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
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
Wireless networking in cyber-physical systems(CPSs) is characteristically different from traditional wireless systems due to the harsh radio frequency environment and applications that impose high real-time and reliab...Wireless networking in cyber-physical systems(CPSs) is characteristically different from traditional wireless systems due to the harsh radio frequency environment and applications that impose high real-time and reliability constraints.One of the fundamental considerations for enabling CPS networks is the medium access control protocol. To this end, this paper proposes a novel priority-aware frequency domain polling medium access control(MAC) protocol, which takes advantage of an orthogonal frequency-division multiple access(OFDMA)physical layer to achieve instantaneous priority-aware polling.Based on the polling result, the proposed work then optimizes the resource allocation of the OFDMA network to further improve the data reliability. Due to the non-polynomial-complete nature of the OFDMA resource allocation, we propose two heuristic rules,based on which an efficient solution algorithm to the OFDMA resource allocation problem is designed. Simulation results show that the reliability performance of CPS networks is significantly improved because of this work.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
A novel mixed polling system with multiple stations is considered. Each station produces two classes of messages served with different disciplines. The real time message served with exhaustive service discipline and t...A novel mixed polling system with multiple stations is considered. Each station produces two classes of messages served with different disciplines. The real time message served with exhaustive service discipline and the unreal time message served with gated service discipline. Using an iterative method, the exact mean waiting times for both message classes are derived. The influence of the gate location of the message class served by the gated service discipline on the mean waiting time is also analyzed. The analytical results are verified with simulation method and agree well with simulation results.展开更多
Recently, applications of real-time polling service (rtPS) in IEEE 802.16 wireless networks have gained considerable popularity. These applications generate large amounts of real time traffic in the network and thus m...Recently, applications of real-time polling service (rtPS) in IEEE 802.16 wireless networks have gained considerable popularity. These applications generate large amounts of real time traffic in the network and thus maintaining the quality of service (QoS) such as packet delay requirement in rtPS dominant networks is critical. Existing dimensioning methodology does not consider QoS parameters of rtPS in network dimensioning. Moreover, exhaustive and time-consuming simulations are required to evaluate the performance and QoS of rtPS. To overcome this problem, we propose an improved radio network dimensioning framework which considers QoS parameters of rtPS in network dimensioning. In this framework, an analytical model is developed to evaluate the capacity and performance of rtPS in IEEE 802.16 wireless networks. The proposed framework provides a fast and accurate means of finding the trade-off between system load and packet delay, thus providing network operators with an analytical tool that jointly considers coverage, capacity and QoS requirements for obtaining the minimum number of sites required. The accuracy of the proposed model is validated through simulations.展开更多
Resilient network infrastructure is pivotal for business entities that are growing reliance on the Internet.Distributed Denial-of-Service(DDOS)is a common network threat that collectively overwhelms and exhausts netwo...Resilient network infrastructure is pivotal for business entities that are growing reliance on the Internet.Distributed Denial-of-Service(DDOS)is a common network threat that collectively overwhelms and exhausts network resources using coordinated botnets to interrupt access to network services,devices,and resources.IDS is typically deployed to detect DDOS based on Snort rules.Although being fairly accurate,IDS operates on a computeintensive packet inspection technique and lacks rapidDDOSdetection.Meanwhile,SNMP is a comparably lightweight countermeasure for fast detection.However,this SNMP trigger is often circumvented if the DDOS burst rate is coordinated to flood the network smaller than theSNMPpolling rate.Besides,SNMP does not scale well if the poll rate is set extremely fine for improved detection accuracy.In this paper,a lightweight 3D SNMP scaling method is proposed to optimize the SNMP poll rate forDDOSmitigation automatically.The 3D-SNMP uses horizontal scaling to dynamically adjust the optimal poll rate through random packet inspection that is selective.Suppose a sign of DDOS is detected,3D-SNMP scales down the poll rate for finer detection.As DDOS subsides,3D-SNMP scales the poll rate up for faster DDOS detection.The equilibrium between scalability and accuracy is determined on the fly depending on the types of DDOS variants.3D-SNMP also adds a vertical scaling to detect non-salient DDOS that falls below the detection threshold.The experimental results showed that 3D-SNMP achieved DDOS detection of 92%while remaining scalable to different DDOS variants and volumes.展开更多
Quality of service (QoS) support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks (LANs) but is limited in 802.11-based wireless LANs. A polling-based sche...Quality of service (QoS) support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks (LANs) but is limited in 802.11-based wireless LANs. A polling-based scheme called the point coordination function (PCF) was developed for 802.11 LANs to support the transmission of multimedia traffic. However, the PCF is not able to meet the desired practical traffic differentiation requirements for real-time data. This paper describes a QoS support polling scheme based on the IEEE 802.11 medium access control (MAC) protocol. The scheme uses a two-level polling mechanism with the QoS classes differentiated by two different access policies. Stations with higher priority traffic such as key or real-time data form the first level and can access the common channel through an exhaustive access policy. Other stations with lower priority traffic form the second level and can access the channel through a gated access policy. A system model based on imbedded Markov chain theory and a generation function were setup to explicitly analyze the mean information packet waiting time of the two-level polling scheme. Theoretical and simulation results show that the new scheme efficiently differentiates services to guarantee better QoS and system stability.展开更多
