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1 Made by :Mohamed Ahmed Abdel Aziz For internal distribution only The source of this presentation from : - My trainings, working and my owned reading in different HUAWEI documents.

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GSM Optimization

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Made by :Mohamed Ahmed Abdel AzizFor internal distribution only

The source of this presentation from :- My trainings, working and my owned reading in different HUAWEI documents.

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I- KPIs (Key Performance Indicators)1. Introduction

2. KPIs classification

3. Main KPIs definitions

II- Problems and Analysis 1. Procedure of CDR Analysis 2. Procedures of Handover problems Analysis 3. Procedure of Congestion Analysis

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I- KPIs (Key Performance Indicators)

1- Introduction

- KPIs refer to Key Performance Indicators which is used to monitor the network performance and detect network problems, The Key Performance Indicators shall be used to measure the performance of the delivery of Services from Huawei Managed Service Team (HMST) to the costumer.

2- KPIs classification - KPIs can be divided into three categories:

a) Accessibility KPIs that mainly indicate the call success rate when a MS accesses the network. Low accessibility KPIs directly lead to low user satisfaction.

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c) Resource Utilization KPIs that are used to monitor the load of hot cells and the network, These KPIs can serve as references for capacity expansion. The traffic volume KPIs help to obtain the ratio of busy-hour traffic to idle-hour traffic, to evaluate the utilization of system resources, The equipment availability KPIs help to know the running status of equipment, such as the running status of channels. If these KPIs are low, equipment and transmission may be faulty.

b) Retainability KPIs these KPIs indicate the capability of providing continuous services.

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2- Main KPIs definition-Accessibility KPIs: - SDCCH Congestion Rate (All Channels Busy)= Failed SDCCH

Seizures due to Busy SDCCH/SDCCH Seizure Requests x 100 %

- Call Drop Rate on SDCCH = Call Drops on SDCCH/Successful SDCCH Seizures x 100%

-TCH Congestion Rate (All Channels Busy) = (Failed TCH Seizures due to Busy TCH (Signaling Channel) + Failed TCH Seizures due to Busy TCH per BSC (Traffic Channel) + Failed TCH Seizures in TCH Handovers due to Busy TCH per BSC (Traffic Channel)) / (TCH Seizure Requests (Signaling Channel) + TCH Seizure Requests in TCH Handovers (Traffic Channel)) X 100%

-Call Setup Successful Rate (CSSR) = (Successful TCH seizures for call/Attempted TCH seizures for call)*(1-SDCCH call drop rate)*100%

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-Retainability KPIs :-TCH Call Drop Rate (including handover)(%) = [(Call Drops on TCH in

stable state (Traffic Channel) + Call Drops in TCH Handovers (Traffic Channel)) / (Successful TCH Seizures (Traffic Channel) + Successful TCH Seizure Requests in TCH Handovers (Traffic Channel))] * 100%

-TCH Call Drop Rate (excluding handover)(%) = [( Call Drops on TCH in stable state (Traffic Channel)) / ( Successful TCH Seizures (Traffic Channel))] * 100%

-Handover Success Rate = (Successful Internal Intra-Cell Handovers per BSC + Successful Internal Incoming Cell Handovers per BSC + Successful External Incoming Cell Handovers per BSC + Successful External Outgoing Cell Handovers per BSC)/(Intra-Cell Handover Requests + Internal Incoming Cell Handover Requests per BSC + External Incoming Cell Handover Requests per BSC + External Outgoing Cell Handover Requests per BSC) x 100%

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- Internal Handover Success Ratio per BSC = (Successful Internal Intra-Cell Handovers per BSC + Successful Internal Incoming Cell Handovers per BSC)/(Internal Intra-Cell Handover Requests per BSC + Internal Incoming Cell Handover Requests per BSC) x 100%

- External Incoming Cell Handover Success Rate = Successful External Incoming Cell Handovers per BSC/External Incoming Cell Handover Requests per BSC x 100%

- External Outgoing Cell Handover Success Rate = Successful External Outgoing Cell Handovers per BSC/External Outgoing Cell Handover Requests per BSC x 100%

- Intra-BSC Radio Handover Success Rate = (Successful Internal Intra-Cell Handovers + Successful Internal Incoming Cell Handovers)/(Internal Intra-Cell Handover Commands + Incoming Internal Inter-Cell Handover Responses) x 100%

