High-Speed Downlink Packet Access (HSDPA)
u HSDPA Background & Basicsu Principles: Adaptive Modulation, Coding, HARQu Channels/ UTRAN Architectureu Principles: Fast scheduling, Mobilityu Performance Results
UMTS Networks 2Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Motivation (as of 2000)
u As the UMTS networks are rolled out, the demand for highbandwidth services is expected to grow rapidly.
u By 2010, 66% of the revenues will come from data services(source: UMTS forum).
u Release 99/4 systems alone will not be capable to meet thesedemands. (Realistic outdoor data rates will be limited to384kbps).
u A more spectral efficient way of using DL resources is required.u Competition with CDMA 2000 1x EV-DO/DV
GSM/GPRS
UMTS Rel. 99
Voice, low speed packet dataNo Multimedia, Limited QOS
Medium rate Packet data Theoretical 2 Mbps but ~384 kbpssubjected to practical constraints
UMTS Networks 3Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Background
u Initial goalsu Establish a more spectral efficient way of using DL resources providing
data rates beyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4Mbps)
u Optimize interactive & background packet data traffic, support streamingservice
u Design for low mobility environment, but not restrictedu Techniques compatible with advanced multi-antenna and receivers
u Standardization started in June 2000u Broad forum of companiesu Major feature of Release 5
u Enhancements in R7 à HSPA+u Advanced transmission to increase data throughputu Signaling enhancements to save resources
UMTS Networks 4Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Basics
u Evolution from R99/ R4u 5MHz BWu Same spreading by OVSF and scrambling codesu Turbo coding
u New concepts in R5u Adaptive modulation (QPSK vs. 16QAM), coding and multicodes
(fixed SF = 16)u Fast scheduling in NodeB (TTI = 2ms)u Hybrid ARQ
u Enhancements in R7 à HSPA+u Signaling enhancementsu 64QAMu MIMO techniques, increase of the bandwidth
UMTS Networks 5Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Techniques
u Adaptive modulation and coding(AMC)u Modulation can be switched
between QPSK and 16QAMu Adaptation of FEC coding rateu Fast feedback from UE about
channel quality (CQI)u Hybrid ARQ
u Fast retransmission in MAC-layer (S&W protocol)
u Retransmitted packetscombined with original ones
u Adaptive redundancyu Fast scheduling
u Allocate resources to userswith good channel quality® Multi-user diversity gain
UMTS Networks 6Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HS-DSCH Principle I
u Channelization codes at a fixed spreading factor of SF = 16u Up to 15 codes in parallel
u OVSF channelization code tree allocated by CRNCu HSDPA codes autonomously managed by NodeB MAC-hs scheduler
u Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4
u 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 7Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HS-DSCH Principle II
u Resource sharing in code as well as time domain:u Multi-code transmission, UE is assigned to multiple codes in the same TTIu Multiple UEs may be assigned channelization codes in the same TTI
u Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active within oneTTI
Data to UE #1 Data to UE #2 Data to UE #3
Time (per TTI)
Code
not used
UMTS Networks 8Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
UMTS Channels with HSDPA
Cell 1
UE
Cell 2
R99 DCH (in SHO)u UL/DL signalling (DCCH)u UL PS serviceu UL/DL CS voice/ data
Rel-5 HS-DSCH§ DL PS service§ (Rel-6: DL DCCH)
= ServingHS-DSCH cell
UMTS Networks 9Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Channels
u HS-PDSCHu Carries the data trafficu Fixed SF = 16; up to 15 parallel channelsu QPSK: 480 kbps/code, 16QAM: 960 kbps/code
u HS-SCCHu Signals the configuration to be used next: HS-PDSCH codes, modulation
