The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theo...The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theory of contact mechanics,a theoretical model of the indentation depth of abrasive grain was developed and the relationships between indentation depth and properties of contact pairs and abrasive back-off were studied.Also,the average surface roughness(Ra)of lapped wafer was approximately calculated according to the obtained indentation depth.To verify the rationality of the proposed model,a series of lapping experiments on lithium niobate(LN)wafers were carried out,whose average surface roughness Ra was measured by atomic force microscope(AFM).The experimental results were coincided with the theoretical predictions,verifying the rationality of the proposed model.It is concluded that the indentation depth of the fixed abrasive was primarily affected by the applied load,wafer micro hardness and pad Young′s modulus and so on.Moreover,the larger the applied load,the more significant the back-off of the abrasive grain.The model established in this paper is helpful to the design of FA pad and its machining parameters,and the prediction of Ra as well.展开更多
The truncated binary exponential back-off algorithm is one of the most effective methods applied in collision resolution process of random multi-access channel.In this study,two new strategies are presented to improve...The truncated binary exponential back-off algorithm is one of the most effective methods applied in collision resolution process of random multi-access channel.In this study,two new strategies are presented to improve the capability of the truncated binary exponential back-off algorithm.In the new strategies,the sizes of the initial window size or the operating window sizes are adjusted dynamically,which always bring a significant improvement for the self-adaptability of the original algorithm.A series of experiments are simulated and the results verify that the new strategies can make the implementation more stable and effective than the original algorithm.展开更多
Any node in a wireless sensor network is a resource constrained device in terms of memory, bandwidth, and energy, which leads to a large number of packet drops, low throughput, and significant waste of energy due to r...Any node in a wireless sensor network is a resource constrained device in terms of memory, bandwidth, and energy, which leads to a large number of packet drops, low throughput, and significant waste of energy due to retransmission. This paper presents a new approach for predicting congestion using a probabilistic method and controlling congestion using new rate control methods. The probabilistic approach used for prediction of the occurrence of congestion in a node is developed using data traffic and buffer occupancy. The rate control method uses a back-off selection scheme and also rate allocation schemes, namely rate regulation(RRG) and split protocol(SP), to improve throughput and reduce packet drop. A back-off interval selection scheme is introduced in combination with rate reduction(RR) and RRG. The back-off interval selection scheme considers channel state and collision-free transmission to prevent congestion. Simulations were conducted and the results were compared with those of decentralized predictive congestion control(DPCC) and adaptive duty-cycle based congestion control(ADCC). The results showed that the proposed method reduces congestion and improves performance.展开更多
Cognitive radio technology makes efficient use of the valuable radio frequency spectrum in a non-interfering manner to solve the problem of spectrum scarcity. This paper aims to design a scheme for the concurrent use ...Cognitive radio technology makes efficient use of the valuable radio frequency spectrum in a non-interfering manner to solve the problem of spectrum scarcity. This paper aims to design a scheme for the concurrent use of licensed frequencies by Underlay Cognitive Users （UCUs）. We develop a new receiver-initiated Medium Access Control （MAC） protocol to facilitate the selections of alternative reliable carrier frequencies. A circuit is designed to establish reliable carrier selections based on the Received Signal Strength Indicator （RSSI） at the receiving end. Based on both packet-level simulations and various performance parameters, a comparison is carried out among conventional techniques, including the Multiple Access with Collision Avoidance （MACA） and MACA by invitation（MACA-BI） techniques, and our scheme. The simulated results demonstrate that when conventional techniques are used, the system overhead time increases from 0.5 s on the first attempt to 16.5 s on the sixth attempt. In the proposed scheme under the same failure condition, overhead time varies from 0.5 s to 2 s. This improvement is due to the complete elimination of the exponential waiting time that occurs during failed transmissions. An average efficiency of 60% is achieved with our scheme while only 43% and 34% average efficiencies are achieved with the MACA and MACA-BI techniques, respectively. The throughput performance of our scheme on the fourth attempt is 7 Mbps, whereas for the MACA and MACA-BI protocols, it is 1.9 Mbps and 2.2 Mbps respectively.展开更多
在无线自组织网络中,合理的退避机制能够有效地利用网络资源,解决多个节点同时抢占共享信道的问题,提高网络带宽利用率。通过建立模型深入分析了由于隐藏终端产生的流不公平问题,给出了一种吞吐量变化率和流不公平度的度量,并提出了一...在无线自组织网络中,合理的退避机制能够有效地利用网络资源,解决多个节点同时抢占共享信道的问题,提高网络带宽利用率。通过建立模型深入分析了由于隐藏终端产生的流不公平问题,给出了一种吞吐量变化率和流不公平度的度量,并提出了一种通过调整退避窗口最小值来改善流公平性的退避算法——BFF(Back-off based on Flow Fairness)算法。通过仿真分析表明算法能够很好地提高公平性,解决BEB算法在实际运用中的流不公平问题。展开更多
基金supported by the Science Foundation of Aviation(No.2014ZE52055)the National Science Foundation of China(No.51675276)+1 种基金the Funding of Jiangsu Innovation Program for Graduate Education(No.KYLX_0231)the Fundamental Research Funds for the Central Universities
文摘The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theory of contact mechanics,a theoretical model of the indentation depth of abrasive grain was developed and the relationships between indentation depth and properties of contact pairs and abrasive back-off were studied.Also,the average surface roughness(Ra)of lapped wafer was approximately calculated according to the obtained indentation depth.To verify the rationality of the proposed model,a series of lapping experiments on lithium niobate(LN)wafers were carried out,whose average surface roughness Ra was measured by atomic force microscope(AFM).The experimental results were coincided with the theoretical predictions,verifying the rationality of the proposed model.It is concluded that the indentation depth of the fixed abrasive was primarily affected by the applied load,wafer micro hardness and pad Young′s modulus and so on.Moreover,the larger the applied load,the more significant the back-off of the abrasive grain.The model established in this paper is helpful to the design of FA pad and its machining parameters,and the prediction of Ra as well.
