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WCDMA, HSPA and advanced
receiversTimo Nihtil, Ph.Lic. (Ph.D. def.)
Senior Research Scientist
Magister Solutions Ltd.
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Readings related to the subject
General readings
WCDMA for UMTSHarri Holma, Antti Toskala HSDPA/HSUPA for UMTSHarri Holma, Antti Toskala
Network planning oriented
Radio Network Planning and Optimisation for UMTSJanna Laiho, Achim
Wacker, Toms Novosad
UMTS Radio Network Planning, Optimization and QoS Management ForPractical Engineering TasksJukka Lempiinen, Matti Manninen
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Outline
Background
Key concepts
Code multiplexing
Spreading
Introduction to WidebandCode Division Multiple Access (WCDMA)
WCDMA Performance Enhancements High Speed Packet Access (HSDPA/HSUPA)
Advanced features for HSDPA
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Background
Why new radio access system
Frequency Allocations
Standardization
WCDMA background and evolution
Evolution of Mobile standards
Current WCDMA markets
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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 andflexible 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)
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Frequency allocations for UMTS
Frequency plans of Europe, Japan and Korea are harmonized
US plan is incompatible, the spectrum reserved for 3G elsewhere iscurrently used for the US 2G standards
IMT-2000 band in Europe:
FDD 2x60MHz
Expected air interfaces and spectrums, source: WCDMA for UMTS
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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
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Standardization
At end of 1998 different standardization organizations got together andcreated 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 respectivestandardization organization.
ETSI Members
ETSI
ARIB Members
ARIB
TTA Members
TTA
T1P1 Members
T1P1
TTC Members
TTC
CWTS Members
CWTS
3GPP
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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)
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WCDMA Background and Evolution
2000 2002 2004 2006 2007200520032001
3GPP Rel -99
12/993GPP Rel 4
03/01
3GPP Rel 5(HSDPA)
03/02
3GPP Rel 6(HSUPA)
2H/04
3GPP Rel 7HSPA+
06/07Further Releases
JapanEurope
(pre-commercial)Europe
(commercial)
HSDPA
(commercial)HSUPA
(commercial)
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Evolution of Mobile standards
EDGE
GPRSGSM
HSCSD
cdmaOne(IS-95)
WCDMAFDD
HSDPA/HSUPA
cdma2000
TD-SCDMATDD LCR
cdma20001XEV - DO
cdma20001XEV - DV
TD-CDMATDD HCR
HSDPA/HSUPA
LTE
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Current 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%)
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Current WCDMA markets
Over 200 million WCDMA subscribers globally (04/08) (www.umts-forum.org)
10 % HSDPA/HSUPA users
Number of subscribers is constantly increasing
Millionsubscribe
rs
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Key concepts
CDMA
Spread Spectrum
Direct Sequence spreading
Spreading and Processing gain
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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 fordifferent 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
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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
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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
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Direct Sequence
In direct sequence (DS) user bits are coded with unique binary
sequence i.e. with spreading/channelization code The bits of the channelization 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 channelization 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 theinterference levels
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Direct Sequence
Transmission (Tx) side with DS
Information signal is multiplied with channelization code => spread signal Receiving (Rx) side with DS
Spread signal is multiplied with channelization 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
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Direct Sequence
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Direct Sequence
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Processing gain and Spreading
Frequency
Despread narrowband signal
Spread wideband signal
W
R
Powerdensity(W
atts/Hz)
Pow
erdensity(Watts/Hz)
Frequency
Transmitted signalbefore spreading
Received signal
before despreading
Interference for the partwe are interested in
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Processing gain and Spreading
Frequency
Powerdensity(W
atts/Hz)
Pow
erdensity(Watts/Hz)
Frequency
Received signalafter despreading b ut
before fi l ter ing
Received signal
after despreading and
after fi l ter ing
Transmitted signal
Interference
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Processing gain and Spreading
Spread spectrum systems reduce the effect of interference due to processinggain
Processing gain is generally defined as follows:
G[dB]=10*log10(W/R), where W is the chip rate and R is the user bit rate
The number of users takes negative effect on the processing gain. The loss isdefined as:
Lp= 10*log10k, where k is the amount of users
Processing gain when the processing loss is taken into account is Gtot=10*log10(W/kR)
High bit rate means lower processing gain and higher power OR smallercoverage
The processing gain is different for different services over 3G mobile network(voice, web browsing, videophone) due to different bit rates
Thus, the coverage area and capacity might be different for different servicesdepending on the radio network planning issues
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Processing gain and Spreading
Processing gain is what gives CDMA systems the robustness against
self-interference that is necessary in order to reuse the available 5
MHz carrier frequency over geographically close distances.
