Date Added: Apr 2011
The authors propose a cooperative beamforming aided incremental relaying scheme to improve spectrum efficiency of cognitive radio systems. In this scheme, the source and relays can exploit cooperative beamforming to activate packet retransmission in busy timeslots or spatial spectrum holes without causing interference to primary users, if the destination fails to decode the packets transmitted by the source. Therefore, cooperative diversity gain is obtained without consuming extra idle timeslots or temporal spectrum holes. Their proposed scheme endeavors to improve the average throughput by dynamically adjusting the proportions of spectrum allocation for new transmission and retransmission.