移动场景下的节点高效寻路RPL路由算法优化

在低功耗有损网络(low power and lossy networks)中,现有的移动性支持路由算法存在控制消息冗余,应用场景不具有普适应,网络丢包率和移动节点能耗较高等问题.针对这些问题,提出一种移动场景下的节点高效寻路RPL路由算法(efficient pathfinding RPL routing algorithm for nodes in mobile scenarios,MSE-RPL).该算法提出的优化思路如下:首先,精简了移动节点的控制消息,并采用自适应黑名单机制建立备选父节点集,从而降低了移动节点的能耗;其次,基于移动节点的移动速度和方向,从备选父节点集中选择移出通信范围预估时间最短的节点作为最优父节点,不但适用于随机移动场景,还降低了平均端到端时延;最后,在链路中断前,利用DIS计时器及时通告DIS消息以快速重构拓扑,降低了丢包率.仿真结果表明,MSE-RPL算法在平均端到端时延、移动节点能耗、丢包率等性能指标方面均有明显改善.     

Sub-packet forward error correction mechanism for video streaming over wireless networks

Traditional Forward Error Correction (FEC) mechanisms can be divided into Packet level FEC (PFEC) mechanisms and Byte level FEC (BFEC) mechanisms. The PFEC mechanism of recovering from errors in a source packet requires an entire FEC redundant packet even though the error involves a few bit errors. The recovery capability of the BFEC mechanism is only half of the FEC redundancy. Accordingly, an adaptive Sub-Packet FEC (SPFEC) mechanism is proposed in this paper to improve the quality of video streaming data over wireless networks, simultaneously enhancing the recovery performance and reducing the end-to-end delay jitter. The SPFEC mechanism divides a packet into n sub-packets by means of the concept of a virtual packet. The SPFEC mechanism uses a checksum in each sub-packet to identify the position of the error sub-packet. Simulation experiments show the adaptive SPFEC mechanism achieves high recovery performance and low end-to-end delay jitter. The SPFEC mechanism outperforms traditional FEC mechanism in terms of packet loss rate and video Peak Signal-to-Noise Ratio (PSNR). SPFEC offers an alternative for improved efficiency video streaming that will be of interest to the designers of the next generation environments.     

Platoon架构下VANETs车间通信过程及性能分析

智能车辆编组platoon的稳定运行需要车辆间实时可靠的信息传输来保证.针对应用专用短程通信（DSRC）技术来实现车载自组织网路（VANETs）车间通信的platoon架构,提出了一种车间通信网络性能的分析方法,分别对platoon组内智能车辆间通信和多个platoons组间通信的过程进行了分析.该方法采用长度有限的M/G/1/K排队模型分析数据包到达媒体访问控制（MAC）层的排队过程,得到不同网络负载下缓冲区排队状态的平稳分布;并且在缓冲区可能处于空闲状态时,利用Markov模型分析方法得到不同车辆位置的车间通信性能.研究结果表明：网络数据流量、信道条件、MAC层缓冲区排队过程、争用信道退避过程以及platoon参数对车间通信的包传输时延和包丢失概率等网络性能有显著影响,数值分析结果验证了专用短程通信技术下的车间通信具有较小的信息传输延时,能够满足platoon稳定运行的要求.     

A network level channel abstraction for multimedia communication inreal-time networks

The design of communication protocols to support guaranteed real-time communication for distributed multimedia systems is examined. A network level abstraction called φ-channel that supports the requirements of real-time applications is proposed. A φ-channel represents a fractional, simplex, end-to-end communication channel between a source and a destination. The channel is characterized by a set of specific performance parameters associated with its traffic. The required performance characteristics of a φ-channel are specified in terms of the packet maximum end-to-end delay and the maximum number of packets that can be sent over that delay. The primary attribute supported by the φ-channel is the on-time reliability. Based on the specified parameters, the underlying delivery system verifies the feasibility of supporting such a channel. The performance of an accepted φ-channel is guaranteed under any conditions, barring hardware failures. The basic scheme that the model uses to verify the feasibility of accepting a φ-channel and the run-time support used to guarantee its performance are described. The results of a simulation experiment implementing the basic functionalities of the proposed scheme are also presented     