Examples: Speech service with a bit rate of 12.2 kbps
processing gain 10 log10(3.84e6/12.2e3) = 25 dB
For speech service the required SINR is typically in the order of 5.0 dB, so
the required wideband signal-to-interference ratio (also called carrier-to-
interference ratio, C/I ) is therefore 5.0 dB minus the processing = -20.0dB.
In other words, the signal power can be 20 dB underthe interference or
thermal noise power, and the WCDMA receiver can still detect the signal.
Notice: in GSM, a good quality speech connection requires C/I= 912 dB.
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Introduction to Wideband Code Division
Multiple Access (WCDMA)Overview
Codes in WCDMA
QoS support
Network ArchitectureRadio propagation and fading
RAKE receiver
Power Control in WCDMA
Diversity
Capacity and coverage
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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
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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
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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
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Codes in WCDMA
For instance, the relation between downlink physical layer bit rates and codes
SpreadingFactor (SF)
Channelsymbol
rate(ksps)
Channelbit rate(kbps)
DPDCHchannel bitrate range
(kbps)
Maximum userdata rate with -
rate coding(approx.)
512 7.5 15 36 13 kbps256 15 30 1224 612 kbps128 30 60 4251 2024 kbps64 60 120 90 45 kbps32 120 240 210 105 kbps16 240 480 432 215 kbps8 480 960 912 456 kbps
4 960 1920 1872 936 kbps4, with 3parallel
codes
2880 5760 5616 2.3 Mbps
Half rate speec
Full rate speec
144 kbps
384 kbps
2 Mbps
Symbol_rate =
Chip_rate/SFBit_rate =
Symbol_rate*2
Control channel
(DPCCH) overheadUser bit rate with coding =
Channel_bit_rate/2
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QoS Support
Key Factors:
Simultaneous support of services with different QoSrequirements:
up to 210 Transport Format Combinations, selectable individually
for every radio frame (10 ms)
going towards IP core networks greatly increases the usage of
simultaneous applications requiring different quality, e.g. real timevs. non-real time
Optimized usage of different transport channels for
supporting different QoS
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QoS support
Example:
DownlinkSharedChannel
DownlinkDedicatedChannels
USER 1
....
10 ms
USER 2 USER 3 USER 1 USER 1
USER 4
DataRate
2 Mbps
Code 5
Code 4
Code 3
Code 2
Code 1USER 1
USER 2
USER 3
USER 4
USER 2
Time
UMTS Terrestrial Radio Access Network (UTRAN)
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( )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 roughlyto 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
UMTS Terrestrial Radio Access Network (UTRAN)
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( )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
UMTS Terrestrial Radio Access Network (UTRAN)
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( )Architecture
Node B
Main function to convert the data flow between Uu and Iub interfaces
Some RRM tasks:
Measurements
Inner loop power control
f
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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, multipathcomponents 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
R di ti d f di
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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
RAKE i
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Every multipath component arriving at the receiver more than one chip
time (0.26 s) apart can be distinguished by the RAKE receiver
0.26 s corresponds to 78 m in path length difference
RAKE assigns a finger to each received component (tap) and alters
their phases based on a channel estimate so that the components can
be combined constructively
Finger #1
Finger #2
Finger #3
RAKE receiver
Transmitted
symbol
Received
symbol ateach time
slot
Phase
modified usingthe channel
estimate
Combined
symbol
P C t l i WCDMA
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Power Control in WCDMA
The purpose of power control (PC) is to ensure that each user
receives and transmits just enough energy to have service but to
prevent:
Blocking of distant users (near-far-effect)
Exceeding reasonable interference levels
UE1UE2
UE3
UE1
UE2
UE3
UE1 UE2 UE3
Without PC received
power levels would
be unequal
With ideal PC
received power levels
are equal
P C t l i WCDMA
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Power Control in WCDMA
1. Open loop power control
Only for the initial power setting of the MS
Based on distance attenuation estimation from the downlink pilot signal
2. Inner loop transmitter power control (CL TPC) at a rate of 1500 Hz
Mitigates fading processes (fast and slow fading)
Tx power is adjusted up/down to reach SIR target
Both in UL and DL
Uses quality targets in MS / BS
3. Outer loop PC at the rate of 100 Hz
Sets the quality target used by the inner loop PC
Compensates the changes in the propagation conditions
Adjusts the quality target Both in UL and DL
Power Control in WCDMA
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Power Control in WCDMA
Inner loop power control in the uplink
Outer loop PC (running in the radio network controller, RNC) defines SIR
target for the BS.
