Opportunistic band sharing for point-to-point link connection of cognitive radios

Cognitive radios are typically known to exploit vacant spectrum resources yet not interfering with primary communication systems. However, cognitive radios may not be able to secure a clear spectrum band, i.e., white hole, in certain environments. Underlay spectrum sharing provides a way to cope with such a spectrum sharing problem in a bustling spectrum band; cognitive radios share the spectrum band with the spectrum licensees, i.e., primary users, by adjusting signal transmit power so as not to severely deteriorate the performance of the primary users. In this paper, we propose an underlay spectrum sharing policy for cognitive radios. Primary users are assumed to form a cellular network, and a point-to-point link of cognitive radio leverages uplink spectrum resource of the primary network. We formulate the transmit power constraints of the cognitive radio transmitter and propose a practical uplink band sharing framework. We also demonstrate that such an uplink band sharing can enhance the throughput performance of point- to-point link, while the interference to the primary users can be regulated under the allowed level decided by the primary users.