Showing papers by "Hyung Yun Kong published in 2015"

Cooperative communication with energy-harvesting relays under physical layer security

Abstract: In this study, the authors propose a cooperative transmission scheme with energy-harvesting (EH) relays under wiretapping of an eavesdropper. In this scheme, the relays harvest energy from radio-frequency (RF) signals of a source through power-splitting receivers, and process arrived signals by amplify-and-forward (EH-AF protocol) and decode-and-forward (EH-DF protocol) technologies. In the proposed protocols, a best relay is selected at the destination so that the end-to-end achievable secrecy rates are maximal. Exact and asymptotic secrecy outage probability expressions are used to evaluate the EH-AF and EH-DF protocols, respectively, and are confirmed by Monte Carlo simulations. The simulation results show that (i) the EH-DF protocol outperforms the EH-AF protocol, and both proposed protocols are improved when the number of cooperative relays and the distances of the relay–eavesdropper links increase and the relays move toward the destination, (ii) the secrecy performance of the EH-AF and EH-DF protocols is the best at optimal power-splitting ratios, which are obtained by the golden section search method, (iii) the energy conversion efficiency and the noise at RF-to-baseband conversion units seriously affect the proposed protocols, and finally, (iv) the theoretical analysis results fit those of the Monte Carlo simulations.

Secrecy Performance Analysis of Multihop Transmission Protocols in Cluster Networks

Abstract: In this paper, we investigate the secured transmission in cluster-based multi-hop networks. In particular, we evaluate the secrecy performance of three various protocols over Rayleigh fading channel. In the first protocol, at each cluster, a relay is randomly selected to forward the source message to the next cluster. In the second and third ones, relay selection methods are applied to enhance secrecy performance. We derive closed-form expressions of secrecy outage probability and capacity, and then perform Monte Carlo simulations to verify the derivations.

Smart Power Allocation for Secrecy Transmission in Reciprocally Cooperative Spectrum Sharing

Abstract: By cooperative spectrum sharing schemes, a primary network (PN) leases a part of the licensed band to a secondary network (SN). A secondary transmitter (ST) acts as a relay for the primary transmitter (PT) to improve the end-to-end link quality of the PN, and as a reward, the ST gets the opportunity to transmit its own data by superposition coding. In this paper, a new cooperative spectrum sharing (CSS) scheme taking into account malicious eavesdropping (wiretapping) by a PN is proposed. In such scheme, licensed band is a decoy to an SN to wiretap the secondary transmission. Thus, secrecy in secondary transmission becomes critical to the SN. To get achievable secrecy (data) rate in secondary transmission and to fulfill the duty as a relay for primary transmission, the SN looks for a smart power-allocation (SPA) parameter that satisfies both goals. SPA parameter $\alpha_{\mathrm{smart}}$ provides the target secrecy data rate, and the achieved data rate at the PN is greater than or equal to the data rate obtained by the direct transmission (DT). Considering a Rayleigh block-fading channel, the SPA parameter is evaluated for each secondary transmission. Details on the evaluation of the SPA parameter are presented, and theoretical outage probabilities of the PN and the SN are derived and validated by simulations.

Outage Performance and Diversity Analysis of Cognitive Triple-Hop Cluster-Based Networks Under Interference Constraint

Abstract: In this paper, a full diversity for a triple-hop underlay cognitive network is investigated In secondary network, multiple decode-and-forward (DF) relays located in two clusters help a source forwarding data to a destination under interference constraint with a primary user We analyze and compare the outage performance and diversity order of two proposed protocols of the three hops model: the hop between a source node and multiple relays in the first cluster, the hop between the first and second clusters, and the hop between the second cluster and a destination node One optimal relay (or a best relay) in each cluster is chosen by the selection strategies of two proposed protocols, which take the role of decoding and forwarding the message from the previous node to the next node To be more specific, the optimal relay in the first cluster decodes the source signal and forward the re-encoded one toward the best relay in second cluster; next, the best relay in this cluster DFs the received signal to the destination node Finally, we determine the approximate expressions of the end-to-end outage probability and obtain the diversity order for each protocol when the value of the Gaussian noise is small

Cooperative Relaying to Improve the Spectrum Utilization of Multi-channel CR Networks

Abstract: Cognitive radio (CR) allows unlicensed users to dynamically access the underutilized frequency bands of licensed primary users, to improve the spectrum utilization. Because of the scarcity of the radio spectrum, improving utilization of the spectrum is the primary design goal of CR systems. In this paper, we employ cooperative relaying to improve the spectrum utilization. Conventionally, cooperative relaying is used to achieve a diversity gain at the cost of spectral efficiency. In the proposed scheme, the relay node uses the spectrum that is not available for the source-to-destination direct link. Hence, it improves spectrum utilization in addition to diversity gain. To achieve diversity gain along with coding gain, we use a coded diversity that transmits incremental redundancy through relay. Tight upper bounds for bit error rate and frame error rate of the proposed scheme are also derived. Analysis and simulation results show that the proposed scheme achieves full diversity, along with improved utilization of the spectrum.

