Reputation-Based Hierarchically Cooperative Spectrum Sensing Scheme in Cognitive Radio Networks

Cooperative spectrum sensing in cog- nitive radio is investigated to improve the det- ection performance of Primary User （PU）. Meanwhile, cluster-based hierarchical coop- eration is introduced for reducing the overhead as well as maintaining a certain level of sens- ing performance. However, in existing hierar- chically cooperative spectrum sensing algo- rithms, the robustness problem of the system is seldom considered. In this paper, we pro- pose a reputation-based hierarchically coop- erative spectrum sensing scheme in Cognitive Radio Networks （CRNs）. Before spectrum sensing, clusters are grouped based on the location correlation coefficients of Secondary Users （SUs）. In the proposed scheme, there are two levels of cooperation, the first one is performed within a cluster and the second one is carried out among clusters. With the reputa- tion mechanism and modified MAJORITY rule in the second level cooperation, the pro- posed scheme can not only relieve the influ- ence of the shadowing, but also eliminate the impact of the PU emulation attack on a rela- tively large scale. Simulation results show that, in the scenarios with deep-shadowing or mul- tiple attacked SUs, our proposed scheme ach- ieves a better tradeoff between the system robustness and the energy saving compared with those conventionally cooperative sensing schemes.     

Variable Persistence Sensing Schemes for Opportunistic Spectrum Access

Cognition technologies can significantly enhance spectrum utilization through secondary usage. Secondary users （SUs） search for spectrum holes which are not used by Primary users （PUs） and communicate through them. The design and analysis of simple opportunistic spectrum access schemes for maximizing utilization efficiency and minimizing delay of SUs under limited sensing bandwidth and energy is still at infancy. In this work, we consider PU＇s frequency occupancy patterns and propose three simple variable persistence sensing schemes for maximum exploitation of idle spectrum chunks by SUs, and perform their theoretical analysis. Numerical case studies are presented to verify the theoretical analysis and illustrate the performance of the schemes proposed.     

Joint impact of sensing time and SPRF parameter on the performance of a continuous energy harvesting cooperative cognitive radio network

Joint impact of sensing time and signal power raise factor is studied for an improved energy detector–based energy harvesting cooperative cognitive radio network. All the cognitive radio nodes harvest energy either from radio frequency resources or from non–radio frequency resources. The probability density function of harvested energy from both the sources is exponentially distributed. Novel theoretical expressions for harvested energy and throughput are derived. Impact of several sensing parameters and a device constraint on the outage is studied. Optimal values of sensing time and signal power raise factor parameter pair are estimated for maximum harvested energy and maximum throughput. Energy efficiency of the network is also evaluated, and impact of sensing time on it is indicated.     

Time Agility Optimization for Dual-stage Collaborative Spectrum Sensing

Cooperative spectrum sensing has been shown to be an effective method to mitigate the impact of hidden terminal and shadow fading in cognitive radio networks. Currently most works focused on either coop- erative sensing or sensing scheduling as a viable means to improve the detection performance without studying their interactions. This paper proposed a dynamic and variable time-division multiple-access scheduling mechanism that was incorporated into a Dual-stage collaborative spectrum sensing （DCSS） model in a less ideal radio environment. Moreover, this paper derived closed-form expressions of sensing time for DCSS, and addressed the critical range of timeslot length. An optimized algorithm to minimize sens- ing time was deduced and verified. The simulation results indicate that average sensing time with DCSS is shortened by 11.5~V0 when compared with that of the Single collabora- tive spectrum sensing （SCSS） while guaranteeing detection error rate requirement of less than 1%.     

Performance optimisation of RF energy harvesting relay-based interweave/underlay cognitive radio network

This paper investigates the performance of energy harvesting (EH) relay-based interweave/underlay cognitive radio network. The relay employs amplify and forward (AF) technique along with time-switching relaying protocol (TSR) for EH. Based on sensing accuracy, we derive an expression for optimisation of charging duration TSR parameter and sensing duration for maximising throughput of interweave cognitive radio (CR). Based on sensing efficiency, throughput and outage probability for underlay CR is analysed considering the interference temperature constraints and optimal power distribution parameter at secondary user (SU) terminals. Variations in the sum-rate and detection probability are considered in terms of cumulative distribution functions (CDF) of the terminal Signal to Noise Ratios (SNRs). We prove that erogodic sum-rate is maximised in underlay CR case, when interference power distribution parameter is half across the SU terminals. The optimised values of switching-time ratios have been derived analytically for both interweave and underlay CR. The results thus obtained are compared by taking symmetrical and asymmetric channels between SU terminals. Analytical results are validated through Monte-Carlo simulations to confirm the accuracy of the derived expressions.     