If the measured SIR at BS is lower than the SIR-target, the MS is
commanded to increases its transmit power. Otherwise MS is commanded
to decrease its power
Power control dynamics at the MS is 70 dB
Power Control in WCDMA
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Power Control in WCDMA
Inner loop power control in downlink:
Outer loop PC (running in the MS) defines SIR target for the MS
If the measured SIR at the MS is lower than the SIR-target, the BS is
commanded to increases its transmit power for that MS. Otherwise, BS is
commanded to decrease its power.
Power control rate 1500 Hz
Power control dynamics is dependent on the service
Theres no near-far problem in DL due to one-to-many scenario. However, itis desirable to provide a marginal amount of additional power to mobile
stations at the cell edge, as they suffer from increased other-cell
interference.
Power Control in WCDMA
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Power Control in WCDMA
Example of inner loop powercontrol behavior:
With higher velocities channel
fading is more rapid and 1500 Hz
power control may not be sufficient
Power Control in WCDMA
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Power Control in WCDMA
Inner loop power control tries to keep the received SIR as close to the target
SIR as possible.
However, the constant SIR alone does not actually guarantee the required
frame error rate (FER) which can be considered as the quality criteria of the
link/service.
Theres no uniqueSIR that automatically gives a certain FER
FER is a function of SIR, but also depends on mobility and propagation environment.
Therefore, the frame reliability information has to be delivered to outer loopcontrol, which can tune the SIR target if necessary.
Diversity
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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
Diversity
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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 Handovers
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WCDMA Handovers
WCDMA handovers can be categorized into three different types
Intra-frequency handover WCDMA handover within the same frequency and system. Soft, softer and
hard handover supported
Inter-frequency handover
Handover between different frequencies (carriers) but within the same
system
E.g. from one WCDMA operator to another
Only hard handover supported
Inter-system handover
Handover between WCDMA and another system, e.g. from WCDMA to
GSM
Only hard handover supported
WCDMA Handovers
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WCDMA Handovers
Soft handover
Handover between different Node Bs
Several Node Bs transmit the samesignal to the UE which combines thetransmissions
Advantages: lower Tx power needed foreach Node B and UE
lower interference, battery saving forUE
Disadvantage: resources (code, power)need to be reserved for the UE in eachNode B
Excess soft handovers limit thecapacity
No interruption in data transmission
Needs RNC duplicating frame
transmissions to two Node Bs
WCDMA Handovers
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WCDMA Handovers
Softer handover
Handover between two sectors of the
same Node B Special case of a soft handover
No need for duplicate frames
Hard handover
The source is released first and then new
one is added
Short interruption in data flow
WCDMA Handovers
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WCDMA Handovers
Some terminology
Active set (AS), represents the Node Bs to which the UE is in soft handover
Neighbor set (NS), represents the links that UE monitors but which are not
already in active set
Received
signalstrength
BS1
BS2Threshold_1
Triggering time_1
Threshold_2
Triggering time_2
BS2 from the NS reaches
the threshold to be added
to the AS BS2 is still after thetriggering time above
threshold and thus added
to the AS
BS1 from the AS reaches
the threshold to be
dropped from the AS
BS1 dropped from the AS
Capacity and coverage
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Capacity and coverage
In WCDMA coverage and capacity are tight together:
When the load increases, the interference levels increases, too, and
therefore also increased transmit powers are needed in order to keepconstant quality.
Due to finite power resources, the more users Node B serves the less
power it has for each UE coverage will decrease
This leads to cell breathing: the coverage area changes as the load of
the cell changes. Therefore, the coverage and
the capacity have to be
planned simultaneously
Radio resource management
(RRM) is needed in WCDMA to
effectively control cellbreathing.
Capacity and coverage
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Capacity and coverage
Received power of one user as afunction of users per cell
Due to finite maximum Tx power ofthe UE coverage is usually limitedby the uplink
Node B does not have this problem
There is enough Tx power totransmit very far to a single user ifnecessary
However, downlink Tx power isdivided between all users and thus
capacity is limited by the downlink
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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
High Speed Downlink Packet Access (HSDPA)
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g p ( )
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
HSDPA features
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Timo Nihtil55 TLT-5606 Spread Spectrum Techniques / 25.4. 2008
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 (TTI = 2 ms)
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)
HSDPA - general principle
16]
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g p p
Fast scheduling is done directly in Node-B based on feedbackinformation from UE and knowledge of current traffic state.
