rach optimization(eran3.0 01)

RACH Optimization eRAN3.0

Feature Parameter Description

Issue 01

Date 2012-03-30

HUAWEI TECHNOLOGIES CO., LTD.

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eRAN

RACH Optimization Contents

Issue 01 (2012-03-30) Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd.

i

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 RACH Optimization ........................................................................................... 2-1

3 Key Techniques of RACH Optimization .............................................................................. 3-1

3.1 RACH Resource Adjustment ......................................................................................................... 3-1

3.2 Adaptive Backoff ............................................................................................................................ 3-3

4 Related Features ....................................................................................................................... 4-1

4.1 Required Features......................................................................................................................... 4-1

4.2 Mutually Exclusive Features ......................................................................................................... 4-1

4.3 Affected Features .......................................................................................................................... 4-1

5 Impact on the Network............................................................................................................. 5-1

5.1 Impact on System Capacity........................................................................................................... 5-1

5.2 Impact on Network Performance ................................................................................................... 5-1

6 Engineering Guidelines ........................................................................................................... 6-1

6.1 When to Use RACH Optimization ................................................................................................. 6-1

6.2 Information to be Collected ........................................................................................................... 6-1

6.3 Network Planning .......................................................................................................................... 6-1

6.4 Overall Deployment Procedure ..................................................................................................... 6-1

6.5 Deploying RACH Optimization ...................................................................................................... 6-1

6.5.1 Deployment Procedure ......................................................................................................... 6-1

6.5.2 Deployment Requirements ................................................................................................... 6-1

6.5.3 Data Preparation................................................................................................................... 6-1

6.5.4 Activation .............................................................................................................................. 6-2

6.5.5 Commissioning ..................................................................................................................... 6-3

6.5.6 Activation Observation .......................................................................................................... 6-3

6.5.7 Reconfiguration .................................................................................................................... 6-4

6.5.8 Deactivation .......................................................................................................................... 6-4

6.6 Optimization .................................................................................................................................. 6-4

6.7 Troubleshooting ............................................................................................................................. 6-4

7 Parameters.................................................................................................................................. 7-1

8 Counters ...................................................................................................................................... 8-1

9 Glossary ...................................................................................................................................... 9-1

10 Reference Documents ......................................................................................................... 10-1

eRAN

RACH Optimization 1 Introduction



1-1

1 Introduction

1.1 Scope

This document describes the key techniques and engineering guidelines for random access channel (RACH) optimization.

Any managed objects (MOs), parameters, alarms, or counters described in this document correspond to the software release delivered with this document. In the event of updates, the updates will be described in the product documentation delivered with the latest software release.

1.2 Intended Audience

This document is intended for:

Personnel who need to understand RACH optimization

Personnel who work with Huawei LTE products

1.3 Change History

This section provides information on changes in different document versions. There are two types of changes, which are defined as follows:

Feature change: refers to a change in the RACH optimization feature of a specific product version.

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

Document Issues

The document issues are as follows:

01 (2012-03-30)

Draft A (2012-01-10)

01 (2012-03-30)

This is the first official release.

Compared with draft A (2012-01-10) of eRAN3.0, issue 01 (2012-03-30) of eRAN3.0 includes the following changes.

Change Type Change Description Parameter Change

Feature change None None

Editorial change Revised chapter 6 "Engineering Guidelines." None

Draft A (2012-01-10)

This is the draft.

Compared with issue 02 (2011-11-30) of eRAN2.2, draft A (2012-01-10) of eRAN3.0 includes the following changes.

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RACH Optimization 1 Introduction



1-2

Change Type Change Description Parameter Change

Feature change None None

Editorial change Added chapter 4 "Related Features" and chapter 5 "Impact on the Network."

None

eRAN

RACH Optimization 2 Overview of RACH Optimization



2-1

2 Overview of RACH Optimization

This feature provides two functions: RACH resource adjustment and adaptive backoff.

RACH resource adjustment

RACH resource adjustment optimizes preamble groups and physical random access channel (PRACH) configurations.

As defined in 3GPP specifications, RACH resources for a cell consist of preambles and PRACH resources. Preambles are further classified as dedicated preambles and random access preambles, which are used for non-contention-based random access and contention-based random access, respectively. RACH resources are configured in semi-persistent mode. Therefore, a change in the traffic model may lead to an insufficiency of RACH resources to meet load requirements. For example, an increased number of handover attempts may cause an insufficiency of dedicated preambles and a longer handover delay. An increased number of random access attempts may cause an insufficiency of random access preambles and PRACH resources and a higher probability of preamble collisions. This further lowers the rate of successful one-time access on the PRACH and prolongs access delays.

