Ccsi - 2G Rno Basic Training: Prepare By: Peter Wylson Marpaung
Ccsi - 2G Rno Basic Training: Prepare By: Peter Wylson Marpaung
Ccsi - 2G Rno Basic Training: Prepare By: Peter Wylson Marpaung
SDCCH TCH
Blocking Blocking
SDCCH
(system) (system)
Success Rate
and and
ACK.
ACK
Check
SETUP (SDCCH) Restrict.
Mobile Originated Call - Speech (2)
MS BTS BSC MSC VLR
SETUP (SDCCH)
CALL PROCEEDING (SDCCH)
ASSIGNMENT REQUEST
PHYS. CONTEXT REQUEST
ALERTING (FACCH)
CONNECT (FACCH)
CONNECT ACK. (FACCH)
Mobile Originated Call - Speech (3)
MS BTS BSC MSC VLR
CONNECT ACK. (FACCH)
DISCONNECT (FACCH)
SACCH RELEASE
DISC. (FACCH)
+ End of
RF.CH. RELEASE
BSC traffic
ACK. Measurement
ACK. & CLEAR COMPLETE
SCCP RELEASE
ACK.
Dropped Calls
Dropped Calls
Dropped calls show the number of abnormal disconnections during call setup or during
conversation. From a subscriber point of view, the most serious dropped calls are those that
interrupts an ongoing conversation, i.e. a call dropped on the TCH.
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Radio Link Failure- Interference
• Category
– Co-channel interference
– Adjacent-channel interference
– Inter-modulation interference and other external interference
C/I : C/A :
GSM Recommendation >9 dB GSM Recommendation >-9 dB
Planning Criteria >12 dB (Non Hopping) Planning Criteria >3 dB
Planning Criteria >9 dB (Hopping) C/A is to measure Adjacent channel Interference
C/I is to measure Co channel Interference tolerance. tolerance.
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Radio Link Failure- Interference
C/I : C/A :
GSM Recommendation >9 dB GSM Recommendation >-9 dB
Planning Criteria >12 dB (Non Hopping) Planning Criteria >3 dB
Planning Criteria >9 dB (Hopping) C/A is to measure Adjacent channel Interference
C/I is to measure Co channel Interference tolerance. tolerance.
Page 13
Radio Link Failure- Interference
Analysis:
1. If Scan-TRX of cell results in the interference band 3, 4, and 5, usually the interference problem
should be taken into consideration.
2. If there are too many times of good Rx-Level but low Rx-Quality, it means: co-frequency or
adjacent frequency interference or external interference.
3. Handover measurement function from outgoing handover attempts distribution. If there are too
many times of handover caused by UL/DL Quality, it indicates possibly there is interference.
4. See from Scan TRX for Rx-Quality level of TRX for reference.
5. See from Scan TRX for Rx-Level and Rx-Quality upon call drop for reference.
Action:
– First check equipment problems for inter-modulation interference. Mostly is bad feeder
installation or bad hardware output signal.
– Perform drive test to check interference area and distribution of Rx-Quality to find the
interferer frequency for internal interference. Then do Cell/Cluster MAL/MAIO/HSN
retune.
– Further search for the interference source with the spectrum analyzer to search
external interferer then escalate to proper part. Mostly repeater or illegal transmitter,
then escalate to proper part.
– Activate Frequency hopping, DTX (Discontinuous Transmit) and power control functions
to reduce internal interference of the system. This is parameter setting.
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Radio Link Failure- Interference
Not Overshoot, but has ICM band 5 and Bad UL Signal Quality
Page 15
Radio Link Failure- Interference
Sample of Clear spectrum result Sample of external interference from CDMA which
impact to Telkomsel cells performance
DL CDMA Band suspected has too high power that disturb TSEL UL GSM Band (900.2Mhz).
16
Radio Link Failure- Interference
Page 18
System Balance
Page 20
Radio Link Failure- Coverage
Analysis:
Drive test result is the best information to found the coverage problem.
1.Idle Receiving level report show proportion of low receiving level times is too large.
2.Inter-cell handover measurement function, the level when triggering a handover is too low and the
average receiving level is too low.
3.Receiving level during a call drop is too low and the TA value before a call drop is big (Check from Scan-
TRX report).
4.From scanning result, founded undefined adjacent cell receiving level is too high (over-shooting
coverage).The average level of undefined adjacent cells is too high (isolated island phenomenon).
5. In outgoing-cell handover measurement function, the handover success rate to a certain adjacent cell is
low.
