missing neighbour analysis in rvs

7/27/2019 Missing Neighbour Analysis in RVS

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Missing

NeighbourAnalysisin A-RVS

ActixProfessionalServices




CONTENTS

INTRODUCTION ........................................................................................................................3

SETTINGS EXPLAINED ...........................................................................................................4 MISSING NEIGHBOURS EXAMPLE ..............................................................................................5 NEIGHBOUR LIST RECOMMENDATIONS REPORT .........................................................................7 MISSING AND REMOVAL NEIGHBOUR ATTRIBUTES ......................................................................8 DROPPED CALL ANALYSIS DUE TO MISSING NEIGHBOURS........................................................11




Introduction

Missing Neighbour Analysis is a fundamental aspect to WCDMA network optimisation. Itshould be performed as part of the rollout phase of a network to construct and/or optimise theadjacency lists of each cell; and throughout the life of the network as changes to traffic and tilt

affect the coverage pattern and interference interaction between the cells.

Missing Neighbour Analysis in Actix RVS solution has been designed to allow engineers togenerate a list of suggested Missing Neighbours and allow engineers to visualise thesuggested cells on a map. Full control of the suggestion criteria is included to allow forchanges in clutter, terrain and rollout phase of the network. These suggestion criteria aredescribed as follows:

New settings inside Tools > Preferences

These criteria are applied to the scanned signal measurements to build a suggested list ofcells. Only cells which satisfy all criteria are included in the final list of suggested MissingNeighbours.




Settings Explained

Criteria Default

Value

Description

Reporting Range (dB) 5 EcIo offset applied to the Best EcIo value. EcIovalues must be within this offset of the Nth_Bestcell to be included as a suggested cell.

Maximum size 32 Maximum size of the suggested list. This shouldbe set to your network infrastructure s maximumadjacency list size.

Addition Threshold (%) 1 The percentage of samples of the suggested cellrelative to the Nth_Best cell must at least equalthis value to be suggested. This is to reduce straysignals affecting the choice.

Removal Threshold (%) 0.2 The percentage of samples that must be achieved

for a cell in the current adjacency list of theNth_Best cell, or it will be recommended forremoval.

Minimal Samples 50 The minimum number of samples of the Nth_Bestcell before it s neighbours will be analysed. This isto remove statistically invalid measurements fromthe suggestions.

Maximum Intersite Distance (metres) 5000 The line-of-sight distance between the Nth_Bestand suggested cell must be less than or equal tothis value. Increase this value for rural areaswhere the average intersite distance is naturallygreater than a dense-urban environment. Set thisvalue to 0 to disable this feature.

Angle to site threshold (degrees) 90 The maximum criteria applied to the anglebetween any point in the drive route and asuggested missing neighbour. This is to ensureMissing Neighbours are not suggested fromreflected signals / back-lobes, and ensure onlycells angled towards the scanned drive aresuggested. Set this value to 0 to disable thisfeature.

Include existing neighbours Disabled This feature controls whether the criteria is appliedto existing neighbours, to validate the currentadjacency list of each cell according to thescanner measurements.

Only process first best SC Enabled By selecting this option, the adjacency list of only

the Nth_Best cells will be included in the creationof the suggested list. By disabling this feature, theadjacency list of all cells that fall within theReporting Range will also be analysed.




Missing Neighbours Example

The following example explains how the Missing Neighbours are calculated:

Example scanner measurement drive. SC 103 on Site 1 is the strongest signal at pointX

In this example, at point X , SC 103 is the Nth_Best SC(CPICH_Scan_SC_SortedBy_EcIo_0). The closest cell to point X is at Site 1

1. Its

adjacency list includes 101, 102, 201 and 202. At point X , the scanned list is as follows:

SC EcIo (dBm) 103 -5202 -6302 -7203 -8402 -9301 -9101 -11303 -15

At point X , the strongest signal is SC 103 is at -5dBm. Applying the Reporting Range of 5dB creates a short-list of SC 202, 302, 203, 402 and301 (greater than -10dBm). The signals from SC 101 and 303 are too weak to beconsidered. SC 202 is are already defined as a neighbour of SC 103, so this is eliminated too, leavingus with a suggested list of 203, 302, 402 and 301. Applying the intersite distance threshold, SC 402 is over 5Km away from SC 103, so it isremoved from the suggested list, leaving us with SC 203, 302 and 301. The angle between the point X and the azimuth of the SC s is now analysed. To beconsidered, the azimuth must fall with +/ - 90 degrees of the line-of-sight vector from the

1Note: The scanner reports SC numbers, so Actix RVS selects the closest cell to the drive

route at that time, with a matching SC.

Scanned route 101

103102

201 203

202

301

303302

point X

401

403402

4.5Km

6Km

Site 1

Site 2

Site 3

Site 4




point X to that site. To allow for the spread of beamwidth, half the beamwidth isadded/subtracted to the azimuth to give extra tolerance of angle.

Example of angle to site threshold for validation of SC 203, 302 and 302

When half the beamwidth is added/subtracted (depending on whether the azimuth is to theleft or right of the vector connecting the scanner point and the cell) to the azimuth of the cell,the final criteria is applied to the cell. If the angle of the cell then falls within the angle settingin Tools > Preferences the cell will be included in the suggested list.

In the example above, SC 302 is included as a Missing Neighbour. The azimuth of SC 301

was originally outside our 90 threshold, but when subtracting half its beamwidth, it falls withinour acceptable range so is therefore included as a Missing Neighbour. The azimuth of SC

203 + half its beamwidth still does not fall within our 90 threshold, so it is not included in thelist.

