Showing papers by "Jia Zhu published in 2020"

Energy-Aware Relay Selection Improves Security-Reliability Tradeoff in Energy Harvesting Cooperative Cognitive Radio Systems

Abstract: This article investigates the physical layer security for a cooperative cognitive radio (CCR) system with energy-harvesting (EH) technique, which consists of a cognitive source (CS), multiple cognitive relays (CRs) and a cognitive destination (CD) as well as multiple eavesdroppers (Es) who are considered to tap the confidential transmission from CS via CRs to CD. Both CS and CRs are equipped with energy-harvesters to harvest energy from the surrounding radio frequency environment. Additionally, in order to guarantee the quality-of-service of primary communications, the transmit powers of CS and CRs are limited by the maximum tolerant power at primary destination. Depending on the availability of channel state information (CSI) of wireless energy links from primary transmitter (PT) to CRs, we respectively propose non-energy aware relay selection (NEARS) and energy aware relay selection (EARS) schemes for protecting the transmission from CS via CRs to CD from leaking to Es. We consider the use of the security-reliability tradeoff (SRT) to measure the performance of NEARS and EARS schemes. For the purpose of comparison, we also carry out the analysis of SRT performance for conventional direct communication (DC). Furthermore, the closed-form expressions of outage probability and intercept probability for NEARS and EARS schemes are derived and numerical results show that the SRT performance of EARS is better than that of DC and NEARS schemes.

Joint Power Splitting and Relay Selection in Energy-Harvesting Communications for IoT Networks

Abstract: In this article, we consider an energy-harvesting (EH) relay system consisting of a source, a destination, and multiple EH decode-and-forward (DF) relays that can harvest the energy from their received radio signals. A power-splitting ratio is employed at an EH DF relay to characterize a tradeoff between the energy used for decoding the source signal received at the relay and the remaining energy harvested for retransmitting the decode outcome. We propose an optimal power-splitting-based relay selection (OPS-RS) framework and also consider the conventional equal power-splitting-based relay selection (EPS-RS) for comparison purposes. We derive closed-form expressions of outage probability for both the OPS-RS and EPS-RS schemes and characterize their diversity gains through an asymptotic outage analysis in the high signal-to-noise ratio region. We further examine an extension of our OPS-RS framework to an EH battery (EHB)-enabled cooperative relay scenario, where the EH relays are equipped with batteries used to store their harvested energies. We propose an amplify-and-forward (AF)-based EHB-OPS-RS scheme and a DF-based EHB-OPS-RS scheme for AF and DF relay networks, respectively. Numerical results show that the proposed OPS-RS always outperforms EPS-RS in terms of outage probability. Moreover, the outage probabilities of the AF- and DF-based EHB-OPS-RS schemes are much smaller than that of the OPS-RS and EPS-RS methods, demonstrating the benefit of exploiting the batteries in EH relays. Additionally, the DF-based EHB-OPS-RS substantially outperforms the AF-based EHB-OPS-RS and such an outage advantage becomes more significant, as the number of EH relays increases.

Power Allocation for Intelligent Interference Exploitation Aided Physical-Layer Security in OFDM-Based Heterogeneous Cellular Networks

Abstract: In this paper, we consider an orthogonal frequency division multiplexing (OFDM) based heterogeneous cellular network consisting of a macro cell and a small cell, where a macro-cell base station (MBS) and a small-cell base station (SBS) communicate with respective macro-cell user (MU) and small-cell user (SU) with the existence of a common eavesdropper across different OFDM subcarriers. In order to make full use of the mutual interference between MBS and SBS against eavesdropping, an artificially designed signal is emitted at MBS to cancel out the interference received at MU as well as to interfere with the common eavesdropper at each subcarriers. For the purpose of further improving the secrecy performance, a sum secrecy rate (SSR) of OFDM-based heterogeneous cellular networks is maximized by optimizing the power allocation between MBS and SBS across different OFDM subcarriers when the eavesdropper owns the global instantaneous channel state information (ICSI), thus called ICSI based SSR maximization (ICSI-SSRM). As for the case when the ICSI of wiretap channels is unknown, we propose a statistical CSI based SSR maximization (SCSI-SSRM) scheme, where the statistical characteristics of channels from MBS and SBS to eavesdropper are employed to optimally allocate powers of MBS and SBS across different subcarriers under the constraint of MBS's total transmit power. The formulated ICSI-SSRM and SCSI-SSRM problems are all non-convex due to form of the difference between two-convex (D.C.) functions. Thus, we utilize the D.C. approximation approach to respectively convert original optimization problems into convex problems. Moreover, iterative optimal power allocation algorithms for ICSI-SSRM and SCSI-SSRM schemes are also presented to obtain their respective SSR values. Simulation results illustrate that the ICSI-SSRM and SCSI-SSRM algorithms can converge to their optimal values, which confirms the correctness and validation of the proposed algorithms. In addition, numerical results are also given to show that the ICSI-SSRM and SCSI-SSRM schemes outperform conventional power allocation methods in terms of their SSR performance.