hspa fundamentals
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HSPA Fundamentals
10/11/2011
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Definitions
HSDPA = High Speed Downlink Packet Access
HSUPA = High Speed Uplink Packet Access
HSPA = HSDPA + HSUPA
HSDPA and HSUPA are improvements on the basic R99 WCDMA system thatapply to packet data users only
HSDPA: higher bitrates and spectral efficiency for downlink
HSUPA: higher bitrates and spectral efficiency for uplink
HSPA in the standards
HSDPA is first introduced in 3GPP Rel 5- Refs: 25.308 (HSDPA overview), 25.321 (MAC),25.977 (HSDPA Iub/Iur)
HSUPA is an enhancement in 3GPP Rel 6 - Refs: 25.309 (EDCH overview), 25.808 (EDCHPHY), 25.214 (PHY layer procedures)
INTRODUCTION
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ARCHITECTURE
RNC
MAC-es
SGSNRNC
NodeB
MGW
GGSN
Iur
Iub
Iu-cs
Iu-ps Gn
L1
MAC
RLC
MAC-d
RLC
UuL1L1
MAC-hs
DL UL
MAC-e
Radio protocol stack in NodeB
Radio protocol stack in RNC
= Impact to Network elements due to HSPA
NodeB PHY layer modified
Part of MAC layer moved from RNC to NodeB
Contains Packet scheduling for HSPA
Specific CE for HSPA BB processing
RNC
Part of MAC layer moved to NodeB
3G SGSN
3G SGSN to realize higher bitrates
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High Speeds with HSDPA
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HSDPA Basic Principles
1. Shared Channel Transmission
2. Higher-order Modulation
3. Short Transmission Time Interval (2 ms)
4. Fast Hybrid ARQ with Soft Combining
5. Fast Link Adaptation
6. Fast Radio Channel Dependent Scheduling
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1.Shared Channel Transmission
Channelization codes allocated
for HS-DSCH transmission
8 codes (example)
SF=16
SF=8
SF=4
SF=2
SF=1
User #1 User #2 User #3 User #4
TTI
Shared
channelizationcodes
Resources are dynamically shared in Time and Code
domain Efficient Radio Resource Utilization
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2.Higher-order Modulation
Higher-order Modulation
HSDPA uses 16QAM, in addition to QPSK
16QAM allows twice the data rates compared to
QPSK
Higher Throughputs in good Radio Conditions
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3.Short Transmission Time Interval
Short Transmission Time Interval
Shorter frames (up to 2ms)
Reduced air-interface delay
Improved end-user performance and spectral efficiencyRequired by TCP at high data rates
Necessary to benefit from other features like
Fast Link Adaptation
Fast hybrid ARQ with soft combining
Fast Channel-dependent Scheduling
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ARQ = Automatic Repeat reQuest (method used for packet
retransmission)
HARQ is a very efficient ARQ that reduces error rates in retransmissions
Perform packet combining operations from retransmissions in the physicallayer
Two different ways of operating HARQSoft combining(or chase combining)
Incremental redundancy(IR)
P1,1
P1,1
P1,2
P1,2
P2,1
P2,1
P2,2
P2,2
P3,1
P1,1 P2,1 P3,1
+ +
Transmitter
Receiver
4.Fast Hybrid ARQ with Soft Combining
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1st Decoding in UE 2nd Decoding in UE Final Picture
During Retransmission, UE performs soft combining to
get the final product
4.Fast Hybrid ARQ with Soft Combining
contd.,
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Two different ways of operating HARQ
Soft combining(or chase combining): all the transmission attempts of a
packet are identical. If the retransmitted packet is again erroneous, then
the previous and current packet are combined to recover from errors
Incremental redundancy(IR): similar to Soft combining, but instead of
being identical to the first transmission attempt, the retransmissioncontains additional redundant bits, which are combined with the previous
transmission to resolve the errors
IR typically outperforms Soft combining at the expense of higher
complexity
Chase Combining was used in WCDMA RAN during Initial launch
4.Fast Hybrid ARQ with Soft Combining
contd.,
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5.Fast Link Adaptation
Adjust transmission parameters to match instantaneous channelconditions