Optimization of Time-Domain Combining Cooperative Spectrum Sensing in Cognitive Radio Networks

In cognitive radio networks, the secondary users take chances to access the spectrum without causing interference to the primary users so that the spectrum access is dynamic and somewhat opportunistic. Therefore, spectrum sensing is of significant importance. In this paper, we propose a novel time-domain combining cooperative spectrum sensing framework, in which the time consumed by reporting for one secondary user is also utilized for other secondary users’ sensing. We focus on the optimal sensing settings of the proposed sensing scheme to maximize the secondary users’ throughput and minimize the average sensing error probability under the constraint that the primary users are sufficiently protected. Some simple algorithms are also derived to calculate the optimal solutions. Simulation results show that fundamental improvement of the achievable throughput and sensing performance can be obtained by optimal sensing settings. In addition, our proposed scheme outperforms the general frame structure on either achievable throughput or the performance of average sensing error probability.     

Optimal Spectrum Sensing in Energy Harvesting Cognitive Radio Systems

In this paper,we consider a cognitive radio system with energy harvesting,in which the secondary user operates in a saving-sensing-transmitting（SST） fashion.We investigate the tradeoff between energy harvesting,channel sensing and data transmission and focus on the optimal SST structure to maximize the SU＇s expected achievable throughput.We consider imperfect knowledge of energy harvesting rate,which cannot be exactly known and only its statistical information is available.By formulating the problem of expected achievable throughput optimization as a mixed-integer non-linear programming one,we derive the optimal saveratio and number of sensed channels with indepth analysis.Simulation results show that the optimal SST structure outperforms random one and performance gain can be enhanced by increasing the SU＇s energy harvesting rate.     

Optimized Reliable Data Combining Cooperative Spectrum Sensing Method in Cognitive Radio Networks

Spectrum sensing is one of the most important tasks of each cognitive radio network. Cooperation among secondary users, by increasing the sensing accuracy can improve the network throughput, but also increases the energy consumption of cognitive radio network. In this paper, we propose the reliable data combining method for cooperative spectrum sensing, according to which the fusion center by using two threshold values, makes the final decision only if it is confident enough in validity of received local data. Otherwise, an additional sensing will be performed. Throughput maximization problems under interference constraints are formulated for both soft and hard fusion schemes and the optimal sensing time and threshold values are obtained. Simulations show that for all SNRs, higher absolute throughput and also higher throughput per energy consumption are accessible, rather than conventional cooperative sensing. Moreover, for a large range of SNRs the less energy is consumed.     

使次系统容量最大化的协作频谱感知性能分析及优化

针对认知无线电网络中SU数、检测门限、带宽、频谱利用率和次系统容量间关系的分析表明,一方面C-CSS不仅可降低虚警率、提高频谱利用率,还可利用较少的SU实现较高的次系统容量;另一方面在SU数一定且满足目标要求时,C-CSS与T-CSS实现最大次系统容量所要求的检测门限不同.提出协作频谱感知优化算法,利用NP准则通过直接对数学模型求解即可得到使次系统容量最大的SU数和相应检测门限.理论分析和仿真结果均表明,所提算法在保证目标检测率的前提下最大化了次系统容量.     

Throughput performance under primary user emulation attack in cognitive radio networks

Spectrum sensing in cognitive radio networks imposes some security threats to the secondary users (SUs) such as primary user emulation attack (PUEA). In the present paper, throughput of an SU is studied for cognitive radio network under PUEA where SU spectrum access is hybrid, ie, either in overlay mode or in underlay mode. A novel analytical expression for throughput of an SU in presence of PUEA is developed. Impact of several parameters such as sensing time, attacker strength, attacker's presence probabilities, maximum allowable SU transmit power, and tolerable interference limit at primary user on the throughput of an SU is investigated. The throughput performance under PUEA and without PUEA is compared.     

