Nbits = 100;
numtrials = 50;
Bs = 1:10;

for k=1:length(Bs)
    B = Bs(k)

    % https://www.mathworks.com/matlabcentral/fileexchange/24336
    H = walshcode(B);
    SF = size(H,1);

    D = kron(eye(Nbits), ones(1, SF));
    Hh = repmat(H, Nbits, 1);

    for trial=1:numtrials
        bits = sign(randn(Nbits, SF));
        bits_cr = upfirdn(bits, ones(1, SF), SF);
        x = sum(bits_cr .* Hh,2);
        x = sign(x-sign(randn(size(x)))*eps); % clip
        y = repmat(x,1,SF) .* Hh;
        bits_hat = sign(D*y);
        BER(trial,k) = sum(sum(bits_hat ~= bits))/SF/Nbits;
    end
end

plot(Bs, mean(BER));xlabel('log(WalshCodeLength)');ylabel('BER');