zigbee_txer.m

function [waveform, txSyms, numPkt] = zigbee_txer(txBits, OSR, ifWEBeeTweak)

    persistent chipLen
    persistent chipMap
    persistent SHR
    persistent PHR
    persistent pulse
    persistent numSampPerWiFiCP
    persistent numBitPerPHYPayload
    persistent numBytePerPHYPayload
    persistent flipQFactor

    if isempty(chipLen)
        chipLen = 32;
    end

    if isempty(chipMap)
        % See Table 73 in IEEE 802.15.4,  2011 revision
        chipMap = ...
            [1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0;
         1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0;
         0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0;
         0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1;
         0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1;
         0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0;
         1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1;
         1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1;
         1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1;
         1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1;
         0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1;
         0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0;
         0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0;
         0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1;
         1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0;
         1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0];

    end

    if isempty(numBitPerPHYPayload)
        % According to WEBee, each ZigBee packet's PHY payload contains 96 bits (i.e., 24 symbols).
        numBitPerPHYPayload = 96;
        numBytePerPHYPayload = numBitPerPHYPayload / 8;
    end

    if isempty(SHR)
        % Synchronization header (SHR)

        % Preamble is 4 octets, all set to 0.
        preamble = zeros(4 * 8, 1);

        % Start-of-frame delimiter (SFD)
        SFD = [1 1 1 0 0 1 0 1]'; % value from standard (see Fig. 68, IEEE 802.15.4, 2011 Revision)

        SHR = [preamble; SFD];
    end

    if isempty(PHR)
        % PHY Header (PHR)
        reservedValue = 0;
        PHR = [int2bit(numBytePerPHYPayload, 7, false); reservedValue];
    end

    if isempty(pulse)
        % Half-period sine wave
        pulse = sin(0:pi / OSR:(OSR - 1) * pi / OSR);
    end

    % Start to generate waveforms
    numPkt = ceil(length(txBits) / numBitPerPHYPayload);

    if mod(length(txBits), numBitPerPHYPayload) > 0
        numPadBits = numBitPerPHYPayload * numPkt - length(txBits);
        txBits = [txBits, zeros(1, numPadBits)];
    end

    txBits = reshape(txBits, [numBitPerPHYPayload, numPkt]);

    numSymPerPkt = (length(SHR) + length(PHR) + numBitPerPHYPayload) / 4;
    txSyms = zeros(numSymPerPkt, numPkt);
    numSampPerPkt = numSymPerPkt * OSR * 16 + OSR / 2;
    waveform = zeros(numSampPerPkt, numPkt);

    if isempty(flipQFactor) && ifWEBeeTweak == true
        flipQFactor = [-1 * ones(1, 10), ones(1, (4 * OSR - 10))];
        flipQFactor = repmat(flipQFactor, 1, (numSampPerPkt - OSR / 2) / length(flipQFactor));
        flipQFactor = [ones(1, OSR / 2), flipQFactor]';
    else
        flipQFactor = ones(1, 4 * OSR);
        flipQFactor = repmat(flipQFactor, 1, (numSampPerPkt - OSR / 2) / length(flipQFactor));
        flipQFactor = [ones(1, OSR / 2), flipQFactor]';
    end

    for ithPkt = 1:1:numPkt

        % PHY protocol data unit:
        PPDU = [SHR; PHR; txBits(:, ithPkt)];

        % pre-allocate matrix for performance
        chips = zeros(chipLen, length(PPDU) / 4);

        for idx = 1:length(PPDU) / 4
            % Bit to symbol mapping
            currBits = PPDU(1 + (idx - 1) * 4:idx * 4);
            symbol = bit2int(currBits, 4, false);
            txSyms(idx, ithPkt) = symbol;

            % Symbol to chip mapping
            chips(:, idx) = chipMap(1 + symbol, :)'; % +1 for 1-based indexing
        end

        % O-QPSK modulation
        % split two 2 parallel streams, also map [0, 1] to [-1, 1]
        oddChips = chips(1:2:end) * 2 - 1;
        evenChips = chips(2:2:end) * 2 - 1;

        % Half-sine pulse filtering
        filteredReal = pulse' * oddChips; % each column is now a filtered pulse
        filteredImag = pulse' * evenChips; % each column is now a filtered pulse

        re = [filteredReal(:); zeros(round(OSR / 2), 1)];
        im = [zeros(round(OSR / 2), 1); filteredImag(:)];
        % Quadrant flipping of WEBee.
        im = im .* flipQFactor;

        waveform(:, ithPkt) = complex(re, im);
    end

    % CP flipping of WEBee.
    if isempty(numSampPerWiFiCP)
        numSampPerWiFiCP = 16;
    end

    if ifWEBeeTweak == true

        for ith = 2:2:(numSymPerPkt * 4)
            waveform(((ith - 1) * 80 + 1):((ith - 1) * 80 + numSampPerWiFiCP), :) = ...
                waveform((ith * 80 - numSampPerWiFiCP + 1):(ith * 80), :);
        end

    end

end