1. UMTS & HSDPA Fundamentals Version 4.0
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Transcript of 1. UMTS & HSDPA Fundamentals Version 4.0
Proprietary and Confidential
UMTS and HSDPA UMTS and HSDPA FundamentalsFundamentals
Version 4.0
West Region - UMTS RF Engineering
Proprietary and Confidential Slide 2
UMTS FundamentalsUMTS Fundamentals• Module OverviewModule Overview
This module provides training material relating to the key UMTS concepts as This module provides training material relating to the key UMTS concepts as is required for the practical optimization of a UMTS network.is required for the practical optimization of a UMTS network.
– System Overview
– WCDMA Air Interface
– Radio Resource Management
– HSDPA
Proprietary and Confidential
WCDMA System OverviewWCDMA System Overview
Proprietary and Confidential Slide 4
WCDMA Network TopologyWCDMA Network Topology
Iu-CS Sig
Iu-CS Sig
IubIub
PSTN
IP Domain
(Wap, Internet, Streaming)GGSN
3GSGSN
WCDMA Air Interface
Uu
Iu-PSIu-PS
User Equipment (UE)& USIM
Node Bs RNC
2G Net
MSC
MGWIu-CS UserIu-CS User
Proprietary and Confidential
UMTS ServicesUMTS Services
Proprietary and Confidential Slide 6
R99 Services - QoSR99 Services - QoS
• Conversational– Voice– Video
• Streaming– Mobile TV
• Interactive– Web Browsing– Email
• Background– File Transfer
Proprietary and Confidential
WCDMA Air Interface WCDMA Air Interface OverviewOverview
Proprietary and Confidential Slide 8
WCDMA Air InterfaceWCDMA Air Interface
• Multiple Access Technology – CDMA
• Modulation – QPSK / 16QAM
• Carrier Spacing – 5MHz on 200khz raster
• Frame Length – 10ms / 2ms
• Slots per frame – 15
• Multiple Rates – Multi-code / Variable Spreading Factor
• Chip rate – 3.84Mcps
• Max Data Rate – 14.4Mbps
• Synchronous – No
• Handover – Soft
Proprietary and Confidential Slide 9
Spectrum Allocation - AWSSpectrum Allocation - AWS
Proprietary and Confidential Slide 10
CDMA - Code Division Multiple AccessCDMA - Code Division Multiple Access
freq
uen
cy
time
code
Proprietary and Confidential Slide 11
ModulationModulation
QPSK
2 bits / symbol
10 00
0111
Q
I
Q
1011 1001
10001010
0001 0011
00100000
0100 0110
01110101
1110 1100
11011111
I
16QAM
4 bits / symbol
Proprietary and Confidential Slide 12
Spreading and DespreadingSpreading and Despreading
Identical codes
Tx Bit Stream
P
f
Code Chip Stream
Spreading
P
f
Channel
Air Interface Chip Stream
P
f
Code Chip Stream
Despreading
P
f
Rx Bit Stream
P
f
Proprietary and Confidential Slide 13
Spreading and Processing GainSpreading and Processing Gain
Proprietary and Confidential Slide 14
WCDMA Spreading CodesWCDMA Spreading Codes
SF 4
SF 8
SF 16
SF 2
• WCDMA used Orthogonal Variable Spreading Factor (OVSF) Codes to spread user data in both the uplink and the downlink
• The maximum spreading factor used in UMTS is 512
• DL Speech uses SF=128
• DL 384k used SF=8
Proprietary and Confidential Slide 15
WCDMA Scrambling CodesWCDMA Scrambling Codes• After spreading the bit stream is scrambled
• In the uplink – one SC per UE
• In the downlink – (typically) one SC per sector
Spreading Code
Spreading
User Bit Stream
Scrambling
Scrambling Code
TX Bit Stream
Proprietary and Confidential Slide 16
WCDMA Code SummaryWCDMA Code SummarySynchronisation Codes Channelisation Codes Scrambling Codes, UL Scrambling Codes, DL
Type
Gold Codes, Primary Synchronization Codes (PSC)
and Secondary Synchronization Codes (SSC)
Orthogonal Variable Spreading Factor (OVSF) codes,
sometimes called Walsh codes
Complex-Valued Gold Code Segments (long) or Complex-
Valued S(2) Codes (short)
Complex-Valued Gold Code Segments
Length 256 chips 4-512 chips 38400 chips /256 chips 38400 chips
Duration 66.67 µs 1.04 µs - 133.34 µs 10 ms / 66.67 µs 10 ms
Number of codes
1 primary code / 16 secondary codes
= spreading factor, 4 ... 256 UL, 4 ... 512 DL
16,777,216512 primary / 15 secondary for
each primary code
Spreading No, does not change bandwidth Yes, increases bandwidth No, does not change bandwidth No, does not change bandwidth
UsageTo enable terminals to locate and synchronise to the cells'
main control channels
UL: to separate physical data and control data from same
terminal. DL: to separate connection to different terminals
in a same cell
Separation of terminal Separation of sectors
Proprietary and Confidential Slide 17
Rake ReceiverRake Receiver• Rake receiver is able to track and actively combine multipath components
of the same signal, this process is called maximal ratio combining.
