Wireless Sensor Networks are composed of many autonomous resource-constrained sensor nodes. Constrains are low energy, memory and processing speed. Nowadays, several limitations exist for heterogeneous Wireless Sensor Networks: various hardware and software are hardly supported at design and simulation levels. Meanwhile, to optimize a self-organized network, it is essential to be able to update it with new nodes, to ensure interoperability, and to be able to exchange not only data but functionalities between nodes. Moreover, it is difficult to make design space exploration, as accurate hardware-level models and network-level simulations have very different (opposite) levels. We propose a simulator-based on SystemC language-that allows such design space explorations. It is composed of a library of hardware and software blocks. More and more sophisticated software support is implemented in our simulator. As trend is to deploy heterogeneous nodes, various software levels have to be considered. Our simulator is also thought to support many levels: from machine code to high level languages.