共查询到20条相似文献，搜索用时 31 毫秒
1.
Considering the interference introduced by primary user, the outage probability of cognitive relay networks under imperfect channel state information is analyzed based, on the relay selection for the maximum channel gain. In addition, the mathematical optimization model of maximizing the spectrum efficiency under the interference constraint of primary user and the QoS requirement of cognitive user is proposed for cognitive relay networks. Then, the optimal solution of the model is obtained with the Lagrangian method. The proposed scheme improves the spectrum efficiency of cognitive relay networks on the premise of guaranteeing the transmission performance of primary user. Simulation results show that the proposed power allocation scheme improves the system performance compared with the traditional equal power allocation scheme. Meanwhile, it indicates that the approximate spectrum efficiency can be obtained under the perfect channel state and the imperfect channel state. Under the imperfect channel state, the feedback information and the complexity of implementation will be reduced, which is beneficial to the engineering application. 相似文献
2.
In order to calculate and analyze the effect of two transmission lines in parallel on the reliability evaluation of bulk power system, a model including independent outage, common mode outage and dependent outage of these lines is deduced and a new algorithm corresponding to the model is presented. Two transmission lines in parallel including common mode outages and dependent outages can be really simulated as a multi-state component. While reliability indices are calculated, the probability and frequency of independent outage, common mode outage and dependent outage of a system failure state can be calculated at the same time, and computation complexity is reduced. The proposed model and algorithm are applied to the RBTS system, IEEE One Area RTS96 system and a real power system for reliability computation and analysis. Results show that the new algorithm is credible and validity. 相似文献
3.
Wang Xiaoru Mi Linshu 《保鲜与加工》1989,(1):26-35
This paper applies the Gear-4 algorithm to constitute the companion models lor the circuit elements and electromagnetic relays commonly used in relay protective devices. The interface computation, which describes the node equation of companion model and differential equation of mechanical moving part for the electromagnetic Jelay, is also presented. For the reason mentioned above, it makes possible* to solve more accurately the transient process of relay protective devices including electromagnetic relay using the companion model method. The simplicity and effectiveness of interface computation have been proved by the example calcultaion. 相似文献
4.
This paper proposes a control strategy for the optimal control of the outsourcing production inventory system based on production point and production batch. The statistical probability distribution is used to describe the uncertainty of the production capacity of cooperative enterprises and the transportation time. The optimization model of the control parameters is developed with random production capacity for cooperative enterprises and random transportation time in order to minimize the holding cost,setup cost as well as the cost of production capacity waste. A simulation-based control parameters optimization algorithm is designed to solve the proposed model. The control strategy of production inventory system and the control parameters optimization algorithm proposed are validated by an example. We analyze the influence of the variation of the production point and production batch to the performance of the outsourcing production inventory system. 相似文献
5.
Aiming at the shortcomings of the existing RSS(received signal strength) based localization algorithm for wireless sensor networks (WSN), a cooperative localization algorithm (CLA) is proposed. A reference anchor node is introduced to tolerant some minor error including the node position error. Dixon detection method is applied to remove abnormal RSS values, while the standard deviation threshold of RSS and learning model are introduced to reduce the RSS ranging error and effectively improve the precision. Simulation experiments are performed to evaluate the performance of the proposed algorithm. The results demonstrate that the localization accuracy is improved effectively, while the stability and robustness are better. 相似文献
6.
For complex cooperative control problem of multi-agent systems, a distributed model predictive control scheme based on the dynamic cooperative rules is proposed. The collision avoidance constraint is transformed into hybrid rules based on the positions, and the Boolean function term was introduced in the cost function. In order to accommodate the complex time-varying environment, at each sample moment, the dynamic cooperative rules are designed according to the relative positions among the agents and the relative distances between the agents and the destination, so as to determine the weights in the Boolean function. This scheme reinforces consistencies of motion direction and control action, and improves stability and feasibility of distributed predictive control. As the control target can be achieved via a small prediction horizon, this scheme also enhances the real-time ability and practicality of distributed model predictive control. Simulation examples are given to illustrate the effectiveness of the proposed scheme. 相似文献
7.
Xu Guoyu Zhu Jizhong 《保鲜与加工》1990,(2)
A new approach of the automatic contingency selection and ranking with the network flow programming (NFP) is presented in this paper. NFP is adaptable to change the network topology as the transmission or generation branches arc in single or multiple outage. Thus the fast calculation of the contingency states by NFP cm provide the urgent information in real time N- 1 security analysis. In the paper, automatic contingency selection and ranking forP- and Q-type subproblem arc solved by an unified network flow model and algorithm. It is based on the existence of weak coupling between real and reactive quantities in power systems. The performance indices to assess the severity of contingencies are defined as the total real and reactive load required to be curtailed. The proposed ACS technique including the model and its algorithm are examined with IEEE 5-, 14-, 30-, 57- and 118- bus test systems on M-340. And the encouraging results are given in the paper. 相似文献
8.
