step() for constant gamma clutter

Hello,

I am running some code with the constant gamma clutter step() function. My waveform is changed to "sample" output, not the default "pulse" output.

When I run the step function twice in a row, the first time I get my correct MxN matrix (M number of samples, N number of antenna elements in my array). However, the second sequential step() gives an incorrectly sized matrix.

The third time in a row, it's correct MxN again, and so on.

How can I try to troubleshoot this?

Thank you for any ideas!

[Honglei Chen]

Do you have an example code to illustrate this? Thanks

[Chris Jagielski]

Yes: it's lengthy but here it is.

if true
  % test code
% 
% this shows that calling step twice on the clutter model creates an issue
% where the size of the output matrices are different each time
% 
% 5 October 2015
% 
% 
% ver
% ----------------------------------------------------------------------------------------------------
% MATLAB Version: 8.3.0.532 (R2014a)
% MATLAB License Number: ••••••
% Operating System: Linux 3.5.0-37-generic #58~precise1-Ubuntu SMP Wed Jul 10 17:48:11 UTC 2013 x86_64
% Java Version: Java 1.7.0_11-b21 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
% ----------------------------------------------------------------------------------------------------
% MATLAB                                                Version 8.3        (R2014a)
% Communications System Toolbox                         Version 5.6        (R2014a)
% Curve Fitting Toolbox                                 Version 3.4.1      (R2014a)
% DSP System Toolbox                                    Version 8.6        (R2014a)
% Fixed-Point Designer                                  Version 4.2        (R2014a)
% Instrument Control Toolbox                            Version 3.5        (R2014a)
% Mapping Toolbox                                       Version 4.0.1      (R2014a)
% Parallel Computing Toolbox                            Version 6.4        (R2014a)
% Phased Array System Toolbox                           Version 2.2        (R2014a)
% Signal Processing Toolbox                             Version 6.21       (R2014a)
% Statistics Toolbox                                    Version 9.0        (R2014a)
% 

clear all

c = physconst('LightSpeed');
fc = 10e9;
numSamples = 100;

targetVel = [10 10 10];
targetPos = [3700 10 700];

max_unambiguous_range = 15000;      %[m] this affects the PRF
range_resolution_required = 50;     %[m] this affects the pulse BW
tx_gain = 20;                       %[dB]

platformheight = 500;               %[m]
txPos = [0; 0; platformheight];
txVel = [0; 0; 0];
platformDirection = [0;0];

pulse_bw = c/(2*range_resolution_required);  % Pulse bandwidth [Hz]
pulse_width = 10/pulse_bw;                   % Pulse width [seconds]
prf = c/(2*max_unambiguous_range);           % Pulse repetition frequency
fs = 10*pulse_bw;                            % Sampling rate [Hz]

myFreqValues =    [0 1e20];
myFreqResponses = [0 0];

Az = -180:1:180;
El = -90:1:90;
AzEl_RadPattern = ones(length(El),length(Az));

h_antenna = phased.CustomAntennaElement(...
    'AzimuthAngles',Az,...
    'ElevationAngles',El,...
    'RadiationPattern',AzEl_RadPattern,...
    'FrequencyVector',myFreqValues,...
    'FrequencyResponse',myFreqResponses);

trgamma = surfacegamma('flatland');
rx_speed = sqrt((txVel(1))^2 + (txVel(2))^2 + (txVel(3))^2);

h_clutter = phased.ConstantGammaClutter(...
    'Sensor',h_antenna,...
    'PropagationSpeed',c,...
    'OperatingFrequency',fc,...
    'SampleRate',fs,...
    'TransmitSignalInputPort',true,...
    'PRF',prf,...
    'Gamma',trgamma,...
    'PlatformHeight',platformheight,...
    'PlatformSpeed',rx_speed,...
    'PlatformDirection',platformDirection,...
    'BroadsideDepressionAngle',0,...
    'MaximumRange',max_unambiguous_range,...
    'AzimuthCoverage',360,...
    'PatchAzimuthWidth',10,...
    'SeedSource','Property',...
    'Seed',2015,...
    'OutputFormat','Samples',...
    'NumSamples',numSamples);

h_wave = phased.LinearFMWaveform(...
    'PulseWidth',pulse_width,...
    'PRF',prf,...
    'SweepBandwidth',pulse_bw,...
    'SampleRate',fs,...
    'OutputFormat','Samples',...
    'NumSamples',numSamples);

h_tx = phased.Transmitter(...
    'Gain', tx_gain, ...
    'LossFactor', 0, ...
    'PeakPower', 500, ...
    'InUseOutputPort', true, ...
    'CoherentOnTransmit', false, ...
    'PhaseNoiseOutputPort', true );

% -------------------------------------------------------

% Generate pulse
x = step(h_wave);

% Transmit pulse
release(h_tx);
[s, tx_status, pnoise] = step(h_tx,x);

% Y = step(H,X) specifies the transmit signal in X. Transmit signal refers
% to the output of the transmitter while it is on during a given pulse. 
% This syntax is available when you set the TransmitSignalInputPort 
% property to true.

csig1 = step(h_clutter,s(abs(s)>0));
csig2 = step(h_clutter,s(abs(s)>0));
csig3 = step(h_clutter,s(abs(s)>0));
csig4 = step(h_clutter,s(abs(s)>0));

size(csig1)
size(csig2)
size(csig3)
size(csig4)

% Note that the size changes!

end

[Chris Jagielski]

Is anyone able to duplicate this? Perhaps I am using it wrong, any guidance would be very helpful.