hsdpa(ran14.0_04).pdf

HSDPA RAN14.0

Feature Parameter Description

Issue 04

Date 2013-05-10

HUAWEI TECHNOLOGIES CO., LTD.

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WCDMA RAN

HSDPA Contents

Issue 04 (2013-05-10) Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.

ii

Contents

1 Introduction ................................................................................................................................ 1-1

1.1 Scope ............................................................................................................................................ 1-1

1.2 Intended Audience......................................................................................................................... 1-1

1.3 Change History .............................................................................................................................. 1-1

2 Overview of HSDPA .................................................................................................................. 2-1

2.1 General Principles of HSDPA ........................................................................................................ 2-1

2.2 HSDPA Channels .......................................................................................................................... 2-1

2.2.1 HS-DSCH and HS-PDSCH .................................................................................................. 2-2

2.2.2 HS-SCCH ............................................................................................................................. 2-2

2.2.3 HS-DPCCH ........................................................................................................................... 2-2

2.2.4 DPCCH and DPCH/F-DPCH ................................................................................................ 2-2

2.3 Impact of HSDPA on NEs .............................................................................................................. 2-3

2.4 HSDPA Functions .......................................................................................................................... 2-4

2.4.1 HSDPA Control Plane Functions .......................................................................................... 2-4

2.4.2 HSDPA User Plane Functions .............................................................................................. 2-5

3 Control Plane ............................................................................................................................. 3-1

3.1 Bearer Mapping ............................................................................................................................. 3-1

3.2 Access Control .............................................................................................................................. 3-2

3.3 Mobility Management .................................................................................................................... 3-2

3.4 Channel Switching......................................................................................................................... 3-2

3.5 Load Control .................................................................................................................................. 3-5

3.6 Power Resource Management ...................................................................................................... 3-5

3.7 Code Resource Management ....................................................................................................... 3-6

3.7.1 HS-SCCH Code Resource Management ............................................................................. 3-6

3.7.2 HS-PDSCH Code Resource Management........................................................................... 3-6

3.7.3 Dynamic Code Tree Reshuffling ........................................................................................... 3-8

4 User Plane ................................................................................................................................... 4-1

4.1 Flow Control and Congestion Control ........................................................................................... 4-1

4.1.1 Flow Control ......................................................................................................................... 4-2

4.1.2 Congestion Control ............................................................................................................... 4-2

4.2 Impact of HSDPA on the RLC and MAC-d Entities ....................................................................... 4-3

4.2.1 Impact on the RLC Entity ...................................................................................................... 4-3

4.2.2 Impact on the MAC-d Entity .................................................................................................. 4-3

4.3 MAC-hs Scheduling ...................................................................................................................... 4-3

4.3.1 Determining the Candidate Set ............................................................................................ 4-4

4.3.2 Calculating Scheduling Priorities .......................................................................................... 4-4

4.3.3 Time and HS-PDSCH Codes Multiplex ................................................................................ 4-8

4.4 HARQ ............................................................................................................................................ 4-9

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4.4.1 HARQ Retransmission Principles ......................................................................................... 4-9

4.4.2 Soft Combining During HARQ ............................................................................................ 4-10

4.4.3 Preamble and Postamble ................................................................................................... 4-10

4.5 TFRC Selection ........................................................................................................................... 4-11

4.6 HSDPA Remaining Power Appending ......................................................................................... 4-12

4.7 CQI Adjustment Based on Dynamic BLER Target ...................................................................... 4-13

4.8 BLER Optimization for HSDPA Burst Services ........................................................................... 4-14

4.9 Modulation Scheme .................................................................................................................... 4-14

5 QoS Management and Management over Differentiated Services .............................. 5-1

5.1 QoS Management ......................................................................................................................... 5-1

5.2 Diff-Serv Management .................................................................................................................. 5-2

6 Related Features ....................................................................................................................... 6-1

6.1 WRFD-010610 HSDPA Introduction Package .............................................................................. 6-1

6.1.1 Prerequisite Features ........................................................................................................... 6-1

6.1.2 Mutually Exclusive Features ................................................................................................. 6-1

6.1.3 Impacted Features ................................................................................................................ 6-1

6.2 WRFD-010653 96 HSDPA Users per Cell .................................................................................... 6-1



6.2.3 Impacted Features ................................................................................................................ 6-1

6.3 WRFD-010654 128 HSDPA Users per Cell .................................................................................. 6-1



6.3.3 Impacted Feature ................................................................................................................. 6-1

6.4 WRFD-030010 CQI Adjustment Based on Dynamic BLER Target ............................................... 6-2




6.5 WRFD-140221 HSDPA Scheduling based on UE Location .......................................................... 6-2




7 Network Impact .......................................................................................................................... 7-1


7.1.1 System Capacity ................................................................................................................... 7-1

7.1.2 Network Performance ........................................................................................................... 7-1

7.2 WRFD-010653 96 HSDPA Users per Cell .................................................................................... 7-1

7.2.1 System Capacity ................................................................................................................... 7-1


7.3 WRFD-010654 128 HSDPA Users per Cell .................................................................................. 7-1

7.3.1 System Capacity ................................................................................................................... 7-1

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7.4 WRFD-030010 CQI Adjustment Based on Dynamic BLER Target ............................................... 7-1

7.4.1 System Capacity ................................................................................................................... 7-1


7.5 WRFD-140221 HSDPA Scheduling based on UE Location .......................................................... 7-2

7.5.1 System Capacity ................................................................................................................... 7-2


8 Engineering Guidelines ........................................................................................................... 8-1


8.1.1 When to Use HSDPA Introduction Package ......................................................................... 8-1

8.1.2 Information to Be Collected .................................................................................................. 8-1

8.1.3 Feature Deployment ............................................................................................................. 8-1

8.1.4 Performance Monitoring ....................................................................................................... 8-2

8.2 WRFD-01061001 15 Codes per Cell ............................................................................................ 8-3

8.2.1 When to Use 15 Codes per Cell ........................................................................................... 8-3



8.3 WRFD-01061018 Time and HS-PDSCH Codes Multiplex ............................................................ 8-5

8.3.1 When to Use Time and HS-PDSCH Codes Multiplex .......................................................... 8-5



8.4 WRFD-01061009 HSDPA H-ARQ & Scheduling (MAX C/I, RR, and PF) .................................... 8-6

8.4.1 When to Use HSDPA H-ARQ & Scheduling (MAX C/I, RR, and PF .................................... 8-6



8.5 WRFD-01061005 HSDPA Static Code Allocation and RNC-Controlled Dynamic Code Allocation

............................................................................................................................................................. 8-7

8.5.1 When to Use HSDPA Static Code Allocation and RNC-Controlled Dynamic Code Allocation

....................................................................................................................................................... 8-7



8.6 WRFD-01061010 HSDPA Flow Control ........................................................................................ 8-8

8.6.1 When to Use HSDPA Flow Control ...................................................................................... 8-8



8.7 WRFD-01061006 HSDPA Mobility Management ........................................................................ 8-10

8.7.1 When to Use HSDPA Mobility Management ...................................................................... 8-10

8.7.2 Information to Be Collected ................................................................................................ 8-10

8.7.3 Feature Deployment ........................................................................................................... 8-10

8.8 WRFD-01061002 HSDPA UE Category 1 to 28 ......................................................................... 8-11

8.8.1 When to Use HSDPA UE Category 1 to 28 ........................................................................ 8-11


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8.9 WRFD-010629 DL 16QAM Modulation ....................................................................................... 8-11

8.9.1 When to Use DL 16QAM Modulation ................................................................................. 8-11



