High-Speed Downlink Packet Access (HSDPA)
HSDPA Background & BasicsPrinciples: Adaptive Modulation, Coding, HARQChannels/ UTRAN ArchitecturePrinciples: Fast scheduling, MobilityPerformance Results
UMTS Networks 2Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Motivation (as of 2000)
As the UMTS networks are rolled out, the demand for high bandwidth services is expected to grow rapidly. By 2010, 66% of the revenues will come from data services (source: UMTS forum).Release 99/4 systems alone will not be capable to meet these demands. (Realistic outdoor data rates will be limited to 384kbps).A more spectral efficient way of using DL resources is required.Competition with CDMA 2000 1x EV-DO/DV
GSM/GPRS
UMTS Rel. 99
Voice, low speed packet data No Multimedia, Limited QOS
Medium rate Packet data Theoretical 2 Mbps but ~384 kbps subjected to practical constraints
UMTS Networks 3Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Background
Initial goalsEstablish a more spectral efficient way of using DL resources providing data rates beyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4 Mbps)Optimize interactive & background packet data traffic, support streaming serviceDesign for low mobility environment, but not restrictedTechniques compatible with advanced multi-antenna and receivers
Standardization started in June 2000Broad forum of companiesMajor feature of Release 5
Enhancements in R7 HSPA+Advanced transmission to increase data throughputSignaling enhancements to save resources
UMTS Networks 4Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Basics
Evolution from R99/ R45MHz BWSame spreading by OVSF and scrambling codesTurbo coding
New concepts in R5Adaptive modulation (QPSK vs. 16QAM), coding and multicodes (fixed SF = 16)Fast scheduling in NodeB (TTI = 2ms)Hybrid ARQ
Enhancements in R7 HSPA+Signaling enhancements64QAMMIMO techniques, increase of the bandwidth
UMTS Networks 5Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Higher Order Modulation
Standard modulation scheme in UMTS networksQPSK 2 bit per symbol
With HSDPA, modulation can be switched between two schemesQPSK 2 bit per symbol16-QAM 4 bit per symbol
Low bitrate robust High bitrate Sensitive to disturbances
UMTS Networks 6Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Key Principles
Adaptive Modulation and Coding(Mother Turbo code rate = 1/3)
For wireless data, link adaptation through Rate Control is more effective then Power Control.Users in favorable channel conditions (based on Channel Quality indication) are assigned higher code rates and higher order modulation (16QAM).This means higher data rates = Reduced latency
But what about when channel is changing at high rate;Can AMC guarantee reliability?
UMTS Networks 7Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Hybrid ARQ
H-ARQ automatically adapts to instantaneous channel conditions by:fast retransmissions at physical layeradding redundancy only when needed
The retransmitted packets are combined with original packet to improve the decoding probability.Simple form of Hybrid ARQ shows significant gains over link adaptation alone. Different schemes can be used for retransmission of original data packet.
Chase combiningIncremental Redundancy
No. In fast fading conditions, AMC alone is not enough.
UMTS Networks 8Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Fast Scheduling
Channels are uncorrelated Multi-user diversityAssign the resources to the best user(s) in time to maximise throughputGains increase with number of users
Max C/IProportional fair Round Robin
10
With HSDPA Scheduling function is moved from RNC to Node-B.
Fading is good in multi-user environment!!
UMTS Networks 9Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HS-DSCH Principle I
Channelization codes at a fixed spreading factor of SF = 16Up to 15 codes in parallel
OVSF channelization code tree allocated by CRNCHSDPA codes autonomously managed by NodeB MAC-hs scheduler
Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4
Additionally, HS-SCCH codes with SF = 128 (number equal to simult. UE)
SF=8
SF=16
SF=4
SF=2
Physical channels (codes) to which HS-DSCH is mapped CPICH, etc.