Path loss and shadowing
Interference variations
Fast multi-path fading
HS-DSCH: Rate control (constant power)
Adapt on 2 ms TTI basis 500 times per sec
Encoding rate, number of Channelization codes
and modulation type adapted based on available Power
16 QAM: twice the data rate of QPSK
More sensitive to interference (use with good C/I)
Higher Speeds Close to cell site
High data rate
Low data rate
16QAM
4 bits
2 bits
QPSK
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Physical Channel Structure
A-DCHDPDCH-Dedicated Physical Data channel(UL)
DPCCH-Dedicated Physical control Channel(UL)
DPCH-Dedicated Physical Channel(DL)
Associated Dedicated
Channels(A-DCH)
HS-Control Channels1.HS-SCCH:Shared Control Channel(DL)
2.HS-DPCCH-Dedicated Physical Control Channel(UL)
AB
HSDPA Channels
3GPP Release 5 extends the specification of WCDMA
with a new downlink transport channel for packet data -High Speed Downlink Shared Channel (HS-DSCH)
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HSDPA Channels contd.,
HS-DSCH (High Speed Downlink Shared Channel) :
Common Downlink channel used for data
Supports link adaptation, hybrid ARQ and scheduling
Does not support soft handover or power control
Always associated with a DPCH
Fixed spreading factor (SF16)
Mapped to one or several HS-PSDCH, depending on number of codes (up to 15)
Timeslots & codes shared between users
HS-SCCH (High Speed Shared Control Channel)
Control Downlink signaling to the mobile(s) scheduled in a 2 ms interval
1 HS-SCCH can handle only 1 user in one timeslot, multiple HS-SCCH required
for code multiplexing( Max 4 can be enabled)
SF 128
HS-DPCCH (High Speed Dedicated Physical Control Channel)
Uplink Channel containing ACK/NACK information for fast ARQ
DL Channel Quality indicator (CQI), estimated transport block size, modulation &
codes that can be received in the DL with reasonable BER
HS-DPCCH: CQI,ACK/NACK
HS-DSCH: Data Transfer
HS-SCCH:DL Control Information
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HS-DSCH Overview
CN RNC RBS UE
-
DPCCH
DP DCH
HS DPCCH
HS-SCCH
HS-PDSCHHS -DSCH
DCCH
DCCH
DTCHInteractive PS RAB
DTCHInteractive PS RAB
DTCH
Interactive PS RAB
DCCHNAS
DCCHNAS
RRC
User 1
User 2
User n
For eachuser
Radio Access Bearers:- Intera ctive- Background
Logical Channels:
-Dedicated Control Channel, DCCH
-Dedicated Traffic Channel, DTCH
Transport Channels:
-Dedicated Channel, DCH
-High-Speed Downlink Shared Channel, HS-DSCH
Physical Channels:
-Dedicated Physical Channel, DPCH
-DPCCH, Dedicated Physical Control Channel
-DPDCH, Dedicated Physical Data Channel
-HS-DPCCH, HS-DSCH Dedicated Physical Control Channel
-HS-DSCH Shared Control Channel, HS-SCCH
-High Speed Physical Downlink Shared Channel, HS-PDSCH
DPCHDCH
DCH
Iu Iub Uu
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HSDPA Power
t
Dedicated channels (power controlled)
Common channels
HS-DSCH
Totalcellpower
HSDPA power is used based on remaining
power not used by Voice and R99
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HSDPA Code Tree
SF2 SF4 SF8 SF16 SF32 SF64 SF128 SF256
5 codes reserved for HSDPA
(40 potential codes not used for voice)
Every single SF16 code can
potentially carry 8 typical
voice calls (SF128)
10 codes reserved for HSDPA wouldleave room for 36 voice users in the cell
With 15 HSDPA codes there is room
for only 4 voice calls in the cell
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HS-DSCH UE Categories
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HS-DSCH Bit-Rate
Maximum achievable bit-rate on HS-DSCH will depend
upon
Radio condition
16QAM (or 64QAM) availability
Available HS-DSCH power
Available number of HS-PDSCH codes and
UE category
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1. Resource estimation:
estimates the amount of power and codes available for HSDPA traffic
2. Queue validation:
checks if it is possible to transmit data to a priority queue e.g. radio quality
sufficient, UE capable to receive data, presence of data in the buffers,)3. Queue selection:
selects which user the system shall transmit to in the next TTI based on resource
estimation & Queue validation checks.
