In this paper, we first propose a joint user and relay selection (JURS) scheme to enhance physical layer security in a multi-user multi-relay network, where the best pair of the user and relay that maximizes the user-to-destination signal-to-interference-to-noise ratio (SINR) is jointly selected. We analytically examine the secrecy outage probability (SOP) of this scheme, based on which the optimal power allocation between the useful signal and artificial noise at the users is determined in order to minimize the corresponding SOP. To avoid the high complexity of the joint selection, we also propose a separate user and relay selection (SURS) scheme, where one relay is firstly selected to maximize the relay-to-destination SINR and a user is then selected to maximize the SINR from the user to the selected relay. We also derive the SOP of the SURS scheme and determine the corresponding optimal power allocation. As expected, the JURS scheme can outperform the SURS scheme. However, our examination also indicates that the low-complex SURS scheme can achieve similar secrecy performance as the high-complex JURS scheme under some specific conditions, e.g., when the number of users is much larger than that of the relays or when the average signal-to-noise ratio of user-to-relay channel is much higher than that of the relay-to-destination channel.
In this paper, we first propose a joint user and relay selection (JURS) scheme to enhance physical layer security in a multi-user multi-relay network, where the best pair of the user and relay that maximizes the user-to-destination signal-to-interference-to-noise ratio (SINR) is jointly selected. We analytically examine the secrecy outage probability (SOP) of this scheme, based on which the optimal power allocation between the useful signal and artificial noise at the users is determined in order to minimize the corresponding SOP. To avoid the high complexity of the joint selection, we also propose a separate user and relay selection (SURS) scheme, where one relay is firstly selected to maximize the relay-to-destination SINR and a user is then selected to maximize the SINR from the user to the selected relay. We also derive the SOP of the SURS scheme and determine the corresponding optimal power allocation. As expected, the JURS scheme can outperform the SURS scheme. However, our examination also indicates that the low-complex SURS scheme can achieve similar secrecy performance as the high-complex JURS scheme under some specific conditions, e.g., when the number of users is much larger than that of the relays or when the average signal-to-noise ratio of user-to-relay channel is much higher than that of the relay-to-destination channel.
We study a relay and user selection scheme to improve the secrecy performance of cooperative multi-user multiple amplify-and-forward (AF) relay network. Nevertheless, relay transmission is highly susceptible to eavesdropping since confidential information is broadcasted twice, i.e., by the source and the relay. In particular, we propose a cooperative jamming aided secure transmission through the relay path. Furthermore, with the presence of the direct path, a transmission mode selection scheme is elaborated in such a way to reduce the amount of information leaked to non-selected users in the system, who may overhear the source message as eavesdroppers. Specifically, the selected relay is only activated when it has better secrecy performance than the source. We study the impact of outdated channel state information (CSI) on the system by deriving a closed-form lower bound for the secrecy outage probability (SOP). By investigating the effect of the jamming power level and the correlation coefficients imbalance, a comparison reveals that the proposed scheme outperforms the fixed transmission modes and its signal-to-noise ratio based counterpart. It is shown that the secrecy outage probability can be decreased as the number of destinations grows unless the number of relays is small. Importantly, optimal relay location and jamming power allocation significantly enhance the secrecy performance.
In this chapter, we will present criteria for user selection and relay selection to enhance the physical layer security in multiuser multi-relay networks. Specifically, for multiuser networks with multiple amplify-and-forward (AF) relays, we present three criteria to select the best relay and user pair. Criteria I and II study the received signal-to-noise ratio (SNR) at the receivers and perform the selection by maximising the SNR ratio ofthe user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximises the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio.
This paper proposes relay selection to increase the physical layer security in multiuser cooperative relay networks with multiple amplify-and-forward relays, in the presence of multiple eavesdroppers. To strengthen the network security against eavesdropping attack, we present three criteria to select the best relay and user pair. Specifically, criteria I and II study the received signal-to-noise ratio (SNR) at the receivers, and perform the selection by maximizing the SNR ratio of the user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximizes the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio. From the asymptotic analysis, an interesting observation is reached: for each criterion, the system diversity order is equivalent to the number of relays regardless of the number of users and eavesdroppers.
