Africa Review takes a bird’s eye view of the elections taking place in Africa during 2012 a dozen african countries will be either holding or have planned elections this year, fittingly flagged off by the oft-praised...Africa Review takes a bird’s eye view of the elections taking place in Africa during 2012 a dozen african countries will be either holding or have planned elections this year, fittingly flagged off by the oft-praised democracy that is senegal which展开更多
ON March 28, Nigerians made history. On this day, for the first time since the end of colonial rule in 1960, a president was voted out of office not by the barrel of a gun, but by the people through a democratic elect...ON March 28, Nigerians made history. On this day, for the first time since the end of colonial rule in 1960, a president was voted out of office not by the barrel of a gun, but by the people through a democratic election. Retired General Muhammadu Buhari, who had a short taste of pow- er in the early 1980s as a military ruler, defeated incumbent President Goodluck Jonathan in a hotly contested presiden- tial election. The election was postponed by six weeks due to the unresolved Boko Haram militants crisis.展开更多
Happiness may be'U-shaped,'but a recent survey suggests that,despite their problems,the Chinese may be the world’s leading optimists.In'What Worries the World,'a study by global market-research firm I...Happiness may be'U-shaped,'but a recent survey suggests that,despite their problems,the Chinese may be the world’s leading optimists.In'What Worries the World,'a study by global market-research firm Ipsos,87 percent of Chinese adults said their country was'heading in the right direction,'while 60 percent of citizens of 25 other surveyed countries considered theirs on the wane.Western Europe and other high-income nations—where contentment is said to decline between ages 18 and 40展开更多
This paper analyzes a queue mode] of the polling system with limited service (K=1) in discrete time. By the imbedded Markov chain theory and the probability generating function method, the mean values of queue length ...This paper analyzes a queue mode] of the polling system with limited service (K=1) in discrete time. By the imbedded Markov chain theory and the probability generating function method, the mean values of queue length and message waiting time are explicitly obtained. Also, we give the simulation results. The results obtained by H. Tagai (1985) are revised.展开更多
We present a discrete time single-server two-level mixed service polling systems with two queue types, one center queue and N normal queues. Two-level means the center queue will be successive served after each normal...We present a discrete time single-server two-level mixed service polling systems with two queue types, one center queue and N normal queues. Two-level means the center queue will be successive served after each normal queue. In the first level, server visits between the center queue and the normal queue. In the second level, normal queues are polled by a cyclic order. Mixed service means the service discipline are exhaustive for center queue, and parallel 1-limited for normal queues. We propose an imbedded Markov chain framework to drive the closed-form expressions for the mean cycle time, mean queue length, and mean waiting time. Numerical examples demonstrate that theoretical and simulation results are identical the new system efficiently differentiates priorities.展开更多
In Wireless Sensor Networks(WSNs),polling can obviously improve the throughput and decrease average access delay by allocating bandwidth efficiently and reasonably.In this paper,a Dynamic Polling Media Access Control ...In Wireless Sensor Networks(WSNs),polling can obviously improve the throughput and decrease average access delay by allocating bandwidth efficiently and reasonably.In this paper,a Dynamic Polling Media Access Control (DPMAC) scheme designed according to WSNs' features is proposed.DPMAC is a priority based access control protocol with the characteristics that its polling table is dynamically refreshed depending on whether the sensor node is active and that the bandwidth is dynamically allocated according to the traffic types.The access priorities are determined by the emergency levels of events and the scheduler proposed in our MAC is preemptive based on the deadline of the events.Simulation results show that DPMAC can efficiently utilize bandwidth and decrease average access delay and response time for emergency events with different access priorities in WSNs.展开更多
There has been a significant interest of researchers to combine different schemes focused on optimizing energy performance while developing aMAC protocol for Wireless Sensor Networks(WSNs).In this paper,we propose to ...There has been a significant interest of researchers to combine different schemes focused on optimizing energy performance while developing aMAC protocol for Wireless Sensor Networks(WSNs).In this paper,we propose to integrate two cross-layer schemes:dynamic channel polling and packet concatenation using a recent asynchronous MAC protocol“Adaptive&Dynamic Polling MAC”(ADPMAC).ADP-MAC dynamically selects the polling interval distribution based on characterization of incoming traffic patterns using Coefficient of variation(CV).Packet Concatenation(PC)refers to combining the individually generated data packets into a single super packet and sending it at the polling instant.Also,the Block Acknowledgement(BA)scheme has been developed for ADP-MAC to work in conjunction with the packet concatenation.The proposed schemes have been implemented in Tiny-OS for Mica2 platform and Avrora emulator has been used for conducting experiments.Simulation results have revealed that the performance both in terms of energy&packet loss improves when ADP-MAC is used in conjunction with the additional features of PC&BA.Furthermore,the proposed scheme has been compared with a stateof-art packet concatenation primitive PiP(Packet-in-Packet).It has been observed that ADP-MAC supersedes the performance of PiP in terms of PDR(Packet Delivery Ratio)due to better management of synchronization between source and sink.展开更多
A solution is imperatively expected to meet the efficient contention resolution schemes for managing simultaneous access requests to the communication resources on the Network on Chip (NoC). Based on the ideas of conf...A solution is imperatively expected to meet the efficient contention resolution schemes for managing simultaneous access requests to the communication resources on the Network on Chip (NoC). Based on the ideas of conflict-free transmission, priority-based service, and dynamic self-adaptation to loading, this paper presents a novel scheduling algorithm for Medium Access Control (MAC) in NoC with the researches of the communication structure features of 2D mesh. The algorithm gives priority to guarantee the Quality of Service (QoS) for local input port as well as dynamic adjustment of the performance of the other ports along with input load change. The theoretical model of this algorithm is established with Markov chain and probability generating function. Mathematical analysis is made on the mean queue length and the mean inquiry cyclic time of the system. Simulated experiments are conducted to test the accuracy of the model. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments. Further more, the analytical findings of the system performance demonstrate that the algorithm enables effectively strengthen the fairness and stability of data transmissions in NoC.展开更多
文摘Africa Review takes a bird’s eye view of the elections taking place in Africa during 2012 a dozen african countries will be either holding or have planned elections this year, fittingly flagged off by the oft-praised democracy that is senegal which
文摘ON March 28, Nigerians made history. On this day, for the first time since the end of colonial rule in 1960, a president was voted out of office not by the barrel of a gun, but by the people through a democratic election. Retired General Muhammadu Buhari, who had a short taste of pow- er in the early 1980s as a military ruler, defeated incumbent President Goodluck Jonathan in a hotly contested presiden- tial election. The election was postponed by six weeks due to the unresolved Boko Haram militants crisis.
