lte eran6.0 rach optimization issue1.00

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LTE eRAN6.0 RACH Optimization


Objectives

Upon completion of this course, you will be able to:

Configure advanced RACH parameters

Understand RACH Optimization feature

Configure RACH Optimization feature

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Contents

1. Overviewa) Prerequisites for RACH Optimization

b) Zero Correlation Zone Config

c) Contention-Based vs. Contention-Free Random Access

2. RACH Resource Adjustmenta) Dedicated Preamble Group Adjustment

b) Multiplexing of Dedicated Preambles

c) PRACH Configuration Index Adjustment

d) Adaptive Backoff

3. MML screenshots

4. Impact of RACH Optimization

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RACH Optimization Overview

Decrease call setup/HO/initial packet delay

Increase preamble detection probability

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Prerequisites for RACH Optimization Correct Planning of Root sequence index with the

highest possible reuse distance. Correct planning of Cell radius parameter which

directly determines zeroCorrelationZoneConfig parameter (0~15)

Correct High Speed Flag setting Correct configuration of Preamble format [0, 1, 2,

3, 4(TDD)]

SIB2:

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Zero Correlation Zone ConfigzeroCorrelationZoneConfi

g

Ncs value

Unrestricted set Restricted set

0 0 15

1 13 18

2 15 22

3 18 26

4 22 32

5 26 38

6 32 46

7 38 55

8 46 68

9 59 82

10 76 100

11 93 128

12 119 158

13 167 202

14 276 237

15 419 -

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Contention-based vs. Contention-Free Random Access (RA)

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64 preambles in each cell are classified into 3

groups: random access preambles group A random access preambles group B dedicated preamble group

For contention-based RA, if 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 RA preambles from group B. Otherwise, the UE selects RA preambles from group A

For non-contention-based (Contention-Free) RA, UEs use dedicated preambles (i.e. during handover procedure while connecting on target cell)


Contention-based vs. Contention-Free Random Access (Cont.)

Random Access

Preamble Group A

Random Access

Preamble Group B

Dedicated Preamble

Group

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#0

#51 (numberOfRA-Preambles -1)

#63

#27 (sizeOfRA-PreamblesGroupA -1)

SIB2:

Huawei default configuration of preamble groups:

#28 (sizeOfRA-PreamblesGroupA )

#52 (numberOfRA-Preambles )


RACH Optimization Algorithm

RACH Optimization algorithm evaluates following

parameters:

allocation of dedicated preambles,

detection of random access preambles, and

load on the physical uplink shared channel (PUSCH)

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Dedicated Preamble Group Adjustment

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RACH Optimization Algorithm will:

Decrease the number of dedicated preambles if there

are sufficient idle dedicated preambles and the eNodeB

receives a large number of random access preambles.

Increase the number of dedicated preambles if idle

dedicated preambles are insufficient.


Multiplexing of Dedicated Preambles

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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.


Multiplexing of Dedicated Preambles (Cont.)

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PRACH Mask Index Allowed PRACH (FDD)

0 All

1 PRACH Resource Index 0










11 Every, in the time domain, even PRACH opportunity 1st PRACH Resource Index in subframe

12 Every, in the time domain, odd PRACH opportunity 1st PRACH Resource Index in subframe

13 Reserved

14 Reserved

15 Reserved


PRACH Configuration Index Adjustment

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RACH Optimization Algorithm will:

Decrease 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.

Increase 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.


Adaptive Backoff

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.

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Adaptive Backoff (Cont.)

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Index Backoff Parameter value (ms)

0 0

1 10

2 20

3 30

4 40

5 60

6 80

7 120

8 160

9 240

10 320

11 480

12 960

13 Reserved

14 Reserved

15 Reserved


RACH Optimization Algorithm Switch MML MOD CELLALGOSWITCH

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RACH Configuration MML

MOD RACHCFG

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Impact of RACH Optimization

Benefits: low miss detection rate and error detection rate of

preambles. support for higher RACH load :

Risks: UE may fail in random access procedure if SIB2 is being

updated in the same time.

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RACH Optimization OFF ON

support of non-contention based RA attempts per second

100 20 ~ 350

support of contention based RA attempts per second

20Mhz: 10010Mhz: 50

20Mhz: 32~12010Mhz: 32~60

UL overhead for PRACH 20Mhz: 1.2%10Mhz: 1.2%

20Mhz: 0.6~1.2%10Mhz: 1.2%

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lte eran6.0 rach optimization issue1.00

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