COGNITIVE radio (CR) with spectrum sharing is regarded as a promising solution to enhance spectral efficiency and alleviate the issue of spectrum scarcity . On the other hand, cooperative relaying can provide remarkable performance advantages in ameliorating the An Efficient Distributed Link Selection Scheme for AF-Based Cognitive Selection Relaying Networks reliability and throughput of wireless systems. In recent years, incorporating relays into cognitive networks has received tremendous attentions, owing to its aforementioned merits. Previous related works are briefly introduced next. In , the authors proposed a novel design paradigm to maximize the cognitive user’s (CU’s) rate for MIMO CR under a minimum primary user (PU) rate constraint. and studied the performance of amplify-and-forward-based (AF-based) cognitive relay networks (CRNs) over Nakagami-m fading. An Efficient Distributed Link Selection Scheme for AF-Based Cognitive Selection Relaying Networks Considering both high and low-to-medium signal-to-noise ratio (SNR) regimes, and derived closed-form expressions for the outage probability of an interference-limited AF-based CRN with only one PU. Further, the authors of investigated the scenario with multiple PUs. However, since the direct link between the source and destination was ignored in both, the resulting systems may suffer from potential diversity losses . Later, by incorporating the direct path into an An Efficient Distributed Link Selection Scheme for AF-Based Cognitive Selection Relaying Networks AF-based CRN, Duong et al. investigated the outage performance of a cognitive system, where a centralized link selection protocol was employed. Although the centralized selection criterion can improve outage behavior, its feedback overhead is considerable. Recently, inspired by an idea of distributed decision feedback, the authors of established several novel link/antenna selection schemes for An Efficient Distributed Link Selection Scheme for AF-Based Cognitive Selection Relaying Networks AF-based relaying systems, which significantly reduce the feedback overhead of link/antenna selection. Knowing that acquiring the instantaneous channel state information (CSI) of the interference links may incur additional cost, examined cognitive cooperative systems where only imperfect CSI of the interference links can be obtained at the secondary transmitters. An Efficient Distributed Link Selection Scheme for AF-Based Cognitive Selection Relaying Networks Motivated by the foregoing observations, in this paper we advocate a distributed link selection mechanism for a cognitive AF selection relaying network. Specifically, by adopting an approximation to the received SNR at the destination, the tractable closed-form expression for the outage lower bound and the average feedback overhead of the secondary system are derived, where the cognitive transmitters can acquire either the instantaneous or statistical CSI pertaining to the interference links. Particularly, no matter whether the CSI knowledge of the interference links at the secondary nodes is perfect or not, the proposed scheme can alleviate the CSI feedback overhead while maintaining almost the same outage performance with that of , rendering it an attractive solution in practice.