Gaojie Chen

Physical Layer Network Security in the Full-Duplex Relay System

This paper investigates the secrecy performance of full-duplex relay (FDR) networks. The resulting analysis shows that FDR networks have better secrecy performance than half duplex relay networks, if the self-interference can be well suppressed. We also propose a full duplex jamming relay network, in which the relay node transmits jamming signals while receiving the data from the source. While the full duplex jamming scheme has the same data rate as the half duplex scheme, the secrecy performance can be significantly improved, making it an attractive scheme when the network secrecy is a primary concern. A mathematic model is developed to analyze secrecy outage probabilities for the half duplex, the full duplex and full duplex jamming schemes, and the simulation results are also presented to verify the analysis.

Max-Ratio Relay Selection in Secure Buffer-Aided Cooperative Wireless Networks

This paper considers the security of transmission in buffer-aided decode-and-forward cooperative wireless networks. An eavesdropper which can intercept the data transmission from both the source and relay nodes is considered to threaten the security of transmission. Finite size data buffers are assumed to be available at every relay in order to avoid having to select concurrently the best source-to-relay and relay-to-destination links. A new max-ratio relay selection policy is proposed to optimize the secrecy transmission by considering all the possible source-to-relay and relay-to-destination links and selecting the relay having the link which maximizes the signal to eavesdropper channel gain ratio. Two cases are considered in terms of knowledge of the eavesdropper channel strengths: exact and average gains, respectively. Closed-form expressions for the secrecy outage probability for both cases are obtained, which are verified by simulations. The proposed max-ratio relay selection scheme is shown to outperform one based on a max-min-ratio relay scheme.

Buffer-Aided Max-Link Relay Selection in Amplify-and-Forward Cooperative Networks

This paper investigates the outage performance of an amplify-and-forward (AF) relay system that exploits buffer-aided max-link relay selection. Both asymmetric and symmetric source-to-relay and relay-to-destination channel configurations are considered. We derive the closed-form expressions for the outage probability and analyze the average packet delays. We prove that the diversity order is between N and 2N (where N is the relay number), corresponding to a relay buffer size between 1 and ∞, respectively. We also analytically show the coding gain. Numerical results are given to verify the theoretical analyses.

Decode-and-Forward Buffer-Aided Relay Selection in Cognitive Relay Networks

This paper investigates decode-and-forward (DF) buffer-aided relay selection for underlay cognitive relay networks (CRNs) in the presence of both primary transmitter and receiver. We propose a novel buffer-aided relay selection scheme for the CRN, where the best relay is selected with the highest signal-to-interference ratio (SIR) among all available source-to-relay and relay-to-destination links while keeping the interference to the primary destination within a certain level. A new closed-form expression for the outage probability of the proposed relay selection scheme is obtained. Both simulation and theoretical results are shown to confirm performance advantage over the conventional max-min relay selection scheme, making the proposed scheme attractive for CRNs.

Study of Relay Selection in a Multi-Cell Cognitive Network

This paper studies best relay selection in a multi-cell cognitive network with amplify-and-forward (AF) relays. We derive the analytical integral-form expression of the cumulative distribution function (CDF) for the received signal-to-noise-plus-interference-ratio (SINR) at the destination node, based on which the closed-form of the outage probability is obtained. Analysis shows that the proposed relay selection scheme achieves the best SINR at the destination node with interference to the primary user being limited by a pre-defined level. Simulation results are also presented to verify the analysis. The proposed relay selection approach is an attractive way to obtain diversity gain in a multi-cell cognitive network.

Outage probability analysis for a cognitive amplify-and-forward relay network with single and multi-relay selection

The authors evaluate the outage probability of a cognitive amplify-and-forward relay network with cooperation between certain secondary users, chosen by single and multi-relay (two and four) selection, based on the underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection is performed either on the basis of a max-min strategy or one based on maximising exactly the end-to-end signal-to-noise ratio. To realise the relay selection schemes within the secondary networks, a predetermined threshold for the power of the received signal in the primary receiver is assumed. To assess the performance advantage of adding additional secondary relays, we obtain analytical expressions for the probability density function and cumulative density function of the received SNR and thereby provide closed form and near closed form expressions for outage probability over Rayleigh frequency flat fading channels. In particular, the authors present lower and upper bound expressions for outage probability and then provide a new exact expression for outage probability. These analytical results are verified by numerical simulation.

