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WCDMA/HSPA basics for UMTS
Kari Aho
Project and Business Development Manager
Disclaimer
Effort has been put to make material as correct as possible,however, it is still suggested that reader confirms the latestinformation from official sources like 3GPP specs(http://www.3gpp.org/Specification-Numbering)
necessarily the views of their employers or customers
Use/reproduction of this material is forbidden without apermission from the author
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Trainer introduction
Work history
01/2009 Project and business development manager at Magister
01/2008 12/2008 Senior research scientist at Magister
01/2006 12/2007 Researcher / Research trainee at University ofJyvskyl
Education
Ph.D. 2009-2010, L.Sc. 2007-2009, M.Sc. 2003-2006, University ofJyvskyl
International publications
20 conference papers
2 journal articles
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Magister Solutions (1/2)
Strong background in wireless network research 2 Professors, 9 Doctors, 16 Masters of Sciences / Ph.D students, and
2 Masters Degree students
Over 100 academic publications and several patents
Research to support standardization and implementation
Technology road mapping
Technology training
References
R&D co-operation with largest mobile and network manufacturers
Leadership and membership on customers R&D project teams
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Magister Solutions (2/2)
Technology competence Second generation cellular systems
GSM, GPRS, EDGE
Third generation cellular systems WCDMA, TD-(S)CDMA, HSDPA / HSUPA, HSPA+
Next generation cellular systems LTE, LTE-A
WiMAX, Flash-OFDMA
Special areas of interest Voice over IP
Radio resource management development
System level performance analysis
Mobility management
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Course schedule
Introductory
WCDMA technology overview
Standardization
Market and performance situation
Rel99 WCDMA
Codes
Power Control
Mobility
Multimedia Broadcast Multicast Service
HSPA
HSDPA
HSUPA
Continuous Packet Connectivity
Internet HSPA
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Motivation and Goals
Main things to learn
Architecture (elements, data flow)
Power control (fast, slow)
Mobility (soft, softer, hard handover)
What changes in Rel99 WCDMA when HSPA is introduced
All of the issues form a basis for HSPA and HSPA+ systems andthose are still in use
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Readings related to the subject
General readings
WCDMA for UMTS H. Holma, A. Toskala
HSDPA/HSUPA for UMTS H. Holma, A. Toskala
3G Evolution - HSPA and LTE for Mobile Broadband - E. Dahlman, S.Parkvall, J. Skld and P. Beming,
Network planning oriented
Radio Network Planning and Optimisation for UMTS J. Laiho, A.Wacker, T. Novosad
UMTS Radio Network Planning, Optimization and QoS ManagementFor Practical Engineering Tasks J. Lempiinen, M. Manninen
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Why new radio access system for UMTS (1/2)
Need for universal standard
Universal Mobile Technology System (UMTS)
Support for packet data services
IP data in the core network
IP radio access
New services in mobile multimedia need higher data rates andflexible utilization of the spectrum
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Why new radio access system for UMTS (2/2)
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
TDMA
FDMAWastestime
resources
Wastesfrequencyresources
Example Global System for Mobile Communication (GSM)
Code Division Multiple Access (CDMA)
Same frequency and time but users are separated from eachother with codes
Example WCDMA/UMTS
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Code
Frequency
Time
1
2
N
CDMA
Can exploitboth time and
frequency
WCDMA Systems (1/3)
Wideband CDMA (WCDMA) means that
Bandwidth is not dependent of the information signal
Transmission bandwidth is much larger than the informationbandwidth i.e. transmitted signal is spread
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Frequency
Despread narrowband signal, i.e, original data signal
Spread wideband signal which will be sent
Transmitted signalbefore spreading
WCDMA Systems (2/3)
Benefits
More securecommunication
Reduces the impactof interference (and
jamming) owerdensity(Watts/Hz) Received signal
after despreading butbefore filtering
Received despred signal
Interference
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Frequency
Powerdensity(Watts/Hz)
Frequency
Received signalafter despreading andafter filtering
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WCDMA Systems (3/3)
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
an ave separate z requency an s
Users are separated from each other with codes and thus frequencyreuse factor equals to 1
WCDMA is the most common radio interface for UMTS systemsincluding HSPA and HSPA+
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WCDMA Key Features (1/4)
Fast power control (PC)
Reduces the impact of channel fading and minimizes the interference
UE1 UE2
Without PC received
power levels would
be unequal
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UE3
UE1
UE2
UE3
UE1 UE2 UE3
In theory with PC
received power levels
would be equal
WCDMA Key Features (2/4)
Soft handover
Improves coverage, decreases interference
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UE1BS 1
BS 2
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WCDMA Key Features (3/4)
Robust and low complexity RAKE receiver
Utilizes multipath diversity
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WCDMA Key Features (4/4)
Considerably higher bit rates than with 2G systems
With Release 99 theoretically 2 Mbps
The highest implemented is however 384 kbps
Support for flexible bit rates
Mu tipexing o i erent services wit i erent QoS require on asingle physical connection
Real-time, (voice, video telephony)
Streaming (video and audio)
Interactive (web-browsing)