C16,0C16,15
UMTS Networks 10Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HS-DSCH Principle II
Resource sharing in code as well as time domain:Multi-code transmission, UE is assigned to multiple codes in the same TTIMultiple UEs may be assigned channelization codes in the same TTI
Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active within one TTI
Data to UE #1 Data to UE #2 Data to UE #3
Time (per TTI)
Code
not used
UMTS Networks 11Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
UMTS Channels with HSDPA
Cell 1
UE
Cell 2
R99 DCH (in SHO)UL/DL signalling (DCCH)UL PS serviceUL/DL CS voice/ data
Rel-5 HS-DSCHDL PS service(Rel-6: DL DCCH)
= Serving HS-DSCH cell
UMTS Networks 12Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Channels
HS-PDSCHCarries the data trafficFixed SF = 16; up to 15 parallel channelsQPSK: 480 kbps/code, 16QAM: 960 kbps/code
HS-SCCHSignals the configuration to be used next: HS-PDSCH codes, modulation format, TB informationFixed SF = 128Sent two slots (~1.3msec) in advance of HS-PDSCH
HS-DPCCHFeedbacks ACK/NACK and channel quality information (CQI)Fixed SF = 256, code multiplexed to UL DPCCHFeedback sent ~5msec after received data
UMTS Networks 13Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Timing Relations (DL)
NodeB Tx viewFixed time offset between the HS-SCCH information and the start of the corresponding HS-DSCH TTI: HS-DSCH-control (2 Tslot= 1.33msec)HS-DSCH and associated DL DPCH not time-aligned
TB size & HARQ Info
Downlink DPCH
HS-SCCH
DATA HS-PDSCH
3 Tslot (2 msec)
HS-DSCH TTI = 3 Tslot (2 msec)
HS-DSCH-control = 2 Tslot
Tslot (2560 chips)
ch. code & mod
UMTS Networks 14Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Timing Relations (UL)
UE Rx viewAlignment to m 256 to preserve orthogonality to UL DPCCHHS-PDSCH and associated UL DPCH not time-aligned (but “quasi synch”)
DATA
Uplink DPCCH
HS-PDSCH
HS-DPCCH
3 Tslot (2ms)
m 256 chips
UEP = 7.5 Tslot (5ms) 0-255 chips
Tslot (0.67 ms)
CQI A/NCQI A/NCQI A/NCQI A/N
UMTS Networks 15Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Architecture
MAC-c/sh
MAC-d
RLC
RRC PDCP
Logical Channels
Transport Channels
MAC-b
BCH
BCCHDCCHDTCH
SRNC
CRNC
NodeB
DCH
Upper phy
DSCHFACH
Evolution from R99/R4
• HSDPA functionality is intended for transport of dedicated logical channels
• Takes into account the impact on R.99 networks
MAC-hs
HS-DSCH
HSDPA in R5
• Additions in RRC to handle HSDPA
• RLC nearly unchanged(UM & AM)
• Modified MAC-d with link to MAC-hs entity
• New MAC-hs entity located in the Node B
w/o
MAC
-c/s
h
UMTS Networks 16Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
MAC-hs in NodeB
MAC-hs
MAC – Control
HS-DSCH
Priority Queue distribution
MAC-d flows
Scheduling
Priority Queue
Priority Queue
Priority Queue
UE #1 UE #2
UE #N
MAC-hs FunctionsPriority handlingFlow Control
To RNCTo UE
SchedulingSelect which user/queue to transmitAssign TFRC & Tx powerHARQ handling
Service measurementse.g. HSDPA provided bitrate
TFRC: Transport Format and Resource Combination
UMTS Networks 17Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
MAC-hs in UE
MAC-hs
MAC – Control
Associated Uplink Signalling HS-DPCCH
To MAC-d
Associated Downlink Signalling HS-SCCH
HS-DSCH
HARQ
Reordering Reordering
Re-ordering queue distribution
Disassembly Disassembly
MAC-hs Functions
HARQ handling
ACK/ NACK generation
Reordering buffer handling
Associated to priority queues
Flow control per reordering buffer
Memory can be shared with AM RLC
Disassembly unit
UMTS Networks 18Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Data Flow through Layer 2
Higher Layer
L1
Higher Layer PDU
RLC SDU
MAC-d SDU
MAC-d PDU
…RLCheader
RLCheader…
MAC-d SDU
MAC-d PDU
CRC
……
MAC-dheader
MAC-dheader L2 MAC-d
(non-transparent)
L2 RLC(non-transparent)Segmentation
&Concatenation
Reassembly
Higher Layer PDU
RLC SDU
MAC-hs SDU MAC-hs SDU…MAC-hsheader L2 MAC-hs
(non-transparent)Transport Block (MAC-hs PDU)
