无线城域网中MPEG视频传输的上行调度算法

针对现有无线城域网中MPEG视频传输的实时轮询服务算法的不足,提出了一种更为有效的媒体接入控制上行调度算法。该算法无需基站周期地提供带宽请求机会,而是在视频应用的连接建立以后,主动周期地分配固定带宽来传输视频数据的特定部分,剩余部分的带宽通过携带请求的方式获得,以此保证更好的服务质量。仿真中使用典型的视频测试源,结果表明,新算法在近似现有算法的信道利用率的情况下,具有更小的视频帧延迟和抖动。     

An efficient bandwidth allocation algorithm for real-time VBR stream transmission under IEEE 802.16 wireless networks

This paper investigates variable rate control strategies for real-time multimedia variable bit rate (VBR) services over IEEE 802.16 broadband wireless networks. A data rate control mechanism is derived for the case where the uplink channel provides real-time services and the traffic rate parameter remains constant. This paper shows that the common queuing scheduling algorithms have some bandwidth allocation fairness problems for the real-time polling service (rtPS) in the MAC layer. In other words, the use of a VBR for the rtPS by a WiMAX system results in additional access latency jitter and bandwidth allocation disorder in the transmitted multimedia streams during the regular time interval polling of subscribe stations (SSs) for the contention bandwidth request period. However, the proposed scheduling algorithm solves these SSs contending with bandwidth resource allocation problems based on an extended rtPS (ertPS) of quality-of-service (QoS) pre-programming for a ranging response non-contention polling period. The adopted bandwidth allocation of max–min fairness queue scheduling uses a time constraint condition to transmit real-time multimedia VBR streaming in an IEEE 802.16 broadband wireless environment. In addition, we use the ns-2 simulation tool to compare the capacity of multimedia VBR stream and show that the proposed ertPS scheduling algorithm outperforms other rtPS scheduling algorithms.     

An adaptive QoS guaranteeing MAC protocol for real-time traffic in TDMA-based wireless ATM networks

This paper presents a new media access control (MAC) protocol based on forward error control (FEC), which is appropriate for supporting real-time traffic with strict QoS requirements in wireless ATM networks. As the channel BER in wireless environments is very high and varying 10⁻⁵–10⁻², previous schemes that use powerful FEC have combated to overcome this noisy channel condition at the cost of valuable bandwidth. As most previous works have been dedicated to maximize the channel efficiency, they were not able to meet QoS requirements of real-time applications in wireless networks. A new MAC protocol proposed in this paper is designed to guarantee the throughput requested by a real-time traffic user while keeping the bandwidth consumption at a minimum. The proposed scheme is for a TDMA system and uses adaptive FEC. We analyze the wireless channel and model it as a two-state error control system to design an efficient MAC protocol. We use simulation experiments to show how the proposed scheme provides QoS guarantees, and compare it with the CDMA system in terms of capacity, i.e. the number of users that can be supported.     

一种能量有效的无线传感器网络轮询接入控制协议

周期性休眠的PCF机制虽然较好地解决了无线传感器网络的能耗问题,但没有考虑节点的负载状态,降低了系统性能,也增加了系统的查询能耗.以限定(K=1)服务为基础,提出了一种改进的PCF轮询控制协议,即具有混合服务策略的无线传感器网络轮询接入控制协议PCF-SS.该协议在保障公平性的前提下,能够根据节点状态动态调整优先级并改变服务K值,中心服务器AP则根据各节点的服务K值在每轮服务时对节点的下一轮服务时间进行预估计,并采用统一的服务时间表唤醒节点,达到节能的效果.仿真实验表明系统的平均等待时间、平均排队队长等性能指标比周期性休眠的PCF机制要好,能量的有效利用率更高,具有更长的生命周期,适合作为无线传感器网络的MAC控制协议.     

A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.     

Real-time network monitoring scheme based on SNMP for dynamic information

An efficient and automated network management is required in large and complex networks since it is very difficult to manage them only with human effort. In response to this need, the Simple Network Management Protocol (SNMP) has been developed and adopted as the de facto standard. Some management information changes with time and the management station needs to monitor its value in real time. In such a case, polling is generally used in the SNMP because the management station can query agents periodically. However, the polling scheme needs both request and response messages for management information every time, which results in network traffic increase. In this paper, we suggest a real-time network monitoring method for dynamic information to reduce the network traffic in SNMP-based network management. In the proposed strategy, each agent first decides its own monitoring period. Then, the manager collects them and approves each agent's period without modification or adjusts it based on the total traffic generated by monitoring messages. After receiving a response message containing the monitoring period from the management station, each agent sends management information periodically without the request of management station. To evaluate the performance of the proposed real-time monitoring method, we implemented it and compared the network traffic and monitoring quality of the proposed scheme with the general polling method.     

