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We consider wireless-powered amplify-and-forward and decode-and-forward relaying in cooperative communications, where an energy constrained relay node first harvests energy through the received radio-frequency signal from the source and then uses the harvested energy to forward the source information to the destination node. We propose time-switching based energy harvesting (EH) and information transmission (IT) protocols with two modes of EH at the relay. For continuous time EH, the EH time can be any percentage of the total transmission block time. For discrete time EH, the whole transmission block is either used for EH or IT. The proposed protocols are attractive because they do not require channel state information at the transmitter side and enable relay transmission with preset fixed transmission power. We derive analytical expressions of the achievable throughput for the proposed protocols. The derived expressions are verified by comparison with simulations and allow the system performance to be determined as a function of the system parameters. Finally, we show that the proposed protocols outperform the existing fixed time duration EH protocols in the literature, since they intelligently track the level of the harvested energy to switch between EH and IT in an online fashion, allowing efficient use of resources.Radio frequency (RF) or wireless energy harvesting has recently emerged as an attractive solution to power nodes in future wireless networks [2]- [6]. Wireless energy harvesting techniques are now evolving from theoretical concepts into practical devices for low-power electronic applications [7]. The feasibility of wireless energy harvesting for low-power cellular applications has been studied using experimental results, which have been summarised in [2]. With wireless energy harvesting, there is a choice between harvesting energy from ambient sources or by carefully designing wireless power transfer links. For instance, a power density of around 1 mW/m 2 is reported around 50 meter distance from the base station in the GSM band (935 MHz -960 MHz) [4], which means that a wireless device with a typical size of around 100 cm 2 can harvest power in the range of tens of µW. Such an amount of harvested power could be sufficient for relaying nodes in sensor networks with sporadic activities. For devices that need to support frequent communication activities, harvesting ambient RF energy is not sufficient. Instead, harvesting wireless energy from carefully designed power transfer links is needed. In addition, the energy conversion efficiency of the wireless energy harvesting plays an important role in determining the amount of energy that can be harvested. Employing different circuit design technologies, wireless energy harvesting with energy conversion efficiency in the range of 10%-80% has been reported over a wide range of frequencies, e.g., 15 MHz -2.5 GHz [2], [8]. More specifically, energy conversion efficiency of around 65% has been reported in the ISM band (900 MHz, 2.4 GHz) with 13 nm CMOS techno...

In this paper, we consider a decode-and-forward (DF) relaying network based on wireless energy harvesting. The energy constrained relay node first harvests energy through radio-frequency (RF) signals from the source node. Next, the relay node uses the harvested energy to forward the decoded source information to the destination node. The source node transfers energy and information to the relay node through two mechanisms, i) time switching-based relaying (TSR) and ii) power splitting-based relaying (PSR). Considering wireless energy harvesting constraint at the relay node, we derive the exact analytical expressions of the achievable throughput and ergodic capacity of a DF relaying network for both TSR and PSR schemes. Through numerical analysis, we study the throughput performance of the overall system for different system parameters, such as energy harvesting time, power splitting ratio, and signal-tonoise-ratio (SNR). In particular, the throughput performance of the PSR scheme outperforms the throughput performance of the TSR scheme for a wide range of SNRs.

Abstract-In this paper, we propose to use a wireless-powered friendly jammer to enable secure communication between a source node and destination node, in the presence of an eavesdropper. We consider a two-phase communication protocol with fixed-rate transmission. In the first phase, wireless power transfer is conducted from the source to the jammer. In the second phase, the source transmits the information-bearing signal under the protection of a jamming signal sent by the jammer using the harvested energy in the first phase. We analytically characterize the long-term behavior of the proposed protocol and derive a closed-form expression for the throughput. We further optimize the rate parameters for maximizing the throughput subject to a secrecy outage probability constraint. Our analytical results show that the throughput performance differs significantly between the single-antenna jammer case and the multi-antenna jammer case. For instance, as the source transmit power increases, the throughput quickly reaches an upper bound with single-antenna jammer, while the throughput grows unbounded with multiantenna jammer. Our numerical results also validate the derived analytical results.Index Terms-Physical layer security, friendly jammer, cooperative jamming, wireless power transfer, throughput.

This paper derives the exact cumulative density function of the distance between a randomly located node and any arbitrary reference point inside a regular $\el$-sided polygon. Using this result, we obtain the closed-form probability density function (PDF) of the Euclidean distance between any arbitrary reference point and its $n$-th neighbour node, when $N$ nodes are uniformly and independently distributed inside a regular $\ell$-sided polygon. First, we exploit the rotational symmetry of the regular polygons and quantify the effect of polygon sides and vertices on the distance distributions. Then we propose an algorithm to determine the distance distributions given any arbitrary location of the reference point inside the polygon. For the special case when the arbitrary reference point is located at the center of the polygon, our framework reproduces the existing result in the literature.Comment: 13 pages, 5 figure