###### Abstract
Specifically, TSCH simultaneously uses one or more slotframes with different lengths to efficiently support various communication schedules that vary depending on the network topology and traffic type. Each slotframe consists of multiple cells expressed as a pair with a timeslot and channel offset, and the length of each slotframe is determined according to the number of timeslots. Thus far, several studies have proposed TSCH scheduling schemes using multiple concurrent slotframes to support the network topology and traffic type. In [27; 28; 29], the authors employed three types of slotframes. Each slotframe is used for the enhanced beacon (EB), CM, and data. The length of each slotframe is empirically determined, considering the amount of traffic that varies depending on the network topology. However, TSCH scheduling schemes are specialized only for data delivery and use a slotframe structure in which one cell for data transmission and one cell for data reception are allocated within a slotframe based on the sensor node ID. Therefore, their inflexible slotframe structure is unsuitable to support the WPT operation required by the sensor nodes. In [30], the authors increased the link capacity using a resource allocation algorithm based on the network topology information to support WPT and data transmission in a WSN. However, in [30], a homogeneous network environment composed only of sensor nodes was considered; thus, it is unsuitable for WPT and data transmission operations between heterogeneous devices in WPT-enabled WSNs, including both PTU and PRU. In [31], the authors proposed a TSCH-based MAC protocol to support energy harvesting and data transmission of sensor devices with different transmission periods. In [31], the sensor devices perform cell allocation using a concurrent slotframe with the same length as their transmission period, causing frequent overlap between cells, and the computational load for solving this increased. This paper proposes a multiple concurrent slotframe scheduling (MCSS) protocol, supporting a cluster-tree network topology and various traffic types in WPT-enabled WSNs. To this end, MCSS uses three types of TSCH concurrent slotframes: the CM slotframe, HAP slotframe, and WPT slotframe. Each slotframe is dedicated to transmitting the CM traffic, inter-cluster traffic, and intra-cluster traffic. To mitigate the influence of overlapped schedules (i.e., overlapped cells) among slotframes on the network performance, MCSS sets the length of each TSCH concurrent slotframe to be mutually prime and determines the transmission priority of slotframes considering the characteristics of the transmitted traffic. In addition, MCSS determines the WPT slotframe length for each cluster using the numbers of required power and data cells, including the number of overprovisioned cells. The contributions of this work are summarized as follows:  
* First, multiple TSCH concurrent slotframes with different lengths are used according to the three traffic types (i.e., CMs traffic, inter-cluster traffic, and intra-cluster traffic) so that MCSS can support a cluster-tree network comprising heterogeneous devices (i.e., HAPs and sensor nodes), which is a general form of the WPT-enabled WSN. * Second, the WPT slotframe length may be set differently for each cluster based on the amount of intra-cluster traffic, reducing the number of empty cells within the WPT slotframe and improving the channel utilization for energy harvesting and data transmission of sensor nodes. * Finally, the lengths of TSCH concurrent slotframes are set to be mutually prime to each other, and their transmission priorities are differentiated, thereby, reducing the influence of overlapped cells among the concurrent slotframes. To verify the superiority of MCSS, we performed an experimental simulation and compared the performance of MCSS with that of the legacy TSCH MAC protocol with a single slotframe.