This paper presents an analytical framework which lays the foundation for distributed massive multiple-input multiple-output (MIMO) supported wireless power transfer for wearable devices. In our approach, we consider multiple users, each wearing a number of wireless sensors along with one body worn hub which acts as a relay to forward information from the on-body sensors to nearby access points (APs). Each AP is equipped with a large number of antennas and is not only responsible for receiving data sent from the hubs, but also supplying wireless power to them. Interaction between hubs and APs is not exclusive to a single pairing, with APs assigned to supply energy to and receive data from more than one hub. More precisely, APs perform the downlink energy transmission and the uplink data transmission using maximum-ratio combining. Analytical approximations of the outage probability and spectral efficiency are derived. Based on these analytical results, two modes of operation are investigated. These are outage probability prioritized and spectral efficiency prioritized. For each mode, maxmin power controls are proposed to ensure a uniformly good service throughout the area of coverage. By contrasting with the IEEE 802.15.6 standard, the numerical results illustrate that while using collocated massive MIMO may provide unsatisfactory performance, the distributed setting shows much promise for enabling wireless power transfer for wearable devices.

Device‐to‐device (D2D) communications have emerged as a promising solution that can enable new wireless local services and can enhance the performance of wireless services in cellular networks. However, D2D links in a cellular network are difficult to establish because of mutual interference between cellular and D2D transmissions. Hence, it is of primary importance to devise a radio resource allocation scheme that can maximise the spectrum utilisation and at the same time minimise the impact of interference. In this article, we propose a novel resource allocation method for D2D communications underlaying cellular networks. The proposed method divides D2D pairs into several groups and allows spatially separated D2D users to belong to the same group so that they can exploit the same resource. An appropriate cellular device is selected to share its uplink resources with the D2D pairs in each group in such a way that an adequate signal‐to‐interference‐plus‐noise ratio for both cellular and D2D links can be guaranteed. We also propose a power control strategy for D2D links in order to maximise the number of D2D pairs that can be served. Copyright © 2015 John Wiley & Sons, Ltd.

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In this paper, the performance of opportunistic relay selection (ORS) in a cognitive radio is analyzed over flat Rayleigh fading channels. Data transmission between source and destination is assumed to be entirely performed via the relays. Relay nodes are assumed to have ability to harvest energy from the source signal and use that harvested energy to forward the information to the destination. Specifically, we derive an exact expression for the outage probability of the secondary system considering the maximum transmit power at the secondary transmitter and relays, energy harvesting efficiency at relays, and interference constraint at the primary receiver. Under the assumption of perfect channel state information at the receivers, we evaluate the outage probability of a cognitive radio system with ORS and energy harvesting.

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