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Calculating the probability of interference

After the simulation of events had been completed by the EGE, the SEAMCAT workspace will have obtained and stored the vectors of wanted (dRSS) and unwanted (iRSS) signals. You may proceed to use the facilities of the Interference Calculation Engine (ICE) in order to evaluate the probability of interference for the simulated scenario.

The probability of interference is caluclated by the ICE with the following choice of input parameters:

• Calculation mode: compatibility or translation
• Which type of interference signal is considered for calculation: unwanted, blocking, intermodulation or their combination
• Interference criterion: C/I, C/(N+I), (N+I)/N or I/N

If more than one interference calculation was done (i.e. with different combination of interference criterion), you may scroll through all of them by using the Previous / Next buttons.

• Interference calculation results:
  • single interference probability value (compatiblity mode)
  • probability as function of the translation parameter (translation mode)

When the Translation mode is chosen, the user may calculate and display as chart the probability of interference as function of one of the following input parameters:

• Output power of Interfering transmitter
• Blocking response level of Victim receiver
• Intermodulation response level of Victim receiver

The following information on the interference criteria can be found in details here (10 pages).

• METHODOLOGY ASSOCIATED TO THE (C/I) CRITERION
• PROBABILITY OF INTERFERENCE
  • Compatibility calculation mode
  • Translation calculation mode
• ICE Control Parameters
  • ICE Graphical User Interface
  • Interference Calculation Engine Control
  • Interference Calculation Engine
  • Interference criteria C/I, C/(N+I), (N+I)/N ,I/N relationship

The ICE interface may be found by pressing on the Interference Calculations tab as shown below

ID	Description	Comments
1	Calculation mode/Compatibility: The result is a probability of interference.	Compatibility: Gives the probability of being interfered by the Blocking interference and/or by the Unwanted interference and/or by intermodulation interference.
2	Calculation mode/Translations: the result is a graph.	In this case all the following parameters should be independent from frequencies: Receiver blocking response mask, Receiver intermodulation rejection mask, power distribution of interfering transmitter, Unwanted emission floor mask. Calculation of the probability of interference as a function of the reference parameters (Power supplied by the It for the unwanted, Blocking response level of the Vr for the Blocking, And intermodulation rejection level for the Vr). These parameters are varying on user-defined definition domain defined by the number of points where the software has to calculate the probability.
3	Signal type	Choose the interference studied: Unwanted and/or Blocking and/or Intermodulation.
4	Algorithm	formerly known as “Complete 1”
5	Samples	It represents the number of events to calculate the probability from. The accuracy of the probability results derives from this parameters.
6	Interference criterion	Choose between C/I, C/(N+I), (N+I)/N, I/N)
7	Translation parameters: If translation was chosen	Number of points between the min and max, where the software will calculate the probability.
8	Calculation control	Delete a result, and see the last results
9	Result / Compatibility	Probability of interference: 1 - always interfered, 0 - never interfered
10	Result / Translation	Gives the graph, showing the resulting probability of interference vs. the selected values of translation parameter. The average of the graph depends of the number of points, but the higher the number is, the longer the calculations are.

Interference calculation algorithm

Up to version 2, SEAMCAT had a choice of 3 different ICE algorithms, as described in ERC Report 68: the most universal (hence more complex) one and two of its simplified versions. However, when developing newest version, it was felt that the choice between those three algorithms might have been cause of certain confusion to the SEAMCAT users, and then the recent advances in PC computational speeds rendered the different complexities of algorithm implementation meaningless, therefore it was decided to retain only one, the most universal ICE algorithm in SEAMCAT. It corresponds to the algorithm called Complete-1 in the original set of SEAMCAT-2 ICE algorithms.

The algorithm takes one-by-one the corresponding dRSS and iRSS vector results generated by EGE, sums the values from several iRSS vectors if there are more than one interfering link or if user have chosen more than one interference type (i.e. unwanted, blocking, and intermodulation), and then compares that composite iRSS value with dRSS value in that snapshot and with sensitivity floor in accordance with the chosen interference criteria (i.e. C/I, C/(I+N), I/N or I/(I+N)).

If the dRSS signal is above the sensitivity floor, it is counted as qualifying snapshot and if then the composite iRSS signal satisfies the criteria (e.g. if dRSS-iRSS>C/I), then the system notes that the given snapshot produced the non-interfered communication attempt.

The final estimate of probability of interference is calculated as one minus ratio of non-interfered trials to the total number of qualifying snapshots.

Detailed algorithm work-flow is described in the annexed letter.