• UE uses a rake receiver with 3 – 6 fingers
• Node B uses rake receiver with 6 – 8 fingers
Proprietary and Confidential Slide 18
Downlink Channel MappingDownlink Channel Mapping
BCCHBroadcast Control Ch.
PCCHPaging Control Ch.
CCCHCommon Control Ch.
DCCHDedicated Control Ch.
DTCHDedicated Traffic Ch. N
BCHBroadcast Ch.
PCHPaging Ch.
FACHForward Access Ch.
DCHDedicated Ch.
P-CCPCH(*)Primary Common Control Physical Ch.
S-CCPCHSecondary Common Control
Physical Ch.
DPDCH (one or more per UE) Dedicated Physical Data Ch.
DPCCH (one per UE)Dedicated Physical Control Ch.
Pilot, TPC, TFCI bits
SSCi
Logical Channels(Layers 2+)
Transport Channels(Layer 2)
Physical Channels(Layer 1)
DownlinkRF Out
DPCH (Dedicated Physical Channel)One per UE
HS-DSCHHigh Speed DL Shared Ch.
CPICHCommon Pilot Channel
Null Data
Data Encoding
Data Encoding
Data Encoding
Data Encoding
Data Encoding
HS- PDSCH (one or more per UE) High Speed Physical Downlink shared Channel
S/P
S/P
S/P
I+jQI/Q
Modulator
Q
I
Cch
Cch 256,1
Cch 256,0
GS
PSC
GP
Sync Codes(*)
* Note regarding P-CCPCH and SCH
Sync Codes are transmitted only in bits 0-255 of each timeslot;P-CCPCH transmits only during the remaining bits of each timeslot
Filter
Filter
Gain
Gain
Gain
SCH (Sync Channel)
DTCHDedicated Traffic Ch. 1
DCHDedicated Ch.
Data Encoding M
UX
MUX
CCTrCH
DCHDedicated Ch.
Data Encoding
Sdl,n
Sdl,n
Sdl,n
S/P
Cch GainSdl,n
S/P
C16 GainSdl,n
AICH (Acquisition Indicator Channel)
PICH (Paging Indicator Channel )
Access Indication data
Paging Indication bits S/P
S/P
Cch
CchGain
Gain
Sdl,n
Sdl,n
HS-SCCH (<=4 per UE)High Speed Shared Control Channel .
S/P
C128 GainSdl,n
TFRI, UE Identity, HARQ
SS
SS
E-AGCH (<=4 per UE, serving cell)E-DCH Absolute Grant Channel
S/P
C256 GainSdl,n
C128 GainSdl,n
E-HICH (E-DCH Hybrid ARQ Indication Channel)
E-RGCH (non-serving cell)(E-DCH Relative Grant Channel)
ACK/NACK
Relative grant
Activation flagPower ratio
Data Encoding
Data Encoding
EUL
HSDPA
Proprietary and Confidential Slide 19
Uplink Channel MappingUplink Channel MappingLogical Channels(Layers 2+)
Transport Channels(Layer 2)
Physical Channels(Layer 1)
UplinkRF Out
UEScrambling
Code
I+jQI/Q
Mod.