电网发生大面积冰灾情况时,多条输电线路存在覆冰故障隐患,电网稳定运行受到严重威胁,需要提前制定输电线路融冰方案,合理安排融冰顺序。针对此问题,分析输电线路覆冰继续运行给电网带来的停电风险,将与待融冰输电线路相关联的变电站的电气主接线展开,将传统削负荷模型改进后应用于输电网与变电站主接线的组合网络,建立断路器可靠性模型,计算靠后融冰线路因继续运行的电网停电风险;利用计及风速及降雨影响的输电线路覆冰增长预测模型,计算输电线路的覆冰率,根据覆冰率门槛值确定待融冰线路集,基于覆冰严重度模型构建系统全局的覆冰指数指标;综合考虑电网停电风险及系统全局覆冰指数建立输电线路融冰紧迫度指标,动态更新待融冰线路并决策融冰顺序。最后,以IEEE RBTS系统进行算例分析,验证了所提方法的可行性与合理性。 相似文献
9.
通过揭示组织邻近性各维度与合作农业推广绩效间的关系，提高多元农业推广组织合作绩效。研究以实地调查和访谈法获取案例信息，对6 个合作农业推广项目进行探索性案例分析，包括案例内分析和案例间分析2 个阶段，构建“组织邻近性—合作模式—合作绩效”的理论预设。组织邻近性与合作绩效呈正相关关系，但具体维度的相关性存在差异，其中组织条件邻近与合作绩效关系不明确，组织结构邻近与合作绩效略为正相关，组织运作和关系邻近均与合作绩效正相关，而合作模式在组织邻近性与合作绩效间起部分中介作用。不同农业推广组织应根据组织邻近程度大小选择适当的合作模式，优化合作结构，维系合作关系，从而提高合作绩效。 相似文献
10.
Chen Wanming Zhou Jiaqi 《保鲜与加工》1992,(3):37-42
An A. C. load flow analysis of the reliability evaluation of composite generation and transmission systems is presented on the basis of a fast outage simulation algorithm and an optimal model of active and reactive power adjustment after outage contingencies. The information of the first -level outage events is utilized for simulating higher -level outage events in the fast outage simulation algorithm ; the optimal model is satisfactory in speed and accuracy with the application of concentric relaxation and linear increment constraint on the comprehensive adjustment of active and reactive power. As an example. the IEEE Reliability Test System is tested and the results show that the method is accurate and well-matched in speed with the method studied by R. Bllinton, et al. 相似文献
11.
Ran Li Ren Zhen Jiang Zejia 《保鲜与加工》1988,(6)
An optimal active power adjustment model is deve in this paper for hybrid AC/DC systems after outage contingencies. The objective of the model is to minimize the rejection of load when some elements are out of service, with adjustment strategy approaching practical system operation. A large number of outage contingencies are simulated when the Monte-Carlo Method is emyloyed to evaluate the system reliability, requiring fast calculation of each simulation. The model and computer method proposed in this paper satisfy such a requirment because of the application of concentric relaxation, recursive branch constraint treatment in linear programming and a direct method for B-1 matrix modification. This paper is concerned with the simplified steady state conditions of the system based on DC load-flow, which implies the reliability indices calculated are the measures about static loss of load. The results for a 14-bus hybrid AC/DC system are given. 相似文献
12.
《Journal of Landscape Research》2013,(Z1)
Ecological security of tourism destination is an important factor for the sustainable development of tourism industry, and many tourism destinations are threatened by various ecological problems. A complete understanding of eco-security situation is the foundation of maintaining sustainable development for tourism destinations. However, study on tourism destination eco-security has remained in the initial stage, based on domestic and international researches, the connotations and dynamic characteristics of tourism destination eco-security were discussed. Then, evaluation method of tourism destination eco-security and standard system were proposed, also dynamic evaluation method of tourism destination eco-safety based on the situation evaluation and trend was analyzed. 相似文献
13.
To increase the multicasting efficiency of Ad hoc networks, a fuzzy logic multicasting algorithm (FLMA) is proposed. FLMA adopts the fuzzy logic to tolerate the imprecise information caused by dynamic network topology. The two input variables of the fuzzy logic system are the relative degree of the additional coverage node number and the relative degree of the residual energy. The deferring time of rebroadcast is the output variable of the fuzzy logic system, which is used to optimize the priority of the nodes to rebroadcast. FLMA reduces the redundant retransmission and the chance of the contention and collision, while balances the energy consumption of the nodes. Simulation results reveal that the FLMA achieves better performance than BCAST in terms of the network lifetime, average end-to-end delay, the average number of drops per node and the throughput. 相似文献
14.
