Radio Network Optimization Guideline

Radio Network Optimization

Guideline

Statement of Confidentiality Copyright in this document is the property of RIC and its contents shall be held in strict confidence by the recipient hereof and shall be used solely for the purposes of RIC. Neither this document nor its contents shall be disclosed to any other person or used for any other purpose without prior written permission of RIC.

Reference: RIC/NWG/RNP/OPTIMIZATION GUIDELINE of 40 Date: 7/16/2006

DOCUMENT RELEASE HISTORY

VERSION NO.

RELEASE DATE PURPOSE

1.0 29P

THP APRIL 2006 DRAFT ISSUE PREPARED BY SALAM AL-AIESHY

2.0 12P

THP JULY 2006 REVIEWED BY RASHID GHAZI WITH MODIFICATIONS

3.0 16P

THP JULY 2006 ISSUED BY SALAM AL-AIESHY

DOCUMENT REVIEW TEAM: NAME POSITION / DEPARTMENT

SALAM AL-AIESHY HEAD OF RADIO NETWORK PLANNING DEPARTMENT

ALA NAZARI CTO

RADIO NETWORK PLANNERS RNP/BSS PLANNING DEPARTMENT

APPROVALS APPROVED BY SIGNATURE DATE MR. NAZARI

CTO, RIC


TABLE OF CONTENTS

TU1.UT TUSCOPE AND PURPOSE OF DOCUMENTUT ...................................................................................5 TU2.UT TUINTRODUCTIONUT ............................................................................................................................5 TU3.UT TUNEIGHBOUR ANALYSISUT ..............................................................................................................6

TU3.1UT TUAnalysis of existing neighboursUT ...................................................................................6 TU3.1.1UT TUFinding non-mutual neighboursUT..........................................................................6 TU3.1.2UT TUCorrect non-mutual neighboursUT ..........................................................................7 TU3.1.3UT TUFinding neighbours with same BCCH in source and target cellUT.........................7 TU3.1.4UT TUDelete or correct neighbours with same BCCH in source and target cellUT ..........7

TU3.2UT TUAdd Missing Neighbours UT..............................................................................................7 TU3.3UT TURemove not required neighboursUT................................................................................12

TU4.UT TUFREQUENCY PLANNING UT ...........................................................................................................12 TU4.1UT TUChoose Frequency Planning MethodologyUT ................................................................12 TU4.2UT TUAnalysis of existing frequency planUT ...........................................................................14 TU4.3UT TUCreation of a new frequency planUT...............................................................................16

TU5.UT TUANTENNA HEIGHT, AZIMUTH AND TILT ANALYSISUT ..............................................................18 TU5.1UT TUIdentify overshooting cells and optimize antenna tilts, heights and azimuthsUT ...........18

TU6.UT TUANALYSIS OF DRIVE TEST LOGFILES UT ....................................................................................23 TU6.1UT TUDrive Test Methodology UT.............................................................................................23 TU6.2UT TUAnalysis of scanning data UT ...........................................................................................23 TU6.3UT TUAnalysis of dedicated mode data (long call) UT ..............................................................25

TU7.UT TUANALYSIS OF STATISTICS UT .......................................................................................................28 TU7.1UT TUAnalysis of daily reportsUT.............................................................................................28

TU8.UT TUBSS PARAMETER SETTINGSUT ...................................................................................................31 TU8.1UT TUGeneral guidelinesUT ......................................................................................................31 TU8.2UT TUTaliya default settingsUT.................................................................................................32

TU9.UT TUCAPACITY PLANNINGUT ...............................................................................................................32 TU9.1UT TUAveraging of traffic UT ....................................................................................................32 TU9.2UT TUTCH and SDCCH capacity dimensioning UT ..................................................................32

TU10.UT TULOCATION AREA DIMENSIONINGUT .......................................................................................33 TU10.1UT TUCCCH channel configurationsUT ................................................................................33 TU10.2UT TUPaging Dimensioning GuidelinesUT............................................................................33 TU10.3UT TUPaging statisticsUT .......................................................................................................34

TU11.UT TUAPPENDIX A UT ...........................................................................................................................35 TU11.1UT TUSummary of optimization flowUT ...............................................................................35

TU11.1.1UT TUNeighboursUT........................................................................................................35 TU11.1.2UT TUFrequency PlanUT .................................................................................................36 TU11.1.3UT TUAntenna OptimizationUT.......................................................................................37 TU11.1.4UT TUDrive TestsUT........................................................................................................37 TU11.1.5UT TUStatisticsUT............................................................................................................38 TU11.1.6UT TUBSS ParametersUT ................................................................................................38


TU11.1.7UT TUSDCCH and TCH CapacityUT ..............................................................................39 TU12.UT TUAPPENDIX B UT ...........................................................................................................................40 TU13.UT TUAPPENDIX C UT ...........................................................................................................................40


1. SCOPE AND PURPOSE OF DOCUMENT This document describes the optimization process that should be used in Taliya network in Iran. All basic steps in the optimization process are included but general radio planning guidelines are not covered by this document. The purpose of having a common optimization guideline nation wide is to achieve a high quality level for all regions regardless of the experience of each individual in each region. This document is supposed to be a support for all radio planners/optimization engineers in Tehran and the regions in their daily work. It is recommended that all personnel at RNP department read this document and the new RNP staff receive this document as a part of an introduction package. Comments and improvement proposals of the optimization guideline are welcomed and should be send to the RNP manager to be evaluated to see if optimization guideline should be updated or not.

2. INTRODUCTION There are many different ideas how GSM radio networks shall be optimized. It takes long time before having a full understanding of how different modifications of the radio network will affect the network quality. Without any clear guideline there is a risk for mistakes and that a lot of optimization work might result in very small improvements or even cause more problems. This document describes a straight forward optimization methodology based on many years of experience. As a result optimization will be fast and efficient with very small risks of making fundamental mistakes. The radio planner/optimization engineers’ main task is to maximize the utilization of frequency spectrum and BSS equipment. In other words to maximize coverage, quality and capacity with as small number of sites as possible and at the same time designing a network with high scalability to cater for future traffic and network growth with minimum modifications of the existing sites. I.e. a design including very high sites to provide maximum coverage is not acceptable since it most probably will fail to meet the quality, capacity and scalability criteria for the radio network design. Below a step by step optimization process is described. It is recommended to follow this process in order to optimize the radio network in the most efficient way.


