Y = step(SFS,F,origin_pos,dest_pos,origin_vel,dest_vel)
returns
the resulting signal Y
= step(SFS
,F
,origin_pos
,dest_pos
,origin_vel
,dest_vel
)Y
when the narrowband signal F
propagates
in free space from the position or positions specified in origin_pos
to
the position or positions specified in dest_pos
.
For nonpolarized signals, either the origin_pos
or dest_pos
arguments
can specify more than one point. Using both arguments to specify multiple
points is not allowed. The velocity of the signal origin is specified
in origin_vel
and the velocity of the signal
destination is specified in dest_vel
. The dimensions
of origin_vel
and dest_vel
must
agree with the dimensions of origin_pos
and dest_pos
,
respectively.
Note:
The object performs an initialization the first time the 

Propagated signal, returned as a Melement complexvalued column vector, MbyN complexvalued matrix or MATLAB structure containing complexvalued fields. If If The output 
When the origin and destination are stationary relative to each
other, the output Y
of step
can
be written as Y(t) = x(tτ)/L.
The quantity τ is the signal delay and L is
the freespace path loss. The delay τ is
given by R/c,
where R is the propagation distance and c is
the propagation speed. The free space path loss is given by
$$L=\frac{{(4\pi R)}^{2}}{{\lambda}^{2}}$$
where λ is the signal wavelength.
This formula assumes that the target is in the farfield of the transmitting element or array. In the nearfield, the freespace path loss formula is not valid and can result in a loss less than one, equivalent to a signal gain. For this reason, the loss is set to unity for range values, R ≤ λ/4π.
When there is relative motion between the origin and destination, the processing also introduces a frequency shift. This shift corresponds to the Doppler shift between the origin and destination. The frequency shift is v/λ for oneway propagation and 2v/λ for twoway propagation. The parameter v is the relative speed of the destination with respect to the origin.
For further details, see [2].
[1] Proakis, J. Digital Communications. New York: McGrawHill, 2001.
[2] Skolnik, M. Introduction to Radar Systems, 3rd Ed. New York: McGrawHill, 2001.