Secrecy Performance of TAS in MIMOME System with Outdated CSI

In this paper, we investigate secure communication for a dual-hop multiuser relay network, where a source communication with N ( N ≥ 1 ) destinations via an untrusted variable gains relay. To exploit multiuser diversity while protecting source’s confidential message, we first propose a joint destination-based jamming and opportunistic scheduling (DJOS) scheme. Then, we derive closed-form approximated and asymptotic expressions of the secrecy outage probability (SOP) for the considered system with DJOS. Furthermore, we determine an asymptotical optimal power allocation (OPA), which minimizes the asymptotic SOP, to further improve the secrecy performance. Our analytical results show that the achievable secrecy diversity order in terms of SOP with fixed power allocation is min ( 1 , N 2 ) , whereas, with OPA, the achievable secrecy diversity order can be improved up to min ( 1 , 2 N N + 2 ) . This interesting result reveals that OPA can improve the secrecy diversity order of the single-user network. This is intuitive since full diversity order of 1 cannot be achieved when N = 1 , thus leaving some space for OPA to improve the diversity order. Nevertheless, for N ≥ 2 , the effect of OPA is to increase the secrecy array gain rather than the secrecy diversity order since full diversity order 1 has been achieved by the OS scheme. Finally, simulation results are presented to validate our analysis.

In this paper, we consider relay selection for turbo coded cooperative networks subject to Nakagami-m fading when the channel state information (CSI) is known at the receiver but is not necessarily ideal. This non-ideality may be due to a feedback delay caused by the difference between the instantaneous CSI during the transmission and the CSI at the time of relay selection, resulting in outdated CSI phenomena. The impact of the outdated CSI on the proposed scheme is well investigated. A closed-form expression for the exact outage probability is derived as well as its asymptotic expression in the high signal-to-noise (SNR) regime. Moreover, upper bounds on the bit-error rate (BER) are presented and a study of the diversity order reveals that for ideal CSI, full diversity in the number of relays and fading parameters m is achieved as opposed to outdated CSI where the achievable diversity is equivalent to the diversity of a coded cooperative network with a single relay.

Physical layer security in SWIPT-based cooperative vehicular relaying networks

Unlike prior works assuming perfect attack detection, this paper investigates the physical layer security of a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided network under a full-duplex active eavesdropper in the more realistic scenario where its jamming remains undetected by the legitimate transmitter. Assuming Nakagami-m fading channels, we first derive the probability density functions (PDFs) of the signal-to-interference ratios (SIRs) at both the legitimate user and the eavesdropper. Then, using the PDFs, we obtain novel closed-form expressions for key secrecy metrics, including the probability of nonzero secrecy capacity (PNSC), secrecy outage probability (SOP), and average secrecy capacity (ASC). Moreover, the asymptotic PNSC, SOP, and ASC at high signal-to noise ratio (SNR) are also derived. Based on those asymptotic expressions, we present compact expressions for several key performance indicators: 1) the secrecy diversity order and the secrecy array gain of the SOP, and 2) the high SNR slope and the high SNR power offset of the ASC. Results demonstrate that, compared to the passive eavesdropper scheme, the active jamming attack carried out by Eve will not cause any loss in secrecy diversity gain and high SNR slope, but only result in the loss of secrecy array gain and high SNR power offset. Finally, we verify our analytical results via simulations.

In this study, the secrecy outage probability (SOP) of a dual-hop energy harvesting (EH) non-orthogonal multiple access (NOMA) system is investigated. In order to improve the signal quality at the transmitter node, the transmitter antenna selection (TAS) method is applied, while the generalized selection combining (GSC) technique is used to increase the reliability at the users and maximum ratio combining (MRC) is utilized at eavesdropper (EVE). In the system, the relay node harvests energy from the signals received from the base station (BS) and transmits messages to the users with the amplify-and-forward (AF) protocol. In the study, the findings for the SOP are presented with Monte Carlo simulations. The study shows that there is a trade-off between harvested energy, data rate and SOP performance, while power allocation factors have an impact on secrecy performance.