Background (e-mail download)
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Standardization (1/2)
WCDMA was studied in various research programs in themilitary, industry and universities
First publications: late 40s First applications: Military from the 50s
Rake receiver patent 1956
ll l l lll l l l
Investigations for cellular use 80s
IS-95 standard 1993 (2G)
WCDMA was chosen as 3G technology in late 1997/early 1998 bymany forums like
European Telecommunications Standards Institute (ETSI)
Association of Radio Industries and Business (ARIB, Japan)
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Standardization (2/2)
During 1998 parallel work proceeded (mainly) in ETSI and ARIB
Resource consuming for companies with global presence andnot likely to arrive to identical specifications globally
The same discussion e.g. in ETSI and ARIB sometimes endedup to different conclusions
or was a so on-go ng n an orea
At end of 1998 Third Generation Partnership Project (3GPP) wasfounded
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Third Generation Partnership Project (1/2)
Members Founding members
ETSI EU
ARIB Japan
Telecommunications Technology Committee (TTC) Japan
Telecommunications Technology Association Korea i l l i ii l l i i
China Communications Standard Association (CCSA) China later
Different companies, like Nokia, are members through theirrespective standardization organization
Original scope was to produce Technical Specifications (TS) andTechnical Reports (TR) for a 3G Mobile System but later themaintenance and development of GSM including evolved radioaccess technologies (e.g. GPRS and EDGE) was also included
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Third Generation Partnership Project (2/2)
3GPP work is divided into Technical Specification Groups (TSG)
GSM EDGE Radio Access Network (GERAN)
Radio Access Network (RAN)
Service & System aspects (SA)
Core network & terminals (CT)
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3GPP RAN (1/2)
RAN1 covers, for instance,
Physical channel structures and mappings
Physical layer multiplexing, and channel coding and error detection
Spreading, modulation and other physical layer procedures
Measurements and their provision to the upper layers
RAN2 covers, for instance,
Radio interface architecture and protocols between UE and RAN
Services offered by the physical layer to upper layers
Cell selection and re-selection procedures
UE capabilities for UE - RAN interface
Definition of RRM strategies to be supported by RAN
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3GPP RAN (2/2)
RAN3 covers, for instance,
Overall UTRAN and E-UTRAN architecture
Synchronization in UTRAN and E-UTRAN
Interface protols for Radio Network Controller (RNC) RNC (Iur),NodeB RNC (Iub) and RNC Core Network (Iu) communication
RAN4 covers, for instance,
Requirements for radio link, Radio Resource Management (RRM)performance and accuracy of measurements
Radio system scenario analysis and simulation
RAN5 covers, for instance,
Development of UE conformance test specifications
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CommercialHSUPA
networks
CommercialHSDPA
networks
Timeline
1999 2002 2005 2006 2007 2008 2009 2010 2011
R99 Rel-4 Rel-5 Rel-6 Rel-7 Rel-8 Rel-9 Rel-10Standard
First majormilestone by
3GPP
Japan launchedfirst commercial
Rel99 3Gnetwork
Commercialnetworks in
Europe
WCDMA HSDPA HSUPA HSPA Evolutions (HSPA+)
LTE LTE-Advanced 4G3G
3.5G
3.75G
Technique
Naming
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Market and performance situation (1/5)
In Finland alone there are over 8 million GSM and WCDMA-HSPAmobile subscriptions
World wide over 4.7 billion subscriptions
3G (incl. HSPA) Over 650 million 3G subscriptions
Commercially launched by 383 operators in 156 countries
Network peak data rates
247 commercial HSPA networks, i.e 65%, support 7.2 Mbps (peak DL) orhigher
58 HSUPA networks support up to 5.8 Mbps peak UL and another 5networks support 11.5 Mbps peak
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Market and performance situation (2/5)
Device peak data rates (excl. notebooks, e-book readers)
2,221 (out of 2922) devices support 3.6 Mbps peak or higher
1,435 devices support 7.2 Mbps peak or higher
Operating band
27 commercial UMTS900 operators launched in 20 countries (i.e. HSPAlaunched in the 900 MHz band; some have launched HSPA+)
2,183 HSPA devices (90%) operate in 2100 MHz band
817 tri-band HSPA devices 850/1900/2100 MHz
Source: Global mobile Suppliers Association (GSA) surveys
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Market and performance situation (3/5)
One Song
Whole Album
DVD-Movie
HD-Movie
Market and performance situation (4/5)
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Source: Ficora Telecommunication Markets in the Nordic Countries
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Market and performance situation (5/5)
Almost 10- foldwhen compared
Unit Magnitude
Exabyte 1,000,000,000,000,000,000
Petabyte 1,000,000,000,000,000
Terabyte 1,000,000,000,000
o yearGigabyte 1,000,000,000
Megabyte 1,000,000
Kilobyte 1,000
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(WCDMA)
Contents
Codes
UMTS Architecture
Power Control
Handovers
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Codes in WCDMA (1/4)
Channelization Codes (=short codes)
Defines how many chips are used to spread a single information bit
and thus determines the end bit rate Length is referred as spreading factor
Used for:
Downlink: Separation of downlink connections to different users within onecell
Uplink: Separation of data and control channels from same terminal
Same channelization codes in every cell / mobiles
additional scrambling code is needed
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Codes in WCDMA (2/4)
Scrambling codes (=long codes)
Very long (38400 chips), many codes available
Does not spread the signal
Used for
Downlink: to separate different cells/sectors
li i illi i il