8.10 WRFD-010631 Dynamic Code Allocation Based on NodeB ..................................................... 8-13

8.10.1 When to Use Dynamic Code Allocation Based on NodeB ............................................... 8-13

8.10.2 Information to Be Collected .............................................................................................. 8-13

8.10.3 Feature Deployment ......................................................................................................... 8-13

8.11 WRFD-010611 HSDPA Enhanced Package ............................................................................. 8-16

8.11.1 When to Use HSDPA Enhanced Package ........................................................................ 8-16



8.12 WRFD-01061103 Scheduling based on EPF and GBR ............................................................ 8-16


8.13 WRFD-010653 96 HSDPA Users per Cell ................................................................................ 8-17

8.13.1 When to Use 96 HSDPA Users per Cell ........................................................................... 8-17



8.14 WRFD-010654 128 HSDPA Users per Cell .............................................................................. 8-19

8.14.1 When to Use 128 HSDPA Users per Cell ......................................................................... 8-19



8.15 WRFD-030010 CQI Adjustment Based on Dynamic BLER Target ........................................... 8-21

8.15.1 When to Use CQI Adjustment Based on Dynamic BLER Target ...................................... 8-21



8.15.4 Feature Monitoring ........................................................................................................... 8-22

8.16 WRFD-140221 HSDPA Scheduling based on UE Location ...................................................... 8-22

8.16.1 When to Use HSDPA Scheduling based on UE Location ................................................ 8-22


8.16.3 Performance Optimization ................................................................................................ 8-24

8.17 HSDPA Remaining Power Appending ....................................................................................... 8-24

8.17.1 When to Use HSDPA Remaining Power Appending ........................................................ 8-24



8.17.4 Performance Optimization ................................................................................................ 8-26

8.18 BLER Optimization for HSDPA Burst Services ......................................................................... 8-26

8.18.1 When to Use BLER Optimization for HSDPA Burst Services ........................................... 8-26



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9 Parameters.................................................................................................................................. 9-1

10 Counters.................................................................................................................................. 10-1

11 Glossary .................................................................................................................................. 11-1

12 Reference Documents ......................................................................................................... 12-1

WCDMA RAN

HSDPA 1 Introduction



1-1

1 Introduction

1.1 Scope

This document describes the HSDPA functional area. It provides an overview of the main functions and goes into details regarding HSDPA control and user plane functions.

1.2 Intended Audience

This document is intended for:

Personnel who are familiar with WCDMA basics

Personnel who need to understand HSDPA

Personnel who work with Huawei products

1.3 Change History

This section provides information on the changes in different document versions.

There are two types of changes, which are defined as follows:

Feature change: refers to the change in the HSDPA feature.

Editorial change: refers to the change in wording or the addition of the information that was not described in the earlier version.

Document Issues

The document issues are as follows:

04 (2013-05-10)

03 (2012-11-30)

02 (2012-07-20)

01 (2012-04-30)

Draft A (2012-02-15)

04 (2013-05-10)

This is the document for the fourth commercial release of RAN14.0.

Compared with issue 03 (2012-11-30) of RAN14.0, this issue incorporates the changes described in the following table.

Change Type Change Description Parameter Change

Feature change None None

Editorial change

Added the description about related features and network impact of the following features and optimized the description about engineering guidelines:

WRFD-010610 HSDPA Introduction Package

WRFD-010653 96 HSDPA Users per Cell

WRFD-010654 128 HSDPA Users per Cell

WRFD-030010 CQI Adjustment Based on Dynamic

None

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1-2

BLER Target

WRFD-140221 HSDPA Scheduling Based on UE Location

For details, see chapters as follows:

6 Related Features

7 Network Impact

8 Engineering Guidelines

03 (2012-11-30)

This is the document for the third commercial release of RAN14.0.



Feature change Added the HSDPA remaining power appending algorithm. For details, see section 4.6 "HSDPA Remaining Power Appending."

Added the BLER Optimization for HSDPA Burst Services function and the engineering guidelines about this function. For details, see section 4.8 "BLER Optimization for HSDPA Burst Services" and 8.18 "BLER Optimization for HSDPA Burst Services."

None

Editorial change

Optimized the description to increase the readability. None

02 (2012-07-20)

This is the document for the second commercial release of RAN14.0.




Editorial change Added the procedures for deploying features used in this document. For details, see 8 "Engineering Guidelines."

None

01 (2012-04-30)

This is the document for the first commercial release of RAN14.0.

Compared with issue Draft A (2012-02-15) of RAN14.0, this issue incorporates the changes described in the following table.

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Editorial change The description about performance monitoring of the feature HSDPA scheduling based on UE location is modified.

None

Draft A (2012-02-15)

This is the first draft of the document for RAN14.0.

Compared with 03 (2011-10-30) of RAN13.0, this issue incorporates the following changes:


Feature change The EPF_LOC algorithm (WRFD-140221 HSDPA Scheduling based on UE Location) is added. For details, see 4.3 "MAC-hs Scheduling. "

The added parameter is LOCWEIGHT.

Editorial change The description is optimized. None

WCDMA RAN

HSDPA 2 Overview of HSDPA



2-1

2 Overview of HSDPA

2.1 General Principles of HSDPA

To meet the rapidly growing demands for data services on the mobile network, 3GPP Release 5 introduced HSDPA in 2005. HSDPA improves the downlink capacity, increases the user data rate greatly, and reduces the transmission delay on the WCDMA network.

The characteristics of HSDPA are as follows:

Fast scheduling Fast scheduling introduced into the NodeB determines the UEs for data transmission in each TTI (2 ms) and dynamically allocates resources to these UEs. It improves the usage of system resources and increases the system capacity.

For details about how Huawei RAN implements fast scheduling, see section4.3 "MAC-hs Scheduling."

Fast HARQ Fast hybrid automatic repeat request (HARQ) is used to rapidly request the retransmission of erroneously received data.

Specifically, when the UE detects an erroneous data transmission, it saves the received data and requests the NodeB to retransmit the original data at the physical layer. Before decoding, the UE performs soft combining of the saved data and the retransmitted data. The combining fully uses the data transmitted each time and therefore increases the decoding success rate. In addition, the retransmission delay at the physical layer is reduced greatly, compared with that at the RLC layer.

For details about how Huawei RAN implements fast HARQ, see section 4.4 "HARQ."

Fast AMC To compensate for channel variations, the DCH performs power control. To achieve this goal, HSDPA also performs fast adaptive modulation and coding (AMC), that is, adjusts the modulation scheme and coding rate in each TTI. AMC is based on the channel quality indicator (CQI) reported by the UE, and its purpose is to select an appropriate transmission rate to meet channel conditions. When the channel conditions are good, 16QAM or 64QAM can be used to provide higher transmission rates. When the channel conditions are poor, QPSK can be used to ensure the transmission quality.

For details about how Huawei RAN implements fast AMC, see section 4.5 "TFRC Selection."

The MAC-hs, a new MAC sublayer, is introduced into the UE and NodeB to support HSDPA.

2.2 HSDPA Channels

To support the HSDPA technologies, 3GPP defines one transport channel (HS-DSCH) and three physical channels (HS-PDSCH, HS-SCCH, and HS-DPCCH).

Figure 2-1 shows the physical channels of HSDPA in the shaded area.

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2-2

Figure 2-1 Physical channels of HSDPA

2.2.1 HS-DSCH and HS-PDSCH

HS-DSCH is a high-speed downlink shared channel. Its TTI is fixed to 2 ms. It may be mapped onto one or more HS-PDSCHs.