Channel quality
(CQI, Ack/Nack, TPC)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 16
-20
2468
10121416
Time [number of TTIs]
QPSK1/4
QPSK2/4
QPSK3/4
16QAM2/4
16QAM3/4
Inst
antaneousEsNo[dB]
HSDPA functionality
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y
Scheduling responsibility has been moved from RNC to Node B
Due to this and the short TTI length (2 ms) the scheduling is dynamic
and fast
Support for several parallel transmissions
When packet A is sent it starts to wait for an acknowledgement from the
receiver, during which other packets can be sent via a parallel SAW (stop-
and-wait) channels
Pkt A
Pkt B
Pkt C
Pkt D
Pkt EPkt F
Ack B
HSDPA functionality
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UE informs the Node B regularly of its channel quality by CQI messages
(Channel Quality Indicator)
HSDPA functionality
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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
HSDPA channels
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User data is sent on High Speed Downlink Shared Channel (HS-
DSCH)
Control information is sent on High Speed Common Control Channel
(HS-SCCH)
HS-SCCH is sent two slot before HS-DSCH to inform the scheduled
UE of the transport format of the incoming transmission on HS-DSCH
High Speed Uplink Packet Access (HSUPA)
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Peak data rates increased to significantly higher than 2 Mbps;Theoretically reaching 5.8 Mbps
Packet data throughput increased, though not as high throughput aswith 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)
HSPA Peak Data Rates
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5 codes QPSK
# of codes Modulation
5 codes 16-QAM
10 codes 16-QAM
15 codes 16-QAM
15 codes 16-QAM
1.8 Mbps
Maxdata rate
3.6 Mbps
7.2 Mbps
10.1 Mbps
14.4 Mbps
2 x SF42 ms
10 ms
# of codes TTI
2 x SF2 10 ms
2 x SF2 2 ms
2 x SF2 +2 x SF4
2 ms
1.46 Mbps
Maxdata rate
2.0 Mbps
2.9 Mbps
5.76 Mbps
Downlink HSDPA
Theoretical up to 14.4 Mbps
Initial capability 1.83.6 Mbps
Uplink HSUPA
Theoretical up to 5.76 Mbps
Initial capability 1.46 Mbps
f f S f
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Performance of advanced HSDPA features
Advanced receivers with HSDPA
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Timo Nihtil64 TLT-5606 Spread Spectrum Techniques / 25.4. 2008
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
Advanced receivers with HSDPA
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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
Advanced receivers with HSDPA
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LMMSE equalizer (Equ in the
figure) offers a very good
performance for the userespecially 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
Advanced HSDPA scheduling
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Timo Nihtil67 TLT-5606 Spread Spectrum Techniques / 25.4. 2008
Node B has a limited amount of scheduling opportunities
The amount of data transmitted by the network must be maximized
whilst offering the best possible quality of service to all users
The scheduling can be improved by an advanced algorithm
Advanced HSDPA scheduling
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An improved scheduling
algorithm (Proportional Fair,
PF) offers significant gain overa conventional algorithm
(Round Robin, RR)
PF has a very good price-
quality ratio User equipment needs no
changes
Node Bs need only minor
changes
Femtocells
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Timo Nihtil69 TLT-5606 Spread Spectrum Techniques / 25.4. 2008
More and more consumers want to use their mobile devices at home,
even when theres a fixed line available
Providing full or even adequate mobile residential coverage is a significantchallenge 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 operators network using residential DSL 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, without needing to introduce WiFi enabled handsets
Femtocells
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The study considers the system performance of an HSDPA network consisting of macro cells andvery low transmit power (femto) cells
The impact of using 64QAM in addition to QPSK and 16QAM in order to benefit from the high SINR
is studied The network performance is investigated with different portions of users created in the buildings (0-
100%)
Femtocells
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Timo Nihtil71 TLT-5606 Spread Spectrum Techniques / 25.4. 2008
Femtocells provide maximum of 15-
17 % gain to network throughput
already without dedicated indoor
users
The gain is visible with high load in
the network and comes directly from
the increased number of access
points in the network
Average load of a cell is decreased
and users can be scheduled more
often
SchemeOffered load
Medium High Congested
Rake 1x1 3 % 8 % 15 %
Rake 1x2 -1 % 19 % 13 %
Equ 1x1 -2 % 18 % 15 %
Equ 1x2 -1 % 3 % 17 %
Table: Network throughput gain of
femto cells to macro users
Femtocells
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When the amount of dedicated indoor
users increase, the gain of femto cells
explodes
Gain is in the range of hundreds of
percents even with small portion of
indoor users