为了降低IEEE 802.15.4MAC层数据帧丢包率,在分析丢包率的原因基础上,提出了一种基于Markov链的信道竞争机制模型.通过对网络发送、退避和信道检测状态的稳态概率进行数学推导,研究了信道碰撞和数据帧的丢包率分析式,研究了参数数据包到达速率、节点数量、误码率、后退指数、后退等待次数对碰撞概率和丢包率的影响.实验结果表明,与节点无休眠态的IEEE 802.15.4网络相比,节点丢包率平均降低了23.7％,模型较好地描述了提出的MAC层信道访问机制,合理的网络参数设置能够优化数据帧丢包率,研究结果对无线传感网的应用提供了可靠传输优化参考.

为了提高802.15.4网络吞吐量性能,设计了一种改进的节点状态转换过程,提出了一种考虑隐藏终端问题和重传的节点接入信道模型,并对模型进行分析计算.基于计算结果和信道状态模型分析,对考虑隐藏终端问题的数据碰撞概率、丢包率和网络吞吐量进行推导.最后研究了数据包到达率、退避指数和隐藏终端对网络吞吐量性能的影响.实验表明,模型较好地描述了节点接入信道过程,能够对网络吞吐量进行精准的动态分析.实验结果表明,与无重传机制的802.15.4网络相比,网络吞吐量增加了83.9％左右.与部分条件休眠的方法比较,网络吞吐量平均增加了13.3％,提出的模型能够有效提升网络吞吐量性能.

针对基于隐藏终端的802.15.4网络数据丢包问题,提出了一种时隙CSMA/CA算法的数学模型.基于模型推导建立数据丢包概率的数学模型,并研究隐藏终端对数据丢包现象的影响.然后研究不同网络参数如隐藏终端数、 λ、N、minBE和NB对数据丢包的影响.实验表明:通过合理的参数配置能够改善网络丢包问题,且相对于不考虑隐藏终端的情形,隐藏终端导致的丢包问题更加严重(高出25.2%).实验结果说明提出的算法模型较好的描述了802.15.4网络实际运行特征.

In order to improve the data transmission reliability in Media Access Control (MAC) layer for 802.15.4 network,this paper proposes a Markov chain model of node working process based on unsaturated state,and the derivation calculation is carried out for the steady-state probability of the node status.The two factors affecting the transmission reliability in MAC layer are researched:the failure of node access channel and the limit of maximum retransmission times,and the analytical formula of reliability performance is derived.The influence of the parameters including minBE,NB and λ and two factors on the reliability is analyzed,and the effects of the two kinds of factors on the reliability performance are compared.Experimental results show that compared with the node working model without sleep mechanism,the proposed model can greatly reduce channel conflict,and improve network reliability.

In order to decrease the frame packet lost rate in 802 . 15 . 4 network , this paper analyzed the packet lost rate based on the retransmission mechanism , proposed the mathematical model for the working process of network node in MAC layer , and derived the steady-state probability of the main state . Afterwards , this paper carried out the mathematical analysis for the retransmission probability and the packet lost rate . Finally , the effect of MAC layer parameters minBE , NB and network environment parameter λ、N、BER on the retransmission probability and the packet loss rate was compared through the experimental analysis . Experimental re-sults show that the node packet loss rate is reduced by 88 . 9%, compared with the data transmission performance without retrans-mission mechanism . And the model could accurately reflect the node data transmission characteristics . Furthermore , equilibrium pa-rameter deployment could effectively improve the data transmission success rate , and theoretical research could provide the reference for 802 . 15 . 4 network standard .

Aiming at the optimization problems of the data packet average service time of 802.15.4 MAC layer,this paper proposed a conversion mechanism of node state based on super frame structure,and analyzed the definition of the data packet average service time.After that,it derived the steady-state probability of the main state and the formula of the data packet aver-age service time by establishing the model of Markov chain on the state of the node.At last,this paper researched the influ-ence of the protocol parameters such as NB,BE,SO to the data packet service time of the steady-state probability.The research results show that,the data packet average service time is reduced by 2.3%,compared with other dormant node models.The model describes the working characteristics of 802.15.4 network nodes very well.The balanced configuration of protocol pa-rameters can improve the packet transmission performance.And the model can provide the reference for raising the real-time performance of the network.

针对IEEE 802.15.4 WSNs数据传输可靠性优化问题,提出了一种基于单跳通信的信道竞争算法模型。基于模型的数学推导,研究了MAC层数据包传输可靠性的影响因素,然后建立了可靠性性能指标的数学分析式;最后研究了协议参数minBE、NB和N对可靠性的影响,并分析了参数配置对信道接入失败和重传次数的影响。研究表明,相对于无休眠态的信道竞争算法,在网络规模较大时可靠性提高了94.5%,提出的算法模型能够有效改善数据传送的可靠性性能。

针对《汇编语言与微机原理》课程教学效果欠佳的问题,通过构建研究性课程,基于课程知识体系和学生兴趣,合理选择研究性教学内容,不断改进教学方法、注重理论联系实际,构建仿真实践平台和设计仿真案例.通过加强实践能力的培养,激发学生的学习兴趣等措施,以期提高课程教学效果和学生的创新能力,为社会培养具有较强动手能力和创新精神的微机应用型人才.

