This paper comprehensively studies the secure decode-and-forward (DF) relaying transmission in slow fading channels. To maximize the secrecy throughput under a secrecy outage probability constraint, we propose three adaptive transmission schemes (ATSs) with different complexity and flexibility, and design system parameters according to the instantaneous channel state information of the legitimate receiver. Specifically, in ATS-SW, source and relay use the same codeword, and eavesdropper employs the maximal ratio combining (MRC) reception; whereas in ATS-DWSR and ATS-DBDR, the source and relay either use independent codewords with identical code rates, or different codebooks with different code rates so that the eavesdropper can only decode the two-hop signals individually instead of MRC method. For all the three ATSs, we provide explicit solutions on the optimal system parameters, including the resource allocation between the source and relay, and the code rates. We also present numerical results and comparisons on the secrecy throughput of these schemes.
This paper comprehensively studies the secure decode-and-forward (DF) relaying transmission in slow fading channels. To maximize the secrecy throughput under a secrecy outage probability constraint, we propose three adaptive transmission schemes (ATSs) with different complexity and flexibility, and design system parameters according to the instantaneous channel state information of the legitimate receiver. Specifically, in ATS-SW, source and relay use the same codeword, and eavesdropper employs the maximal ratio combining (MRC) reception; whereas in ATS-DWSR and ATS-DBDR, the source and relay either use independent codewords with identical code rates, or different codebooks with different code rates so that the eavesdropper can only decode the two-hop signals individually instead of MRC method. For all the three ATSs, we provide explicit solutions on the optimal system parameters, including the resource allocation between the source and relay, and the code rates. We also present numerical results and comparisons on the secrecy throughput of these schemes.
In this paper, we provide a comprehensive study of secrecy transmission in decode-and-forward (DF) relay networks subjected to slow fading. With only channel distribution information (CDI) of the wiretap channels, we aim at maximizing secrecy throughput of the two-hop transmission under a secrecy outage constraint through optimizing transmission region, rate parameters of the wiretap codes and power allocation between the source and relay. We propose fixed transmission parameter scheme (FTPS) and variable transmission parameter scheme (VTPS), which are based on the CDI and instantaneous channel state information of the main channels, respectively. In both schemes, source and relay use the same codeword, and the eavesdropper can use maximum ratio combining (MRC) reception. To improve the secrecy throughput, we further propose VTPS-D1 and VTPS-D2 schemes, where the source and relay either use independent codewords with identical code rates, or different codebooks with different code rates so that the eavesdropper can only decode the two-hop signals individually rather than using MRC. We provide explicit results on the design for all proposed schemes. Numerical results and comparisons on the secrecy throughput of these schemes are presented to reveal their respective superiorities and give some insights into the choice of design scheme.
In this paper, we derive and compare the performance of relay selection strategies presence of an active adversary under a cooperative setting. The system consists of a source, a destination, multiple decode-and-forward relays and an active eavesdropper. These DF relays correctly decode source message, if their signal-to-noise ratio is above a certain threshold. The channels experience independent but not identical Rayleigh fading. We assume both source and eavesdropper can exploit direct and relaying channel. Two relay selection schemes are performed by the eavesdropper, which is assumed to be a part of the system and active. A conventional all-performing relays (using maximal ratio combining) scheme is compared with the above mentioned schemes. We obtain closed-form expressions for the secrecy outage probability of these three strategies. An asymptotic analysis is presented only when relay selection is performed by the eavesdropper. From numerical results, it is observed that relay selection performed by the active eavesdropper proves to be the worst from the perspective of legitimate receiver. Also restriction on either of the two hops results in flooring of secrecy performance.
Exploiting relays in millimeter wave (mmWave) systems is an effective way to extend the communication coverage and overcome the blockage problem. This paper comprehensively studies secure transmissions in mmWave decode-and-forward (DF) relay systems. Depending on the overlapped resolvable paths between the main channel and the wiretap channel in each transmission stage, we consider three eavesdropping scenarios, namely two-stage eavesdropping (TSE), single-stage eavesdropping (SSE) and no eavesdropping (NE). We investigate secrecy performance and optimal parameter design of these eavesdropping scenarios under the same codeword transmission (SCT) scheme and the different codewords transmission (DCT) scheme, where source and relay utilize same codeword or different codewords. Specifically, we derive closed-form expressions for connection probability and secrecy outage probability, and then give solution to the secrecy throughput maximization problem. Furthermore, we investigate the effectiveness of the artificial noise (AN) by evaluating the secrecy performance of AN assisted transmissions. Numerical results are provided to verify our theoretical analysis. Our results give insights into the secure transmission scheme selection and the impact of various parameters, such as number of antennas, power allocation between source and relay, number of overlapped paths, and distances between different nodes, on the secrecy performance of the mmWave relay system.
