Queueing analysis of buffered slotted multiple access protocols

Much of the literature on the performance evaluation of multiple access protocols has assumed a buffer capacity of one unit. This assumption is not realistic. In practice the buffer capacities used are larger than one unit in order to reduce the probability of packet rejection. This is more crucial for multiple access protocols, which allow moderate to high values of the expected throughput (URN, Random TDMA etc.).In this paper, a model appropriate for the analysis of buffered slotted multiple access schemes is proposed. The method can be applied to several multiple access protocols such as the URN protocol, the ALOHA protocol, Random TDMA etc. The cases of infinite and finite buffer capacity are examined separately but under the same basic assumptions. The analysis is based on the assumption that each user process can be modelled as an M/G/1 queueing system. The proposed method requires a small amount of computation and is characterized by a high speed, a fact that simplifies the buffer's design as well. The solution obtained is extremely accurate and exhibits excellent agreement with simulation results, which corroborate the accuracy of the model. The special case when the buffer capacity is equal to 1 is examined. In that case, the present approach also allows for computation of the packet delay distribution.     

P坚持时隙ALOHA稳定性

动态频谱共享无线通信系统使用时隙ALOHA协议完成对数据信道的竞争,稳定性问题是时隙ALOHA协议的固有特性。通过建立p坚持时隙ALOHA的系统模型,分析了在重传概率确定情况下,新包的生成率对系统稳定性的影响,以及新包的生成率已知情况时,重传概率对系统稳定的影响;通过数值计算与仿真,给出了两种情况下系统稳定的条件。     

几种随机接入协议的仿真性能比较分析

本文对纯ALOHA（P-ALOHA）、时隙ALOHA（S-AIDHA）和载波监听多路访问（CSMA）等三种随机接入协议的工作原理进行了介绍。对三种协议进行了理论分析,采用OPNET对协议进行了仿真性能比较,得出了相关重要结论,为提高随机接入协议性能提供了新的参考。     

时隙ALOHA协议下的网络化控制系统协同设计

针对网络化控制系统中信道容量有限的问题,本文提出一种基于时隙ALOHA通信协议的控制与通信协同设计方法.将控制系统的采样周期划分为若干等长度的时隙,在每个时隙中,系统的分布式传感器通过时隙ALOHA协议来随机竞争接入网络.由于在不同的采样周期各个传感器的接入状态不同,整个状态反馈控制系统将在若干子系统之间进行切换.据此,本文建立了离散的切换系统模型,并利用分段李雅普诺夫函数方法和平均驻留时间技术得到了能够保证系统指数稳定的充分条件.然后,给出能够保证控制系统稳定所需的信道吞吐率的界限,进而得到了时隙ALOHA协议中的最大重传次数与控制系统衰减率的定量关系.通过上述方法,本文建立了控制-通信协同设计的框架结构,可将控制器的增益矩阵和时隙ALOHA通信协议进行协同设计.最后,通过仿真验证了本文所提出的协同设计方法的有效性.     

Evaluating a new communication protocol for real-time distributed control

The recent trend in distributed automation and control systems has been towards event-triggered system architectures such as UML and IEC 61499. Although existing communication protocols (e.g., Ethernet) can support high-level communication within these systems, there is contention as to which low-level protocol to use, or if any exist that meet the requirements of being event-triggered and hard real-time. This paper proposes a new way to measure communication performance. The goal of the new measurement method is to stress the necessity that a real-time communication protocol needs to be both efficient and fair. This is illustrated by comparing three communication strategies: Controller Area Network (CAN), Time-Triggered CAN (TTCAN) and Escalating Priority CAN (EPCAN). The first two represent the extremes between event-triggered and time-triggered communication strategies; the third is introduced to illustrate the benefits of a new event-based communication protocol proposed by the authors.     

Ad Hoc网络通信协议的设计与实现

提出一种自组织、自管理的Ad Hoc网络通信协议SOSM。该协议包括网络同步、广播消息、加入/退出网络、点到点数据传输等子协议,当节点加入或退出时网络能够自动识别和更新,节点之间能进行可靠数据传输,并采用频分多址、时分多址、载波监听多路访问等技术解决无线通信碰撞问题。应用实例表明,该协议易于实现,运行稳定。     

Topology-transparent reservation time division multiple access in multihop ad hoc networks

In this paper, an optimal topology-transparent reservation time division multiple access (OTTR-TDMA) protocol is proposed for multihop ad hoc networks. Our MAC protocol is based on a slotted TDMA architecture in which every slot is divided into reservation phase and data transmission phase. Every node not only transmits data in its assigned slots that are computed by Chlamtac’s algorithm, but it also utilizes free slots among its non-assigned slots through reservation. Through theoretical analysis, we derive the proper parameter for the best performance. We compare our protocol with other TDMA protocols and find that it gives better performance. Simulation results show that they are consistent with our analytical results.     

