Impact of outdated channel estimates on a distributed link-selection scheme for AF relaying networks

We investigate the impact of outdated channel estimates on the outage performance of a distributed link-selection scheme recently proposed for variable-gain amplify-and-forward relaying networks. In this scheme, either the direct link or the relaying link is preselected before each transmission, based on a distributed mechanism. We begin by showing that an exact analysis is rather intricate, yielding a multifold integral-form solution. Motivated by this, we then derive a simple closed-form lower bound, which, importantly, proves to be a very tight approximation to the exact outage probability. We also assess the system diversity order via asymptotic analysis42185188COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão te

An Adaptive Transmission Scheme For Cognitive Decode-and-forward Relaying Networks: Half Duplex, Full Duplex, Or No Cooperation

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)We propose an adaptive transmission scheme for cognitive decode-and-forward relaying networks, whereby, before each communication process, one out of three transmission modes is dynamically selected in order to maximize the instantaneous capacity of the system, namely, half-duplex (HD) relaying, full-duplex (FD) relaying, or direct transmission with no cooperation. The following key issues, relevant to underlay spectrum sharing and cooperative relaying, are considered: 1) the overall transmit power at the secondary network is constrained by both the maximum tolerable interference at the primary receiver and the maximum transmit power available at the secondary nodes; 2) under FD operation, the secondary relay is subject to residual self-interference, which is modeled as a fading channel; and 3) the signals coming from the secondary source and relay are handled at the secondary destination via maximal-ratio combining, in the HD relaying mode, and via a joint-decoding technique, in the FD relaying mode. We derive an exact analytical expression for the outage probability of the proposed scheme. Then, an approximate closed-form expression is proposed, and a corresponding asymptotic expression is derived. Monte Carlo simulations are run to validate the accuracy of the presented mathematical analysis and to showcase the tightness of the proposed approximation.15855865602Brazilian Ministry of Education Coordenacao de Aperfeicoamento de Pessoal de Nivel SuperiorFinnish Centre for International MobilityTekesAcademy of FinlandCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

On the secrecy performance and power allocation in relaying networks with untrusted relay in the partial secrecy regime

Abstract Recently, three useful secrecy metrics based on the partial secrecy regime were proposed to analyze secure transmissions on wireless systems over quasi-static fading channels, namely: generalized secrecy outage probability, average fractional equivocation, and average information leakage. These metrics were devised from the concept of fractional equivocation, which is related to the decoding error probability at the eavesdropper, so as to provide a comprehensive insight on the practical implementation of wireless systems with different levels of secrecy requirements. Considering the partial secrecy regime, in this paper we examine the secrecy performance of an amplify-and-forward relaying network with an untrusted relay node, where a destination-based jamming is employed to enable secure transmissions. In this regard, a closed-form approximation is derived for the generalized secrecy outage probability, and integral-form expressions are obtained for the average fractional equivocation and the average information leakage rate. Additionally, equal and optimal power allocation schemes are investigated and compared for the three metrics. From this analysis, we show that different power allocation approaches lead to different system design criteria. The obtained expressions are validated via Monte Carlo simulations

Wireless-powered full-duplex UAV relay networks over FTR channels

Abstract A thorough understanding of fundamental limits of wireless-powered unmanned aerial vehicle (UAV) relay networks in millimeter waves is still missing. We narrow this gap by investigating the outage performance of a UAV-assisted wireless network over fluctuating two-ray (FTR) channels. The FTR fading model is particularly appealing since well characterizes the wireless propagation in a wide range of frequencies, including those in millimeter waves. The proposed setup consists of a source-destination pair communicating with the assistance of a UAV, which is a wireless-powered relay station operating in full-duplex mode under the amplify-and-forward protocol. For the wireless energy harvesting at the UAV, wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT), and self-recycling energy techniques are employed together. To characterize the system outage probability, we obtain an integral-form expression derived from an approximate analysis and a simple closed-form expression derived from an asymptotic analysis at the high signal-to-noise ratio (SNR) regime. Monte Carlo simulations are provided to validate the correctness of our theoretical results and provide insights on the network performance in terms of key system parameters. Interestingly, obtained results show that the FTR fading parameters corresponding to the first hop and second hop play no role on the system outage performance at high SNR. Instead, it is mainly governed by the effect of the residual self-interference at the UAV, leading to outage floors

Outage performance of spectrally efficient schemes for multiuser cognitive relaying networks with underlay spectrum sharing

