Multiple Cognitive Relay Research Articles

Energy-Aware Relay Selection Improves Security-Reliability Tradeoff in Energy Harvesting Cooperative Cognitive Radio Systems

This article investigates the physical layer security for a cooperative cognitive radio (CCR) system with energy-harvesting (EH) technique, which consists of a cognitive source (CS), multiple cognitive relays (CRs) and a cognitive destination (CD) as well as multiple eavesdroppers (Es) who are considered to tap the confidential transmission from CS via CRs to CD. Both CS and CRs are equipped with energy-harvesters to harvest energy from the surrounding radio frequency environment. Additionally, in order to guarantee the quality-of-service of primary communications, the transmit powers of CS and CRs are limited by the maximum tolerant power at primary destination. Depending on the availability of channel state information (CSI) of wireless energy links from primary transmitter (PT) to CRs, we respectively propose non-energy aware relay selection (NEARS) and energy aware relay selection (EARS) schemes for protecting the transmission from CS via CRs to CD from leaking to Es. We consider the use of the security-reliability tradeoff (SRT) to measure the performance of NEARS and EARS schemes. For the purpose of comparison, we also carry out the analysis of SRT performance for conventional direct communication (DC). Furthermore, the closed-form expressions of outage probability and intercept probability for NEARS and EARS schemes are derived and numerical results show that the SRT performance of EARS is better than that of DC and NEARS schemes.

Relay Selection for Improved Security in Cognitive Relay Networks With Jamming

In this letter, we consider an underlay cognitive radio network in which a secondary transmitter (ST) communicates with a secondary destination (SD) with the aid of multiple cognitive relays, and multiple colluding eavesdroppers attempt to intercept the secondary transmission. Assuming that there is no ST-SD link, one of the cognitive relays is selected to convey the confidential information, while the others cooperate in jamming the eavesdroppers by transmitting artificial noise. Since the eavesdroppers’ channel information state is considered to be absent, two opportunistic relay selection schemes are proposed to enhance the security of the system. We derive novel closed-form expressions for the secrecy outage probability. Simulation results are presented to validate our analysis.

Power allocation design and optimization for secure transmission in cognitive relay networks

AbstractIn this paper, physical layer security is investigated in the dual‐hop amplify‐and‐forward cognitive relay network with one secondary source, one secondary destination, multiple cognitive relays under the presence of multiple primary receivers and eavesdroppers which can be either primary receivers or secondary receivers. The power allocation method at secondary source and artificial noise at relays are utilized to secure the secondary source‐destination transmission. Two optimization problems, namely, to maximize the received signal‐to‐interference‐and‐noise ratio of secondary source in the lightly‐loaded relay cluster situation, and to minimize the relay cluster total power in the fully‐loaded relay cluster situation, are formulated. In addition, these two problems should ensure both physical‐layer security and lower interference temperature. The semi‐definite relaxation technique is used to solve the considered optimization problems. In the second problems, we further optimize the performance with the help of the bisection method. Complexity analysis shows that our proposed method is efficient and also can be solved in polynomial time. Theoretical analysis and the Monte‐Carlo simulation results validate the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.

认知无线电系统中的多中继分布式波束成形方法

In this paper, the cognitive scenario where a source-destination pair of secondary users coexists with a licensed transmitter-receiver pair with the help of a group of cognitive relay nodes is considered. To exploit the spatial spectrum holes, we study the distributed beamforming of multiple cognitive relay nodes each equipped with a single antenna for the maximization of signal-to-interference-plus-noise ratio (SINR) at the cognitive destination, while keeping the interference power at the licenced receiver below a certain threshold and satisfying the individual power constraint. Two beamforming schemes are proposed: 1) the optimal scheme maximizing SINR; and 2) a suboptimal zero-forcing scheme. The optimal beamforming problem can be reformulated as a quasi-convex optimization problem using semide nite relaxation (SDR), then the bisection and interior point methods can be used to solve this problem. It can also be proved that SDR yields the optimal solution to the original problem. The suboptimal zero-forcing scheme eliminates the interference at the licensed receiver as well as the signals from the licensed transmitter. It has a low complexity without iterations and simple constraint functions. Numerical results are presented to show the impacts of the number of relay nodes, the maximum transmit power of cognitive nodes, and the threshold of power of interferences at the licenced receiver to the average achievable rates of the two schemes. Furthermore, the performance will be improved if the impact of signals from licenced transmitter is taken into account, which is veri ed through simulation experiments.

Distributed space‐time–frequency block code for cognitive wireless relay networks

In this study, the authors consider cooperative transmission in cognitive wireless relay networks (CWRNs) over frequency-selective fading channels. They propose a new distributed space-time–frequency block code (DSTFBC) for a two-hop non-regenerative CWRN, where a primary source node and multiple secondary source nodes convey information data to their desired primary destination node and multiple secondary destination nodes via multiple cognitive relay nodes with dynamic spectrum access. The proposed DSTFBC is designed to achieve spatial diversity gain as well as allow for low-complexity decoupling detection at the receiver. Pairwise error probability is then analysed to study the achievable diversity gain of the proposed DSTFBC for different channel models including Rician fading and mixed Rayleigh–Rician fading.

Performance Analysis of Amplify and Forward (AF)-based Cooperative Spectrum Sensing in Cognitive Radio Networks

Cognitive radio has been recently considered a promising technology to improve spectrum utilization by enabling secondary access to licensed bands that are not used by primary users temporarily or spatially. A prerequisite to this secondary access is the lack of interference to the primary system. This requirement makes spectrum sensing a key process for cognitive radio. In this study, we consider amplify and forward (AF)-based cooperative spectrum sensing for cognitive radio networks where multiple relay nodes are utilized to amplify and forward the primary user signal for better spectrum sensing, and maximum ratio combining is used for fusion detection by a cognitive coordinator. Further, the detection probability and the bit error rate of AF-based cooperative spectrum sensing are analyzed in fading multiple cognitive relay channels. The simulation results show that the AF-based cooperative spectrum sensing scheme outperforms the conventional scheme.

A Novel Transmission Scheme of Multiple Cognitive Relay Based on Network Coding

多中继感知协作通信技术是无线通信领域中，利用时空分集提升网络吞吐量的热门研究方向。该文首次提出了感知无线网中分布式译码转发后的中继冗余问题，并在理论与仿真上证明了现有传输协议不仅不足以支持多中继感知通信，而且由于其衍生了大量冗余而降低了网络吞吐量。针对该问题，该文提出了在缓存队列中结合随机网络编码的中继机制，从而有效地避免了中继冗余，使得多中继感知的吞吐量接近理想上界，减少缓存空间的占用，仿真结果表明该文提出的机制是一种高效实用的感知中继传输机制。

Energy Detection Based Cooperative Spectrum Sensing in Cognitive Radio Networks

Detection performance of an energy detector used for cooperative spectrum sensing in a cognitive radio network is investigated over channels with both multipath fading and shadowing. The analysis focuses on two fusion strategies: data fusion and decision fusion. Under data fusion, upper bounds for average detection probabilities are derived for four scenarios: 1) single cognitive relay; 2) multiple cognitive relays; 3) multiple cognitive relays with direct link; and 4) multi-hop cognitive relays. Under decision fusion, the exact detection and false alarm probabilities are derived under the generalized "k-out-of-n" fusion rule at the fusion center with consideration of errors in the reporting channel due to fading. The results are extended to a multi-hop network as well. Our analysis is validated by numerical and simulation results. Although this research focuses on Rayleigh multipath fading and lognormal shadowing, the analytical framework can be extended to channels with Nakagami-m multipath fading and lognormal shadowing as well.