function [s] = pammod(N_symbols,M)
% Randomly produces a sequence of N_symbols symbols, using a PAM modulation
% with parameter M, giving the number of possible symbol values. M should
% be a power of 2 ; the number of bits per symbol is then given by log_2(M)

symbols_TX = (rand(N_symbols,1)-0.5)*M;

s = zeros(N_symbols,1);

for i = 1:N_symbols
    if symbols_TX(i) == 0
        s(i) = -1;
    elseif symbols_TX(i) < 0
        s(i) = floor(symbols_TX(i))*2+1;
    elseif symbols_TX(i) > 0
        s(i) = ceil(symbols_TX(i))*2-1;
    end
end

end