Polling system models have a wide range of important applications including time-sharing computer systems, industrial control, communications, and computer networks. In this paper, we propose a two-class priority- bas...Polling system models have a wide range of important applications including time-sharing computer systems, industrial control, communications, and computer networks. In this paper, we propose a two-class priority- based polling system that uses gated and exhaustive services to achieve the priority-based scheme. This model is set up according to the method of the imbedded Markov chain theory and the generation function and explicitly analyzes key system performance characteristics including mean queue length, cyclic time, and throughput. Theoretical and simulation results are identical and demonstrate the efficiency of the model.展开更多
Wireless local area networks (WLANs) are a viable technology for multimedia traffic. One of the most common WLANs standards being adopted as a mature technology is the IEEE 802.11 standard. This paper presents a new...Wireless local area networks (WLANs) are a viable technology for multimedia traffic. One of the most common WLANs standards being adopted as a mature technology is the IEEE 802.11 standard. This paper presents a new polling strategy for wireless multimedia LANs with variable packet lengths, which synchronizes polling and transmission of the information packets. A mathematical model based on imbedded Markov chain theory and the generation function was used to predict the mean queue length and information packet waiting time. The efficiency of the new strategy was validated by mathematical analysis and simulations. The results show that parallel system's mean queue length, information packet waiting time and polling cycle time are all less than for the non-parallel system and that the improved system is more stable and has greater capacity.展开更多
The scheduling algorithm based on the three-way handshaking scheme in IEEE 802.16d-2004 standard has some serious problems because of the complexity of the algorithm and low scheduling efficiency. To enhance the sched...The scheduling algorithm based on the three-way handshaking scheme in IEEE 802.16d-2004 standard has some serious problems because of the complexity of the algorithm and low scheduling efficiency. To enhance the scheduling efficiency and improve the performance of multi-hop wireless mesh networks (WMNs), one distributed scheduling algorithm that can maximize the spatial and time reuse with an interference-based network model is proposed. Compared to the graph-based network model, the proposed network model can achieve a better throughput performance with maximal spatial reuse. Furthermore, this proposed scheduling algorithm also keeps fairly scheduling to all links, with a priority-based polling policy. Both the theoretical analysis and simulation results show that this proposed distributed scheduling algorithm is simple and efficient.展开更多
Next-generation passive optical networks(PONs)demand power conservation to create a green environment.A reduction in power consumption of the traditional Ethernet passive optical network(EPON)can be achieved by increa...Next-generation passive optical networks(PONs)demand power conservation to create a green environment.A reduction in power consumption of the traditional Ethernet passive optical network(EPON)can be achieved by increasing the sleep count in optical network units(ONUs).In this paper,this is accomplished by introducing a first-in-last-out(FILO)polling sequence in the place of a fixed polling sequence to increase the number of ONUs entering sleep mode(sleep count).In a fixed polling sequence,the optical line terminal(OLT)allocates idle time to the ONUs based on the overall load of the ONUs.This leads to a situation that whenever the idle time does not meet the wakeup time threshold of sleep mode,the ONUs are put into doze/active mode,which consumes more power.In the FILO polling sequence,the first polled ONU in the current cycle is made to be polled last in the following cycle.Polling continues in this way,and by this rearrangement,the idle time of delayed poll ONUs increases;hence,it helps to reduce the power consumption.Additionally,a modified load adaptive sequence arrangement(MLASA)method is suggested,where the ONUs are categorized into doze ONUs and sleep ONUs.A numerical simulation of the FILO polling sequence with a vertical cavity surface emitting laser(VCSEL)ONU shows a maximum reduction in power consumption of 15.5 W and a 20%improvement in energy savings compared with the traditional fixed polling sequence.The MLASA method results in better power consumption with minimum delay than that of the proposed FILO and existing LASA methods.展开更多
This paper addresses the issue of real-time data transmission in vehicles to roadside (V2R) environment by the hybrid coordination function (HCF) of controlled channel access (HCCA) specified by the IEEE 802.1 l...This paper addresses the issue of real-time data transmission in vehicles to roadside (V2R) environment by the hybrid coordination function (HCF) of controlled channel access (HCCA) specified by the IEEE 802.1 lp standard. HCCA is one of the medium access mechanisms in the IEEE 802.11 standard, and uses the polling scheme similar to the point coordination function (PCF) to provide reliable quality of service (QoS), which may cause resource overshooting and high time consuming. This paper tries to improve the performance of the HCCA polling scheme and designs new data transmission scheduling scheme. The simulation results of the proposal are compared with those of the standard strategy. Simulation results demonstrate that the improved HCCA has lower delay, loss rate, and higher throughput than those of the standard one.展开更多
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.
