generatePN3phase.m

function [txA, txB, txC, txChipA, Fs, samplesPerChip] = generatePN3phase(pnLength, samplesPerChip, chipRate, mode)
% generatePN3phase
% ----------------------------------------------------
% Generates three PN sequences (A,B,C) for 3-phase STDR.
% Output waveforms are upsampled by samplesPerChip.
%
% INPUTS:
%   pnLength        Length of PN sequence (e.g., 511, 1023)
%   samplesPerChip  Upsampling factor (e.g., 20)
%   chipRate        Chip rate in Hz (e.g., 500 kHz)
%   mode            'orthogonal' or 'same'
%
% OUTPUTS:
%   txA, txB, txC   Upsampled bipolar PN waveforms (-1, +1)
%   txChipA         Base chip-level PN sequence (before upsampling)
%   Fs              Sample frequency = chipRate * samplesPerChip
%
% MATLAB R2024b compatible
% Requires: Communications Toolbox

%% Compute sampling frequency
Fs = chipRate * samplesPerChip;

%% Create PN generators using different polynomials for orthogonality
switch lower(mode)
    case 'orthogonal'
        % Use 3 independent maximal-length sequences
        pnA = comm.PNSequence('Polynomial','x^10 + x^3 + 1', ...
                              'SamplesPerFrame', pnLength, ...
                              'InitialConditions',[1 zeros(1,9)]);
        pnB = comm.PNSequence('Polynomial','x^10 + x^5 + 1', ...
                              'SamplesPerFrame', pnLength, ...
                              'InitialConditions',[1 zeros(1,9)]);
        pnC = comm.PNSequence('Polynomial','x^10 + x^7 + 1', ...
                              'SamplesPerFrame', pnLength, ...
                              'InitialConditions',[1 zeros(1,9)]);

    otherwise
        % All phases use the same PN → not recommended but allowed
        pnA = comm.PNSequence('Polynomial','x^10 + x^3 + 1', ...
                              'SamplesPerFrame', pnLength, ...
                              'InitialConditions',[1 zeros(1,9)]);
        pnB = pnA;
        pnC = pnA;
end

%% Generate sequences
seqA = pnA();
seqB = pnB();
seqC = pnC();

%% Convert to bipolar (-1, +1)
txChipA = 2*seqA - 1;
txChipB = 2*seqB - 1;
txChipC = 2*seqC - 1;

%% Upsample
txA = upsample(txChipA, samplesPerChip);
txB = upsample(txChipB, samplesPerChip);
txC = upsample(txChipC, samplesPerChip);
end