Abstract
This paper jointly investigates the downlink/uplink of wireless powered networks (WPNs), which are exposed to the effect of the cascaded near-far problem , i.e., the asymmetric overall degradation of the users’ performance, due to different path-loss values. More specifically, assuming that the users are able to harvest energy both from interference and desired signals, higher path loss reduces the downlink rate of the far user, while it also negatively affects its uplink rate, since less energy can be harvested during downlink. Furthermore, if the far user is located at the cell edge, its performance is more severely impaired by interference, despite the potential gain due to energy harvesting from interference signals. To this end, we fairly maximize the downlink/uplink users’ rates, by utilizing corresponding priority weights. Two communication protocols are taken into account for the downlink, namely, time division multiple access and non-orthogonal multiple access (NOMA), while NOMA with time sharing is considered for the uplink. The formulated multidimensional non-convex optimization problems are transformed into the equivalent convex ones and can be solved with low complexity. Simulations results illustrate that: 1) a relatively high downlink rate can be achieved, while the required energy is simultaneously harvested by the users for the uplink and 2) dowlink NOMA is a more appropriate option with respect to the network topology, especially when a high downlink rate is desired.
Highlights
T HE opportunities arising from the recent adnavces in multimedia, along with the emerging future internet-ofthings (IoT) applications, such as smart cities, health monitoring devices, and driverless cars, are limited by the finite battery capacity of the involved wireless communication devices [1], [2]
Motivated by the energy efficiency and the resilience towards low levels of interference that NOMA presents compared to time-division miltiple access (TDMA), we present numerical results for the case of interference-free communication, in order to investigate the performance gains offered by NOMA in the downlink, compared to TDMA, in absence of interfering sources
Two different protocols were utilized for the downlink, i.e., NOMA and TDMA, while NOMA with time sharing was used for the uplink
Summary
T HE opportunities arising from the recent adnavces in multimedia, along with the emerging future internet-ofthings (IoT) applications, such as smart cities, health monitoring devices, and driverless cars, are limited by the finite battery capacity of the involved wireless communication devices [1], [2]. For this reason, harvesting energy from radio frequency signals, which transfer information, seems to be an interesting alternative This technique, referred to as simultaneous wireless information and power transfer (SWIPT), presupposes the efficient design of the communication system that receives information and energy simultaneously [4], [5], which depends on the specific system implementation [6], [7]. In this framework, the nodes use the power of the received signal to charge their batteries [8], or to transmit the information to the base station (BS) [9], [10]. The idea of SWIPT has been reported in various scenarios, such as one source-destination pair [8], multiple-input multipleoutput (MIMO) communications systems [17]–[21], orthogonal frequency division multiple access (OFDMA) [8], [22]– [24], cooperative networks [25]–[32], communication systems with security [33]–[35], and cognitive radio [36], [37]
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