This paper represents a pc-based tool for simulation and rapid control prototyping of Software Defined Radio (SDR) technology. The tool describes a software platform implemented to facilitate the SDR software architecture at the analysis, design and implementation stages. SDRsim is a prototyping platform which provides modularity, and requires minimal implementation effort to accommodate the SDR device. It is able to demonstrate the practical use of software prototyping in reducing the complexity of product analysis and design. This simulator provides the flexibility to modify and analyze the impact of various architecture parameters and components as well as enable more detailed statistics collection than real SDR device.