The correlation between two codes (two mobiles/NodeBs) is low
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Codes in WCDMA (3/4)
Channelization
codes separate
different
connections
Channelization
codes separate
data/control
channels
Downlink
Scrambling
codes separate
cells/sectors
Uplink
Scrambling codes
separate different
mobiles
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Codes in WCDMA (4/4)
Spreading
Factor (SF)
Channel
symbolrate(kbps)
Channel
bit rate(kbps)
DPDCH
channel bitrate range(kbps)
Maximum user
data rate with -rate coding(approx.)
512 7.5 15 36 13 kbps
256 15 30 1224 612 kb sHalf rate speech
Symbol_rate =Chip_rate/SF
Bit_rate =Symbol_rate*2
Control overhead User_bit_rate =Channel_bit_rate/2
128 30 60 4251 2024 kbps
64 60 120 90 45 kbps
32 120 240 210 105 kbps
16 240 480 432 215 kbps
8 480 960 912 456 kbps
4 960 1920 1872 936 kbps
4, with 3parallel
codes
2880 5760 5616 2.3 Mbps
Full rate speech
144 kbps
384 kbps
2 Mbps
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Questions
To what purpose channelization codes are used in the downlink?
To what purpose scrambling codes are used in the uplink?
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UMTS Terrestrial Radio Access Network (UTRAN)Architecture (1/3)
New Radio Access networkneeded mainly due to newradio access technology
Core Network (CN) is
based on GSM/GPRS
RNC
NodeBUECN
Uu interfaceIub interface
Radio Network Controller(RNC) corresponds roughlyto the Base StationController (BSC) in GSM
Node B correspondsroughly to the Base Stationin GSM
NodeB
NodeBRNC
UE
Iur interface
UTRAN
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UMTS Terrestrial Radio Access Network (UTRAN)Architecture (2/3)
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 controll
Outer loop power control
Admission Control
Initial power and SIR setting
Radio resource reservation
Code allocation
Load Control
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UMTS Terrestrial Radio Access Network (UTRAN)Architecture (3/3)
Node B
Main function to convert the data flow between Uu and Iubinterfaces
Some RRM tasks:
Measurements
Innerloop power control
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Questions
Name three main elements in the UMTS architecture
What would be the responsibility of UEs
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Power Control in WCDMA (1/4)
The purpose of power control (PC) is toensure that each user receives andtransmits just enough energy to prevent:
Blocking of distant users (near-far-effect)
Exceeding reasonable interference levelsUE1 UE2
Without PC received
power levels would
be unequal
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UE3
UE1
UE2
UE3
UE1 UE2 UE3
In theory with PC
received power levelswould be equal
Power Control in WCDMA (2/4)
Power control can be divided into two parts:
Open loop power control (slow power control)
Used to compensate e.g. free-space loss in the beginning of the call
Based on distance attenuation estimation from the downlink pilot signal
Closed loop power control (fast power control)
Used to eliminate the effect of fast fading li i i
Applied 1500 times per second
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Power Control in WCDMA (3/4)
Closed loop power control can also be divided into two parts:
Innerloop power control
Measures the signal levels and compares this to the target value and ifthe value is higher than target then power is lowered otherwise power isincreased
Outerloop power control Adjusts the target value for innerloop power control
Can be used to control e.g. the Quality of Service (QoS)
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Power Control in WCDMA (4/4)
Example of inner looppower control behavior:
With higher velocitieschannel fading is more
control may not besufficient
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WCDMA Handovers (1/7)
WCDMA handovers can be categorized into three different typeswhich support different handover modes
Intra-frequency handover
WCDMA handover within the same frequency and system. So f t , so f t e r
and h ard h an d ov ersupported
Inter-frequency handover
Handover between different frequencies but within the same system.Only h ard h an d ov ersupported
Inter-system handover
Handover to the another system, e.g. from WCDMA to GSM. Only h ardh an d ov ersupported
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WCDMA Handovers (2/7)
Soft handover Handover between different
base stations
Connected simultaneously tomultiple base stations
The transition betweenthem should be seamlessl l
Downlink: Several Node Bstransmit the same signal tothe UE which combines thetransmissions
Uplink: Several Node Bsreceive the UEtransmissions and it isrequired that only one ofthem receives thetransmission correctly
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UE1BS 1
BS 2
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WCDMA Handovers (3/7)
Softer handover
Handover within the
coverage area of one basestation but betweendifferent sectors
Procedure similar to softhandover
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UE1BS 1
BS 2
WCDMA Handovers (4/7)
Hard handover
The source is released first and then new one is added
Short interruption time
Terminology
Active set (AS), represents the number of links that UE is connectedto
Neighbor set (NS), represents the links that UE monitors which arenot already in active set
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WCDMA Handovers (5/7)
Handover parameters
Add window
Represents a value of how much worse a new signal can be compared tothe best one in the current active set in order to be added into the set
Adding link to combining set can be done only if maximum number of
links is not full yet (defined with parameter). Moreover a new link is added to the active set only if the difference
between the best and the new is still at least as good after the add timeris expired. Timer is started when the signal first reaches the desiredlevel.
