The data driven property and the real-time requirement are two important features of Digital Signal Processing (DSP) systems. The dataflow models of computation are widely used to represent architecture of DSP applications for their data driven nature. Multi-rate Digital Signal Processing (DSP) algorithms are usually modeled by Synchronous Data-Flow Graphs (SDFGs). Performing with high enough throughputs is a key real-time requirement of a DSP algorithm. Therefore, how to decrease the iteration period of an SDFG to meet the real-time requirement of the system under consideration is a very important problem. Retiming is a prominent graph transformation technique for performance optimizing.