Distributed Beamforming Scheme In Cognitive Radio Networks

Cognitive radio (CR) is a promising technology to improve the radio electromagnetic spectrum utilization, and it provides the capability to share the wireless channel with a primary network to which the spectrum is initially licensed. While a cognitive radio network sharing the spectrum with a primary network, one of the major concerns is that harmful interference to the primary users should be avoided.In this paper, an opportunistic distributed beamformer in cognitive network with limited feedback is proposed. The proposed beamforming scheme opportunistically selects a subset of cognitive source nodes whose phases may be pre-compensated according to the phases of channels between source nodes and destination nodes, so that the received signals can combine in a quasi-coherent manner at the cognitive destination node and the interference to the primary destination node is not destructive. Then the cognitive destination node feedback only a few bits to each cognitive source node to decide if it should or should not participate in the distributed beamforming and how to pre-compensate phase. Three algorithms are proposed in this paper. Simulation results demonstrate the good performance of the proposed algorithms.In many applications, reachback communication from nodes in the sensor network to a relatively distant destination node can be a significant source of power consumption in the network. This paper presents a time-slotted round-trip beamforming technique in cognitive radio networks, which needs few feedback from destination to source, under the duplexing constraints of the wireless channel. The simulation results presented in terms of average received power at cognitive destination and the received noise in the primary destination demonstrates that most beamforming gains can be achieved and the interference to primary destination is weak.