Drop window
Represents a value of how much poorer the worst signal can be whencompared to the best one in the active set before it is dropped out
Similarly to adding, signal which is to be dropped needs to fulfill the dropcondition after the corresponding drop timer is expired.
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WCDMA Handovers (6/7)
Replace window
Represents a value for how much better a new signal has to be compared
to the poorest one in the current active set in order to replace its place Replace event takes place only if active set is full as otherwise add event
would be applied
Similarly to add and drop events, also with replace event there exist al il i
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WCDMA Handovers (7/7)
Exercises: Replace Threshold_1, Triggering time_1, etc with correct handover
parameter names.
Which event is missing from the example?
BS1Triggering time_1 Triggering time_2
Receivedsignal
strengthBS2
BS3
Threshold_1Threshold_2
BS2 from the NS reachesthe threshold to be added
to the AS
BS1 from the AS reachesthe threshold to be
dropped from the AS
BS1 dropped from the AS
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Questions
To which parts can the fast i.e. closed loop power control bedived into?
To how many base stations UE is connected to when it makes ahard handover?
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Multimedia Broadcast Multicast Service
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Multimedia Broadcast Multicast Service(MBMS) Background
Before MBMS broadcast and multicast transmissions were dealtwith using somewhat inefficient techniques
Cell Broadcast Service (CBS)
Only message-based services with low bit rates
IP Multicast Service (IP-MS)
No ca abilit to use shared radio or core network resourcesili i
Nowadays clear need for efficient group transmission method
Multimedia Broadcast Multicast Service
Digital Video Broadcast - Handheld (DVB-H) / Digital MultimediaBroadcasting (DMB)
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MBMS Introduction (1/3)
Allows different forms of multimedia content to be deliveredefficiently by using either broadcast or multicast mode
Mobile TV, weather reports, local information,
The term broadcast refers to the ability to deliver content to allusers who have enabled a specific broadcast service and find
themselves in a broadcast area
Multicast refers to services that are delivered solely to users whohave joined a particular multicast group. Multicast group can be, forexample, a number of users that are interested in a certain kind ofcontent, such as sports
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MBMS Introduction (2/3)
More efficient use of network resources and capacity fordelivering identical multimedia content to several recipients in
the same radio cell
Built on top of the existing 3G network
All MBMS services can be provided with cellular point-to-point(p-t-p) or with point-to-multipoint (p-t-m) connections
Optimizing the usage of radio resources
Users receives the data with fixed bit rate
e.g. 64, 128 or 256 kbps
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MBMS Introduction (3/3)
MBMS has so called co unting
methods to indicate when the
transition from p -t-p to p-t-m mode is
reasonable
p-t-p p-t-m
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MBMS Quality of Service (1/4)
Lack of uplink traffic with MBMS leads to not having
Feedback information available
Individual retransmissions
In order to improve the reliability of MBMS transmissionsper o c repet t ons o content can e use
Repetitions are not precluded by the lack of uplink traffic becausethe service provider can transmit them without feedback from theUE
Periodical repetitions are done on RLC level with identical RLCsequence numbers and Protocol Data Unit (PDU) content
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MBMS Quality of Service (2/4)
As data loss is required to be minimal also during cell change,there has been made effort to achieve this e.g. by using soft and
selective combining MBMS is most likely to be available through large parts of the
network thus macro diversity combining i.e. combining theinformation coming from different NodeBs could be utilized
Moreover, also antenna diversity techniques can be consideredas an option to improve the reliability
Multiple transmit (Tx) and/or receive (Rx) antennas
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Multimedia Broadcast Multicast Service(MBMS) Quality of Service (3/4)
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Multimedia Broadcast Multicast Service(MBMS) Quality of Service (4/4)
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MBMS performance in WCDMA networks
Cell throughput with 2-
antenna terminal and soft
combining 1500-2500 kbps =
12-20 x 128 kbps TVchannels
-
terminal and soft combining
600-1000 kbps = 5-8 x 128 kbps
TV channels
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Questions
What does multicast mean?
