Driven by the desire of people to communicate more efficiently, more flexibly and more reliably, tremendous changes are occurring in the wireless world. As one of the dominant drivers for the semiconductor industry, the wireless evolution towards higher data rate and higher capacities presents numerous opportunities. However, it also introduces many challenges to the current design technology, particularly, the demanding requirement for low power or even ultra-low power consumption. The rapid growth of various wireless services increased the need for highly integrated and low-cost solutions with very demanding performances. The fast growing market and heated competition require very short system development cycle. To cope with this constantly increasing system complexity, higher performance demands and tight time-to-market constraints, it is imperative to develop new design techniques for wireless systems to cope with these challenges. This dissertation presents a design approach for wireless systems where the design requirements are demanding in terms of contradicting objectives. The approach is based on the paradigm of platform based design, featuring in the adoption of higher levels of abstraction, better reusability and early consideration of system performance. Wireless receivers are used to demonstrate the approach proposed here. A receiver is a complicated system consisting of RF, analog and mixed-signal components. Traditionally, when developing a wireless system, system design and circuit design are conducted separately. Our research shows that effective interactions between different levels are critical to obtain an optimal system. In this research, systematic design space exploration is necessary to facilitate the trade-off evaluations and system partitioning. To demonstrate this concept, the platform-based receiver system design is presented from system level down to circuit design, focusing on the minimization of the overall power dissipation while maintaining system performance. Two application scenarios are explored. One is a receiver front-end for an MB-OFDM UWB system. The other one is an ultra-low power mostly-analog baseband design for wireless sensor networks. In the context of the proposed design approach, several representative challenges in the wireless receiver design are investigated, which include how to improve the system robustness against various interferences, how to quickly estimate the wireless system performance in an analytical approach, how to validate a system algorithm in a heterogenous simulation environment, how to build the abstracted behavioral models and use them to perform the design space exploration, etc. The circuit level design concerns and subthreshold design techniques are also demonstrated. Finally, system-level optimization is performed using behavioral models and, to preserve fidelity, the models are constrained by the achievable performance of actual circuit implementations. The resulting two designs show that significant power savings can be accomplished through systematic design space exploration in the platform-based design framework.