With the two RACH optimization mechanisms, preamble groups and PRACH configurations, the number of preambles in each group and the number of PRACHs allocated each second smoothly adapt to the dynamic change in the traffic model. This increases RACH resource utilization efficiency and decreases the access delay for heavy RACH loads.

Adaptive backoff

If multiple UEs use the same preamble to quickly initiate contention-based random access, continual preamble collisions may occur. After a preamble collision occurs, only one UE can access the network as usual, and the remaining UEs that use the same preamble must initiate random access again on the same PRACH, which may lead to another preamble collision. Continual preamble collisions cause extra access delays for UEs. UE is short for user equipment.

To solve this problem, 3GPP specifications introduce the adaptive backoff function. A backoff time is specified for each UE that has experienced a preamble collision and failed the random access procedure. A UE can initiate random access again using the same preamble at a random time point within the specified backoff period. Adaptive backoff enables the eNodeB to specify the backoff period for UEs based on the contention-based random access load. This function reduces both the probability of continual preamble collisions and the access delays for UEs.

This document describes the optional feature LOFD-002015 RACH Optimization. For details about random access procedures and basic concepts related to random access preambles, see the Connection Management Feature Parameter Description.

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RACH Optimization 3 Key Techniques of RACH Optimization



3-1

3 Key Techniques of RACH Optimization

3.1 RACH Resource Adjustment

Preambles of a cell are generated based on root Zadoff-Chu (ZC) sequences. UEs initiate random access by transmitting preambles over the PRACH.

As defined in 3GPP specifications, each cell can be configured with 64 preambles. The 64 preambles are classified as random access preamble group A, random access preamble group B, and a dedicated preamble group, as shown in Figure 3-1. UEs use dedicated preambles to initiate non-contention-based random access. For contention-based random access, when the path loss of a UE is less than a particular protocol-defined threshold and the msg3 length is greater than the value of MessageSizeGroupA, the UE selects random access preambles from group B to initiate contention-based random access. Otherwise, the UE selects random access preambles from group A to initiate contention-based random access.

Figure 3-1 Preamble groups

PRACH configurations depend on PRACH configuration indexes stipulated in 3GPP specifications. Setting the PRACH configuration index determines the number of PRACH opportunities and the subframe numbers at which a random access preamble is transmitted. For details about PRACH configuration indexes, see reference document [1]. Table 3-1 lists the frame structure type 1 random access configuration for preamble formats 0 to 3.

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Table 3-1 Frame structure type 1 random access configuration for preamble formats 0-3

As listed in Table 3-1, the Subframe Number column specifies PRACH opportunities reserved for the subframes of a radio frame in each PRACH configuration. For example, PRACH configuration index 7 specifies that random access preambles are transmitted at subframes 2 and 7 of each radio frame, and PRACH configuration index 3 specifies that random access preambles are transmitted only at subframe 1 of each radio frame.

Based on the allocation of dedicated preambles, detection of random access preambles, and load on the physical uplink shared channel (PUSCH), RACH optimization adaptively groups preambles and adjusts PRACH configurations as follows:

Decreases the number of PRACH opportunities within each radio frame if the eNodeB receives a small number of random access preambles and the PUSCH load is high. It will impact the uplink traffic volume if

Increases the number of PRACH opportunities within each radio frame if the eNodeB receives a large number of random access preambles and the PUSCH load is not high.

Decreases the number of dedicated preambles if there are sufficient dedicated preambles and the eNodeB receives a large number of random access preambles.

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Increases the number of dedicated preambles if dedicated preambles are insufficient.

If preamble groups or PRACH configurations change, the eNodeB sends the new PRACH configuration to the UE through system information block type 2 (SIB2). Then, the UE uses the new PRACH configuration to optimize random access performance.

RachAdjSwitch under the RachAlgoSwitch parameter controls RACH resource adjustment.

3.2 Adaptive Backoff

The eNodeB sends a backoff index in an MAC control element (MCE) to a UE to prevent the UE from retransmitting a random access preamble immediately. This reduces the probability of preamble collisions and reduces the processing loads of the eNodeB.

The UE queries the backoff time corresponding to the backoff index received from the eNodeB against Table 3-2. Then, the UE retransmits the random access preamble within the backoff time. For details, see reference document [2].

Table 3-2 Backoff parameter values

Adaptive backoff enables the eNodeB to measure the average number of random access preambles. The policies are as follows:

If the number is large, the eNodeB increases the backoff time.

If the number is small, the eNodeB decreases the backoff time.

If the number changes slightly, the eNodeB does not change the backoff time.