HS-PDSCH is a high-speed physical downlink shared channel. Its spreading factor is fixed to 16. According to 3GPP TS 25.433, a maximum of 15 HS-PDSCHs can be used for transmission at the same time. The number of HS-PDSCHs per cell is configurable.

The use of 2 ms TTI reduces the round trip time (RTT) on the Uu interface and, together with AMC, improves the tracking of channel variations. In addition, the use of 2 ms TTI enables fast scheduling and resource allocation and therefore improves the usage of transmission resources.

In each TTI, HSDPA assigns the HS-PDSCHs onto which the HS-DSCH maps. More HS-PDSCHs can provide higher transmission rates.

Unlike the DCH, the HS-DSCH cannot support soft handover. The reason is that this type of handover requires different cells to use the same radio resource for sending the same data to the UE, but the scheduling function can be performed only within the cell.

2.2.2 HS-SCCH

HS-SCCH is a high-speed shared control channel. It carries the control information related to the HS-PDSCH. The control information includes the UE identity, HARQ-related information, and information about transport format and resource combination (TFRC). For each transmission of the HS-DSCH, one HS-SCCH is required to carry the related control information. One cell can be configured with several HS-SCCHs. The number of HS-SCCHs determines the maximum number of UEs that can be scheduled simultaneously in each TTI.

2.2.3 HS-DPCCH

HS-DPCCH is a high speed dedicated physical control channel. In the uplink, each HSDPA UE must be configured with an HS-DPCCH. This channel is mainly used by the UE to report the CQI and whether a transport block is correctly received. The information about the transport block is used for fast retransmission at the physical layer. The CQI is used for AMC and scheduling to allocate Uu resources.

2.2.4 DPCCH and DPCH/F-DPCH

DPCCH is a dedicated physical control channel in the uplink. DPCH is a dedicated physical channel in the downlink. F-DPCH is a fractional dedicated physical channel in the downlink.

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The HSDPA UE must be configured with dedicated physical control channels in both the uplink and the downlink.

The uplink DPCCH is used for closed-loop power control by working with the DPCH or F-DPCH. In addition, the uplink DPCCH power is used as a reference for the HS-DPCCH power.

The downlink DPCH is used for inner-loop power control and as a reference for the HS-PDSCH power.

Like the downlink DPCH, the F-DPCH is also used for inner-loop power control. The difference is that each UE must have a downlink DPCH (SF256) whereas 10 UEs can share an F-DPCH (SF256) to save downlink channel codes.

2.3 Impact of HSDPA on NEs

HSDPA has the following impacts on the RNC, NodeB, and UE.

On the control plane of the network side, the RNC processes the signaling about HSDPA cell configuration, HS-DSCH related channel configuration, and mobility management. On the user plane of the network side, the RLC layer and MAC-d of the RNC are unchanged. At the NodeB, the MAC-hs is added to implement HSDPA scheduling, Uu resource allocation, AMC, and Iub flow control. The MAC-hs implements these management functions in a short time. Therefore, it reduces both unnecessary delays and processing complexity caused by Iub message exchange.

On the UE side, the MAC-hs is added between the MAC-d and the physical layer for data reception. To support HSDPA (without considering HSPA evolution), 3GPP defines 12 UE categories. These UEs support different peak rates at the physical layer, ranging from 912 kbit/s to 14 Mbit/s. The UE of category 10 supports the highest rate. The UE of category 11 or 12 supports only the QPSK mode. For details, see 3GPP TS 25.306. Huawei RAN supports all the UE categories.

Table 2-1 lists the capabilities of HSDPA UEs of different categories.

Table 2-1 Capabilities of HSDPA UEs of different categories

UE Category

Maximum Number of HS-DSCH Codes

Minimum TTI Maximum Number of Data Blocks

Maximum Data Rate (Mbit/s)

1 5 3 7298 1.2

2 5 3 7298 1.2

3 5 2 7298 1.8

4 5 2 7298 1.8

5 5 1 7298 3.6

6 5 1 7298 3.6

7 10 1 14411 7.2

8 10 1 14411 7.2

9 15 1 20251 10.2

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10 15 1 27952 14.4

11 5 2 3630 0.9

12 5 1 3630 1.8

2.4 HSDPA Functions

HSDPA functions are implemented on the HSDPA control plane and user plane.

2.4.1 HSDPA Control Plane Functions

The control plane is responsible for setting up and maintaining HS-DSCH connections and managing cell resources.

Figure 2-2 shows the HSDPA control plane functions based on the service connection setup and maintenance procedure.

Figure 2-2 HSDPA control plane functions

The HSDPA control plane functions are described as follows:

Bearer mapping

The bearer mapping is used by the network side to configure the RAB during the setup of a service connection in the cell. The network side then configures bearer channels for the UE based on the requested service type, service rate, UE capability, and cell capability.

For details, see section 3.1 "Bearer Mapping."

Access control

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Access control, a sub-function of load control, checks whether the current resources of the cell are sufficient for the service connection setup. If the resources are insufficient, intelligent access control is triggered. If the resources are sufficient, the service connection can be set up.

For details, see section 3.2 "Access Control."

Mobility management

For the established HS-DSCH connection, mobility management decides whether to switch it to another cell for providing better services, based on the channel quality of the UE.

For details, see section 3.3 "Mobility Management."

Channel switching

Channel switching is responsible for switching the transport channel among the HS-DSCH, DCH, and FACH based on the requirements of mobility management or load control.

For details, see section 3.4 "Channel Switching."

Load control

When the cell load increases, the load control function adjusts the resources configured for the established radio connections to avoid cell overload.

For details, see section 3.5 "Load Control."

Resource management

Resource management coordinates the power resource between the HS-DSCH and the DCH and the code resource between the HS-SCCH and the HS-PDSCH. The downlink power and codes are the bottleneck resources of the cell. Resource management can increase the HSDPA capacity.

Power resource management reserves power for channels of different types and allocates power for them. For details, see section 3.6 "Power Resource Management."

Code resource management allocates and reserves code resources for channels of different types. In addition, it collects and reshuffles idle code resources.

For details, see section 3.7 "Code Resource Management."

2.4.2 HSDPA User Plane Functions

After the service is set up, the user plane is responsible for implementing data transmission. Figure 2-3 shows the HSDPA user plane functions based on the data processing procedure.

Figure 2-3 HSDPA user plane functions

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The service data is passed to the RLC layer and MAC-d of the RNC for processing and encapsulation. Then, the MAC-d PDU is formed and passed through the Iub/Iur interface to the NodeB/RNC. To avoid congestion, the flow control and congestion control functions control the traffic on the Iub/Iur interface through the HS-DSCH frame protocol (3GPP TS 25.435).

After the MAC-d PDU is received by the NodeB, it is passed through the MAC-hs to the physical layer and then sent out through the Uu interface. The MAC-hs provides MAC-hs scheduling, TFRC selection, and HARQ. MAC-hs scheduling determines the HSDPA users in the cell for data transmission. TFRC selection determines the transmission rates and Uu resources to be allocated to the HSDPA UEs. HARQ is used to implement the hybrid automatic repeat request function.

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HSDPA 3 Control Plane



3-1

3 Control Plane

This chapter consists of the following sections:

Bearer Mapping

Access Control

Mobility Management

Channel Switching

Load Control

Power Resource Management

Code Resource Management

3.1 Bearer Mapping

The HS-DSCH can carry services of multiple types and service combinations, as listed in Table 3-1.

Table 3-1 Bearer mapping

CN Domain Service Type Can Be Carried on HS-DSCH?

Optional Feature?