Try-once-discard scheduling for stochastic networked control systems

In practical networked control systems (NCS), such as smart grids, cooperative robotics, and sensor networks, often multiple control applications share a communication infrastructure, requiring a smart and efficient scheduling mechanism to coordinate the access to the capacity-limited communication medium. In this article we consider the problem of event-based scheduling design for NCSs consisting of multiple control loops over a shared communication medium. We extend the notion of Try-Once-Discard (TOD), which is one of the basic deterministic event-based scheduling protocols for resource constrained NCSs, to the case of multiple stochastic control systems coupled via a shared communication medium subject to capacity limitation and stochastic packet delivery failure. Showing that the overall network-induced error is a homogeneous Markov chain in our stochastic set-up, we first study stability properties of such networked systems under the TOD scheduling scheme employing the concepts of stochastic stability. Then, we derive sufficient stability conditions under the TOD rule assuming that the communication channel is not ideal, i.e. a scheduled data packet for transmission might be lost in the communication channel with a non-zero probability. Furthermore, we derive analytic performance bounds by finding uniform upper-bounds for an average quadratic cost function. The numerical simulations are performed for variety of system parameters and NCS set-ups to strengthen our stability claim as well as illustrating performance bounds. Additionally, we show that the TOD scheduling rule outperforms the conventional time-triggered, and uniform and non-uniform random channel access arbitration mechanisms, in terms of efficient coordination of channel access in stochastic NCSs.     

扩频时隙ALOHA及其在CDMA通信中的应用

文章在分析传统ALOHA随机多址协议不足的基础上对扩频时隙ALOHA的基本原理及其性能进行了研究,并对其在第三代CDMA移动通信系统中的应用作了探讨。     

微小区一点多址无线紧急呼叫系统的设计与实现

首先说明微小区中用户紧急情况下需要无线呼叫业务,接着阐述一点多址无线通信系统的基本工作原理和多址协议主要类型及特点,最后讨论无线紧急呼叫系统的组成和基本结构,并详细说明用单片机实现微小区一点多址无线紧急呼叫系统的方法     

基于FlexRay总线的分布式测控系统

介绍了一种高可靠性分布式测控系统设计,采用FlexRay网络作为现场测控网络.该总线采用时间触发方式,并具有数据传输速率高、可靠性高和实时性好等优点,它给工业领域监控系统中原有的RS485、CAN总线等通信方式带来了更新换代的可能性.研究了FlexRay总线技术的硬件结构和通信协议,利用飞思卡尔单片机MC9S 12XF512作为主芯片,实现了多节点间的通信,为FlexRay总线技术在分布式测控系统中的应用奠定了基础.     

一种可靠可伸缩组通信系统设计与实现

组通信系统是支持一致性和容错的分布式协同系统中非常重要的组成部分.为了满足大规模协同应用的需求,文中采用了基于流言的协议与确定性协议组合的方法设计并实现了一种可靠可伸缩组通信系统SGCS.该系统主要包括可靠消息传输服务与组成员管理服务,其中基于流言的可靠多播协议和确定的消息恢复、流量控制、排序协议的组合,基于流言的失败检测协议与确定的视图一致化协议的组合以及乐观虚同步机制应用使系统具有良好的可伸缩性、可靠性和灵活性.     

甚小孔径终端(VSAT)卫星网络拓扑结构及接入方式

本文主要叙述VSAT—卫星网络类型及接入方式。从网络拓扑结构出发分析星形和网状两种网络形式、特点及通信业务。由中心站和若干个VSAT站组成的星形网络有三种通信方式:单跳、双跳和单、双混合式。在中心站的控制下,VSAT站之间通信要通过中心站经卫星线路实现,不能直接进行通信,线路延时较大,且通信业务受限。网状拓扑网络没有中心站,VSAT站之间可直接进行双向通信,线路延时小,在业务范围上也有新的突破。 VSAT网络接入方式极其重要,它决定着VSAT的性能,业务量及线路延时。不同的接入方式将影响卫星的利用率,信道容量的稳定性,结构的简易性,网络造价及组网灵活性等。据以上衡量标准,分别对TDM/FDMA、SCPC/FDMA、TDMA、CDMA和DAMA方式进行了分析,可根据用户不同的业务需求,组合并用,满足各种VSAT站灵活组网需要。     