文摘Happiness may be'U-shaped,'but a recent survey suggests that,despite their problems,the Chinese may be the world’s leading optimists.In'What Worries the World,'a study by global market-research firm Ipsos,87 percent of Chinese adults said their country was'heading in the right direction,'while 60 percent of citizens of 25 other surveyed countries considered theirs on the wane.Western Europe and other high-income nations—where contentment is said to decline between ages 18 and 40
文摘This paper analyzes a queue mode] of the polling system with limited service (K=1) in discrete time. By the imbedded Markov chain theory and the probability generating function method, the mean values of queue length and message waiting time are explicitly obtained. Also, we give the simulation results. The results obtained by H. Tagai (1985) are revised.
基金Supported by the National Natural Science Foundation of China (No. 61072079)Science Foundation of Yunnan Provincial Department (No. 2011Y117)
文摘We present a discrete time single-server two-level mixed service polling systems with two queue types, one center queue and N normal queues. Two-level means the center queue will be successive served after each normal queue. In the first level, server visits between the center queue and the normal queue. In the second level, normal queues are polled by a cyclic order. Mixed service means the service discipline are exhaustive for center queue, and parallel 1-limited for normal queues. We propose an imbedded Markov chain framework to drive the closed-form expressions for the mean cycle time, mean queue length, and mean waiting time. Numerical examples demonstrate that theoretical and simulation results are identical the new system efficiently differentiates priorities.
基金supported by the National Natural Science Foundation of China under Grants No.61172068,61003300the Key Program of NSFC Guangdong Union Foundation under Grant No.U0835004+2 种基金the National Grand Fundamental Research 973 Program of China under Grant No.A001200907the Fundamental Research Funds for the Central Universities under Grant No.K50511010003Program for New Century Excellent Talents in University under Grant No.NCET-11-0691
文摘In Wireless Sensor Networks(WSNs),polling can obviously improve the throughput and decrease average access delay by allocating bandwidth efficiently and reasonably.In this paper,a Dynamic Polling Media Access Control (DPMAC) scheme designed according to WSNs' features is proposed.DPMAC is a priority based access control protocol with the characteristics that its polling table is dynamically refreshed depending on whether the sensor node is active and that the bandwidth is dynamically allocated according to the traffic types.The access priorities are determined by the emergency levels of events and the scheduler proposed in our MAC is preemptive based on the deadline of the events.Simulation results show that DPMAC can efficiently utilize bandwidth and decrease average access delay and response time for emergency events with different access priorities in WSNs.
文摘There has been a significant interest of researchers to combine different schemes focused on optimizing energy performance while developing aMAC protocol for Wireless Sensor Networks(WSNs).In this paper,we propose to integrate two cross-layer schemes:dynamic channel polling and packet concatenation using a recent asynchronous MAC protocol“Adaptive&Dynamic Polling MAC”(ADPMAC).ADP-MAC dynamically selects the polling interval distribution based on characterization of incoming traffic patterns using Coefficient of variation(CV).Packet Concatenation(PC)refers to combining the individually generated data packets into a single super packet and sending it at the polling instant.Also,the Block Acknowledgement(BA)scheme has been developed for ADP-MAC to work in conjunction with the packet concatenation.The proposed schemes have been implemented in Tiny-OS for Mica2 platform and Avrora emulator has been used for conducting experiments.Simulation results have revealed that the performance both in terms of energy&packet loss improves when ADP-MAC is used in conjunction with the additional features of PC&BA.Furthermore,the proposed scheme has been compared with a stateof-art packet concatenation primitive PiP(Packet-in-Packet).It has been observed that ADP-MAC supersedes the performance of PiP in terms of PDR(Packet Delivery Ratio)due to better management of synchronization between source and sink.
基金Supported by the National Natural Science Foundation of China(No.61072079)
文摘A solution is imperatively expected to meet the efficient contention resolution schemes for managing simultaneous access requests to the communication resources on the Network on Chip (NoC). Based on the ideas of conflict-free transmission, priority-based service, and dynamic self-adaptation to loading, this paper presents a novel scheduling algorithm for Medium Access Control (MAC) in NoC with the researches of the communication structure features of 2D mesh. The algorithm gives priority to guarantee the Quality of Service (QoS) for local input port as well as dynamic adjustment of the performance of the other ports along with input load change. The theoretical model of this algorithm is established with Markov chain and probability generating function. Mathematical analysis is made on the mean queue length and the mean inquiry cyclic time of the system. Simulated experiments are conducted to test the accuracy of the model. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments. Further more, the analytical findings of the system performance demonstrate that the algorithm enables effectively strengthen the fairness and stability of data transmissions in NoC.