3. NEIGHBOUR ANALYSIS

3.1 Analysis of existing neighbours Following needs to be checked of the existing neighbor definitions:

1. Non-mutual neighbors 2. Neighbors with same BCCH in source and target cell

3.1.1 Finding non-mutual neighbours All neighbors in Taliya radio network shall have mutual neighbor relations. Non-mutual neighbors are found by looking into each of the BSC database dumps. A macro have been created in order to facilitate the cross check of the neighbor definitions. The macro by the name ’BSC extractor’ can be found on the server.

Figure 1:BSC Extractor for BSC Database checks

It is also possible to check the neighbor definitions by excel. One example of how to find non-mutual neighbors in Excel is described below: UExample, One-way neighbors Assume there are three cells ABC1, ABC2 and ABC3. ABC1 and ABC2 have a mutual neighbor relation and ABC1 and ABC3 have a non-mutual neighbor relation. To find non-mutual neighbors it is recommended to concatenate the Cell IDs in two different columns forwards and backwards and finally use “vlookup” formula to find out if the each single item in column 1 (named concat1) can be found in column 2 (named concat2) as shown below:

Source Cell Target Cell Concat1 Concat2 VlookupABC1 ABC2 ABC1ABC2 ABC2ABC1 ABC2ABC1ABC2 ABC1 ABC2ABC1 ABC1ABC2 ABC1ABC2ABC1 ABC3 ABC1ABC3 ABC3ABC1 #N/A

Table 1: Table showing how to find one-way neighbours


Since ABC1 and ABC2 have a mutual neighbor relation the “Vlookup” column returns the correct text strings. The neighbor relation ABC1 to ABC3 is one-way and is found by “vlookup” by returning “#N/A”.

3.1.2 Correct non-mutual neighbours If non-mutual neighbors are found the neighbor definition should be deleted or defined as mutual.

3.1.3 Finding neighbours with same BCCH in source and target cell In order for the MS to distinguish between the serving cell and its neighbors and to minimize handover problems, source cell and target cell in a neighbor relation must have different BCCH frequencies. To find neighbor relations with same BCCH frequencies for both source and target cell it is recommended to use the BSC extractor in order to generate into excel the neighbors with the BCCH for the source and target cell. Then simply use the formula “Exact” to find out if the BCCH frequencies for source cell and target cells are the same as shown below:

Source Cell Source BCCH Target Cell Target BCCH ExactABC1 1 ABC2 6 FALSE ABC2 6 ABC1 1 FALSE ABC1 1 ABC3 1 TRUE

Table 2: Table showing how to find source and target cells with same BCCH frequencies

As shown in XTable 2X ABC1 and ABC3 have same BCCH and is found by the “exact” formula by returning the value “TRUE” in column “Exact”.

3.1.4 Delete or correct neighbours with same BCCH in source and target cell Neighbors with same BCCH frequency for source and target cell must be deleted. If the neighbor is required the BCCH frequency of either the source cell or target cell must be changed. This is required to be checked after each new frequency plan and neighbor definition.

3.2 Add Missing Neighbours To make it possible to do handovers, neighbor definitions are required. If there are any missing neighbors in the network, the best servers cannot be allocated. As a result the customer perceived coverage and quality will be worse than the actual situation and cause an increased Call Drop Rate. Therefore it is essential that there are no missing neighbors in the network. To find all missing neighbors both drive test logfiles and existing neighbors displayed in Asset must been analyzed. Drive tests should include both a MS in scanning mode (BCCH frequencies) and a MS in dedicated mode. If the MS in scanning mode found a cell with higher signal strength than the cell that is allocated by the MS in dedicated mode and a handover is not made to the best scanned cell, the neighbor is probably missing. Below the dedicated mode and the strongest scanned frequency are compared. As long as the MS in dedicated mode is using the same frequency as the strongest scanned channel no neighbors are missing:


Figure 2: TEMS plot showing the serving cell frequency of the MS in dedicated mode and the strongest scanned

channel. In this example both frequencies are the same and no missing neighbour is detected.

To facilitate finding missing neighbors it is recommended to include all neighbors in the TEMS cell file. TEMS Investigation will highlight all neighbors with a different color as shown below and it will be clear if a neighbor is missing:

Figure 3: TEMS Investigation with a cell file with neighbours. Neighbouring cells are shown with a different color


Note: Sometimes neighbors far away are required according to TEMS measurements. The solution is to tilt the cell that covers too far instead of adding a neighbor relation if possible. Below a simple process of finding missing neighbors is described:

1. Create a tab delimited .txt import file from the DB dumps and the BSC extractor of the on-air sites as shown below. Make sure to modify the cell ID’s in Asset in order to match with the import file. All cells for the on-air sites should be named with a site-id and a number representing the sector, e.g. 10001, 10002 and 10003. Example of the import file can be found in the RNP server under ‘’Tools\Asset\Asset import files’’.

NBR_CELL_FROM NBR_CELL_TO HO_MARGIN

10001 10651 6710001 10653 6710001 10041 6710001 12791 6710001 12792 6710001 12793 67

Table 3: Example of Asset neighbour import file

2. Import the .txt file including all the neighbors into Asset using GSM Import/neighbors

Figure 4: GSM Import


Figure 5: Import Carriers and neighbours


3. Using 2D view, show all on-air sites. Create Best server array. Note: 15km to 20km calculation radius is recommended. Check each cell one by one if there are any obvious neighbors missing.

Figure 6: Neighbours displayed in Asset

4. Using Best Server array the Asset tool can be used to find missing neighbors using

“NEIGHBOR ANALYSIS”. Consequently, the tool will give you which neighbor definition has to be added or deleted based on existing/on-air neighbor definition. Note that indoor sites have to be treated separately.

5. Generate a report in excel to verify neighbor definitions suggested by Asset (refer to

REPORT generator in asset). The excel report from asset will show substantial info like coverage overlap in sq km and in percentage. Use this info to have a broad stroke filter on the most obvious missing neighbors.