…
UMTS Networks 19Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Hybrid Automatic Repeat Request
HARQ is a stop-and-wait ARQUp to 8 HARQ processes per UE
Retransmissions are done at MAC-hs layer, i.e. in the Node BTriggered by NACKs sent on the HS-DPCCH
The mother code is a R = 1/3 Turbo codeCode rate adaptation done via rate matching, i.e. by puncturing and repeating bits of the encoded dataTwo types of retransmission
Incremental RedundancyAdditional parity bits are sent when decoding errors occuredGain due to reducing the code rate
Chase CombiningThe same bits are retransmitted when decoding errors occuredGain due to maximum ratio combining
HSDPA uses a mixture of both types
UMTS Networks 20Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HARQ Processes
HARQ is a simple stop-and-wait ARQ Example
RTTmin = 5 TTISynchronous retransmissions (MAC-hs decides on transmission)
UE support up to 8 HARQ processes (configured by NodeB)Min. number: to support continuous receptionMax. number: limit of HARQ soft bufferNumber of HARQ processes configured specifically for each UE category
1
1
2 2
2
3 4 5 3
3 4 5
1
RTTHARQ
DataHS-PDSCH
ACK/NACKHS-DPCCH
UMTS Networks 21Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA UE Categories
The specification allows some freedom to the UE vendors
12 different UE categories for HSDPA with different capabilities (Rel.5)
The UE capabilities differ inMax. transport block size (data rate)Max. number of codes per HS-DSCHModulation alphabet (QPSK only)Inter TTI distance (no decoding of HS-DSCH in each TTI)Soft buffer size
The MAC-hs scheduler needs to take these restrictions into account
UMTS Networks 22Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA – UE Physical Layer Capabilities
HS-DSCH Category
Maximum number of HS-DSCH
multi-codes
Minimum inter-TTI interval
Maximum MAC-hs TB size
Total number of soft channel
bits
Theoretical maximum data rate (Mbit/s)
Category 1 5 3 7298 19200 1.2
Category 2 5 3 7298 28800 1.2
Category 3 5 2 7298 28800 1.8
Category 4 5 2 7298 38400 1.8
Category 5 5 1 7298 57600 3.6
Category 6 5 1 7298 67200 3.6
Category 7 10 1 14411 115200 7.2
Category 8 10 1 14411 134400 7.2
Category 9 15 1 20251 172800 10.1
Category 10 15 1 27952 172800 14.0
Category 11* 5 2 3630 14400 0.9
Category 12* 5 1 3630 28800 1.8
cf. TS 25.306Note: UEs of Categories 11 and 12 support QPSK only
UMTS Networks 23Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Channel Quality Information (CQI)
Signalled to the Node B in UL each 2ms on HS-DPCCH
Integer number from 0 to 30 corresponds to a Transport Format Resource Combination (TFRC) given by
ModulationNumber of channelisation codesTransport block size
For the given conditions the BLER for this TFRC shall not exceed 10%
Mapping defined in TS 25.214 for each UE category
UMTS Networks 24Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
CQI – Mapping Table
CQI value Transport Block Size
Number of HS-PDSCH Modulation
Reference power adjustment
NIR XRV
0 N/A Out of range
1 137 1 QPSK 0
6 461 1 QPSK 0
7 650 2 QPSK 0
15 3319 5 QPSK 0
16 3565 5 16-QAM 0
23 9719 7 16-QAM 0
24 11418 8 16-QAM 0
25 14411 10 16-QAM 0
26 17237 12 16-QAM 0
27 21754 15 16-QAM 0
28 23370 15 16-QAM 0
29 24222 15 16-QAM 0
30 25558 15 16-QAM 0
28800 0
Tables specified in TS 25.214
For each UE categoryCondition: BLER 10%
Example for UE category 10
UMTS Networks 25Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
3G (Rel.99)with dedicated channels
C/IC/I
C/I
CQI
CQI
CQI
2 TTI @1.2M
2 TTI @76k
7 TTI @614k
1 TTI @1.2M
64k64k
64k
Note: No fast channel quality feedback
3G with high speed feedback/scheduling on shared channels
HSDPA Fast Scheduling
UMTS Networks 26Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Scheduler Inputs
Scheduler
QoS & Subscriber ProfileQoS: guar. bitrate, max. delay
GoS: gold/ silver/ bronce
Feedback from UL (CQI, ACK/NACK)
HistoryHow long hadthe user been
waiting?
