MATLAB: Collect 400 samples from a LFM (5MHz bandwidth) signal modulated on 18GHz

antenna array collect dataPhased Array System ToolboxSignal Processing Toolbox

f_sweep = 5e6; fs = f_sweep * 4.121; sLFM = phasedLinearFMWaveform('SampleRate',fs,'SweepBandWidth',f_sweep,'PulseWidth',1e-3); lfmwav = setp(sLFM); collector = phase.WidebandCollector('Sensor',URA, 'SampleRate',fs,'CarrierFrequency',18e9); S1=awgn(lfmwav,-10,'measured'); Y=collector(S1(1:400),[20;30]);

Best Answer

Your sampling rate is set at fs, which is about 20 MHz, this means your Nyquist is about 10 MHz, regardless what your carrier is, i.e., your signal is aliased. If you want to see 18 GHz at the center, you will have to sample at 36 GHz, this is obviously very expensive. On the other hand, the first step in receiver is normally mix it down so the carrier frequency is really used for transmission, and does not affect the signal processing much (except we need to compensate for RF distortions). This is why we often simply simulate at base band because it captures all the band that interests us.

HTH

Related Solutions

MATLAB: What is the difference between “phased.LinearFMWaveform” and “phased.FMCWWaveform”

Hi Ali,

LinearFMWaveform is a pulse waveform, meaning that in general the system only transmit a very short period of time during one cycle and uses the rest of cycle to receive. On the other hand, FMCWWaveform is a continuous waveform, so the system transmits and receives at the same time and the duty cycle for the waveform is always 1.

Currently you cannot specify the starting and ending frequencies in LinearFMWaveform. However, depending on the system setup, you may still be able to simulate your case. For example, if your system's center frequency is 15 MHz, then your situation is just a symmetric sweeping over a 10MHz range.

I don't have that particular paper handy so I cannot comment much on your third question without seeing some code snippet.

HTH

MATLAB: How to generate complex envelop signal using chirp function

One way to get the complex chirp is to form analytical signal, e.g.,

f1 = 0; f2 = 10;
t = 0:0.01:1;
xi = chirp(t,f1,1,f2);
x = hilbert(xi);

Alternatively, you can just use a complex chirp signal equation to derive it, like

x1 = exp(1i*pi*(f2-f1)*t.^2);

To modulate to the carrier, you need to multiply the carrier signal, like

fc = 50;
xm = x.*exp(1i*2*pi*fc*t);

However, most simulation is done in complex baseband and even in RF simulation it models the effect of RF distortion on the baseband signal.

HTH

Best Answer

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