DTS: Dynamic TDMA scheduling for Networked Control Systems

Networked Control Systems (NCSs) are pervasively applied in modern industry. With increasing functionalities, modern NCSs tend to have dynamic workload by holding a variety of applications via a shared network. To handle workload variations and provide performance guarantees, dynamic network scheduling scheme is highly desired in NCSs. In this paper, we propose a network scheduling scheme, referred to as DTS, that can make on-the-fly decisions to schedule the applications in NCSs. DTS aims at NCSs that use time-triggered network as shared medium and Time division multiple access (TDMA) as network access method. DTS dynamically changes the network accessing sequence of the applications in a way to provide optimal system performance and maintain control stability in NCSs. DTS adopts a decentralized schedule mechanism where each application can make its local schedule decision, enhancing the scalability of NCSs. Simulation results demonstrate the effectiveness of the proposed scheme by improving the network bandwidth and providing better system performance in NCS comparing with the existing time-triggered scheduling schemes.     

On design and formal verification of SNSP: a novel real-time communication protocol for safety-critical applications

The correct operation of time-triggered protocols highly depends on the well-synchronized clocks of the system. To maintain the global time, one strict constraint must be exerted on communication activities (e.g. temporal padding and sparse time base etc.), which not only increases complexity of the protocol design but also incurs a penalty in the network utilization. While for event-triggered protocols, it is difficult to achieve the real-time requirement and determinism. Therefore, it is necessary to explore the combination of the advantages of these two categories of protocol for applications in different scenarios. This paper proposes the Safe Node Sequence Protocol (SNSP), which is a variant of full time-triggered protocol TTP/C. In SNSP, a strict node sequence is defined and the order of communication events is established by this pre-configured order without binding to global time, so the protocol changes communication activities and error detection to an event-triggered model. Therefore, SNSP possesses the characteristics of both time-triggered and event-triggered model. Also, the potential impact of global time, such as byzantine clock failure, on the protocol is eliminated. At the same time, the formal verification of SNSP is much easier in the absence of global time. Moreover, we model the protocol and use formal checker SPIN to validate the basic fault-tolerant requirement of SNSP. The simulation results show the protocol enables better resource utilization and is more effective.     

自适应动态时隙ALOHA防碰撞算法的研究

时隙ALOHA算法是射频识别系统中通过分时复用方式的一种防碰撞算法,应答器在分配到的时隙中与阅读器进行数据交互.提出一种改进的自适应帧时隙ALOHA防碰撞算法,能够使得时隙到优化分配,进一步提高应答器的识别效率.     

On the use of learning automata in the control of broadcast networks: a methodology

Due to its fixed assignment nature, the well-known time division multiple access (TDMA) protocol suffers from poor performance when the offered traffic is bursty. In this paper, an adaptive TDMA protocol, which is capable of operating efficiently under bursty traffic conditions, is introduced. According to the proposed protocol, the station which is granted permission to transmit at each time slot is selected by means of learning automata (LA). The choice probability of the selected station is updated by taking into account the network feedback information. The system which consists of the LA and the network is analyzed and it is proven that the choice probability of each station asymptotically tends to be proportional to the probability that this station is not idle. Although there is no centralized control of the stations and the traffic characteristics are unknown and time-variable, each station tends to take a fraction of the bandwidth proportional to its needs. Furthermore, extensive simulation results are presented, which indicate that the proposed protocol achieves a significantly higher performance than other well-known TDMA protocols when operating under bursty traffic conditions.     

一种星球探测系统多机器人通信机制研究

分析了一种可重构星球探测系统中多机器人通信的特点．根据多机器人系统的功能要求，在TDMA（时分多址）分时共享信道原理和击鼓传花机制的启发下，提出了一种新颖的多机器人无线通信机制．详细介绍了该通信机制和通信协议．仿真和通信实验同时验证了该机制的可行性和实用性．     

Power level selection schemes to improve throughput and stability of slotted ALOHA under heavy load

We propose and analyse three different power selection schemes for slotted ALOHA random access protocol operating under multiple power levels. Through analysis and numerical examples we demonstrate that these schemes can significantly improve the performance of slotted ALOHA, in terms of throughput and stability, under heavy load. The proposed schemes are truly distributive in nature and can be easily implemented in wireless access systems without requiring any centralised control.     

A New Token-Based Channel Access Protocol for Wavelength Division Multiplexed Multiprocessor Interconnects

This paper presents a new token-based channel access protocol for wavelength division multiplexed optically interconnected multiprocessors. Our empirical study of access protocols based on slotted time division multiplexed data and control channels reveals that such protocols typically suffer from excessive slot synchronization latency due to static slot preallocation. The proposed token-based time division multiple access protocol minimizes latency by allowing dynamic allocation of slots to use channels efficiently. Simulation results indicate that the proposed scheme can significantly increase the performance for protocols based on preallocation and also those based on preallocation-controlled reservation of multiple channels.