6. Analyze TEMS drive test logfiles to find missing neighbors by comparing the serving

cell of the MS in dedicated mode with the strongest scanned frequency.

7. Finally, re-validation of neighbor has to be made with reference to actual drive test and proximity of the sites.

8. Send work order to NMC to add all missing neighbors.

9. After all work orders have been implemented, check the neighbors from the NMC are

the same as the new .txt file to verify that all new planned neighbors have been added to the radio network This can be done by importing the DB dumps into BSC extractor.


3.3 Remove not required neighbours It should be avoided that the cells far away capture traffic (preferably with correct antenna tilting). Calls served by cells far away will have an increased risk for dropped calls since the fading (variation) of the signal level is high. Too many neighbors are in general not a big problem. Many neighbor definitions per cell slightly reduce the time for the MS to measure on each single neighbor. As a result handovers will be based on less reliable measurements and there might be a small risk that handovers are done to non-best servers. Missing neighbors result more often in dropped calls than too many neighbors. Therefore it is better to have too many neighbors than missing neighbors. To find neighbors that shall be removed is more difficult than to find missing neighbors and should be done very carefully. If a required neighbor is removed call drop rate will be increased immediately. To find not required neighbors it is recommended to

1. Use statistics showing number of handover attempts per day for all neighbors and then remove the neighbors showing that very few handover attempts are made.

2. If new sites have been added, neighbors can be removed if it is very clear that the old neighbors are not required anymore.

4. FREQUENCY PLANNING

4.1 Choose Frequency Planning Methodology A good frequency plan is necessary to create good quality and C/I values in the network. The frequency plan can be adjusted to compensate for bad site locations e.g. high sites can have a more loose frequency re-use to avoid interference and low sites can use a tighter re-use which should not cause any quality problems if the cell coverage is well controlled. To be able to create the best possible frequency plan, knowledge of the actual coverage from each cell is important. There are three basic ways of allocating frequencies:

1. UDeterministic Allocation Any frequencies can be allocated in any sectors. 2. UGroup Planning Frequencies are defined in different frequency groups i.e. the first group of frequencies shall be used for sector1, second group of frequencies shall be used for sector2 and the third group of frequencies shall be used for sector3. 3. UAutomatic Frequency Planning e.g. ILSA Frequencies are allocated automatically by a tool to minimize the interference based on predictions and a cost matrix.

There are many different opinions of which frequency planning methodology is the best to use. Usually a combination of all three frequency planning methodologies results in the best network quality in a big network covering both rural and dense urban areas. It is important to


understand when a specific frequency planning methodology is most suitable. This guideline recommends using group planning since predictions are usually not very accurate in cities due to a mixture of buildings with different sizes and wide, straight streets. Also the digital maps used might not be up to date. Cells that are facing out from the city that are coverage limited can use frequencies from other groups to minimize interference in the outskirts of the city if allocated carefully. Below an example of a frequency allocation used in Tehran is shown:

A1 B1 C1 D1 E1 A2 B2 C2 D2 E2 A3 B3 C3 D3 E3BCCH 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47TCH h h h h h h h h h h h h h h h h

Sector 2 Sector 3Sector 1

Figure 7: Example of a frequency allocation based on group planning used in Tehran. Note’’ h’’ stand for hopping

group which is 19-30

By using group planning there is no risk that antennas with crossing azimuths will be allocated the same frequency since only sectors shooting in the same directions can have the same frequencies. Note, do NOT use a strict frequency re-use where sites are divided into A, B, C, and D etc as shown below since the flexibility of allocating frequencies freely within each frequency group is removed:

A1 B1 C1 D1 E1 A2 B2 C2 D2 E2 A3 B3 C3 D3 E3BCCH 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47TCH h h h h h h h h h h h h h h h h

Sector 1 Sector 2 Sector 3

Figure 8: A strict frequency group pattern that is NOT recommended to use

Automatic or deterministic frequency planning can create good frequency plans if used properly but also result in fundamental mistakes by allocating the same frequencies to cells shooting into each other as shown in the figure below:


Figure 9: Example of bad frequency allocation where same frequencies are shooting into each other

The quality of a frequency plan generated by an automatic frequency planning tool e.g. ILSA is dependent on accurate predictions and mapping data. If predictions are good ILSA can help to create very good frequency plans but it is always needed to do manual checks and modifications after ILSA’s initial frequency suggestions to avoid interference problems. Hence depending on mapping data, prediction model and experience of ILSA and how to use ILSA in the best way, ILSA might generate the best frequency plan. It is recommended to test ILSA on a number of sites first to get familiar with the tool and what it does before using ILSA in a larger scale. E.g. the setup of the cost matrix must be done properly as well as the final manual modifications. If there are very few sites, the best possible frequency plan can be made with as few restrictions as possible. Group planning might result in tighter frequency reuse than necessary. Due to the limited number of sites it is easy to make sure that cells with different azimuths with same frequencies are shooting into each other even if no group planning is used. It is recommended to use group planning as a base even for a few numbers of sites. When fine tuning the plan, more violation from the group plan can be allowed than for a large number of sites as long as no sector with co-channels are crossing each others azimuths in their serving areas.

4.2 Analysis of existing frequency plan To check if the existing frequency plan needs to be modified or be replaced by a new frequency plan following steps must to be done:

1. Create a tab delimited .txt Asset import file from the adjacent cell list from NMC-R as shown below. Make sure to modify the cell ID’s in Asset in order to match with the import file. All cells for the on-air sites should be named with a site-id and a number representing the sector, e.g. 10001, 10002 and 10003. Example of the import file can be found in the RNP server under ‘’Tools\Asset\Asset import files’’.


CELL_ID ARFCN CarLay ARFCN2 CarLay2 ARFCN3 CarLay3 ARFCN4 CarLay4 ARFCN5 CarLay5 ARFCN6 CarLay6 Cell Layer Name BCC Car Req HSN Hopping Type NCC10001 11 BCCH GSM-Default 2 -1 5 Synthesized 010002 6 BCCH GSM-Default 5 -1 5 Synthesized 010003 14 BCCH GSM-Default 3 -1 5 Synthesized 510011 5 BCCH GSM-Default 7 -1 9 Synthesized 010012 10 BCCH GSM-Default 4 -1 9 Synthesized 010013 16 BCCH GSM-Default 5 -1 9 Synthesized 7

Table 4: Asset Carrier Import File

2. Import the .txt file into Asset with GSM Import/Import carriers. 3. Create an interference array in Asset to find possible problem areas. An interference

plot from Asset is shown below:

Figure 10: Interference plot from Asset showing possible problem areas.