In this paper, a source communicates to the destination with the cooperation of a relay, in the presence of an eavesdropper. All the links undergo Rayleigh fading and perfect decoding at the relays is not considered. The secrecy outage probability expression is evaluated for a decode-and-forward (DF) dual-hop cooperative relay network, both with and without the presence of direct source to eavesdropper transmission link. The performance of the maximal ratio combining (MRC) and selection combining (SC) diversity at the eavesdropper is investigated. Asymptotic and diversity gain analysis for both the single relay and multi-relay system is obtained, when average SNRs of source-relay and relay-destination links are balanced or unbalanced. We have shown that the increase in target secrecy rate and eavesdropper channel quality significantly affects the outage performance of the system. We have investigated the outage probability of optimal relay selection scheme, when either full instantaneous channel state information (ICSI) or statistical channel state information (SCSI) of all the links is available and have shown that there is improvement in the secrecy performance with the increase in the number of relays.
Transmit beamforming is a diversity technique in multiple-input multiple-output (MIMO) systems. It improves the diversity order and enhances the information security of the MIMO systems. In this paper, we mathematically analyze the secure performance of a MIMO decode-and-forward (DF) relay system under the presence of an eavesdropper and with the imperfect channel state information (CSI) of the eavesdropping channel. To enhance the secrecy performance, we employ multiple antennas at all legitimate nodes and utilize two linear beamforming schemes, i.e., maximal ratio transmission (MRT) and transmission zero-forcing (TZF), at the transmitter and maximal ratio combining (MRC) scheme at the receiver. The probability density function (PDF) of the output SNR for different numbers of antennas at the transmitter and receiver is plotted and discussed. After that, we apply this PDF to derive the closed-form expressions of the secrecy outage probability (SOP) and ergodic secrecy capacity (ESC) of the considered MIMO-DF relay system over Rayleigh fading channels for MRT/MRC and TZF/MRC schemes. In addition, based on the obtained analysis results, we provide the location of the relay that minimizes the system SOPs. All the analysis results are validated by Monte-Carlo simulations. The results show that the TZF/MRC scheme provides better SOP and ESC than the MRT/MRC scheme. Moreover, the number of antennas at the legitimate nodes and the location of the eavesdropper significantly impact the secrecy performance.
In this paper, we investigate the secrecy outage performance of decode-and-forward (DF) buffer-aided relaying networks with a multi-antenna destination in the presence of an eavesdropper. In order to take full advantage of the benefits provided by the multiple antennas at the destination and the available relays, we adopt the max-link relay selection scheme and propose a half-duplex and two full-duplex secure transmission schemes for secrecy improvement, i.e., 1) maximal-ratio combining (MRC), 2) maximal-ratio combining/cooperative jamming (MRC/CJ), and 3) zero-forcing beamforming/cooperative jamming (ZFB/CJ). For all proposed schemes, we present exact and asymptotic closed-form expressions of the secrecy outage probability by modeling the dynamic buffer state transitions as a Markov chain. Moreover, simple and informative asymptotic results are provided under both L → ∞ and L → ∞ scenarios (where L denotes the buffer size), from which we can obtain further insights on the secrecy diversity gain and the secrecy coding gain. The highlights of this paper can be summarized as follows: 1) Under L → ∞ scenario, the secrecy diversity gains of all proposed schemes both reach M. When L → ∞, the secrecy diversity gains of MRC, MRC/CJ and ZFB/CJ increase to M (1 + ND), MND and 2M respectively, where M is the number of relays and ND represents the number of antennas at the destination; 2) The secrecy coding gain of the system differs with different schemes, and it improves with the increase of M and ND under both the two scenarios; and 3) Under the scenario L → ∞, ZFB/CJ outperforms MRC and MRC/CJ across the entire signal-to-noise ratio (SNR) range of interest, however, when L→ ∞, ZFB/CJ outperforms MRC/CJ and MRC in the low SNR regime, while the opposite holds in the high SNR regime.