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Amplitude and Phase Modulation Examples

These examples demonstrate amplitude and phase modulation techniques.

Apply APSK Modulation Modifying Symbol Ordering

Plot APSK constellations for Gray-coded and custom-coded symbol mappings.

Define vectors for modulation order and PSK ring radii. Generate bit data for constellation points.

M = [8 8];
modOrder = sum(M);
radii = [0.5 1.5];
x = 0:modOrder-1;

The apskmod function assumes the single channel binary input is left-MSB aligned and specified column-wise. Use the int2bit function to express the integer input symbols as a single column binary vector.

xBit = int2bit(x,log2(modOrder));

Apply APSK modulation to the data using the default phase offset. Since element values for M are equal and element values for phase offset are equal, the symbol mapping defaults to 'gray'. Plot the constellation using binary input to highlight the Gray-coded nature of the constellation mapping.

y = apskmod(xBit,M,radii,PlotConstellation=true,InputType='bit');

Create a custom-coded symbol mapping vector. This custom mapping happens to be another Gray-coded mapping.

cmap = [0;1;9;8;12;13;5;4;2;3;11;10;14;15;7;6];

Apply APSK modulation with a custom-coded symbol mapping. Plot the constellation using binary input to highlight that the custom mapping defines different Gray-coded symbol mapping.

z = apskmod(xBit,M,radii, ...
    SymbolMapping=cmap, ...
    PlotConstellation=true, ...

Demodulate MIL-STD-188-110C Specific 64-QAM Signal

Demodulate a 64-QAM signal that was modulated as specified in MIL-STD-188-110C. Compute hard decision bit output and verify that the output matches the input.

Set the modulation order and generate random bit data.

M = 64;
numBitsPerSym = log2(M);
x = randi([0 1],1000*numBitsPerSym,1);

Modulate the data. Use name-value pairs to specify bit input data and to plot the constellation.

txSig = mil188qammod(x,M,InputType='bit',PlotConstellation=true);

Demodulate the received signal. Compare the demodulated data to the original data.

z = mil188qamdemod(txSig,M,OutputType='bit');
ans = logical

Plot Noisy DVB-S APSK Constellation using Simulink

Apply DVB-S APSK modulation to random data symbols, pass the modulated signal through an AWGN channel, and then plot the signal constellation.

The slex_dvbs_apsk_mod model is configured for the S2 standard suffix and modulation order 16. For you to get desired results, all blocks in the model must align their configuration to the same modulation order. To set the modulation order for the DVBS-APSK Modulator Baseband block, select a value from the dropdown list in the block mask. The set of modulation orders available varies depending on the DVB standard suffix parameter setting. The InitFcn callback defines the workspace variable, M = 16, and this variable is used to set the:

The Constellation Diagram block has the Reference constellation parameter set to Custom and the Custom value parameter set to align with the modulation order of the DVBS-APSK Modulator Baseband block. To see the values, open Reference Constellation in the Measurements tab on the Constellation Diagram window.

Change the EbN0 of the AWGN channel block to 10 dB. Run the model and observe the increase in noise shown in the plotted constellation diagram.

You can try running the model with a different modulation order. To adjust the modulation order, you must align the:

  • Modulation order setting in the DVBS-APSK Modulator Baseband block

  • Value of the workspace variable M

  • Reference constellation in the Constellation Diagram block

If these parameters are not aligned with each other, the reference constellation and input signal do not display the desired constellation.

Demodulate Noisy 16-APSK Signal Using Simulink

Apply 16-APSK modulation to a signal of random data. Pass the modulated signal through an AWGN channel. Demodulate the noisy 16-APSK signal. The example reports bit error rate (BER) and symbol error rate (SER) at two SNR settings.

The slex_16apsk_mod model passes a 16-APSK modulated signal through an AWGN channel, demodulates the signal and then computes the error rate statistics. The upper workflow computes the BER and the lower workflow computes the SER. Some block parameters get set by using workspace variables initialized in the PreLoadFcn callback function loads simulation variables into the workspace. For more information, see Model Callbacks (Simulink).

Run the model with the AWGN channel blocks set to EbN0 = 6 dB and display the computed BER and SER. The AWGN Channel block in the lower workflow converts the EbN0 setting to an EsN0 setting. The results are saved to the workspace variables BERVec and SERVec in 1-by-3 row vectors. The first element contains the error rate.

With EbN0 set to  6.00 dB, BER: 0.070
With EsN0 set to 12.02 dB, SER: 0.160

Change the EbN0 of the AWGN channel block to 10 dB. Run the model, display the computed BER and SER, and observe the decrease in error rate.

With EbN0 set to 10.00 dB, BER: 0.016
With EsN0 set to 16.02 dB, SER: 0.051

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