Virtual occupancy in cognitive radio

Cognitive radio technologies have the potential to increase the efficiency and effectiveness with which the radiofrequency spectrum is used. However, before cognitive radio devices are brought into widespread use, planning and regulatory arrangements must be considered and developed where appropriate to ensure adequate protection for existing users. This paper addresses the issue of harmful intermodulation interference caused by the mixing of a transmission from a cognitive radio device with that from a licensed transmitter in the land mobile radio service. Due to the generation of intermodulation products, seemingly open channels may be unable to be used by cognitive radio devices. This situation is termed virtual occupancy. In this paper, a model is described to characterise the effect of virtual occupancy on the availability of channels for use by a cognitive radio device in the land mobile service in the radiofrequency band from 450 to 470 MHz. The results show that for areas where the spectrum is highly allocated, virtual occupancy could be a significant barrier to the deployment of cognitive radios in the land mobile radio service.