![]() For example, in broadcast channels scenario, the authors in focused on the trade-off of wireless energy and information transfer by adjusting TS ratio, and the authors in maximized the minimum throughput among all terminals by optimizing the downlink/uplink TS ratio, the downlink energy beamforming, and the uplink power allocation (PA) as well as receive beamforming. In this scheme, TS ratio is an important parameter to evaluate system performance. One transmission scheme based on TS protocol is wireless powered communication network (WPCN) in which each terminal harvests power on the downlink in the first slot and then transmits its information on the uplink in the second slot. ![]() To perform RF EH, two main protocols adopted at terminals are time-switching (TS) protocol and power-splitting (PS) protocol. Compared with natural energy sources, radio frequency (RF) EH is nominated as the best EH scheme due to the stability and the ability of transforming the RF signals into voltage to charge the terminal battery. Although some natural energy sources such as sunshine and wind can be considered, they are usually not as effective as expected due to the inconsistent and unforeseeable nature of ambient sources. Motivated by this, the energy harvesting (EH) technique has gained much attention in both academia and industry as it provides a promising approach to prolong the lifetime of energy-constrained terminals. For some special applications such as military communications, medical implants and mining, one of the key challenges in such networks is how to supply sufficient energy to network terminals for successful communications. The proliferation of wireless networks leads to a large number of smart terminals. Numerical results manifest that the proposed algorithm can provide good SE by optimizing relevant system parameters, and the system model can help to discuss the TS, PS or hybrid protocol for only uplink data transmission, only downlink data transmission or joint data transmission of uplink and downlink in the considered system. Finally, the feasibility of the proposed algorithm is analyzed by simulations. Additionally, the convergence and complexity of the proposed algorithm are discussed as well. To provide a solution, an iteration algorithm is proposed by utilizing one-dimensional search technique and successive approximation method based on geometric program. As the designed optimization problem is non-linear and non-convex, it is hard to solve directly. According to these expressions, the joint SE of uplink and downlink maximization problem is designed with some practical constraints. Then, closed-form lower bound expressions on SE for each terminal are obtained on the uplink and downlink, respectively. As a result, a general analytical framework is formulated. Based on the hybrid wireless EH protocol, a general system model is developed, which can switch to either only uplink data transmission or only downlink data transmission. The hybrid wireless energy harvesting (EH) protocol is applied for each terminal, which can switch to either existing time-switching (TS) protocol or power-splitting (PS) protocol. This paper investigated the spectral efficiency (SE) in massive multiple-input multiple-output systems, where all terminals have no fixed power supply and thus need to replenish energy via the received signals from the base station.
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