1
HSDPA
by
Devendra Sharma
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Sequence of Presentation
• History / Motivation
• Introduction to New Features/ Transport Ch
• Feature Explanation
– AMC
– HARQ
– Scheduler
• Transport / Control Channel Explanation
– HS DPCCH
– HS SCCH
– HS DSCH
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Sequence of Presentation
• Architectural Changes
- RAN Architecture
- MAC (hs, sh/c/m, d)
- UE
• Mobility in HSDPA
- Intra & Inter Node B HS DSCH Handover
- HS DSCH to DCH Handover
✓ Q&A
4
Motivation
• Sophisticated UE applications need higher bit rates
• Primary target of HSDPA is to enhance system throughput with minimum changes in network architecture
• Is an extension to WCDMA Release ’(”99”)
Release 5 - HSDPA (High Speed Downlink Packet Access)
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Transition from Present UMTS system
• Current WCDMA network can be upgraded to support
HSDPA
• Does not change network architecture dramatically
• There can be HSDPA supported cells and regular cells
• If HSDPA is not accessible at UE location it will use
normal Release 99 (DCH) to communicate at regular
service speeds
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HSDPA Research
• Motorola and Nokia supporting the start of work on HSDPA from the vendor side and BT/Cellnet, T-Mobile and NTT DoCoMo from the operator side
• Physical layer retransmissions, BTS-based scheduling and adaptive modulation and coding were studied.
• Investigations were done for multi-antenna transmission and reception technology, titled ‘multiple input multiple output’ (MIMO), as well as on fast cell selection
• Based on the above study the specifications were developed
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HSDPA Introduction
• HSDPA was standardised as 3GPP release 5
• The HSDPA peak data rate available in the terminals is initially 1.8Mbps and will
increase to 3.6 and 7.2 Mbps during 2006 and 2007, and potentially beyond 10Mbps.
• HSDPA can share same CN element
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Radio Capability Evolution
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Transition from Present UMTS system
• Current WCDMA network can be upgraded to support
HSDPA
• Does not change network architecture dramatically
• There can be HSDPA supported cells and regular cells
• If HSDPA is not accessible at UE location it will use
normal Release 99 (DCH) to communicate at regular
service speeds
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HSDPA Introduction
• Relase 99 provide data rates of 384Mbps to 2Mbps
• HSDPA
- Increase peak data rates upto 14Mbps
- Reduce the round trip delay
- Will increase the UTRAN network capacity
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Radio resource management architecture
• Relase 99 RRM Architecture
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Radio resource management architecture -
cont
• HSDPA/HSUPA RRM architecture
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HSDPA Impact on UTRAN Interfaces
Presentation on HSDPA…Continues
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HSDPA Impact on UTRAN Interfaces - ctd
• HSDPA flow control
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HSDPA Impact on UTRAN Interfaces - ctd
• HSDPA added functionalities
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HSDPA Impact on UTRAN Interfaces - ctd
• HSDPA protocol states
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HSDPA Principles
Introduction/New Features
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Release 99 DL Packet Capabilities
• Dedicated Channel( DCH )
• Downlink-shared Channel( DSCH )
• Forward Access Channel( FACH )
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HSDPAWhat comes in? & What goes out?
• Two fundamental features of WCDMA are disabled:
– Variable SF
– Fast Power Control
• These two features are replaced by
– Adaptive Modulation and Coding (AMC)
– Fast retransmission strategy (HARQ)
– Scheduling Algorithm
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New Channels Introduced
in HSDPA (R – 5)
• HS-DSCH (High Speed Down link Shared Channel)
TO support the HS-DSCH Operation
Two Control Channels are added
• HS-SCCH (High Speed Shared Control Channel)
DL channel
• HS- DPCCH (High Speed Dedicated Physical Control Channel)
UL Channel
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Comparison of
DSCH and HS_DSCH
Feature DCH HS-DSCH
Variable Spreading Factor No No
Fast Power Control Yes No
AMC No Yes, Extended
Multi Code Operation Yes Yes
Physical Layer Retransmission No Yes
BTS based Scheduling and Link
AdaptationNo Yes
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Node B Protocol Stack In R99
E1
ATM
AAL2 AAL5
SSCOP
SSCF – UNI
STC.2 NBAP
ALCAP
FP
PHY
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Node B Protocol Stack In R-5
E1
ATM
AAL2 AAL5
SSCOP
SSCF – UNI
STC.2 NBAP
ALCAP
FP
PHY
MAC - hs
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UE Protocol Stack In R-5
CM
MM
RRC
RLC
MAC
PHY – UP
PHY
MAC - hs
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Feature Explanation
Presentation on HSDPA…Continues
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BTS Retransmission Handling
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Adaptive Modulation & Coding
• Aimed at changing the modulation and coding format with variations in the
channel conditions
• Role: Continuously Optimisation of :
• Code Rate – 3/4 rate or 1/4 rate Turbo Code or Convolution Coding
• Modulation Scheme (16 QAM, QPSK)
→ (Based on CQI Feedback from UE) or transmission power of other DL
channels under power control
•Hence different Combinations of:
• Modulation
• Ch Code Rate
(Based on TFRC, Transport Format & Resource Combination)
Can provide different Peak Data Rates.
