[ns] How to define different transmit range?

[chen guoming]

Dear All:
  I want to define different node with different transmit ranges, how to do
it?
Phy/WirelessPhy set CSThresh_ 1.559e-11
Phy/WirelessPhy set RXThresh_ 3.652e-10         ;# 250m
the two lines above define the transmit range to 250m. However, all the node
will have the same transmit range if I use this method.
What can I do to define different transmit range?
Thanks a lot!
Regards
David