远程实时控制系统EPON动态分配研究

以太无源光网络(EPON)结合了以太网技术和无源光网络技术的优势,能够以较低的价格实现高速接入.随着远程分布控制系统实时性要求的不断提高,将EPON引入到控制系统中,是一种理想的选择.首先简要介绍了整个远程控制系统拓扑结构,然后根据该系统的特点,提出了一种改进的上行动态带宽分配算法,结合了轮询机制和实时性优先级.通过建模仿真,验证了该算法可以取得较高的实时性和带宽利用率.     

A Priority-aware Frequency Domain Polling MAC Protocol for OFDMA-based Networks in Cyber-physical Systems

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.      

基于歧视性的第二价格拍卖算法的激励机制

在基于对等网(P2P)的大数据实时应用中,针对如何遏制视频点播(VOD)系统中的节点搭便车行为,提出了基于歧视性的第二价格拍卖算法的激励机制。节点之间以分布式动态拍卖的方式获取各自所需视频数据块,拍卖中,拍卖节点首先根据歧视性原则判断竞标节点的预算是否足以参与竞标,并根据允许参与竞标的节点数目设置上传带宽;然后根据竞标节点的出价确定赢得竞标的节点;最后竞标节点在接收到数据块后根据第二价格方案支付拍卖节点仅次于拍卖最高价格的第二高价格的要价作为节点的收益。分析节点的收益、节点带宽的利用率以及贡献节点/自私节点的比例,表明该方案能有效地激励节点积极地参与视频数据块的共享,同时高效地利用节点的上传带宽。     

Orthogonal signaling-based queue status investigation method in IEEE 802.11

IEEE 802.11 specifies four different medium access control (MAC) protocols to coordinate multiple access in a wireless local area network (WLAN). Since several tens of stations can operate in a WLAN, the performance of MAC protocols is important for overall network efficiency. It has been observed that the IEEE 802.11 MAC protocols can be improved by knowing which station has a non-empty queue, i.e., queue status. The point coordination function (PCF) can use this information to avoid polling a station that has no pending data. The HCF controlled channel access can adapt polling parameters based on queue status information, especially when scheduling a bursty and variable bit-rate traffic. Previously suggested methods are rather limited in terms of accuracy and efficiency.In this paper, we propose a novel method to investigate the queue status of multiple stations by exploiting orthogonal signaling. With synchronous transmission of orthogonal codes and symbol level signal processing, the method allows all of the associated stations to report their queue status at the same time. Challenges that can arise in the implementation of the proposed method are identified, and their solutions are suggested. The feasibility of detecting orthogonal signals is thoroughly tested on a realistic channel model. To demonstrate the performance improvement of a MAC protocol, we applied the proposed method to PCF. Both analysis and simulation show that the modified PCF significantly outperforms not only the original PCF but also other previously suggested PCF enhancements.     

WiMAX系统突发实时业务调度算法的改进

针对现有WiMAX系统MAC层没有提供不同优先级业务具体调度方案的现状,在分析传统分级调度算法的基础上,提出一种针对实时业务突发性的改进DFPQ调度算法实现方案。该方案在带宽分配过程中,通过判断实时业务突发性增多,强制将低优先级业务的一部分带宽分配给实时业务。GloMoSim网络仿真环境下的仿真结果证明,该调度策略在满足各业务QoS要求方面优于传统分级调度策略。     

一种超宽带MAC层信道时间分配的改进方法

针对超宽带媒体访问控制(MAC)层的信道资源分配在可变比特率业务和不定比特率业务中可能存在的丢帧或带宽利用率低的问题,提出了一种基于开槽ALOHA协议即时抢占信道时间分配的改进方法,为数据流分配空闲的信道时间。仿真结果表明,与IEEE802.15.3建议的分配方式相比,这种改进方法能够在一定程度上降低任务失败率和延迟抖动,提高有效吞吐量,从而有效地支持高QoS要求的传输。     

Statistical real-time channels on multiaccess bus networks

Real-time communication with performance guarantees is expected to become an important and necessary feature of future computer networks. In this paper, we present a scheme which can provide real-time communication services with both absolute and statistical performance guarantees on multiaccess bus networks for given input traffic characteristics and performance requirements. The proposed scheme reserves network bandwidth for real-time connections according to their needs. It also allows for independent addition and deletion of real-time connections while preserving existing guarantees. Our extensive simulation results for motion video communication have shown the proposed scheme to outperform the other well-known schemes     

ADD:一种无线局域网MAC层竞争窗口退避算法

在无线局域网(WLANs)中,介质访问控制(MAC)协议的设计是一个核心的问题。MAC协议应该满足较高的吞吐量和较好的公平性等要求。根据802.11分布式协同函数(DCF),提出了一种新的高效的竞争窗口(CW)处理机制,称作自适应倍乘增加倍乘减小算法(ADD)。该算法的基本思想如下:每个站点在成功地连续发送n个数据包后,其MAC层的竞争窗口减小为原值的一半,而且n的值根据接入节点(AP)的瞬时流量自适应地调节。大量仿真实验表明:该算法可以通过有效地降低站点之间的冲突概率,来增加系统整体的吞吐量,同时增加不同站点之间的公平性。     

