The physical layer of most wireless protocols is traditionally implemented in custom hardware to satisfy the heavy computational requirements while keeping power consumption to a minimum. These implementations are time consuming to design and difficult to verify. A programmable hardware platform capable of supporting software implementations of the physical layer, or software defined radio, has a number of advantages. These include support for multiple protocols, faster time-to-market, higher chip volumes, and support for late implementation changes. The challenge is to achieve this without sacrificing power. In this paper, we present a design study for a fully programmable architecture, SODA, that supports software defined radio - a high-end signal processing application. Our design achieves high performance, energy efficiency, and programmability through a combination of features that include single-instruction multiple-data (SIMD) parallelism, and hardware optimized for 16bit computations. The basic processing element is an asymmetric processor consisting of a scalar and SIMD pipeline, and a set of distributed scratchpad memories that are fully managed in software. Results show that a four processor design is capable of meeting the throughput requirements of the W-CDMA and 802.11a protocols, while operating within the strict power constraints of a mobile terminal.