gprs dt analyse and case
TRANSCRIPT
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GPRS DT ANALYSE AND CASE
KEY WORDS:
GPRS DT, SYSTEM INFORMATION, CELL RESELECTION
ABSTRACT:
This report summarizes all kinds of problems in GPRS DT and corresponding methods to
solving them. And it gives more detailed analyze and related cases.
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CATALOG
SYSTEM INFORMATION 2Ter ........................................................................................3
RESOURCE NOT ENOUGH .............................................................................................5MEASUREMENT FREQUENCY LACK ..........................................................................7
CELL RESELECTION OPTIMIZING (A) .........................................................................8
CELL RESELECTION OPTIMIZING (B) .......................................................................10
UPLINK INTERFERENCE TO DATA TRANSFER ...................................................... 11
TEST EQUIPMENT CAUSE ............................................................................................13
FREQUENCY INTERFERENCE .....................................................................................15
NEW SITE IMPROVE COVERAGE ...............................................................................16
MODIFY ANTENNA TO COVER .................................................................................. 19
GPRS FEATURE DISABLE ............................................................................................ 21
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SYSTEM INFORMATION 2Ter
QUESTION
The signal strength and quality in cell A (900M) is poorer and poorer. When MS
moves in opposite direction, the signal strength and quality in cell B (1800M) is
very good. But at this time, MS could not occupies cell B, even C1 and C2 value
of cell B do not exist in TEMS C1 and C2 Chart.
ANALYSING
We could find MS receives System Information 13 before getting system
information 2 ter. So MS requests channel and gets corresponding channel for
data transfer in cell A. MS could not select cell B with strong signal strength and
good quality because of the lost of 1800M neighboring cell ARFCN.
Related explanation in GSM specification below.
METHOD
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Strengthening signal coverage of both 900M and 1800M synchronously, which
could ensure the strong signal strength, good quality and high speed of data
transfer when not receiving System Information 2ter.
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RESOURCE NOT ENOUGH
QUESTION
The data speed transfers slowly when MS reselect to one cell.
ANALYSING
After reselect to this cell, MS only gets 2 PDCHs. When gets 3 PDCHs, two
users share these 3 PDCHs. Data transfers slowly. The layer 3 signaling figure is
shown below.
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This cell exists serious congestion through STS and the number of PDCH
establish failure, PDCH preempt and TBF release are more somewhat. So the
resource of this cell is not enough.
METHOD
The resource need to be increase. The speed of data transfer improves after the
number of frequency carriers is increased. The comparison figures are shown
below.
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MEASUREMENT FREQUENCY LACK
QUESTION
In one road, both signal strength and quality are very poor, and speed of data
transfer is low. The cell reselection queue should be A->B->Cstrongest signal
strength->D->E in the first DT test. But the queue is A->F->E in this DT test.
ANALYSING
After the fist test, the CRO of cell B is changed from 8 to 5, which result in no
reselection from cell A to cell B. But the signal strength of cell B is not the
strongest, and cell C is the best selection through the first DT log.
The MS does not reselect from cell A to C because of relation lack between cell
A and C. And measurement frequency is not added in idle mode list of cell A.
METHOD
Adding measurement frequency of cell C to cell A in idle mode. Even the relation
between the two cells could be ignored.
The signal strength and quality of this road is improved after adding
measurement frequency of cell A in idle mode. The comparison figures are
shown below.
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CELL RESELECTION OPTIMIZING (A)
QUESTION
In one road, the cell reselection is so fast and frequent, which results in low data
transfer.
ANALYZING
The cell reselection queue is A->B->A->C. After reselection from cell B to A, the
signal strength in cell A is very poor and data transfer stopped nearly. The signal
strength in cell C is strong, but cell B is not reselect to C, because the ACCMIN
98 and CRO 8 in cell B give cell B a too big coverage in idle mode.
METHOD
Modify ACCMIN in cell B from 98 to 94 and CRO from 8 to 4. The possibility of
selection to cell B is decreased and corresponding C is increased. The signal
strength and quality of Cell A and C is good compared to B.
The cell reselection in the first DT test is A->B->A->C.
The queue in the second DT test is A->C.
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The cell selection is from cell A to C directly and cell B is not be added. The
number of cell reselection is decreased from 4 to 2. The data transfer is improved
therefore. The effect of the second DT test is shown below.
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CELL RESELECTION OPTIMIZING (B)
QUESTION
In this road, the cell reselection is from cell A to B directly. But the signal strength
is very poor in cell A when reselection happens.
ANALYZING
When cell A reselects to B, the signal strength is very poor. Considering cell C
should be transition cell between cell A and B.
