The cumulative probability distribution function of a Rayleigh fading distribution is given by p(r < R) = 1 - exp(-R2/2 sigma 2). where sigma 2 is the variance of the distribution. Explain what the cumulative probability distribution function indicates in this case. If the rms value is given by 2 sigma, compute the percentage of time that a signal is 12 dB or more below the rms value for a Rayleigh fading signal.