The relentless expansion of communications services and applications in 5G networks and their further projected growth bring the challenge of necessary spectrum scarcity, a challenge which might be overcome using the concept of cognitive radio. Furthermore, an extremely high number of low-power devices are introduced by the concept of the Internet of Things (IoT), which also requires efficient energy usage and practically applicable device powering. Motivated by these facts, in this paper, we analyze a wirelessly powered underlay cognitive system based on a realistic case in which statistical channel state information (CSI) is available. In the system considered, the primary and the cognitive networks share the same spectrum band under the constraint of an interference threshold and a maximal tolerable outage permitted by the primary user. To adopt the system model in realistic IoT application scenarios in which network nodes are mobile, we consider the randomly moving cognitive user receiver. For the analyzed system, we derive the closed-form expressions for the outage probability, the outage capacity, and the ergodic capacity. The obtained analytical results are corroborated by an independent simulation method.

The relentlessly increasing number of small-sized devices with limited powering and computational capabilities requires the adoption of new approaches to spectrum access. In this paper, we analyze an underlay cooperative cognitive wireless system based on available statistical channel state information (CSI) that is applicable to the cognitive system with limited computational resources due to its low complexity. We considered the scenario where the primary and the cognitive network coexist in the same spectrum band, under the constraints of interference threshold and maximal tolerable outage permitted by the primary user. The communication in the secondary decode-and-forward (DF) relaying system is established via a self-sustainable relay, which harvests energy from both cognitive and primary transmitters. The closed-form expressions for the outage probability of the cognitive network are derived, which are valid for both time-switching relaying (TSR) and power-splitting relaying (PSR) protocols. We analyze the influence of both cognitive and primary systems as well as the impact of channel parameters on the cognitive system outage performance. The derived analytical results are corroborated by an independent simulation method.

Due to the need for the implementation of various IoT services, novel generation networks are often characterized by a constant requirement for their expansion and a rising number of nodes. The IoT network nodes are usually low power, so security becomes a challenging issue as conventional cryptographic techniques are hard to implement due to power and computational limitations. Besides, wireless power transfer is an appealing approach for powering IoT systems in scenarios where many nodes are placed in hardly accessible areas. Finally, due to a variety of applications, network nodes are often mobile. Motivated by these facts, in this paper, we investigate physical layer security in IoT systems powered by means of a power beacon, where a legitimate user or eavesdropper can be mobile. The closed-form approximate secrecy outage probability expressions are derived for the Nakagami-m fading environment and three scenarios of receiving node mobility, described by using a random waypoint model with mobility patterns in one, two or three dimensions. The accuracy of the obtained analytical expressions is corroborated by an independently developed simulation model.