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HSDPA
PART 1
Tee Kok Keong
November 2008
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Introduction
High Speed Downlink Packet Access (HSDPA) concept is a natural extension of the
Downlink Shared Channel where it is mainly intended for non-real time traffic but
can also be used for traffic with tighter delay requirements.
HSDPA implementation includes advanced techniques such as
New High Speed Downlink Shared Channel (HS-DSCH)
Time and code multiplexing of UE
Fast Scheduling (every 2ms in the Node B)
Adaptive modulation and coding (QPSK and 16-QAM Modulation)
Advanced retransmission mechanism (Hybrid ARQ)
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Introduction
With the same radio resources, how is HSDPA capable in providing higher spectral
efficiency?
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Key Points
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Channel Structure
Physical Channel
There are three new physical channels; two for downlink and one for uplink
Downlink (DL)
1. High Speed Physical Downlink Shared Channel (HS-PDSCH)
QPSK or 16 QAM Modulation Fixed Spreading Factor at 16
Contain Data and 24 bit CRC
Does not support SHO
2. High Speed Shared Control Channel (HS-SCCH)
QPSK Modulation
Spreading Factor at 128
One UE can listen to a maximum of 4 HS-SCCHs/cell and up to 4 UEs/TTI
Does not support SHO
Uplink (UL)
1. High Speed Dedicated Physical Control Channel (HS-DPCCH)
BPSK Modulation
Spreading Factor at 256
Contain Ack/Nack and CQI
Does not support SHO
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Channel Structure
HS-PDSCH
There are three slots in one TTI where one time slot contains 2560 chips. Dependingon the modulation type, the symbol rate for QPSK and 16 QAM are 2 and 4respectively.
For QPSK modulation,
One time slot = 2 x 10 x 2 = 320 bits For 16 QAM modulation
One time slot = 4 x 10 x 2 = 640 bits
Slot #0 Slot#1 Slot #2
Tslot= 2560 chips, M*10*2k
bits (k=4)
Data
Ndata1bits
1 HS-PDSCH subframe: T f= 2 ms
4
4
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Channel Structure
HS-SCCH
HS-DPCCH
Slot #0 Slot#1 Slot #2
Tslot= 2560 chips, 40 bits
Data
Ndata1bits
1 HS-DSCH subframe: T f= 2 ms
Subframe #0 Subframe #i Subframe #4
HARQ-ACK CQI
One radio frame Tf= 10 ms
One HS-DPCCH subframe (2 ms)
2Tslot= 5120 chipsTslot= 2560 chips
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Channel Structure
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Channels Overview
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Protocol Stack
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Protocol Stack
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Radio Resource Allocation
Why is a shared channel more efficient to carry packet bursty traffic than a
dedicated channel?
WCDMA / R99
The WCDMA System normally carries user data over dedicated transport channel, DCH, which
brings maximum system performance with continuous user data. The DCH are code multiplexed onto one RF carrier.
HSDPA / R5
The HSDPA uses a shared channel known as HS-DSCH.
For bursty traffic, the demand for high data rate is sporadic. When a DCH isallocated, the resources are then dedicated to the respective UE. On the contrary,
when HS-DSCH is used, the resources are only allocated to the respective UE only
when the UE requests for it, thus maximising the used of the channel.
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Radio Resource Allocation
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Throughput Management
There is no more fast power control for HSDPA. As such, the modulation as well as
the number of codes are changed according to the radio conditions, where as for
R99, it offers constant data rate using power adaptability.
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Adaptive Modulation & Coding
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Adaptive Modulation & Coding
The Adaptive Modulation & Coding (AMC) optimises the spectral efficiency depending
on the radio conditions by maximising the user bit rate during its transmission time.
For example, when a SNR > y dB, the AMC selects 16 QAM as the modulation type
and a coding rate of and when a SNR < y dB, the AMC selects QPSK and a codingrate of .
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Agenda
1
2
3
4
5
6
Introduction
Channel Structure
Radio Resource Allocation
Throughput Management
Adaptive Modulation & Coding
HARQ
7
8
Fast Scheduling
UE Categories
9 Code Tree Allocation
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Hybrid Automatic Repeat Request (HARQ)
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Hybrid Automatic Repeat Request (HARQ)
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Hybrid Automatic Repeat Request (HARQ)
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Hybrid Automatic Repeat Request (HARQ)
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Hybrid Automatic Repeat Request (HARQ)
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HARQ - Parameter
This parameter is used to stop the retransmission of MAC-hs PDU.
This parameter defines the maximum number of MAC-hs retransmission.
This parameter defines the time to live for a MAC-hs SDU starting from the instant ofits arrival into an HSDPA PQ
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Fast Scheduling
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Fast Scheduling
Node B
DTCH
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Fast Scheduling First Stage
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Fast Scheduling First Stage
There are 5 types of scheduler (Proportional Fair, Alcatel Lucent Proportional Fair,
Max C/I, Round Robin and Fair) that can be employed in HSDPA. However, only two
types of scheduler are able to be used in UA5.1 namely Proportional Fair and Nortel
Proportional Fair.
Depending on the scheduler type, the scheduler will first select the Priority Queue
(PQ) based on the followings: Priority of the PQ (Priority 15 = Highest Priority, Priority 0 = Lowest Priority)
The number of Queue IDs (QID) present in the PQ
Cost function of the PQ (The evaluation of the cost relies on the credits of the queue and the
total number of PDUs already transmitted during past rounds. The PQ with the lowest cost
function is selected) Once the selection of the PQ is done, then the scheduler will assign the
corresponding credits to the respective PQ. The highest priority will be given the
greatest credit and the lowest priority will be give the smallest credit.
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Fast Scheduling Second Stage
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Fast Scheduling Second Stage
In the second stage, the aim is to share the resources among all users of the same
priority. In the PQ, there are at least one QID and as such some PQs may have more
than one QID. The selection of the QID is based on the followings:
Scheduler Type
SPI and UE category
When the QID is selected, it will then determine the amount of data to transfer, the
number of codes and the power to use.
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Fast Scheduling
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Fast Scheduling
1. Alcatel Lucent Proportional Fair
Users are chosen according to the number of transmitted bits and the reported CQI.
2. Proportional Fair
Users are chosen according to the instantaneous CQI versus the average CQI.3. Round Robin
Users are chosen one after the other.
4. Max C/I
Users with the best CQI are scheduled first.
5. Fair Users with the lowest throughput are scheduled first.
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Scheduling - Parameter
This parameter defines the forgetting factor of the averaging window used by the cost
function of the scheduler
This parameter allows the user to chose the scheduler type whether Alcatel Lucent
Proportional Fair, Proportional Fair, Round Robin, Max CQI and Fair. In UA5.1, only
Alcatel Lucent Proportional Fair and Proportional Fair are used.
This parameter is used to determine the relative throughput per SPI.
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Scheduling - Parameter
This parameter defines the UE category management. When ueCategoryEquity is
chosen, then all UE categories will reach the same throughput in average at the sameCQI. When ueCategoryProportionality is chosen, then the UEs throughput depend ontheir category.
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C d T All i
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Code Tree Allocation
Other Common Channels such as CPICH, PICH,
AICH and P-CCPCH are at SF256.
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