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This paper proposes a new artificial noise (AN) scheme that combines with the relay selection techniques to improve the physical layer security for a wiretap full-duplex decode-and-forward cooperative network. The communication consists of two phases. In the first phase, the source transmits a message to the selected full-duplex relay, which simultaneously injects AN to mitigate eavesdropping attacks. In the second phase, the selected relay decodes the source message, XORs the source message and AN, and then broadcasts the mixed-signal to the destination. Different form existing schemes, the proposed AN scheme makes the eavesdropper fail in obtaining any information about the source message directly in the second phase. We take into account the correlation of the channel coefficients for the same link during different phases in the performance analysis of AN-aided max-min (MM) and partial (Par) relay selection schemes, and characterize the security-reliability trade-off (SRT) of the proposed schemes by the closed-form expressions of outage probability and intercept probability. Numerical results show that the proposed AN-aided MM/Par relay selection achieves a better SRT performance than the corresponding full-duplex mode assisted AN-aided relay selection scheme in existing literature. Furthermore, the MM scheme outperforms the Par scheme in terms of the SRT, and the SRT of the MM scheme can be substantially improved by increasing the number of relays, while the improvement of the Par scheme is limited.

This study solves the transmit power minimisation problem subject to a target quality-of-service constraint of a full-duplex (FD) two-way decode-and-forward relaying system with asymmetric packet-rates, where the two-way relaying system can operate in two different styles, i.e. half-duplex sources with full-duplex relaying (HDS-FDR) and full-duplex sources with full-duplex relaying (FDS-FDR) styles. For the FDS-FDR style, the relay node can use two strategies to handle the received signals from the sources, namely, physical-layer network coding (PNC) and physical-layer superposition coding (PSC), both of which are referred to as FDS-FDR-PNC and FDS-FDR-PSC styles, respectively. By transforming the transmit power minimisation problem into a two-stage problem, optimum power control (OPC) techniques are developed for the HDS-FDR, FDS-FDR-PNC and FDS-FDR-PSC styles, respectively, giving closed-form solutions for individual transmit power at the relay and the sources. Computer simulations are conducted and the results validate the proposed OPC techniques. It is shown that the FDS-FDR-PNC style performs best in terms of energy saving when the two sources' packet-rates are moderately asymmetric or symmetric. For the case that the packet-rates are strongly asymmetric, the FDS-FDR-PSC style can save more energy than the other two styles.

We consider an underlay wiretap cognitive two-way relay network (CTWRN), where two secondary sources exchange their messages via multiple secondary decode-and-forward digital network coding relays in the presence of an eavesdropper by using a three-phase time division broadcast protocol and sharing the licensed spectrum of primary users. To mitigate eavesdropping attacks, an artificial noise (AN)-aided opportunistic relay selection scheme, called generalized max-min (GMM) relay selection is proposed to enhance physical layer security for the wiretap CTWRNs. The performance of the GMM scheme is analyzed, and evaluated by the exact closed-form outage probability and intercept probability. Additionally, we also provide asymptotic approximations for the outage probability and intercept probability at high signal-to-noise ratio. For comparison, we analyze the performance of the conventional max-min (MM) relay selection scheme as well. It is shown that the GMM scheme outperforms the MM scheme in terms of the security-reliability tradeoff (SRT), where the security and reliability are quantified by the intercept probability and outage probability, respectively. Moreover, the SRTs of the MM and GMM schemes can be substantially improved by increasing the number of secondary relays, while the improvement of the GMM scheme is more evident than that of the MM scheme.

Based on the partially observable Markov decision process, this paper investigates spectrum access in cognitive networks and proposes an optimal spectrum access algorithm to maximize the throughput. The suboptimal solution to the optimal spectrum access strategy is given by use of the greedy algorithm. In order to achieve the optimal channel access, the channel access state of authorized users is estimated according to the historical information of spectrum sensing. Simulation results show that the optimal spectrum access algorithm would make the secondary users achieve a higher throughput and the networks have the higher spectrum utilization. Compared with the random access and the optimal cognitive MAC protocol, the optimal spectrum access algorithm would improve the throughput by 25–40% and 8–12%, respectively.

We develop a secure random linear network coding scheme on wiretap networks where a wiretapper can only eavesdrop on a limited number of channels. On one hand, by refining Lima's "locked coefficien ...

In this paper, we consider the problem of secure communication over wiretap multicast networks. Noticing that network coding renders the intermediate nodes to mix information from different data flows, we propose a secure communication scheme based on cryptographic means and network coding. Specifically, we employ a confidential cryptosystem to encrypt the source message packets, then treat the secret key as a message packet and mix the key with the obtained cryptograms. Furthermore, we can prove that, under suitable conditions, the wiretapper is unable to gain the secret key. Meanwhile, the confidential cryptosystem prohibits the wiretapper from extracting meaningful information from the obtained cryptograms. Our scheme doesn’t need a private channel to transmit the secret key and enables the utilization of network capacity to reach 1 n n .

Note that network coding allows immediate nodes to mix information from different data flows. On the basis of this observation, we prove that under suitable conditions, communicators can communicate with perfect secrecy over wiretap networks. Our method of secure communication over wiretap networks without keys is fundamentally distinct from cryptographic means. Furthermore, a linear network code with perfect secrecy is available for a given wiretap multicast network provided that the cardinality of the alphabet is larger than a constant. Comparing with other approaches, no network capacity is lost by our method.

We propose a construction method for constructing quasi-cyclic low-density parity-check (QC LDPC) codes based on subgroup's coset. Our construction method is available not only for the prime circulants size, but also for the nonprime circulants size in some conditions. And it is showed that these conditions are easy to satisfy. Regular QC LDPC codes with various lengths and rates can be easily constructed with girth at least 6. Simulation results show that they are have almost the same performance as random regular LDPC codes over AWGN channel.