Note that there might be areas with bad quality that are not found by Asset but can be found with drive tests. 4. Use the frequency reuse option in Asset to plot the best server areas using same

frequencies with same colors.

Figure 11: Frequency Re-Use plot in Asset


Note that the main cause to interference problems is co-channel interference. It is very rare that adjacent channel interference causes problems since the interferer must be at least have 9 dB higher signal level than the source cell according the GSM specifications (minimum C/A = -9 dB). For co-channel interference the GSM specifications states C/I = 12 dB for non-hopping systems and C/I = 9 dB for hopping systems. Due to the high GSM requirements on suppression of adjacent channel interference adjacent channel interference is very unlikely to occur unless there are missing neighbors and/or significant overshooting since HO to the interfering cell would normally happen before any problems perceived. Therefore it is recommended to not create any restrictions in the frequency plan due to adjacent channel interference except that one guard channel between the BCCH layer and TCH layer is required. It is not necessary to have one channel separation within same site.

4.3 Creation of a new frequency plan If the existing frequency plan is not good or if many new sites are planned to be on-air, a new frequency plan is required. A manual frequency plan based on group planning is recommended to be created as described below:

1. Identify all sites that should be included in the frequency plan i.e. on-air sites and planned sites that will be on-air shortly. If planned sites are included in the frequency plan is not on-air when the new frequency plan is loaded into the network there is big risk for quality problems since the actual frequency re-use will differ from the planned frequency re-use

2. Plot all sites to be planned on a A3 or bigger size paper 3. Use the define frequency strategy used in the RNP department for BCCH and TCH.

The strategy to be used is group planning with the BCCH frequencies divided into three frequency groups to be used for sector1, sector2 and sector3 as shown in XFigure 7X.

4. Plan all frequencies manually sector by sector and write down the frequencies on the

printout with a pencil. Do not use a pen since many changes might be required. A tip can be to write 1, 2, 3, etc, instead of e.g. 32, 33, 34 etc to facilitate the frequency allocation. The temporary numbers will be re-placed easily later by the correct ARFCNs.

5. Create an Asset carrier import file as shown in XTable 4X.

6. Import the carrier import file into Asset

7. Make prediction with at least 20 km radius for all planned sites

8. Create a Best Server and Interference Array as shown below:


Figure 12: Interference prediction before optimizing frequency plan

9. Analyze interference levels and identify problem areas. Interference shall be removed

from areas with many sites and pushed from city areas to rural areas.

10. Replace bad frequency allocations with new frequencies by using the frequency re-use option in Asset to find better frequencies. Update the new frequencies by updating the import file. It is recommended to update the frequency plan both on the paper and in the carrier import file and not directly in Asset. This will facilitating keeping track on all changes and if a frequency is changed by mistake the mistake can be found and corrected more easily.

11. Use the frequency reuse option in Asset to plot the best server areas using same

frequencies with same colors. Plot one frequency group at the time and primary look for cells shooting into each other with same frequency and try to distribute frequencies to maximize the re-use distance of each frequency.

12. Repeat step 6 to 11 until satisfying results are achieved.

Figure 13: Interference predication after optimizing the frequency plan


13. Delete all neighbors with same BCCH frequencies 14. Create a new BSIC Plan by sorting all BCCH frequencies in Excel and give all cells a

unique BCCH - BSIC combination if possible. If allocating unique BCCH – BSIC combination is not possible, the reuse should be as far as possible. More than one NCC value can be used if the area is far away from the country border but then the parameter NCC permitted must be updated too.

BCCH BCC NCC BSIC8 0 0 008 1 0 108 2 0 208 3 0 308 4 0 408 5 0 508 6 0 608 7 0 708 0 1 018 1 1 118 2 1 218 3 1 318 4 1 418 5 1 518 6 1 618 7 1 718 0 2 028 1 2 128 2 2 228 3 2 328 4 2 428 5 2 528 6 2 628 7 2 728 0 3 038 1 3 138 2 3 238 3 3 338 4 3 438 5 3 538 6 3 638 7 3 73

Figure 14: Example of BSIC allocation

15. Issue work orders for the new frequencies and the deletion of neighbors. Make sure to

schedule the implementation during low traffic hours since this is a service affecting activity. Normally the activity should be scheduled after midnight.

16. Verify that all implemented frequencies are implemented correctly by comparing the

new BCCH by the DB dumps from the NMC with the planned frequencies in the import file

17. When new frequencies/work orders are implemented in the network, drive tests must

be done immediately to verify new frequency plan and to make sure that all sites are back on-air properly.

5. ANTENNA HEIGHT, AZIMUTH AND TILT ANALYSIS

5.1 Identify overshooting cells and optimize antenna tilts, heights and azimuths Having good site locations and site designs i.e. sites with correct heights, no obstacles and to coverage area of importance are essential to get good network quality. Network quality can be improved by optimization of antenna tilt, heights and azimuths but optimization


can never take the network quality to a higher level than the restrictions set by the current site locations. Therefore it is of the outmost importance that radio planners make sure that new site locations are the best possible when creating the nominal plan and accepting the sites at both SSRs and TSS stage of the rollout.

To minimize interference levels in the network cells must not cover more than planned. Cells having too big best server areas or having discontinuous best server areas must be down tilted or lowered. Antennas must NOT be down tilted if:

• Coverage of the cell coverage is already bad in the planned best server area • The “overshooting” is very weak i.e. the coverage far away is very poor but no

other cell covers that area.

