less samples cause a low 3g to 2g ho success rate
TRANSCRIPT
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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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7/29/2019 Less Samples Cause a Low 3G to 2G HO Success Rate
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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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7/29/2019 Less Samples Cause a Low 3G to 2G HO Success Rate
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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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7/29/2019 Less Samples Cause a Low 3G to 2G HO Success Rate
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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..