Methodologies for bandwidth allocation,transmission scheduling,and congestion avoidance in broadband ATM networks

The call types supported in high-speed packet networks vary widely in their bandwidth requirements and tolerance to message delay and loss. In this paper, we classify various traffic sources which are likely to be integrated in broadband ATM networks, and suggest schemes for bandwidth allocation and transmission scheduling to meet the quality and performance objectives. We propose ATM cell-multiplexing using a Dynamic Time-Slice (DTS) scheme which guarantees a required bandwidth for each traffic class and/or virtual circuit (VC), and is dynamic in that it allows the different traffic classes or VCs to share the bandwidth with a soft boundary. Any bandwidth momentarily unused by a class or a VC is made available to the other traffic present in the multiplexer. The scheme guarantees a desired bandwidth to connections which require a fixed wide bandwidth. Thus, it facilitates setting up circuit-like connections in a network using the ATM protocol for transport. The DTS scheme is an efficient way of combining constant bit-rate (CBR) services with variable bit-rate (VBR) stastically multiplexed services. We also described methodologies to schedule delivery of delay-tolerant data traffic within the framework of the DTS scheme. Important issues such as buffer allocations, guarantee of service quality, and ease of implementation are also discussed.     

基于预约和反馈的无线传感器网络MAC协议研究

针对无线传感器网络中对通信实时性要求较高的应用环境,引入信道预约机制和反馈机制到S-MAC协议,提出了一种低时延的RF-MAC协议。该协议在有数据需要发送时先预约信道,各节点根据预约时间表进行数据传输。采用在数据传输过程中向源节点发送反馈信息的方法,实现后续数据的提前发送。通过仿真实验表明:RF-MAC协议有效地降低了数据传输的时延,同时改善了丢包率和网络吞吐量。     

On the wireless local area network design problem with performance guarantees

In this paper, we propose a model for the wireless local area network (WLAN) design problem with performance guarantees. This problem consists of selecting the location of the access points (APs) as well as the power and the channel of each AP. The performance guarantees we refer to are coverage and minimum bandwidth guarantees. Since this problem is -hard, we propose a tabu search algorithm to find solutions for real-size instances of the problem. Finally, numerical results are presented. The results show that good solutions can be found with the proposed algorithm in a reasonable amount of time.     

Performance analysis of Markovian polling systems with single buffers

In this paper, we analyze the Markovian polling system with single buffers, asymmetric arrival rates, service times, and switchover times. A virtual buffer model is introduced to derive the relationship of the joint generating function for the queue length of each station at a polling instant. The Laplace-Stieltjes transforms of the cycle time and the intervisit time are obtained from the marginal generating function. We analyze the cyclic, load-oriented-priority, and symmetric random polling schemes which are classified by adjusting the transition probabilities, and compare the merits and demerits of each scheme for the performance measures. In particular, we prove that the mean queue lengths at the polling instants are the same for all stations in case of the load-oriented-priority polling scheme for the buffer relaxation system in which a new message is stored as soon as the transmission of the message currently in the buffer is initiated.     

无线局域网多机器人系统轮询MAC协议研究

多机器人系统是一个结构复杂的团体,为了实现机器人之间的高效合作,必须解决机器人间的信息交互问题,提出将无线局域网的多机器人系统与轮询系统结合的MAC（multiple access control）协议。首先,研究MAC协议中PCF（point coordination function）访问机制,建立轮询系统模型,将该模型应用于多机器人集中式体系架构中,并对其数据传输方式进行分析;推导了门限、完全、限定K=1机器人系统信息传输的平均排队队长、时延、轮询周期的表达式;最后通过MATLAB及ROS系统对三种系统的理论值和仿真值进行分析比较。结果表明,该多机器人系统的信息传递率随着到达率的增加而显著增加。综合对比实验结果,在保证公平性的前提下,门限服务系统在加速信息处理速率、改善系统性能方面比其他两种服务策略更加稳定;在机器人增加时,完全服务系统在信息处理速度上较其他两种服务更好。     

Provably secure cloud storage for mobile networks with less computation and smaller overhead

Secure cloud storage (SCS) guarantees the data outsourced to the cloud to remain intact as it was before being outsourced. Previous schemes to ensure cloud storage reliability are either computationally heavy or admitting long overheads, thus are not suitable for mobile networks with strict computation/bandwidth restrictions. In this paper, we build an efficient SCS system for mobile networks based on homomorphic MAC and propose domain extension to enhance the security level and flexibility of the system. In addition, we give a formal security model which is compatible to previous ones and analyze our system in that model. We also give implementations on mobile devices to verify the effectiveness of our system.