Until now, the performance analysis of Generalized Selection Combining (GSC) applied to cooperative diversity networks in the presence of outdated channel state information (CSI) is still not available in the literature. In this paper, therefore, we derive closed-form expressions of the ergodic capacity and outage probability for amplify-and-forward GSC over independent and identically distributed Rayleigh channels. Monte-Carlo simulations are set up to corroborate the correctness of our theoretical analysis. The analytical and numerical results reveal that GSC is an effective way to combat the effect of outdated CSI. When using the perfect CSI, a full diversity on the number of all cooperating relays K is available. With the outdated CSI, where the performance of the conventional opportunistic relaying drastically degrades and its diversity order is limited to 1 (i.e., no diversity), a diversity order on the number of selected relays N can still be achieved. However, the performance gain on the diversity comes at the price of sacrifice in the spectral efficiency.

Prior results on performance analysis for cognitive relay networks mainly involve perfect channel state information (CSI), which is not readily available. Thus, the effects of outdated CSI on the performance of a multi-antenna multi-relay cognitive radio system are investigated in this work. To exploit the benefits of multiple antennas, collaborative zero-forcing beamforming at the secondary source is proposed to enhance the system performance under the outdated CSI. At the destination, the maximum ratio combining (MRC) diversity scheme is adopted. The Nth best relay selection strategy is applied before the secondary data transmission process. Closed-form expressions for the exact and asymptotic outage probabilities are derived for the secondary user over the Rayleigh fading in the first hop and Nakagami-m fading in the second hop with and without feedback delay. These analytical results can reveal the system diversity order and coding gain. Monte Carlo simulations are carried out to verify the correctness of our analysis. These new analytical results can reveal insights into the characteristics of the proposed system over the outdated fading channels, and can provide useful design criteria for relay-assisted spectrum sharing networks.

We design new secure on-off transmission schemes
\nin wiretap channels with outdated channel state information
\n(CSI). In our design we consider not only the outdated CSI from
\nthe legitimate receiver but two distinct scenarios, depending on
\nwhether or not the outdated CSI from the eavesdropper is known
\nat the transmitter. Under this consideration our schemes exploit
\nthe useful knowledge contained in the available outdated CSI,
\nbased on which the transmitter decides whether to transmit or
\nnot. We derive new closed-form expressions for the transmission
\nprobability, the connection outage probability, the secrecy outage
\nprobability, and the reliable and secure transmission probability
\nto characterize the achievable performance. Based on these
\nresults, we present the optimal solutions that maximize the
\nsecrecy throughput under dual connection and secrecy outage
\nconstraints. Our analytical and numerical results offer detailed
\ninsights into the design of the wiretap coding parameters and
\nthe imposed outage constraints. We further show that allowing
\nmore freedom on the codeword transmission rate enables a larger
\nfeasible region of the dual outage constraints by exploiting the
\ntrade-off between reliability and security.

Reconfigurable intelligent surfaces (RIS) have emerged as a promising approach to enhance the secrecy performance of wireless networks from a physical layer security perspective. However, its effectiveness critically depends on the availability of accurate instantaneous channel state information (CSI) at the RIS controller. This work evaluates the impact of outdated CSI on the secrecy performance of a multiple RIS-aided wireless network. To this end, a closed-form expression for the secrecy outage probability (SOP) is derived assuming the availability of an outdated CSI at the RIS controller. The obtained results demonstrate the network’s secrecy degradation level due to the CSI outdatedness, while the increase in the number of RISs can compensate for such a secrecy loss. For instance, incorporating three RISs improves the SOP by two orders of magnitude with respect to a single RIS for 25% of CSI outdatedness. Furthermore, the results reveal that, under specific scenarios of several channel outdatedness, a baseline single RIS with a perfect CSI can outperform multiple RISs with outdated CSI. These findings highlight a critical limitation in incorporating multiple RISs in a wireless network with severe channel aging, requiring the increase of the RISs size or the number of RISs to combat its effect.

We have considered a dual-hop wireless network consisting of a decode-and-forward (DF) relay in presence of an eavesdropper. Relay can correctly decode and retransmit only if the received signal-to-noise ratio (SNR) meets a particular threshold. The eavesdropper can tap signals both from the relay and the source. The performance of the maximal ratio combining (MRC) and selection combining (SC) diversity at the eavesdropper is investigated. Whether knowledge of channel state information (CSI) at the transmitter is available or not is considered for the performance evaluation in secrecy outage probability and ergodic secrecy rate. Asymptotic analyses of performances are provided. We show that direct link has a significant impact on system secrecy. It is found that secrecy performances are the best if the relay is always able to decode correctly. We also found that knowledge of CSI helps to achieve better secrecy at lower rate. It is observed that unbalance created due to constraint on either of the source-relay link average SNR or relay-destination link average SNR does not yield similar secrecy outage performance but both can limit the secrecy outage performance. On the contrary, it is found that only source-relay link quality can limit the ergodic secrecy rate performance.