- Signaling (SRB) Yes Yes

Feature name: SRB over HSDPA

CS Voice Yes Yes

Feature name: CS Voice over HSPA/HSPA+

Videophone No No

Streaming No No

PS Conversational Yes Yes

Feature name: VoIP over HSPA/HSPA+

Streaming Yes Yes

Feature name: Streaming Traffic Class on HSDPA

Interactive Yes No

Background Yes No

IMS signaling Yes Yes

Feature name: IMS Signaling over HSPA

MBMS PTP Yes Yes

Feature name: MBMS P2P over HSDPA

During the service setup, the RNC selects appropriate channels based on the UE capability, cell capability, and service parameters to optimize the use of cell resources and ensure the QoS. Huawei RAN supports the setting of the types of RABs carried on the HS-DSCH according to service requirements. For details, see Radio Bearers Feature Parameter Description.

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3-2

3.2 Access Control

Access control determines whether an HS-DSCH connection can be set up under the precondition that the QoS is ensured. The determination is based on the status of cell resources and the situation of Iub/Iur congestion. When the resources are insufficient, the HS-DSCH is switched to the DCH and only the DCH connection is set up. When the resources are sufficient, the DCH is switched to the HS-DSCH. The implementation of this function requires the support of channel switching. For details, see Call Admission Control Feature Parameter Description.

Access control allows the HSDPA UE to access an inter-frequency neighboring cell that has the same-coverage area as the source cell. The purpose is to achieve load balance between the cells and improve HSDPA user experience. This is HSDPA directed retry decision (DRD), an optional feature. For details, see Directed Retry Decision Feature Parameter Description.

3.3 Mobility Management

The DCH supports soft handover, and therefore downlink data can be concurrently sent out from all the cells in the active set in DCH transmission. In comparison, the HS-DSCH does not support soft handover, and therefore downlink data can be sent out only from the HS-DSCH serving cell and inter-cell handover has to be performed through the change of the serving cell. Therefore, HSDPA mobility management (WRFD-01061006 HSDPA Mobility Management) focuses on the change of the HS-DSCH serving cell.

For the UE with the HS-DSCH service, the best cell in the active set acts as the HS-DSCH serving cell. When the best cell changes, the UE disconnects the HS-DSCH from the source cell and attempts to set up a new HS-DSCH connection with the new best cell. For details, see Handover Feature Parameter Description. By changing the HS-DSCH switching threshold, you can modify the conditions for triggering the change of the best cell. Lowering this threshold can increase both the handover frequency and the sensitivity of HS-DSCH switching to signal variations in the serving cell. Raising this threshold can reduce the handover frequency but may increase the probability of the HS-DSCH service being discontinuous or even dropping on the cell edge. For the HS-DSCH service, Huawei supports inter-cell intra-frequency handover, inter-cell inter-frequency handover, and inter-RAT handover.

Mobility management may trigger the switching from the HS-DSCH to the DCH. If the UE with the HS-DSCH service cannot set up the HS-DSCH connection with the target cell, the channel switching function, together with mobility management, switches the HS-DSCH to the DCH. When the HS-DSCH connection is available, the channel switching function switches the DCH back to the HS-DSCH. When the HSDPA user returns from the DCH cell to the HSDPA cell, the DCH is set up to ensure successful handover. A certain period (ChannelRetryHoTimerLen) later after the handover, the channel switching function switches the DCH to the HS-DSCH. For details, see Handover Feature Parameter Description and section 3.4 "Channel Switching."

3.4 Channel Switching

After the HS-DSCH is introduced, the UE can stay in a new state, CELL_DCH (with HS-DSCH). Therefore, there are additional transitions between CELL_DCH (with HS-DSCH) and CELL_FACH and transitions between CELL_DCH (with HS-DSCH) and CELL_DCH even when both the cell and the UE support the HS-DSCH, as shown in Figure 3-1.

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Figure 3-1 UE state transition (WRFD-01061111 HSDPA State Transition)

Table 3-2 lists new state transition and new channel switching.

Table 3-2 New state transition and new channel switching

New State Transition New Channel Switching

CELL_DCH (with HS-DSCH) CELL_FACH HS-DSCH FACH

CELL_DCH (with HS-DSCH) CELL_DCH HS-DSCH DCH

Here, the switching between HS-DSCH and FACH can be triggered by traffic volume, which is similar to the switching between DCH and FACH. For details, see State Transition Feature Parameter Description.

In addition, when the cell load is too high, load control may also trigger the switching from the HS-DSCH to the FACH to relieve congestion. For details, see Load Control Feature Parameter Description.

As the HS-DSCH is introduced later, it is inevitable that some cells support the HS-DSCH but others do not. This is also the case with UEs. When a service is set up, the channel switching function selects an appropriate bearer channel based on the cell capability and UE capability to ensure the QoS while efficiently using the cell resources. When the user is moving, the channel switching function adjusts the channel type based on the UE capability to ensure service continuity while improving user experience.

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Figure 3-2 Relationships between channel switching and other functions

Triggers for switching from the HS-DSCH to the DCH are as follows:

The HS-DSCH is selected during the service setup but neither the resources of the serving cell nor the resources of the inter-frequency same-coverage neighboring cell are sufficient. In this case, the HS-DSCH is switched to the DCH. This function is achieved by means of non-periodic directed retry decision (DRD). For details about non-periodic DRD, see Directed Retry Decision Feature Parameter Description.

The HS-DSCH serving cell changes. The UE attempts to set up a new HS-DSCH connection with the new best cell. In such a case, the possible scenarios are as follows:

If the new best cell does not support the HS-DSCH, the UE cannot set up the HS-DSCH connection. In this case, the HS-DSCH is switched to the DCH.

If the new best cell supports the HS-DSCH but a new HS-DSCH connection cannot be set up because the resources are insufficient, the DCH connection is set up and the HS-DSCH is switched to this DCH.

For details, see Handover Feature Parameter Description.

The user moves from a cell supporting the DCH but not supporting the HS-DSCH to a cell supporting the HS-DSCH. In this case, the DCH connection is also set up because the DCH supports soft handover, which can increase the handover success rate.

In one of the cases described previously, the DCH connection is set up in a cell supporting the HS-DSCH or in an inter-frequency same-coverage neighboring cell supporting the HS-DSCH. Then, the DCH is switched to the HS-DSCH by either of the following mechanisms:

Channel switching based on timer

After the DCH connection is set up, this mechanism periodically attempts to switch the DCH to the HS-DSCH. This function is achieved by means of periodic DRD. For details about periodic DRD, see Directed Retry Decision Feature Parameter Description.

Channel switching based on traffic volume

When the traffic volume of the UE increases and the RNC receives an 4A event report, this mechanism attempts to switch the DCH to the HS-DSCH. For details on the 4A event report, see State Transition Feature Parameter Description.

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3.5 Load Control

When the cell is congested, load control selects some users (including HSDPA users) for congestion relief. The selection is based on the integrated priority, which considers the allocation retention priority (ARP), traffic class (TC), traffic handling priority (THP), and bearer type. When the cell load is high, the basic congestion control selects some HSDPA users for handover to an inter-frequency same-coverage neighboring cell or an inter-RAT neighboring cell with lower load. When the cell load is too high, the overload congestion control selects some HSDPA BE services for the switching to a common channel or releases some HSDPA services. For details, see Load Control Feature Parameter Description.

3.6 Power Resource Management

Power resource management (WRFD-01061019 HSDPA Dynamic Power Allocation) determines the transmit power of the HS-PDSCH, HS-SCCH, and HS-DPCCH.

