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Over the last several years, the interface between the digital and analog RF subsystems of a radio (the analog RF-digital interface) has become increasingly important. this article first discusses the different technology alternatives that exist for this interface and the rationale behind them. the emergence of cognitive radio technology is identified as a trend that increases the importance of the analog RF-digital interface. then the article discusses in detail the VmE bus International trade association (VIta) 49 standard. VIta 49 is a packet-based protocol to convey digitized signal data and metadata (or context data) pertaining to different reference points within a radio receiver. the metadata includes analog front-end parameters such as RF center frequency, bandwidth, If center frequency, sampling rate, gain, location, etc. this standard allows all information about the spectrum as seen by a radio at its antenna to be described, stored, and transported to other systems. VIta 49 is identified as a hierarchical radio description language that is a new paradigm for radio architectures.