The required signal strength in the best server area is defined by the verification levels which is the design level – outdoor fading margin (from link budgets). Usually a good level in the best server area in dense urban should be around -75 dBm measured by TEMS with external antenna. When deciding antenna azimuths overlapping between cells, coverage gaps and purpose of the site coverage must be taken into consideration. Adjusting antenna azimuths from the nominal azimuths must be done very carefully since different antenna azimuths can cause quality problems to other sites (create too much overlaps and coverage gaps) and makes frequency planning more difficult. Overshooting cells can be identified by: 1. Make drive tests with an MS in scanning mode (use BSIC decoding) and preferably

with an additional MS in dedicated mode 2. Export the TEMS logfiles to Mapinfo. The information elements that should be

exported are at least “Strongest Scanned ARFCN” and “Strongest Scanned RxLev”. It is recommended to export these information element with argument 0, 1 and 2 to get the 3 strongest cells in each location as shown below:


Figure 15: Export window from TEMS showing the export from TEMS to Mapinfo of scanning data

3. Check the best server areas by plotting Strongest Scanned ARFCN with different colors and look for overshooting as shown below:

Figure 16: Strongest Scanned ARFCN from TEMS plotted in Mapinfo

Note that sectors can be shown with the same color as the BCCH allocated which makes it easy to see which cell that providing coverage in the area. It also makes it easier to find swapped feeders as shown below:


Figure 17: Plot showing how a feeder swap is detected by giving sectors and measured frequencies different

colors.

4. Identify how much the signal level must be reduced to remove the overshooting. In the figure below a small overshooting is identified

Overshooting from 00223

Overshooting from 00111

Figure 18: Plot showing how much the overshooting cell must be attenuated in order to remove

overshooting

5. Identify the height difference between the cell and the area of interest


Figure 19: Height profile form Asset that in this case can be used to get the height difference between the source

of interference and the affected area.

6. Identify the antenna type used in the cell 7. Use an Excel sheet that takes the antenna diagram and the height difference of the cell

and area of interest into account to calculate the required tilt to get the required reduction of signal strength. Below an example of an Excel calculation is shown where the antenna gain of the main lobe at ground level is calculated.

CTSDG-06515-0DM

-15

-10

-5

0

5

10

15

20

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Distance to site

Ant

enna

Gai

n

Figure 20: Plot from an Excel program that calculates the gain of the antenna main lobe where the main lobe hits

the ground.

Hence put in different tilts or heights and see what the expected change in signal strength will be. Remember to use the antenna pattern for antenna used in the cell of interest. Otherwise faulty antenna tilt decisions will be made. The excel diagram file can be found in the RNP server.


6. ANALYSIS OF DRIVE TEST LOGFILES

6.1 Drive Test Methodology Drive tests are necessary to get a good understanding of the actual quality in the network. Statistics and predictions might not give you the full picture of all network problems e.g. missing neighbors or quality problems. It is recommended to use two MS when drive testing for optimization purposes. One MS in dedicated mode (long call) to measure quality and one MS in scanning mode to scan all BCCH frequencies (tick the decode BSIC box) to measure coverage and best server areas. For simplicity reasons it is recommended to always define the MS in dedicated mode as MS1 and the MS in scanning mode as MS2. Do NOT use an MS in Idle Mode since there is no value of idle mode measurements since the idle mode behavior is different from the dedicated mode and coverage and best server areas will be affected by possible missing neighbors and slow MS measurements. Always use external antenna since the fading due to car penetration loss is high and unpredictable. If an external antenna is not used, some interferers might be attenuated and it will be more difficult to understand the actual coverage level and to find missing neighbors. It is not true that by not using an external antenna, the real user experienced quality will be measured. The reasons are that depending on the design of the car, placement of the MS in the car, speed of the car and the placement of the car on the road might result in measurement result with big differences. Even if the same route and the same car is used different results will be achieved. Besides some users might not be driving at all but walking outside or in a building next to the street.

6.2 Analysis of scanning data Scanning data shall be used for verifying coverage and overshooting since the scanning data is not affected by missing neighbors, handover margins or faulty BSS parameter settings as idle mode or dedicated mode measurements are. It is recommended to do following steps to analyze the scanning data:

1. Export the information elements Strongest Scanned ARFCN and Strongest Scanned RxLev for MS2 (MS used for scanning) for the 3 strongest scanned channels i.e. with argument 1, 2 and 3 to Mapinfo format as shown below.


Figure 21: TEMS Export to Mapinfo

2. Plot the strongest scanned RxLev in Mapinfo and create a legend that shows indoor

coverage, in-car coverage and outdoor coverage as shown below:

Figure 22: Strongest Scanned RxLev plot

3. Check for bad overage near sites and identify sites that are not transmitting and cells with poor coverage and investigate possible reasons. Panoramic pictures in TSSR, daily statistics from the SPEPBH report and alarms sent from the NMC can be a good help to find causes to problems.

4. Plot the strongest scanned ARFCN and create a legend including all BCCH

frequencies.


Figure 23: Strongest Scanned ARFCN plot

Note: if having more than 16 frequencies for BCCH Mapinfo will be unable to give all frequencies a unique color so analyze the frequencies outside the legend extra carefully or divide the frequencies into two groups.

5. Analyze overshooting and undefined coverage i.e. areas covered by many cells with approximately the same signal level. If sites are overshooting, check how strong the second best server is and define how much the signal level of the overshooting cell must be reduced as shown in XFigure 2 X, see chapter XR R5X for more details of making tilt decisions.

6.3 Analysis of dedicated mode data (long call) The main purposes of the dedicated mode measurements are to find quality problems and missing neighbors. It is recommended to analyze the dedicated mode measurements in following steps:

1. Export most of the information elements related to dedicated mode for MS1 (MS in dedicated mode). The most important information elements are: RxLevSub, RxQualSub, ARFCN BCCH, C/I Worst, Neighbor cell RxLev, Neighbor cell ARFCN, Cell Name, Hopping and TA. Refer to Appendix C.


Figure 24: TEMS export of dedicated mode data to Mapinfo

Note: use sub values for RxLev and RxQual when DTX is activated in the network 2. Plot RxLevSub in Mapinfo. Look for areas with bad coverage near sites that might

indicate problems like missing neighbors. Problems can also be found by comparing the coverage from the scanning measurements and dedicated mode measurements. Coverage should be almost the same if there are no problems.

Figure 25: RxLevSub from the MS in dedicated mode

3. Plot ARFCN BCCH and compare with strongest scanned ARFCN to find overshooting. The dedicated mode data helps to identify the cell of the overshooting cell since cell ID can be exported and will be shown by clicking on the dedicated mode measurements in Mapinfo.


