Power allocation and achievable data rate in spectrum-sharing channels under adaptive primary service outage constraints

Abstract

In this paper, we focus on a cognitive radio network where adaptive modulation is adopted in primary links. The gap between the primary user (PU)'s received signal-to-noise ratio (SNR) and the lower SNR boundary of the modulation mode that is being used, provides an interference-tolerable zone. Based on this gap, a secondary user (SU) has an increased opportunity to access the licensed spectrum and to determine the transmit power it should use to keep the PU's quality-of-service (QoS) unaffected. However, since the SU cannot obtain perfect information on the PU's received SNR, it has to choose an SNR point between the lower and upper boundaries of the PU's current modulation mode as if this point were the real SNR received by the PU. Considering this issue, in order to quantify the effect of the SU's transmissions on the PU's QoS, we define the PU's service outage probability and obtain its closed-form expressions by taking into account whether the peak transmit power constraint is imposed on the secondary's transmission or not. Subsequently, we derive the SU's achievable data rate in closed form for counterpart scenarios. Numerical results provided here quantify the relation between the PU's service outage probability and the SU's achievable data rate, which further demonstrate that the higher the peak transmit power a secondary transmitter can support, the better performance the cognitive radio network can achieve.