Downlink Packet Access (HSDPA) concept was
added to Release 5 to support higher downlink data rates
• It is mainly intended for non-real time traffic, but can also be used for
traffic with tighter delay requirements.
• Peak data rates up to 10 Mbit/s (theoretical data rate 14.4 Mbit/s)
• Reduced retransmission delays
• Improved QoS control (Node B based packet scheduler)
• Spectrally and code efficient solution
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
HSDPA features
• Agreed features in Release 5– Adaptive Modulation and Coding (AMC)
• QPSK or 16QAM
– Multicode operation
• Support of 1-15 code channels (SF=16)
– Short frame size
– Fast retransmissions using Hybrid Automatic Repeat Request (HARQ)
• Chase Combining
• Incremental Redundancy
– Fast packet scheduling at Node B
• E.g. Round robin, Proportional fair
• Features agreed in Release 7– Higher order modulation (64QAM)
– Multiple Input Multiple Output (MIMO)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
HSDPA - general principle
• Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state.
Channel quality(CQI, Ack/Nack)
Data
Users may be time and/or code multiplexed
New base station functions
• HARQ retransmissions
• Modulation/coding selection
• Packet data scheduling (short TTI)
UE
0 20 40 60 80 100 120 140 160-2
02468
10121416
Time [number of TTIs]
QPSK1/4
QPSK2/4
QPSK3/4
16QAM2/4
16QAM3/4
Inst
anta
neo
us
EsN
o [
dB
]
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
HSDPA functionality• UE informs the Node B regularly of its channel quality by CQI messages
(Channel Quality Indicator)
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
HSDPA functionality
• Node B can use channel state information for several purposes
– In transport format (TFRC) selection
• Modulation and coding scheme
– Scheduling decisions
• Non-blind scheduling algorithms can be utilized
– HS-SCCH power control
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
High Speed Uplink Packet Access (HSUPA)
• Peak data rates increased to significantly higher than 2 Mbps; Theoretically reaching 5.8 Mbps
• Packet data throughput increased, though not as high throughput as with HSDPA
• Reduced delay from retransmissions.
• Solutions
– Layer1 hybrid ARQ
– NodeB based scheduling for uplink
– Frame sizes 2ms & 10 ms
• Schedule in 3GPP
– Part of Release 6
– First specifications version completed 12/04
– In 3GPP specs with the name Enhanced uplink DCH (E-DCH)
Performance of advanced HSDPA features
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Advanced receivers with HSDPA
• UE receiver experiences significant interference from different sources
– In a reflective environment the signal interferes itself
– Neigboring base station signals interfere each other
– One solution to decrease mainly own base station signal interference is to
use an equalizer before despreading
Own cell interference
Other cell interference
Own signal
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Advanced receivers with HSDPA
• In a frequency-selective channel there is a significant amount of
interfering multipaths
• Linear Minimum Mean Squared Error (LMMSE) equalizer can be used
to make an estimate of the original transmitted chip sequence before
despreading
– The interfering multipath components are removed
– The channel becomes flat again
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Advanced receivers with HSDPA
• LMMSE equalizer (Equ in the
figure) offers a very good
performance for the user
especially near the base station
• Using antenna diversity (1x2) the
throughput can be doubled
compared to a single antenna
• Both techniques increase the
cost of a mobile unit
Timo Nihtilä , TLT-5606 Spread Spectrum Techniques www.tut.fi
Femtocells
• More and more consumers want to use their mobile devices at home,
even when there‟s a fixed line available
– Providing full or even adequate mobile residential coverage is a significant
challenge for operators
– Mobile operators need to seize residential minutes from fixed line providers,
and compete with fixed and emerging VoIP and WiFi services
=> There is trend in discussing very small indoor, home and campus NodeB
layouts
• Femtocells are cellular access points (for limited access group) that
connect to a mobile operator‟s network using residential DSL (digital
subscriber line) or cable broadband connections
• Femtocells enable capacity equivalent to a full 3G network sector at
very low transmit powers, dramatically increasing battery life of
existing phones
Zhong Zheng noppa.aalto.fi
Why femtocells?
• Low manufacturing cost, short radio coverage home base station
operates in licensed spectrum
• Radio traffic is backhauled by premises broadband connection (DSL)
to mobile network
Zhong Zheng noppa.aalto.fi
Why femtocells?