Figure 26: ARFCN BCCH from the MS in dedicated mode

4. Plot C/I Worst in Mapinfo and create a suitable legend and identify bad quality areas.

C/I values > 12 dB are considered as good and C/I values < 9 dB are considered as bad.

Figure 27: C/I Worst plot

5. Investigate the reasons for the bad quality e.g. overshooting, missing neighbors, bad frequency allocations (only applicable for BCCH frequencies) or possible HW problems. Interference is identified by high signal level and bad quality. Hence if the signal strength is low e.g. lower than -80 dBm the actual problem is more related to


poor coverage than bad frequency allocations. Usually is not easy to find better frequency allocations and therefore frequency re-allocations shall be avoided unless it is absolutely necessary.

6. Play all logfiles one by one to find all possible optimization issues like overshooting,

bad quality or missing neighbors. Note that the TEMS feature “leave trail” can be used to find overshooting, see below:

Figure 28: TEMS logfile played with the “leave trail” option that helps to find overshooting

7. Issue work orders to solve quality problems. 8. Verify that all work orders are implemented.

7. ANALYSIS OF STATISTICS

7.1 Analysis of daily reports Statistics is very good for identifying problematic cells since all cells are covered and many calls are included. Hence a good rule is to use statistics to find the quality problems and to use drive test to find the specific reasons for the quality problems. To make it easier to find the problems it is recommended to show the statistics geographically in Asset or Mapinfo with a color legend. It is recommended using Busy Hour (BH) or Daily Average values or both depending on which KPIs that are analyzed. Use BH values for:

• TCH Carried Traffic (for cell capacity dimensioning purposes) • SDCCH Carried (for cell capacity dimensioning purposes) • Loss (for cell capacity dimensioning purposes) • Call Drop Rate • Handover Success Rate • Handover Cause Distribution

Use Daily average values for:

• TCH Availability


• Carried Traffic To find problematic cells it is recommended to check at least following statistics:

1. Call Drop Rate (CDR) High CDR can be caused by missing neighbors, bad quality or HW problems. Cells that are coverage limited e.g. cells on city borders usually have a higher CDR than cells in the city center. Focus on lowering CDR for cells in city center first. Busy hour call drop rate can be imported into Asset in a ‘’traffic.tps’’ file format which can be found on RNP server.

Figure 29: Call Drop Rate presented geographically

2. Carried Traffic Cells with no traffic or very low traffic can have HW problems, very bad quality or possible no best server areas. Busy hour traffic can be imported into Asset in a ‘’traffic.tps’’ file format which can be found on RNP server.

Figure 30: Carried traffic shown geographically

3. Handover success rate Low handover success rate can be an indication of bad BCCH frequency allocation, possible missing neighbors causing handovers to non best servers or too many urgent (imperative) HO e.g. level or quality handovers.


30

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Figure 31: HO success rate and HO drop rate

4. Percentage of quality and level handovers Many quality and level handovers indicate bad quality and many level handovers indicate poor coverage.

HO Distribution March 11th

it e UQ (Nr) , 0, 0%it e DQ (Nr) , 0, 0%it e US (Nr), 48598, 12%

it e DS (Nr), 130508, 32%

it e Dist (Nr) , 0, 0%

it e DR (Nr) , 5359, 1%

it r UQ (Nr), 6450, 2%

it e BC (Nr), 207848, 51%

it r DQ (Nr), 10167, 2%

Figure 32: HO cause distribution

5. TCH Mean Holding Time A very low mean holding time can be an indication of bad quality or HW problems.


tch MHT (Sec)

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of d

rops

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our [

#]

tch MHT (Sec)

.

Figure 33: TCH Mean Holding Time

6. Interference Band 5 and 4 Indication of external interference e.g. jammers, especially if downlink quality is good or internal interference, if both uplink and downlink quality are bad.

Idle Channel Measurements 27th May 2006

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ifBandRate 5ifBandRate 4

Figure 34: Graph showing the percentage of UL interference band 4 and 5

8. BSS PARAMETER SETTINGS

8.1 General guidelines In GSM systems there are many radio network features and parameters that can be used and optimized to improve network quality. There is a risk to make mistakes and cause


problems that are difficult to foresee without making a full analysis how parameters interact with each other. The very best way of having full understanding of the radio network behavior, functionality and BSS parameter setting that are used is to keep the radio network as simple as possible. The BSS parameter setting must be consistent to avoid that any unpredicted behavior of the network is achieved. Therefore it is recommended to use the following rules: 1. Use the Taliya’s BSS default settings for all cells in the network. Check the BSS

parameter consistency every week. 2. Do not enable BSS functionalities unless the RNP department has approved that the

function will be good for network quality

3. Do not use cell specific parameter settings since it makes consistency checks difficult and it can creates many problems since the combination of that specific setting has not been analyzed carefully. Please keep in mind that the actual problem that is trying to be solved by cell specific parameter settings can be solved in other ways. There might be other reasons for the problems e.g. HW faults. If it is found out that Taliya default setting is not good, it is recommended that a test of the new parameter settings is done for all cells in one BSC. If the new BSS parameter setting is verified to be better the default settings shall be updated and the new parameter setting should be applied for the whole network. The only possible exceptions from this rule are cells belonging to different frequency bands (900 or 1800), indoor solutions or Macro/Micro cells (currently no micro cells are used).

4. If it is suggested to test a new parameter setting the suggestion should be presented

for the RNP manager. If it is agreed, the new parameter setting should be tested for all cells in one BSC to get sufficient date to evaluate. If the test is successful Taliya’s default parameter set shall be updated and the new parameter setting shall be applied for all cells in the network.

8.2 Taliya default settings Please see Appendix B

9. CAPACITY PLANNING

9.1 Averaging of traffic To make accurate and reliable capacity dimensioning, average values of the traffic must be used. Otherwise it is a risk that capacity is added or reduced based on insufficient data and might cause faulty capacity dimensioning. It is recommended to measure the raw blocking values for 10 busiest hours per cell of the offered traffic for a 4 week period both for TCH and SDCCH capacity dimensioning. If the average of the raw blocking values are higher than the predefined GoS target defined in chapter XR R9.2X capacity must be added to the cell.