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- Resource Utilization KPIs:

- TCH Traffic VolumeDescription: Traffic volume carried on the TCH (Erlang)

- SDCCH Traffic VolumeDescription: Traffic volume carried on the SDCCH (Erlang)

- TCH Availability = Mean Number of Available Channels (TCH)/Mean Number of Dynamically Configured Channels (TCH) x 100%

- SDCCH Availability = Mean Number of Available Channels (SDCCH)/Mean Number of Dynamically Configured Channels (SDCCH) x 100%

- Call Complete Success Rate = (1 - SDCCH Congestion Rate) x (1 - SDCCH Call Drop Rate) x (1 - TCH Congestion Rate) x (1 - TCH Call Drop Rate) x 100%

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II- Problems & Analysis1. Procedure of CDR Analysis2. Procedures of Handover problems Analysis3. Procedure of Congestion Analysis

1. Procedure of CDR Analysis

1.1. Definition of Call Drop- There are two types of call drop: TCH call drop and SDCCH call drop:TCH call drop means TCH channel is released abnormally after it is occupied successfully.SDCCH call drop means SDCCH channel is released abnormally after it is occupied successfully.

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1.2. Formula of call drop rate TCH Call Drop Rate (including handover)(%) = [(Call Drops on TCH in stable state (Traffic Channel) + Call Drops in TCH Handovers (Traffic Channel)) / (Successful TCH Seizures (Traffic Channel) + Successful TCH Seizure Requests in TCH Handovers (Traffic Channel))] * 100%

TCH Call Drop Rate (excluding handover)(%) = [( Call Drops on TCH in stable state (Traffic Channel)) / ( Successful TCH Seizures (Traffic Channel))] * 100%SDCCH Call Drop Rate = Call Drops on SDCCH/Successful SDCCH Seizures x 100%

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1.3 Causes of call drop

According to the definition of call drop, call drop is usually caused by the following:

Radio link fault. During the communication, messages can not be received correctly.

Call drop during handover.

Other system faults.

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1.3.1. Causes of Radio Link Fault

-The causes of radio link fault can be-Interference

-Internal interference-External interference-Equipment interference

-Poor coverage -Coverage hole-Isolated island-Uplink/downlink imbalance

-Improper parameter setting-Equipment problem (Antenna, feeder, combiner, TRX)-Transmission problem

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Radio Link Fault

- Radio link fault means that the communication link is lost during communication. During communication, due to interference in the system or low receiving level, the voice or data often becomes too deteriorated. And finally as a result, MS or network cannot correctly decode the information sent from the opposite side; moreover this cannot be controlled in any other ways. In this case, the system will conclude that a radio link fault occurs and the MS will either start call re-establish or forcedly disconnect the link. Forced link disconnection will lead to a call drop. Therefore, a radio link fault will be concluded by the system only when the communication quality is unacceptable.

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-Diagram of radio link timeoutRadio Link Fault

-System information data: Radio Link Timeout (effective on MS), 32 or 56 recommended.Cell data: SACCH multi-frames, 31 recommended

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1.4 CDR analysis procedure:1- Find out which status the call drops happened mostly, handover status or stable status? If most of call drops happened in handover status, you can reference HO analysis procedure to analysis the issue.

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2- Check the alarm history from the BSC6000 LMT and if there is an alarm affect the CDR it must be cleared first

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3- Check the interference band to see if there is interference for this cell (Internal interference can’t be find in interference band). In this situation, you should check neighbour cells’ frequency. Some time, interference can be caused by equipment itself. If there are results in the interference band 3, 4, and 5, usually the interference problem should be taken into consideration. The interference band is reported to BSC by the BTS via the RF resource indication message when the carrier channel is idle

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Requirement for C/I

All useful signals carrierAll useless signals interference

=

GSM standard: Co-Channel C/I >= 9dB (In practical projects: C / I >= 12dB )

First adjacent Channel C/I >= -12dB

Second adjacent Channel C/I >= -41dB

Useful signal Noise from environment

Other signals

C/I =

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As any one of us knows that there is different between Co-channel interference and Adjacent channel interference, the point is:For Co-channel interference if the interferer less than the carrier it can make interference But for Adjacent channel interference the Adjacent interferer should be higher than the carrier with at least 12 dB (theoretical) or 9 dB (practical in project) to make the interference