The downlink power resources of HSDPA can be dynamically allocated as follows:

1. The downlink power resources are first reserved for common physical channels and allocated to the DPCH. The remaining power resources are available for HSPA, including HSUPA and HSDPA.

2. The HSPA power resources are first allocated to the HSUPA downlink control channels, including the E-AGCH, E-RGCH, and E-HICH. The remaining power resources are available for HSDPA.

3. The HSDPA power resources are first allocated to the downlink control channel HS-SCCH. For details, see Power Control Feature Parameter Description. The remaining power resources are allocated to the traffic channel HS-PDSCH.

For details on power resource allocation, see section 4.5 "TFRC Selection."

Figure 3-3 shows the dynamic HSDPA power resource allocation.

Figure 3-3 Dynamic HSDPA power resource allocation

Every TTI, the NodeB detects the power usage of R99 channels to determine the power available for HSPA. To reserve the power for R99 power control itself, the power margin PwrMgn needs to be set on the NodeB side. In addition, the power allocated to HSPA must not exceed the maximum permissible power HspaPower, which can be set on the RNC side.

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For details on uplink HS-DPCCH power control, see Power Control Feature Parameter Description.

3.7 Code Resource Management

Code resource management allocates code resources to the HS-SCCH and HS-PDSCH.

The NodeB supports HS-DSCH transmissions to multiple users in parallel in a TTI. If more than one HS-PDSCH code can be allocated by the NodeB, then code multiplexing can be used to allocate the codes to multiple users to improve resource usage and system throughput.

3.7.1 HS-SCCH Code Resource Management

Each HS-SCCH uses an SF128 code. The number of HS-SCCHs determines the maximum number of HSDPA users that can be scheduled simultaneously in a TTI. Generally, the number of HS-SCCHs depends on the traffic characteristics of the cell. The default number is 4, which is specified by the parameter HsScchCodeNum on the RNC side. If the default number is used, the HS-PDSCH can use only 14 SF16 codes. To enable the HS-PDSCH to use 15 SF16 codes, you are advised to configure 2 HS-SCCHs.

3.7.2 HS-PDSCH Code Resource Management

This section describes the feature WRFD-01061005 HSDPA Static Code Allocation and RNC-Controlled Dynamic Code Allocation and the feature WRFD-010631 Dynamic Code Allocation Based on NodeB.

The transport channel HS-DSCH is mapped on one or several High-Speed Physical Downlink Shared Channels (HS-PDSCHs) which are simultaneously received by the UE. As indicated in 3GPP specifications, there are up to 15 HS-PDSCHs per cell with the spreading factor fixed to 16.

The number of the HS-PDSCHs per NodeB is configurable and dependent on the license. The license specifies the maximum number of SF16 codes purchased by the operator. The license works at the NodeB level, which means all cells under a NodeB share the license. The NodeB can dynamically allocate license codes to the HS-PDSCHs between cells based on the actual requirements. The number of available HS-PDSCH codes for a cell is the number of license codes allocated by the NodeB or the number of HS-PDSCH codes allocated by the function of HS-PDSCH code resource management, whichever is smaller.

The function of HS-PDSCH code resource management is used to share the cell code resources between DPCH and HS-PPDCH in a cell. As the DPCH and the HS-PDSCH coexist in a cell, sharing the cell code resources between them is of critical importance in HSDPA code resource management.

The function of HS-PDSCH code resource management supports both RNC-level and NodeB-level code resource management. RNC-controlled static or dynamic code allocation is enabled through the parameter AllocCodeMode. NodeB-controlled dynamic code allocation is enabled through the parameter DynCodeSw.

If the RNC-controlled static code allocation is used:

The number of reserved HS-PDSCH codes is specified by the cell-level parameter HsPdschCodeNum. Based on the reserved number, the RNC reserves codes for the HS-PDSCH. The DPCH, HS-SCCH, and common channels use the other codes. The cell-level parameter HsPdschCodeNum can be set based on the traffic characteristics of the cell.

Figure 3-4 shows the RNC-controlled static code allocation.

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Figure 3-4 RNC-controlled static code allocation

If the RNC-controlled dynamic code allocation is used:

The minimum number of HS-PDSCH codes is specified by the cell-level parameter HsPdschMinCodeNum. The purpose of this setting is to prevent too many DCH users from being admitted and to ensure the basic data transmission of the HS-PDSCH.

The maximum number of HS-PDSCH codes is specified by the cell-level parameter HsPdschMaxCodeNum. The purpose of this setting is to prevent too many codes from being allocated for the HS-PDSCH and to prevent DCH users from preempting codes during admission.

The number of codes that can be shared between HS-PDSCH and DPCH is equal to the value of HsPdschMaxCodeNum minus the value of HsPdschMinCodeNum, as shown in Figure 3-5. When a code that can be shared is idle, it can be allocated to the HS-PDSCH if the idle code is adjacent to the allocated HS-PDSCH codes.

Figure 3-5 RNC-controlled dynamic code allocation

If the NodeB-Controlled Dynamic Code Allocation is used:

Generally, the NodeB can use the HS-PDSCH codes only allocated by the RNC. The NodeB-controlled dynamic code allocation, however, allows the NodeB to temporarily allocate idle codes to the HS-PDSCH.

Every TTI, the NodeB detects the SF16 codes that are not allocated to the HS-PDSCH. If such an SF16 code or any of its subcodes is allocated by the RNC to the DCH or a common channel, this SF16 code is regarded as occupied. Otherwise, it is regarded as unoccupied. Therefore, the available HS-PDSCH codes include the codes reserved by the RNC and the idle codes adjacent to the allocated HS-PDSCH codes.

If the setup of an RL requires a DPCH code that is already allocated by the NodeB to the HS-PDSCH, the NodeB releases this code and allocates it to an R99 user. Then, the NodeB sends an NBAP message to the RNC, indicating that the RL is set up successfully.

Figure 3-6 NodeB-controlled dynamic code allocation

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The dynamic code allocation controlled by the NodeB is more flexible than the dynamic code allocation controlled by the RNC. The dynamic code allocation controlled by the NodeB shortens the code allocation duration and reduces the number of Iub signaling messages transmitted for code reallocation.

If NodeB-controlled dynamic code allocation is enabled, the RNC-controlled dynamic code allocation is disabled dynamically.

Huawei recommends the following code allocation modes, where the first mode is preferred:

Configure the RNC to use static code allocation and the NodeB to use dynamic code allocation.

If the NodeB does not support dynamic code allocation, configure the RNC to use dynamic code allocation.

If not all the NodeBs controlled by an RNC support dynamic code allocation, the RNC-controlled dynamic code allocation is recommended. In this case, the NodeB-controlled dynamic code allocation can also be enabled for those supporting NodeBs.

3.7.3 Dynamic Code Tree Reshuffling

RegardlessThe HS-PDSCH can use only continuous SF16 codes, regardless of whether the RNC or NodeB controls the dynamic code allocation. By reallocating DPCH or F-DPCH codes, the dynamic code tree reshuffling function can maximize the number of continuous SF16 codes available for the HS-PDSCH.

Dynamic code tree reshuffling takes effect only when the following conditions are met:

The cell is not in the basic congestion state that is triggered by code resource. For details about basic congestion state, see Load Control Feature Parameter Description.

The switch parameter CodeAdjForHsdpaSwitch is set to ON. In this case, the RNC moves the codes occupied by R99 users leftward along the code tree and thereby releases shared codes that are close to HS-PDSCH codes. Figure 3-7 shows how this works.

