Scheduling Strategy Design Framework for Cyber–Physical System with Non-Negligible Propagation Delay

Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies.     

A novel scheme based on minimum delay at the edges for optical burst switching networks

This paper proposes a novel scheme based on minimum delay at the edges (MDE) for optical burst switching (OBS) networks. This scheme is designed to overcome the long delay at the edge nodes of OBS networks. The MDE scheme features simultaneous burst assembly, channel scheduling, and pre-transmission of control packet. It also features estimated setup and explicit release (ESXR) signaling protocol. The MDE scheme can minimize the delay at the edge nodes for data packets, and improve the end-to-end latency performance for OBS networks. In addition, comparing with the conventional scheme, the performances of the MDE scheme are analyzed in this paper.     

联合空时编码的水声多用户节点协同并行传输多址接人协议设计

针对水声信道长传播时延特点导致水声通信网吞吐量低的问题,提出了一种多节点协同并行传输的多址接入协议。该协议由接收端发起预约,在距离认知的基础上对预约节点划分协同传输小区,从而构建多用户节点的多输入多输出集中式网络架构;采用空时码对数据包编码,并合理规划数据包的发送时刻,使同一小区的多个用户节点发送的数据包在设定时间偏差范围内同时到达接收端,而不同小区的数据包以包链形式到达,实现多用户节点的无干扰、高效并行传输。仿真实验结果表明,与已有的其它两种协议相比,设计的协议通过空时复用的方法大幅缩短了平均端到端时延,显著提升了归一化网络吞吐量。      

基于EPL的分布式时钟同步方法

工业以太网协议Ethernet POWERLINK(EPL)分布式站点的时钟同步方法并不能在实时运行过程中保持很高的同步精度,无法满足特定环境下的控制要求。研究了工业以太网协议EPL的两种时钟同步机制,通过数理计算分析了时钟同步误差产生的原因,针对误差较大的缺点,提出了减小误差的方法。通过迭代计算消除了主从站同步报文往返的路径延迟,并设计基于现场可编程门阵列(FPGA)的集线器(Hub)用于EPL菊花链网络拓扑结构,有效地克服了时钟同步报文往返传输延时不一致的缺点,测试结果表明新方法明显优于协议自身的时钟同步方法,对于实现基于EPL的高精度分布式时钟同步网络具有重要意义。     

Parameterizing both path amplitude and delay variations of underwater acoustic channels for block decoding of orthogonal frequency division multiplexing

There are no commonly-agreed mathematical models for the input-output relationship of underwater acoustic channels. For each path in a time-varying multipath channel within a short period of time (e.g., one short data block), this paper proposes to use one polynomial to approximate the amplitude variation and another polynomial up to the first order to approximate the delay variation within a block duration. Under such a channel parameterization, the discrete-time channel input- output relationship tailored to zero-padded orthogonal-frequency-division-multiplexing (OFDM) transmissions is then derived, based on which an OFDM receiver is validated using experimental data collected during the 2008 Surface Processes and Acoustic Communications Experiment. For channels with a short coherence time, the numerical results show that incorporating both the amplitude and delay variations improves the system performance.     

光网络中视频业务传输的节点排队机制

对服务质量(QoS)中的队列机制进行了重点的分析, 并对先进先出(FIFO)以及具有优先级(PQ)的两种队列机制的特点进行了详细的比较。具有优先级(PQ)队列可以降低高优先级业务的平均排队时延, 但却无法保证时延抖动的要求。提出了基于具有优先级队列机制的改进方案。仿真结果表明, 新的排队机制有效得解决了具有优先级(PQ)排队机制中无法保证高优先级(视频)业务传输中的时延抖动问题, 当初始时延分布差别很大的数据包在经过节点排队调度之后, 时延抖动有了明显改善。     

Low-Latency Short-Packet Transmission over a Large Spatial Scale

Short-packet transmission has attracted considerable attention due to its potential to achieve ultralow latency in automated driving, telesurgery, the Industrial Internet of Things (IIoT), and other applications emerging in the coming era of the Six-Generation (6G) wireless networks. In 6G systems, a paradigm-shifting infrastructure is anticipated to provide seamless coverage by integrating low-Earth orbit (LEO) satellite networks, which enable long-distance wireless relaying. However, how to efficiently transmit short packets over a sizeable spatial scale remains open. In this paper, we are interested in low-latency short-packet transmissions between two distant nodes, in which neither propagation delay, nor propagation loss can be ignored. Decode-and-forward (DF) relays can be deployed to regenerate packets reliably during their delivery over a long distance, thereby reducing the signal-to-noise ratio (SNR) loss. However, they also cause decoding delay in each hop, the sum of which may become large and cannot be ignored given the stringent latency constraints. This paper presents an optimal relay deployment to minimize the error probability while meeting both the latency and transmission power constraints. Based on an asymptotic analysis, a theoretical performance bound for distant short-packet transmission is also characterized by the optimal distance–latency–reliability tradeoff, which is expected to provide insights into designing integrated LEO satellite communications in 6G.     