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4- Check the coverage of the cellDrive test is the most direct way to locate down a coverage problem. Traffic measurement can be another useful method and we can check the following:1. In power control measurement function, the average uplink and downlink signal intensity is too low.2. In cell measurement function/inter-cell handover measurement function, the level when originating a handover is too low and the average receiving level is too low.3. In call drop measurement function, the level during a call drop is too low and the TA value before a call drop is abnormal.4. In undefined adjacent cell measurement function, the undefined adjacent cell average receiving level is too high (over-shooting coverage) or (missing neighbor) .5. The average level of undefined adjacent cells is too high (isolated island phenomenon).6. In power control measurement function, the maximum distance between MS and BTS exceeds the normal value frequently.7. In outgoing-cell handover measurement function, the handover success rate to a certain adjacent cell is low.8. Mean TA during the radio link failure. Meanwhile, you can check the data from Radio link failure Measurement in MR Measurement, to check the radio link failure distribution based on Trx , and the area Radio link failures happened mostly

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9. Register “uplink and downlink balance measurement function” in traffic measurement and analyze whether uplink and downlink are imbalanced.Most of MRs are supposed to be in the range of 8,9,10, otherwise, there is unbalance existed. The suggestion is that check the equipment from antenna to Trxs.

Rank-1 The downlink receiving power is more than 15dBm smaller than the uplink receiving power.

Rank-2 The downlink receiving power is 10-14dBm smaller than the uplink receiving power.

Rank-3 The downlink receiving power is 6-10dBm smaller than the uplink receiving power.

Rank-4 The downlink receiving power is 3-5dBm smaller than the uplink receiving power.

Rank-5 The downlink receiving power is 0-2dBm smaller than the uplink receiving power.

Rank-6 The uplink and downlink are balanced (ideal condition).Rank-7 The downlink receiving power is 1-2dBm larger than the uplink receiving power.Rank-8 The downlink receiving power is 3-5dBm larger than the uplink receiving power.

Rank-9 The downlink receiving power is 6-10dBm larger than the uplink receiving power.

Rank-10 The downlink receiving power is 10-14 larger than the uplink receiving power.Rank-11 The downlink receiving power is more than 15dBm larger than the uplink

receiving power.

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5- Check check some parameters like:

- SACCH Multi-Frames (SACCH period(480ms)), Radio Link Timeout:When these two parameters are too small, the radio link fault can easily occur and thus call drop will happen. If difficult access or serious call drop is caused by too bad downlink radio environment, properly increase the value of the Radio Link Timeout parameter. If difficult access or serious call drop is caused by too bad uplink radio environment, properly increase SACCH multi-frames.

- RXLEV_ACCESS_MIN

This parameter indicates the minimum receiving signal level for MS to access the cell. If this parameter is too low, as a result, many MSs with low receiving level will reside in the cell, so the cell load will be increased and call drop occurs more frequently.

- Call re-establishment permittedIn case of the call drop due to a radio link fault because of sudden interference or coverage hole, MS will start the call re-establishment process to recover conversation if permitted. Call re-establishment can make the service better, but it takes long time. It can be applied to suburbs or city areas with bad coverage.

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2. Procedure of Handover problem Analysis

2.1. Measurement Points of Intra BSC Handover MS BTS(Source) BSC BTS(Target) MSC Measurement Report Measurement Report Handover decision Channel Activation Channel Activation ACK Handover Command (Old FACCH) Handover Access (New FACCH) Handover Complete (New FACCH) RF Channel Release Handover Performed

Attempted internal inter cell H.O

Internal inter cell H.O

Successful internal inter cell H.O

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2.1. Measurement Points of Intra BSC Handover

-Handover formula definition- Inter cell radio handover success rate =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Incoming internal inter cell handovers + Outgoing internal inter cell handovers )- Internal inter cell handover success rate =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Attempted incoming internal inter cell handovers + Attempted outgoing internal inter cell handovers)

Inter cell radio handover success rate >= Internal inter cell handover success rate

