More Related Content Similar to Wcdma systems 003 Similar to Wcdma systems 003 (20) More from Basil John (20) 1. 1
WCDMA, HSPA and advanced receivers
Timo Nihtil , Ph.Lic. (Ph.D. def.)ä
Senior Research Scientist
Magister Solutions Ltd.
2. TLT-5606 Spread
© Timo Nihtilä2
Readings related to the subject
• General readings
– WCDMA for UMTS– HarriHolma, AnttiToskala
– HSDPA/HSUPA for UMTS –Harri Holma, Antti Toskala
• Network planning oriented
– Radio NetworkPlanning and Optimisationfor UMTS– Janna Laiho, Achim Wacker, Tomás Novosad
– UMTS Radio Network Planning, Optimizationand QoS Management For PracticalEngineering Tasks –Jukka Lempiäinen, Matti
Manninen
3. TLT-5606 Spread
© Timo Nihtilä3
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 featuresfor HSDPA
4. 4
Background
•Why new radio access system
•FrequencyAllocations
•Standardization
•WCDMA background and evolution
•Evolution of Mobile standards
•Current WCDMA markets
5. TLT-5606 Spread
© Timo Nihtilä5
Why new radio access system
• Need for universal standard (Universal Mobile Telecommunication System)
• Support for packet data services
– IP data incore 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 wastestime resources
– FDMA wastes frequencyresources
• CDMA can exploit the whole bandwidth constantly
• Wideband CDMA was selected for a radio access system for UMTS (1997)
– (Actuallythe superiorityof OFDMwas not fullyunderstood bythen)
6. TLT-5606 Spread
© Timo Nihtilä6
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”
7. TLT-5606 Spread
© Timo Nihtilä7
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
8. TLT-5606 Spread
© Timo Nihtilä8
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.
E T S I M e m b e r s
E T S I
A R I B M e m b e r s
A R I B
T T A M e m b e r s
T T A
T 1 P 1 M e m b e r s
T 1 P 1
T T C M e m b e r s
T T C
C W T S M e m b e r s
C W T S
3 G P P
9. TLT-5606 Spread
© Timo Nihtilä9
WCDMA Background and Evolution
• First major milestone wasRelease ‘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)
10. TLT-5606 Spread
© Timo Nihtilä10
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+
06/07
Further Releases
Japan
Europe
(pre-commercial)
Europe
(commercial)
HSDPA
(commercial)
HSUPA
(commercial)
11. TLT-5606 Spread
© Timo Nihtilä11
Evolution of Mobile standards
EDGE
GPRS
GSM
HSCSD
cdmaOne
(IS-95)
WCDMA
FDD
HSDPA/
HSUPA
cdma2000
TD-SCDMA
TDD LCR
cdma2000
1XEV - DO
cdma2000
1XEV - DV
TD-CDMA
TDD HCR
HSDPA/
HSUPA
LTE
12. TLT-5606 Spread
© Timo Nihtilä12
Current WCDMA markets
• Graph of the technologiesadopted bythe wireless users worldwide:
• Over 3.5 billionwireless users worldwide
• GSM+WCDMA share currentlyover 88 % (www.umts-forum.org)
• CDMA share isdecreasing every year
GSM (80.9%)
CDMA (12%)
WCDMA (4.6%)
iDEN (0.9%)
PDC(0.8%)
US TDMA (0.8%)
13. TLT-5606 Spread
© Timo Nihtilä13
Current WCDMA markets
• Over 200 millionWCDMA subscribers globally(04/08) (www.umts-forum.org)
– 10 % HSDPA/HSUPA users
• Number of subscribers isconstantlyincreasing
Millionsubscribers
15. TLT-5606 Spread
© Timo Nihtilä15
Multiple Access Schemes
• FrequencyDivision Multiple Access(FDMA), different frequencies for different users
– example Nordic Mobile Terminal (NMT) systems
• Time DivisionMultiple Access (TDMA), same frequencybut different timeslots for different users,
– example Global System for Mobile Communication (GSM)
– GSM also uses FDMA
• Code Division Multiple Access(CDMA), same frequencyand time but users are separated from each other with orthogonalcodes
Code
Frequency
Time
1
2
N
…
TDMAFDMA CDMA
16. TLT-5606 Spread
© Timo Nihtilä16
Spread Spectrum
• Means that the transmission bandwidth is much larger than the information bandwidth i.e. transmitted signal is spread to a wider bandwidth
– Bandwidthis not dependent onthe informationsignal
• Benefits
– More secure communication
– Reducesthe impact of interference (and jamming) due toprocessing 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
17. TLT-5606 Spread
© Timo Nihtilä17
Spread Spectrum
• Where does spread spectrum come from
– First publications, late 40s
– First applications: Militaryfrom the 50s
– Rake receiver patent 1956
– Cellular applicationsproposed late 70s
– Investigations for cellular use 80s
– IS-95 standard 1993 (2G)
– 1997/1998 3G technologychoice
– 2001/2002 Commerciallaunchof WCDMA technology
18. TLT-5606 Spread
© Timo Nihtilä18
Direct Sequence
