This paper describes a software-radio architecture developed for providing realtime wide-band radio communication capabilities in a form attractive for advanced 3G systems research. It is currently being used to implement signaling methods and protocols similar, but not limited to, evolving 3G radio standards (e.g. UMTS, CDMA2000). An overview of the hardware system is provided along with example software implementations on both high-performance DSP systems and conventional microprocessors.