When the RNC-controlled dynamic code allocation or the NodeB-Controlled Dynamic Code Allocation is enabled, codes released by means of dynamic code tree reshuffling can be used by the HS-PDSCH to improve throughput for HSDPA users.

Whether the F-DPCH codes can be reallocated through dynamic code tree reshuffling is determined by the parameter RsvdPara1: RSVDBIT6 in the MML command ADD UCELLALGOSWITCH

When dynamic code tree reshuffling takes effect, the RNC reshuffles the codes used by the DPCH/F-DPCH to provide more continuous SF16 codes for HSDPA through this function. This function is described as follows:

Every time the codes used by the DPCH are changed, the RNC will choose an SF16 subtree that are not used by HS-PDSCH from right to left. The selected subtree must meet the following conditions:

The selected subtree belongs to the code trees that can be shared between HS-PDSCH and DPCH.

The number of DPCHs and F-DPCHs on the selected subtree is smaller than or equal to the threshold specified by the parameter CodeAdjForHsdpaUserNumThd.

The parameter CodeAdjForHsdpaUserNumThd limits the number of users that can be reshuffled each time, to prevent too many users from being reshuffled in a short time and therefore to avoid affecting user experience.

When the above conditions are met, the RNC will select this subtree for reshuffling and relocate the users to the positions where the codes are idle.

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Figure 3-7 Dynamic code tree reshuffling

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4 User Plane

This chapter consists of the following sections:

Flow Control and Congestion Control

Impact of HSDPA on the RLC and MAC-d Entities

MAC-hs Scheduling

HARQ

TFRC Selection

HSDPA Remaining Power Appending

CQI Adjustment Based on Dynamic BLER Target

BLER Optimization for HSDPA Burst Services

Modulation Scheme

4.1 Flow Control and Congestion Control

HSDPA flow control (WRFD-01061010 HSDPA Flow Control) and congestion control are used to control the HSDPA data flow on the Iub and Iur interfaces. HSDPA data packets are sent through the Iub interface to the NodeB and then through the Uu interface to the UE. Therefore, congestion may occur on the Uu, Iub, or Iur interface. Flow control is used to relieve Uu congestion, and congestion control is used to relieve Iub/Iur congestion. The two types of control are implemented by the NodeB. HSDPA flow control and congestion control are part of the HSDPA Iub frame protocol (3GPP TS 25.435). They are implemented for each MAC-hs queue through the Capacity Request message sent by the RNC and the Capacity Allocation message sent by the NodeB.

Figure 4-1 shows the basic principles of flow control and congestion control.

Figure 4-1 Basic principles of Iub flow control and congestion control

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4.1.1 Flow Control

For each MAC-hs queue, flow control calculates the pre-allocated Iub bandwidth based on the Uu transmission rate and the amount of data buffered in the NodeB. The Uu transmission rate of the MAC-hs queue is determined by the scheduling algorithm. For each MAC-hs queue, if the Iub transmission rate is higher than the Uu transmission rate, the data packets are buffered. Too much data buffered in the NodeB leads to transmission delay and even packet loss. Therefore, each MAC-hs queue should not have too much data buffered in the NodeB. On the other hand, it should keep a certain amount of data to avoid wasting the Uu resources due to no data to transmit.

The flow control procedure is as follows:

1. The NodeB measures the buffered data amount of each MAC-hs queue and the average Uu transmission rate.

2. The NodeB estimates the buffering time based on the measurements.

3. The NodeB adjusts the Iub bandwidth pre-allocated to the MAC-hs queue.

The pre-allocated Iub bandwidth is adjusted as follows:

If the buffering time is too short, you can infer that the RNC slows down the data transmission, that is, the Iub transmission rate is lower than the Uu transmission rate. In this case, the pre-allocated Iub bandwidth is adjusted to a value greater than the average Uu transmission rate.

If the buffering time is appropriate, the pre-allocated Iub bandwidth is adjusted to the average Uu transmission rate.

If the buffering time is too long, the pre-allocated Iub bandwidth is adjusted to a value smaller than the average Uu transmission rate.

For details on flow control, see Transmission Resource Management Feature Parameter Description.

4.1.2 Congestion Control

The Iub bandwidth may be lower than the Uu bandwidth. If the RNC uses the Iub bandwidth pre-allocated to each MAC-hs queue, the Iub bandwidth for HSDPA is insufficient. This may lead to congestion and even packet loss.

The amount of data to be transmitted is sent by the RNC to each MAC-hs queue through the Capacity Request message. Based on this amount and the total Iub bandwidth available for HSDPA, the congestion control function adjusts the bandwidth pre-allocated to each MAC-hs queue. Therefore, congestion control ensures that the total bandwidth actually allocated to all the MAC-hs queues is not higher than the total available Iub bandwidth.

The total Iub bandwidth available for HSDPA depends on the variations in HSDPA packet delay and the situation of packet loss. HSDPA shares the bandwidth with the DCH and control signaling, and the DCH and control signaling has higher priorities than HSDPA. Therefore, when the HSDPA packet delay or packet loss increases, you can infer that the number of DCHs or the amount of control signaling increases. In such a case, the bandwidth available for HSDPA decreases and the bandwidth actually allocated for HSDPA decreases.

For details on congestion control, see Transmission Resource Management Feature Parameter Description.

For the Iur interface, flow control and congestion control are also applied. The control principles and processing procedures are the same as those for the Iub interface.

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4.2 Impact of HSDPA on the RLC and MAC-d Entities

4.2.1 Impact on the RLC Entity

One of the main purposes of HSDPA is to reduce latency by handling retransmissions at NodeB level. Retransmissions, however, may still be triggered at the RLC layer of the RNC under the following circumstances:

The NodeB misinterprets an NACK sent by the UE.

The number of HARQ retransmissions exceeds the maximum permissible number.

The data buffered in the NodeB is lost when the HS-DSCH serving cell changes.

Therefore, HARQ retransmission cannot totally replace RLC retransmission, which is described in 3GPP TS 25.322. For services with high requirements for data transmission reliability, Huawei recommends that the RLC acknowledged mode (AM) also be used to ensure correct transmission on the Uu interface even when the services such as the BE service are carried on HSDPA channels.

Before the introduction of HSDPA, the size of an RLC PDU is usually 336 bits, where 320 bits are for the payload and 16 bits for the RLC header. Without additional overhead, the MAC PDU is of the same size as the RLC PDU. According to the 3GPP specifications, a maximum of 2,047 RLC PDUs can be transmitted within an RLC window, and the RTT at the RLC layer is about 100 ms (50 TTIs).

In this condition, the maximum peak rate can only be 336 bits x (2047/50)/2 ms = 6.88 Mbit/s. To reach higher rates, an RLC PDU of 656 bits is introduced, where 640 bits are for the payload and 16 bits for the RLC header. The RLC PDU size can be set for each typical service. For high-speed services, the size is set to 656 bits by default.

In addition, the RLC PDU size is fixed to 656 bits, and a transport block of 27,952 bits can contain a maximum of 42 PDUs. Therefore, the maximum RLC payload rate is (656 bits - 16 bits) x 42/2 ms = 13.44 Mbit/s.

For example, 3GPP specifies that the UE of category 10 can use a maximum of 15 codes and receive a transport block with a maximum of 27,952 bits. For details, see 3GPP TS 25.306. Therefore, the theoretical peak rate is 27952 bits/2 ms = 13.976 Mbit/s. In practice, the radio channel quality, retransmission probability, and available power also need to be considered. Therefore, the UE of category 10 cannot reach 13.44 Mbit/s at the RLC layer in most tests.