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Adaptive Modulation & Coding
The main benefits are:
• Higher data rates for users in favourable condition, which in turn increases the average throughput of the cell,
• Since the transmit power is fixed (no fast power control) , the interference to other users is significantly reduced
(chip rate) (16QAM) (SF) (Codes) (Turbo) (Puncture)
3.84M chips/s * 4 bits/chip * 1/16 *15 * 1/3 * 3/1 = 14.4M bits/sec
This Rate in a real system Remains very unlikely as it would require an unloaded
system serving a single User extremely close to the Node B
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HARQHARQ schemes combine the conventional ARQ with FEC
• Role
➢ It is the Re-Tx Mechanism selected for HSDPA
➢ Allows UE to Re-Tx rapidly of erroneous transport block until are
successfully Rx.
• Location
➢ HARQ is implemented at the MAC-hs (in Node B).
➢ Terminated at Node B as opposed to the SRNC (RLC) . Hence
Re-TX delays is much lower in HSDPA than in Rel 99.
➢ How?
✓ NACk may require less than 10msec at the MAC Layer.
✓ Approx.100msec is required at the RLC layer when Iub
signalling is involved.
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HARQ
• Waiting Time Utility
➢ Multiple processes can run for the same UE using separate TTIs.
• HARQ Types
➢ Type I: Same PDU is retransmitted
➢ Type II: Incremental redundancy is employed
➢ Type III: Consistent redundancy (codes) is employed. Also called chase combining.
• The scheduler in UTRAN determines the redundancy version parameters for HARQ functional entities in NODE Bs
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HARQ
HSDPA is the Combination of AMC and HARQ
• leads to an integrated, robust and high performance solution,
• AMC provides the coarse data rate selection,
• HARQ provides for fine data rate adjustment based on channel condition
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Scheduler
• It’s the key element in HSDPA
• Scheduler base it’s decisions on
➢Channel quality as used by link adaptation,
➢current load of the cell,
➢traffic priority classes
• Scheduler for HSDPA is fast
➢ Compared to R99 scheduler is moved from RNC to Node B
• Fundamental task of scheduler is to schedule the transmission for users
• For each TTI, it determines which terminal or terminals HS-DSCH should be transmitted to and inconjunction with the AMC
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SchedulerTypes
• Round Robin (RR):▪ Schedules USers to a 1st in 1st out approach,
▪ No of time slots allocated are inversely propotional to user data rates,
▪ Provides higher degree of fairness between users,
▪ But at an expense of overall Through-put of the system,
▪ No differentiation in the quality of services for different classes of users.
• Max carrier-to-interface(C/I):▪ Schedules Users with the highest C/I during current TTI.
▪ Naturally leads to a higher Through-put of the system, as users with best channels are served.
▪ Fairness is effected in this scheduler, specially users at cell edge will have service delays and significant Outage.
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SchedulerTypes
– Proportioanl Fair (PF):
• Offers good trade between RR & Max C/I.
• Schedules Users according to the Ratio between their
Instantaneous achievable Data rate and their Average
Served Data rate.
• Results in all Users having equal probability of being served
even though they may experience very different average
Chanel quality.
• Good Balance between System Through-put & Fairness.
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Transport / Control
Channel
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HS-DSCH - Basics
• Lack of fast power control. Instead, link adaptation
selects the suitable combination of codes, coding
rates and modulation to be used.
• Support of higher order modulation than the DCH.
• User allocation with base station based
scheduling every 2ms, with fast physical layer
signalling
• Use of physical layer retransmissions and
retransmission combining.
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HS-DSCH - Basics
• Lack of soft handover hence data are sent from one
serving HS-DSCH cell only.
• Lack of physical layer control information on the HS-
PDSCH.
• Multicode operation with a fixed spreading factor of 16.