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-The difference between "Internal inter cell handover success rate " and "Cell radio handover success rate " : As viewed from formulas, both numerators are success times of handover, while the denominators are different. While viewed from the measurement points of the counter, Attempted inter cell handovers >= inter cell handovers, so intra BSC handover success rate <= cell radio handover success rate. In practice: If "Internal inter cell handover success rate "="cell radio handover success rate ", this indicates that there is no problem with data, the unsuccessful handovers are caused by radio interfaces, and the radio reasons like interference and coverage should be checked. If "Internal inter cell handover success rate " < "cell radio handover success rate", this indicates that failures may exist in the process from “Channel_ Activate” to "HO-COMD", and there might be data problem or congestion.

2.1. Measurement Points of Intra BSC Handover

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2.2. Measurement Points of InterBSC Handover MS BTS(Source) BSC MSC BSC BTS(Target) Measurement Report Handover Required Handover Request Channel ACT Channel ACT ACK Handover Request ACK Handover Command Handover Access Handover Detect Handover Complete Handover Complete Clear Command (HO successful)

Attempted incoming inter BSC inter cell H.O

Successful outgoing inter BSC H.O

Attempted outgoing inter BSC inter cell H.O

Successful incoming inter BSC H.O

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2.2. Measurement Points of InterBSC Handover

Inter BSC handover Success rate

=(Successful incoming inter BSC inter cell handovers + Successful outgoing inter

BSC inter cell handovers) / (Attempted incoming inter BSC inter cell handovers +

Attempted outgoing inter BSC inter cell handovers )

Incoming BSC handover Success rate

=(Successful incoming inter BSC inter cell handovers) / (Attempted incoming inter

BSC inter cell handovers)

Outgoing BSC handover Success rate

=(Successful outgoing inter BSC inter cell handovers ) / (Attempted outgoing inter

BSC inter cell handovers)

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2.3. Handover Data Process:- BCCH frequencies of all adjacent cells in BA2 table are sent to MS on system message 5 ,5bis and 5ter.- MS reports measurement report to BTS. It includes the BCCH , BSIC and signal level of the adjacent cells and serving cells. - When the measurement report is preprocessed, BSC determines the CGI of all adjacent cells through BCCH frequency and BSIC .-BSC executes handover judgment flow such as basic cell ranking . Once a proper target cell is found, the handover decision message will be sent ,at the same time BSC send the “channel active” to the BTS.- If the target cell triggered by BSC is an external cell, the CGI of the target cell and service cell is sent to MSC on the handover required.- By matching the CGI of the target cell, MSC searches target cell . Once the cell is found, MSC will confirm which BSC is belonged to, and send the handover request message to this BSC.- If there is no CGI of the target cell , MSC will check “Adjacent MSC Table" and find the target MSC, then send the handover request message to that MSC.

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3.4.Types of Handover Problems

- Possible Results

No handover - Cause call drop

Handover failure - Affect the conversation quality, and call drop.

Frequent handover - Affect the conversation quality and increase load of

the system

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3.5. Causes of Handover Problem

-Coverage -Interference -Antenna and feeder system-Base station hardware-Transmission-BSC hardware-Data Configuration-Target cell congestion

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3.4. Handover Problems analysis from the traffic statistics1- We can query Intra-Cell Handover Measurement per Cell, Incoming Internal Inter-Cell Handover Measurement per Cell, Outgoing Internal Inter-Cell Handover Measurement per Cell in M2000 and find the cells which Handover Failure Times are large and calculate the HOSR

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2- Query the Intra-Cell Handover, GSM Cell to GSM Cell Incoming Handover Measurement, GSM Cell to GSM Cell Outgoing Handover Measurement in M2000 to analyzes, and find the type of Handover Failure.

Find out Handover Failure happen whether in all neighbour cells or one or two neighbour cells. Take the neighbour cell which the Handover Failure Times is the largest one to do the deeper analyzes.

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3- Check alarm in BSC6000 There are some alarms which will affect the HO:LAPD alarm/TRX communication alarm, E1 remote alarm (flash), VSWR alarm so the suggestion here to clear the alarm.

