Hello everybody!

I have started using SEAMCAT few weeks ago. I would like to use the program to evaluate interferences between DVB, TETRA and LTE. We have the protection margins for all these technologies. However, after reading SEAMCAT manuals about unwanted and blocking interferences I do not understand at all the difference between these two calculations. 

In fact, blocking interference and the protection ratio / sensitivity mode are the options I do not understand how to use.

I would really appreciate any further help.

Thank you in advance.

In fact, blocking interference and the protection ratio / sensitivity mode are the options I do not understand how to use. ... ".

Dear Concepción,

Which of the three options User defined, Protection ratio or Sensitivity you want to choose as Blocking mode depends mainly on the values of the limits given by the relevant standard(s). As nowadays most of the standards provide the limits as absolute values in dBm, the Sensitivty mode is the appropriate one, as you can use the limits 'unchanged' as entries of the blocking mask.

If the values are given as C/I - e.g. for DVB - you may rather choose Protection ratio, but in this case you would have to 'convert' negative values of C/I into positive. If the standard provides positive values in terms of I/C no change is required.

Both Blocking modes above require and consider (!) C/(N+I). Therefore its value should be set correctly.

The third Blocking mode User defined supposes positive values in terms of "blocking response", i.e. the required C/(N+I) is already taken into account by the limits.

You may find some additional information on the attachment. The figures in there are part of that I'm going to present to the next SEAMCAT Workshop 11. - 12. June 2013.

Regards,
Karl

..."Both Blocking modes above require and consider (!) C/(N+I). Therefore its value should be set correctly.

The third Blocking mode User defined supposes positive values in terms of "blocking response", i.e. the required C/(N+I) is already taken into account by the limits".

Dear Karl,

Thank you for your response. In fact, I am working with SEAMCAT v4.0.0 and using the files of the CEPT Report 104 because our studies are simmilar. However, in this report the SEAMCAT version used is version 3 and I do not know if the calculation of blocking attenuation is the same in both versions.

What I do not understand at all is why in this report (Annex 2) C=I=NoiseFloor and therefore C/I=0, C/(N+I)= -3 dB ... and the relationship with the figure you attached in your previous post.

Thank you in advance.

Best.

P.S.: you may also use beta 16 e.g. for cross checking. But there is a small bug. When importing the blocking mask on the receiver panel of the workspace, it is erroneously called “Import Spectrum Emission Mask”. Fortunately this is only editorial J

Dear Karl,

In fact, if I think "close to physics", from my point of view I would use the protection ratio (minimum C/I for avoiding interference) as a C/I criteria for unwanted emissions. 

In the blocking mode, from your figure (assuming (N+I)/N= 3 dB for SEAMCAT 4), the attenuation is computed by using the protection ratio in order to make Interference=Noise. Correct? Maybe I do not understad correctly the blocking mode concept but I am not sure at all which is the relationship between the protection ratio between technologies (defined mostly by ITU recommendations) and the blocking-protection ratio mode.

Thank you in advance.

Dear Concepción,

I fear that there is a basic misunderstanding.

The blocking modes “user defined”, “protection ratio” and “sensitivity” do NOT present physically different mechanisms. They provide “only” - depending on the “meaning” of the values of the blocking mask (which only the user can know) - the appropriate calculation algorithms.

• If the values provide the limits in terms of absolute allowed power, “sensitivity” is the correct mode.

• If the values consider already the required C/(N+I), “user defined” has to be used, otherwise C/(N+I) would be taken into account twice.

Please find on the attachments some more background information.

Regards,
Karl

Dear Karl,

Thank you for your response and your documents. After reading your answer I have realised that may be I am wrong with the concept "Blocking".

As I can see in the Handbook: "Note that the definition of avr in the final relationship is based on the assumption that the interfering signal is reduced by the receiver filter to the level of thermal noise". Why the attenuation of the receiver it is supposed to reduce the interference to the termal noise? Because in a real system this will not usually be true.

Thank you again.

Best,

Conchi 

" ... As I can see in the Handbook: "Note that the definition of avr in the final relationship is based on the assumption that the interfering signal is reduced by the receiver filter to the level of thermal noise".

Dear Conchi,

The quoted part of the handbook is continued with: “…, thus causing increase of overall receiver in band noise by 3 dB”. This is (only) an example for I/N = 0 dB, additionally assuming that the noise figure of the receiver is equal to 0 dB, but unfortunately not explicitly mentioned there.

In fact, the filter should reduce the interfering signal to that level which causes the acceptable increase of the receiver noise (which includes of course its noise figure; see also the attachment). For instance, a desensitisation (increase of the receiver noise) of 1 dB allows only an in band power of 6 dB below the receiver noise.

Regards,
Karl

Dear Karl,

Thank you for your answer. As far as I can understand blocking interference is related also with the overloaded threshold (maybe sensitivity mode)? Becuase other iRSS measurement is the iRSS overloading...

Thank you in advance.

"Becuase other iRSS measurement is the iRSS overloading...".

Dear Conchi,

Sorry, but now I cannot follow :(
Would you like to specify your point?

Regards,
Karl