• With HSDPA only turbo-coding is used.
• No discontinuous transmission (DTX) on the slot level. The
HS-PDSCH is either fully transmitted or not transmitted at all
during the 2-ms TTI.
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HS-DSCH - Basics
•No discontinuous transmission (DTX) on the slot
level. The HS-PDSCH is either fully transmitted or
not transmitted at all during the 2-ms TTI.
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HS-DSCH
• HS-DSCH consists of:
– With in each TTI = 2ms
– SF = 16 is made fixed
– Channelization (spreading) codes=15: Shared by active HSDPA terminals
in a cell
• Users can Share Resources, all users in a Particular sector as users
are allocated within different TTIs
• Transmission Time Interval (TTI) = 2ms as compared to 10ms in R99
• By reducing TTI reduces :
– The Round Trip delay &
– Improve Link Adaptation Rate/ efficient AMC
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HS-DSCH – Coding Chain
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HS-DSCH
• Turbo Coding is used for HS-DSCH
– With in each TTI = 2ms
– SF = 16 is made fixed
– Channelization (spreading) codes=15: Shared by
active HSDPA terminals in a cell
• 16 QAM is used by HS-DSCH
• Bit Scrambling on the physical layer for
HS_DSCH
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• HSPDA codes allocated by CRNC• Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4
• Real-time allocation of these codes by NodeB scheduler• Transmit power set by scheduler, constant during one TTI
Channelisation codes at a fixed spreading factor of SF = 16
Up to 15 codes in parallel
SF=8
SF=16
SF=4
SF=2
Physical channels (codes) to which HS-PDSCH is mappedCPICH, etc.
C16,0C16,15
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HS-DSCH
The Codes can all be assigned to One User in 2ms or Split across Several Users.
The assigning of Codes Depends of following Factors:
• Cell Load
• QoS requirement
• UE Code Capabilities
HSDPA permits sumultaneous transmissions i.e. two or four users can can be supported within the same TTI by using different subset of the channelization codes allocated to HS-DSCH
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DL-DPCH & UL-DPCH
• The DL-DPCH carries HSDPA Indicatior (HI)
• HI indicates which HS-SCCH subset the terminal should monitor in order to obtain the signalling information
• The UL_DPCH carries power control signals for the DL-DPCH
• The UL-DPCH power control signal information and feedback information from HS-DPCCH can be used by the network to estmate the channel quality.
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HS-SCCH
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HS-SCCH
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HS-SCCH
• Two slots offset compared to HS_DSCH
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• The first part contains the following information:– Information needed to be availbale to enable de-spreading of correct codes.
– Modulation information
• Second part contains less urgent information such as – Which ARQ process is being tramsmitted
– An indication whether the transmission is new or related to an earlier transmitted packet is also included.
– Iformation on the redundancy version and the contellation.
– Transport block size
HS-SCCH
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• The HS-SCCH coding and multiplexing chain
HS-SCCH
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• The first part contains the following information:– UE – ID – 16 bits
– HARQ related Information – 3 bits
– Parameters of the HS-DSCH Transport Format Selection by the Link
Adaptation Mechanism – 6 bits
• UE can be assigned upto ”4” HS-SCCH out of 32 parallel HS-SCCH. Which needs monitoring continuously
• When HSDPA is operated using the time multiplexing principle, then only one HSSCCH can be configured. In this case only one user receives data at a time.
HS-SCCH
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• In any given TTI:
– Max. of ”1” of HS-SCCH may address a particular UE
– UE detects msg addressed to him on a Specific HS-SCCH
– It may restrict its monitoring of HS-SCCH to only that one
HS-SCCH in next TTI.
