LAUSR

Dynamic spectrum access (DSA) is a promising solution for enhancing the utilization efficiency of spectrum resources. In DSA, spectrum sensing is crucial and cooperative spectrum sensing has been confirmed as a promising technology that can combat the wireless channel fading problem. Most current works have assumed that the secondary users (SUs) are synchronous with the primary users' (PUs) network. However, on one hand, the SUs may have no information about the PUs' communication protocols. On the other hand, communications among the PUs are not based on synchronous operation in some systems. In order to address such problems, the DYWAMIT, an asynchronous wideband DSA system, is proposed. In this scheme, the SUs need not maintain synchronism with the PUs, enabling the SUs to cognitively and asynchronously access primary channels even without knowing the communication protocols of the PUs. Performance analysis and simulations are conducted to evaluate the proposed DYWAMIT algorithm; in particular, the average throughput of the SUs, accounting for the asynchronism between the SUs and PUs, is derived for four cases of interest. Some important future research challenges are highlighted.