The present document is a study item that can be used in the normative process within ETSI TC RRS@ when defining normative system requirements@ architecture@ and interfaces for Mobile Device (MD) Software Defined Radio (SDR). The TR 102 680 [i.1] presents a reference architecture for Software Defined Radio (SDR) mobile devices from a radio computer viewpoint. Such a device can run radio applications on shared platform resources@ and install new ones even during run-time@ much like a personal computer with regular computer programs. The reference architecture details the internals of a possible mobile device SDR subsystem@ but is not meant to be a normative architecture. Instead@ it identifies various key interfaces that may be generalized in order for the multiradio computer vision to be realized. These interfaces may be normative. SDR can be on one hand considered as an implementation technology that replaces legacy ASICs when suitable cost and power tradeoffs can be found; this track is not in the scope of ETSI TC RRS. On the other hand@ SDR can be considered as an enabling technology for Cognitive Radio (CR) systems. It is in the scope of ETSI TC RRS to define the responsibilities of various subsystems in a complete CR system. The TR 103 062 [i.2] lists high level use scenarios for SDR based mobile devices@ to be used in this process. The two approaches meet at the interface to the SDR subsystem. This is called the Multiradio Interface (MURI) in the reference architecture. The purpose of this technical report is to outline the functionality at this interface@ both from SDR technology and CR system perspectives. The use scenarios are analyzed first@ in order to partition the responsibilities between the SDR subsystem and the CR entities on top of it. Then the SDR subsystem is taken a deeper look@ based on TR 102 680 [i.1] and technology deployment scenarios. Finally the MURI functionality is sketched from these basis.