coherent and non-coherent addition- ICI cancellation technique

[ReComm]

Dear all,

Iam working in ICI cancellation technique .
I read the following documents
www.insipub.com/ajbas/2010/5621-5629.pdf
which state in "simulation results" page 5627 that :
" It is worth mentioning that the proposed ICI cancelling demodulation also improves the system signal-to noise ratio. The signal level increases by a factor of 2, due to coherent addition, whereas the noise level is
proportional to √2 because of non coherent addition of the noise on different sub-carriers".

Can any one help me why non-coherent noise addition proportional to√2 ?
any it's communication base?

Thanks,

 

[zorro]

Hi ReComm,

Let see this example:

R1 = S + n1
R2 = S + n2

where S is the "useful signal" and n1, n2 are non-correlated noise contributions with zero mean and standard deviation sigma.
The addition is

R = R1 + R2 = 2*S + n1+n2

The total signal is 2*S and the total noise contribution is zero-mean, but its standard deviation is sqrt(2)*sigma.
Signal was added coherently (the same in R1 and R2) but noise was aded incoherently (non correlated between R1 and R2).
Regards

Z