How the lack of uplink transmissions with MBMS can becompensated so that the QoS is improved?
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Conclusion (1/4)
Need for universal standard and improved packet datacapabilities were among the key factors towards a new radio
network interface, Wideband Code Division Access (WCDMA)
3GPP is currently the main standardization body in charge of
Market share for WCDMA is growing rapidly
More than 650 million subscribers (incl. HSPA)
Fueled by various services (facebook, twitter, youtube, etc.)
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Conclusion (2/4)
Codes in WCDMA Channelization Codes
Spreads the information signal
Separates of downlink connections (DL) or data and control channelsfrom same terminal (UL)
Scrambling codes i l i l
Separates different cells/sectors (DL) or different mobiles (UL)
UTRAN Needed mainly due to new radio access technology
Node B responsible of handling connections to and from the UE
RNC responsible of radio resource management
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Conclusion (3/4)
Fast power control (PC)
To ensure that each user receives and transmits with just enoughenergy
Open loop PC for the connection setup and fast closed loop PC forthe actual connection
WCDMA Handovers
Intra-, interfrequency and intersystem handovers
Soft(er) handover for seamless hand-off
Hard handovers with small interruption time when HO is made
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Conclusion (4/4)
MBMS was introduced to more efficient utilization of limited radionetwork resources with multimedia content provision
Improved even further with macro diversity combining and diversitytechniques
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Contents
Introduction
HSDPA
HSUPA
Continuous Packet Connectivity
I-HSPA Conclusion
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High Speed Packet Access (1/3)
There were number of pushing forces to improve the packet datacapabilities of WCDMA even further, e.g.
Growing interest towards rich multimedia content in the wireless domain
Competitive technologies such as WIMAX
High Speed Packet Access (HSPA) evolution introduced first downlinkcounterpart of the evolution called High Speed Downlink Packet Access(HSDPA) in Release 5
Uplink evolution followed later in Release 6 by the name of High SpeedUplink Packet Access (HSUPA)
HSPA was originally designed for non-real time traffic with hightransmission rate requirements
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High Speed Packet Access (2/3)
HSPA features/properties include e.g.
Higher order modulation and coding
Higher throughput and peak data rates
In theory up to 11.4 Mbps in the uplink and 28 Mbps in the downlinkwithout Multiple Inputs and Multiple Outputs (MIMO) in Release 7
system Multiple Inputs and Multiple Outputs (MIMO)
Roughly speaking equals to additional transmitter and receiver antennas
Enables simulaneous spatially separated data streams -> multiplied datarates!
2x2 DL MIMO in Release 7 doubles the theoretical data rate to 56 Mbps
Fast scheduling in the Node B
Possibility to take advantage of channel conditions with lower latency
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High Speed Packet Access (3/3)
Link adaptation in downlink
Possibility to adjust the used modulation and coding scheme in order to beappropriate for current radio channel conditions
Improved retransmission capabilities
Newly introduced layer one retransmissions called as Hybrid Automatic RepeatRequest (HARQ) => reduced delay
Radio Link Control (RLC) level retransmissions still possible
Shorter frame sizes and thus Transmission Time Intervals (TTI)
With HSDPA 2ms and with HSUPA 10ms and 2ms
Multicarrier HSPA (Rel. 8-10)
Two or more 5 Mhz carriers in use simultaneously
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CommercialHSUPA
networks
CommercialHSDPA
networks
Timeline
1999 2002 2005 2006 2007 2008 2009 2010 2011
R99 Rel-4 Rel-5 Rel-6 Rel-7 Rel-8 Rel-9 Rel-10Standard
First majormilestone by
3GPP
Japan launchedfirst commercial
Rel99 3Gnetwork
Commercialnetworks in
Europe
WCDMA HSDPA HSUPA HSPA Evolutions (HSPA+)
LTE LTE-Advanced 4G3G
3.5G
3.75G
Technique
Naming
Questions
Why were the packet data capabilities of WCDMA improved evenfurther?
For what kind of services was HSPA originally designed?
