Wireless Power Transfer (WPT) will be a key enabler of Internet-of-Things (IoT) networks that consist of low-power devices that harvest energy from Radio Frequency (RF) signals emitted by base stations or access points. Hence, future networks will likely have both low-power RF-energy harvesting devices as well as legacy users such as laptops. In particular, both devices and users will share the same wireless channel to receive RF energy as well as transmit data. To ensure they share the spectrum efficiently, this thesis considers resource allo- cation problems in Orthogonal Frequency Division Multiple access (OFDMA) net- works. In particular, it considers sub-band/sub-carrier allocation problems that aim to meet the requirement of low-power devices and legacy users when they co-exist in the same network. Specifically, for low-power devices, developed solutions must en- sure low-power devices receive sufficient energy to collect samples or have sufficient energy to transmit frequently to a gateway. Similarly, these solutions must ensure legacy users are able to transmit at a given data rate. The first resource allocation problem concerns two-tier OFDMA based Hetero- geneous Networks (HetNets). Specifically, it aims to minimize the downlink sum transmit power of both femto and macro base-stations subject to legacy users and RF-energy harvesting devices receiving a given data rate and amount of energy, respectively. It studies sub-carrier and transmit power allocation, and investigates novel questions related to interference, which reduces network capacity but im- proves the amount of harvested energy by RF-energy harvesting devices. To study these questions, the problem is formulated as a Mixed-Integer Non Linear Program (MINLP). It contributes three linear approximations to the MINLP where devices are either assigned one or multiple sub-carriers. Numerical results show that RF- energy harvesting IoT devices will not affect network capacity if they can harvest sufficient energy from data transmissions to legacy devices. In addition, if multiple sub-carriers can be assigned to devices, the results show that the sum transmit power decreases by approximately 15% as compared to assigning a single sub-carrier to these devices.