• Contents per channel per TTI:–RNTI of selected UE (masked in)
–HS-PDSCH code(s) - up to 15
–Modulation (QPSK or 16QAM)
–TB size (TFRI) 137-27952 bits
–Hybrid-ARQ information (retransmission or new block)
–CRC
HS-SCCH
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HS-DPCCH
HS-DPCCH Usage – ACK/NACK
There is one HS-DPPCH for each active terminal using HSDPA services
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HS-DPCCH
HS-DPCCH Usage – CQI
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HS-DPCCH
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CQI
• Information is Based on (Cpich) Common Pilot Channel
• Is used to estimate the following:– Transport Block Size
– Modulation Type
– No. of Channelisation Codes (that can be supported at a given
reliability level)
• The feedback of CQI can be set as Network parameter in a
Predefined steps of 2ms
• When longer feedback cycles are used, the (PDCH) Power Control
Command can be used to update the channel quality estimation
• CQI (0-30) => UEs estimates highest value with probability of TB
error < 10% for the next transmission slot, and with various power
assumptions
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Architectural Changes
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HSDPA Architecture
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Node B Protocol Stack In R99
E1
ATM
AAL2 AAL5
SSCOP
SSCF – UNI
STC.2 NBAP
ALCAP
FP
PHY
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Node B Protocol Stack In R99
E1
ATM
AAL2 AAL5
SSCOP
SSCF – UNI
STC.2 NBAP
ALCAP
FP
PHY
MAC - hs
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Radio Access Network Architecture
• All Release 4 transport channels
are terminated at the RNC
– Retransmission procedure is
located in serving RNC
• In Release 5 an additional
HSDPA MAC layer (MAC-HS) is
installed in the Node B
– Retransmissions will happen closer
to air interface - in the Node Bs
– Faster retransmissions
– Shorter delays with packet data
operation
• Flow control mechanism is
needed in Iub interface between
Node B and RNC to ensure
correct Node B data buffering (to
prevent data losses at Node B)
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Radio Access Network Architecture
• RNC handles RLC (Radio Link Control)
functionalities
– If e.g. HS-DSCH TX from Node B fails for some
reason
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MAC-hs (UTRAN side)• One MAC-hs entity in UTRAN for each cell
that support HS-DSCH transmission
• Scheduling/priority handling
– Manages HS-DSCH resources
between HARQ entities and data
flows according to their priority
– Determines either to send a new
transmission or a retransmission
based on uplink signalling
– Determines QueueID and TSN for
each new MAC-hs PDU
• HARQ
– One HARQ entity per user
– Multiple instances of stop and wait
HARQ protocols supported for each
HARQ entity
• TFRC selection
– Selection of appropriate transport
format and resource for the data
MAC-hs
MAC – Control
HS-DSCH
TFRC selection
Priority Queuedistribution
Associated DownlinkSignalling
Associated UplinkSignalling
MAC-d flows
HARQ entity
Priority Queuedistribution
PriorityQueue
PriorityQueue
PriorityQueue
PriorityQueue
Scheduling/Priority handling
To UE
From network
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MAC-hs (UE side)
• HARQ
– Handles all the tasks that are required for hybrid ARQ
– Generates ACKs or NACKs
– Configurations of the H-ARQ protocol is provided by RRC over the MAC-Control SAP
• Re-ordering queue distribution
– Reorders incoming MAC-hs PDUs to ordering buffer based on queue ID
• Reordering
– Reorders received PDUs according to received transmission sequence number (TSN)
– Delivers complete objects to disassembly function
– PDUs are not delivered if PDUs with lower TSN are missing
• Disassembly
– Removes MAC-hs header and padding bits and passes the MAC-d PDU to higher layers
MAC-hs
MAC – Control
Associated Uplink Signalling
To MAC-d
Associated Downlink Signalling
HS-DSCH
HARQ
Reordering Reordering
Re-ordering queue distribution
Disassembly Disassembly
UE side MAC-hs details
From network
To UE
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MAC - hs in Node B
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 Functions
• Priority handling
• Flow Control• To RNC
• To UE
• Scheduling
• HARQ handling
• (CQI) Service
measurements• e.g. HSDPA
provided bitrate
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MAC - hs PDU
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Node B conceptual per-UE data flow
Scheduler
Qual/Ack-Nak
DL
Queue
Xmit Info
Bearer Data
Bearer Data
Bearer Data
UE
Qual/Ack-Nak
RNC
(reported
user buffer
size)
(HS-DPCCH)
(HS-SCCH)
(HS-PDSCH)
Coding/
Modulation
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Mobility in HSDPA
HSPA does not support soft handovers
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Mobility in HSDPA
• No soft handovers in HS-DSCH
• HSDPA control channels are sent via only one of the radio links assigned to UE
(from serving HS-DSCH cell)
• UTRAN determines the serving HS-DSCH cell for an HSDPA capable UE
• Synchronized change of serving HS-DSCH cell is supported between UTRAN and
UE connectivity is achieved if UE moves from one cell to another
• Serving HS-DSCH cell change is triggered by UE measurement reports and
determined by UTRAN
• UTRAN (RNC) dictates the time moment when serving cell is changed
• This gives full mobility and coverage to exploit the advantages for HSDPA over
Release 4 channels
• Serving HS-DSCH cell can be changed:
– Without changing user’s active set for Release 4 dedicated channels
– In combination with establishment, release or reconfiguration of Release 4 dedicated
channels
• A new UE measurement event is needed to provide these properties
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Mobility in HSDPA
• Three handover types
– Intra-Node B HS-DSCH to HS-DSCH
handover
– Inter-Node B HS-DSCH to HS-DSCH
handover
– HS-DSCH to DCH handover
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Mobility in HSDPA
• All transmission from the source cell stops at that specified time and the packet scheduler in the target cell is then allowed to control transmission to UE
• MAC-hs preservation:
– Buffered data (for H-ARQ protocol: data waiting acknowledgement or new PDUs) in source cell is moved to target cell inside the Node B no data loss!
