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In wireless powered communication networks (WPCNs), base station (BS) and power beacons (PBs) can offer supplement power for uplink transmission of user equipments (UEs). However, aggregate power consumption of massively deployed PBs may exceed that of a BS. We propose a non-uniform deployment scheme for PBs in WPCNs, where a cell is divided into inner and outer areas, such that BS and PBs can cooperate to power UEs. To be more specific, a BS located in the center of a cell provides downlink power supply for the inner area UEs and uplink information decoding for all the UEs in the cell; while the PBs power UEs in the outer area. With multiple antennas, maximum ratio transmission and maximum ratio combining are adopted for downlink energy beamforming and IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. XX, NO. XX, MONTH XX 2019 2 uplink information reception. Considering a finite area of the network, we derive the distribution of the distance from a non-center-located UE to its nearest PB in the outer area. An optimization problem is formulated to minimize total average power consumption, while satisfying BS average transmission power constraint and coverage probability threshold. Moreover, coverage probability is derived for performance evaluation. Numerical results show that the power consumption of the proposed scheme is reduced significantly compared to PB-only WPCNs. Index Terms-Wireless powered communication network; Wireless energy transfer; Non-uniform deployment.

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Abstract-Wireless energy transfer (WET) has been a promising technology to tackle the lifetime bottlenecks of energy-limited wireless devices in recent years. In this paper, we study a WET enabled multiple input multiple output (MIMO) system including a base station (BS) and a user equipment (UE), which has a finite battery capacity. We consider slotted transmissions, where each slot includes two phases, namely downlink (DL) WET phase and uplink (UL) wireless information transmission (WIT) phase. In the WET phase (a fraction τ of a slot), the BS transfers energy and the UE stores the received energy in the battery. In the WIT phase (a fraction 1 − τ of a slot), the UE transmits information to the BS by using the energy in the battery. Considering the power sensitivity α of the radio frequency (RF) to direct current (DC) conversion circuits, the BS transfers energy only if the UE received power is larger than α, and the downlink WET is formulated as a Bernoulli process. Based on the formulation, we propose an online power and time allocation algorithm to maximize the average data rate of uplink WIT. We also extend the proposed algorithm to multiple user systems. The numerical results show that the proposed algorithm outperforms the existing schemes in terms of average data rate, energy efficiency and outage probability.Index Terms-WET, MIMO, online power and time allocation, finite battery size.

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