power measurement -plzz help

[watsup]

Hi all ,
how to calculate the average power of digital samples(I and Q) ??
in my project ..i am feeding IF signal ( GMSK modulated with power of -20db to -60db) to ADC (analog to digital converter ) and from ADC to digital down converter chip , i need to calculate the power of digital output samples (I and Q) of Down converter chip

for 156 samples , the average power would be : ((I^2+Q^2))/156.
if-20 db power is fed as an input .. the calculated value with the formula is not matching to -20db .. ??
kindly help
naresh

 

[klystron]

For the I and Q chaneels on ther own :
Qualculate the mean for the 156 samples
For each point subtract the mean then square, sum together and divide by number of points (Root Mean Square)
Then take the sqrt(o Irms ^2 + Qrms^2) That is your answer

 

[watsup]

yeah thats true but .. after calculating the average power using the ((i ^2 +q^2)/156) formula i am getting values as positive integer (2048 for -20db and 14000 for 0 db)
how to map this values 2048 ,14000 as powers corresponding to -20db and 0 db ??