Propagation calculation, interference matrix, and prediction plot creation

Calculation in Atoll includes two parts, one is propagation calculation and interference matrix, the other is to calculate prediction plot.

3.6.2.1 Propagation calculation and interference matrix

1、 Propagation calculation

Propagation calculation – calculate path loss for each bin in calculation area. The results are stored in path loss matrix. The size of a bin is the calculation resolution of a transmitter. Right click Transmitters folder, choose Calculations-> Calculate Path Loss Matrices to start calculation. As shown in below picture:

Atoll Getting Started-GSM Version 3.1.2

2、 Interference matrix

（1） Calculate interference matrix – calculate probability of C/I for each transmitter pair. The

principle is to set a frequency for all TRXs and calculate interference probabilities between each pair by considering their location, antennas, power and digital map etc.

Atoll Getting Started-GSM Version 3.1.2

（2） In the pop-up window, define a service zone and handover margin. If you want to take into account shadowing margin, you need to check this option and define a cell edge coverage probability. You also need to choose a method to spread traffic. As shown below:

（3） For the generated interference matrix, you can right click Interference Matrix folder to access properties window. As shown below:

（4） The user can click Externalise button to export the interference matrices results. By doing so you can reduce the size of Atoll document. The exported results can be re-imported whenever needed.

Atoll Getting Started-GSM Version 3.1.2

（5） If you get your interference matrix by other source and import it to Atoll, then you can define where it is from and other settings in Advanced tab of interference matrix properties. This definition will be used in interference matrices combination.

Atoll Getting Started-GSM Version 3.1.2

3.6.2.2 Prediction study creation

Prediction study creation – that is what we call coverage prediction. Atoll reads data from path loss matrix, then calculate prediction results and display them on the map.

After path loss matrix calculation, Atoll will keep their path loss if no change applied to radio parameters of transmitters (e.g. location, antenna type, azimuths). If you change these parameters of a transmitter, Atoll will recalculate its path loss before calculate prediction.

Interference matrix will be used in automatic frequency allocation. If you change radio parameters of transmitters (e.g. location, antenna type, azimuths), then you need to recalculate the interference matrix.

Atoll Getting Started-GSM Version 3.1.2

In the Study types dialogue window, 8 default prediction items are listed. The former 3 items only consider downlink power. You can calculate them before traffic capture and frequency allocation.

1、 Best cell coverage plot generation

（1） Choose Coverage by transmitters, click OK button to open the properties window of that prediction. Define the resolution of the plot in General tab.

Atoll Getting Started-GSM Version 3.1.2

（2） In Condition tab, define a bottom threshold for received power, e.g. -120dBm, and a Server as Best signal level per HCS layer. Reception from TRXs is BCCH.

Atoll Getting Started-GSM Version 3.1.2

In 3.1.2 version, the Cell Edge Coverage Probability is 90% by default, that’s to say, if you define in Clutter classes a model std. deviation for each clutter, then each plot you generate will have a shadowing margin. Atoll support a cell edge coverage probability lower than 50% as well.

（3） Set display properties in Display tab, such as transparency of the plot.

（4） Click OK button to close the window. You can now right click Coverage by Transmitter

under Prediction folder and choose Calculate command, or click icon in tool bar

(shortcut F7), Atoll will start running. An Event Viewer window will pop up. You can see the process of calculation.

Atoll Getting Started-GSM Version 3.1.2

After Propagation calculation (as mentioned above) finished, Atoll will create the coverage plot. The result is shown as below. Every prediction plot generated by user will be saved under Predictions folder.

The generated prediction plots will be locked automatically. They will not be changed even you change radio parameters. So if you want to recalculate a prediction plot, you need to unlock it first (to uncheck Study locked on the right click menu).

2、 Signal level coverage plot

（1） In Study type dialogue window, choose Coverage by signal level.

Atoll Getting Started-GSM Version 3.1.2

（3） Set display properties in Display tab, such as intervals and colors of legends. In legend column, you can change Min and Max values and their colors, or click Actions->Shading, set start break, last break and interval.

Atoll Getting Started-GSM Version 3.1.2

（4） After that, click icon on tool bar (or F7) to start calculating.

Note: since you have completed propagation calculation when creating Coverage by transmitter plot and no parameter has been changed, so Atoll calculates prediction only.

Atoll Getting Started-GSM Version 3.1.2

3、 Overlapping zone coverage

（1） In Study type dialogue window, choose Overlapping zones.

（2） In Condition tab, set a bottom threshold for received power as -120dBm, the Server is Best signal level per HCS layer, with a margin 4dB.

Reception form TRX is BCCH.

Atoll Getting Started-GSM Version 3.1.2

Number of servers >=2 represents there are two cells with a difference of signal level in 4 dB in this area.

Number of servers >=3 represents there are three cells with a difference of signal level in 4 dB. And so on.

3.6.2.3 Force calculation

As mentioned before, if no parameter has been changed, Atoll will not recalculate path losses for cells. But Atoll provides you a Force calculation feature to rerun path losses for all cells.

Click icon on tool bar to force recalculate the whole path loss matrix.

3.6.2.4 Save template

The default setting of legend provided by Atoll may be not what you like. So Atoll provides you a feature to save the settings you changed as a template.

（1） Right click a prediction you need to save, choose Save as Customised Prediction command.

Atoll Getting Started-GSM Version 3.1.2

Atoll Getting Started-GSM Version 3.1.2