Improvement of packet transmission scheduling and delivery rate in wireless Ad-Hoc networks

The principal purpose of Ad-Hoc wireless networks is to increase service efficiency in terms of transmission scheduling and packet transfer rate. The approaches that assume frame unicity to satisfy a given set of packets minimize the end-to-end delay. However, they do not guarantee a maximum packet delivery rate due to the difficulty of establishing robust paths for packet transfer across nodes deployed in the network, especially in a three-dimensional (3D) environment. The objective is to minimize the end-to-end delay by ensuring the maximum delivery of packets to their destinations. Furthermore, the signal-to-interference-and-noise-ratio (SINR) model is considered to optimize transmission scheduling. In this paper, an optimal node coordinates optimization approach is proposed to extend two recently investigated schemes in the literature (S-RDSP and I-RDSP). The developed algorithms, named S-MPDR and I-MPDR, seek to reduce the end-to-end delay by delivering a collection of inserted packets over a 3D environment while also maximizing the delivery rate of these packets. Desirability functions are used to evaluate the network’s performance in various scenarios involving two different environments, Level 0 and Level 1. Numerical results demonstrate that the developed algorithms outperform both schemes in terms of end-to-end delay and packet delivery rate. In the Level 0 environment, the overall minimum delay and packet delivery rate scores provided by S-MPDR are increased by 28% and 88% compared to S-RDSP, respectively. In comparison, those provided by I-MPDR are increased by 24% and 16% compared to I-RDSP. Similarly, in the Level 1 environment, the scores provided by S-MPDR are increased by 25% and 100% compared to S-RDSP, respectively, while those provided by I-MPDR are increased by 23% and 25% compared to I-RDSP.     

分布式无线地震数据采集同步技术研究

针对目前分布式无线地震数据采集中由于采集节点增多、无线传输延时等因素导致的各采集节点间数据采集同步精度不高的问题,研究并设计了一种针对分布式无线数据同步采集中各个节点同步授时以及对采集数据包进行精确时间标记的方案。采用GPS(Global Positioning System)授时技术对各个采集节点时钟进行授时,同时利用GPS精准的秒脉冲对本地压控晶振器频率误差进行实时修正。采用在地震采集数据包中加入精确的时间戳信息的方法,保证了各个节点间同步误差限制在0.1ms以内。即使在GPS失效的情况下,压控晶振器和计数器联合作用仍可保证各节点同步采集稳定工作6小时。     

A clustering-driven medium access control protocol for WDM star networks

Channel assignment and nodes’ service order are two key issues that have to be addressed when designing medium access control (MAC) protocols for WDM star networks. Traditional scheduling techniques consider either channel assignment or nodes’ service order issues. Furthermore, they make use of information such as data channels or receivers’ availability, without combining it with senders’ demands. This paper introduces a novel approach to message scheduling algorithms for WDM star networks, which is driven by clustering techniques. The proposed clustering driven-minimum scheduling latency (CD-MSL) scheme combines all the aforementioned information to create groups of similar source nodes on the basis of the destination nodes of their messages, aiming at rearranging nodes’ service order and improving network performance. Extensive simulation results are presented, which indicate that the proposed clustering-driven scheme leads to a significantly higher throughput-delay performance, in comparison to conventional scheduling algorithms.     

一种通用的时隙环网时隙调度机制

提出一种新颖的时隙环网公平机制——环分布式时隙调度(DTSR), 该机制是分布式的, 适合所有目的节点剥离业务的时隙环网。DTSR通过在单向信道上循环传输的时隙控制头(TCH)内增加一个简单的域, 实现对环上“饿死”节点信息的动态收集, 协调各个节点占用资源的时间, 确保各节点之间的公平性; 在发现环上有“饿死”节点后, DTSR利用时隙环网空间重用的特性, 调度相关节点向不经过“饿死”节点的其他节点发送数据, 充分利用了环网资源; 此外DTSR机制具有良好的算法收敛性, 且接入时延较传统算法更小。最后,对DTSR的性能进行仿真, 并和几个典型的时隙环网的公平机制进行了比较。     

无线传感器网络中基于最小延时的数据汇集树构建与传输调度算法

无线传感器网络的数据通信模式问题是目前的研究热点,针对现有的无线传感器网络数据汇集算法延时较大这一不足,对最小延时数据汇集树和传输调度问题进行了研究。提出一种基于度约束的汇集树构建算法(DCAT)。该算法按照 BFS 方式遍历图,当遍历到每个节点时,通过确定哪些节点与汇点更近来确定潜在母节点集合。然后,选择图中度数最小的潜在母节点作为当前被遍历节点的母节点。此外,为了在给定的汇集树上进行高效地数据汇集,还提出两种新的基于贪婪的TDMA传输调度算法：WIRES-G 和 DCAT-Greedy。利用随机生成的不同规模的传感器网络,参照当前最新算法,对文中方法的性能进行了全面评估。结果表明,与当前最优算法相比,文中调度算法与文中汇集树构建算法结合起来,可显著降低数据汇集的延时。     

