Non-Cooperative Spectrum Sensing Based on Cyclostationary Model of Digital Signals in the Context of Cognitive Radio

This paper addresses the problem of the opportunistic spectrum access in Cognitive Radio. Indeed, most spectrum sensing algorithms suffer from a high computational cost to achieve the detection process. They need a prior knowledge of signal characteristics and present a bad performance in low Signal to Noise Ratio (SNR) environment. The choice of the optimal detection threshold is another issue for these spectrum sensing algorithms. To overcome the limits of spectrum detectors, we propose in this paper, a blind detection method based on the cyclostationary features of communication signals. Our detector evaluates the level of hidden periodicity contained in the observed signal to make decision on the state of a bandwidth. In order to reduce the computational cost, we take advantage of the FFT Accumulation Method to estimate the cyclic spectrum of the observed signal. Then, we generate the Cyclic Domain Profile of the cyclic spectrum which allows us to evaluate the level of the hidden periodicity in the signal. This level of periodicity is quantified through the crest factor of Cyclic Domain Profile, which represents the decision statistic of the proposed detector. We have established the analytic expression of the optimal threshold of the detection and the probability of detection to evaluate the performance of the proposed detector. Simulation results show that the proposed detector is able to detect the presence of a communication signal on a bandwidth in a very low SNR scenario.

Common Prosperity and Reshaping China's Economic Cycle: Theoretical Logic and Empirical Evidence from a Political Economic Perspective

Fostering a new development dynamic is in nature about reshaping the relations between domestic and international economic cycles to achieve self-reliance and self-strengthening at higher levels.Economic cycle is the integration of various links such as production,distribution,exchange and consumption.This paper attempts to study the influence on economic cycle from income distribution based on the principles of political economy and therefore link common prosperity with the new development dynamic.It finds that labor income share is central to income distribution.On the supply side,income distribution affects choice of technology and production eficiency through changing wages;on the demand side,it influences size of demand and level of capacity utilization both directly and indirectly.Specifically,changing wages lead to changing size of reproduction and consumption by laborers in the direct way and cause changing profit margins and thus affect accumulation in the indirect way.The two channels produce effects simultaneously,yet in opposite directions,which justifies the categorization of economies into"profit-oriented"and"wage-oriented"ones according to the different influence of changing wages on the level of capacity utilization.In this theoretical logic,the paper comprehensively analyzes China's income distribution,wages,all labor productivity,organic composition of capital,profit margins,accumulation rates,level of capacity utilization and relations between domestic and international economic cycles,and finds that Chinese economy has turned from"profit-oriented"to"wageoriented"since the turning point of 2010.It signals both necessity and feasibility of promoting common prosperity and fostering a new development dynamic.This paper also proposes some policy suggestions on promoting common prosperity from the perspectives of ownership,distribution,government-market relations and spatial structure.

An orthogonally accumulated projection method for symmetric linear system of equations

A direct as well as iterative method(called the orthogonally accumulated projection method, or the OAP for short) for solving linear system of equations with symmetric coefficient matrix is introduced in this paper. With the Lanczos process the OAP creates a sequence of mutually orthogonal vectors, on the basis of which the projections of the unknown vectors are easily obtained, and thus the approximations to the unknown vectors can be simply constructed by a combination of these projections. This method is an application of the accumulated projection technique proposed recently by the authors of this paper, and can be regarded as a match of conjugate gradient method(CG) in its nature since both the CG and the OAP can be regarded as iterative methods, too. Unlike the CG method which can be only used to solve linear systems with symmetric positive definite coefficient matrices, the OAP can be used to handle systems with indefinite symmetric matrices. Unlike classical Krylov subspace methods which usually ignore the issue of loss of orthogonality, OAP uses an effective approach to detect the loss of orthogonality and a restart strategy is used to handle the loss of orthogonality.Numerical experiments are presented to demonstrate the efficiency of the OAP.

Effect of low temperature in the development cycle of Lucilia sericata (Meigen) (Diptera, Calliphoridae): implications for the minimum postmortem interval estimation

Knowledge of necrophagous insects' developmental data is necessary for the forensic entomologist to estimate a reliable minimum postmortem interval (PMImin).Among the most represented necrophagous species,Lucilia sericata (Diptera,Calliphoridae) is particularly interesting.It is regularly identified in samples,with a predominance in summer,and is commonly used by analysts of our entomology department (Institut de Recherche Criminelle de la Gendarmerie Nationale) to estimate the PMImin with the accumulated degree days (ADD) method.This method requires the mathematical lower thermal threshold to be known.This value dictates the quality of the applied ADD method but cannot be considered as fixed,especially when insect development occurs at temperatures close to the biological threshold.In such conditions,it is necessary to study the influence of such temperatures on development rate,as well as the consequences of estimating the period of first oviposition on cadavers,when using the ADD method.Seven replicate rearings were conducted at six different temperatures: 30 ℃,24 ℃,18 ℃,15 ℃,12 ℃ and 10 ℃.Time of development and time of emergence were recorded.The effect of low temperature on the development cycle and the reliability of the ADD method under this entire temperature spectrum were studied using different linear regression models.Calculated durations of total insect time development and experimental rearing duration were then compared.A global linear model cannot be used on the whole temperature spectrum experienced by L.sericata without resulting in an overestimation at some temperatures.We found a combination of two linear regression models to be suitable for the estimation of the total development time,depending on the temperature experienced by L.sericata.This approach allowed us to obtain a variation lower than 2% at 12 ℃ and 10 ℃ between the calculated duration and experimental duration of development.In comparison,the results obtained with a global model show a variation higher than 3% at 12 ℃ and 10%at 10℃.