BackOffSwitch under the RachAlgoSwitch parameter controls adaptive backoff.

eRAN

RACH Optimization 4 Related Features



4-1

4 Related Features

4.1 Required Features

None

4.2 Mutually Exclusive Features

None

4.3 Affected Features

None

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RACH Optimization 5 Impact on the Network



5-1

5 Impact on the Network

5.1 Impact on System Capacity

This feature has no impact on system capacity. For example, this feature does not affect the number of online users or throughput.

5.2 Impact on Network Performance

This feature dynamically adjusts the preamble configuration and therefore reduces the probability of preamble collision. As a result, this feature can reduce access delays and handover delays.

eRAN

RACH Optimization 6 Engineering Guidelines



6-1

6 Engineering Guidelines

6.1 When to Use RACH Optimization

RACH optimization is recommended if operators require improvements in random access performance in terms of the one-time random access success rate and access delay.

6.2 Information to be Collected

None

6.3 Network Planning

N/A

6.4 Overall Deployment Procedure

N/A

6.5 Deploying RACH Optimization

6.5.1 Deployment Procedure

None

6.5.2 Deployment Requirements

Requirements for the Operating Environment

None

Requirements for Transmission Networking

None

Requirements for Licenses

Operators must purchase and activate the following license.

Feature License Control Item Name License Control Item ID

LOFD-002015 RACH Optimization RACH Optimization(FDD) LLT1RAOP01

Other Requirements

Before deploying this feature, trace the SIB2 message over the Uu interface and record the values of the IEs prach-ConfigIndex and preamblesGroupAConfig. For details about how to trace the message and obtain the IE values, see section 6.5.6 "Activation Observation."

6.5.3 Data Preparation

This section describes generic data and scenario-specific data to be collected. Generic data is necessary for all scenarios and must always be collected. Scenario-specific data is collected only when necessary for a specific scenario.

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There are three types of data sources:

Network plan (negotiation required): Parameters are planned by operators and negotiated with the EPC or peer transmission equipment.

Network plan (negotiation not required): Parameters are planned and set by operators.

User-defined: Parameters are set as required by users.

Generic Data

None

Scenario-specific Data

The following table describes the parameters that must be set in the CellAlgoSwitch managed object (MO) to configure RACH resource adjustment and adaptive backoff.

Parameter Name

Parameter ID Source Setting Description

Local cell ID

CellAlgoSwitch.LocalCellId

Network plan (negotiation not required)

This parameter specifies the local ID of the cell. It uniquely identifies a cell within an eNodeB.

RACH algorithm switch

RachAlgoSwitch

Network plan (negotiation not required)

The following switches in this parameter are related to RACH optimization:

RachAdjSwitch: specifies the switch for RACH resource adjustment. If this switch is turned on, the RACH resource adjustment function adaptively adjusts the RACH resources in the cell based on the random access type and the number of random access times. If this switch is turned off, RACH resource adjustment is disabled.

BackOffSwitch: specifies the switch for adaptive backoff. If the switch is turned on, adaptive backoff is enabled. If this switch is turned off, adaptive backoff is disabled.

Select the RachAdjSwitch and BackOffSwitch check boxes.

6.5.4 Activation

Configuring a Single eNodeB Using the GUI

Configure a single eNodeB in the general configuration window on the Configuration Management Express (CME) based on the MO and parameters as described in section 6.5.3 "Data Preparation."

See the M2000 Help for more information about operations in the general configuration window. Press F1 to launch M2000 Help. Navigate to Introduction to the LTE General Configuration Window and refer to the generic procedure for setting parameters using the CME graphical user interface (GUI).

To find MOs in the planned area, use either of the following methods:

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In the Object Group pane, find MOs in the navigation tree. This method applies to users who are familiar with the navigation tree.

In the Search pane, search an MO. This method applies to users who are unfamiliar with the navigation tree.

Configuring eNodeBs in Batches

To configure eNodeBs in batches, perform the following steps:

Step 1 On the GUI, set the parameters listed in the following table for a specific scenario in this section, and save the parameter settings as a user-defined template.

The parameters are the same as those described in section 6.5.3 "Data Preparation."

Step 2 Fill in the summary data file with the name of the user-defined template.

The parameter settings in the user-defined template will be applied to the eNodeBs after you import the summary data file into the CME.

----End

For descriptions of the user-defined template and summary data file and also the detailed procedure for configuring eNodeBs in batches, see eNodeB Initial Configuration Guide.

MO Parameter Group Name Parameter

CellAlgoSwitch

CellAlgoSwitch Local cell ID, RACH algorithm switch

Configuring a Single eNodeB Using MML Commands

To activate RACH resource adjustment and adaptive backoff, run the MOD CELLALGOSWITCH command with the RachAdjSwitch and BackOffSwitch check boxes selected under the RachAlgoSwitch parameter.