9.2 TCH and SDCCH capacity dimensioning TCH and SDCCH capacity dimensioning are done in the same way. The only difference is the GoS targets.


Following GoS targets shall be used: • TCH GoS – 2% • SDCCH GoS – 0.5%

10. LOCATION AREA DIMENSIONING

10.1 CCCH channel configurations The common control channels (CCCH) consists of PCH and AGCH used for paging and immediate assignment messages. The CCCH is broadcasted on time slot 0 together with the BCCH and can be configured in different ways. The two basic CCCH channel configurations are called combined CCCH and non-combined CCCH channel configurations. The differences are that in combined CCCH configuration, CCCH channels are combined with 4 SDCCH subslots on time slot 0 and for non-combined CCCH configuration no SDCCH time slots are configured on time slot 0. Another difference that can be found is the 51 multiframe structure that is used in GSM. For combined CCCH configurations there is 3 CCCH blocks/multiframe and for non-combined CCCH configurations there are 9 CCCH blocks per multiframe. Each CCCH block can be used by either PCH or AGCH set by a cell parameter (NBLKACGR). Therefore paging capacity is dependent on the CCCH configuration and the setting of the cell parameter for blocks reserved for AGCH. Paging messages are send out to all cells in one LA. Therefore paging dimensioning must be done at LA level, not on cell level to get the same paging capacity for all cells. All cells shall use non-combined CCCH channel configurations with 2 CCCH blocks reserved for AGCH. It is recommended that all cells shall have following BSS parameter setting: CHTYPE= MAINBCCH SDCCH TCHF_HLF (non-combined CCCH results in 9 CCCH blocks per multiframe) NBLKACGR = 2 (2 CCCH blocks per multiframe are reserved for AGCH) NFRAMEPG = 5 (5 multiframes between paging of same paging group) T3212 = 40 (4 hours between periodic LA updates if necessary) MSC Detach Timer = 4 hours + 5 minutes (time before the MSC detach the MS)

10.2 Paging Dimensioning Guidelines In theory the number of mobile that can be paged per hour is given by the formula assuming the recommended parameter settings in chapter XR R8X: Paging capacity = 3600 * (9-2)/0.235 pagings/hour Where 0.235 is the duration of one mutiframe in seconds Hence the paging capacity in theory is: Paging capacity = 107234 pagings/hour However a safety margin should be applied and in practice it will not be possible to have 100% capacity utilization before paging success rate start to decrease significantly. In order


to have a high paging success rate, assuming the parameter settings in chapter XR R8X is applied; it is recommended to not exceed: Total number of paging attempts per LA/BH = 70 000 pagings per LA/busy hour Note: The actual paging capacity in terms of number of mobiles that can be paged per hour is dependent on the paging type. The number of mobiles that can be paged per paging message vary from 1 to 4 depending on the usage of IMSI or TMSI. Refer to GSM specification 05.02.

10.3 Paging statistics There are two main KPIs related to paging:

• Number of pagings per LA/BH (< 70 000) • Paging Success Rate (>90%)

If there is a correlation between a high number of pagings and low paging success rate there is a PCH or AGCH capacity problem. Otherwise a low paging success rate can indicate poor radio network quality if we assume the core part is working properly.


11. APPENDIX A

11.1 Summary of optimization flow

11.1.1 Neighbours 1. Analysis of existing neighbors

a. Find non-mutual neighbors. b. Make all non-mutual neighbors mutual or delete the neighbor definitions if

they are not required. c. Find and neighbors with same BCCH in source and target cell. d. Delete neighbor definitions with same BCCH in source and target cell or

change the BCCH frequency of either the source cell or the target cell.

2. Add Missing Neighbors a. Create a tab delimited .txt import file from the DB file dumps and the BSC

extractor tool for all the on-air sites. b. Import the .txt file including all neighbors into Asset using GSM

Import/neighbors. c. Using 2D view, show all on-air sites. Create Best server array. Note: 15km to

20km calculation radius is recommended. Check each cell one by one if there are any obvious neighbors missing.

d. Using Best Server array Asset can be used to find missing neighbors using “NEIGHBOR ANALYSIS”. Consequently, the tool will give you which neighbor definition has to be added and which has to be deleted based on the imported neighbor definition. Note that INDOOR sites have to be treated separately.

e. Generate a report in excel to verify neighbor definitions suggested by Asset (refer to REPORT generator in asset). The excel report from asset will show substantial info like coverage overlap in sq km and in percentage. Use this info to have a broad stroke filter on the most obvious missing neighbors.

f. Analyze TEMS drive test logfiles to find missing neighbors by comparing the serving cell of the MS in dedicated mode with the strongest scanned frequency.

g. Finally, re-validation of neighbor has to be made with reference to actual drive test and proximity of the sites.

h. Send work order and planned works to NMC to add all missing neighbors. i. After all work orders have been implemented, check the neighbors from the

DB dumps are the same as the new .txt file to verify that all new planned neighbors have been added to the radio network.

3. Removing not required neighbors

a. Use statistics showing number of handover attempts per day for all neighbors and then remove the neighbors showing that very few handover attempts are made.

b. If new sites have been added neighbors can be removed if it is very clear that the old neighbors are not required anymore.


11.1.2 Frequency Plan 4. Analysis of existing frequency plan

a. Create a tab delimited .txt Asset import file from the DB dumps and the BSC extractor tool.

b. Import the .txt file into Asset with GSM Import/Import carriers. c. Create an interference array in Asset to find possible problem areas. d. Use the frequency reuse option in Asset to plot the best server areas using

same frequencies with same colors. Plot one frequency group at the time and primary look for cells shooting into each other with same frequency.