A fixed RLC PDU size results in lower transmission efficiency due to unnecessary filler data and redundant RLC PDU headers. Another reason why a fixed RLC PDU size is not desirable is that high-speed transmission requires a large RLC PDU size required whereas edge coverage requires a small RLC PDU size. Downlink layer 2 enhancement can be used to address these problems.

With downlink layer 2 enhancement, the RLC AM entity supports a variable PDU size, and the RLC layer does not segment upper-layer packets whose sizes are smaller than the maximum RLC PDU size. The RLC layer can flexibly adapt to traffic variations and reduce the overheads caused by RLC PDU headers. For details about downlink layer 2 enhancement, see HSPA Evolution Feature Parameter Description.

4.2.2 Impact on the MAC-d Entity

The MAC-d functionality is unchanged after the introduction of HSDPA. The HS-DSCH bearers are mapped onto MAC-d flows on the Iub/Iur interface. Each MAC-d flow has its own priority queue.

4.3 MAC-hs Scheduling

This section describes the feature WRFD-01061009 HSDPA H-ARQ & Scheduling (MAX C/I, RR, and PF).

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With the limited Uu resources for HSDPA in a cell, the user expects to maximize the service rate while the telecom operator expects to maximize the system capacity. MAC-hs scheduling is used to coordinate the Uu resources, user experience, and system capacity. It is implemented at the NodeB MAC-hs.

The scheduling algorithm consists of two steps. At first, the algorithm determines which initial transmission queues or retransmission processes can be put into the candidate set for scheduling. Then, the algorithm calculates their priorities based on factors such as the CQI, user fairness, and differentiated services. If the algorithm is weighted more towards the channel quality of the UE, the HSDPA cell can have a higher capacity but user fairness and differentiated services may be affected. If the algorithm is weighted more towards user fairness and differentiated services, the system capacity may be affected.

Huawei provides five scheduling algorithms: maximum C/I (MAXCI), round-robin (RR), proportional fair (PF), Enhanced Proportional Fair (EPF), and EPF based on UE location (EPF_LOC). The EPF and EPF_LOC are optional.

4.3.1 Determining the Candidate Set

The candidate for scheduling contains new data packets (initial transmission queues) or data packets to be retransmitted (retransmission processes), with the following exceptions:

If the UE starts the compressed mode, its data cannot be put into the candidate set during the GAP.

If the UE category requires the UE to wait for several TTIs before it can be scheduled again, its data cannot be put into the candidate set in this period. The UE of category 1 or 2 needs to wait for 3 TTIs, and the UE of category 3, 4, and 11 must wait for 2 TTIs.

If the number of retransmissions of a data packet reaches or exceeds the maximum number, the data of this UE cannot be put into the candidate set. The data should be discarded.

Huawei supports that the maximum number of retransmissions is set on a service basis:

MaxNonConverHarqRt: the maximum number of non-conversational service retransmissions in the CELL_DCH state

MaxEfachHarqRt: The UE in the enhanced CELL_FACH state does not report ACK, NACK, or CQI in the uplink. The HARQ processes of the UE use the blind retransmission mechanism. The maximum number of retransmissions for the UE in Enhanced CELL_FACH Operation is specified by this parameter.

The CQI reported by the UE is 0.

There is no data in the Mac-ehs or Mac-hs queue for the UE.

The uplink channel quality of UEs is poor and the uplink channels of these UEs are carrying PS conversational services or SRBs.

The MAC-hs can schedule data packets and select Transport Format and Resource Combine (TFRC) entities for UEs whose uplink channel quality is poor and CQI is not 0 when the following conditions are met:

The MAC-hs queue contains the data packets of these UEs and the data size is not 0.

The scheduling time does not fall into the GAP.

For new data packets, the MAC-hs calculates the scheduling priority for the follow-up data packet scheduling and TFRC entity selection based on the principle that applies to a CQI of 12 (CQI adjustments are not performed). For data packets to be retransmitted, the MAC-hs schedules these data packets and selects TFRC entities in the same way as it operates on UEs with good uplink channel quality.

4.3.2 Calculating Scheduling Priorities

Five algorithms are available for calculating the priorities of data packets in the candidate set. The scheduling policies vary according to the algorithms for calculating the priorities of data packets. The algorithm to be used is specified by the parameter SM on the NodeB LMT.

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Comparison of Five Algorithms

Table 4-1 lists the factors considered in the five scheduling algorithms.

Table 4-1 Factors considered in the five scheduling algorithms

Factor MAXCI RR PF EPF EPF_LOC

Service type No No No Yes Yes

Initial transmission or retransmission Yes Yes Yes Yes Yes

Maximum power No No No Yes Yes

Waiting time No Yes No Yes Yes

CQI Yes No Yes Yes Yes

Actual throughput No No Yes Yes Yes

SPI No No No Yes Yes

SPI Weight No No No Yes Yes

GBR No No No Yes Yes

HBR No No No Yes Yes

UE Location No No No No Yes

Table 4-2 lists the effects of the five scheduling algorithms.

Table 4-2 Effects of the five scheduling algorithms

Item MAXCI RR PF EPF EPF_LOC

System capacity Highest High Higher Higher Higher

User fairness Not guaranteed Best Guaranteed Guaranteed Not guaranteed

Differentiated services Not guaranteed Not guaranteed Not guaranteed Guaranteed Guaranteed

Real-time services Not guaranteed Not guaranteed Not guaranteed Guaranteed Guaranteed

MAXCI Algorithm

The retransmission processes unconditionally have higher priorities than the initial transmission queues. The retransmission processes are sorted in first-in first-out (FIFO) mode. The initial transmission queues are sorted in the CQI order. A higher CQI means a higher data priority.

The MAXCI algorithm aims to maximize the system capacity but cannot ensure user fairness and differentiated services.

The UE estimates the CQI based on the assumption that the transmit power of the HS-PDSCH on the network side is as follows:

CPICHPDSCHHS PP

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where

PCPICH is the transmit power of the CPICH.

is the measurement power offset (MPO). It is specified by the parameter HsPdschMPOConstEnum on the RNC side and sent to the NodeB and UE.

is the reference power adjustment. It is set to 0 in most cases. For details, see 3GPP TS 25.214.

RR Algorithm

The retransmission processes unconditionally have higher priorities than the initial transmission queues. The retransmission processes are sorted in FIFO mode. The initial transmission queues are sorted in the order of the waiting time in the MAC-hs queue. A longer waiting time means a higher data priority.

The RR algorithm aims to ensure user fairness but cannot provide differentiated services. Not considering the CQI reported by the UE leads to lower system capacity.

PF Algorithm

The retransmission processes unconditionally have higher priorities than the initial transmission queues. The retransmission processes are sorted in FIFO mode. The initial transmission queues are sorted in the order of R/r. Here, R represents the throughput corresponding to the CQI reported by the UE, and r represents the throughput achieved by the UE. A greater R/r value means a higher data priority.

The PF algorithm aims to make a tradeoff between system capacity and user fairness. It provides the user with an average throughput that is proportional to the actual channel quality. The system capacity provided by PF is between the system capacity provided by RR and that provided by MAXCI.

EPF Algorithm

The EPF algorithm (WRFD-01061103 Scheduling based on EPF and GBR) is an enhanced algorithm developed based on the PF algorithm. The EPF algorithm defines more priorities than the PF algorithm to better meet the QoS requirements of different services. The EPF algorithm can meet the requirements of telecom operators related to user fairness and differentiated services and also provide a high system capacity.

The EPF algorithm follows certain criteria to prioritize queues:

Service types are the first to be considered. They are prioritized in a sequence: SRB and IMS > voice services > streaming services > BE services.

