Matlab code for generating autocorrelation function for random process(zero mean random process)

For a specific time ?1 and a specific delay ?1, the channel coefficient ?(? ̃ 1, ?1) will be a complex variable, where the magnitude represents the attenuation factor and the phase shift factor. On the other hand, due to the constant changes in the environ- ment and the possible relative movement between transmitter and receptor, these factors are time dependent.?(?, ?) ̃ can be modeled as a complex stochastic process composed of the sum of a deterministic part (the ensemble average of ?(?, ?) ̃ ) and a random part (zero mean random process). From this point, we will only consider the random part (an assumption generally accepted when a channel simulator is developed). The autocorrelation function of this random process is equal to ??̃ (?1, ?2; ?1, ?2)=?(? (? ̃ 1, ?1) ?̃∗ (?2, ?2))