The transmit antenna selection/maximal-ratio combining (TAS/MRC) scheme is proposed to improve the secrecy performance of dual-hop randomize-and-forward (RaF) cognitive multiple-input multiple-output ...(MIMO) wiretap networks when the channel state information (CSI) is outdated. In this network, the secondary transmitter adopts TAS scheme to choose the strongest antenna to transmit signals, while MRC scheme is used by secondary receiver and eavesdropper to strengthen their received signals. Firstly, we investigate the secrecy outage probability (SOP) of dual-hop RaF cognitive MIMO wiretap networks. To gain more observation on the influence of the proposed TAS/MRC scheme and outdated CSI, we further present tractable asymptotic SOP at high SNR regimes. From the analysis, we derive that outdated CSI will affect SOP by decreaseing the secrecy coding gain of TAS/MRC scheme. In addition, the RaF relaying strategy can achieve better secrecy performance than that of DF relaying strategy for dual-hop cognitive MIMO wiretap networks.
Molecular communication is set to play an important role in the design of complex biological and chemical systems. An important class of molecular communication systems is based on the timing ...channel, where information is encoded in the delay of the transmitted molecule - a synchronous approach. At present, a widely used modeling assumption is the perfect synchronization between the transmitter and the receiver. Unfortunately, this assumption is unlikely to hold in most practical molecular systems. To remedy this, we introduce a clock into the model - leading to the molecular timing channel with synchronization error. To quantify the behavior of this new system, we derive upper and lower bounds on the variance-constrained capacity, which we view as the step between the mean-delay and the peak-delay constrained capacity. By numerically evaluating our bounds, we obtain a key practical insight: the drift velocity of the clock links does not need to be significantly larger than the drift velocity of the information link, in order to achieve the variance-constrained capacity with perfect synchronization.
In this paper, the impact of multiple eavesdroppers on cooperative single carrier systems with multiple relays and multiple destinations is examined. To achieve the secrecy diversity gains in the ...form of opportunistic selection, a two-stage scheme is proposed for joint relay and destination selection, in which, after the selection of the relay with the minimum effective maximum signal-to-noise ratio (SNR) to a cluster of eavesdroppers, the destination that has the maximum SNR from the chosen relay is selected. In order to accurately assess the secrecy performance, the exact and asymptotic expressions are obtained in closed-form for the ergodic secrecy rate in frequency selective fading. Based on the asymptotic analysis, key design parameters such as multiplexing gain, and power cost are characterized, from which new insights are drawn. Moreover, it is concluded that capacity ceiling occurs when the average received power at the eavesdropper is proportional to the counterpart at the destination.
In this paper, we propose generalized selection combining/zero forcing beamforming (GSC/ZFB) scheme to improve the secrecy performance of spectrum-sharing wiretap networks with a full-duplex Bob. ...Specifically, the full-duplex Bob selects L B strongest antennas to receive the signals from Alice and simultaneously transmits jamming signals with the remaining (N B -L B ) antennas based on ZFB algorithm. We first derive exact closed-form expression for the secrecy outage probability of full-duplex multi-antenna spectrum-sharing wiretap networks with GSC/ZFB scheme. Then, we derive tractable asymptotic expression for the secrecy outage probability, which reveals that there exists a secrecy outage floor for the proposed GSC/ZFB scheme in high SNR region. The simulation results demonstrate that the proposed scheme achieves better performance than traditional GSC scheme with half-duplex technique. In addition, different from the traditional GSC scheme, the secrecy performance of the proposed GSC/ZFB scheme is not always improved with the increase of L B under a given N B .
Cognitive relay technology has been envisioned as a promising transmission scheme to enhance the reliability and coverage of secondary networks. However, the performance of cognitive relay networks ...(CRNs) is limited by the lack of accurate channel state information (CSI). As such, this paper adequately addresses the impact of imperfect CSI on the performance of cognitive multihop networks by proposing a simple yet effective backoff control power method. In addition, novel exact and asymptotic expressions for outage probability and ergodic capacity over Rayleigh fading channels are also derived. These tractable analytical results reveal new insight into the design, e.g., the number of hops for secondary network, and optimization of cognitive multihop networks.