format, TB informationu Fixed SF = 128u Sent two slots (~1.3msec) in advance of HS-PDSCH
u HS-DPCCHu Feedbacks ACK/NACK and channel quality information (CQI)u Fixed SF = 256, code multiplexed to UL DPCCHu Feedback sent ~5msec after received data
UMTS Networks 10Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Timing Relations (DL)
u NodeB Tx viewu Fixed time offset between the HS-SCCH information and the start of the
corresponding HS-DSCH TTI: tHS-DSCH-control (2 ´ Tslot= 1.33msec)u HS-DSCH and associated DL DPCH not time-aligned
TB size & HARQ Info
Downlink DPCH
HS-SCCH
DATAHS-PDSCH
3 ´ Tslot (2 msec)
HS-DSCH TTI = 3 ´ Tslot (2 msec)
tHS-DSCH-control = 2 ´ Tslot
Tslot (2560 chips)
ch. code & mod
UMTS Networks 11Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Timing Relations (UL)
u UE Rx viewu Alignment to m ´ 256 to preserve orthogonality to UL DPCCHu HS-PDSCH and associated UL DPCH not time-aligned
(but “quasi synch”)
DATA
Uplink DPCCH
HS-PDSCH
HS-DPCCH
3 ´ Tslot (2ms)
m ´ 256 chips
tUEP = 7.5 ´ Tslot (5ms)0-255 chips
Tslot (0.67 ms)
CQIA/NCQIA/NCQIA/NCQI A/N
UMTS Networks 12Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
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 isintended for transport ofdedicated logical channels
• Takes into account theimpact on R.99 networks
MAC-hs
HS-DSCH
HSDPA in R5
• Additions in RRC to handleHSDPA
• RLC nearly unchanged(UM & AM)
• Modified MAC-d with link toMAC-hs entity
• New MAC-hs entity locatedin the Node B
w/o
MAC
-c/s
h
UMTS Networks 13Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
MAC-hs in NodeB
MAC-hs
MAC – Control
HS-DSCH
Priority Queuedistribution
MAC-d flows
Scheduling
PriorityQueue
PriorityQueue
PriorityQueue
UE #1UE #2
UE #N
MAC-hs Functionsu Priority handlingu Flow Control
u To RNCu To UE
u Schedulingu Select which user/queue
to transmitu Assign TFRC & Tx
poweru HARQ handling
u Service measurementsu e.g. HSDPA provided
bitrate
TFRC: Transport Format and Resource Combination
UMTS Networks 14Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
MAC-hs in UE
MAC-hs
MAC – Control
Associated Uplink SignallingHS-DPCCH
To MAC-d
Associated Downlink SignallingHS-SCCH
HS-DSCH
HARQ
Reordering Reordering
Re-ordering queue distribution
Disassembly Disassembly
MAC-hs Functions
u HARQ handling
u ACK/ NACK generation
u Reordering buffer handling
u Associated to priorityqueues
u Flow control perreordering buffer
u Memory can be sharedwith AM RLC
u Disassembly unit
UMTS Networks 15Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
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 16Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Hybrid Automatic Repeat Request
u HARQ is a stop-and-wait ARQu Up to 8 HARQ processes per UE
u Retransmissions are done at MAC-hs layer, i.e. in the Node Bu Triggered by NACKs sent on the HS-DPCCH
u The mother code is a R = 1/3 Turbo codeu Code rate adaptation done via rate matching, i.e. by puncturing and
repeating bits of the encoded datau Two types of retransmission
u Incremental Redundancyu Additional parity bits are sent when decoding errors occuredu Gain due to reducing the code rate
u Chase Combiningu The same bits are retransmitted when decoding errors occuredu Gain due to maximum ratio combining
u HSDPA uses a mixture of both types
UMTS Networks 17Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HARQ Processes
u HARQ is a simple stop-and-wait ARQu Example
u RTTmin = 5 TTIu Synchronous retransmissions (MAC-hs decides on transmission)
u UE support up to 8 HARQ processes (configured by NodeB)u Min. number: to support continuous receptionu Max. number: limit of HARQ soft bufferu Number 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 18Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA UE Categories
u The specification allows some freedom to the UE vendors
u 12 different UE categories for HSDPA with different capabilities(Rel.5)
