Problems with the use of ray-tracing techniques in indoor propagation envir
onments are identified, and a new set of widely applicable diffraction coef
ficients is developed. The limitations on the accuracy of the ray-tracing m
ethod in indoor propagation environments are first assessed. The effects of
scatterers with dimensions approaching the wavelength of operation and of
scatterers with finite conductivity are considered, The accuracy of ray tra
cing is quantified by comparison to a full-wave simulation technique, which
combines the finite-difference time-domain method with a spatial transform
ation technique, the Kirchhoff surface integral formulation. Simulation res
ults demonstrate that when the magnitude and phase of the received signal c
omponents are properly accounted for, the ray-tracing solution mag be accur
ate down to a fraction of a wavelength. A new set of diffraction coefficien
ts is presented for calculations involving obstacles with finite conductivi
ty. The new coefficients eliminate an artificial dip in the diffracted fiel
d strength, which is often encountered when currently available techniques
are used. Validation is provided by comparison with full-wave simulations a
nd measurements, improved accuracy in both the illuminated and shadowed reg
ions is demonstrated.