An efficient scheme for optimizing channel utilization in OBS networks

Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over DWDM links. In order to make OBS a viable solution, the wavelength scheduling algorithms need to be able to utilize the available wavelengths efficiently, while being able to operate fast enough to keep up with the burst incoming rate. Unfortunately, horizon scheduling cannot utilize the voids created by previously scheduled bursts, resulting in low bandwidth utilization. To date, Min-SV is the fastest scheduling algorithm that can schedule wavelengths efficiently. However, its complexity is O (log m) and it requires 10 log (m) memory accesses to schedule a single burst. This means that it can take upto several microseconds for each burst request, which is still too slow to make it a practical solution for OBS deployment. In this paper, an efficient scheme has been proposed for optimizing channel utilization in OBS networks. In the proposed approach, a burst is represented by an interval of time. The process of scheduling a number of bursts, thus, turns to be a process of fitting a set of the corresponding time intervals on a channel time line that represents a channel-time resource. By doing so, the scheduling process can be formulated as a combinatorial optimization problem. Then, graph theory is applied to schedule as many non-overlapping intervals as possible onto the channel time line. The underlying concept of the proposed scheduling scheme is that of briefly delaying the scheduling of a burst so that a much better decision can be made about a number of bursts all-together. This scheme is shown, through simulations, to improve performance in terms of burst loss probability, channel utilization, fairness-control and data throughput over existing schemes. Thus the proposed scheme is well suited for high performance networks in terms of reliability.     

A QoS-Guanranteed Scheduling Algorithm with High Throughput for Edge Nodes of Optical Burst Switching Networks

A scheduling algorithm for the edge nodes of optical burst switching (OBS) networks is proposed to guarantee the delay re quirement of services with different CoS (Class of Service) and provide lower burst loss ratio at the same time. The performance of edge nodes based on the proposed algorithm is presented.     

基于引力约束的复杂网络拥塞问题研究

如何在保证网络传输效率的同时提高网络的吞吐量是目前研究的主要问题. 通过研究节点对数据包传递过程的引力作用,提出了一种具有引力约束的路由算法. 为检验算法的有效性,通过引入一个状态参数H, 利用由稳态到拥塞状态的指标流量相变值来度量网络的吞吐量, 同时利用数据包的最大传输时间〈T_max〉 与平均传输时间 〈T_avg〉来分析网络的传输效率. 针对算法在不同引力约束条件下的路由情况进行了仿真.仿真结果表明, 若数据传递过程只考虑路径长度最短,则会导致网络吞吐量较低且流量分布极不均匀; 若只顾及等待时间最短,会导致传输路径过度迂回且大部分节点都会陷入拥塞状态; 同时考虑路径长度和等待时间的引力作用并选取适当引力的节点进行传递, 可以显著提高网络吞吐量并缓解网络的拥塞程度.     

Time-slot interchange of 40 Gbits/s variable length optical packets using conversion-dispersion-based tunable delays

We demonstrate tunable time-slot interchange of 40 Gbits/s optical data packets using a conversion-dispersion-based tunable optical delay element. Odd and even data packets are extracted from an input signal, delayed relative to one another in a highly dispersive medium, and then multiplexed back together. Tunability is demonstrated by operating with two different packet lengths, 182 and 288 bits/packet, and a bit error rate of <10(-9) is achieved.     

一种基于分层的量子分组传输方案及性能分析

大规模量子通信网络中,采用量子分组传输技术能有效提升发送节点的吞吐量,提高网络中链路的利用率,增强通信的抗干扰性能.然而量子分组的快速传输与路由器性能息息相关.路由器性能瓶颈将严重影响网络的可扩展性和链路的传输效率.本文提出一种量子通信网络分层结构,并根据量子密集编码和量子隐形传态理论,给出一种基于分层的量子分组信息传输方案,实现端到端的量子信息传输.该方案先将量子分组按照目的地址进行聚类,再按聚类后的地址进行传输.仿真结果表明,基于分层的量子分组信息传输方案能够有效减少量子分组信息在量子通信网络中的传输时间,并且所减少的时间与量子路由器性能与发送的量子分组数量有关.因此,本文提出的量子分组信息传输方案适用于大规模量子通信网络的构建.     

An adaptive reservation scheme for optical network

In this paper, the various Optical Burst Switching (OBS) reservation schemes have been examined in order to reduce data loss caused by either channel scheduling or resources. A novel multi-service OBS edge node with synchronized bandwidth reservation mechanism (SRM) has been proposed, which enables high-speed network transport nodes to dynamically reserve bandwidth needed for active data burst flows. The performance of the proposed mechanism is evaluated by means of NS-2 simulation. The results show that the packet delay is kept within the constraint for each traffic flow and the performance metrics such as burst loss rate, throughput and fairness are remarkably improved.