Wireless communications technology continues to change and yield new standards for satisfying the user demands. As a result, multiple standards coexist and wireless communications systems supporting different air interfaces cannot interact with one another. Software-defined radio is regarded as the most promising solution to cope with this problem. In this paper, we discuss the design considerations of SDR systems from a base station point of view and propose new architecture which meets the inherent requirements of SDR platform. We then introduce hardware/software of SDR platform we accomplished on the basis of the new architecture. In addition, the results of basic transmission and receiving performance are presented to prove the feasibility of the proposed platform as a base station.