• In direct sequence (DS) user bits are coded with unique binary sequence i.e. with spreading/channelization code
– The bits of the channelizationcode are called chips
– Chip rate (W) is typicallymuchhigher than bit rate (R)
– Codes need to be insome respect orthogonalto eachother (cocktail partyeffect)
• Length of a channelization code
– defineshow manychips are used tospread a single informationbit 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 areascovered based on the interference levels
19. TLT-5606 Spread
© Timo Nihtilä19
Direct Sequence
• Transmission (Tx) side with DS
– Information signal is multiplied with channelizationcode => spread signal
• Receiving (Rx) side with DS
– Spread signal ismultiplied withchannelizationcode
– Multiplied signal (spread signalx code) isthenintegrated (i.e.summed together)
• If the integration results in adequately high (or low) values, the signal is meant for the receiver
22. TLT-5606 Spread
© Timo Nihtilä22
Processing gain and Spreading
Frequency
Despread narrowband signal
Spread wideband signal
W
R
Powerdensity(Watts/Hz)Powerdensity(Watts/Hz)
Frequency
Transmitted signal
before spreading
Received signal
before despreading
Interference for the part
we are interested in
23. TLT-5606 Spread
© Timo Nihtilä23
Processing gain and Spreading
Frequency
Powerdensity(Watts/Hz)Powerdensity(Watts/Hz)
Frequency
Received signal
after despreading but
before filtering
Received signal
after despreading and
after filtering
Transmitted signal
Interference
24. TLT-5606 Spread
© Timo Nihtilä24
Processing gain and Spreading
• Spread spectrum systems reduce the effect of interference due to processing gain
• Processing gainisgenerallydefined as follows:
– G[dB]=10*log10(W/R), where ’W’ is the chip rate and ’R’ is the user bit rate
• The number of userstakes negative effect onthe processing gain. The lossis defined as:
– Lp = 10*log10k, where ’k’ is the amount of users
• Processing gainwhenthe processing loss is takeninto account is
– Gtot=10*log10(W/kR)
• Highbit rate means lower processing gainand higher power OR smaller coverage
• The processing gainis 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 services depending on the radio network planning issues
25. TLT-5606 Spread
© Timo Nihtilä25
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 speechservice the required SINR istypicallyinthe order of 5.0 dB, sothe required wideband signal-to-interference ratio (alsocalled “carrier-
to-interference ratio, C/I) is therefore “5.0 dB minusthe processing” = -20.0 dB.
– In other words, the signal power can be 20 dB under the interference or thermalnoise power, and the WCDMA receiver canstilldetect the
signal.
– Notice: inGSM, a good qualityspeechconnectionrequires C/I= 9–12 dB.
26. 26
Introduction to Wideband Code Division Multiple Access (WCDMA)
•Overview
•Codes inWCDMA
•QoS support
•NetworkArchitecture
•Radio propagationand fading
•RAKE receiver
•Power Control inWCDMA
•Diversity
•Capacityand coverage
27. TLT-5606 Spread
© Timo Nihtilä27
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 smallguard bandsbetweenthe carriers
• Users share the same 5 MHz frequency band and time
– ULand DL have separate 5 MHz frequencybands
• High bit rates
– WithRelease ’99 theoretically 2 Mbps bothUL and DL
– 384 kbps highest implemented
• Fast power control (PC)
=> Reduces the impact of channel fading and minimizes the interference
28. TLT-5606 Spread
© Timo Nihtilä28
WCDMA System
• Soft handover
– Improves coverage, decreases interference
• Robust and low complexityRAKEreceiver
– Introduces multipath diversity
• Variable spreading factor
– Support for flexible bit rates
• Multiplexing of different services ona single physical connection
– Simultaneous support of services with different QoS requirements:
• real-time
– E.g. voice,video telephony
• streaming
– streaming videoand audio
• interactive
– web-browsing
• background
– e-mail download
29. TLT-5606 Spread
© Timo Nihtilä29
Codes in WCDMA
• ChannelizationCodes (=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 dataandcontrol channelsfrom 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
30. TLT-5606 Spread
© Timo Nihtilä30
Codes in WCDMA
• For instance, the relationbetweendownlinkphysical layer bit rates and codes
Spreading
Factor (SF)
Channel
symbol
rate
(ksps)
Channel
bit rate
(kbps)
DPDCH
channel bit
rate range
(kbps)
Maximum user
data rate with ½-
rate coding
(approx.)