A RT Steganalytic Method for Optimal Parity Assignment Algorithm

Steganography is the art of transmitting a message by embedding it into multimedia data without drawing any suspicions. OPA （Optimal parity assignment） algorithm is one of the most secure steganographlc methods for palette format images. In this paper, we present RT （Replacement transfer） steganalytic algorithm for detecting the secret messages embedded by OPA and the improved algorithm. Based on the analysis of Replacementtransfer structure （RTS） of colors, we explore the singular statistics of core colors in OPA stego-images via replacement operation. In addition, we can estimate statistics of the cover-image from the corresponding stego-lmage by an average filtering operation. With the estimation of statistics of the cover image and the singular statistics of the stego-image, the length of secret messages embedded in palette format images with OPA and the improved algorithm can be estimated. The experimental results indicate that the RT steganalytic algorithm is eiTective and accurate.     

Home Energy Management System Using NILM and Low-Cost HAN

Home energy management systems(HEMs) are used to provide comfortable life for consumers as well as to save energy. An essential component of HEMs is a home area network(HAN) that is used to remotely control the electric devices at homes and buildings. Although HAN prices have dropped in recent years but they are still expensive enough to prohibit a mass scale deployments. In this paper, a very low cost alternative to the expensive HANs is presented. We have applied a combination of non-intrusive load monitoring(NILM) and very low cost one-way HAN to develop a HEM. By using NILM and machine learning algorithms we find the status of devices and their energy consumption from a central meter and communicate with devices through the one-way HAN. The evaluations show that the proposed machine learning algorithm for NILM achieves up to 99% accuracy in certain cases. On the other hand our radio frequency(RF)-based one-way HAN achieves a range of 80 feet in all settings.     

Automatic Recognition Algorithm of AM Signals Based on Spectrum and Modulation Characters

To meet the actual requirement of automatic monitoring of the shortwave signals under wide band ranges, a technique for automatic recognition is studied in this paper. And basing upon the spectrum and modulation characters of amplitude modulation （AM） signals, an automatic recognition scheme for AM signals is proposed. The proposed scheme is achieved by a joint judgment with four different characteristic parameters. Experiment results indicate that the proposed scheme can effectively recognize AM signals in practice.     

A Pulse Immunization Model for Inhibiting Malware Propagation in Mobile Wireless Sensor Networks

Mobile wireless sensor networks （MWSNs） may be under attack due to their large-scale characteristics. One of the main threats is to inject malware into some nodes. To prevent malware from spreading in a largescale MWSN, an effective measure is to immunize susceptible nodes by disseminating and installing security patches. This work suggests a novel modeling framework and some mathematical models based on the pulse differential equation and the epidemic theory, in which the immunization operations are implemented on susceptible nodes in a pulse way. The maximum immunization period of time is derived to minimine the number of immunization operations while ensuring malware extinct over time in the MWSN. The theoretical results are confirmed by extenslve simulations.     

认知无线网络中应用空闲认知用户的联合随机频谱检测策略

针对认知网络中主用户状态的不确定性和随机检测策略无法保证认知用户准确地寻找可用信道的问题,该文提出一种利用认知无线网络中空闲认知用户进行联合随机检测的策略。在加入空闲认知用户进行检测后,利用马尔科夫模型对认知基站获得的可用信道数进行描述,推导出此时认知网络的检测性能。理论分析和仿真结果表明,利用空闲认知用户可以减少服务时延,提高认知网络的吞吐量。在考虑认知用户汇报检测信息所占用的时长后,通过优化算法得出最优的参与联合检测的空闲认知用户数。     

On l-th NMDS Codes

Linear codes with Singleton defects equivalent to 0, 1, 2 are studied, and they have good properties. They are called MDS codes, NMDS codes, NNMDS cdoes, respectively. In this paper, we study linear codes with large Singleton defects and these codes have same good properties with MDS codes, NMDS codes, NNMDS codes. We call them l-th NNIDS codes. A series of iff con- ditions of l-th NMDS codes is presented. And we give an upper bound on length of l-th NMDS codes. In the last, some examples of l-th NMDS codes are given.     

