# How to generate BPSK signal

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Meshari Alsahli on 20 Apr 2020
Edited: MathWorks Support Team on 13 Jul 2021 at 20:38
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.

MathWorks Support Team on 13 Jul 2021 at 4:00
Edited: MathWorks Support Team on 13 Jul 2021 at 20:41
% 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));
% Multiply received signal with carrier
rxSignal = txSignal .* conj(carrier);
% Low pass match filter to account for pulse shaping
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))

Maadhav Akula on 23 Apr 2020

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