We investigate the effect of the outdated channel state information (CSI) on the secondary relay-aided network's performance. We carry out the analysis of the outage probability as well as the diversity order of the secondary network (SN) considering three key constraints: 1) maximum transmit power at the secondary transmitter, 2) peak interference power at the primary receiver, and 3) outdated CSI at the secondary-to-primary and secondary-to-secondary links. The performance results show that the relay cluster position, the imperfect CSI of the interference links and of the second hop are the key optimization factors. We show that the correlation coefficient of the second hop link is the key optimization parameter of the diversity order.

In this paper, we analyze the outage probability and average throughput of opportunistic relaying with ARQ when the outdated channel state information (CSI) is available for relay selection. Its diversity order is analyzed to show that it is determined by the number of relays and the maximum number of ARQ rounds. Numerical results verify our analysis by comparison with computer simulation and show the effect of outdated CSI on its outage probability, diversity order, and average throughput.

In this paper, we investigate the impact of the outdated Channel State Information (CSI) and the Co-Channel Interference (CCI) on the performance of Transmit Antenna Selection with Selective Combining (TAS/SC) in a dual-hop amplify-and-forward (AF) Multiple-Input Multiple-Output (MIMO) relay network. We derive the exact closed-form and asymptotic expressions for the outage probability in the cases of perfect and outdated CSI, respectively. The simulation results match the theoretical analysis well. The findings suggest that the outdated CSI and CCI have significant impacts on the outage probability of an AF MIMO relay system with TAS/SC.

In this paper, we consider secure communication via a wireless-powered untrusted relay with outdated channel state information (CSI). The low security clearance of the relay means that both the source and destination wish to keep information confidential from it. To prevent the relay from decoding the source information, the destination emits a jamming signal to the relay during data transmission by the source. The wireless-powered relay uses both the data and the jamming signals as valuable sources of energy for the amplify-and-forward relaying process. In addition, it can adopt either a power splitting or a time switching policy to determine the proportions of energy harvesting and information processing. However, when the CSI of the relay-to-destination link is outdated, the destination cannot remove the jamming signal completely from the relaying signal due to imperfect channel reciprocity. To evaluate the effect of outdated CSI on the secrecy performance, we derive the analytical expressions of two performance metrics, outage probability (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ) for delay-limited transmission and ergodic secrecy rate (R̅) for delay-tolerant transmission. The results of the analysis also allow us to find the jamming power level and energy harvesting ratio to optimize P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> and R̅, respectively. Numerical simulations are used to verify the precision of our analysis, and confirm that the proposed secure relaying protocols accomplish near-optimal secrecy performances. Our results indicate that there is a need to reduce the jamming power level to ensure secure communication when the channel is severely outdated, while outdated CSI has a relatively low impact on the energy harvesting ratio.

In this paper, we study the physical layer security of a downlink multi-input single-output non-orthogonal multiple access (NOMA) system, in which transmit antenna selection (TAS) scheme, users’ quality of service (QoS) requirements, Nakagami-m fading channel, and user selection solution are considered for secure NOMA transmission. Specifically, we investigate the scenario that a base station (BS) (source) communicates with two legitimate user (LU) clusters with different priority depending on their QoS requirements in the presence of multiple passive eavesdroppers over Nakagami-m fading. To enhance the secrecy performance, we examine a TAS scheme and a user selection method. In this context, prior to transmission, a transmit antenna and a user in high-priority LU cluster are jointly selected to maximize the channel quality of the link from the BS to the selected user. Furthermore, together with the selected high-priority user, a user in low-priority LU cluster, which has the best channel condition, is chosen for performing two-user NOMA. In order to evaluate the secrecy performance, tight and asymptotic closed-form expressions of secrecy outage probability for selected LUs and overall system are derived. Our theoretical results confirmed by Monte–Carlo simulation show that in QoS-based NOMA system, high-priority users cause the higher effects on the overall secrecy performance in comparison with low-priority users. Finally, these results also indicate that our proposed communication protocol achieves the secrecy performance greater than conventional protocol.