As one of important channels in rural revitalization and development, rural tourism obtains a lot of remarkable achievements in rural development. However, relatively single product and homogenized development model make competition gradually intensify, and many once glorious rural tourist destinations gradually decline. Xishan District of Kunming City of Yunnan Province is taken as research object in this paper. Via literature research, field survey and depth interview, development process, status quo and existing problems of its rural tourism are deeply explored. Based on above research results, development idea, strategy and countermeasure for quality improvement and effect increase of traditional rural tourism destination are proposed, and cooperative development, mutual benefit and win-win are taken as the ultimate development goals. 相似文献
15.
An orphogonal frequency division multiplexing(OFDM) based cognitive radio architecture was designed to meet the transmission requirements of a cognitive radio system. After finishing the allocation of subtransmission, and keeping BER within the limit that ensures service quality, an adaptive bit allocation method was proposed to allocate the bit and energy of subtransmission dynamically. The total power for launching needed reached its minimum (or SNR per bit reached its maximum). Compared with the fixed bit allocation method, the proposed method is simpler, decreases the system transmission power, and has better BER performance. 相似文献
16.
HU Xiao-bing~ 《保鲜与加工》2004,(8):132-135
In this paper the ant colony algorithm is applied to path planning problem in 3-D space for robot. First of all, the space between the origin where the robot is located and destination was divided into a three dimensional grid, at the same time the valid path from origin to destination is defined, then all the ants will leave from the origin, selecting next vertex independently in three dimensional grid, to the destination on a valid path. The simulated experiment shows that the algorithm is efficient and has a great convergence rate. 相似文献
17.
The mathematic models and basic theory of constant modulus algorithm (CMA) for blind channel equalization are introduced. An improved algorithm with variable step size is proposed based on CMA. The improved algorithm uses the mean square error (MSE) to obtain the new variable step size to solve the contradiction between the convergence rate and accuracy in traditional CMA with fixed step. To smooth the MSE learning curve for easy comparison, an ensemble average technique is used to analyze the performance of convergence with different step sizes. The theoretical analysis and the simulation results show that the improved algorithm is superior to the traditional constant modulus(CM) in terms of convergence speed and residual error. 相似文献
18.
玉米–大豆带状套作行距配置对作物生物量、根系形态及产量的影响 总被引：10，自引：0，他引：10
空间配置是影响间作套种作物生长和产量构成的关键因素之一。本研究固定玉米–大豆套作带宽200 cm,玉米采用宽窄行种植,设置4个玉米窄行行距为20 cm(A1)、40 cm(A2)、60 cm(A3)和80 cm(A4)套作处理,2个玉米和大豆净作对照处理,研究行距配置对套作系统中玉米和大豆生物量、根系及产量的影响。结果表明,套作大豆冠层光合有效辐射和红光/远红光比值均低于净作,且随着玉米窄行的增加而降低。套作系统中大豆地上地下生物量、总根长、根表面积和根体积从第三节龄期(V3)到盛花期(R2)逐渐增加,但随着玉米窄行的增加而降低。套作玉米地上地下生物量从抽雄期到成熟期逐渐增加,根体积却逐渐降低,但这些参数随玉米窄行的变宽而增加。玉米和大豆在带状套作系统中产量均低于净作,且随玉米窄行的变宽,玉米产量逐渐增加,2012和2013两年最大值平均为6181 kg hm–2,而大豆产量逐渐降低,两年最大值平均为1434 kg hm–2,产量变化与有效株数和粒数变化密切相关。此外,玉米–大豆带状套作群体土地当量比(LER)大于1.3,最大值出现在A2处理,分别为1.59(2012年)和1.61(2013年),且最大经济收益也出现在A2处理(2年每公顷平均收益为1.93万元)。因此,合理的行距配置对玉米–大豆带状套作系统中作物的生长、产量构成和群体效益具有重要的作用。 相似文献
19.
In order to comprehensively consider the possibility and the severity of frequency instability risk, this paper proposes the risk evaluation model and algorithm for frequency collapse of power grid. The uncertainties in generating dispatch, network topology and component outage are considered. The calculation method for system frequency variation is depicted while considering the active power deficiency arising from random failure of generating units, and then various probabilistic risk indices for frequency collapse are defined. The presented method can provide important reference information for evaluating the frequency collapse risk of power grid. The non-sequential Monte Carlo simulation-based results of IEEE-RTS79 show the correctness of the method. 相似文献
20.
For high precise frequency estimation of the short sinusoid signal at low signal-to-noise ratio (SNR), a weighted fusion algorithm for frequency estimation of the short signal with the same frequency and length (SFL-Signal) is proposed. The spectrum model of SFL-Signal and the phase compensation matrix with phase coherent and noise cancellation are constructed. Secondly, the SFL-signal spectrum is weight-fused with the phase compensation matrix to obtain the result almost the same as that of the spectrum of the phase-coherent sinusoid signal. Consequently, high frequency estimation precision is obtained with spectral peak searching of the weight-fusion spectrum. Algorithm analysis and simulation results show that, compared with the existing methods,the proposed algorithm works better in term of precision, calculation complexity, noise immunity, and fits for any type of SFL-Signal. 相似文献