The lifetime of the conventional energy-constrained wireless networks is limited by the operational time of batteries of the wireless communication devices . The network lifetime can be enhanced by employing recent advances in wireless power transfer (WPT) technology in which the wireless devices are powered by continuous (uninterrupted) energy from dedicated wireless power transmitters . One of the important applications of WPT is wireless powered communication networks (WPCN) , where the wireless devices are powered by the wireless energy in the downlink phase in order to transfer information in the uplink phase . In this thesis two new system model is presented for WPCN. The first system model studies a general multi-user wireless powered interference channel (IFC) , where the communication in channel coherence time consists of two phases , namely wireless energy transfer (WET) and wireless information transfer (WIT) . In the first phase , all energy transmitters (ETs) transmit energy signals to information transmitters (ITs) via collaborative waveform design , while in the second phase , each IT transmits an information signal to its intended ET using the harvested energy in the previous phase . The aim is to jointly design the WET-WIT time allocation , the (deterministic) transmit signal at the first phase , and the transmit power of ITs in the second phase to optimize the network throughput . We consider the uncertainty in the channel state information (CSI) and devise a robust design methodology (against imperfect CSI) for both sum and minimum throughput maximizations . In the second system model a new K -link cooperative WPCN is studied. In this model the HAP broadcasts wireless energy to ? K users in the downlink and the users transmit their independent information to the HAP in the uplink. We propose a user cooperation method in the WPCN where the users which are nearer to the HAP and have a better channels for downlink energy harvesting as well as uplink information transmission, use part of their allocated uplink time and downlink harvested energy to help to relay the far user's informations to the HAP, in order to achieve more throughput. In this model, in addition to designing the energy beamforming matrix in downlink, we further consider the transmit covariance matrices in uplink as well as the time allocation parameters as design variables to optimize the maxmin fair problem. The design problems for both models are non-convex and hence difficult to solve globally . To deal with them , we propose efficient iterative algorithms based on alternating projectio then , the majorization-minimization technique is used to tackle the non-convex sub-problems in each iteration.The proposed algorithms are locally convergent providing quality solutions to the design problems . Simulation results show the effectiveness of the proposed algorithms under various setups . cooperative communication, interference channel, wave form design, wireless powered communication networks