IFLB RAB Distribution Under Ideal Conditions

8/10/2019 IFLB RAB Distribution Under Ideal Conditions

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Expected IFLB RAB Distribution

under Ideal Conditions


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Introduction

IFLB is used to control the RAB distribution between LTE

frequencies Current practice uses a basic model to predict the distribution

That model does not consider lbThreshold, the minimum load

need to trigger offloading

This over site is significant at typical loading levels and has leadto the erroneous belief that the feature is not working

In this presentation we will

Calculate the expected distribution ratio using the current

method Expand the method to include lbThreshold

Compare both methods with field results


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Parameter settings 1

Cell A Cell B

cellSubscriptionCapacity 100000 100000

qciSubscriptionQuanta 500 500

lbThreshold 0.05 0.05

Expected Distribution1 50% 50%

Threshold in RABs2 10.0 10.0

1 qciSubscriptionQuanta / qciSubscriptionQuantaCell

2 cellSubscriptionCapacity x lbThreshold / qciSubscriptionQuanta


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lbThreshold Impact at Low load

Consider two cells with an IFLB relationshipenabled

RABs are added one at a time to Cell A

Cell A can have 10 UEs before off loading toCell B

This means for less than 10 UEs the RAB

distribution will be 100% on Cell A Clearly this is very far from the expected

distribution


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Modeling lbThreshold Impact

Our model must include the 100% distribution at low load andprogress towards the Expected Distribution

We do this by considering two extreme situations

Only adding RABs to Cell A

Only adding RABs to Cell B

To facilitate the formation of a mathematical model we make

the following assumption:

When the number of RABs is greater than the threshold,

RABs will be distributed proportional to the Expected

Distribution


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Only adding to Cell A

By only adding to Cell A, Cell B

must have 0 RAB when below the

lbThreshold (10 RAB)

Then for every RAB on Cell A,

there must be one on Cell B asthe Expected Distribution is 50%

Formula to describe this is:

Cell A RAB Cell B RAB

0 0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

10 0

11 1

12 2

13 3

14 4

RB= MAX(0,RAx QA/ QB- TB)

RXNumber of RAB on Cell X

QXQCISubscriptionQanta for Cell X

TXThreshold for activation for Cell X [RAB]


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Only adding to Cell B

By only adding to Cell B, Cell B

must have 10 RAB before the first

appears on Cell A (10 RAB)

Then for every RAB on Cell A,

there must be one on Cell B asthe Expected Distribution is 50%

Formula to describe this is:

RB= MAX(0,RAx QA/ QB+ TB)

RXNumber of RAB on Cell X

QXQCISubscriptionQanta for Cell X

TXThreshold for activation for Cell X [RAB]

Cell A RAB Cell B RAB

0 10

1 11

2 12

3 13

4 14

5 15

6 16

7 17

8 18

9 19

10 20

11 21

12 22

13 23

14 24


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Plotting Results

Formula for distribution of RAB on Cell A is straight forward

RA/ (RA+ RB)

Plotting shows we do tend to the Expected Distribution while also modeling

the predicted low load behavior


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Parameter settings 2

Field Settings

Frequency A Frequency B

cellSubscriptionCapacity 115000 115000

qciSubscriptionQuanta 500 700

lbThreshold 0.05 0.05

Expected Distribution1 58.3% 41.7%

Threshold in RABs2 11.5 8.2

1 qciSubscriptionQuanta / qciSubscriptionQuantaCell

2 cellSubscriptionCapacity x lbThreshold / qciSubscriptionQuanta


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Field Results

Results were collected from an IFLB field trial

Average RRC Connections was used as a proxy for

the number of RAB

Cells had up to 8 IFLB neighbors

The median value for RAB Distribution was

43.3% on Frequency A

The design was for 58.3%

So lets examine factor in the number of

RABs


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Field Results

The plot below shows that the number of RRC connections significantly

impacts the distribution of RABs.

The distribution of RABs for cells with greater than 40 RCC connections is

close to the Expected Distribution

The majority of Freq A cells are below the 40 RRC Connection point


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Field Results vs Model

The model reasonably predicts the spread distribution with low loading

It suggests that the Add to Cell B Only phenomenon is dominate in the network

This indicates that Freq B is attracting initial attaches

Idle mode users having a preference for Freq B is one possible explanation


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Conclusion

We demonstrated that the impact from the load balancing

threshold is significant at low loading We developed a model to more accurately predict low load

distribution

We demonstrated the expected load balancing distribution will

fall in a range of values That median of RAB distributions is not an accurate indication

of IFLB design efficacy

That field results are likely being impacted by

Many cells with a low number of connections Freq B attracting initial connections


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THNAK YOU

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IFLB RAB Distribution Under Ideal Conditions