[Ns-developers] [all versions] definition of power values in Tcl scripts

[antoine.trux@nokia.com]

Hi,

Power values are often conveniently expressed in dBm units, but most
(all?) Tcl variables that hold power values are expressed in watts. For
example, in ns-2.33/tcl/lib/ns-default.tcl:

	Phy/WirelessPhyExt set noise_floor_ 7.96159e-14           ;#-101
dBm

Why not instead use a conversion function? Something like this:

	# Return the value in watts that corresponds to `dBm_value'.
	proc dBmsToWatts {dBm_value} {
	    return [expr 0.001 * pow(10, $dBm_value / 10.0)]
	}

	[...]

	Phy/WirelessPhyExt set noise_floor_ [dBmsToWatts -101.0]

This would result in easier-to-maintain code and more precise results.

Antoine Trux
Nokia Research Center