无线传感网中数据传输延时优化的路由协议

针对无线传感器网络中存在的数据包丢失严重以及端到端延时较高的问题,提出了一种数据传输延时优化的路由协议（RPODTD）。首先,根据数据包传输结果对信道探测情况进行分类,引入有效探测占比与传输效率作为节点的评价指标;然后,通过实际延时以及理论延时的差值估算数据包的排队延时;最后,给定最大和最小排队延时阈值,根据排队延时所属的区间判断是否更改传输路径。在OMNeT++上进行的仿真实验中,与基于链路质量和延时的复合负载均衡路由协议（ComLoB）和拥塞避免多路径路由协议（CA-RPL）相比,RPODTD节点的平均端到端延时分别降低了78.87%和51.81%,节点丢包率分别降低了40.71%和68.43%,节点的死亡率分别降低了25.42%和44.62%。仿真结果表明,RPODTD能有效地减少端到端延时,降低丢包率,延长网络生命周期。     

LQG-like control of scalar systems over communication channels: The role of data losses,delays and SNR limitations

In this work we address the problem of feedback control design for scalar systems in the presence of a non-ideal communication channel, which gives rise to tightly coupled limitations in terms of quantization errors, decoding/computational delays and packet loss affecting the closed loop control performance. We restrict our analysis to the context of LQG-like control, where the estimator and controller gains are forced to be constant, subject to SNR limitations, packet loss, and constant delay, and we derive their impact on the optimal design of the controller parameters. In particular, we show that the stability of the closed loop system depends on a tradeoff among SNR, packet loss probability and delay. Through this analysis we are also able to recover, as special cases, several results already available in the literature that have treated packet loss, quantization error and delay separately. We also show that the estimator and controller cannot be designed independently even if the controller has full knowledge of the packet loss sequence and the control inputs to the plant. In fact the optimal control gain, when accounting for the communication constraints is, in general, different from the optimal gain derived under the classical LQG scenario, which is recaptured when the SNR over the channel goes to infinity.     

衰落信道下V2V通信系统性能分析

针对V2V通信的连接性能问题,将衰落引起的信道随机性纳入分析,提出了一种在衰落信道中对V2V连接性能的分析算法,并将物理层和MAC层相结合,分析了不同衰落模型下V2V通信系统性能,包括对包丢失率、吞吐量、平均延时等通信性能指标,并通过仿真验证。仿真结果表明,瑞利信道的连接性能比Nakagami-m信道高,但信号的传输性能Nakagami-m信道全面优于Rayleigh信道。     

Estimating and Controlling the Renewable Microgrid States Using IoT Infrastructure

This paper considers the optimal filter design issue for microgrid state estimation and stabilisation under packet loss conditions. The considered internet of things (IoT) technologies collect system state information from sensors and send control messages to actuators where they are connected over a lossy communication network. From signal processing point of view, this paper develops an optimal state estimation algorithm using the mean squared error principle. Then a feedback controller is designed under the condition of packet dropouts in the communication network. Finally, the convergence of the developed algorithm is numerically shown. The performance of the proposed schemes are demonstrated using the renewable microgrid.     

移动边缘计算环境下基于改进GPSR的VANET路由算法

针对车辆自组织网络(VANET,vehicular ad-hoc network)中现有路由协议存在的路由选择错误、丢包率较高、服务质量低等问题,提出了移动边缘计算环境下,结合改进贪婪周边无状态路由(GPSR,greedy perimeter stateless routing)和自适应链路质量评估的VANET路由算法;首先,结合边缘计算构建了VANET通信模型,对其车辆位置和速度进行系统的理论分析;将边缘计算架构应用于VANET能够有效缓解计算量大、与车辆有限且不均的资源分布之间的矛盾;然后,提出了基于节点移动速度和节点间距离的改进GPSR协议,通过自适应链路稳定性和链路传递速率评估来选择合适的中继节点,动态更新链路;通过SUMO仿真平台对路由算法的性能进行评估,实验结果表明,相对于其他算法,所提算法受车辆密度、交通流以及车辆相对速度的影响较小,且提高了分组传送率(车辆数为300时传送率达到92%),减少端到端延迟(交通流为5时延迟降低到1.5 s),从而降低了通信开销。     