METHOD
Modify CRO in cell A from 6 to 4 and CRO in cell C from 0 to 4, which result
in cell reselection queue A->C-> B.
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UPLINK INTERFERENCE TO DATA TRANSFER
QUESTION
After cell reselection to cell A, data transfer is poor.
ANALYZING
The uplink interference of cell A impacts quality in air-interface. The uplink
interference in STS is shown below.CELL DATE PERIOD NOACCUF ITFUSIB1 ITFUSIB2 ITFUSIB3 ITFUSIB4 ITFUSIB5
A 060825 0000-0100 360 889 40 1175 9963 1928
A 060825 0100-0200 360 1536 1456 5886 5752 206
A 060825 0200-0300 360 2316 3405 6293 3144 48
A 060825 0300-0400 360 3432 4806 5039 1138 13
A 060825 0400-0500 360 3912 5227 5142 1050 11
A 060825 0500-0600 360 6646 4504 3126 919 12
A 060825 0600-0700 360 3525 1877 3338 5082 503
A 060825 0700-0800 360 663 224 2087 7916 1265
A 060825 0800-0900 360 99 106 1013 4178 334
A 060825 0900-1000 360 68 13 34 5338 1505
A 060825 1000-1100 360 59 29 12 1198 2583A 060825 1100-1200 360 214 85 731 4183 688
A 060825 1200-1300 360 89 12 24 2585 3309
A 060825 1300-1400 360 100 75 385 3257 1896
A 060825 1400-1500 360 372 41 94 1680 1179
A 060825 1500-1600 360 122 11 71 987 1884
A 060825 1600-1700 360 109 9 17 744 2341
A 060825 1700-1800 360 182 26 13 418 2482
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A 060825 2000-2100 360 58 6 195 3063 2273
A 060825 2100-2200 360 94 15 188 5158 1689
A 060825 2200-2300 360 208 429 2188 5913 690
A 060825 2300-0000 360 7260 602 1788 2423 77
METHOD
Modify CRO in cell A from 5 to 0 to avoid to reselect to this cell.
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TEST EQUIPMENT CAUSE
QUESTION
The signal strength and quality are very good, but the data transfer is not perfect.
ANALYZING
The operating system in test PC that day is E/// ESOE which sends special
network information on time. When MS reselects to cell A, the PC sends a series
of query indication to network side, which impacts the normal FTP download.
The abnormal indication is shown below through Ethereal software.
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FREQUENCY INTERFERENCE
QUESTION
After selecting cell A, the speed of data transfer is changed poor.
ANALYZING
C/I is so low in cell A. It is the most important reason to poor data transfer.
MOTHED
The C/I of frequency 23 and 65 is the lowest, modifying 23 65 -- > 12 60. The
data transfer speed is improved. The comparison figures are shown below.
BEFORE AFTER
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NEW SITE IMPROVE COVERAGE
QUESTION
The signal strength of some cells covering one road is less than or equal to
-80dBm, and the corresponding quality is changed to poor.
ANALYING
In this road, the signal strength of every cell is very low. So the coverage is not
so good to this road. The DT chart is shown below.
At the same time, the serious bit error rate could be seen in the layer 3 sheet of
TEMS Investigation. Abundant data retransmissions take place and data transfer
is interrupt usually. Related error bit is shown below.
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There are many high resident buildings around this road. Some signal from micro
cellular leaks to the road, but it should be avoided and can not cover the whole
road. The below figure shows the low signal strength road, serving cell and micro
cells around.
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METHOD
Advise to add new site in order to cover this road well.
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MODIFY ANTENNA TO COVER
QUESTION
One site consists of 1800M and 900M, no cover by 1800M to its west direction
road.
ANALYZING
In the first test, MS selects this cell, but does not receive System Information
2Ter. So MS measures 1800M frequency only, and signal strength and quality is
changed poor when it moves from this site to the west direction because the MS
could not measure 900M frequency. Eventually data transfer is stopped. The DT
figure is shown below.
METHOD
Modify antenna angle from 60 to 90.
In the test later, signal strength of 1800M is improved and MS selects 900M cells
more easily. The DT figure is shown below.
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GPRS FEATURE DISABLE
QUESTION
In some tests e.g. airport road, the FTP download and GPRS attach could both
not be operated effectively.
ANALYZING
This kind of problem took place hardly. Radio parameter and BSC parameter are
correct through careful check. No abnormal problems are found.
METHOD
Finally restarting cell GPRS feature solves this problem using RLGSE and
RLGSI commands. FTP data transfer is performed normally. This method is
produced through test, so problem should take place in HW or SW feature usage
and maintenance.