Page 21
2. Layer 2 Time-Out
T200 is a timer of acknowledgement transmission from BTS to MS through LAPD. When BTS transmits a
acknowledgement message to MS, T200 times is started in LAPD. If this acknowledgement message is not
received by MS until T200 timer is expired then the transmission will be repeated (retransmission).The maximum
retransmission is N200+1 times. T200 will be restarted in each retransmission. So, N200 is the maximum number
of retransmission of LAPD (Layer-2). If until N200+1 times of retransmission the acknowledgement message, MS
still doesn’t receive this message, then the connection will be dropped.
Shorter T200 Value , means Faster BSS to trigger disconnection. This will cause low “SDSR”.
Shorter T200 value , means easy for BSS to release channel which hold by UE previously. This will
reduce congestion at cell channel due to shorter channel holding time.
3. Excessive Timing Advance
The TCH Drop counters due to Excessive Timing Advance will pegged during the time of disconnection, the last Timing Advance value
recorded was higher than the Max TA Parameter. This drop reason is commonly apparent to isolated or island sites with a wide
coverage area.
Action:
Check if the cell parameter Max TA is < 63.
Check if the co-channel cells are overshooting.
Solution:
Set Max TA to a value close to 63.
Activate TAHOEN.
Faster handover trigger due to TA -> Adjust “TALIMIT” to proper TA value base on site to site distance.
Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.
On 16th Nov. the power control optimization, improved DL/UL quality to reduce drop
calls due to handover.
5. Poor Quality on Downlink or Uplink or Both Links
Problem on Bad Quality is usually associated with Co-channel Interference on BCCH or TCH. Faulty MAIO assignment can cause
frequency collisions on co-sited cells especially on 1x1 Reuse. External interference is also one possible cause of problem on quality.
Action:
Check C/I and C/A plots.
Check Frequency Plan (Co-BCCH or Co-BSIC Problem).
Check MAIO, HOP, HSN parameters.
Check FHOP if correctly configured (BB or SFH).
Check for External Interference.
Perform drive tests.
Solution:
Change BCCH frequency.
Change BSIC.
Change MAIO, HOP, HSN.
Change MAL.
Adjusted 119 cells INTRACELLHOEN YES->NO at 16 Nov, Observe the performance of the adjusted,
Call Drops on Radio Interface in Handover State decreased, Call Drops on Radio Interface in Stable
State did not significantly improve. Significantly improved the overall call drop number.
8. Bad Parameter Configuration
Some idle and dedicated parameter which adjusted not in rule will cause KPI degradation.
Action: Check parameter setting.
Solution: Correct strange and erroneous parameter setting. Below is the sample
After the cell Handover parameters optimization, improved the handover performance to
reduce drop calls due to handover.
SDCCH Drop Performance
Probable Reasons of Drops on SDCCH
Low Signal Strength on Down or Uplink
The reason for poor coverage could be too few sites, wrong output power, shadowing, no indoor coverage or network
equipment failure.
Action: Check coverage plots. Check output power. Perform drive tests. Check BTS error log
Solution:
Add new sites.
Increase output power.
Repair faulty equipment.
Adjust TRX POWER parameter (POWT/POWL)
Adjust antenna direction & Tilt
Mobile Error
Some old mobiles may cause dropped calls if certain radio network features are used. Another reason is that the MS is
damaged and not working properly.
Action: .Check MS type from Core team.
Solution: Inform operator.
Probable Reasons of Drops on SDCCH
Subscriber Behavior
Poorly educated subscribers could use their handsets incorrectly by not raising antennas, choosing ill-advised
locations to attempt calls, etc.
Action: Check customer complaints and their MS.
Batery Flaw
When a subscriber runs out of battery during a conversation, the call will be registered as dropped call due to low
signal strength or others.
Action: Check if MS power regulation is used. Check if DTX uplink is used.
Congestion on TCH
The SDCCH is dropped when congestion on TCH.
Action: Check TCH congestion
Solution: Increase capacity on TCH or using features like Assignment to another cell (Direct retry), Cell Load Sharing,
HCS, Half rate parameter(TCHAJFLAG,TCHBUSYTHRESH) etc.
Handover Performance
Handover Performance
Handover is a key function in a GSM network and a key technology of mobile communication system
which make continued conversation become possible. If the handover performance is poor the
subscriber will perceive the quality of the network as bad.
MSC 2
BSC 1 MSC 1
target
intra
inter
cell source
BSC
MSC controlled
out-
going
HW faults.
Action: Check BTS error log.
False Accesses
No response from MS after Channel Request. The system waits about T200 seconds before performing a
disconnection and the channel is available again.
