The quality of optical communication systems can be effectively improved by controlling soliton interactions. In this paper, periodic interactions of optical in optical fibers are studied. Analytic two-soliton solutions of a variable-coefficient higher-order nonlinear Schrodinger equation are presented, and the influences of the corresponding model parameters are discussed. Both the in-phase and out-of-phase interactions of optical solitons are analyzed. The numerical results indicate that the periodic interactions of optical solitons can be controlled in order to decrease the bit error rate of fiber communication systems.