Traffic ModelMorning AfternoonEvening Off peak
UE capability
Radio resourcesPower, OVSF codesBuffer Status
Scheduled Users & Packet Formation Strategy
UMTS Networks 27Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Packet Formation Strategy
Scheduler Outputs
Selected UserAdaptive Transport Block size
Adaptive Coding
or redundancy
Adaptive Modulation
(QPSK, 16 QAM)
# of OVSFcodes
So thatQoS/GoS constraints are satisfied andNetwork throughput is maximized, while
Subject to constraints (standards restrictions and service requirements)Maintain fairness across UEs and traffic streams
UMTS Networks 28Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Classical Scheduling Disciplines
Round Robin: allocate the users consecutivelyAdvantage: - Offers fair time allocation
- One of the simplest solutionsDisadvantage: - Low cell and user throughput
Best Effort scheduler: prefer the users with good channel conditionsAdvantage: - Highest system throughput and easy to
implementDisadvantage: - Starvation to users with low C/I
Proportional Fairness: equalise the channel rate / throughput ratio Advantage: - Higher throughput than Round RobinDisadvantage: - Does not use QoS information
HSDPA scheduler runs every TTI (2 msec)
UMTS Networks 29Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Comparison of Schedulers
Simple Round Robin doesn’t care about actual channel rateProportional Fair offers higher cell throughputQoS aware algorithm offers significantly higher user perceived throughput than PF with similar cell throughput
aggregated cell throughput
0
500
1000
1500
2000
2500
Round Robin Proportional Fair QoS aw are
aver
age
thro
ughp
ut [k
bps]
user perceived throughput
0%
20%
40%
60%
80%
100%
0 100 200 300 400 500 600average throughput [kbps]
Perc
enta
ge o
f use
rs
rece
ivin
g th
roug
hput
Round Robin
Proportional Fair
QoS aw are
UMTS Networks 30Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Mobility Procedures I
HS-DSCH for a given UE belongs to only one of the radio links assigned to the UE (serving HS-DSCH cell)The UE uses soft handover for the uplink, the downlink DCCH and any simultaneous CS voice or data
Using existing triggers and procedures for the active set update (events 1A, 1B, 1C)
Hard handover for the HS-DSCH, i.e. Change of Serving HS-DSCH Cell within active set
Using RRC procedures, which are triggered by event 1D
UMTS Networks 31Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Mobility Procedures II
Inter-Node B serving HS-DSCH cell changeNote: MAC-hs needs to be transferred to new NodeB !
NodeB
NodeB
MAC-hs
NodeB
NodeB
MAC-hs
Source HS-DSCH Node B
Target HS-DSCH Node B
Serving HS-DSCH radio link
Serving HS-DSCH radio link
s t
CRNC CRNC
UMTS Networks 32Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HS-DSCH Serving Cell Change
Event 1D: change of best cell within the active setHysteresis and time to trigger to avoid ping-pong(HS-DSCH: 1…2 dB, 0.5 sec)
Reporting event 1D
Measurement quantity
Time
CPICH 2
CPICH 1
CPICH3
Hysteresis
Time to trigger
UMTS Networks 33Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Handover Procedure
Example: HS-DSCH hard handover (synchronized serving cell change)
SRNC =
DRNC Target
HS-DSCH cell UE
RL Reconfiguration Prepare RL Reconfiguration Ready
Radio Bearer Reconfiguration
Radio Bearer Reconfiguration Complete
Source HS-DSCH cell
ALCAP Iub HS-DSCH Data Transport Bearer Setup If new NodeB
Synchronous Reconfiguration with Tactivation RL Reconfiguration Commit
ALCAP Iub HS-DSCH Data Transport Bearer Release
DATA
Reset MAC-hs entity
Serving HS-DSCH cell change decision i.e. event 1D
RL Reconfiguration Prepare RL Reconfiguration Ready
RL Reconfiguration Commit
UMTS Networks 34Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA – Managed Resources
a) OVSF Code Tree
b) Transmit Power
SF=8
SF=16
SF=4
SF=2
Codes reserved for HS-PDSCH/ HS-SCCH
C16,0 C16,15
Codes available for DCH/ common channels
Border adjusted by CRNC
Tx power available for HS-PDSCH/ HS-SCCH Tx power available for DCH/ common channels
Border adjusted by CRNC
Note: CRNC assigns resources to Node B on a cell basis