Action: Check frequency plan. Check interference.
Solution: Improve frequency plan and reduce interference. Reduce T200 SDCCH value.
Faulty Transceiver
Action: Check BTS error log.
Solution: Change & repair faulty equipment
TCH Congestion
Probable Reasons of TCH Congestion
Increasing Traffic Demand
The high traffic could be related to an occasional event or due to a long term growth.
Action:. Check if short term traffic growth. Make trend comparisons..Check TCH dimensioning. Check the use of
congestion relieving features such as Assignment to Worse cell, Cell Load Sharing and HCS.
Solution: Increase the number of transceivers. But check for frequency availability.
Bad Dimensioning
Bad allocation of TCH in a system may cause unnecessary congestion. Investigate if possible to move transceivers
from non-congested areas to congested areas (Rebalancing). Of course, the base station type, current number of
transceivers, floor space, combiner type, etc., should be considered before a recommendation to move
transceiver could be made.
Action: Check TCH traffic and dimensioning.
Solution: Re-dimension the TCH.
Abis Congestion
2G system using PCM30 technology. 1E1=2.048Mbps. 1 E1=32 Abis Timeslot. 1 Abis timeslot=4 Sub slot.
Action: Check Abis Load between E1 if Site has more than 1 E1. Sometime, 1 Sites has 3 E1 (example), but load mostly at
E1 number 2. This is not good for TR which connected to E1 number 2.
Solution: Balance E1 Load with TRX-E1 mapping. Add E1 if existing E1 already has >80% utilization.
E1 Description
If user get 1 E1 sub slot and single/alone TBF in 1 PDTCH, then he has
16 Kbps throughput at maximum (Theoretical). Then we have coding
scheme to compress the data become smaller. GPRS has CS1-
CS4/EDGE has MCS1-9.
Probable Reasons of Low PS Access Success
HI TBF number In Uplink and Downlink
High PS traffic compare to TBF capacity in 1 PDTCH.
Action:. Check for maximum TBF in BH.
Solution: Adjust UL/DL multiplexing. Too high will cause throughput degradation/Too Small will cause high
throughput but small TBF capacity.
Before LA 500ms 40 40 70 80
Although GPRS and EDGE share the same symbol rate, the modulation bit rate differs.
EDGE can transmit three times as many bits as GPRS during the same period of time. This is the main reason
for the higher EDGE bit rates.
GPRS AND EDGE
3. Enhanced SFH
Frequency Hopping Parameter
C2 is the GSM cell reselection algorithm. Once the MS (Mobile Station) has camped
onto a cell it will continue to assess the surrounding cells to ensure it is monitoring
the cell that will offer the best radio connection. As the user moves the camped on
cell may become unsuitable. This situation will generate a cell reselection.
C31 is a criteria based algorithm used as part of the GPRS cell reselection process. It is
used to assess if prospective cells qualify as reselection candidates prior to applying
the C32 GPRS cell reselection algorithm.
C32 is the GPRS cell reselection algorithm. Once the MS (Mobile Station) has camped
onto a cell it will continue to assess the surrounding cells to ensure it is monitoring
the cell that will offer the best radio connection. As the user moves the camped on
cell may become unsuitable. This situation will generate a cell reselection.
Cell “Selection” Parameter
C1 = (A−max(B,0))
where
•A = Average Received level from Cell − RX_ACCESS_MIN (in dBm)
•B = MS_TXPWR_MAX_CCH − P (in dBm).
•The Average received level (AV_RXLEV) is found by averaging RXLEV samples over a period.
•RX_ACCESS_MIN is a cell parameter which set minimum allowed RXLEV for an MS to access that cell.
•MS_TXPWR_MAX_CCH is the maximum TX power an MS may use when accessing the system (using RACH).
•P is the maximum RF output power of the MS, usually 33dBm for a handheld GSM900 and 30dBm for a handheld
GSM1800 MS. Often the latter term in C1 equals 0 and equation (1) can be simplified to;
C1 = AV_RXLEV − RX_ACCESS_MIN
For example, if the minimum allowed level to gain access to a cell is −100dBm and the received average
level at the cell’s BCCH frequency is -80 dBm, MS calculates C1 as +20 for that particular cell. MS camps
to the cell with the highest C1 value.
There is an exception to the standard procedure described above. When MS evaluates C1 values for cells
belonging to a different Location Area (LA), it subtracts a parameter called CELL_RESELECT_HYSTERESIS
from the C1 value, which means that those cells are given a negative offset. The reason for this is that
changing LA requires a Location Update (LU) procedure that consumes network signaling capacity. Thus,
by assigning a negative offset to C1, unnecessary LUs caused by slow fading can be reduced. MS receives
information of the cell dependent CELL_RESELECT_HYSTERESIS values through BCCH.