u The UE capabilities differ inu Max. transport block size (data rate)u Max. number of codes per HS-DSCHu Modulation alphabet (QPSK only)u Inter TTI distance (no decoding of HS-DSCH in each TTI)u Soft buffer size
u The MAC-hs scheduler needs to take these restrictions into account
UMTS Networks 19Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA – UE Physical Layer Capabilities
HS-DSCHCategory
Maximumnumber ofHS-DSCH
multi-codes
Minimum inter-TTI interval
MaximumMAC-hs TB size
Total number ofsoft channel
bits
Theoreticalmaximum datarate (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 20Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Channel Quality Information (CQI)
u Signalled to the Node B in UL each 2ms on HS-DPCCH
u Integer number from 0 to 30 corresponds to a Transport Format ResourceCombination (TFRC) given byu Modulationu Number of channelisation codesu Transport block size
u For the given conditions the BLER for this TFRC shall not exceed 10%
u Mapping defined in TS 25.214 for each UE category
UMTS Networks 21Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
CQI – Mapping Table
CQI value TransportBlock Size
Number ofHS-PDSCH Modulation
Reference poweradjustment D
NIR XRV
0 N/A Out of range
1 137 1 QPSK 0
¼
6 461 1 QPSK 0
7 650 2 QPSK 0
¼
15 3319 5 QPSK 0
16 3565 5 16-QAM 0
¼
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
u Tables specified in TS25.214u For each UE categoryu Condition:
BLER £ 10%u Example for
UE category 10
UMTS Networks 22Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
3G (Rel.99)with dedicated channels
C/IC/I
C/I
CQI
CQI
CQI
2 TTI@76k
7 TTI@614k
64k64k
64k
Note: No fast channel quality feedback
3G with high speed feedback/schedulingon shared channels
HSDPA Fast Scheduling
UMTS Networks 23Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Resource Allocation
Scheduler
QoS & Subscriber ProfileQoS: guar. bitrate, max. delay
GoS: gold/ silver/ bronze
Feedback from ULCQI, ACK/NACK
UE capabilitiesmax. TFRC
Radio resourcesPower, OVSF codes
UE service metricsThroughput, Buffer Status
Scheduler Output• Scheduled Users• TFRC: Mod., TB size, # codes, etc.• HS-PDSCH power
• Scheduling targets- Maximize network throughput- Satisfy QoS/ GoS constraints- Maintain fairness across UEs and traffic streams
UMTS Networks 24Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Scheduling Disciplines
u Tasku Select UEs (and associated priority queues) to transmit within next TTIu Usually this is done by means of ranking lists
u Depending on the ranking criterion it can be distinguished between threemajor categoriesu Round Robin: allocate each user equal amount of timeu Proportional Fair: equalise the channel rate / throughput ratiou Max C/I: prefer the users with good channel conditions
u To provide GoS/ QoS additional inputs are to be usedu Additional scheduling weights and rate constraints based on the
requested GoS/ QoSu This can be traded-off with channel conditionsu Special scheduling schemes are needed for providing delay critical
services, e.g. VoIP
UMTS Networks 25Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Comparison of Schedulers
u Simple Round Robin doesn’t care about actual channel rateu Proportional Fair offers higher cell throughputu QoS 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
geof
user
sre
ceiv
ing
thro
ughp
ut
Round Robin
Proportional Fair
QoS aw are
UMTS Networks 26Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Mobility Procedures I
u HS-DSCH for a given UE belongs to only one of the radio links assigned tothe UE (serving HS-DSCH cell)
u The UE uses soft handover for the uplink, the downlink DCCH and anysimultaneous CS voice or datau Using existing triggers and procedures for the active set update
(events 1A, 1B, 1C)u Hard handover for the HS-DSCH, i.e.