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(HSDPA)
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Contents
Introduction to HSDPA
Link Adaptation
Fast Retransmissions
Downlink Scheduling
HSDPA Mobility
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Introduction to HSDPA
HSDPA Improvements for packet data performance both in termsof capacity and practical bit rates are based on
The use of link adaptation,
Higher order modulation,
Fast scheduling,
ll ,
Physical layer retransmission
HSDPA operates on top of Rel99 and is not a stand alone system
HSDPA does not support Rel99 features like fast power controlor soft handover
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Link Adaptation (1/3)
UE informs the Node B regularly of its channel quality by CQImessages (Channel Quality Indicator)
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Link Adaptation (2/3)
Adaptive modulation and higher order modulation (16/64QAM)with HSDPA
810121416
usEsNo[dB]
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0 20 40 60 80 100 120 140 160-2
0
24
Time[ number of TTIs]
QPSK1/4
QPSK2/4
QPSK3/4
16QAM2/4
16QAM3/4
Instantane
Link
adaptation
adjusts the
mode within
few ms based
on CQI
Link Adaptation (3/3)
Link adaptation is not used in uplink, though
More complex modulation schemes require more energy per bit tobe transmitted than simply going for transmission with multipleparallel code channels, thus HSUPA benefits more from usingmultiple codes as PC keeps the signal levels quite good anyway
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Fast Retransmissions (1/3)
PacketRetransmisson
Packet
Rel 99 HSPA
RNC
Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA
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RLC ACK/NACK
Layer 1
ACK/NACK
Retransmisson
NodeB
UE
Fast Retransmissions (2/3)
RNCNodeBUE
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ser ata
RLC
MAC-d
Layer1
MAC-hs
HARQ (N)ACK
(Re)transmission
RLC (N)ACK
(Re)transmission
Fast Retransmissions (3/3)
Layer 1 signaling indicates the need of retransmission which leads tomuch faster round trip time that with Rel 99
Retransmission procedure with layer 1 retransmissions (HARQ) is doneso that decoder does not get rid of the received symbols if the
transmission fails but combines them with new transmissions
Retransmissions can operate in two ways:
Identical retransmissions (soft/chase combining)
Non-identical retransmissions (incremental redundancy)
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Questions
What is CQI?
What does link adaptation do?
Which entity initiates RLC re-transmissions?
Which entity initiates HARQ re-transmissions?
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Downlink scheduling (1/5)
NodeB has certain amount of users connected to it and it needsto schedule the different users for transmission in differentfractions of time (Transmission Time Intervals)
Certain fairness for scheduling time for each user should bemaintained
Resources should be utilized in optimal mannerl l l
There exists different ways that users can be scheduled indownlink, e.g.
Round Robin
Proportional Fair
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Downlink scheduling (2/5)
Round Robin (RR)
Simplest scheduling algorithms
Assigns users in order i.e. handling all users without priority
Positive sides
Easy to implement
ll ll
Negative sides
No channel conditions are taken into account and thus resources mightbe wasted
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Downlink scheduling (3/5)
Proportional Fair (PF) Compromise-based scheduling algorithm
Based upon maintaining a balance between two competing interests Maximize network throughput i.e. users are served in good channel
conditions
Allowing all users at least a minimal level of service
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Downlink scheduling (4/5)
PF is assigning each user a scheduling priority that is inverselyproportional to its anticipated resource consumption High resource consumption => low priority
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Downlink scheduling (5/5)
In general priority metric for certain user can be defined as follows
,r
dpriority
where instantaneous data rate, d, is obtained by consulting the link adaptation
algorithm and average throughput, r, of the user is defined and/or updated as
,otherwise,*)1(
servedisuserif,**)1(
old
old
ra
darar
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follows
where is so called forgetting factor. Hence, equals the equivalent averaging
period in a number of TTIs for the exponential smoothing filter
a 1a
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Mobility with HSDPA (1/4)
Handovers are roughly tradeoff between two issues
When channel conditions are getting worse, handover to better cell
should be made so that packets wont get lost due to poor channelconditions
However, each time when the (inter-site) handover is made,transmission buffers in the Node B are flushed resulting to additionaldelays from RLC level retransmission or disruption of service
When regarding HSDPA, the user can be connected only to oneserving HSDPA Node B at the time
Leading to hard handover when the handover between HSDPA NodeBs is required in contrary to DCH soft handover
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Mobility with HSDPA (2/4)
Even though there is only one serving HSDPA cell, the associatedRel99 channels can be in soft(er) handover and maintain theactive set as in Rel99
Node B,
Serving HSDPA
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DCH
UE
Node B,
Part of DCH active setHS-SCCH
DCH/HSDPA
DCH
DCH
Mobility with HSDPA (3/4)
HSDPA handover procedure includes following steps
Serving cell change procedure is initiated when a link in (Rel99)active set becomes higher in strength and stays stronger for certainperiod of time, referred as time-to-trigger
If the condition mentioned above is met then the measurement
report is sent from the UE to the Node B, which forwards it to theRNC
If e.g. the admission control requirements are met the RNC can thengive the consent for the UE to make the handover by sending socalled Signaling Radio Bearer (SRB) (re)configuration message
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Mobility with HSDPA (4/4)
In the case of intra Node B handover, the HARQ processes(transmissions) and Node B buffers can be maintained and thus
there is only minimal interruption in data flow However, with inter Node B handover i.e. between Node Bs, the
Node B packet buffers are flushed including all unfinished HARQprocesses which are belonging to the UE that is handed off
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Questions
How does Round Robin allocate resources for the users?
