Pulse Doppler radar system simulation using MATLAB

How to code this project in MATLAB

I'd tried coding this project (prob. 3-2, third paragraph) in MATLAB through this tutorial :

https://www.mathworks.com/help/phased/ug/doppler-shift-and-pulse-doppler-processing.html

I'd changed PRF to 100 and pulse width to 5e-4 , And made Velocity of target one dimensional:

    waveform = phased.RectangularWaveform('SampleRate',5e6,...
    'PulseWidth',5e-4,'OutputFormat','Pulses',...
    'NumPulses',1,'PRF',100);
    target = phased.RadarTarget('Model','Nonfluctuating',...
    'MeanRCS',1,'OperatingFrequency',1e9);
    targetpos = phased.Platform('InitialPosition',[1000; 0; 0],...
    'Velocity',[-100; 0; 0]);
    antenna = phased.IsotropicAntennaElement(...
    'FrequencyRange',[5e8 5e9]);
    transmitter = phased.Transmitter('PeakPower',5e3,'Gain',20,...
    'InUseOutputPort',true);
    transpos = phased.Platform('InitialPosition',[0;0;0],...
    'Velocity',[0;0;0]);
    radiator = phased.Radiator('OperatingFrequency',1e9,'Sensor',antenna);
    collector = phased.Collector('OperatingFrequency',1e9,'Sensor',antenna);
    channel = phased.FreeSpace('SampleRate',waveform.SampleRate,...
    'OperatingFrequency',1e9,'TwoWayPropagation',false);
    receiver = phased.ReceiverPreamp('Gain',0,'LossFactor',0,...
    'SampleRate',5e6,'NoiseFigure',5,...
    'EnableInputPort',true,'SeedSource','Property','Seed',1e3);

I did not change anything here :

    NumPulses = 10;
    sig = waveform(); % get waveform 
    transpos = transpos.InitialPosition; % get transmitter position
    rxsig = zeros(length(sig),NumPulses);
    % transmit and receive ten pulses
    for n = 1:NumPulses
        % update target position
        [tgtpos,tgtvel] = targetpos(1/waveform.PRF);
        [tgtrng,tgtang] = rangeangle(tgtpos,transpos);
        tpos(n) = tgtrng;
        [txsig,txstatus] = transmitter(sig); % transmit waveform
        txsig = radiator(txsig,tgtang); % radiate waveform toward target
        txsig = channel(txsig,transpos,tgtpos,[0;0;0],tgtvel); % propagate waveform to target
        txsig = target(txsig); % reflect the signal
        % propagate waveform from the target to the transmiter
        txsig = channel(txsig,tgtpos,transpos,tgtvel,[0;0;0]);
        txsig = collector(txsig,tgtang); % collect signal
        rxsig(:,n) = receiver(txsig,~txstatus); % receive the signal
    end

    prf = waveform.PRF;
    fs = waveform.SampleRate;
    fasttime = unigrid(0,1/fs,1/prf,'[)');
    rangebins = (physconst('LightSpeed')*fasttime)/2;

    probfa = 1e-9;
    NoiseBandwidth = 5e6/2;
    npower = noisepow(NoiseBandwidth,...
        receiver.NoiseFigure,receiver.ReferenceTemperature);
    thresh = npwgnthresh(probfa,NumPulses,'noncoherent');
    thresh = sqrt(npower*db2pow(thresh));
    [pks,range_detect] = findpeaks(pulsint(rxsig,'noncoherent'),...
        'MinPeakHeight',thresh,'SortStr','descend');
    range_estimate = rangebins(range_detect(1));

    ts = rxsig(range_detect(1),:).';
    [Pxx,F] = periodogram(ts,[],256,prf,'centered');
    plot(F,10*log10(Pxx))
    grid
    xlabel('Frequency (kHz)')
    ylabel('Power (dB)')
    title('Periodogram Spectrum Estimate')

    [Y,I] = max(Pxx);
    lambda = physconst('LightSpeed')/1e9;
    tgtspeed = dop2speed(F(I)/2,lambda);
    fprintf('Estimated range of the target is %4.2f meters.\n',...
        range_estimate)

    fprintf('Estimated target speed is %3.1f m/sec.\n',tgtspeed)
    
    if F(I)>0
        fprintf('The target is approaching the radar.\n')
    else
        fprintf('The target is moving away from the radar.\n')
    end

I really have no idea why this new pulse give me this output :

Estimated range of the target is 750350.54 meters.
Estimated target speed is -4.9 m/sec.
The target is moving away from the radar.

I would be appreciated if anyone could give me an advice or a solution.

Many thanks!