Change of Serving HS-DSCH Cell within active setu Using RRC procedures, which are triggered by event 1D
UMTS Networks 27Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Mobility Procedures II
u Inter-Node B serving HS-DSCH cell changeu Note: 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
ServingHS-DSCHradio link
ServingHS-DSCHradio link
s t
CRNC CRNC
UMTS Networks 28Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HS-DSCH Serving Cell Change
u Event 1D: change of best cell within the active setu Hysteresis and time to trigger to avoid ping-pong
(HS-DSCH: 1…2 dB, 0.5 sec)
Reportingevent 1D
Measurementquantity
Time
CPICH 2
CPICH 1
CPICH3
Hysteresis
Time totrigger
UMTS Networks 29Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Handover Procedure
u Example: HS-DSCH hard handover (synchronized serving cell change)
SRNC=
DRNCTarget
HS-DSCH cellUE
RL Reconfiguration Prepare
RL Reconfiguration Ready
Radio Bearer Reconfiguration
Radio Bearer Reconfiguration Complete
SourceHS-DSCH cell
ALCAP Iub HS-DSCH Data Transport Bearer Setup If new NodeB
SynchronousReconfigurationwith TactivationRL Reconfiguration Commit
ALCAP Iub HS-DSCH DataTransport Bearer Release
DATA
Reset MAC-hs entity
Serving HS-DSCHcell change decisioni.e. event 1D
RL Reconfiguration Prepare
RL Reconfiguration Ready
RL Reconfiguration Commit
UMTS Networks 30Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
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
C16,0C16,15
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
u Note: CRNC assigns resources to Node B on a cell basis
UMTS Networks 31Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Cell and User Throughput vs. Load
u 36 cells networku UMTS composite channel modelu FTP traffic model (2 Mbyte
download, 30 sec thinking time)
u The user throughput is decreasedwhen increasing load due to thereduced service time
u The cell throughput increaseswith the load because overallmore bytes are transferred in thesame time
0
500
1000
1500
2000
2500
4 6 8 10 12 14 16 18
Thro
ughp
ut[k
bit/
s]
Number of Users/ Cell
Load Impact
Mean User Throughput
Aggregated Cell Throughput
UMTS Networks 32Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA Performance per Category
u 36 cells networku UMTS composite channel modelu FTP traffic model (2 Mbyte
download, 30 sec thinking time)
u Higher category offers highermax. throughput limitu Cat.6: 3.6 MBit/secu Cat.8: 7.2 MBit/sec
uMax. user perceived performanceincreased at low loading
u Cell 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 33Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Impact from Higher Layers
uMaximum MAC-hs throughput isdetermined by the MAC-d PDUsize and the max. number ofMAC-d PDUs, which fit into themax. MAC-hs PDU
uMaximum RLC throughput isfurther limited byuThe RLC window size, which
is limited to 2047 PDUsuRound-trip time RTT
0
2000
4000
6000
8000
10000
12000
14000
Cat.6 – 336bit Cat.8 – 336bit Cat.8 – 656bit Cat.10 – 336bit Cat.10 – 656bit
Thro
ughp
ut[k
bit/
s]
Higher Layer Impact
Max. RLC Throughput, RTT = 120msec
Max. RLC Throughput, RTT = 80msec
Max. MAC-hs Throughput
UMTS Networks 34Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
Coverage Prediction with HSDPA
uExample Scenariou 15 users/cellu Pedestrian A channel
modelu Plot generated with field
prediction tool
HSDPA Throughputdepends on location
UMTS Networks 35Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
HSDPA References
u Papers:u Arnab Das et al: “Evolution of UMTS Toward High-Speed Downlink Packet
Access,” Bell Labs Technical Journal, vol. 7, no. 3, pp. 47 – 68, June2003
u A. Toskala et al: “High-speed Downlink Packet Access,” Chapter 12 inHolma/ Toskala: WCDMA for UMTS, Wiley 2010
u T. Kolding et al: “High Speed Downlink Packet Access: WCDMAEvolution,” IEEE Veh. Techn. Society News, pp. 4 – 10, February 2003
u H. Holma/ A. Toskala (Ed.): “HSDPA/ HSUPA for UMTS,” Wiley 2006
u Standardsu TS 25.xxx series: RAN Aspectsu TR 25.858 “HSDPA PHY Aspects”u TR 25.308 “HSDPA: UTRAN Overall Description (Stage 2)”u TR 25.877 “Iub/Iur protocol aspects”
UMTS Networks 36Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012
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