512 7.5 15 3–6 1–3 kbps
256 15 30 12–24 6–12 kbps
128 30 60 42–51 20–24 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 3
parallel
codes
2880 5760 5616 2.3 Mbps
Half rate speech
Full rate speech
144 kbps
384 kbps
2 Mbps
Symbol_rate =
Chip_rate/SF
Bit_rate =
Symbol_rate*2
Control channel
(DPCCH) overhead
User bit rate with coding =
Channel_bit_rate/2
31. TLT-5606 Spread
© Timo Nihtilä31
QoS Support
• Key Factors:
– Simultaneous support of services with different QoS requirements:
• 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 time
vs. non-real time
– Optimized usage of different transport channels for supporting different QoS
32. TLT-5606 Spread
© Timo Nihtilä32
QoS support
Example:
Downlink
Shared
Channel
Downlink
Dedicated
Channels
USER 1
....
10 ms
USER 2 USER 3 USER 1 USER 1
USER 4
Data
Rate
2 Mbps
Code 5
Code 4
Code 3
Code 2
Code 1USER 1
USER 2
USER 3
USER 4
USER 2
Time
33. TLT-5606 Spread
© Timo Nihtilä33
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
34. TLT-5606 Spread
© Timo Nihtilä34
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
• Radio network controller (RNC)
– Ownsand controls the radio resources inits 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
35. TLT-5606 Spread
© Timo Nihtilä35
UMTS Terrestrial Radio Access Network (UTRAN) Architecture
• Node B
– Mainfunctiontoconvert the data flow betweenUu and Iub interfaces
– Some RRM tasks:
• Measurements
• Inner loop power control
36. TLT-5606 Spread
© Timo Nihtilä36
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 onthe phases of the multipathcomponents
37. TLT-5606 Spread
© Timo Nihtilä37
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
– Resultsina fade
• Coherent phases are combined constructively
38. TLT-5606 Spread
© Timo Nihtilä38
• Every multipath component arriving at the receiver more than one chip time (0.26 μs) apart can be distinguished by the RAKE
receiver
– 0.26 μs corresponds to 78 m inpath lengthdifference
• 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 at
each time
slot
Phase
modified using
the channel
estimate
Combined
symbol
39. TLT-5606 Spread
© Timo Nihtilä39
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
UE1
UE2
UE3
UE1
UE2
UE3
UE1 UE2 UE3
Without PC received
power levels would
be unequal
With ideal PC
received power levels
are equal
40. TLT-5606 Spread
© Timo Nihtilä40
Power Control in WCDMA
1. Open loop power control
• Onlyfor the initial power setting of the MS
• Based on distance attenuationestimationfrom the downlinkpilot signal
1. 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 reachSIR target
• BothinULand DL
• Usesqualitytargets in MS /BS
1. Outer loop PC at the rate of 100 Hz
• Sets the qualitytarget used bythe inner loop PC
• Compensates the changes inthe propagationconditions
• Adjusts the qualitytarget
• BothinULand DL
41. TLT-5606 Spread
© Timo Nihtilä41
Power Control in WCDMA
• Inner loop power control in the uplink
– Outer loop PC (running inthe radio network controller, RNC) definesSIR target for the BS.
– If the measured SIR at BS is lower thanthe SIR-target, the MSis commanded to increases its transmit power. Otherwise MS is
commanded todecrease its power
– Power controldynamics at the MS is 70 dB
42. TLT-5606 Spread
© Timo Nihtilä42
Power Control in WCDMA
• Inner loop power control in downlink:
– Outer loop PC (running inthe MS) defines SIR target for the MS
– If the measured SIR at the MS is lower thanthe SIR-target, the BSis commanded to increasesits transmit power for that MS.