• Macrocell base station covers up to a few hundred square meters
area and Signal quality decays along with transmit distance in the form
of
• Under non-line-of-sight condition, signal is blocked by large
shadowing or building wall at 2GHz band
Zhong Zheng noppa.aalto.fi
Why femtocells?
• Technical motivation
• Reduced separation distance between transmitter and
receiver
• Interference is isolated by building structure
• Limited number of users
• Business motivation
• Half of voice calls and a majority of data traffic originate
indoor
• Operators expand network capacity and coverage
without much investments on infrastructure.
• Subscribers get better radio service at low price
Zhong Zheng noppa.aalto.fi
3GPP standardization on femtocells
• New interface Iuh is created between femto base station and HNB-
GW (home node B gateway)
• HNB-GW utilizes standard Iu interface to mobile network
• Iuh traffic is tunneled through public Internet
• In 3GPP Release 8, femtocell access is granted to Close Subscriber
Group (CSG). Handover between femtocells is not allowed.
Zhong Zheng noppa.aalto.fi
More about WCDMA
– WCDMA for UMTS – Harri Holma, Antti Toskala
Zhong Zheng noppa.aalto.fi
END
Thanks for your attention!
arusu[@]comm.pub.ro
An Introduction to
3GPP Long Term Evolution (LTE)
www.3gpp.org
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
Outline
History of 3GPP LTE
Basic Concepts of LTE
Introduction to LTE Protocol
Compare with LTE and LTE-Advanced
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
What is LTE ?
In Nov. 2004, 3GPP began a project to
define the long-term evolution (LTE) of
Universal Mobile Telecommunications
System (UMTS) cellular technology
Higher performance
Backwards compatible
Wide application
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
Evolution of Radio Access
Technologies
LTE (3.9G) :
3GPP release 8~9
LTE-Advanced :
3GPP release 10+
802.16d/e
802.16m
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
LTE Basic Concepts
LTE employs Orthogonal Frequency
Division Multiple Access (OFDMA) for
downlink data transmission and Single
Carrier FDMA (SC-FDMA) with Discrete
Fourier Transform for uplink transmission
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
LTE network architecture: Evolved Packet System
Geert Heijenk http://wwwhome.cs.utwente.nl
Multipath-Induced Time Delays Result
in Inter-Symbol Interference (ISI)
)()()()( tnmtStSty
y(t) : output signal
S(t) : input signal
S(t-m) : delayed m time input signal
n(t) : noise
y(t)
βS(t-m)
S(t)
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
FDM vs. OFDM
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
Frequency Selective Fading
the coherence bandwidth of the channel is
smaller than the bandwidth of the signal
It may be useless to increase the
transmission powerTsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
OFDM transmission scheme
Cyclic Prefix
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
Is a repetition of the last part of the symbol, placed at the beginning of the symbol
LTE-Downlink (OFDM)
Improved spectral
efficiency
Reduce ISI effect
by multipath
Against frequency
selective fading
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
LTE Uplink (SC-FDMA)
SC-FDMA is a new single carrier multiple access technique which has similar structure and performance to OFDMA
An advantage of
SC-FDMA over
OFDM is low to
Peak to Average
Power Ratio
(PAPR) :
Increasing
battery life
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
Multi-antenna techniques
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
LTE Release 8 Key Features (1/2)
High spectral efficiency
OFDM in Downlink
Single‐Carrier FDMA in Uplink
Very low latency
Short setup time & Short transfer delay
Short hand over latency and interruption time
Support of variable bandwidth
1.4, 3, 5, 10, 15 and 20 MHzTsung-Yin Lee
http://ants.iis.sinica.edu.tw/ants_70/
LTE Release 8 Key Features (2/2)
Compatibility and interworking with earlier
3GPP Releases
FDD and TDD within a single radio access
technology
Efficient Multicast/Broadcast
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_
70/
Evolution of LTE-Advanced
Asymmetric transmission bandwidth
Layered OFDMA
Advanced Multi-cell Transmission/Reception Techniques
Enhanced Multi-antenna Transmission Techniques
Support of Larger Bandwidth in LTE-Advanced
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_
70/
Enhanced Multi-antenna
Transmission Techniques
In LTE-A, the MIMO scheme is further improved in the area of spectrum efficiency, average cell throughput and cell edge performances
For LTE-A the antenna configurations of 8x8 in DL and 4x4 in UL are planned
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
LTE vs. LTE-Advanced
Tsung-Yin Lee http://ants.iis.sinica.edu.tw/ants_70/
END
Thanks for your attention!
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