How to generate BPSK signal

1. Generate 1000 random binary data bits.
2. Convert unipolar to bipolar in the databits.
3. Modulate the bipolar bits with Binary Phase Shift Keying (BPSK).
4. Multiply the baseband BPSK with a carrier fc = 100 Hz.
5. The modulated BPSK signals will be transmitted through a Noiseless channel. At the receiver side demodulate the received signal by multiplying it with a carrier and passing it through a Low Pass Filter (LPF).
6. Decode the BPSK signal using match filtering and sgn function.

[Usama Saleem]

: Apply the concept of conversion of a double word into another word and implement it on Arduino and verify with the help of an Example.

Answer 1

[MathWorks Support Team]

% Set up 
% Specified parameters
M = 2;        % Modulation order (BPSK)
nData = 1000; % Number of bits
Fc = 100;     % Carrier frequency, Hz

% Assumed parameters
Fb = 100;      % Bit (baud) rate, bps
Fs = 8*Fc;     % Sampling frequency, Hz
Ts = 1/Fs;     % Sample time, sec
Td = nData/Fb; % Time duration, sec
spb = Fs/Fb;   % Samples per bit
fSpan = 4;     % Filter span in symbols

% Visualize the spectrum of baseband BPSK & modulated carrier
specAn1 = dsp.SpectrumAnalyzer("SampleRate", Fs, "Method","Filter bank","AveragingMethod","Exponential","Title", "Pulse Shaped Baseband BPSK");
specAn2 = dsp.SpectrumAnalyzer("SampleRate", Fs, "Method","Filter bank","AveragingMethod","Exponential","Title", "BPSK Modulated Carrier");

% Transmitter
% Generate random data bits
data = randi([0 M-1],nData,1);
% Modulate and plot the data
% pskmod() effectively converts unipolar to bipolar bits and performs BPSK
% modulation
modData = real(pskmod(data,M));
% Pulse shape & upsample to match carrier's sampling rate. Pulse shaping is
% used to reduce intersymbol interference and to reduce spectral width of
% the modulated signal.
txFilter = comm.RaisedCosineTransmitFilter("FilterSpanInSymbols",fSpan,"OutputSamplesPerSymbol",spb);
txfilterOut = txFilter(modData);
specAn1(txfilterOut);

% Multiply modulated & pulse shaped signal with carrier
sine = dsp.SineWave("Frequency",Fc,"SampleRate",Fs,"ComplexOutput",false,"SamplesPerFrame",Td/Ts);
carrier = sine();
txSignal = txfilterOut .* carrier;
specAn2((txSignal));

% Receiver
% Multiply received signal with carrier
rxSignal = txSignal .* conj(carrier);
% Low pass match filter to account for pulse shaping
rxFilter = comm.RaisedCosineReceiveFilter("FilterSpanInSymbols",fSpan,"InputSamplesPerSymbol",spb,"DecimationFactor",spb);
rxFilterOut = rxFilter(rxSignal);
% Demodulate
% For BPSK, pskdemod() is equivalent to sign function
dataOut = pskdemod(rxFilterOut,M);

% Each of the tx and rx filters introduces a delay of fSpan/2 symbols, for
% a total delay of fSpan symbols (= bits for BPSK). Delay received bits by
% fDelay for accurate comparison with transmitted bits.
fDelay = fSpan;
[numErr, ber] = biterr(data(1:nData-fDelay),dataOut(fDelay+1:nData))

[Jaweed Raza]

I tried running the above scripts but generated that there are errors in

specAn1 = dsp.SpectrumAnalyzer("SampleRate", Fs, "Method","Filter bank","AveragingMethod","Exponential","Title", "Pulse Shaped Baseband BPSK");

specAn2 = dsp.SpectrumAnalyzer("SampleRate", Fs, "Method","Filter bank","AveragingMethod","Exponential","Title", "BPSK Modulated Carrier");

I am not sure why these errors are generated. The lines are identical for SpecAn1 and SoecAn2. What's the difference and how do they differentiate to display the pulse and spectrum?

Answer 2

[Maadhav Akula]

You can use the follllowing system objects to perform BPSK Modulation and Demodulation:

https://in.mathworks.com/help/comm/ref/comm.bpskmodulator-system-object.html

https://in.mathworks.com/help/comm/ref/comm.bpskdemodulator-system-object.html