Our final list of Missing Neigbours is then 301 and 302. Due to the fact that SC 302 has astronger EcIo value than SC 301 at point X , the Missing Neighbours at point X are asfollows: Missing_Neighbours_0 = 302 Missing_Neighbours_1 = 301

relative to CPICH_Scan_SC_SortedBy_EcIo_0 = 103 at point X .

This is repeated for all points in the scanned drivetest route, creating an array of SC s at eachpoint, sorted by their EcIo value, which satisfy the selection criteria and are not currentlydefined as a neighbour of the Nth_Best_0 cell at that time.

If the Only use Nth Best cell option is disabled, not only the Nth_Best cell will be considered.Using the principle that if cell A and cell B are within 5dB, and cell A and cell C are within 5dB,the relationship between cell B and cell C should be analysed too. This obviously increasesthat processing needed at each point, and is recommended for neighbour list optimisation ofmore mature networks.

Once the final list of suggested Missing Neighbours has been compiled, the results can beviewed in two ways: through the Accelerated Network Rollout analysis pack report (Neighbour

List Recommendations), and also by visualising them on the map/chart/table.

201 203

202

301

303302

point X

+90

+90

-90

-90

Site 3

Site 2




Neighbour List Recommendations report

Once this report has been run from the ANR analysis pack, the recommended additions / removals / retentions are presented in a tabular format as follows:

Nth_BestSC Site Cell SampleCount Action Nbr SC SampleCount % IntersiteDistance 110 Site123 Site123-a 5000 Add 200 1250 25 2.5

Retain 112 500 10 3.5 Remove 113 5 0.1 3.5

In this example, SC 110 (Site123-a) was the Nth_Best measurement for 5000 samples duringthe scanner measurement. It s current adjacency list includes SC 112 and 113. While SC111 was the Nth_Best cells, there were 1250 samples of SC 200, 500 samples for SC 112and only 5 samples for SC 113 (sorted by % samples).

SC 200 is not already in the adjacency list for SC 110, all criteria have been met for this cell,

so it is suggested as a Missing Neighbour. SC 112 was scanned enough times to recommend to be kept in the adjacency list. SC 113 (at the same site as SC 112, 3.5Km away from SC 110) was only scanned 5 times,so it has been recommended to be removed.

NOTE: It is important to drive enough routes and collect enough data to ensure these cellsuggestions are statistically valid.




Missing and Removal Neighbour attributes

In the workspace explorer, a new grouping has been introduced Neighbour Analysiscontaining 2 sorted lists, for Missing Neighbour suggestions and Removal suggestions.

Workspace Explorer showing new Neighbour Analysis group

The lists are sorted by signal strength and contain the SC values of the cells in the list at eachpoint in the scanned drivetest. The strongest Missing Neighbour (Missing_Neighbour_0)should be analysed first, as it could potentially be the strongest pollution source at that time.Drag the parameter onto the map and open the Top 10 Scan Measurements stateform(optionally dock it to under the Workspace Explorer). The legend of the map gives you the listof SCs that were the strongest Missing Neighbour at any point in the drive. The mostfrequent SC should be targeted first, and by selecting any point in the map, the stateform will

synchronise to show the top 10 scanned measurements giving the Nth_Best SC at the topof the list2. A decision needs to be made whether to add this suggested Missing NeighbourSC into the adjacency list of the Nth_Best SC.

2In the case of repeated SC values, the closest cell with a matching SC to the Nth_Best_0

cell will be selected.




Screenshot of Nth_Best SC (CPICH_Scan_SC_SortedBy_EcIo_0) plotted on the map.Missing_Neighbours_0 is added to the map, and synchronised to the Top 10 ScanMeasurements stateform. The Display Cell Data view shows the adjacency list of cellexample0184c (SC 242).

Once all the strongest Missing Neighbours have been analysed, the next strongest signalshould be analysed. Following this process with ensure that the most important MissingNeighbours are analysed first. The same SC could appear as a Missing Neighbour formultiple Nth_Best cells, so it may be easier to create a crosstab query with two dimensions:Missing_Neighbours_0 and Nth_Best_0, to give all occurrences of the combinations. This listcan then be filtered from the Statistics Explorer to filter the map view for single SCcombinations individually.




Screenshot showing validation of intersite distance between Nth-Best SC 242 at siteExample0184 and Missing Neighbour 202 at site Example0199. The map s distancetool has been used and the distance 1.7046Km is underlined.




Dropped Call Analysis due to Missing Neighbours

Neighbour list analysis can also be used verify the reason behind a dropped call. Thismethod uses the process of combining the scanner and UE together and checking the Active

and Monitored Sets for the UE against the scanned measurements at the point of a droppedcall.

Screenshot showing synchronised scanner and handset traces, indicating MissingNeighbour 202 (and differences between best scanned SC 242 and Active Set SC 338.

This requires the scanner and UE traces to be collected at the same time, and for theresulting collection files to be superstreamed together (and correcting any time offset betweenthe collection devices). See the online Help for instructions on superstreaming using TimeOffsets. Once the files have been combined, parameters such as the

UTRA_UE_CarrierRSSI and the Uu_CallDropped event can be dragged onto the map. Byopening the UE Missing Neighbours stateform for the superstream and synchronising it withdropped call, the top 10 scanned measurements can be visually compared to the Active andMonitored sets for the UE at the time.




Screenshot showing how dropped calls from the handset can be viewed with theMissing Neighbour attributes when the scanner and handset are synchronised. Herethe Active Set and Monitored Set SC s are at very low RSCP values, and poor EcNotoo. The scanner detected 3 other SCs, and a missing neighbour just before the drop.

This allows the engineer to understand whether the UE had dropped a call due to a missingneighbour not being defined in the cell s adjacency list, or whether it was a handset problem,resulting in a neighbour that had already been defined not being added to the Monitored Set,and therefore never being able to be added to the Active Set.

missing neighbour analysis in rvs

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