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 National Natural Science Foundation of China(61304263,61233007)the Cross-disciplinary Collaborative Teams Program for Science,Technology and Innovation of Chinese Academy of Sciences-Network and System Technologies for Security Monitoring and Information Interaction in Smart Arid
文摘Wireless networking in cyber-physical systems(CPSs) is characteristically different from traditional wireless systems due to the harsh radio frequency environment and applications that impose high real-time and reliability constraints.One of the fundamental considerations for enabling CPS networks is the medium access control protocol. To this end, this paper proposes a novel priority-aware frequency domain polling medium access control(MAC) protocol, which takes advantage of an orthogonal frequency-division multiple access(OFDMA)physical layer to achieve instantaneous priority-aware polling.Based on the polling result, the proposed work then optimizes the resource allocation of the OFDMA network to further improve the data reliability. Due to the non-polynomial-complete nature of the OFDMA resource allocation, we propose two heuristic rules,based on which an efficient solution algorithm to the OFDMA resource allocation problem is designed. Simulation results show that the reliability performance of CPS networks is significantly improved because of this work.
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.
基金Sponsored by the National Natural Science Foundation of China (No .60474031) the National"863"Program Project (2002AA412010-08)
文摘A novel mixed polling system with multiple stations is considered. Each station produces two classes of messages served with different disciplines. The real time message served with exhaustive service discipline and the unreal time message served with gated service discipline. Using an iterative method, the exact mean waiting times for both message classes are derived. The influence of the gate location of the message class served by the gated service discipline on the mean waiting time is also analyzed. The analytical results are verified with simulation method and agree well with simulation results.
文摘Recently, applications of real-time polling service (rtPS) in IEEE 802.16 wireless networks have gained considerable popularity. These applications generate large amounts of real time traffic in the network and thus maintaining the quality of service (QoS) such as packet delay requirement in rtPS dominant networks is critical. Existing dimensioning methodology does not consider QoS parameters of rtPS in network dimensioning. Moreover, exhaustive and time-consuming simulations are required to evaluate the performance and QoS of rtPS. To overcome this problem, we propose an improved radio network dimensioning framework which considers QoS parameters of rtPS in network dimensioning. In this framework, an analytical model is developed to evaluate the capacity and performance of rtPS in IEEE 802.16 wireless networks. The proposed framework provides a fast and accurate means of finding the trade-off between system load and packet delay, thus providing network operators with an analytical tool that jointly considers coverage, capacity and QoS requirements for obtaining the minimum number of sites required. The accuracy of the proposed model is validated through simulations.
文摘Resilient network infrastructure is pivotal for business entities that are growing reliance on the Internet.Distributed Denial-of-Service(DDOS)is a common network threat that collectively overwhelms and exhausts network resources using coordinated botnets to interrupt access to network services,devices,and resources.IDS is typically deployed to detect DDOS based on Snort rules.Although being fairly accurate,IDS operates on a computeintensive packet inspection technique and lacks rapidDDOSdetection.Meanwhile,SNMP is a comparably lightweight countermeasure for fast detection.However,this SNMP trigger is often circumvented if the DDOS burst rate is coordinated to flood the network smaller than theSNMPpolling rate.Besides,SNMP does not scale well if the poll rate is set extremely fine for improved detection accuracy.In this paper,a lightweight 3D SNMP scaling method is proposed to optimize the SNMP poll rate forDDOSmitigation automatically.The 3D-SNMP uses horizontal scaling to dynamically adjust the optimal poll rate through random packet inspection that is selective.Suppose a sign of DDOS is detected,3D-SNMP scales down the poll rate for finer detection.As DDOS subsides,3D-SNMP scales the poll rate up for faster DDOS detection.The equilibrium between scalability and accuracy is determined on the fly depending on the types of DDOS variants.3D-SNMP also adds a vertical scaling to detect non-salient DDOS that falls below the detection threshold.The experimental results showed that 3D-SNMP achieved DDOS detection of 92%while remaining scalable to different DDOS variants and volumes.
