  We calculate the magnetic field dependence of quasiparticle transport
properties in the vortex state of a d-wave superconductor arising solely from
the quasiparticle's Doppler shift in the superflow field surrounding the
vortex. Qualitative features agree well with experiments on cuprate and heavy
fermion superconductors at low fields and temperatures. We derive scaling
relations in the variable $T/H^{1/2}$ valid at sufficiently low temperatures
$T$ and fields $H$, but show that these relations depend on the scattering
phase shift, and are in general fulfilled only approximately even in the clean
limit, due to the energy dependence of the quasiparticle relaxation time.
