A rewriting logic framework for soft constraints. Soft constraints extend classical constraints to deal with non-functional requirements, over-constrained problems and preferences. Bistarelli, Montanari and Rossi have developed a very elegant and abstract semiring-based theory of soft constraints where many different kinds of soft constraints can be represented and combined in a uniform way over so-called constraint semirings. In this paper we present a framework for prototyping of soft constraints `a la Bistarelli, Montanari and Rossi in rewriting logic. As a case study we present an application of soft constraints to the new area of software-defined radio networks. We model the problem of “optimal” parameter assignments for software-defined radios as a soft constraint solving problem, prove the correctness of the constraint solving algorithm, implement the solution in our prototypical rewriting logic framework for soft constraints, and embed our soft constraint solver in SRI’s policy-aware, goal-oriented distributed architecture (PAGODA) for modelling radio networks.