Q
IFilter
Filter
IDPDCH #1Dedicated Physical Data Ch.
Q
DPCCHDedicated Physical Control Ch.
Pilot, TPC, TFCI bits
Ch256,0 Gd
j
DCCHDedicated Control Ch.
DTCHDedicated Traffic Ch. N
DCHDedicated Ch.
Data Encoding
DTCHDedicated Traffic Ch. 1
DCHDedicated Ch.
Data Encoding M
UX
CCTrCH
DCHDedicated Ch.
Data Encoding
HS-DPCCHHigh Speed Dedicated Physical Control Ch.
Chd,1 Gd
CCCHCommon Control Ch.
RACHRandom Access Ch.
PRACHPhysical Random Access Ch.
Data Coding
j
RACH Control Part
Chd Gd
Chc Gc
Ch256 Gd
QE-DPDCH #2
Ch 4,1
GdE-DCH
E-DPCCH
I
Ch 256,1Gd
E-DPDCH #1
Ch 4,1 Gd
j
RSNE-TFCI
Happy bit
Data Encoding
MAC-esMAC-e
Data Encoding
ACK, CQI
HSDPA
EUL
Proprietary and Confidential
WCDMA WCDMA Air Interface Key Air Interface Key ConceptsConcepts
Proprietary and Confidential Slide 21
CPICH – Pilot / BeaconCPICH – Pilot / Beacon
• The Common Pilot Indication Channel (CPICH) is broadcast from every cell
• It carries no information and can be thought of as a “beacon” constantly transmitting the Scrambling Code of the cell
• It is this “beacon” that is used by the phone for its cell measurements for network acquisition and handover purposes (Ec, Ec/Io).
CPICH
Proprietary and Confidential Slide 22
3G Coverage Measurements3G Coverage Measurements• The majority of 3G coverage measurements are based upon measurements
of the CPICH
• In 3G, coverage is defined by Ec and EcIo
• Golden Rule: If the UE can’t see the CPICH the UE can’t see the cell.
• Three key related measurements for 3G optimisation are– RSCP - The Received Signal Level of a particular CPICH (dBm)– Io - The Total Received Power (dBm)– Ec/Io - The CPICH Quality (The ratio of the above two values)
Proprietary and Confidential Slide 23
CPICH MeasurementsCPICH Measurements
• Io is the total received power (also referred to as RSSI), this includes all wanted and unwanted signals as well as noise in dBm.
• RSCP is the received power of a single scrambling code (also referred to as Ec) in dBm
• EcIo is the ratio of RSCP to Io in dB
Io
RSCP
EcIodB
m
Ec1Ec2EcIo1EcIo2
Proprietary and Confidential Slide 24
CPICH Measurements - CPICH Measurements - ExampleExample
• Ec2 = -85 dBm
• EcIo1 = -10dB
• Io = -70dBm
• What is the RSCP for SC1?
• What is the EcIo for SC2?