Otherwise, BS iscommanded to decrease its power.
– Power controlrate 1500 Hz
– Power controldynamics is dependent onthe service
– There’s no near-far problem inDL due to one-to-manyscenario.However, it is desirable to provide a marginalamount of additional power to mobile
stations at the cell edge, astheysuffer from increased other-cell interference.
43. TLT-5606 Spread
© Timo Nihtilä43
Power Control in WCDMA
• Example of inner loop power control behavior:
• With higher velocities channel fading is more rapid and 1500 Hz
power control may not be sufficient
44. TLT-5606 Spread
© Timo Nihtilä44
Power Control in WCDMA
• Inner loop power controltries to keep the received SIR as close to the target SIR aspossible.
• However, the constant SIR alone does not actually guarantee the required frame error rate (FER) which canbe considered as the qualitycriteria of
the link/service.
– There’s no unique SIR that automatically gives a certain FER
– FER is a function of SIR, but also depends on mobility and propagation environment.
• Therefore, the frame reliabilityinformationhas to be delivered toouter loop control, whichcantune the SIR target if necessary.
45. TLT-5606 Spread
© Timo Nihtilä45
Diversity
• Transmitting ona single pathonlycanlead to seriousperformance degradationdue tofading
• As fading is independent betweendifferent times and spacesit is reasonable to use the available diversityof them todecrease 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 existsdifferenttypes of diversitywhichcan be used to improve the quality, e.g.:
– Multipath
• RAKE receiver exploitstaps arrivingat different times
– Macro
• Different Node Bs sendthe same information
– Site Selection Transmit Diversity (SSTD)
• Maintain alist of available base stationsand choose the best one, from which the transmission isreceivedandtell the others not totransmit
46. TLT-5606 Spread
© Timo Nihtilä46
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
47. TLT-5606 Spread
© Timo Nihtilä47
WCDMA Handovers
• WCDMA handovers can be categorized into three different types
• Intra-frequency handover
– WCDMA handover withinthe same frequencyand system. Soft, softer and hard handover supported
• Inter-frequency handover
– Handover betweendifferent frequencies (carriers) but within the same system
– E.g. from one WCDMA operator to another
– Onlyhard handover supported
• Inter-system handover
– Handover betweenWCDMA and another system, e.g.from WCDMA to GSM
– Onlyhard handover supported
48. TLT-5606 Spread
© Timo Nihtilä48
WCDMA Handovers
• Soft handover
– Handover betweendifferent Node Bs
– Several Node Bstransmit the same signalto the UE whichcombines
the transmissions
• Advantages: lower Tx power needed for each Node B and UE
– lower interference, battery saving for UE
• Disadvantage: resources (code, power) need to be reserved for the UE in each
Node B
– Excess soft handovers limit the capacity
– No interruptionindata transmission
– Needs RNC duplicating frame transmissions to two Node Bs
49. TLT-5606 Spread
© Timo Nihtilä49
WCDMA Handovers
• Softer handover
– Handover betweentwo sectors of the same Node B
• Special case of a soft handover
• No need for duplicate frames
• Hard handover
– The source isreleased first and then new one is added
– Short interruption indata flow
50. TLT-5606 Spread
© Timo Nihtilä50
WCDMA Handovers
• Some terminology
– Active set (AS), represents the Node Bs to whichthe UEis in soft handover
– Neighbor set (NS), representsthe links that UE monitorsbut whichare not already in active set
Received
signal
strength
BS1
BS2
Threshold_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 the
triggering 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
51. TLT-5606 Spread
© Timo Nihtilä51
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 inorder to keep constant quality.
– Due to finite power resources, the more users Node B servesthe less power it has for eachUE coverage willdecrease
• 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 cell breathing.
