A technique for numerical modeling of the time autocorrelation function (ACF) of the electric field scattered from a concentrated dispersion, which is illuminated by a plane wave, has been developed as an approach to estimate the particle dynamics and multiple scattering effects in photon correlation spectroscopy measurements. Systematic error of the modeling of the particle dynamics and the error of the ACF estimation were investigated for Brownian free particles. It has been found that systematic error and the decreased dynamic delay-time range of the ACF exponential behavior for free particles are caused by low- and high-frequency oscillations of integrated functions. An optimization of the numerical model has been carried out in order to reach a required magnitude of the systematic error and a maximum of the dynamic delay-time range by a minimum of calculation expenditures. The dynamics of an ensemble of particles was generated by a stochastic technique. Practical application of the proposed technique was shown by modeling of the first-order ACF for the depolarized component of the backscattered electric field. Influence of multiple-scattering by interacting spheres on this ACF was investigated for different sphere diameters and dispersion concentrations by using a rigorous multiple-scattering technique. This model can be used to further develop photon correlation spectroscopy for the characterization of particles in concentrated and turbid media : in a following paper, the multiple-scattering suppression by one-beam cross correlation is simulated, taking into account geometrical parameters of a setup.