less samples cause a low 3g to 2g ho success rate

7/29/2019 Less Samples Cause a Low 3G to 2G HO Success Rate

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Less Samples Cause a Low 3G to 2G HO Success Rate

1 Introduction

2G3G interoperability is a common and frequent problem in 3G optimization work.

There already have many ways to optimize this problem. This document shows you a

different situation that the current 2G network cannot reselect to 3G then find a new

way by analyzing user behavior and Mathematical deduction and bring up a new index

Inter-RAT HO to Traffic Ratio to solve this problem at last.

2 Description

3G Operator network has been put into commercial. The Inter-RAT handover succe

ss rate of is Unstable, the value is between 60% to 85%. Both of the two RNCs are t

he same and all the parameters are correct.

After continually optimization work, the Inter-RAT handover success rate grow up t

o 80%-90% but still unstable seems cannot be improved anymore.

3 Analysis

The NUM of Inter-RAT handover is so little that some accidental failures will have

great effect on the KPI. At the same time we did DT for the Inter-RAT handover, the

detail information about the DT as below:

1>3G to 2G handover test

Date : 28-Apr afternoon.


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Equipment : ZTE T7(test phone) & Nokia E62(compare to each other).

Method :

First, we let the two phones under 3G service.

Then, select the phone to auto network selection mode.

Then, one phone call the other and start to drive out of Bulawayo in four direction. ke

ep the connection until it handover to 2G or drop.

Result:

All the road out of Bulawayo have handover to 2G successfully.

Time

Source 3G cell Target 2G cell

CID,PSC

CELL

CID

CELL

15:37:54

12042,8

4

Belmont PO_

2

320

07 ILANDA3

15:56:07

12071,1

01 Montrose_1

320

02 MONTROSE3

16:16:24

12171,1

70

Nkulumane_

1

106

14 NKULUMANE1

16:43:02

12141,1

24

Entumbane_

1

106

13 LOBENGULA1

17:02:50

12081,1

02 Ilanda_1

202

40

KHUMALONRT2

Location


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2G to 3G reselection test

Date : 28-Apr afternoon.

Equipment : ZTE T7(test phone) & Nokia E62(compare to each other).

Method :

First, we let the two phones under 2G service.

Then, select the phone to auto network selection mode.

Then, keep two phones in idle mode and drive around the dense urban of Bulawayo, w

here the 3G signal is very good.


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Result: We drive about two hours, but the two phones never reselect to 3G.

Conclusion:

1>The function and parameter settings of 3G to 2G handover is OK.

2>2G cannot reselect to 3G, where it should do.

(usually, where if 3G Ec/Io>-12db, UE should reselect to 3G automatically)

The test result shows the 3G to 2G handover is OK, but 2G cannot reselect to 3G.

2>User behavior analysis and Mathematical deduction

After Communication we find Operator forbid 2G reselect to 3G, because they are

afraid the poor 3G coverage will cause a lot of complains and they think this 2G strate

gy will have no effect on 3G inter-RAT HO success rate, so they insist 3G part to solv

e the problem alone.

According to this situation, I decide to do a theoretical analysis and send this repo

rt in written form then push Operator to solve. The user behavior analysis and Mathem

atical deduction as below:


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figure2 Mathematical deduction about the less samples cause a low 3G to 2G HO

Success Rate

Explain: For the succeed ones, they will stay in 2G and will never come back in c

ase they restart the phone or reselect to 3G manually. I have asked many people that

very few of them do like this, so that the Success NUM will decrease a lot and the To

tal NUM will decrease as well.

For the Failure ones, they will stay in 3G and keep on making failures. So the Fail

NUM will keep more or less the same.

So ,the situation will become:

The 3G->2G HO success rate will surely decrease a lot.

3>Bring up a new index for further analysis

From the analysis above, we can see the total samples will decrease a lot, but ho

w much exactly? We need a reliable estimate . How to estimate? The best way is refer

to the normal commercial network.

Here I bring up a new index called Inter-RAT HO to Traffic Ratio . The formul


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a is: Inter-RAT HO to Traffic Ratio= NUM of Inter-RAT HO/Traffic. This index r

eflect how many Inter-RAT HO will happened while one Erl traffic was come out(or one

MB). Its easy to understand that if the 3G coverage is good this value will be smaller,

otherwise this value will be bigger, theres a case need to pay attention , this index s

hould calculate separately by CS & PS service.