Optimal energy efficiency capacity under joint design of sensing and transmission duration for cognitive radio system

Due to its opportunistic spectrum sharing capability, cognitive radio （CR） has been proposed as a fundamental solution to alleviate the contradiction between spectrum scarcity and inefficient utilization of licensed spectrum. In CR system （CRS）, to efficiently utilize the spectrum resource, one important issue is to allocate the sensing and transmission duration reasonably. In this paper, the evaluation metric of energy efficiency, which represented the total number of bits that were delivered with per joule of energy consumed, is adopted to evaluate the proposed scheme. We study a joint design of energy efficient sensing and transmission durations to maximize energy efficiency capacity （EEC） of CRS. The tradeoff between EEC and sensing and transmission durations are formulized as an optimization problem under constraints on target detection probability of secondary users （SUs） and toleration interference threshold of primary users （PUs）. To obtain the optimal solution, optimizing sensing duration and transmission duration will be first performed separately. Then, a joint optimization iterative algorithm is proposed to search the optimal pair of sensing and transmission durations. Analytical and simulation results show that there exists a unique duration pair where the EEC is maximized, and that the EEC of the proposed joint optimization algorithm outperforms that of existed algorithms. Furthermore, the simulation results also reveal that the performance of the proposed low complexity iterative algorithm is comparable with that of the exhaustive search scheme.     

Energy Detection in Hoyt/Gamma Fading Channel with Micro-Diversity Reception

Spectrum sensing is the important function of cognitive radio and energy detection is the most popular technique used for spectrum sensing. Detection of the availability of unused spectrum for the secondary user becomes difficult when the channel is affected by composite multipath/shadowed fading. In this paper, the performance analysis of an Energy Detector in Hoyt/gamma composite fading channel with Maximum Ratio Combining employing micro-diversity is analyzed. Analytical expressions for performance parameters, i.e., the average probability of detection and the average area under the receiver operating characteristics curve are evaluate. The effect of diversity on the performance of energy detector is also studied. Monte-Carlo simulation results have verified the accuracy of the proposed analysis.     

Stable Throughput of Cognitive Radios With and Without Relaying Capability

A scenario with two single-user links, one licensed to use the spectral resource (primary) and one unlicensed (secondary or cognitive), is considered. According to the cognitive radio principle, the activity of the secondary link is required not to interfere with the performance of the primary. Therefore, in this paper, it is assumed that the cognitive link accesses the channel only when sensed idle. Moreover, the analysis includes: (1) random packet arrivals; (2) sensing errors due to fading at the secondary link; (3) power allocation at the secondary transmitter based on long-term measurements. In this framework, the maximum stable throughput of the cognitive link (in packets/slot) is derived for a fixed throughput selected by the primary link. The model is modified so as to allow the secondary transmitter to act as a ldquotransparentrdquo relay for the primary link. In particular, packets that are not received correctly by the intended destination might be decoded successfully by the secondary transmitter. The latter can, then, queue and forward these packets to the intended receiver. A stable throughput of the secondary link with relaying is derived under the same conditions as before. Results show that benefits of relaying strongly depend on the topology (i.e., average channel powers) of the network.     

Carrier Frequency Offset Estimation for MIMO over Spatially Correlated Flat-fading Channels

This paper deals with Carrier frequency offset （CFO） estimation for Multiple-input multiple-output （MIMO） systems. A Rayleigh fiat-fading channel model is considered and spatial correlation among channels corresponding to different pairs of transmit and receive antennas is taken into account. A Data-aided （DA） Maximum likelihood （ML）CFO estimator based on the marginal likeli- hood function is proposed. It can exploit spatial diversity and make use of the knowledge of spatial correlation by averaging the conditional likelihood function over all realizations of the channel. The Cramer-Rao bound （CRB） for the problem is derived as a benchmark. Simulation results are given to illustrate the performance of the pro- posed estimator. It is shown that its performance is close to the CRB at high Signal-to-noise ratio （SNR） region and improved with decrease of the spatial correlation and in- crease of the number of receive antennas.