The use of multiple source nodes with wireless backhaul is considered for secrecy enhancement through source node selection in future wireless networks. The ergodic secrecy rate (ESR) of optimal source node selection in the presence of multiple eavesdroppers over independent non-identically distributed (INID) Rayleigh fading channels is evaluated in closed-form. At high signal-to-noise ratio (SNR), the ESR is expressed as a simple weighted summation where each term relates to the contribution of an individual source and eavesdropper. An asymptotic analysis shows the effect of the system parameters and backhaul reliability on the performance. The proposed method can provide a generalized solution for the ESR of optimal transmit antenna selection in multi-antenna systems, optimal source node selection, and optimal relay selection with or without unreliable backhaul.
The use of multiple source nodes with wireless backhaul is considered for secrecy enhancement through source node selection in future wireless networks. The ergodic secrecy rate (ESR) of optimal source node selection in the presence of multiple eavesdroppers over independent non-identically distributed (INID) Rayleigh fading channels is evaluated in closed-form. At high signal-to-noise ratio (SNR), the ESR is expressed as a simple weighted summation where each term relates to the contribution of an individual source and eavesdropper. An asymptotic analysis shows the effect of the system parameters and backhaul reliability on the performance. The proposed method can provide a generalized solution for the ESR of optimal transmit antenna selection in multi-antenna systems, optimal source node selection, and optimal relay selection with or without unreliable backhaul.
Abstract Due to the exponential growth of interconnected devices and reduced cell coverage, beyond fifth‐generation networks will be dense. Thus, instead of wired backhaul, wireless backhaul will be cost‐effective and flexible. For security in multi‐transmitter systems, sub‐optimal and optimal transmitter selection schemes exist. However, including backhaul activity knowledge available (BKA) and backhaul activity knowledge unavailable (BKU) cases and transmitter selection schemes, there is no generalized secrecy analysis method. Moreover, evaluation of the ergodic secrecy rate (ESR) of the optimal selection schemes is impossible using existing solution approaches. To address these, two sub‐optimal and optimal transmitter selection schemes are proposed for a small‐cell multi‐transmitter system in BKU or BKA cases in the presence of multiple colluding eavesdroppers. The distribution of the ratio of the destination channel SNR and eavesdropping channel SNR is derived, thereby providing different secrecy performance metrics uniformly irrespective of selection schemes and BKU or BKA cases. Simplified asymptotic expressions are provided to elucidate the influence of the system parameters and of the backhaul reliability. It is observed that the secrecy performance improves when the knowledge of backhaul link activity is utilized, and the improvement is most noticeable when the backhaul is highly unreliable. It is also observed that while the secrecy performance degrades with an increasing number of eavesdroppers, neither the asymptotic saturation value of the secrecy outage probability nor the rate of improvement of the ESR with signal‐to‐noise‐ratio depends on the number of eavesdroppers.
This paper investigates the secrecy performance of sub-optimal transmitter selection and optimal selection schemes in a system comprising multiple transmitters, multiple eavesdroppers, and a single destination in frequency-selective fading channels with single-carrier cyclic-prefixed modulation. Considering unreliable backhaul links between the access point and the transmitters, we analyze secrecy performance in two scenarios: when backhaul activity knowledge is available (KA) and when backhaul activity knowledge is unavailable (KU). Closed-form expressions for the secrecy outage probability (SOP) and the ergodic secrecy rate (ESR) are derived. Our analytical results show that in the backhaul KA scenario, the asymptotic limit of the SOP and the slope of the ESR are affected only by the number of transmitters and the backhaul reliability factor, and not by other system parameters. In contrast, only the backhaul reliability factor affects these two performances in the backhaul KU scenario. These performances are independent of the number of eavesdroppers in both backhaul KA and KU scenarios. Our findings demonstrate that acquiring knowledge of the activity of backhaul links yields better secrecy performance as compared to acquiring knowledge of the channel state information of the eavesdroppers. We also show that the secrecy diversity order of both selection schemes under perfectly reliable (wired) backhaul links is identical.
This paper investigates the secrecy performance of a finite-sized in-band selective relaying system with M transmitters connected via unreliable backhaul links, N decode-and-forward relays, and K collaborative eavesdroppers. To send the source message to the destination, a transmitter-relay pair that achieves the highest end-to-end signal-to-noise ratio is selected for transmissions, while the K eavesdroppers combine all the received signals from the selected transmitter and relay using maximal ratio combining. The proposed model introduces backhaul reliability and eavesdropping probability parameters to investigate practical constraints on the transmitter-relay cooperation and eavesdropper collaboration, respectively. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate for non-identical frequency-selective fading channels with robust cyclic-prefixed single carrier transmissions. These results show that the asymptotic secrecy outage probability and probability of non-zero achievable secrecy rate are exclusively determined by the number of transmitters M and their corresponding set of backhaul reliability levels. Under unreliable backhaul connections, it is found that the secrecy diversity gain is determined by M, N, and the number of multipath components in the frequency selective fading channels. Link-level simulations are conducted to verify the derived impacts of backhaul reliability and collaborative eavesdropping on the secrecy performance.
Wireless backhaul is a cost-effective and flexible alternative to wired backhaul, yet it suffers from unreliability. This paper studies the secrecy performance of a relay network with such unreliable wireless backhaul. Bernoulli process is adopted to model the wireless backhaul reliability. In the network, a relay employing time-switching-based radio frequency harvesting technique aids in forwarding the signal from the best transmitter. An eavesdropper, which is able to wiretap signals from both the transmitter and the relay, uses selection combining to maximize its received signal-to-noise ratio. Analytical expressions for secrecy outage probability, ergodic secrecy rate and non-zero achievable secrecy rate are derived, which can reveal the effect of the number of transmitters and backhaul reliability on the system performance. Furthermore, for the first time the impact of energy harvesting time fraction upon secrecy performances under unreliable backhaul is presented.
In this paper, the impacts of unreliable backhaul links on the secrecy performance of cooperative single carrier heterogeneous networks in the presence of eavesdroppers are investigated. A two-phase transmitter/relay selection scheme is proposed, where the best transmitter is selected to maximize signal-to-noise ratio at the relays in the first phase and the best relay is chosen in the second phase to minimize the signal-to-interference-plus-noise ratio of the eavesdroppers with the aid of a friendly jammer. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate. The asymptotic performance analysis is furthermore performed to explicitly reveal the impacts of unreliable backhaul links on the secrecy performance. Our results show that the diversity gain cannot be achieved in the presence of imperfect backhaul links.
In this paper, the secrecy performance of finite-sized cooperative cyclic prefixed single carrier systems with multiple eavesdroppers and unreliable wireless backhaul connections across multiple transmitters is investigated. For nonidentical frequency-selective fading channels between the relay and destination nodes, secrecy performance metrics including the secrecy outage probability, ergodic secrecy rate, and probability of nonzero achievable secrecy rate are derived. Furthermore, the existence of performance limits on the secrecy outage probability and probability of non-zero achievable secrecy rate are verified for various backhaul scenarios. These limits are found to be exclusively determined by the backhaul reliability. For imperfect backhaul connections, it is found that the diversity gain promised by cooperative cyclic prefixed single-carrier systems cannot be achieved in the conventional asymptotic high signal-to-noise ratio region. Link-level simulations are conducted to verify the derived impact of backhaul reliability on the secrecy performance.