Now I use the existing date to calculate the value:

1>Operator A 3G network Inter-RAT HO to Traffic Ratio

Begin time

Inter-RAT HO to T

raffic Ratio (CS,Er

l)

Inter-RAT HO to T

raffic Ratio(PS,M

B)

2011-01-10 18.4057971 1.83565972

2>Operator B Inter-RAT HO to Traffic Ratio

Begin time

Inter-RAT HO to T

raffic Ratio(CS,Erl)

Inter-RAT HO to T

raffic Ratio(PS,M

B)

2011-09-10 5.422366819 1.329927001

2011-09-11 6.829227666 1.732457781

2011-09-12 6.077752884 1.683087374

2011-09-13 6.129878094 1.73063497

2011-09-14 6.039713496 1.926980134

2011-09-15 6.493291552 2.077293214

2011-09-16 6.444757408 1.997815984

3>Current Operator 3G network Inter-RAT HO to Traffic Ratio

Begin ti

me

Number

of attem

pted out

going CS

inter-RA

T hando

vers

Cell T

raffic

Volu

me, C

S(Erl)

Inter-RAT

HO to Tr

affic Ratio

(CS,Erl)

Numb

er of

attem

pted

outgoi

ng PS

inter

-RAT

hando

vers

Total PS

Traffic MB

Inter-RAT

HO to Tr

affic Ratio

(PS,MB )


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2012-05-

14454

499.6

608

0.90861640

51163

10984.809

24

0.10587348

2

2012-05-

15446

486.3

928

0.91695436

31231

10330.947

0.11915655

2012-05-

16518

491.0

356

1.05491333

1222

10020.576

44

0.12194907

2

2012-05-

17434

500.2

817

0.86751124

41288

10412.226

78

0.12370072

5

2012-05-

18465

475.5

364

0.97784312

61388

9370.5292

16

0.14812397

1

2012-05-

19750

515.2

625

1.45556876

31683

10472.070

1

0.16071321

2012-05-

20 476

507.8

369

0.93730880

9 1377

10478.549

78

0.13141131

4

Because the radio environment of Operator A have a great difference with Current

Operator So the Operator B date is more useful to reference but the coverage of Ope

rator B is much more better than Current Operator, according to the formula the value

of Current Operator will be bigger than Operator B

Conservative estimate:Inter-RAT HO to Traffic Ratio(CS,Erl)>5,Inter-RAT HO

to Traffic Ratio(PS,MB )>1,

That is: the NUM of Inter-RAT CS HO should >2500, the NUM of Inter-RAT PS HO

should >10000; So, the Inter-RAT HO success rate should more than 95%.

S olution and Result

According to the plan, on 14:00,6JUN Telecel modified one BSCs 2G->3G reselecti

on parameter, detail is: Qsearch_I =7 FDD_Qoffset =0 FDD_Qmin =7

Means:

While in GSM model the UE(support both 2G and 3G) will always search for 3G si

gnal.

When the Ec/Io of 3G signal is better than-12db, the UE will start to reselect from

2G to 3G.

Because the result is very good in the following 2 days after the parameter modifi

cation, Current Operator did parameter modification to the other BSC. After checking K

PIs for several days we find after the modification the Inter-RAT HO success rate have

grown up a lot and kept on stable, other KPIs like Traffic volume, NUM of access also


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increase a lot. Current Operator Radio manager is very satisfied with the result.

The KPIs changes after 2G parameter modification as below:

figure3 NUM of inter-RAT HO changes


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figure4 Inter-RAT HO success rate changes

figure5 NUM of Access changes

figure6 Traffic changes


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After the KPIs became normal the Inter-RAT HO to Traffic Ratio turn to:

Begin ti

me

Number

of attem

pted out

going CS

inter-RA

T hando

vers

Cell T

raffic

Volu

me, C

S(Erl)

Inter-RAT

HO to Tr

affic Ratio

(CS,Erl)

Numb

er of

attem

pted

outgoi

ng PS

inter

-RAT

hando

vers

Total PS

Traffic MB

Inter-RAT

HO to Tr

affic Ratio

(PS,MB)

2012-06-

1812639

1213.

6667

10.4138969

9

44454

16959.742

96

2.62114821

6

2012-06-

1913219

1208.

4864

10.9384764

3

45696

16325.896

86

2.79898864

9

2012-06-

2012810

1175.

8292

10.8944394

3

48127

17455.973

21

2.75705052

2012-06-

2112971

1206.

15

10.7540521

5

47125

18305.446

48

2.57437042

3

2012-06-

2214508

1279.

5175

11.3386491

4

47976

18195.402

32

2.63671004

2

2012-06-

2316803

1394.

7425

12.0473850

9

54943

17206.769

29

3.19310377

6

2012-06-

2414060

1172.

0358

11.9962205

9

47366

16965.943

072.7918283

5 Conclusion

This document find a new way by analyzing user behavior and Mathematical deduc

tion and bring up a new index Inter-RAT HO to Traffic Ratio to solve the 23G inter

operability problem at last..

less samples cause a low 3g to 2g ho success rate

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