[ns] Calculating Transmit power

[Ahsa Shrestha]

Hi,
I am trying to implement power control for wireless
networks, and according to various papers available, I
have used received signal strength (Pr),
signal-to-noise ratio(SNR) + its threshold of
10dB(SNRth) and transmitted power signal(Pt) to
calculate the minimum power required(Pmin). The
formula I use is:
SNR = Pr/Pn, where Pn is the sum of all signals at the
receiving nodes when the packet is received.
SNR = (Pt * Pathloss)/Pn
SNRth = (Pmin * Pathloss)/Pn
thus, assuming similar path loss, 
Pmin = (SNRth * Pt)/SNR = (SNRth * Pt) / (Pr/Pn)
My problem is that in ns2, there is no inbuilt model
for calculating SNR, so I implemented one, but when
there is not much happening nearby, there is no noise,
or very small, so SNR becomes infinity, or very large,
causing the Pmin to be nearly 0. Does any one have any
idea to handle this case such that it is quite close
to reality? I was thinking of adding a constant
background (thermal) noise for all noise values, but I
am not sure what is a realistic value for such noise.
Is there any other way where power control can be done
by using SNR, Pt, Pr? Please let me know what has been
done so far in this respect.
Thanks a lot in advance.
Regards,
Ahsa

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