A cooperative network in which confidential messages are conveyed from a source to a legitimate destination with the help of decode-and-forward relays in the presence of a malicious eavesdropper is ...considered. Tight upper bounds on the ergodic secrecy rate are derived in the cases of i) cooperative beamforming and ii) multi-user selection. Further, a new concept of cooperative diversity gain, namely, adapted cooperative diversity gain (ACDG), is investigated. It is shown that the ACDG can be seen as an effective metric to evaluate the security level of a cooperative wireless network in the presence of eavesdroppers. Also, the ACDG obtained in the cooperative beamforming scenario is equal to the traditional cooperative diversity gain of traditional multiple-input single-output networks, while the ACDG obtained in the multiuser scenario is equal to that of traditional single-input multiple-output networks.
During a disaster, communication systems are partially (or completely) interrupted with very limited resources due to infrastructures destruction and hence the lack of essential services. Meanwhile, ...the demand for communication reaches its highest peak ever since users need to contact loved ones and make sure they are safe, inform first responders and local governments about surrounding conditions, and receive urgent instructions for safety and resilience. Rather than only high quality of service (QoS), the affected users now require high quality of sustainability (QoSus) of communications that are characterized by high response, interoperable and robust connections, high hit rate and delivery capacity of contents, and resource savings. In this paper, we therefore design a QoSuS model for Mobile Ad Hoc Networks (MANET) to reduce as much harm as possible when a disaster strikes. To this end, we propose optimization problems that we solve for high QoSus of MANET in three-tier cellular networks (i.e., macrocells, femtocells, and mobile devices). Our optimal results include a number of replicas of each cached content, a set of femtocells to cache the replicas, a set of cellular users to share their sub-channels with other mobile devices, and a set of relay nodes for mobile device-to-device communications. We further take into account the constraints of co-channel interference due to many simultaneous channel accesses, storage resource of femtocells, and energy resource of mobile devices, to efficiently gain high performance of solution. Simulation results demonstrate that our proposed solutions provide the best possible QoSus under such severe conditions.
This paper tackles the important question of how to compensate the inherent spectrum efficiency loss in cognitive relay networks. Particularly, by considering two-way cognitive relaying, we seek to ...enhance the performance of the secondary network in terms of the reliability due to limited transmit power, and the spectral efficiency of the half-duplex dual-hop relay transmission. We derive new closed-form expressions for the outage probability of a cognitive relay network with two-way communications in the presence of multiple primary users. Our expressions accurately take into account the impact of the maximum allowable interference constraint at the primary users on the secondary network.
In this paper, we investigate the secure communication of cognitive full-duplex relay networks in the presence of multiple eavesdroppers and multiple primary receivers. In the considered network, ...multiple full-duplex relays are deployed to transfer information in the secondary network, under the malicious attempts of non- colluding/colluding eavesdroppers. Meanwhile, the transmit powers of secondary transmitters are constrained by the quality-of-service of the primary network. The optimal relay selection scheme is proposed to enhance the secrecy performance of the considered system. We study the secrecy performance by providing the exact closed- form and asymptotic expressions of the proposed system secrecy outage probability. We have demonstrated that increasing the number of full- duplex relays can improve the security performance. At the illegitimate side, using colluding eavesdroppers and increasing the number of eavesdroppers put information confidentiality at a greater risk. Besides, the transmit power and the desired outage probability of the primary network have great influences on the secrecy outage probability of the secondary network.
In this paper, we formulate the interference alignment (IA) problem for a multiuser multiple-input multiple-output (MIMO) system in the presence of an eavesdropper as a rank constrained rank ...minimization (RCRM) problem. The aim of the proposed rank minimization IA schemes is to find the precoding and receiver subspace matrices to align interference and wiretapped signals into the lowest dimension subspaces while keeping the desired signal subspace spanning full available spatial dimensions. To deal with the nonconvexity of the rank function, we present two convex relaxations of the RCRM problem, namely nuclear norm (NN) and reweighted nuclear norm (RNN), and transform the rank constraints to equivalent and tractable ones. We then derive a coordinate decent approach to obtain the solutions for IA schemes. The simulation results show that our proposed IA designs outperform the conventional IA design in terms of average secrecy sum rate. On the other hand, our proposed designs perform the same or better than other secure IA schemes which account for low interference and wiretapped signal power rather than for low dimensions of interference and wiretapped signal matrices in the systems which achieve the perfect IA.
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