Research On Interference Alignment With Cognitive Radio Networks

In today's world,the wireless communication services are gradually taking the place of cable services,dominating the field of communications.People prefer the convenient and flexible wireless networks which can simplify their own work and life.With the rapid increase of the wireless communication services and wireless devices,the spectrum resource crisis gets worse and worse.In order to solve this problem,scholars have proposed cognitive radio network technology.By introducing users with cognitive ability to the traditional network,the spectrum utilization and channel capacity get improved effectively.Thus,the cognitive radio network has drawn lots of scholars' attention.With the number of wireless communication devices grows,the newly introduced wireless devices will inevitably interfere with the existing system.Besides,the introduced new wireless devices will also interfere with each other.In order to solve the interference problem among different users,scholars have proposed interference alignment technology.Interference alignment technology take advantage of the well designed beamforming matrix so that in a multi-user network,each user's performance will not decrease linearly as the number of users increases,which greatly improves the whole network's throughput.Due to the newly introduced secondary users,the cognitive network is also a multi-user network which has interference problem to solve.This article does a deep research on interference alignment in cognitive networks,focusing on how to apply the interference alignment technology to cognitive network,solving the interference problem of cognitive networks among multiple users and improving the network's throughput.In traditional cognitive networks,we focus on the primary user's performance mostly.Therefore,the primary user usually uses water-filling algorithm to maximize its own rate.The secondary users take advantage of interference alignment technology to form the interference-free transmission paths for all users.But this kind of schemes has an obvious drawback.Sometimes we hope that as long as the primary user's rate reaches the target rate,the rest resources can be used by the secondary users.In this scenario,traditional interference alignment technique is not applicable.This paper proposes an adaptive number eigenmodes beamforming technology in underlay mode instead of the traditional water-filling algorithm,which greatly improves the secondary user's rate,especially in the scenarios with high SNR value.Meanwhile,we extend the results of underlay mode to overlay mode.In the overlay mode,the secondary transmitter has non-causal knowledge of the primary message,which not only transmits its own message,but also helps the primary user relay the primary message.Numerical simulation results show that our scheme not only improves the secondary user's performance in the scenario with high SNR value,but also improves the throughput of the entire cognitive network.