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We propose relay-based wireless-powered uplink cellular networks in which users first harvest energy from RF transmissions of base station/relay nodes and then use that energy for uplink transmission. Given the limited total transmission time and available energy at the relay node, we propose different resource allocation frameworks for the proposed relay-based networks considering two different relay-based harvest-then-transmit scenarios. We first propose iterative algorithm to determine time and relay node power allocation (for downlink wireless charging and uplink data transmission/relaying) for both scenarios. We then perform joint optimal time and power allocation for one scenario. Resource allocation results show that most of the available resources (transmission time and relay node energy) are allocated for wireless energy harvesting which is similar to that observed for downlink simultaneous wireless information and power transfer (SWIPT) in the existing literature. Simulation results on comparison of different relay-based scenarios reveal interesting insights and demonstrate remarkable improvement of different performance metrics of wireless-powered cellular networks in the presence of relay node.

In this paper, a joint resource optimization scheme is designed for orthogonal frequency division multiple access (OFDMA) cellular wireless networks with multi-user cooperation. Joint relay selection, subcarrier allocation and pairing and power allocation algorithms are developed with the objective of maximizing the total capacity of the system considering the quality of service (QoS) requirements of the users. The optimization problem is a mixed integer nonlinear program (MINLP), which is often very difficult to solve in its original form. We provide a novel optimization framework to solve such non-linear optimization problems. The joint relay selection and subcarrier allocation problem is modified to a linear assignment problem and an efficient algorithm is developed to obtain the optimal assignment solution based on the Hungarian method. We propose computationally efficient solution to the joint resource optimization problem via dual decomposition method. Numerical results demonstrate the effectiveness of our proposed scheme. I. INTRODUCTIONCooperative relaying technology has been found to greatly improve the spectral efficiency, coverage area, and network lifetime. This technology is promising for next generation wireless networks such as 3GPP, LTE-A and IEEE 802.16. There are different relaying protocols and among them decodeand-forward (DF) and amplify-and-forward (AF) are more popular [1]. In DF relaying, the relay receives the signal from the source, decodes it, and forwards it to the destination, while in AF relaying, the relay simply amplifies the received signal from the source and forwards it to the destination. However, installing fixed relay nodes has a significant increase in cost for the operators. Therefore, users with good channel condition and low traffic demands can be used as mobile relays without increasing infrastructure cost to the operators [2], [3].Orthogonal frequency division multiple access (OFDMA) systems are appealing for broadband cellular networks. In OFDMA systems, the frequency spectrum is divided into a number of smaller bands known as subcarriers which can be allocated to multiple users. Due to frequency diversity and multiuser diversity, OFDMA systems have high spectral efficiency and they are robust against multipath interference. These properties make OFDMA suitable for wireless networks such as worldwide interoperability for microwave access (WiMAX) and LTE-A. To improve the performance with OFDMA further, several works have been done combining OFDMA with cooperative relaying systems [4]- [6].

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