4. Remaining resource check function for Code Multiplexing:
Is to check if more users can be selected if power & codes are available.
The Flexible Scheduler function consists of four main procedures,
performed in the following order every TTI:
MAC-hs Scheduler contd.,
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Call Process Overview
Interactive RAB is mapped on
Radio Bearer to be transmitted
over HS-DSCH.This Bearer is then Processed
by RLC & MAC-d Protocol Layer
in RNC
Resulting MAC-d PDUs are
transmitted over Iub to RBS using
HS-DSCH Frame Protocol.
Flow Control protocol in RBS &
RNC enables efficient control of
the PDUs over Iub.
MAC-d PDUs are buffered in Priority
queues to be transmitted over Uu to UE.
The Flexible Scheduler selects the userto be served in Next TTI & assigned HS-
DSCH.
The user data to transmit on the HS-
DSCH is put into one of several HARQ
processes in the MAC-hs HARQ protocol.
The amount of data to be transmitted is
determined by the TFRC selection
algorithms.
CQI adjustment algorithm
which adjusts the channel
quality reports from the UEbefore the channel quality
estimates are used by the
Flexible Scheduler and TFRC
selection algorithms
http://edw//alex?ac=image&fn=93_1553-HSD10102_4Uen.A-cpi-hsdpa-user-plane-figure-protocols.pdf -
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Iub Flow Control
http://edw//alex?ac=image&fn=93_1553-HSD10102_4Uen.A-cpi-hsdpa-user-plane-figure-flowctrl.pdf -
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New channel, time & code multiplexed - Dynamic
utilization of parallel codes (up to 15)
2 ms TTI: faster dynamics, reduced delays
Fast scheduler adapting to radio conditions (2ms)
Codes with fixed spreading factor (SF 16)
No power control: link quality controlled by adaptive
modulation and coding formats
No soft handover on the shared channel
Hybrid ARQ: fast retransmission with combining
16QAM modulation in addition to QPSK
2 ms
HSDPA Fundamentals - Summary
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HSUPA
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HSUPA Basics
Enhancement of existing DCH (E-DCH) to support up to 5.76Mbps
Soft handover and fast power control occursVariable spreading factor
Use of QPSK only
No time multiplexing
Main changesUse of HARQ
Multiple parallel codes
Faster dynamics: reduced TTI (10 and 2 ms options)
Special RRM
Fast uplink scheduler in NodeB (proportional fair is the optimum)
Faster outer loop power control (that adapts to the new shorter TTI)
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HSUPA Protocol Stack
Similar change to HSDPA
MAC layer split into MAC-d, MAC-es and MAC-e
MAC-d (dedicated)
Located in RNC
Same functionality as HSDPA MAC-d
MAC-es (enhanced, serving RNC)located in SRNC (Serving RNC)
Reordering + SHO combining functionality
MAC-e (enhanced)
located in the NodeB
HARQ, scheduling and PDU demultiplexing
Phy.
MAC-es/
MAC-e
UE
IP
Phy.
MAC-es
PDCP
RLC
IP relay
RNC
UTRAN
PDCP
Node B
Phy.
FP
Phy.
MAC-e FP
MAC-d
RLC
MAC-d
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HSUPA Terminal categories
Category Nr of codes TTI
Spreading
factor
Max
Throughput
1 1 10ms 4 700 kbps
2 2 10 and 2ms 4 1.44 Mbps
3 2 10ms 4 1.44 Mbps
4 2 10 and 2ms 2 2.88 Mbps
5 2 10ms 2 1.92 Mbps
6 4 10 and 2ms 2 5.76 Mbps
SF2: Higher speeds, but
lower processing gain
(requires better channel
conditions)
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EUL Overview
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