You are here: Manual / Algorithms / Intermodulation Signals

---

Bug warning: Note that the current implementation of IM is not running properly in SEAMCAT, Therefore, calculation of probability of intermodulation for selected signal type "Inter-modulation" will produce erroneous results. This issue is under the consideration of the SEAMCAT Technical Group. Users are advised not to use this module.

Calculation of intermodulation signal iRSS_intermod

General case

An instant value of the iRSS_intermod signal, i.e. the interference signal appearing at the input of Victim Receiver (VR) due to intermodulation effect, is calculated by SEAMCAT in the following manner.

For each couple of distinct interfering transmitters (It_i, It_j), the interfering intermodulation signal iRSS_intermod received by VR is given by:

Note: This formula is built from definition of the iRSS_intermod as the power of intermodulation product above the noise floor of victim receiver. For further explanation of this formula, please refer to Appendix 9 to Annex 2 of the ERC Report 68 (available at  the ERO Document Database).

where:

and:

intermod(f₀-f_vr) - is the intermodulation rejection of VR, defined in the scenario.

If more than one distinct pair of ITs are present in the scenario, then the total iRSS_intermod will be obtained by the power-summation of the individual iRSS_intermod signals calculated for each distinct (It_i, It_j).

VR bandwidth considerations

If the intermodulation response of victim receiver was defined as frequency dependent function (i.e. the mask), this function should then provide sufficient attenuation of intermodulation products outside the victim receiver bandwidth, i.e. the function values outside the VR bandwidth should show very high attenuation.

When scenario contains a constant value for the intermodulation rejection, then the intermodulation products falling outside the VR bandwidth are rejected and the corresponding iRSS_intermod value is set to -1000 dBm.