Cooperative spectrum sensing in cognitive radio networks using random adaptive access

Recent research shows that more than 70% of the available spectrum is not utilized efficiently. The bandwidth becomes expensive due to a shortage of frequencies. Therefore for efficient utilization of spectrum, we need to sense the spectrum to determine whether it is being used by primary user or not. Opportunistic unlicensed access to the (temporarily) unused frequency bands across the licensed radio spectrum is currently being investigated as a means to increase the efficiency of spectrum usage. Such opportunistic access calls for implementation of safeguards so that ongoing licensed operations are not compromised. Among different candidates, sensing based access, where the unlicensed users transmit if they sense the licensed band to be free, is particularly appealing due to its low deployment cost and its compatibility with the legacy licensed systems. The ability to reliably and autonomously identify unused frequency bands is envisaged as one of the main functionalities of cognitive radios. The energy detector senses spectrum holes by determining whether the primary signal is absent or present in a given frequency slot. The energy detector typically operates without prior knowledge of the primary signal parameters. A new cooperative spectrum sensing scheme using random access is proposed in a cognitive radio network. In typical cooperative spectrum sensing situations, spectrum sensing data of several secondary users are collected before sensing decision. Yet how to collect the sensing data is not an easy problem because coordination between secondary users is needed. This study addresses this problem. The proposed scheme uses random access to report the sensing data of the secondary users. In the proposed scheme, the length of the sensing data collection period is determined adaptively based on the current status of the collected sensing data. We apply backward induction approach to decide when to stop the collection procedure of the sensing data. The proposed scheme does not need complex slot management to collect sensing data and shows performance improvement over conventional methods.