To reduce the delay of channel contention at the Medium Access Control(MAC) layer for IEEE 802.15.4 networks,a channel contention mechanism for nodes,with unsaturated load is designed.A mathematical model is built and a derivation is carried on to obtain the steady-state probability of the main state.According to the result of the model,the formula of channel access delay is derived based on the modeling of channel state conversion process.The impact of protocol parameters such as λ,NB and minBE on the performance of node access delay is researched,and it is compared with the delay performance of the saturated load network.Analysis results show that the new model can describe and evaluate the mechanism of channel contention access very well,and the competition optimization mechanism can reduce effectively the deterioration degree of channel.Moreover,settings of protocol parameters can improve the performance of channel contention delay.

针对C语言课程教学效果欠佳的现状,提出基于OBE教育理念的C语言课程教学方案.以最终学习目标为出发点进行反向课程设计,主要从教学内容、教学策略、拓展实践、考核方式等方面进行C语言课程教学模式研究和改革.在C语言课程教学中实施基于成果导向教育的教学模式,能够使学生清晰的了解学习本课程后会达到的学习成果和能力,从而激发学生的自主学习兴趣,有效的提高C语言课程的教学质量、教学水平和学生的学习成效.

To optimize the performance of media access control( MAC) protocol for ZigBee network,a mechanism based on saturated traffic for channel competitive access is proposed. This paper establishes a Markov chain model for the process of node state transition. The numerical analysis of throughput and node average power consumption based on the mechanism is carried out. The impact of protocol parameters such as NB and aminBE on the performance of conflict probability,throughput and node average power consumption is researched. The results show that this model can describe the mechanism of channel competitive access well and that the reasonable settings for parameters can improve the performance of the MAC protocol.

To optimize the performance of MAC in 6LoWPAN,this paper proposed a mechanism based on saturated traffic for slotted CSMA/CA algorithm,and it established a Markov chain model for it.Then,this paper gave ont an expression using the new model for calculating the main parameters.Furthermore,it carried out the numerical analysis based on the model of the node access delay and channel access probability,and analyzed the impact of protocol parameters to the node average access delays.Finally,by the theoretical analysis showes that the model describes the slotted CSMA/CA mechanism well,and reasonable settings for CSMA/CA parameters can improve the performance of node average access delay.

Aiming at energy consumption optimisation of 6LoWPAN network,in this paper we propose a channel access mechanism in which the packet arrival rate subjects to Poisson distribution: in active period of the superframe,those nodes without data transmission or unable to send data temporarily will transfer to dormant period for energy saving,then we set up a Markov chain model for this mechanism.Based on the model,we carry out mathematical analysis on the steady state probability of node dormant status,the service time of data packets and the average energy consumption of the node,and study the impact of protocol parameters such as λ and BO on network performance.Mathematical analyses demonstrate that the improved model describes channel competitive process of 6LoWPAN network well and reduces the average energy consumption of node effectively.

In order to improve the performance of energy consumption for 6LoWPAN network,a channel contention mechanism based on superframe sleep period was proposed.Then a Markov chain model was established for the mechanism.Based on this model,the mathematical analysis on the steady-state probability of sending state,channel conflict probability and node average energy consumption was performed,and moreover the influence of the protocol parameters λ、minBE and NB on the network performance such as energy consumption was also analyzed.Finally,it is showed by the theoretical analysis that our model describes the MAC protocol of 6LoWPAN very well.The new mechanism reduces the network energy consumption,and the performance of protocol is improved.

Aiming at the problems of the lowly energy efficiency in LEACH protocol,we proposed an energy consumption mode of WSNs clustering protocol in the condition that sensor nodes followed the Poisson distribution.Firstly,we inferred the power consumption of cluster head,node and the clustering protocol.Secondly,the optimization analysis of cluster numbers based on the power consumption was carried out,and the network lifetime was calculated.Finally,we analyzed the network performance which was impacted by sensor nodes Poisson distribution density.The theoretical analysis and simulation results show that both the energy performance and the network lifetime of WSNs clustering protocol could be improved effectively by increasing the node Poisson distribution density suitably and choose the optimal cluster numbers.

A clustering method based on element of XML schema is brought forward in this paper.The key of clustering is to aggregate the similar things together.Therefore,the similarity is the important foundation for XML clustering.Schema is the representation of document structure,and clustering of XML documents can be achieved through clustering of XML schemas.The authors of this paper cluster documents by calculating the similarity of elements,because elements are the main body in XML.The approach takes full account of the structure and semantics of elements,and makes a more accurate calculation of similarity.In the meanwhile,it improves the accuracy of clustering and makes it easy to extract the common XML schema.

Programming experimental teaching is an important link in computer education. Aiming at the problems in experimental teaching of programming, the authors of this paper present the reform way from the aspects of the experimental teaching content, teaching methods, teaching management, and assessment methods.

In order to reduce the energy consumption of a 6LoWPAN node,a channel contention access mechanism based on enabled node sleep state is proposed.In the mechanism,nodes can appropriately sleep during both the superframe backoff period time and the superframe dormant period.Then a Markov chain model is established for the mechanism,and the corresponding mathematical derivation is carried out.Based on this model,the mathematical analysis on the average energy consumption,the steady-state probability of sending packets and the packet service time is performed,and moreover the influence of the protocol parameters NB and minBE on the network performance is also analyzed.The mathematical analysis shows that the model describes the channel contention access mechanism of 6LoWPAN very well,and the mechanism effectively reduces the average consumption and greatly improves the protocol performance.