Resource Allocation for Full-Duplex Relay-Assisted Device-to-Device Multicarrier Systems

This letter analyzes the resource allocation problem for full-duplex relay-assisted device-to-device (D2D) multicarrier systems, where multiple D2D user groups (UGs) coexist in an underlaying manner. We formulate the optimization problem, which takes the maximization of the system throughput as an objective. Two resources, i.e., subcarrier and transmit power are considered to be appropriately allocated to UGs in order to meet the objective. The formulated problem can be independently divided into a quasi-concave problem and a mixed binary integer programming (MBIP) problem. The MBIP problem is NP-hard. Therefore, to solve this problem efficiently by standard optimization techniques, we propose an alternative algorithm, which is the linear relaxation of the MBIP problem. Then, we mathematically prove and numerically verify the equivalence of the MBIP problem and its linear relaxation. By this way, the resource allocation for UGs can be carried out by a small amount of computational overhead.

Independent vector analysis with a generalized multivariate Gaussian source prior for frequency domain blind source separation

Abstract Independent vector analysis (IVA) is designed to retain the dependency within individual source vectors, while removing the dependency between different source vectors. It can theoretically avoid the permutation problem inherent to independent component analysis (ICA). The dependency in each source vector is retained by adopting a multivariate source prior instead of a univariate source prior. In this paper, a multivariate generalized Gaussian distribution is adopted as the source prior which can exploit frequency domain energy correlation within each source vector. As such, it can utilize more information describing the dependency structure and provide improved source separation performance. This proposed source prior is suitable for the whole family of IVA algorithms and found to be more robust in applications where non-stationary signals are separated than the one preferred by Lee. Experimental results on real speech signals confirm the advantage of adopting the proposed source prior on three types of IVA algorithm.

Outage probability in distributed transmission based on best relay pair selection

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays and thereby mitigate the deleterious effect of fading channels in transmission. In an environment where multiple relays are available, selection of a subset of such relays may be required as, for example, in distributed space-time coding. In this study, the authors therefore use local measurements of the instantaneous channel conditions to select the best relay pair from a set of N available relays, which both come from the same cluster or different clusters, and then use these best relays for cooperation between the source and the destination. The authors also show that the best relay pair selection scheme has robustness against feedback error and outperforms a scheme based on selecting only the best single relay. The authors obtain analytical expressions for the probability density function, cumulative density function and the moment generating function of the received signal-to-noise ratio to derive closed-form expressions for outage probability over Rayleigh frequency flat-fading channels. The analytical results are supported by simulation studies.

Outage probability analysis of cognitive relay network with four relay selection and end-to-end performance with modified quasi-orthogonal space–time coding

In this study, the authors evaluate the outage probability performance of an amplify-and-forward cooperative relay network where the relays are equipped with cognitive radios. When the number of available relays is more than four the authors use the channel conditions in order to select the best four cognitive relays from a set of M cognitive relay nodes and then they are used for cooperation between the source and the destination nodes. Expressions for outage probability are determined for a frequency flat Rayleigh-fading environment from the received signal-to-noise ratio with perfect and imperfect spectrum acquisition. In addition, a modified distributed quasi-orthogonal space–time block coding scheme with increased code gain distance is considered for use within the proposed cognitive relay network. To utilise the available spectrum opportunities with the modified quasi-orthogonal space–time block code, the code matrix can be adapted to the number of available relays. Simulation results show that the four relay selection improves the system performance. This is confirmed by the outage probability analysis. The simulations also show that the modified code can significantly enhance the performance of the system and improve the reliability of the link as compared with the conventional distributed quasi-orthogonal space–time block coding.