Joint adaptive modulation and cooperation for throughput enhancement in cognitive network

In this contribution, a cognitive radio scenario is considered, where secondary users are allowed to communicate concurrently with primary users provided that they do not create harmful interference to the licensed users. Here, we aim to improve the throughput of unlicensed system. For this aim, we propose to use cooperative techniques only if the resulting average interference power at the primary receiver is above a certain threshold. Therefore, an adaptive modulation is used in order to compensate the throughput loss due to the relaying. For relaying scenario, we propose to use a cooperative space-time coding protocols based on Alamouti ST code as well as an Amplify and forward protocol. We investigate the system performance under different sets of conditions. Simulation results show that, these adaptive cooperative protocols have better performance compared with the classical cognitive system. Additionally, results highlight that space-time coding protocol is more powerful than the AF scheme.