We analyze the outage performance of two spectrally efficient schemes for exploiting multiuser diversity in cognitive relaying networks. We consider a secondary network composed by one source node communicating with the best one out of L available destinations, selected according to the channel quality of the direct links. If the transmission through the selected direct link drops below a given threshold, then a half-duplex decode-and-forward relaying transmission is invoked. At this stage, two schemes are considered. In the first scheme, the previously selected secondary destination employs maximal-ratio combining to handle the signals received from the secondary source and relay. In the second scheme, maximal-ratio combining is employed as well, but at a possibly different secondary destination, selected so as to maximize the signal-to-noise ratio at the combiner output. In both schemes, we consider an underlay spectrum-sharing mechanism. We derive exact analytical expressions for the outage probability of the proposed schemes and validate them by Monte Carlo simulations. An asymptotic analysis reveals that the proposed schemes can achieve full diversity order, equal to L+1. Importantly, we show that, at high signal-to-noise ratio, the mean spectral efficiency of the proposed schemes approximates that one attained by direct transmission131266296642COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão tem24th IEEE International symposium on personal, indoor and mobile radio communicatio

An adaptive transmission scheme for amplify-and-forward relaying networks

In this paper, an adaptive scheme for amplify-andforward relaying networks is proposed, which selects a certain transmission mode for each communication process. Depending on the instantaneous channel conditions, one of the following modes is selected: direct transmission with no cooperation, cooperative transmission with half-duplex relaying and maximalratio combining at the destination, or cooperative transmission with full-duplex relaying and maximal-ratio combining at the destination. A three-node network is considered, containing a singleantenna source, a two-antenna relay that is able to implement full-duplex communication, and a single-antenna destination. Energy normalization per block is assumed, so that in those modes using cooperation, the system's transmission power is shared between source and relay. The performance analysis is provided in terms of outage probability and energy efficiency. We derive a tight approximate expression in closed form for the outage probability and an approximate expression in integral form for the mean energy consumption. The results show that our scheme outperforms all of transmission modes separately in terms of outage probability, while being more energy efficient than the cooperative transmission modes. In addition, the asymptotic analysis proves that the proposed scheme achieves full diversity order equal to 2, thus outperforming those schemes with direct transmission or full- duplex cooperation only206516678COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão temThis work was supported in part by the Brazilian Ministry of Education (CAPES), the Finnish Centre for International Mobility (CIMO), and the Tekes and Academy of Finland (AKA

Impact of wireless energy transfer strategies on the secrecy performance of untrustworthy relay networks

Abstract This work investigates the secrecy outage performance of a dual-hop relaying network with an untrustworthy energy-constrained amplify-and-forward relay. A destination-based jamming technique is adopted in order to prevent the relay from decoding confidential messages from the source. Additionally, three time switching-based wireless energy transfer strategies are investigated for supplying power to the relay. For these three strategies, we derive simple closed-form asymptotic expressions for the secrecy outage probability at high signal-to-noise ratio. Moreover, we provide analytical expressions for the optimum power allocation factor for the information transmission phase. Finally, Monte Carlo simulations are carried out to verify the theoretical results through different illustrative cases

An adaptive transmission scheme for cognitive decode-and-forward relaying networks: half duplex, full duplex, or no cooperation

We propose an adaptive transmission scheme for cognitive decode-and-forward relaying networks, whereby, before each communication process, one out of three transmission modes is dynamically selected in order to maximize the instantaneous capacity of the system, namely, half-duplex (HD) relaying, full-duplex (FD) relaying, or direct transmission with no cooperation. The following key issues, relevant to underlay spectrum sharing and cooperative relaying, are considered: 1) the overall transmit power at the secondary network is constrained by both the maximum tolerable interference at the primary receiver and the maximum transmit power available at the secondary nodes; 2) under FD operation, the secondary relay is subject to residual self-interference, which is modeled as a fading channel; and 3) the signals coming from the secondary source and relay are handled at the secondary destination via maximal-ratio combining, in the HD relaying mode, and via a joint-decoding technique, in the FD relaying mode. We derive an exact analytical expression for the outage probability of the proposed scheme. Then, an approximate closed-form expression is proposed, and a corresponding asymptotic expression is derived. Monte Carlo simulations are run to validate the accuracy of the presented mathematical analysis and to showcase the tightness of the proposed approximation15855865602COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão temThis work was supported in part by the Brazilian Ministry of Education Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, in part by the Finnish Centre for International Mobility, and in part by the Tekes and Academy of Finlan

Safeguarding MTC at the physical layer:potentials and challenges

Abstract 5G networks must provide a highly resilient, secure, and privacy-protected platform to support the emergence of new business and technologies expected from the so-called vertical-industry paradigm. However, as the definition and implementation of 5G networks are in progress, many security challenges arise. Thus, special emphasis will be given in the coming years to provide security and privacy for 5G and beyond networks. In this regard, physical layer security has been recognized as a potential solution to safeguard the confidentiality and privacy of communications in such stringent scenarios. In light of this, herein we provide an overview on some promising physical-layer techniques, focusing on the requirements and design challenges for machine-type communication scenarios. Key issues are discussed along with potential solutions