How intra- and inter-Node B handovers differ from each other?
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(HSUPA)
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Contents
Introduction to HSUPA
Multicodes with HSUPA
Uplink Scheduling
HSUPA Mobility
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Introduction to HSUPA (1/2)
Roughly three years later when HSDPA was introduced uplinkcounterpart of the high speed packet access evolution wasintroduced in Release 6
In 3GPP original name was not HSUPA but Enhanced DedicatedChannel (E-DCH)
The obvious choices for uplink evolution was to investi ate thel ltechniques used for HSDPA and, if possible, adopt them for theuplink as well
Improvements in HSUPA when compared to Rel99
Layer 1 Hybrid ARQ (HARQ) i.e. fast retransmissions
Node B based scheduling
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Introduction to HSUPA (2/2)
Easier multicode transmissions
Shorter frame size, 10ms mandatory for all HSUPA capable devicesand 2 ms as optional feature
Higher order modulation (Release 7)
,basic features of the WCDMA Rel99
Cell selection and synchronization,
random access,
basic power control loop functions,
basic mobility procedures (soft handover), etc.
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Multicodes with HSUPA
Even though Rel99 supports in theory multicode transmissionsin practice only HSUPA can support multicode transmissions and
thus higher bitrates In theory Rel99 can use 6xSF4
HSUPA can in practice support 2xSF2 + 2xSF4
The reason why Rel99 does not support multicodes is that thescheduling is controlled by RNC and thus rather slowlycontrollable
Potentially wasted resources due to changing channel conditions andslow adjustment
Also, the lack of HARQ with Rel99 means lower packet error targetfor the system and thus higher resources for UE
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Questions
What new features on top of multicodes and shorter frame sizesdo HSUPA offer?
Is DCH part of the HSUPA?
Why does not DCH support multicodes in practice?
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Uplink scheduling (1/5)
With HSDPA all the cell power can be directed to a single user fora short period of time
Very high peak data rates achievable for certain UE and all theothers can be left with a zero data rate
However, in the next time instant another UE can be served and so
on
With HSUPA HSDPA type of scheduling is not possible
HSUPA is a many-to-one scheduling
The uplink transmission power resources are divided to separatedevices (UEs) which can be used only for their purposes and notshared as with HSDPA
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Uplink scheduling (2/5)
The shared resource of the uplink is the uplink noise rise(*), or thetotal received power seen in the Node B receiver
Typically, one UE is unable to consume that resource alone completelyand it is very beneficial for the scheduler to know at each time instanthow much of that resource each UE will consume and to try to maintainthe interference level experienced close to the maximum
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(*)ratio between the total power received from all of the UEs at the base station and the thermal noise
Uplink scheduling (3/5)
Two different scheduling schemes are defined for HSUPA traffic
Scheduled transmissions controlled by Node B which might notguarantee high enough minimum bit rate. In addition each requestrequires time consuming signaling
Non-scheduled transmissions (NST) controlled by radio networkcontroller (RNC) which defines a minimum data rate at which the UEcan transmit without any previous request. This reduces signalingoverhead and consequently processing delays
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Uplink scheduling (4/5)
Scheduled transmissions
The scheduler measures the noise level and decides whether
Additional traffic can be allocated
Should some users have smaller data rates
The scheduler also monitors the uplink feedback
Transmitted on E-DPCCH in ever TTIi i
Referred to as happy bits
Tells which users could transmit at a higher data rate both from thebuffer status and the transmission power availability point of view
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Uplink scheduling (5/5)
Depending on possible user priorities given from the RNC, thescheduler chooses a particular user or users for data rate
adjustment The respective relative or absolute rate commands are then send on the
E-RGCH or E-AGCH
UE in soft handover receives only relative hold/down commandsrom o er an servn o e
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Questions
What is the shared resource in the uplink if power is in thedownlink?
What kind of scheduling possibilities HSUPA offer?
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Mobility in HSUPA (1/2)
HSUPA supports the soft(er) handover procedure similar toWCDMA Rel99
The HARQ operation in HSUPA soft handover situation is done in
following manner any o e n t e act ve set sen s an , t en t e n ormat ongiven to the Medium Access Control (MAC) layer is that an ACK hasbeen received and the MAC layer will consider the transmissionsuccessful
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Mobility in HSUPA (2/2)
RNC
NodeBCorrectly
received
Packet
reordering
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Data
Layer 1
ACK/NACK
UE
NodeB
Layer 1
ACK/NACKpacket
Questions
Which logical entity handles packet reordering and initiates RLCretransmissions if necessary
If UE is in a two-way soft handover how does the HARQ operate?
