Interference Management in Decode-and-Forward Cognitive Radio Networks with Cooperative Beamforming

Interference Management in Decode-and-Forward Cognitive Radio Networks with Cooperative Beamforming

In this paper, a more realistic cognitive radio (CR) model is investigated and a cooperative beamforming (BF) method is proposed for the model. Two steps of transmission between secondary transceivers are described. At first step, all secondary transmitters can simultaneously broadcast their information to the relays when primary link is idle. This is the main benefit of the proposed model. At second step, if the channel is occupied by the primary link, the relays which have correctly detected the source information forward decoded versions of them towards the secondary destination using the proposed cooperative BF. Otherwise, these relays employ the zero-forcing beamforming (ZFBF). The proposed cooperative BF strategy enables the network to maximize the received signal power at the secondary destinations while keeping the interference plus noise power at the primary destination below a predefined threshold level. The effects of channel occupancy probability of the primary user (PU) on the received signal power at the secondary destinations and received interference plus noise power at the primary destination is also investigated. Results of simulations confirm validity of the method in which received signal power at the SU receiver decreases as the channel occupancy probability of the PU increases.