Different services of the same type are prioritized as follows:

Retransmission queues are prioritized over initial transmission queues.

Guaranteed bit rate (GBR) queues that have not arrived are prioritized over GBR queues that have already arrived.

Queues with high SPI weights are prioritized over those with low SPI weights.

High bit rate (HBR) queues that have not arrived are prioritized over HBR queues that have already arrived.

User fairness is implemented in EPF as follows:

EFP algorithm guarantees the user fairness in the same way as that PF algorithm. HBR and Resource Limit is used in EPF to limit the use of single users and improve fairness.

HBR is used to determine the throughput expected by the user based on a study on user experience.

When the rate for a user reaches the HBR, the scheduling probability for the user is decreased. The HBR is specified by the parameter HappyBR on the RNC side.

Resource Limit is used to prevent the users in areas with poor coverage from consuming too many cell resources so that there is no decrease in system capacity.

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When the resource limitation switch (RscLmSw) is on, the algorithm allocates the lowest priority to a queue whose power consumption exceeds the threshold. If the power available to the queue is limited, the queue's priority is always considered as meeting the GBR. The ratio of the maximum available power of a queue to the total power of the cell is specified by the NodeB MML command SET RSCLMTPARA.

Differentiated service is implemented in EPF as follows:

Differentiated services are provided based on SPI and SPI weights.

SPI is a parameter specified based on service types and users priorities.

SPIweight can be specified according to the SPI to provide differentiated services.

The SPI weight affects the calculation of queue priorities. It is used to quantify the differentiated services. If resource is insufficient, the proportion of SPI weights determines the approximate proportion of rates among users. For example, for three throughput-sensitive service users with the same channel quality, the same GBR and the proportion of SPI weights is 100:50:30, the proportion of actual rates is close to 100:50:30.

For details on the parameters related to QoS management, such as the GBR, SPI, SPI weight, and HBR, see QoS Management Feature Parameter Description.

EPF_LOC Algorithm

UEs' location in a cell can be defined as a near, middle, or far distance from the NodeB. HSDPA UEs

closer to the NodeB have better channel environments and report higher CQIs, as shown in Figure 4-2.

Figure 4-2 UE locations and CQIs

With the EPF/PF algorithm, UEs that have the same SPI weight value but are at different distances from the NodeB have roughly equal scheduling opportunities.

The EPF_LOC algorithm (WRFD-140221 HSDPA Scheduling based on UE Location) builds on the EPF algorithm and considers UE locations as HSDPA scheduling weights. While ensuring GBRs for all UEs, the EPF_LOC algorithm gives more scheduling opportunities to UEs that are close to the NodeB in order to improve throughput for these UEs. Since these UEs can obtain larger transmission blocks than UEs farther from the NodeB, the overall throughput of the cell is improved.

CQIs indirectly reflect UE locations. A CQI reported by a UE implies the UE's location, a near, middle, or far distance either between the UE and the NodeB, or between the UEs within a cell. Assuming that there are two UEs far from the NodeB and the CQIs reported by them are 15 and 13, respectively, the UE that reports the CQI 15 has more scheduling opportunities and higher downlink throughput.

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The PF and EPF algorithms consider the value R/r, where R is the throughput corresponding to the CQI reported by the

UE. The EPF_LOC algorithm is based on the EPF algorithm. In addition to R/r, the EPF_LOC algorithm also considers UE

locations indicated by CQIs.

If a larger value is set for the LOCWEIGHT parameter, UE locations weigh more in the EPF_LOC algorithm. Theoretically, this results in a higher downlink throughput of the cell and greater differentiation between UEs at different distances from the NodeB. UEs closer to the NodeB have more scheduling opportunities and higher throughput, which is the other way around for UEs farther from the NodeB.

UEs closer to the NodeB have more scheduling opportunities and therefore higher throughput. This improves the cell throughput.

UEs farther from the NodeB have fewer scheduling opportunities and therefore lower throughput.

To ensure user experience at cell edges, it is recommended that GBRs be configured for all BE services. To configure GBRs, run the SET UUSERGBR command on the RNC.

The LOCWeight and SPIWeight parameters simultaneously affect HSDPA scheduling weights. UEs far from the NodeB will experience decreased downlink rates after this feature is activated. If high rates need to be ensured for gold users, it is recommended that higher GBRs or SPI weight values be set for gold users.

The EPF_LOC algorithm gives more scheduling opportunities to UEs closer to the NodeB and increases the downlink overall throughput of the cell. Cell throughput gains relate to UEs' CQIs. With EPF_LOC algorithm, HSDPA UEs at cell edges have fewer scheduling opportunities and lower throughput. If GBRs are not configured for BE services, HSDPA UEs at cell edges may have to wait a long time before they have scheduling opportunities. As a result, traffic radio bearers (TRBs) are more likely to reset and the call drop rate increases. The magnitude of this impact depends on factors such as UE location distribution and service distribution in the cell. It is recommended that GBRs be configured for BE services to ensure network performance.

4.3.3 Time and HS-PDSCH Codes Multiplex

This section describes the feature WRFD-01061018 Time and HS-PDSCH Codes Multiplex.

After scheduling, HSDPA users will be allocated to different time and code. Figure 4-3 shows the time division and code division over the air interface for HSDPA users in one cell.

Figure 4-3 HSDPA scheduling based on time division and code division

The feature of time and HS-PDSCH codes multiplex enables the allocation of different codes in the same TTI to different users or the time division multiplexing of the same code in different TTIs for different users to provide the utilization of code resources and the system throughput.

WCDMA RAN

HSDPA 4 User Plane



4-9

The parallel data transmission of multiple users over HS-DSCH requires more HS-SCCH codes and HS-PDSCH codes within a single TTI. Code multiplexing is adopted and is found useful when the NodeB has more HS-PDSCH codes for allocation than those supported by the UE. For instance, the UE supports 5 codes and the NodeB has 10 codes available in a single TTI. The code multiplexing can increase the resource utilization and system throughput.

4.4 HARQ

The main purpose of introducing HARQ is to reduce the retransmission delay and improve the retransmission efficiency. HARQ enables fast retransmission at the physical layer. Before decoding, the UE combines the retransmitted data and the previously received data, making full use of the data transmitted each time. In addition, HARQ can fine-tune the effective rate to compensate for the errors made by TFRC section.

4.4.1 HARQ Retransmission Principles

The HARQ process of HSDPA involves only the NodeB and the UE, without involving the RNC. After receiving a MAC-hs PDU sent by the NodeB, the UE performs a CRC check and reports an ACK or NACK on the HS-DPCCH to the NodeB:

If the UE reports an ACK, the NodeB transmits the next new data.

If the UE reports an NACK, the NodeB retransmits the original data. After receiving the data, the UE performs soft combining of this data and the data received before, decodes the combined data, and then reports an ACK or NACK to the NodeB.

RLC retransmission on the DCH involves the RNC, and therefore the RTT is relatively long. In comparison, HARQ involves only the physical layer and MAC-hs of the NodeB and those of the UE, and therefore the RTT is reduced to only 6 TTIs (12 ms).

After a transmission, the HARQ process must wait at least 10 ms before it can transmit the next new data or retransmit the original data. Therefore, to improve transmission efficiency, other HARQ processes can transmit data during the waiting time. A maximum of six HARQ processes can be configured in each of the NodeB HARQ entity and the UE HARQ entity. Note that not all UE categories support six HARQ processes. For example, the UEs of some categories can receive data every one or two TTIs. Therefore, only two or three HARQ processes can be con