The if77 module is an ns-3 contrib module which implements a new PropagationLossModel which can be used to calculate propagation loss of wireless signals in ns-3 simulations. The PropagationLossModel defined by this contrib module is a wrapper around a Fortran library which implements the IF-77 model.
The IF-77 model is an electromagnetic wave propagation model developed for the Federal Aviation Administration by M.E. Johnson and G.D. Gierhart. The model is applicable to air/air, air/ground, air/satellite, ground/ground, and ground/satellite paths for frequencies in the range 100Mhz to 20GHz.
More information about the If-77 model, including the original paper and Fortran source code, can be found here
This ns-3 extension is one or more contributed modules.