UMTS Networks 35Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Cell and User Throughput vs. Load
36 cells networkUMTS composite channel modelFTP traffic model (2 Mbyte download, 30 sec thinking time)
The user throughput is decreased when increasing load due to the reduced service time
The cell throughput increases with the load because overall more bytes are transferred in the same time
Load Impact
0
500
1000
1500
2000
2500
4 6 8 10 12 14 16 18
Number of Users/ Cell
Thro
ughp
ut [
kbit
/sec
]
Mean User ThroughputAggregated Cell Throughput
UMTS Networks 36Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Performance per Category
36 cells networkUMTS composite channel modelFTP traffic model (2 Mbyte download, 30 sec thinking time)
Higher category offers higher max. throughput limit
Cat.6: 3.6 MBit/secCat.8: 7.2 MBit/sec
Max. user perceived performance increased at low loadingCell performance slightly better
Cat 6 - Cat 8 Comparison
0
500
1000
1500
2000
2500
Cat 6/ 10 users Cat 8/ 10 users Cat 6/ 20 users Cat 8/ 20 users
thro
ughp
ut (k
bps)
Mean User ThroughputPeak User ThroughputAggregated Cell Throughput
UMTS Networks 37Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Coverage Prediction with HSDPA
Example Scenario15 users/cellPedestrian A channel modelPlot generated with field prediction tool
HSDPA Throughput depends on location
UMTS Networks 38Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA Summary
New downlink transmission conceptOptimised for interactive & background, support of streamingDesign for indoor & urban environment
Improved PHY approachNew DL transport channel: HS-DSCHAdditional signalling channels to support fast adaptation
Advanced architectureMAC-hs entity located in NodeB
Radio Resource Control procedures similar to DCHHSDPA Resource Management
Cell resources managed by Controlling-RNCRe-use of principles for DCH control (handover, state transition)
Significant improved performance
UMTS Networks 39Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
HSDPA References
Papers:Arnab Das et al: “Evolution of UMTS Toward High-Speed Downlink Packet Access,” Bell Labs Technical Journal, vol. 7, no. 3, pp. 47 – 68, June 2003A. Toskala et al: “High-speed Downlink Packet Access,” Chapter 12 in Holma/ Toskala: WCDMA for UMTS, Wiley 2010T. Kolding et al: “High Speed Downlink Packet Access: WCDMA Evolution,” IEEE Veh. Techn. Society News, pp. 4 – 10, February 2003
H. Holma/ A. Toskala (Ed.): “HSDPA/ HSUPA for UMTS,” Wiley 2006
StandardsTS 25.xxx series: RAN AspectsTR 25.858 “HSDPA PHY Aspects” TR 25.308 “HSDPA: UTRAN Overall Description (Stage 2)”TR 25.877 “Iub/Iur protocol aspects”
UMTS Networks 40Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Abbreviations
ACK (positive) AcknowledgementALCAP Access Link Control Application
ProtocolAM Acknowledged (RLC) ModeAMC Adaptive Modulation & CodingCAC Call Admission ControlCDMA Code Division Multiple AccessCQI Channel Quality InformationDBC Dynamic Bearer ControlDCH Dedicated ChannelDPCCH Dedicated Physical Control ChannelFDD Frequency Division DuplexFEC Forward Error CorrectionFIFO First In First OutGoS Grade of ServiceHARQ Hybrid Automatic Repeat RequestH-RNTI HSDPA Radio Network Temporary
IdentifierHSDPA High Speed Downlink Packet AccessHS-DPCCH High Speed Dedicated Physical Control
ChannelHS-DSCH High Speed Downlink Shared ChannelHS-PDSCH High Speed Physical Downlink Shared
ChannelHS-SCCH High Speed Signaling Control Channel
IE Information ElementMAC-d dedicated Medium Access ControlMAC-hs high-speed Medium Access ControlMux MultiplexingNACK Negative AcknowledgementNBAP NodeB Application PartOVSF Orthogonal Variable SF (code)PDU Protocol Data UnitPHY Physical LayerQoS Quality of ServiceQPSK Quadrature Phase Shift KeyingRB Radio BearerRL Radio LinkRLC Radio Link ControlRRC Radio Resource ControlRRM Radio Resource ManagementSDU Service Data UnitSF Spreading FactorTB Transport BlockTFRC Transport Format & Resource
CombinationTFRI TFRC IndicatorTTI Transmission Time IntervalUM Unacknowledged (RLC) Mode16QAM 16 (state) Quadrature Amplitude
Modulation