Io
RSCP
EcIodB
m
SC1SC2
Proprietary and Confidential Slide 25
Radio Resource ManagementRadio Resource Management
Proprietary and Confidential Slide 26
Radio Resource ManagementRadio Resource Management• Overview of Radio Resource Management (RRM)Overview of Radio Resource Management (RRM)
– Aim of RRM is to efficiently manage the Radio Resources of the WCDMA air interface
– Different vendors have implemented different RRM strategies and algorithms– Generally RRM functions can be group as follows
• Admission Control• Load Control• Packet Scheduler• Resource Management
• Power Control• Handover Control
Cell Based
Connection Based
Proprietary and Confidential Slide 27
Power ControlPower Control
Proprietary and Confidential Slide 28
Power ControlPower Control• Power is a limited resourcePower is a limited resource
– In any CDMA network, the power of the BTS and UE must be tightly controlled to avoid interference to other BTSs/UEs
Proprietary and Confidential Slide 29
Power ControlPower Control• Types of Power ControlTypes of Power Control
– Open Loop Power Control• Used to set the initial transmit power of the BTS/UE
– Closed Loop Power Control• Used to control power of uplink/downlink DCHs• Inner Loop (Or Fast Power Control) used to control TX Power (UL/DL)• Outer Loop (Or Slow Power Control) used to control SIR Targets (UL/DL)
Proprietary and Confidential Slide 30
Open Loop Power ControlOpen Loop Power Control• Open Loop Power Control Open Loop Power Control
– Open Loop Power Control – Used to set the initial transmit power of the UE– UPLINK: Uses a measure of DL path loss to provide estimate uplink path loss– UPLINK: CPICH measurement by the UE along with the reported BTS Noise
Floor are used to determine the initial TX power of the UE
Preamble_Initial_power = CPICH_Tx_power – CPICH_RSCP + UL_interference + UL_required_CI
CPICH_Tx_powerUL_Interference
UL_required_CI
CPICH_RSCP
Proprietary and Confidential Slide 31
Closed Loop Power ControlClosed Loop Power Control• Closed Loop Power ControlClosed Loop Power Control
– Enables the BTS/UE to rapidly adjust their DCH TX powers to track the changing channel conditions (path loss & interference) in order to maintain the required SIR at the receiving UE/BTS
– Uses feedback (power control commands) in the opposite link to adjust Tx power accordingly
Example of Real Fast Fading - Dense UrbanManchester
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Time (secs)
Proprietary and Confidential Slide 32
Closed Loop Power ControlClosed Loop Power Control• Inner Loop Power Control (Fast Power Control)Inner Loop Power Control (Fast Power Control)
– Transmit Power Control (TPC) commands (up/down) issued to UE (Uplink) and BTS (Downlink) to maintain Target SIR every time slot (1500 Hz)
– Power control step size typically 1dB (Algorithm 1)– Below 30km/h 1.5KHz and 1dB is fast enough to track changes– Above 30km/h other schemes such as (Algorithm 2) maybe more suitable
User Equipment (UE)& USIM
Node Bs
UuUu
Inner Loop PC
Inner Loop PC
Required SIRDL
Required SIRUL
Proprietary and Confidential Slide 33
Closed Loop Power ControlClosed Loop Power Control• Outer Loop Power ControlOuter Loop Power Control
– RNC compares uplink BLER with BLER target and sets SIRUL accordingly
– UE compares downlink BLER with BLER target and set SIRDL accordingly
– Frequency 10 to 100 Hz– Step size 0.1 to 1dB
IubIub
User Equipment (UE)& USIM Node Bs RNC
UuUu
Outer Loop PCOuter
Loop PC
Proprietary and Confidential Slide 34
WCDMA HandoversWCDMA Handovers
Proprietary and Confidential Slide 35
Handovers in WCDMAHandovers in WCDMA• Soft Handover
– Intra-system Handover
• Hard Handover– Inter-frequency Handover– Inter-system Handover
Proprietary and Confidential Slide 36
Neighbour Lists & Active SetNeighbour Lists & Active Set• The Neighbor ListThe Neighbor List
– In WCDMA like GSM each cell has to declare at list of valid neighbors• Intra-system neighbors (32 Max)• Inter-frequency neighbors (32 Max)• Inter-system neighbors (32 Max)
• The Active SetThe Active Set– The Active Set is defined as the list of cells the UE is connected to during
dedicated mode– Active set size = 1: UE Not in Soft Handover– Active set size > 1: UE in Soft Handover– Typically Active set size limited to 3
Proprietary and Confidential Slide 37
• Softer handover occurs between sectors of the same site
• Soft handover occurs between sectors of different sites
• For both softer and soft handover UE Ec/Io measurements are used to determine whether a cell should be added or removed from the active set
Soft & Softer HandoverSoft & Softer Handover
Proprietary and Confidential Slide 38
Soft HandoverSoft Handover• Updating the Active SetUpdating the Active Set
IoIo
EcIo1EcIo1
EcIo3EcIo3
-60dBm-60dBm
-5dBm-5dBm
EcIo2EcIo2 -10dBm-10dBm
-18dBm-18dBm
- Addition Window – event 1a
- Drop Window – event 1b
- Replacement Window – event 1c
- Best Server Replacement – event 1d
Proprietary and Confidential Slide 39
Handovers - Inter frequency Handovers - Inter frequency HOHO
• Inter frequency handover occurs between two WCDMA carriers
• This is a hard handover, CM required for UE’s with single receiver
• Used once operator deploys its second carrier, for microcell layer or capacity purposes
f1f2
Proprietary and Confidential Slide 40
Inter system HOInter system HO• Inter system handover occurs between 3G and other systems
• CM required for UE’s with a single receiver
• Voice service is a hard handover and is transparent to the user
• Data service is treated as a reselection not a hard handover and data interruption results.