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5- Check the interference (mentioned before)

6- Check the coverage of the cell (mentioned before)

7- Check the congestion:-TCH congestion can also make failure in handover. We can find the counter Failed Cell Incoming Handovers (Congestion) in GSM Cell to GSM Cell Incoming Handover Measurement to check congestion or not.

- If there is a congestion we can refer to the TCH congestion analysis

4- Check if there is any other cell has the same BSIC same BCCH within the same area or not( if you find you have to change one of them)

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8- Check handover parameters- Some unreasonable handover parameters can also make handover failure. We can check them in BSC6000

Handover Data.

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3. Procedure of congestion Analysis

3.1.1 Definition of TCH congestion rate

TCH congestion rate (excluding handover)

= (TCH seizure failures for call + TCH seizure failures for very early assignment) / (Attempted TCH seizures + Attempted TCH seizures for very early assignment) *100%

3.1. TCH congestion 3.2. SDCCH congestion

3.1. TCH congestion

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TCH congestion rate (including handover)

=(TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (Attempted TCH seizures (all) + Attempted TCH seizures for very early assignment + Attempted TCH seizures for intra BSC incoming cell handover + Attempted TCH seizures for inter BSC incoming cell handover)

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3.1.2 Attempted TCH seizures measurement point Attempted TCH seizures for call

−Receive the MSC assignment request message

Attempted TCH seizures for very early assignment

− When there is no resource for SDCCH allocation and very early assignment is permitted

Attempted TCH seizures for intraBSC incoming cell handover

−When intraBSC incoming cell handover request message is received (non-SDCCH handover request).

Attempted TCH seizures for interBSC incoming cell handover

−When interBSC incoming handover request message is received (handover type is non-SDCCH)

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3.1.3. TCH seizure failures:

TCH seizure failures for call,

TCH seizure failures for very early assignment,

TCH seizure failures for interBSC incoming cell handover,

TCH seizure failures for intraBSC incoming cell handover,

TCH seizure failures for intracell handover.

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Co-frequency and co-BSIC lead to TCH assignment failure in handover

Board fault or unstable performance causes the high congestion rate

BTS hardware is not properly installed, which causes uplink/downlink signal level unbalance and TCH congestion.

The transmitting power of BCCH TRX is too much higher than that of TCH TRX in the same cell.

Interference causes the congestion

TCH assignment failure due to isolated site and complicated topography result in the high congestion rate

3.1.4 Causes of high TCH congestion rate

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3.1.5 TCH congestion analysis procedure from the traffic statistics :1- Check alarm in BSC6000 There are some alarms which will affect TCH congestion:LAPD alarm/TRX communication alarm, E1 remote alarm (flash), VSWR alarm so the suggestion here to clear the alarm.

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2- Check the Interference, we can query Interference Band Measurement per TRX in M2000 to check the Interference Band.Generally, If the value in Interference Band 3,4,5 bigger than 1, that means interference in this cell. This will affect the TCH congestion rate specially the TCH seizer in incoming HO state.

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3- Number of MRs (Uplink-and-downlink Balance) to see if there is unbalance existed. Most of MRs are supposed to be in the range of 8,9,10, otherwise, there is unbalance existed. The suggestion is that check the equipment from antenna to Trxs.

Rank-1 The downlink receiving power is more than 15dBm smaller than the uplink receiving power.

Rank-2 The downlink receiving power is 10-14dBm smaller than the uplink receiving power.Rank-3 The downlink receiving power is 6-10dBm smaller than the uplink receiving power.Rank-4 The downlink receiving power is 3-5dBm smaller than the uplink receiving power.Rank-5 The downlink receiving power is 0-2dBm smaller than the uplink receiving power.

Rank-6 The uplink and downlink are balanced (ideal condition).Rank-7 The downlink receiving power is 1-2dBm larger than the uplink receiving power.Rank-8 The downlink receiving power is 3-5dBm larger than the uplink receiving power.

Rank-9 The downlink receiving power is 6-10dBm larger than the uplink receiving power.Rank-10 The downlink receiving power is 10-14 larger than the uplink receiving power.

Rank-11 The downlink receiving power is more than 15dBm larger than the uplink receiving power.

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4-Check the parameters about TCH half rate:-If we find the traffic volume in this cell is too high, the TCH Traffic Volume per Channel (Erl)

is over 0.6(if this counter is not found use the TRX utilization)-, we need to enable Half Rate and change some parameters about half rate.

