A realistic error model of imperfect CSI in cognitive radio channels

Abstract

Regarding the channel state information (CSI) in a cognitive radio (CR) channel, it is often realistic to assume that the secondary user (SU) knows perfectly its direct link, but it is not realistic to assume that it also knows its interfering links to the primary receivers (PRs). Traditional power allocation and scheduling algorithms in CR channels have been based on the assumption of global perfect channel knowledge at the secondary transmitter (ST). In this paper, we analyze the impact of channel estimation errors on the secondary user and on the primary users as well. We propose a novel error model which is a more realistic error model comparing to the classic one that describe the estimation error of the interfering links to the PRs. On the one hand, the robustness of water-filling algorithms which allow the SU to minimize its power consumption under QoS and CR interference power constraints to channel estimation errors in the SU interfering links. On the other hand, we analyze the possible impact of these estimation errors on the PU interference constraints. We consider the worst case with respect to the estimation errors at the SU as well as the worst estimation error that effect the interference created to the PU. Our analysis shows that the water-filling algorithm not only provides robustness in terms of power consumption but also in terms of scheduling of the SU given the realistic estimation error model.