Given a behavioral description of a DSP algorithm represented by a data-flow graph, we show how to obtain a rate-optimal static schedule with the minimum unfolding factor under two models, integral grid model and fractional grid model, and two kinds of implementations for each model, pipelined implementation and non-pipelined implementation. We present a simple and unified approach to deal with the four possible combinations. A unified polynomial-time scheduling algorithm is presented, which works on the original data-flow graphs without really unfolding. The values of the minimum rate-optimal unfolding factors and the general properties for all the four combinations are proved.