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- So the suggestion in this case will be to Enable Half Rate, decrease the parameters TCH Traffic Busy Threshold ,AMR TCH/H Prior Cell Load Threshold,TCH Traffic Busy Underlay Threshold and TCH Traffic Busy Overlay Threshold which in Channel Management.

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5- finally If the cell has already enabled the half rate, and the value of the half rate parameters have already been changed to smallest, but this cell is still high congestion, we need to expand the TRX of this cell.

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3.2. SDCCH congestion

3.2.2 Causes of SDCCH seizure: SDCCH assignment for MOC

SDCCH assignment for MTC

Location update

SDCCH handover

Short message

IMSI attach and detach

3.2.1. Formula for SDCCH congestion rate: SDCCH congestion rate=Attempted SDCCH seizures meeting a SDCCH blocked state /Attempted SDCCH seizures (all)

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- IMSI attachWhen an MS is switched on, the IMSI attach procedure is executed. This involves the following steps:1. The MS sends an IMSI attach message to the network indicating that it has changed state to idle.2. The VLR determines whether there is a record for the subscriber already present. If not, the VLR contacts the subscriber’s HLR for a copy of the subscription information.3. The VLR updates the MS status to idle.4. Acknowledgement is sent to the MS.

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- If the MS has changed LA while powered off, the IMSI attach procedure may lead to an update to the location of the MS.

During IMSI attach, the VLR may determine that the current LAI of the MS is different from the LAI stored in the MS’s subscription information. If so, the VLR updates the LAI of the

MS.

- Changing Cells within an LA

- MS’s are constantly moving around in the cellular network. The MS location information stored in the VLR is the LA. If an MS changes cells within a LA, the network is not updated.

- The MS knows that the new cell belongs to the same LA by listening to the BCCH in the new cell. The BCCH broadcasts the cell’s LAI. The MS compares the last LAI received with the new LAI. If they are the same, it means that the MS has not changed LA's and does not need to inform the network.

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- Location Updating, Same MSC/VLR

1. The MS listens to BCCH in the new cell to determine the LAI. The received LAI information is compared to the old one. If they differ, a location update is necessary.2. The MS establishes a connection with the network via SDCCH. Authentication is performed.3. If authentication is successful, the MS sends a Location Updating Request to the system.4. The system acknowledges Location Updating and requests BTS and MS to release the signaling channel.

If an MS detects a change in LAI on the BCCH, it informs the network. When the MS sends the Location Updating message, the MSC/VLR determines whether it is an MS, which is already registered, or if it is an MS visiting from another MSC/VLR.

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1- Check the alarm and interference.These two steps just like the TCH congestion analyzing which mentioned before.

3.2.3 SDCCH congestion analysis procedure from the traffic statistics :

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2- Check the parameters.Some parameters implemented by mistake will cause the SDCCH congestion, for example the LAC of the cell in Basic Attribute Parameters. So we need to check the basic parameter and correct the wrong one. This will cause many location area update making SDCCH congestion.

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3-We can query Immediate Assignment Measurement per Cell, which in M2000 to do deeper analyze about SDCCH congestion to see what is the reason of the high request of the SDCCH Location Area Update , SMS , MOC,…………..

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4- If the congestion rate is too high- We can add one static SDCCH or We can enable dynamic SDCCH. Change the SD Dynamic Allocation Allowed to yes to enable dynamic SDCCH

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• - SDCCH dynamic allocation should be activated •       - When the no. of idle SDCCH equal or smaller than Idle SDCCH

Threshold N1

• For the SDCCH dynamic conversion from TCH to SDCCH there are some conditions and parameters responsible for this process as the following:

•           -The sum of the number of idle full-rate channels and half the number of idle half-rate channels is greater than four or the number of TRXs in the cell, and an idle full-rate channel is in the cell;

•           - The sum of the number of SDCCHs in the cell + 8 is smaller than the maximum number of SDCCHs allowed in the cell.

•       - Cell SDCCH Channel Maximum:   is the maximum number of SDCCHs that can be configured in a cell 

- Procedures of SDCCH dynamic conversion:

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Thanks for your effort and your time with me

Mohamed Ahmed Abdel Aziz