Making overlay cognitive radios practical

The overlay approach to dynamic spectrum access recently proposed in information theory allows both primary users (PUs) and secondary users (SUs) to simultaneously access the same spectrum with comparable power levels while ensuring no degradation to the performance of PUs. However, this approach is based on a number of idealized assumptions that are difficult to satisfy in practice, and existing efforts to address this issue fall outside physical layer processing. In this paper, we propose a number of physical layer mechanisms to make the overlay approach practical. In particular, we leverage the broadcast nature of the wireless medium and the latest breakthrough in full-duplex radios to resolve the synchronization problem and to get around the non-causal assumption while naturally offering delay diversity.