Power Allocation for OFDM-Based Cognitive Radio Systems under Outage Constraints

This paper investigates power allocation algorithms for OFDM-based cognitive radio systems, where the intra-system channel state information (CSI) of the secondary user (SU) is perfectly known. However, due to loose cooperation between the SU and the primary user (PU), the inter-system CSI is only partially available to the SU transmitter. Two types of PUs are considered to have different capabilities. One is a dumb (Peak Interference-Power tolerable) system that can tolerate a certain amount of peak interference at each subchannel. The other is a more sophisticated (Average Interference-Power tolerable) system that can tolerate the interference from the SU as long as the average interference over all subchannels is within a certain threshold. Accordingly, we introduce an interference power outage constraint, with which the outage is maintained within a target level. The outage is here defined as the probability that peak or average interference power to the PU is greater than a given threshold. With both this interference-power outage constraint along with a transmit-power constraint, we propose optimal and suboptimal algorithms to maximize the capacity of the SU. We evaluate the spectral efficiency through extensive simulations and show that the SU can achieve higher performance (up to two times) with the more sophisticated PU than with the dumb PU.