基金Supported by the National Natural Science Foundation of China(Nos. F0424104 and 60362001)the Natural Science Foundation of Yunnan Province of China (No. 2004F0011R)
文摘Quality of service (QoS) support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks (LANs) but is limited in 802.11-based wireless LANs. A polling-based scheme called the point coordination function (PCF) was developed for 802.11 LANs to support the transmission of multimedia traffic. However, the PCF is not able to meet the desired practical traffic differentiation requirements for real-time data. This paper describes a QoS support polling scheme based on the IEEE 802.11 medium access control (MAC) protocol. The scheme uses a two-level polling mechanism with the QoS classes differentiated by two different access policies. Stations with higher priority traffic such as key or real-time data form the first level and can access the common channel through an exhaustive access policy. Other stations with lower priority traffic form the second level and can access the channel through a gated access policy. A system model based on imbedded Markov chain theory and a generation function were setup to explicitly analyze the mean information packet waiting time of the two-level polling scheme. Theoretical and simulation results show that the new scheme efficiently differentiates services to guarantee better QoS and system stability.
基金supported by the National Natural Science Foundation of China (Nos. 61072079/F010201 and 61461054)
文摘Polling system models have a wide range of important applications including time-sharing computer systems, industrial control, communications, and computer networks. In this paper, we propose a two-class priority- based polling system that uses gated and exhaustive services to achieve the priority-based scheme. This model is set up according to the method of the imbedded Markov chain theory and the generation function and explicitly analyzes key system performance characteristics including mean queue length, cyclic time, and throughput. Theoretical and simulation results are identical and demonstrate the efficiency of the model.
基金Supported by the National Natural Science Foundation of China (No. 60362001)
文摘Wireless local area networks (WLANs) are a viable technology for multimedia traffic. One of the most common WLANs standards being adopted as a mature technology is the IEEE 802.11 standard. This paper presents a new polling strategy for wireless multimedia LANs with variable packet lengths, which synchronizes polling and transmission of the information packets. A mathematical model based on imbedded Markov chain theory and the generation function was used to predict the mean queue length and information packet waiting time. The efficiency of the new strategy was validated by mathematical analysis and simulations. The results show that parallel system's mean queue length, information packet waiting time and polling cycle time are all less than for the non-parallel system and that the improved system is more stable and has greater capacity.
基金This work is supported by the National Natural Science Foundation of China (60572120, 60602058);the Hi-Tech Research and Development Program of China (2006AA01Z257).
文摘The scheduling algorithm based on the three-way handshaking scheme in IEEE 802.16d-2004 standard has some serious problems because of the complexity of the algorithm and low scheduling efficiency. To enhance the scheduling efficiency and improve the performance of multi-hop wireless mesh networks (WMNs), one distributed scheduling algorithm that can maximize the spatial and time reuse with an interference-based network model is proposed. Compared to the graph-based network model, the proposed network model can achieve a better throughput performance with maximal spatial reuse. Furthermore, this proposed scheduling algorithm also keeps fairly scheduling to all links, with a priority-based polling policy. Both the theoretical analysis and simulation results show that this proposed distributed scheduling algorithm is simple and efficient.
文摘Next-generation passive optical networks(PONs)demand power conservation to create a green environment.A reduction in power consumption of the traditional Ethernet passive optical network(EPON)can be achieved by increasing the sleep count in optical network units(ONUs).In this paper,this is accomplished by introducing a first-in-last-out(FILO)polling sequence in the place of a fixed polling sequence to increase the number of ONUs entering sleep mode(sleep count).In a fixed polling sequence,the optical line terminal(OLT)allocates idle time to the ONUs based on the overall load of the ONUs.This leads to a situation that whenever the idle time does not meet the wakeup time threshold of sleep mode,the ONUs are put into doze/active mode,which consumes more power.In the FILO polling sequence,the first polled ONU in the current cycle is made to be polled last in the following cycle.Polling continues in this way,and by this rearrangement,the idle time of delayed poll ONUs increases;hence,it helps to reduce the power consumption.Additionally,a modified load adaptive sequence arrangement(MLASA)method is suggested,where the ONUs are categorized into doze ONUs and sleep ONUs.A numerical simulation of the FILO polling sequence with a vertical cavity surface emitting laser(VCSEL)ONU shows a maximum reduction in power consumption of 15.5 W and a 20%improvement in energy savings compared with the traditional fixed polling sequence.The MLASA method results in better power consumption with minimum delay than that of the proposed FILO and existing LASA methods.
基金supported by the National Natural Science Foundation of China (61072063, NSFC-11-01-01)
文摘This paper addresses the issue of real-time data transmission in vehicles to roadside (V2R) environment by the hybrid coordination function (HCF) of controlled channel access (HCCA) specified by the IEEE 802.1 lp standard. HCCA is one of the medium access mechanisms in the IEEE 802.11 standard, and uses the polling scheme similar to the point coordination function (PCF) to provide reliable quality of service (QoS), which may cause resource overshooting and high time consuming. This paper tries to improve the performance of the HCCA polling scheme and designs new data transmission scheduling scheme. The simulation results of the proposal are compared with those of the standard strategy. Simulation results demonstrate that the improved HCCA has lower delay, loss rate, and higher throughput than those of the standard one.