Power allocation for two‐user cognitive multiple access channels under primary user outage constraint

Abstract

SummaryWe consider a two‐user spectrum sharing cognitive radio multiple access channel (CR‐MAC) coexisting with a pair of primary users (PUs). Different from the existing works in CR‐MAC where the interference power constraint is applied to protect the PU transmission, a more advanced protection criterion over the interference power constraint, namely, PU outage constraint, is adopted in this paper not only to protect the PU transmission but also improve the performance of the CR‐MAC. Under such a constraint, as well as the transmit power constraint, and assuming that perfect channel state information (CSI) is available, two heuristic power allocation algorithms for the secondary users based on dual optimization are proposed. The objective is to maximize the ergodic sum capacity of the CR‐MAC without successive interference cancelation (SIC). One algorithm applies alternating direction optimization method to derive an iterative power allocation, while the other algorithm adopts exclusive transmission to determine the power allocation. Besides, we extend our results to the multi‐user and partial CSI scenarios. It is shown by extensive simulations that the proposed algorithm based on alternating direction optimization method always outperforms the existing algorithms based on the interference power constraint, while the proposed algorithm based on exclusive transmission outperforms the existing algorithms for medium and large values of the transmit power limit. Copyright © 2015 John Wiley & Sons, Ltd.