wiki:Manual/Algorithms/Basics/UnwantedEmissions

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Calculation of total emissions (including unwanted emissions) of IT falling in VR bandwidth

The emissions of the interfering link transmitter (ILT) are defined by means of emissions mask function dialog of Δf=f-fit which establishes the relative emission power levels as referred to the carrier power (dBc), measured in reference bandwidth bs. The interfering transmitter power PILT (dBm) at fILT has therefore to be added for evaluating the link budget with the wanted receiver (i.e. power control). See the discussion on the reference bandwidth settings at the bottom of this page.

There is no separate parameter for the ILT emissions bandwidth (e.g. channel bandwidth) and therefore the value of the emission bandwidth should be inherently contained in the shape of the ILT emissions mask itself.

The mask can also be expressed as the maximum of

  • the sum of the supplied interfering power Pitsupplied, a relative emission mask (containing the wanted transmission and all unwanted emissions including the emission floor depending on the power control) and the gain power control
  • or the absolute emission floor.

The relative emission mask is described by a triplet (frequency offset (MHz), relative emission level (dBc) and reference bandwidth (MHz)). The interfering transmitter power Pitsupplied (dBm) at fit is used for evaluating the link budget with the wanted receiver (i.e. power control).

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ILT emissions mask

The following equations show the principle of the determination of the interfering power. If fit = fvr, then the interfering frequencies fall exactly in the receiving band of the victim receiver (co-channel interference). For simplification within the algorithms the mask function Pm_it is normalized to 1 Hz reference bandwidth:





Unwanted emission noise floor

The aforementioned formulas are also applicable to derive the unwanted emissions floor value unwantedfloor(dBm) from the unwanted emissions floor function that might be defined in the scenario, except that in the end no power is added since the unwanted emissions floor function is expressed in absolute dBm values.

If the unwanted emission floor (i.e. the noise floor) option is selected in the scenario settings, then SEAMCAT will compare the value of total/unwanted emissions derived from the ILT emissions mask as described in previous section with the value derived using the unwanted emissions floor function and the larger value will be passed on into further calculations of iRSSunwanted.

The comparison involves the power control gain when the ILT power control option is selected. The equation reads then:

Pit(dBm) + unwantedrel(dBc) + GPC > unwantedfloor (dBm)'


Resulting power level for the calculation of iRSS

Note that the value of the emission_floorit is scaled to the Vr bandwidth. This means that assuming a Vr bandwidth of 200 KHz and the value of the Emission mask and Unwanted Emission floor as presented in the figure below, the following emisssionit are calculated:

for a fit = 900.3 MHz and fvr = 900.0 MHz:
emissionit = max (-30 + 5 + 0 , -10)
emissionit = -10 dBm;


for a fit = 900.0 MHz and fvr = 900.0 MHz:
emissionit = max (0 + 5 + 0 , 13)
emissionit = 13 dBm;



illustration of the emission mask and the unwanted emission floor mask.

Examples of dBc emission mask and relation between normalised mask and ref. BW mask

The following range of attenuation is considered, for a system of 30 dBm using a 20 kHz emission bandwidth. The reference bandwidth for the attenuation is 10 kHz. Within the emission bandwidth the reference bandwidth is taken equal to the emission bandwidth.


Emission mask value

The figure below shows the “upper” part of the mask derived from the tableabove, the whole mask is symmetric. The frequency offset is defined in MHz.

Example of “Upper part” of an Emission Mask in dBc

If the mask is symmetric, the whole mask may be obtained by using the “Sym” function. N1 and N2 correspond to the same level of power and correspond to attenuation defined in dBc given in reference bandwidth (kHz) and normalised bandwidth (1 MHz) respectively.

N1 (dBm/Bref) = P (dBm) + Att1 (dBc/Bref)
N2 (dBm/1 MHz) = P (dBm) + Att2 (dBc/1 MHz)

Where P is the Power within the emission bandwidth.

N1 (dBm/Bref) and N2 (dBm/1 MHz) represent the same level of power (Pi):
Pi (dBm) = N1 (dBm/Bref) + 10 log(Bref)
Pi (dBm) = N2 (dBm/1 MHz) + 10 log(1 MHz)

Therefore the relationship between the attenuations in dBc defined in reference bandwidth and in 1 MHz is given by:

Delta = N1 (dBm/1 MHz) - N2 (dBm/Bref)
Delta = Pi (dBm) - 10 log(Bref) - (Pi (dBm) - 10 log(1 MHz))
Delta = 10 log( (1 MHz)/(Bref) )

Note:

  • If the reference bandwidth is larger than the emission bandwidth then the attenuation must be defined with positive sign;
  • If the reference bandwidth is lower than the emission bandwidth then the attenuation must be defined with negative sign;
  • If the reference bandwidth is equal to the emission bandwidth then the attenuation should be set-up at zero.


Link between the normalised mask and the mask given in reference bandwidth

Examples of calculation using dBc

The ITU-R Recommendation ITU-R SM.329 on Unwanted emissions in the spurious domain provides a definition of dBc unit, which is defined as “Decibels relative to the unmodulated carrier power of the emission. In the cases which do not have a carrier, for example in some digital modulation schemes where the carrier is not accessible for measurement, the reference level equivalent to dBc is decibels relative to the mean power P. From this recommendation the following example is presented:

A land mobile transmitter, with any value of emission bandwidth, must meet an attenuation of 43 + 10 logP, or 70 dBc, whichever is less stringent. To measure the emissions the use of a reference bandwidth of 100 kHz is recommended.

With a measured total mean power of 10 W:
Attenuation relative to total mean power = 43 + 10 log(10) = 53 dB
The 53 dBc is less stringent than 70 dBc, so the 53 dBc value is used. Therefore, emissions must not exceed 53 dBc in a 100 kHz reference bandwidth, or converting to an absolute level: 10 dBW – 53 dBc = – 43 dBW in a 100 kHz reference bandwidth.

With a measured total mean power of 1000 W:
Attenuation relative to total mean power = 43 + 10 log(1000 ) = 73 dB
The 73 dBc is more stringent than 70 dBc limit, so the 70 dBc value is used. Therefore, emissions must not exceed 70 dBc in a 100 kHz reference bandwidth, or converting to an absolute level: 30 dBW - 70 dBc = -40 dBW in a 100 kHz reference bandwidth.

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