基金This work was supported by the National Natural Science Foundation of China(No.10371097).
文摘The truncated binary exponential back-off algorithm is one of the most effective methods applied in collision resolution process of random multi-access channel.In this study,two new strategies are presented to improve the capability of the truncated binary exponential back-off algorithm.In the new strategies,the sizes of the initial window size or the operating window sizes are adjusted dynamically,which always bring a significant improvement for the self-adaptability of the original algorithm.A series of experiments are simulated and the results verify that the new strategies can make the implementation more stable and effective than the original algorithm.
文摘Any node in a wireless sensor network is a resource constrained device in terms of memory, bandwidth, and energy, which leads to a large number of packet drops, low throughput, and significant waste of energy due to retransmission. This paper presents a new approach for predicting congestion using a probabilistic method and controlling congestion using new rate control methods. The probabilistic approach used for prediction of the occurrence of congestion in a node is developed using data traffic and buffer occupancy. The rate control method uses a back-off selection scheme and also rate allocation schemes, namely rate regulation(RRG) and split protocol(SP), to improve throughput and reduce packet drop. A back-off interval selection scheme is introduced in combination with rate reduction(RR) and RRG. The back-off interval selection scheme considers channel state and collision-free transmission to prevent congestion. Simulations were conducted and the results were compared with those of decentralized predictive congestion control(DPCC) and adaptive duty-cycle based congestion control(ADCC). The results showed that the proposed method reduces congestion and improves performance.
文摘Cognitive radio technology makes efficient use of the valuable radio frequency spectrum in a non-interfering manner to solve the problem of spectrum scarcity. This paper aims to design a scheme for the concurrent use of licensed frequencies by Underlay Cognitive Users （UCUs）. We develop a new receiver-initiated Medium Access Control （MAC） protocol to facilitate the selections of alternative reliable carrier frequencies. A circuit is designed to establish reliable carrier selections based on the Received Signal Strength Indicator （RSSI） at the receiving end. Based on both packet-level simulations and various performance parameters, a comparison is carried out among conventional techniques, including the Multiple Access with Collision Avoidance （MACA） and MACA by invitation（MACA-BI） techniques, and our scheme. The simulated results demonstrate that when conventional techniques are used, the system overhead time increases from 0.5 s on the first attempt to 16.5 s on the sixth attempt. In the proposed scheme under the same failure condition, overhead time varies from 0.5 s to 2 s. This improvement is due to the complete elimination of the exponential waiting time that occurs during failed transmissions. An average efficiency of 60% is achieved with our scheme while only 43% and 34% average efficiencies are achieved with the MACA and MACA-BI techniques, respectively. The throughput performance of our scheme on the fourth attempt is 7 Mbps, whereas for the MACA and MACA-BI protocols, it is 1.9 Mbps and 2.2 Mbps respectively.
文摘在无线自组织网络中,合理的退避机制能够有效地利用网络资源,解决多个节点同时抢占共享信道的问题,提高网络带宽利用率。通过建立模型深入分析了由于隐藏终端产生的流不公平问题,给出了一种吞吐量变化率和流不公平度的度量,并提出了一种通过调整退避窗口最小值来改善流公平性的退避算法——BFF(Back-off based on Flow Fairness)算法。通过仿真分析表明算法能够很好地提高公平性,解决BEB算法在实际运用中的流不公平问题。