• As with all handovers, accurate adjacencies are required, this is not only important to ensure seamless customer experience when moving in and out of 3G coverage but also to meet the mandated requirements for E911.
3G 2G
Proprietary and Confidential Slide 41
CM – Compressed ModeCM – Compressed Mode• Typical Dual Mode 3G/2G UEs utilize a single TRX
• To detect potential IF/IS handover candidates the UE has to share the receiver.
• To create the time required to measure another frequency/frequencies without disrupting the current service compressed mode is used.
• During compressed mode the UE’s spreading factor is halved and the instantaneous transmit power is increased in the compressed frame in order to keep the quality (BER, FER, etc.) unaffected by the resulting reduction in processing gain.
• This creates a “gap” in which the RX can be retuned and IF or IS neighbors scanned.
Proprietary and Confidential Slide 42
RRM – Cell BasedRRM – Cell Based
Proprietary and Confidential Slide 43
Admission ControlAdmission Control• Admission ControlAdmission Control
– Responsible for determining if the system (Air Interface, Code Tree, Channel Elements, Iub, RNC, Iu etc), can accept the call
• Air Interface (Uplink Load, Downlink Load/Tx Power) ?• Code Tree – Fragmentation ?• NodeB Processing Capacity ?• Iub Capacity ?• RNC Capacity ?
– May give priority to different types of calls• Typically voice/video take precedent
– Considers reports from Load Control Entity to assist decisions
Proprietary and Confidential Slide 44
Load ControlLoad Control• Load ControlLoad Control
– Responsible for ensuring cell does not go into overload condition– Constantly monitoring Uplink Rx power and Downlink Tx power– Preventative action taken to avoid overload condition– Load reports sent to Admission Control and Packet Scheduler
Proprietary and Confidential Slide 45
Packet SchedulerPacket Scheduler• Packet SchedulePacket Schedule
– Responsible for maximizing throughput of cell/users– Considers reports from Load Control Entity to assist decisions– Should allocate the best bearer for the job
• HSDPA / 384k / 128k / 64k / 32k / FACH etc.
Time
Load
Load Target
CS Load
Free Capacity forPS or HSDPA
Proprietary and Confidential Slide 46
Resource ManagerResource Manager• Resource ManagerResource Manager
– Responsible for ensuring efficient use of cells processing capacity• Code use• Channel element use
SF 4
SF 8
SF 16
384 user #1128 user #1
384 user #2
Proprietary and Confidential Slide 47
Q & AQ & A
Proprietary and Confidential Slide 48
HSDPA FundamentalsHSDPA Fundamentals
Proprietary and Confidential Slide 49
What’s New with HSDPAWhat’s New with HSDPA
• HSDPA – High Speed Downlink Packet Access– HSDPA makes use of shared channels, rather than assigning specific resource
for the transfer of user data, users are scheduled on shared channels.
• Fast Link Adaptation– Instead of using power control to compensate for varying radio environment, the
data rate can be adjusted every 2ms.
• Fast HARQ with soft combining– Instead of handling all retransmissions at the RNC, a new HARQ process is
introduced at the Node B to realize rapid retransmission of erroneous data
• Fast Channel Dependent Scheduling– Scheduler is implemented at the Node B as opposed to the RNC to allow for fast
scheduling to accommodate the user environment.