Cell “Re-Selection” Parameter
Cell reselection criterion C2 is defined as
C2 = C1 + CELL_RESELECT_OFFSET − TEMPORARY_OFFSET*H
when
timer T > PENALTY_TIME then H=0 >>>> C2 = C1 + CELL_RESELECT_OFFSET
timer T PENALTY_TIME then H=1 >>>> C2=C1 + CELL_RESELECT_OFFSET − TEMPORARY_OFFSET
Penalty Time=31 >>>> C2 = C1 - CELL_RESELECT_OFFSET
SYSTEM INFORMATION 6:
Cell Global Identity (CGI)
LAI
Cell Option
NCC Permitted
2G CHANNEL CONFIGURATION
IMPORTANT TO KNOW
Important Type of TRX Channel Type
• TCHFR(TCH Full Rate)
– “Can” automatically converted to PDTCH at PS BH base on Dynamic PDTCH Conversion parameter
– It has 13 kbit/s
• TCHHR(TCH Half Rate)
– “Cannot “ automatically converted to PDTCH at PS BH base on Dynamic PDTCH Conversion parameter
– It has 5.6 kbit/s
• SDCCH8(SDCCH8)
– Contain 8 sub slot = 8 user at same time
• MBCCH(Main BCCH)
– Every cell in 2G should have BCCH for system information broadcast
• CBCCH(Combined BCCH)
– BCCH + CCCH
• BCH(BCH),
– Extended BCCH
• BCCH_CBCH(BCCH+CBCH)
– BCCH + Cell Broadcast
• SDCCH_CBCH(SDCCH+CBCH)
– SDCCH/4+ Cell Broadcast
• PDTCH
– For Static PS Channel
– DL have 16 TBF at maximum an UL have 7 TBF capacity at Maximum
• Other:
– PBCCH_PDTCH(PBCCH+PDTCH),
– PCCCH_PDTCH(PCCCH+PDTCH),
– DPDCH(Dynamic PDCH)
Some Sample of Parameter Adjustment
reference
1. Power Control 3
2. INTRACELLHOEN
3. EDGESTAT1/ EDGELAST1
4. EGPRS11BITCHANREQ/LQCMODE
5. MAXRESEND
6. SUPPSDLPC
Power Control 3 Implementation CR
Site Information
1. Change power control type II to power control type III for all cells of cluster Kudus on Mar 26.
2. Type III have more efficient power control than power control II.
3. All CS KPI improve after adjust.
Power Control 3 Implementation
Site Information
CSSR increased after
adjusted
Site Information
1. Adjust parameter INTRACELLHOEN from “Yes” to “No” for all NPI cells on February 10.
2. All cells use the RF Hopping, the all TRX quality almost same in the one cell due to use the same frequency.
3. TDR improve after adjust. but HOSR decreased due to more HO requests in the case of bad quality.
INTRACELLHOEN
Site Information
Site Information
1. Adjust EDGESTAT1/ EDGELAST1 to faster for all cells of cluster Kudus on Mar 12
2. MS easier to execute EDGE Handover in the case of the poor Receive Level.
3. TDR &HOSR improve after adjusted.
EDGESTAT1/ EDGELAST1
Site Information
TDR decreased after
adjusted
Site Information
1. Adjust NO to YES for EGPRS11BITCHANREQ for all cells of cluster Kudus on February 15
2. Speed up the MS access to PDCH channel.
3. IR’s error correction better than LA.
4. The PS performance improved after adjusted.
EGPRS11BITCHANREQ/LQCMODE
Site Information
Downlink TBF
establish Success
Rate increased after
adjust.
MAXRESEND CR
Site Information
1. Adjust 40 to 150 for MAXRESEND for all cells of cluster Purwokerto on February 15
2. The CS performance improved after adjusted.
MAXRESEND
Site Information
Uplink TBF establish
Success Rate
increased after
adjust
Downlink TBF
establish Success
Rate increased after
adjust.
MAXRESEND
Site Information
TDR decreased after
adjusted
1. Feature activation for PS power control for cluster 4 of Yogya on Apr 12.
2. Reduce the PS interference of CS. improve the quality of CS.
3. The TDR&CSSR&HOSR improved after adjusted. But SDSR decreased due to many cells still have
interference.
CR
Page 81
SUPPSDLPC
Parameter Summary
CSSR increased after
adjust