Abstract
This paper studies the performance of wireless power transfer in distributed antenna systems (DAS). In particular, the distributed remote radio heads (RRHs), which are conventionally distributed in the network to enhance the performance, are also used to increase the energy harvesting (EH) at the energy-constrained users. Based on this idea, the network area is divided into two zones, namely: 1) EH zone and 2) interference zone. The users in the EH zones are guaranteed to harvest sufficient energy from the closed RRH, while the users in the interference zones harvest energy from the surrounding RRHs. A harvest-then-transmit protocol is adopted, where in the power transfer phase the multiple antennas RRHs broadcast energy signals to the users. In the information transmission phase, the users utilize the harvested energy to transmit their signals to the RRHs. In addition, zero-forcing is applied at the RRHs receivers, to mitigate the interference. The system spectral efficiency is evaluated in two different scenarios based on the channel state information (CSI) namely: 1) CSI is unknown at the RRHs 2) CSI is perfectly known at the RRHs. In contrast to conventional EH-muliple-input multiple-output (MIMO) systems, performance analysis of EH DAS-MIMO is a challenging problem, because the channels are characterized by non-identical path-loss and EH effects which make the classical analytical methods non-tractable. In light of this, new analytical expressions of the ergodic spectral efficiency are derived and then Monte Carlo simulations are provided to verify the accuracy of our analysis. The effects of main system parameters on the EH-DAS performance are investigated. The results show that there is an optimal value of the EH time for each users locations that maximizes the system performance. In addition, size of the EH-zone area depends on the required harvested power at the users which is dependent essentially on the target spectral efficiency.
Highlights
R ADIO frequency (RF) energy harvesting (EH) in wireless communication networks has attracted significantManuscript received October 27, 2017; revised April 28, 2018 and July 21, 2018; accepted August 7, 2018
We can say that, r denotes the boundary beyond which all EH zone users cannot provide the target spectral efficiency, and their performance depend on the received signals from other the surrounded remote radio heads (RRHs)
It is assumed that each user in the EH zone harvests energy and transmit its data from/to the closest RRH only, i.e, using only one RRH in the derived expressions for users in EH zones, while the users in interference zone harvest energy and transmit data to the all RRHs in the system
Summary
R ADIO frequency (RF) energy harvesting (EH) in wireless communication networks has attracted significant. Date of publication August 14, 2018; date of current version January 15, 2019. This concept depends on the fact that RF signals are able to transfer energy to the nodes in wireless communication systems. Considerable amount of works have been achieved to study the efficiency of wireless-powered communication networks (WPCNs), in which the energy signals are exploited to charge the EH-nodes in the network. Distributed antenna system (DAS) has been proposed to improve the spectral efficiency, power efficiency and to extend the service coverage area of the communication networks [13]–[16]. A beam-forming and power allocation algorithm for a down-link MISO-DAS which maximizes the energy efficiency was proposed in [22]. In [23] the ergodic capacity of down-link DAS was investigated, where each RRH equipped with multiple antennas
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