Proprietary and Confidential Slide 50
HSDPA Protocol StackHSDPA Protocol Stack
Proprietary and Confidential Slide 51
UE CategoriesUE Categories
10
9
7/8
5/6
3/4
1/2
12
11
HSDPACategory
-
-
-
3.6 Mbps
1.8 Mbps
1.2 Mbps
1.8 Mbps
0.9 Mbps
5 Codes
--36302QPSK only
--36301QPSK only
QPSK/16QAM
QPSK/16QAM
QPSK/16QAM
QPSK/16QAM
QPSK/16QAM
QPSK/16QAM
Modulation
14.0 Mbps
10.1 Mbps
-
-
-
-
15 Codes
-279521
-202511
7.2 Mbps144111
-72981
-72982
-72983
10 CodesTransportBlock size
(bits)Inter-TTI (MS)
Proprietary and Confidential Slide 52
Downlink HSDPA Code AllocationsDownlink HSDPA Code Allocations
• SF16 codes assigned to HS-PDSCH, 5, 10 or 15 (3GPP)• SF128 assigned to the HS-SCCH (3GPP) (up to 4)• Maximum of 15 codes in Ericsson and Nokia• HS-PDSCH code resources are assigned to one user at a time
HS-PDSCH
SF=1
SF=2
SF=4
SF=8
SF=16
SF=32
SF=64
SF=128
SF=256
CPICH P-CCPCH
S-CCPCH
HS-SCCH
S-CCPCH
Free code that can be allocated to e.g. DPCH, HS-PDSCH (SF16) or HS-SCCH (SF128).
Code that cannot be allocated due to allocations lower in the code-tree / branch.
Code reserved for a common channel.
Legend:
Proprietary and Confidential Slide 53
Hybrid ARQ (HARQ)Hybrid ARQ (HARQ)
• ARQ = Automatic Repeat Request – uses error detection to determine if a PDU is received in error
• Hybrid ARQ uses forward error correction as well as error detection resulting in improved performance over ARQ.
• Employed between the UE and the Node B
• UE transmits ACK/NACK to indicate the successful / unsuccessful reception of a PDU.
• HARQ round trip time is longer (approx. 12ms) than a TTI period and as such multiple HARQ processes are used to prevent waiting for ACK/NACK before sending the next PDU
• Retransmissions are combined with original transmissions using soft combining (called chase combining) to improve error correction.
Proprietary and Confidential Slide 54
Hybrid ARQ and Soft CombiningHybrid ARQ and Soft Combining
NB. If more than 4 NACK are received for the same packet, the coding rate is changed to higher error correction or the buffer in Node B is flushed and re-filled from the RNC.
Proprietary and Confidential Slide 55
Link AdaptationLink Adaptation
• Transport Format Resource Combination (TFRC) changes on the air interface are adapted depending on a Channel Quality Indicator (CQI) sent from the UE.
• The Node B uses this reported CQI as a reference but fine tunes the actual TFRC assignment depending on the last series of ACKs or NACKs, UE capability, actual transmit power, amount of buffered data etc.
• CQI levels change depending on UE type. Attached is the CQI mapping for a CAT 8 UE.
• The TFRC can be modified in each TTI. -516-QAM101441130
-416-QAM101441129
-316-QAM101441128
-216-QAM101441127
-116-QAM101441126
016-QAM101441125
016-QAM81141824
016-QAM7971923
016-QAM5716822
016-QAM5655421
016-QAM5588720
016-QAM5528719
016-QAM5466418
016-QAM5418917
016-QAM5356516
0QPSK5331915
0QPSK4258314
0QPSK4227913
0QPSK3174212
0QPSK3148311
0QPSK3126210
0QPSK29319
0QPSK27928
0QPSK26507
0QPSK14616
0QPSK13775
0QPSK13174
0QPSK12333
0QPSK11732
019200
0QPSK11371
Out of rangeN/A0
XrvNIRReference power adjustment Modulation
Number of HS-PDSCH
Transport Block Size
CQI value
-516-QAM101441130
-416-QAM101441129
-316-QAM101441128
-216-QAM101441127
-116-QAM101441126
016-QAM101441125
016-QAM81141824
016-QAM7971923
016-QAM5716822
016-QAM5655421
016-QAM5588720
016-QAM5528719
016-QAM5466418
016-QAM5418917
016-QAM5356516
0QPSK5331915
0QPSK4258314
0QPSK4227913
0QPSK3174212
0QPSK3148311
0QPSK3126210
0QPSK29319
0QPSK27928
0QPSK26507
0QPSK14616
0QPSK13775
0QPSK13174
0QPSK12333
0QPSK11732
019200
0QPSK11371
Out of rangeN/A0
XrvNIRReference power adjustment Modulation
Number of HS-PDSCH
Transport Block Size
CQI value
Proprietary and Confidential Slide 56
Power Control in HSDPAPower Control in HSDPA
• Fast Link Adaptation provides a mechanism to adequately accommodate changes in the radio environment.
