function fofx = que_func(x)
% This function computes the value of the Q-function
% listed in Eq.(2.16). It uses the approximation in Eq.s (2.17) and (2.18)
if (x >= 0) 
denom = 0.661 * x + 0.339 * sqrt(x^2 + 5.51);
expo = exp(-x^2 /2.0);
fofx = 1.0 - (1.0 / sqrt(2.0 * pi)) * (1.0 / denom) * expo;
else
denom = 0.661 * x + 0.339 * sqrt(x^2 + 5.51);
expo = exp(-x^2 /2.0);
value = 1.0 - (1.0 / sqrt(2.0 * pi)) * (1.0 / denom) * expo;
fofx = 1.0 - value;
end