– H-ARQ manager will continue without breaks or retransmissions
– No higher layer retransmissions (e.g. from RLC protocol)
Intra-Node B HS-DSCH to HS-DSCH Handover
UE-L1
Node B-L1
SRNC-RRC
UE-RRC
measurement
Measurement report
Serving HS-DSCH cell change decision
Prepare reconfiguration
Reconfiguration ready
CUPHY-RL-commit-REQ
Physical channel reconfiguration
CUPHY-Modify-Req
Physical channel reconfiguration complete
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Mobility in HSDPAIntra-Node B HS-DSCH to HS-DSCH Handover
Target node B
Source Node B SRNC
UE-RRC
measurementMeasurement report
Serving HS-DSCH cell change decision
Radio link setup
Radio link setup ready
CUPHY-RL-commit-REQ
transport channel reconfiguration
transport channel reconfiguration complete
Prepare reconfiguration
Reconfiguration ready
Radio link deletion req
Deletion complete
• At the time of cell change (usually 300-500ms from the RNC decision), the MAC-hs for the user in the source cell is reset (user data in buffers is deleted)
• The reset of the MAC-hs entity is indicated by the flag in transport channle reconfiguration.
• The RLC or Tx/Rx on HSDCH is be stopped at both the UTRAN and UE side prior to recinfiguration and continued when reconfiguration is complete
• If RLC is used in UM mode and if user application does not have retransmission mechanisms, some data is lost forever when a handover occurs
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Mobility in HSDPA
• Needed when user moves from HSDPA capable cell to a cell that
does not support HSDPA
• Node Bs, target cell RNC and the user are informed about
incoming handover event
• Buffers in Node B are reset as in previous case and similar
retransmissions are required because of lost buffer data
HS-DSCH to DCH Handover
• Transmission continues in DCH
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Beyond HSDPA and HSUPA
• 3GPP has started a feasibility study on the UMTS Terrestrial Radio Access Network
(UTRAN)long-term evolution (LTE).
•The work has been started with the following targets defined:
• Radio network user plane latency below 5 ms with 5-MHz or higher spectrum allocation.
With smaller spectrum allocation below, latency below 10 ms should be facilitated.
• Reduced control plane latency.
• Scalable bandwidth up to 20 MHz, with smaller bandwidths covering 1.25MHz, 2.5 MHz,
5 MHz, 10MHz and 15MHz for narrow allocations.
• Downlink peak data rates up to 100 Mbps.
• Uplink peak data rates up to 50Mbps.
• Two to three times the capacity of existing Release 6 reference scenarios with HSDPA or
HSUPA.
• Improved end user data rates at the cell edge.
• Support for the PS domain only.
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Beyond HSDPA and HSUPA - contd
• 3GPP has started a feasibility study on the UMTS Terrestrial Radio Access Network
(UTRAN)long-term evolution (
•The work has been started with the following targets defined:
• Radio network user plane latency below 5 ms with 5-MHz or higher spectrum allocation.
With smaller spectrum allocation below, latency below 10 ms should be facilitated.
• Reduced control plane latency.
• Scalable bandwidth up to 20 MHz, with smaller bandwidths covering 1.25MHz, 2.5 MHz,
5 MHz, 10MHz and 15MHz for narrow allocations.
• Downlink peak data rates up to 100 Mbps.
• Uplink peak data rates up to 50Mbps.
• Two to three times the capacity of existing Release 6 reference scenarios with HSDPA or
HSUPA.
• Improved end user data rates at the cell edge.
• Support for the PS domain only.
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Beyond HSDPA and HSUPA
• Further work for long-term evolution is based on pursuing single-carrier
frequency division multiple access (SC-FDMA)for the uplink transmission
and orthogonal frequency division multiplexing (OFDM)in the downlink
direction.
•To be added:
• To be added
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Any Questions & Comments ?
?