We present two physical layer secure transmission schemes for multiuser multirelay networks, where the communication from M users to the base station is assisted by direct links and by N decode-and-forward relays. In this network, we consider that a passive eavesdropper exists to overhear the transmitted information, which entails exploiting the advantages of both direct and relay links for physical layer security enhancement. To fulfill this requirement, we investigate two criteria for user and relay selection and examine the achievable secrecy performance. Criterion I performs a joint user and relay selection, while Criterion II performs separate user and relay selections, with a lower implementation complexity. We derive a tight lower bound on the secrecy outage probability for Criterion I and an accurate analytical expression for the secrecy outage probability for Criterion II. We further derive the asymptotic secrecy outage probabilities at high transmit signal-to-noise ratios and high main-to-eavesdropper ratios for both criteria. We demonstrate that the secrecy diversity order is min (MN, M + N) for Criterion I, and N for Criterion II. Finally, we present numerical and simulation results to validate the proposed analysis, and show the occurrence condition of the secrecy outage probability floor.
In this paper, a joint relay selection and power allocation (JRP) scheme is proposed to enhance the physical layer security of a cooperative network, where a multiple antennas source communicates with a single-antenna destination in the presence of untrusted relays and passive eavesdroppers (Eves). The objective is to protect the data confidentially while concurrently relying on the untrusted relays as potential Eves to improve both the security and reliability of the network. To realize this objective, we consider cooperative jamming performed by the destination while the JRP scheme is implemented. With the aim of maximizing the instantaneous secrecy rate, we derive a new closed-form solution for the optimal power allocation and propose a simple relay selection criterion under two scenarios of non-colluding Eves (NCE) and colluding Eves (CE). For the proposed scheme, a new closed-form expression is derived for the ergodic secrecy rate (ESR) and the secrecy outage probability as security metrics, and a new closed-form expression is presented for the average symbol error rate as a reliability measure over Rayleigh fading channels. We further explicitly characterize the high signal-to-noise ratio slope and power offset of the ESR to highlight the impacts of system parameters on the ESR. In addition, we examine the diversity order of the proposed scheme to reveal the achievable secrecy performance advantage. Finally, the secrecy and reliability diversity-multiplexing tradeoff of the optimized network are provided. Numerical results highlight that the ESR performance of the proposed JRP scheme for NCE and CE cases is increased with respect to the number of untrustworthy relays.
In this paper, we examine the physical layer security for cooperative wireless networks with multiple intermediate nodes, where the decode-and-forward protocol is considered. We propose a new joint relay and jammer selection (JRJS) scheme for protecting wireless communications against eavesdropping, where an intermediate node is selected as the relay for the sake of forwarding the source signal to the destination and meanwhile, the remaining intermediate nodes are employed to act as friendly jammers, which broadcast the artificial noise for disturbing the eavesdropper. We further investigate the power allocation among the source, relay and friendly jammers for maximizing the secrecy rate of proposed JRJS scheme, and derive a closed-form sub-optimal solution. Specifically, all the intermediate nodes, which successfully decode the source signal, are considered as relay candidates. For each candidate, we derive the sub-optimal closed-form power allocation solution and obtain the secrecy rate result of the corresponding JRJS scheme. Then, the candidate, which is capable of achieving the highest secrecy rate, is selected as the relay. Two assumptions about the channel state information (CSI), namely the full CSI (FCSI) and partial CSI (PCSI), are considered. Simulation results show that the proposed JRJS scheme outperforms the conventional pure relay selection, pure jamming, and generalized singular-value-decomposition-based beamforming schemes in terms of secrecy rate. Additionally, the proposed FCSI-based power allocation and PCSI-based power allocation schemes both achieve higher secrecy rates than the equal power allocation scheme.