52. TLT-5606 Spread
© Timo Nihtilä52
Capacity and coverage
• Received power of one user as a function of users per cell
• Due to finite maximum Tx power of the UE coverage is usually
limited by the uplink
• Node B does not have this problem
– There is enough Tx power to transmit veryfar to a single user if
necessary
– However, downlinkTx power isdivided betweenall users and thus
capacityis limited bythe downlink
54. TLT-5606 Spread
© Timo Nihtilä54
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
55. TLT-5606 Spread
© Timo Nihtilä55
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 (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, Proportionalfair
• Features agreed in Release 7
– Higher order modulation (64QAM)
– Multiple Input Multiple Output (MIMO)
56. TLT-5606 Spread
© Timo Nihtilä56
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, TPC)
Data
Users may be time and/or code multiplexed
New base station functions
• HARQ retransmissions
• Modulation/coding selection
• Packet data scheduling (short TTI)
New base station functions
• HARQ retransmissions
• Modulation/coding selection
• Packet data scheduling (short TTI)
UE
0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0
- 2
0
2
4
6
8
1 0
1 2
1 4
1 6
T im e [ n u m b e r o f T T Is ]
Q P S K 1 / 4
Q P S K 2 / 4
Q P S K 3 / 4
1 6 Q A M 2 / 4
1 6 Q A M 3 / 4
InstantaneousEsNo[dB]
57. TLT-5606 Spread
© Timo Nihtilä57
HSDPA functionality
• 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 issent it starts to wait for anacknowledgement from the receiver, during which other packets canbe sent via a parallel SAW
(stop-and-wait) channels
Pkt A
Pkt B
Pkt C
Pkt D
Pkt E
Pkt F
Ack B
58. TLT-5606 Spread
© Timo Nihtilä58
HSDPA functionality
• UE informs the Node B regularly of its channel quality by CQI messages (Channel Quality Indicator)
59. TLT-5606 Spread
© Timo Nihtilä59
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
60. TLT-5606 Spread
© Timo Nihtilä60
HSDPA channels
• 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
61. TLT-5606 Spread
© Timo Nihtilä61
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)
62. TLT-5606 Spread
© Timo Nihtilä62
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
Max
data rate
3.6 Mbps
7.2 Mbps
10.1 Mbps
14.4 Mbps
2 x SF4
2 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
Max
data rate
2.0 Mbps
2.9 Mbps
5.76 Mbps
Downlink HSDPA
• Theoretical up to 14.4 Mbps
• Initial capability1.8 – 3.6 Mbps
Uplink HSUPA
• Theoretical up to 5.76 Mbps
• Initial capability1.46 Mbps
HSPA Peak Data Rates
64. TLT-5606 Spread
© Timo Nihtilä64
Advanced receivers with HSDPA
• UE receiver experiences significant interference from different sources
– In a reflective environment the signalinterferes itself
– Neigboring base stationsignals interfere eachother
– One solutionto decrease mainlyownbase stationsignal interference is touse anequalizer before despreading
Own cell interference
Other cell interference
Own signal
65. TLT-5606 Spread
© Timo Nihtilä65
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 multipathcomponentsare removed
– The channelbecomes flat again
66. TLT-5606 Spread
© Timo Nihtilä66
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
67. TLT-5606 Spread
© Timo Nihtilä67
Advanced HSDPA scheduling
• 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 canbe improved byanadvanced algorithm
68. TLT-5606 Spread
© Timo Nihtilä68
Advanced HSDPA scheduling
• An improved scheduling algorithm (Proportional Fair,
PF) offers significant gain over a conventional algorithm
(Round Robin, RR)
• PF has a very good price-quality ratio
– User equipment needs no changes
– Node B’s need onlyminor changes
69. TLT-5606 Spread
© Timo Nihtilä69
Femtocells
• More and more consumers want to use their mobile devices at home, even when there’s a fixed line available
– Providing full or evenadequate mobile residentialcoverage is a significant challenge for operators
– Mobile operators need to seize residential minutes from fixed line providers, and compete withfixed and emerging VoIPand WiFiservices
=> There is trend indiscussing verysmallindoor, 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 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
70. TLT-5606 Spread
© Timo Nihtilä70
Femtocells
• The study considers the system performance of an HSDPA network consisting of macro cells and very 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%)
71. TLT-5606 Spread
© Timo Nihtilä71
Femtocells
• Femtocells provide maximum of 15-17 % gainto networkthroughput
alreadywithout dedicated indoor users
• The gainis visible with high load inthe networkand comes directlyfrom
the increased number of access points inthe network
• Average load of a cell is decreased and users canbe scheduled more often
Scheme
Offered 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
72. TLT-5606 Spread
© Timo Nihtilä72
Femtocells
• 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