• Initially power control of the HS-PDSCH was not used, however vendors have now implemented various degrees of power control to reduce HSDPA impact to other services.
• Ericsson – HS-SCCH has power control– HS-DSCH has power control
• For Nokia– HS-SCCH has power control – HS-DSCH is set at minimum power but can absorb extra power if available to increase
throughput.
• Associated DCH is power controlled using fast power control.
Proprietary and Confidential Slide 57
SchedulersSchedulers• The scheduler schedules the information that will be sent from the
Node B to the UE.• The scheduler requires important information from the uplink HS-
DPCCH and other sources
Scheduler
QoS and Subscriber ProfileWho is the subscriber? Platinum, Gold,Silver, Normal.What type of service is the subscriber allowed? High priority, Besteffort
Uplink FeedbackCQI and Ack/Nackinformation
Node B buffer statusHow much data is in bufferHow fast is the data arriving
User HistoryHow long has userbeen waiting
Traffic ModelWhat type of traffic model shouldbe used - according to periodof the day – Peak/Off Peak
Available Radio ResourcesPowerCodes
UE Capability
Users are scheduled according to theirrequirements for transmission by theNode B over the air interface
Proprietary and Confidential Slide 58
• Simplest form of scheduler
• First in First out principle
• Advantages:
• Easy to implement
• Minimises waiting time
• Fair
• Disadvantage:
• System Throughput not optimal.
UE 1 Datasent
UE 2 Datasent
UE 1
UE 6
UE 5
UE 4
UE3
UE 2
UE 3 Datasent
UE 4 Datasent
UE 5 Datasent
UE 6 Datasent
UE 1 DataRequest
UE 2 DataRequest
UE 3 dataRequest
UE 4 Data Request
UE 5 DataRequest
UE 6 DataRequest
NodeB PacketScheduler
Round Robin SchedulerRound Robin Scheduler
NodeB Buffers
Proprietary and Confidential Slide 59
Proportional Fair SchedulerProportional Fair Scheduler
• Schedules users based on– CQI – Average throughput – Retransmission (time between NACK reception and retransmission)– Delay (time since last scheduled)
Proprietary and Confidential Slide 60
HSDPA MobilityHSDPA Mobility
• There is no SHO for the HS-PDSCH channels
• This is due to – Location of the scheduler (Node B level)– Resource requirements on Iub / Channel Elements (CE)
• There are 3 methods for continuing data while HSDPA is in SHO area1. Suspend data till SHO area has expired
2. Radio Bearer reconfiguration to a DCH in SHO area, then re-attempt a HSDPA call setup when SHO area expires
3. SHO of the A-DCH and effectively do a cell reselection for the HS channel to the new best server (depends on vendor support)
• Ericsson Supports SHO of A-DCH in P5, Nokia Supports in RAS 5.1
Proprietary and Confidential Slide 61
HSDPA Mobility - SHO for Associated DCHHSDPA Mobility - SHO for Associated DCH
Proprietary and Confidential Slide 62
HSDPA assignmentHSDPA assignment
• When HSDPA is enabled on a cell – DSP capacity (channel elements) is permanently assigned as a pool, this resource can not be used by other services.
• Only transmits when data is ready to transmit
• Power, code and transmission resource are temporarily reserved as required
• No Hold times in HSDPA state (FACH hold time is applied but no Iub reservation)
• HSDPA is a more efficient way of transporting bursty PS data than DCH ever could be.
Proprietary and Confidential Slide 63
Q & AQ & A