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(CPC)
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Contents
Introduction CPC
UL discontinuous transmission
DL discontinuous reception
HS-SCCH less
Performance example
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Introduction to CPC (1/2)
Continuous Packet Connectivity (CPC) was released in Release 7
Designed to improve the performance of delay critical small bitrate services like VoIP
Eliminates the need for continuous transmission and receptionwhen data is not exchanged. Can be categorized into threefeature
UL discontinuous transmission
DL discontinuous reception
HS-SCCH less for HSDPA VoIP
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Introduction to CPC (2/2)
Benefits
Connected inactive HSPA users need less resources and create lessinterference => more users can be connected
UE power savings => increased talk time (VoIP)
UTRAN resources are saved
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UL discontinuous transmission (1/2)
Before 3GPP Rel7, DPCCH was defined to be transmitted continuouslyregardless is actual user data or not
Highly loading the cell Draining the UE battery
An ideal solution would be to keep the UE silent during the periods thatit is not transmitting any data and activate the control channels just forthe transmissions periods
However, that could compromise, e.g., the fast power control which would bethen updated only during the times when the data is exchanged
Thus, in Rel7 more elaborate solution for UL DTX was formalized
Various cycles and timers quarantee non-compromising discontinuoustransmisson
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UL discontinuous transmission (2/2)
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DL discontinuous reception (1/2)
In DL, Discontinuous Reception (DRx) cycles allow an idle UE topower off the radio receiver for a predefined period so that
DL scheduling is still possible
UE is able to shut-off the receiver circuitry over some periods oftime to yield a non 100 % receiver duty cycle
llchanges in UEs active set due to mobility
When UE wakes up from inactivity
It listens predefined time for incoming transmissions
If it successfully decodes a new transmission during that time itstarts timer for staying active certain period of time
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DL discontinuous reception (2/2)
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HS-SCCH less
HS-SCCH-less HSDPA operation in downlink
Initial transmission of small, periodic packets, such as VoIP packets,can be sent without High Speed Secondary Control Channel (HS-SCCH)
Eliminates the control channel overhead from small packets sentover HSDPA
Retransmissions are sent with HS-SCCH pointing to the initialtransmission
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VoIP performance with and without CPC
In general major performance enhancements visible if circuit switched voice overWCDMA and VoIP over HSPA Rel 7 is compared
With Rel 99 CS voice capacity 60-70 users/cell
With Rel 7 VoIP capacity goes beyond 120 users/cell
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H. Holma, M. Kuusela, E. Malkamki, K. Ranta-aho, C. Tao:VoIP over HSPA with 3GPP Release 7 , PIMRC, 2006.
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Questions
Name one benefit for the UE and one benefit for the network thatUL DTX brings along with it
What kind of constraints there are for configuring a DRX cycle?
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(I-HSPA)
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I-HSPA (1/3)
Internet-HSPA (I-HSPA) aims to provide competitive mobileinternet access with much more simpler network architecturethan it is in normal WCDMA/HSPA systems
Deployable with existing WCDMA base stations
Utilizes standard 3GPP terminals
Simplified architecture brings many benefits such as
Cost-efficient broadband wireless access
Improves the delay performance
Transmission savings
Enables flat rating for the end user
Works anywhere (compared to WLAN or WIMAX)
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I-HSPA (2/3)
UE
NodeB /E-NodeB
RNC
SGSN
GGSN
Internet /
Intranet
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I-HSPA
I-HSPA (3/3)
Round trip time of 32-Byte packet
120
140
160
180
200
Release 99~200 ms
HSDPA
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Conclusions (1/2)
High Speed Packet Access evolution for WCDMA was introduced inRelease 5 and 6 for downlink and uplink, respectively
HSPA offers much higher peak data rates, reaching in theory up to 56Mbps in the downlink and 11.4 Mbps in the uplink (Release 7), inaddition to reduced delays
Key technologies with HSPA are
Fast Layer 1 retransmissions i.e. HARQ
Node B scheduling
Shorter frame size (2ms in DL and 2/10ms UL)
Higher order modulation and coding along with link adaptation in downlink
Support for multicodes in the uplink
In later releases MIMO & multi-carrier
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Conclusions (2/2)
HSPA improves also the performance of delay critical low bit rateservices, like VoIP, even though it was not originally designed forthat
Continuous Packet Connectivity (CPC) enhancements introduced
services even more
I-HSPA was introduced to provide competitive internet accesssolution
High data rates with low delay
Reduced costs => flat rate could be possible
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