Guaranteed quality of service(QoS) support has been an open issue of distributed wireless networks for years. The IEEE802.11 e provides a valuable method for this purpose. However, it could only provide service differ...Guaranteed quality of service(QoS) support has been an open issue of distributed wireless networks for years. The IEEE802.11 e provides a valuable method for this purpose. However, it could only provide service differentiation, rather than service guarantee, for multi-priority traffic. Many studies have tried to improve its QoS ability, but still leave some problems. This paper investigates these problems and proposes a scheme called the priority access based on busy tone(PABT) to improve the Qo S performance. To guarantee the priority channel access, this scheme uses an in-band busy tone to limit the transmission of lower-priority traffic when higher-priority traffic has packets to send. Based on that, it also optimizes the contention window tuning according to the flows number of each traffic type individually, in order to improve the throughput as well as the traffic capacity. Simulation results show that the proposed scheme significantly improves the real-time traffic capacity, throughput, delay, fairness and packet loss rate.展开更多
A novel access protocol called Multiple-Reception Access Protocol (MRAP) and its modification MRAP/WI are proposed. In this protocol, all colliding users with a common code can be identified by the base station due to...A novel access protocol called Multiple-Reception Access Protocol (MRAP) and its modification MRAP/WI are proposed. In this protocol, all colliding users with a common code can be identified by the base station due to the offset of arrival time Thus they can retransmit access requests under the base station's control. Furthermore new arrivals with higher priority level can interrupt the lower retransmission in order to reduce its access delay although it increases the lower priority's delay. Simulation results of MRAP and MRAP/WI are given in order to highlight the superior performance of the proposed approach.展开更多
A new medium access control method is proposed over the predominant Ethernet broadcast channel. Taking advantages of intrinsic variable length characteristic of standard Ethernet frame, message-oriented dynamic priori...A new medium access control method is proposed over the predominant Ethernet broadcast channel. Taking advantages of intrinsic variable length characteristic of standard Ethernet frame, message-oriented dynamic priority mechanism is established. Prioritized medium access control operates under a so-called block mode in event of collisions. High priority messages have a chance to preempt block status incurred by low priority ones. By this means, the new MAC provides a conditional deterministic real time performance beyond a statistical one. Experiments demonstrate effectiveness and attractiveness of the proposed scheme. Moreover, this new MAC is completely compatible with IEEE802.3.展开更多
Under-five mortality remains a major concern in the world and in Senegal. It is mainly due to preventable and treatable diseases with priority life-saving medicines for under-five children. This study evaluated the av...Under-five mortality remains a major concern in the world and in Senegal. It is mainly due to preventable and treatable diseases with priority life-saving medicines for under-five children. This study evaluated the availability, management and use of these drugs in two health districts in Senegal. A descriptive cross-sectional study was conducted in the health districts of Guediawaye and Pete from 01 November 2018 to 31 January 2019. The health district of Guediawaye is in the region hosting the Senegalese capital while that of Pete is located in the region of Saint Louis, northern Senegal. Nine drugs that can prevent and treat malaria, diarrhea, pneumonia and malnutrition were selected. An inventory form and a self-administered questionnaire were used to collect data that was analyzed with SPSS and expressed as a percentage and average. Drug availability was 50.4% and 54.3% in Guediawaye and in Pete, respectively. Average stock-out duration in the past three months was estimated at 22.6 and 26 days, respectively. The drug management was marked, on the one hand, by a good availability of stock cards in the two districts with proportions equal to 100% and 94.1%, respectively, and on the other hand, by the presence of expired stocks in Pete (12.2%). About 79% and 88% of prescribers reported prescribing the basket drug, respectively. These results show that access to priority life-saving medicines for children remains a challenge. Measures to be taken should include improving the distribution channels and training of health professionals. Further studies should be conducted in other health districts to better understand the barriers to access to child health services.展开更多
基金supported by the Special Fund for National Defense Technology Innovation(18-163-11-ZT-003-027-01)
文摘Guaranteed quality of service(QoS) support has been an open issue of distributed wireless networks for years. The IEEE802.11 e provides a valuable method for this purpose. However, it could only provide service differentiation, rather than service guarantee, for multi-priority traffic. Many studies have tried to improve its QoS ability, but still leave some problems. This paper investigates these problems and proposes a scheme called the priority access based on busy tone(PABT) to improve the Qo S performance. To guarantee the priority channel access, this scheme uses an in-band busy tone to limit the transmission of lower-priority traffic when higher-priority traffic has packets to send. Based on that, it also optimizes the contention window tuning according to the flows number of each traffic type individually, in order to improve the throughput as well as the traffic capacity. Simulation results show that the proposed scheme significantly improves the real-time traffic capacity, throughput, delay, fairness and packet loss rate.
文摘A novel access protocol called Multiple-Reception Access Protocol (MRAP) and its modification MRAP/WI are proposed. In this protocol, all colliding users with a common code can be identified by the base station due to the offset of arrival time Thus they can retransmit access requests under the base station's control. Furthermore new arrivals with higher priority level can interrupt the lower retransmission in order to reduce its access delay although it increases the lower priority's delay. Simulation results of MRAP and MRAP/WI are given in order to highlight the superior performance of the proposed approach.
基金This workis partly supported by national 863 project under grant 2002 AA412010 08
文摘A new medium access control method is proposed over the predominant Ethernet broadcast channel. Taking advantages of intrinsic variable length characteristic of standard Ethernet frame, message-oriented dynamic priority mechanism is established. Prioritized medium access control operates under a so-called block mode in event of collisions. High priority messages have a chance to preempt block status incurred by low priority ones. By this means, the new MAC provides a conditional deterministic real time performance beyond a statistical one. Experiments demonstrate effectiveness and attractiveness of the proposed scheme. Moreover, this new MAC is completely compatible with IEEE802.3.
文摘Under-five mortality remains a major concern in the world and in Senegal. It is mainly due to preventable and treatable diseases with priority life-saving medicines for under-five children. This study evaluated the availability, management and use of these drugs in two health districts in Senegal. A descriptive cross-sectional study was conducted in the health districts of Guediawaye and Pete from 01 November 2018 to 31 January 2019. The health district of Guediawaye is in the region hosting the Senegalese capital while that of Pete is located in the region of Saint Louis, northern Senegal. Nine drugs that can prevent and treat malaria, diarrhea, pneumonia and malnutrition were selected. An inventory form and a self-administered questionnaire were used to collect data that was analyzed with SPSS and expressed as a percentage and average. Drug availability was 50.4% and 54.3% in Guediawaye and in Pete, respectively. Average stock-out duration in the past three months was estimated at 22.6 and 26 days, respectively. The drug management was marked, on the one hand, by a good availability of stock cards in the two districts with proportions equal to 100% and 94.1%, respectively, and on the other hand, by the presence of expired stocks in Pete (12.2%). About 79% and 88% of prescribers reported prescribing the basket drug, respectively. These results show that access to priority life-saving medicines for children remains a challenge. Measures to be taken should include improving the distribution channels and training of health professionals. Further studies should be conducted in other health districts to better understand the barriers to access to child health services.
