GSM Interference Matrix

1 Nokia Siemens Networks OS86653EN53GLA0

NetAct Optimizer 3.0 for GSM

GSM Interference Matrix


Nokia Siemens Networks Academy

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At the end of this module the trainee should be able to:

Prepare for the network optimization by creating, verifying,

importing and exporting an interference matrix

Find problem cells that cause interference over a long

distance

Module Objectives



How can I create an Interference Matrix?

How do I check the Interference Matrix on the Map?

How can I find the cells that cause interference far away?


IM Basics

Interference Matrix represents the interference relations between cells

Interference can be computed or expressed with different mathematical methods such as

CIP (Carrier over Interferer Probability), or ARP (Average Received Power), FEP (Frame Erasure Probability) IM set contains CIP, ARP or FEP values for co-channel and adjacent channel between every cell pair in the BSC

If old IM sets are available (from earlier optimisations) it is recommended to combine them with the new IMs to reduce blind spots

Old IM sets are given lower priority than new sets In case of missing or low quality measurement data, it is possible to use predicted interference values to complement measurements

Interference Matrix is used in Optimizer as an input for GSM Adjacency Optimization and GSM Frequency Optimisation

IMs can be exported and imported


Interference Matrices Tab - Measurement Retrieval

Open Interference Matrices tool view

Select one or more BSCs

Select Interference Type CIP or FEP

Retrieve measurements


Common Parameters for Retrieval

Insert measurement start date and end date

How many blind spots should be generated?

If interference value is below the selected threshold, it is ignored

Default values are given to the generated blind spot interferers


Other Parameters for Retrieval


Prediction Parameters

Select a one or more BSCs

Propagation Factor is the exponent of the link loss calculation


Measurement Sets

Assign priority 1 to the most important (newest) set of measurements

Priority is needed for every set to be included in the IM


Managing Interference Matrix

Without priority there is no interference data available in Optimizer

Priority needs to be assigned for each Interference type separately

Import and Export possible (CSV format)


Priority

Priority settings are user specific

If a set has no priority assigned to it, it is not taken into the combined matrix

A combined set may contain blind spots. Blind spots are treated in the following way:

a blind spot value is always replaced with a measured value

if there are two sets with the same priority, the measured set is taken into use

if there is a blind spot and a predicted value for the same cell pair the blind spot (default) value is used if its priority is higher

if the predicted value is higher than the default value for the blind spot, the predicted value is used


Interference Matrix





Interference Matrix on Map

Interference Matrix values between cells can be seen on the map

For each pair of cells the value above threshold is shown on the map as a line between the cells

Interference values represent Carrier over Interference Probability, Frame Erasure Probability, or Average Received Power values from the combined IM

Current allocation is not taken into account

Values exist also between different frequency bands


Interference Lines

Select Other... for Interference Line visualisation

Select Interference Matrix Value


Interference Line Parameters

Select a cell(s) from the map


Exercise

View and visualise measured, predicted or combined sets

It is enough if one person retrieves a set

Export interference matrix in CSV format and study the contents

Try selecting different sets (MEASURED, PREDICTED)

Select different interference types (CIP, ARP, FEP)

Visualise Interference Matrix Values on the map


Interference Analyzer

Interference Analyzer tool allows you to find problematic cells that cause interference over great distances in the network

Only measured Interference Matrix can be used (priority set)

Select BSCs, sites, cells or master BTSs from the Navigator or use the active scope


Interference Analyzer

Example: Show me the cells that interfere over 8 km with > 1.0 % CIP

Adjust the threshold values and click Refresh

Sort according to Distance or IM Value


Problem Cells

Adjust thresholds and Analyse again if needed

Select BTSs and Show Chart or Locate on Map


Interference Analyser Chart

The upper-right cells suffer the most interference over the longest distance


Interference Analysis on the Map


What Can I Do About It?

Tilt down the antenna

Turn the antenna

Lower the antenna

Change the antenna (pattern)

Reduce transmit power

After one or more of these changes new measurements should be performed to get optimum results from the optimisation


Exercise

Analyse one BSC and find the cell that causes interference over the longest distance with the highest C/I probability

Locate the interfering cell and interfered cells on the map

What can you do to these cells before/after the frequency allocation?


Summary Workflow

Select Tools->Network Statistics->Interference Matrices

Select BSCs and interference type for measurement retrieval

Retrieve measurement sets from the correct period

A. Specify the number of blind spots and retrieval threshold

B. Define the default values for blind spot interferers

C. Adjust the BSIC reuse distance and reliability scaling

D. Use Antenna bearing and retrieve traffic, if available

Create predictions to complete the measurements

IMPORTANT! Insert priority values for measured and predicted sets for all interference types (CIP, ARP, FEP) that were retrieved

Verify interference matrix in table view and on the map

Use Interference Analyser to find out if you have problem cells that cause interference over a long distance

Documents

GSM Interference Matrix