The recent trends in RF circuit and system development are that: 1) The baseband algorithms and RF distributed circuits are being co-designed 2) Many RF functions are moving into the algorithmic (baseband DSP) world. 3) The RF function gets controlled by the baseband algorithms. In any case it is imperative that a system level design has to simulate both DSP and RF circuits together using mixed signals. In this paper several flows of DSP-RF co-simulation with mixed signals will be presented along with the technologies that enabled them. This kind of a co-design has several advantages: 1) A baseband algorithmic designer will be able to explore a wide space of test conditions leading to early detection of risks and ability to fix/enhance the algorithms. 2) A system architect will be able to partition the specification more efficiently between baseband and RF. 3) An RF circuit designer will be able to target the design for system level specifications rather than circuit level parametric specifications. 4) All the above lead to improved timeto-market (TTM), better performance and cost effective designs. The paper presents a flow using a few examples that touch 5G and Aerospace areas.