5. Modification or creation of a new frequency plan

a. Identify all sites that should be included in the frequency plan i.e. on-air sites and planned or in-progress sites (reefer to existing Asset filters for Iran project) that will be on-air shortly. If the planned sites are included in the frequency plan and are not on-air when the new frequency plan is loaded into the network there will be a big risk for quality problems since the actual frequency re-use will differ from the planned frequency re-use.

b. Plot all sites to be planned on an A3 or bigger size paper. c. Use the frequency re-use strategy defined in the RNP department for BCCH

and TCH. d. Divide all BCCH frequencies into three frequency groups to be used for

sector1, sector2, and sector3. e. Plan all frequencies manually sector by sector and write down the frequencies

on the printout with a pencil. Do not use a pen since many changes might be required. A tip can be to write 1, 2, 3, etc, instead of e.g. 32, 33, 34 etc to facilitate the frequency allocation. The temporary numbers will be re-placed easily later by the correct ARFCNs.

f. Create an Asset carrier import file as shown in XTable 4X. g. Import the carrier import file into Asset. h. Make prediction with at least 20 km radius for all planned sites. i. Create a Best Server and Interference Array. j. Analyze interference levels and identify problem areas. k. Replace bad frequency allocations with new frequencies by using the

frequency re-use option in Asset to find better frequencies. Update the new frequencies by updating the import file. It is not recommended to update frequencies directly in Asset. Update the carrier import file instead.

l. Repeat step 6 to 11 until satisfying results are achieved. m. Create a new BSIC Plan by sorting all BCCH frequencies in Excel and give all

cells a unique BCCH - BSIC combination if possible, or reuse them far from each other if it is not possible.

n. Delete all neighbors with same BCCH frequencies. o. Issue work orders/planned works for the new frequencies and the deletion of

neighbors. The implementation should be done on low traffic hours. p. Verify that all implemented frequencies are implemented correctly by

comparing the new BCCH allocations from the DB dumps with the planned frequencies in the import file.


q. When new frequencies/work orders are implemented in the network drive tests must be done immediately to verify the new frequency plan and to make sure that all sites are back on-air properly if the BSS database was replaced.

11.1.3 Antenna Optimization 6. Antenna Height, Azimuth and Tilt Analysis

a. Make drive tests with an MS in scanning mode (use BSIC decoding) and preferably with an additional MS in dedicated mode.

b. Export the TEMS logfiles to Mapinfo. The information elements that should be exported are at least “Strongest Scanned ARFCN” and “Strongest Scanned RxLev”. It is recommended to export these information element with argument 1, 2, and 3 to get the 3 strongest cells in each location.

c. Check the best server areas by plotting Strongest Scanned ARFCN and look for overshooting. If a cell is best server far away from the site location cell is considered as overshooting, especially if the best server area is discontinuous. Antennas must not be down tilted if:

i. Coverage of the cell is already bad in the planned best server area. ii. The “overshooting” is very weak i.e. the coverage far away is very

poor but no other cell covers that area. The required signal strength in the best server area is defined by the verification level which is “design level – outdoor fading margin” (from link budgets). Usually a good level in the best server area in dense urban should be around -75 dBm.

d. Identify how many dB the signal level must be reduced to remove the over shooting.

e. Identify the height difference between the cell and the area of interest. f. Identify the antenna type of the cell. g. Use an Excel sheet that takes the antenna diagram and the height difference of

the cell and area of interest into account and calculate the required tilt to get the required reduction of signal strength.

11.1.4 Drive Tests 7. Analysis of drive test scanning data

a. Export the information elements Strongest Scanned ARFCN and Strongest Scanned RxLev for MS2 (MS used for scanning) for the 3 strongest scanned channels i.e. with argument 1, 2 and 3 to Mapinfo format.

b. Plot the strongest scanned RxLev in Mapinfo and create a legend that shows indoor coverage, in-car coverage and outdoor coverage.

c. Check for bad coverage near sites, identify the sites that are not transmitting and cells with poor coverage and investigate possible reasons. Panoramic pictures, statistics and alarms can be a good help.

d. Plot the strongest scanned ARFCN and create a legend including all BCCH frequencies.

Note: In case of having more than 16 frequencies for BCCH in Mapinfo, use “Individual” type instead of “Ranges” type since Mapinfo is unable to give all frequencies a unique color. e. Analyze overshooting and undefined coverage i.e. areas covered by many cells

with approximately the same signal level. If sites are overshooting, check how


strong the second best server is and define how much the signal level of the overshooting cell must be reduced, see chapter XR R5X for more details of making tilt decisions.

8. Analysis of drive test dedicated mode data (long call)

a. Export most of the information elements related to dedicated mode for MS1 (MS in dedicated mode). The most important information elements are: RxLevSub, RxQualSub, C/I Worst, Neighbor cell RxLev, Neighbor cell ARFCN, Cell Name, Hopping and TA.

b. Plot C/I Worst and RxQual in Mapinfo and create a suitable legend and identify bad quality areas.

c. Investigate the reasons for the bad quality e.g. overshooting, missing neighbors, bad frequency allocations (only applicable for BCCH frequencies) or possible HW problems. Interference is identified by high signal level and bad quality. Hence if the signal strength is low e.g. lower than -80 dBm the actual problem is more related to poor coverage than bad frequency allocations. Usually is not easy to find better frequency allocations and therefore frequency re-allocations shall be avoided unless it is absolutely necessary.

d. Play all logfiles one by one to find all possible optimization issues like overshooting, bad quality or missing neighbors. Note that the TEMS feature “leave trail” can be used to find overshooting.

11.1.5 Statistics 9. Analyze following Statistics

a. Call Drop Rate (CDR) b. Carried Traffic c. Handover success rate d. Percentage of quality handovers e. TCH Mean Holding Time f. Interference Band 4 and 5

11.1.6 BSS Parameters 10. Use the Taliya’s BSS default settings for all cells in the network. Check the BSS

parameter consistency after every modification in BSC DB. 11. Do not enable BSS functionalities before approval from the RNP department

manager.

12. Do not use cell specific parameter settings since it makes consistency checks difficult and it can create many problems during the optimization.

13. If it is suggested to test a new parameter setting the suggestion should be presented

for the RNP manager and if approved be tested for all cells in one BSC.


11.1.7 SDCCH and TCH Capacity 14. Check TCH and SDCCH capacity on a monthly basis.

a. Use average value of the 10 busiest hours per 4 week period both for TCH and SDCCH

b. Use following GoS targets: • TCH GoS – 2% • SDCCH GoS – 0.5%


12. APPENDIX B Default BSS parameter settings

13. APPENDIX C Tems Getting started

END OF DOCUMENT

Radio Network Optimization Guideline

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