How do we represent zero interference on db scale?
I am using the following formula for calculating the Received_Power_TH (TH stands for threshold). Received_Power_TH is the power of the received signal required for successful decoding. I am using the following formulation.
SINR=Received_Power - Interference - Noise Or
The Recieved_Power that satisfies the SINR_TH (or in other words the minimum Received_Power required for successful decoding) is given as follows
SINR_TH=Received_Power_TH - Interference - Noise Or
Received_Power_TH =SINR_TH + Interference + Noise
However, i get the following results which seem counter intuitive.
Assuming SINR=25, Interference=-50, Noise= -95
Received_Power_Th =25-50-95=-120
Now if we do not have any interference e.g. in a case when there is only one node transmitting, we get the following
Received_Power_TH=25-95=-70
This result seems counter intuitive as Received_Power_TH for successful reception in case of no interference should drop below the value we get when we have interference whereas in this case the Received_Power_TH is equal to -120 in case of interference and it increases to -70 when there is no interference.
Many thanks
Zero is equal to -infinity in dB scale, since log10(0) = -infinity.
An issue with your computations is that the interference and noise power should be added together in linear scale when computing the SINR, not dB scale. So if the interference is -50 dBm and the noise is -95 dBm, the interference+noise is 10^(-5)+10^(-9.5) mW, which you can then convert to dBm as 10*log10( 10^(-5)+10^(-9.5) ).
Dear Tariq Islam , Adding to Emil Björnson ,
Referring to your question, you gave that:
SINR=Received_Power - Interference - Noise Or
By definition the SIINR= S/ (I+N)
where S is the signal power , I is the interference power and N is the noise power.
As you see here the I and N are added together in the simple ratio definition.
It you want to get such ratio in dB scale then
SINR in dBs= 10 log S - 10 log (I+N)
Which is different from your formulation.
The formula which I brought is the correct fromula and it will give the correct calculated values.
Best wishes
Abdelhalim abdelnaby Zekry Emil Björnson Thank you very much for your answers. Grateful if you could help me with the formulation in the attached file. I have written some equations according to my understanding but I am not too sure about them.
Dear Tariq Islam ,
Hope you are well!
As for the quantities describing transmission, there are absolute quantities such as power and power density which is measured in watt or mw or the watt/m^2 and mwatt/m^2
There is the dB scale where the power must be related to a reference power Pr which is either watt or mw according to the power level of the system
The definition is as:
P in dB or in dBm= 10 log P/Pr
Any ratio can be expressed as an absolute value or a fraction.
Say you have a ratio R= A/B
then in log R= log A-log B
In decibels if R is a signal ratio either voltage or current
Then RndB=20 log R
If it is power ratio the dB scale= 10 log R.
Also you have to be knowledgeable about the rules of the logarithmic operations.
For more information about the calculations of the link budget please follow the book of Gilbert Tomasi , Advanced electronic communication systems.
Best wishes
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