I. Introduction
Due to the pressing demand of efficient frequency spectrum usage, cognitive radio networks (CRNs) [1] have spurred a wide range of research interests and emerged as a promising technology to improve the spectrum utilization. In CRNs, with the proliferation of computationally powerful wireless devices and compelling demand on diversified services, providing multicast services for secondary users (SUs), especially in a multi-hop fashion, is urgently needed [2]–[5]. Therefore, it is crucial to improve the performance of multicast in multi-hop CRNs.