A method enabling exploitation of spatial diversity and physical layer security in an extreme case of source-wiretapping without a jamming beamformer

Abstract: This article exploits spatial diversity for jamming to prevent wiretapping in the extreme case in which an eavesdropper is located near the source and a common jamming signal is unavailable. To address this challenge, the jamming signal is allowed to carry a random binary message. Then, it is proposed that the active intermediate node transmits this jamming signal and the decoding of this signal at both source and destination is physically secured as result of using the physical-layer security method. If the source and the destination securely and correctly decode this jamming message, the source transmits another message which is created from combining its information message and the decoded message using the network-coding method. Therefore, this method prevents the transmissions from being eavesdropped upon by the source-wiretapping.

Combining Binary Jamming and Network Coding to Improve Outage Performance in Two-Way Relaying Networks under Physical Layer Security

Abstract: By generating a jamming message at the jammer node, a system can reduce wiretapping in the physical layer because this message can refuse the illegal eavesdropper node. The network coding technique of operating an XOR between two binary messages improves the performance. In this paper, we propose three protocols that use network coding at the two source nodes and/or the binary jamming technique at a relay in the two-way relaying network under physical layer security, compared to a conventional secrecy transmission protocol. The main idea to improve the system performance is that, if the data is transmitted securely, the next transmission time slots using the digital network coding will not consider the presence of the eavesdropper node, because the eavesdropper node cannot obtain the data. The system performance is analyzed and evaluated in terms of the exact closed-form outage probability over Rayleigh fading channels. The simulation results using a Monte-Carlo simulation are in complete agreement with the theoretical results.

Throughput analysis of dual-hop relaying energy harvesting network with TAS/MRC

Abstract: In this paper, a dual-hop time-switching (TS) energy-harvesting scheme is investigated. The source and destination are multiple-antenna devices, while the relay is an energy-constrained single-antenna node that harvests RF energy from the source and assists the source-to-destination transmission. Transmit antenna selection/maximal ratio combining is applied to exploit diversity gain in both energy-harvesting phase and information-transmitting phase. In particular, we evaluate the scheme on two criteria: outage probability (POut) and throughput (τ). The closed-form expressions of POut and t are derived and verified by the Monte-Carlo simulation. Our results show that the implementation of multiple antennas achieves significant improvement on the system performance.

Binary Jamming Message Solutions for Source-Wiretapping Under Physical-Layer Security: Analysis and Design

Abstract: A distributed zero-beamforming-based cooperative jamming technique is useless when an eavesdropper detects the sharing seed. Further, currently alternatives are very limited when the eavesdropper is located near a source for wiretapping. This paper presents some solutions for this extreme case. The jammer node, which can be a relay or destination node, randomly generates and transmits a binary jamming message to both source and destination or to both source and relay node in the first phase. When these two receivers securely and correctly decode the message, the source creates and transmits another message based on the decoded message and the use of exclusive-or for its information message. Consequently, the next transmission can avoid the eavesdropping. We present a comparison between the proposed protocols and conventional protocols that do not send a binary jamming message. The system performance is analyzed and evaluated in terms of the exact closed-form outage probability over Reyleigh fading channels. The simulation results using a Monte-Carlo simulation are in complete agreement with the theoretical results.

Joint Power Allocation for Energy Harvesting and Power Superposition Coding in Cooperative Spectrum Sharing.

Abstract: In this paper, a decode-and-forward type cooperative spectrum sharing scheme exploiting energy harvesting and power superposition coding is proposed. The secondary transmitter (ST) acting as a relay harvests energy in the first phase of every two phases from the radio frequency signal transmitted by the primary transmitter (PT) of the primary network (PN) and uses it in the second phase for transmitting power superposed codes of primary signal of the PN and secrecy signal of the secondary network (SN). The ST splits the received primary signal with adjustable power splitting ratio for decoding the primary signal and charging the battery. The harvested energy in addition to internal energy from the battery of the ST is used for power superposition coding with variable power sharing coefficient. Our main concern here is to know the impact of the two power parameters on outage performances (probabilities) of the PN and the SN. Impact of the other system parameters on outage performances is also considered to provide more comprehensive view of system operation. Analytical or mathematical expressions of the outage probabilities of the PN and the SN are derived in terms of the power parameters, location of the ST, channel gain, and other system related parameters. Jointly optimal power splitting ratio and power sharing coefficient achieving target outage probabilities of the PN and the SN are found from the expressions.

Exact Outage Probability of Cooperative Secrecy Transmission: Impact of Unavailable Relays

Abstract: The impact of unavailable relays is a serious issue in cooperative communication schemes, where the operation state of relays affects optimal relay selection. In addition, secure signal transmission is an interesting approach to prevent the wiretapping actions of eavesdropper nodes in a wireless environment. In this paper, we propose two cooperative secrecy transmission schemes: a secrecy decode-and-forward protocol and a hybrid of direct secrecy and cooperative secrecy transmission schemes to enhance the spectrum utilization efficiency. In the proposed schemes, a source transmits data signals to a destination with the assistance of relays. At the same time, these data signals are eavesdropped by another node. The best relays are successfully selected in a safe manner based on both decoding from a source to a destination and the available state of cooperative relays. The secrecy performance of each scheme is analyzed and evaluated by the exact outage probability over Rayleigh fading channels. Monte Carlo simulations were performed to verify the theoretical analysis. Finally, a discussion and comparison of the cooperative secrecy transmission schemes and the direct secrecy transmission approach are presented.