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All Rights Reserved Alcatel-Lucent 2008, #####

HSDPA

PART 1

Tee Kok Keong

November 2008


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All Rights Reserved Alcatel-Lucent 2008, TEENovember 2008

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




HARQ

7

8

Fast Scheduling

UE Categories



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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


Uplink (UL)

1. High Speed Dedicated Physical Control Channel (HS-DPCCH)

BPSK Modulation

Spreading Factor at 256

Contain Ack/Nack and CQI



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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




HARQ

7

8

Fast Scheduling

UE Categories



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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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Agenda

1

2

3

4

5

6

Introduction

Channel Structure




HARQ

7

8

Fast Scheduling

UE Categories



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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




HARQ

7

8

Fast Scheduling

UE Categories



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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




HARQ

7

8

Fast Scheduling

UE Categories



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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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