reflect
Description
returns the total reflected signal, Y
= reflect(bicyclist
,X
,ang
)Y
, from a bicyclist. The total
reflected signal is the sum of all reflected signals from the bicyclist scatterers.
X
represents the incident signals at each scatterer.
ang
defines the directions of the incident and reflected signals with
respect to the each scatterers.
The reflected signal strength depends on the value of the radar cross-section at the incident angle. This simplified model uses the same value for all scatterers.
Examples
Radar Signal Backscattered by Bicyclist
Compute the backscattered radar signal from a bicyclist moving along the x-axis at 5 m/s away from a radar. Assume that the radar is located at the origin. The radar transmits an LFM signal at 24 GHz with a 300 MHz bandwidth. A signal is reflected at the moment the bicyclist starts to move and then one second later.
Initialize Bicyclist, Waveform, and Propagation Channel Objects
Initialize the backscatterBicyclist
, phased.LinearFMWaveform
, and phased.FreeSpace
objects. Assume a 300 MHz sampling frequency. The initial position of the bicyclist lies on the x-axis 30 meters from the radar.
bw = 300e6; fs = bw; fc = 24e9; radarpos = [0;0;0]; bpos = [30;0;0]; bicyclist = backscatterBicyclist( ... 'OperatingFrequency',fc,'NumWheelSpokes',15, ... 'InitialPosition',bpos,'Speed',5.0, ... 'InitialHeading',0.0); lfmwav = phased.LinearFMWaveform( ... 'SampleRate',fs, ... 'SweepBandwidth',bw); sig = lfmwav(); chan = phased.FreeSpace( ... 'OperatingFrequency',fc, ... 'SampleRate',fs, ... 'TwoWayPropagation',true);
Plot Initial Bicyclist Position
Using the move
object function, obtain the initial scatterer positions, velocities and the orientation of the bicyclist. Plot the initial position of the bicyclist. The dt
argument of the move
object function determines that the next call to move
returns the bicyclist state of motion dt
seconds later.
dt = 1.0; [bpos,bvel,bax] = move(bicyclist,dt,0); plot(bicyclist)
Obtain First Reflected Signal
Propagate the signal to all scatterers and obtain the cumulative reflected return signal.
N = getNumScatterers(bicyclist); sigtrns = chan(repmat(sig,1,N),radarpos,bpos,[0;0;0],bvel); [rngs,ang] = rangeangle(radarpos,bpos,bax); y0 = reflect(bicyclist,sigtrns,ang);
Plot Bicyclist Position After Position Update
After the bicyclist has moved, obtain the scatterer positions and velocities and then move the bicycle along its trajectory for another second.
[bpos,bvel,bax] = move(bicyclist,dt,0); plot(bicyclist)
Obtain Second Reflected Signal
Propagate the signal to all scatterers at their new positions and obtain the cumulative reflected return signal.
sigtrns = chan(repmat(sig,1,N),radarpos,bpos,[0;0;0],bvel); [~,ang] = rangeangle(radarpos,bpos,bax); y1 = reflect(bicyclist,sigtrns,ang);
Match Filter Reflected Signals
Match filter the reflected signals and plot them together.
mfsig = getMatchedFilter(lfmwav); nsamp = length(mfsig); mf = phased.MatchedFilter('Coefficients',mfsig); ymf = mf([y0 y1]); fdelay = (nsamp-1)/fs; t = (0:size(ymf,1)-1)/fs - fdelay; c = physconst('LightSpeed'); plot(c*t/2,mag2db(abs(ymf))) ylim([-200 -50]) xlabel('Range (m)') ylabel('Magnitude (dB)') ax = axis; axis([0,100,ax(3),ax(4)]) grid legend('First pulse','Second pulse')
Compute the difference in range between the maxima of the two pulses.
[maxy,idx] = max(abs(ymf)); dpeaks = t(1,idx(2)) - t(1,idx(1)); drng = c*dpeaks/2
drng = 4.9965
The range difference is 5 m, as expected given the bicyclist speed.
Input Arguments
bicyclist
— Bicyclist target
backscatterBicyclist
object
Bicyclist, specified as a backscatterBicyclist
object.
X
— Incident radar signals
complex-valued M-by-N matrix
Incident radar signals on each bicyclist scatterer, specified as a complex-valued M-by-N matrix. M is the number of samples in the signal. N is the number of point scatterers on the bicyclist and is determined partly from the number of spokes in each wheel, Nws. See Bicycle Scatterer Indices for the column representing the incident signal at each scatterer.
The size of the first dimension of the input matrix can vary to simulate a changing signal length. A size change can occur, for example, in the case of a pulse waveform with variable pulse repetition frequency.
Data Types: double
Complex Number Support: Yes
ang
— Directions of incident signals
real-valued 2-by-P matrix
Directions of incident signals on the bicyclist scatterers, specified as a
real-valued 2-by-N matrix. N equals the number of
columns in X
. Each column of Ang
specifies the
incident direction of the signal to a scatterer taking the form of an azimuth-elevation
pair, [AzimuthAngle;ElevationAngle]. Units are in degrees. See
Bicycle Scatterer Indices for the column
representing the incident direction at each scatterer.
Data Types: double
Output Arguments
Y
— Total reflected radar signals
complex-valued M-by-1 column vector
Total reflected radar signals, returned as a complex-valued
M-by-1 column vector. M equals the number of
samples in the input signal, X
.
Data Types: double
Complex Number Support: Yes
More About
Bicycle Scatterer Indices
Bicyclist scatterer indices define which columns in the scatterer position or
velocity matrices contain the position and velocity data for a specific scatterer. For
example, column 92 of bpos
specifies the 3-D position of one of the
scatterers on a pedal.
The wheel scatterers are equally divided between the wheels. You can determine the total
number of wheel scatterers, N, by subtracting 113 from the output of the
getNumScatterers
function. The number of scatterers per wheel is
Nsw = N/2.
Bicyclist Scatterer Indices
Bicyclist Component | Bicyclist Scatterer Index |
---|---|
Frame and rider | 1 … 90 |
Pedals | 91 … 99 |
Rider legs | 100 … 113 |
Front wheel | 114 … 114 + Nsw - 1 |
Rear wheel | 114 + Nsw … 114 + N - 1 |
Algorithms
Radar Cross-Section
The value of the radar cross-section (RCS) of a scatterer
generally depends upon the incident angle of the reflected radiation. The
backscatterBicyclist
object uses a simplified RCS model: the RCS pattern of
an individual scatterer equals the total bicyclist pattern divided by the number of scatterers.
The value of the RCS is computed from the RCS pattern evaluated at an average over all
scatterers of the azimuth and elevation incident angles. Therefore, the RCS value is the same
for all scatterers. You can specify the RCS pattern using the RCSPattern
property of the backscatterBicyclist
object or use the default value.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Version History
Introduced in R2021a
See Also
getNumScatterers
| move
| plot
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