Dear editor, Wireless powered communication networks (WPCNs) are popular especially for wireless sensor networks where sensors can be wirelessly powered. For coordinating wireless power and information transfer, Ju and Zhang in their pioneer work [1] proposed a “harvest-then-transmit” protocol for WPCN, where the time for wireless power transfer (WPT) and wireless information transfer (WIT) is divided into two phases: the WPT phase and WIT phase. Meanwhile, cognitive radio (CR) is another important technology that can provide high spectrum efficiency [2]. In CR networks, unlicensed secondary users (SUs) are allowed to coexist with licensed primary users (PUs) under underlay, interweave, or overlay models. In contrast to underlay and interweave models where the PU does not benefit from the SU transmission, for overlay CR model, the SU improves the transmission quality of the PU, and in turn the SU gains transmission opportunities. Naturally, WPT and CR can be considered together to improve spectrum efficiency and provide continuous energy to user equipments [3, 4]. Specifically, a mutual benefit between the SU and PU can be achieved in WPT-based overlay CR networks. However, in existing studies on such networks, only the SU or PU is considered to be wirelessly powered [5, 6], and to the best of our knowledge, no work has considered that both the SU and PU are wirelessly powered in CR networks. Motivated by the above discussion, this study considers that both the SU and PU are wirelessly powered in a multi-carrier WPT-based CR network, and adopts the “harvest-then-transmit” protocol for coordinating WPT and WIT for the SU and PU. The cognitive hybrid access point (CHAP) is assumed to wirelessly broadcast energy in the WPT phase and receive data from the SU on the subcarriers that are permitted to be used in the WIT phase, as long as the PU achieves a minimum rate in the WIT phase, which guarantees quality of service. Such cooperation leads to a win-win situation for both the SU and PU, and can be considered as an overlay CR model. Under the PU minimum rate constraint and the transmit power constraint at the CHAP, the SU rate is maximized by optimizing the transmit power of the CHAP in the WPT phase, the time allocation between the WPT phase and the WIT phase, the subcarrier allocation between the SU and PU in the WIT phase, and the transmit powers of the