6.5.5 Commissioning

N/A

6.5.6 Activation Observation

To verify whether RACH resource adjustment is successfully activated, perform the following steps:

Step 1 On the M2000 client, start a Uu interface tracing task.

Step 2 After a UE accesses the network, trace the SIB2 message and observe the values of the IEs prach-ConfigIndex and preamblesGroupAConfig, as shown in Figure 6-1.

If the values of both IEs change after the RACH resource adjustment function is used, RACH resource adjustment has been successfully activated.

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Figure 6-1 SIB2

---End

6.5.7 Reconfiguration

None

6.5.8 Deactivation

To deactivate RACH resource adjustment and adaptive backoff, run the MOD CELLALGOSWITCH command with the RachAdjSwitch and BackOffSwitch check boxes cleared under the RachAlgoSwitch parameter.

6.6 Optimization

None

6.7 Troubleshooting

None

eRAN

RACH Optimization 7 Parameters



7-1

7 Parameters

Table 7-1 Parameter description

MO Parameter ID MML Command Feature ID Feature Name Description

CellAlgoSwitch LocalCellId LST CELLALGOSWITCH

MOD CELLALGOSWITCH

None None Meaning:Indicates the local ID of the cell. It uniquely identifies a cell within a BS.

GUI Value Range:0~17

Unit:None

Actual Value Range:0~17

Default Value:None

CellAlgoSwitch RachAlgoSwitch MOD CELLALGOSWITCH

LST CELLALGOSWITCH

LBFD-001001 / TDLBFD-001001

LBFD-002010 / TDLBFD-002010

LOFD-002015 / TDLOFD-002015

3GPP R8 Specifications

Random Access Procedure

RACH Optimization

Meaning:RachAdjSwitch: Indicates the switch used to enable or disable random access channel (RACH) resource adjustment, which adaptively adjusts the RACH resources in the cell based on the access type and the number of accesses. If the switch is turned off, RACH resource adjustment is disabled.

HoRaSwitch: Indicates the switch used to control the random access mode applied during handovers.

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If the switch is turned on, the eNodeB instructs UEs to use the non-contention-based random access mode during handovers.

If the switch is turned off, the eNodeB instructs UEs to use the contention-based random access mode during handovers.

UnsyncRaSwitch: Indicates the switch used to control the random access mode applied when UEs are out of synchronization in the uplink.

If the switch is turned on, the eNodeB instructs UEs to use the non-contention-based random access mode upon DL data arrivals in the case of out-of-synchronization.

If the switch is turned off, the eNodeB instructs UEs to use the contention-based random access mode upon DL data arrivals in the case of out-of-synchronization.

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MaksIdxSwitch: Indicates the switch used to control reuse of dedicated preambles between UEs.

If the switch is turned on, the eNodeB enables reuse of dedicated preambles among UEs based on the MaskIndex parameter.

If the switch is turned off, the eNodeB allocates a dedicated preamble to only one UE at a time.

BackOffSwitch: Indicates the switch for backoff control.

If the switch is turned on, backoff control is enabled.

If the switch is turned off, backoff control is disabled.

GUI Value Range:RachAdjSwitch(RachAdjSwitch), HoRaSwitch(HoRaSwitch), UnsyncRaSwitch(UnsyncRaSwitch), MaksIdxSwitch(MaksIdxSwitch), BackOffSwitch(B

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ackOffSwitch)

Unit:None

Actual Value Range:RachAdjSwitch, HoRaSwitch, UnsyncRaSwitch, MaksIdxSwitch, BackOffSwitch

Default Value:RachAdjSwitch:Off, HoRaSwitch:On, UnsyncRaSwitch:On, MaksIdxSwitch:Off, BackOffSwitch:Off

eRAN

RACH Optimization 8 Counters



8-1

8 Counters

There are no specific counters associated with this feature.

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RACH Optimization 9 Glossary



9-1

9 Glossary

For acronyms, abbreviations, terms, and definitions, see the Glossary.

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RACH Optimization 10 Reference Documents



10-1

10 Reference Documents

This chapter lists the reference documents related to RACH optimization.

[1] 3GPP 36.211 "Physical channels and modulation"

[2] 3GPP 36.321 "Medium Access Control (MAC) protocol specification"

[3] eNodeB Performance Counter Reference

[4] eNodeB MO Reference

[5] Connection Management Feature Parameter Description

[6] eNodeB Initial Configuration Guide

rach optimization(eran3.0 01)

Documents

huawei trademarks

huawei proprietary

rach optimization eran3

overview of rach optimization

huawei industrial base

related features

required features

exclusive features