Evaluating transport protocol performance over a wireless mesh backbone

IEEE 802.11n wireless physical layer technology increases the deployment of high throughput wireless indoor mesh backbones for ubiquitous Internet connectivity at the urban and metropolitan areas. Most of the network traffic flows in today’s Internet use ‘Transmission Control Protocol’ (TCP) as the transport layer protocol. There has been extensive works that deal with TCP issues over wireless mesh networks as well as noisy wireless channels. Further, IEEE 802.11n is well known for its susceptibility to increased channel losses during high data rate communication. This paper investigates the dynamics of an end-to-end transport layer protocol like TCP in the presence of burst and correlated losses during IEEE 802.11n high data rate communication, while maintaining fairness among all the end-to-end flows. For this purpose, we evaluate four TCP variants-Loss Tolerant TCP (LT-TCP), Network Coded TCP (TCP/NC), TCP-Horizon and Wireless Control Protocol (WCP), where the first two protocols are known to perform very well in extreme lossy networks, and the last two are specifically designed for mesh networks. Our evaluation shows that WCP performs better in a IEEE 802.11n supported mesh networks compared to other three variants. However, WCP also results in negative impact at high data rates, where end-to-end goodput drops with the increase in physical data rate. The analysis of the results reveals that explicit loss notifications and flow balancing are not sufficient to improve transport protocol performance in an IEEE 802.11n supported mesh backbone, rather a specific mechanism is required to synchronize the transport queue management with lower layer scheduling that depends on IEEE 802.11n features, like channel bonding and frame aggregation. The findings of this paper give the direction to design a new transport protocol that can utilize the full capacity of IEEE 802.11n mesh backbone.     

Congestion Adaptive Routing in Mobile Ad Hoc Networks

Mobility, channel error, and congestion are the main causes for packet loss in mobile ad hoc networks. Reducing packet loss typically involves congestion control operating on top of a mobility and failure adaptive routing protocol at the network layer. In the current designs, routing is not congestion-adaptive. Routing may let a congestion happen which is detected by congestion control, but dealing with congestion in this reactive manner results in longer delay and unnecessary packet loss and requires significant overhead if a new route is needed. This problem becomes more visible especially in large-scale transmission of heavy traffic such as multimedia data, where congestion is more probable and the negative impact of packet loss on the service quality is of more significance. We argue that routing should not only be aware of, but also be adaptive to, network congestion. Hence, we propose a routing protocol (CRP) with such properties. Our ns-2 simulation results confirm that CRP improves the packet loss rate and end-to-end delay while enjoying significantly smaller protocol overhead and higher energy efficiency as compared to AODV and DSR     

基于GM(1,1)预测的MANET拥塞控制

提出一种用于无线移动Ad hoc网络的TCP自适应拥塞控制机制(TCP_Acc),在给定数据链路层统计带宽的情况下,使用GM(1,1)模型预测未来的网络状态,并根据预测得到的带宽信息自适应地调节拥塞窗口。仿真实验结果表明,该机制能够有效地改进无线移动Ad hoc网络中实时TCP通信的可靠性和无线实时通信的服务质量,如较低的丢包率以及端到端延迟等。     

自适应前向纠错增强TCP在无线链路上性能研究

针对无线链路引发的TCP性能缺陷,提出一种适用于TCP端对端前向纠错的自适应算法,并在此基础上利用Reed Solomon码实现一种新的TCP ARS。TCP ARS利用包一级的前向纠错在传输层恢复丢失的分组,并能自适应地根据网络丢包率、往返时延等参数调整前向纠错的冗余信息度,较好地解决了TCP在无线环境中的性能缺陷问题。     

Cross-layer opportunistic adaptation for voice over ad hoc networks

The support of voice communication is fundamental in the deployment of an ad hoc network for the battlefield or emergency response. We use the QoS requirements of voice to identify factors influencing its communication, and validate their significance through statistical analysis. Based on the results, we propose an opportunistic protocol within a cross-layer framework that adapts these factors at different time scales. Hop-by-hop adaptation exploits the PHY/MAC interaction to improve the use of the spectral resources through opportunistic rate-control and packet bursts, while end-to-end adaptation exploits the LLC/application interaction to control the demand per call through voice coding and packet size selection. Our objective is to maximize the number of calls admitted while minimizing loss of quality. We evaluate the performance of the protocol in simulation with real audio traces using both quantitative and mean opinion score (MOS) audio quality metrics, comparing to several standard voice codecs. The results indicate that: (i) compression and packet-size selection play a critical role in supporting QoS over ad hoc networks; (ii) header compression is needed to limit the overhead per packet especially over longer paths; (iii) good voice quality is achieved even in strenuous network conditions.     

有损信道下网络化系统的均方最优渐近跟踪

对于通讯信道具有丢包的网络化反馈控制系统, 运用乘性噪声模型来描述丢包这一信道不确定性, 并根据 网络化系统的结构特点提出了一种渐近跟踪控制器结构, 研究了该结构下系统的均方可镇定性以及均方最优渐近 跟踪与均方可镇定性的等价关系. 在此基础上, 运用随机均方最优控制理论给出了该系统均方最优渐近跟踪设计方 法, 该方法取决于广义代数黎卡提方程(MARE)的均方镇定解. 进一步, 本文提出了求解上述均方镇定解的新算法. 最后的仿真验证了对于信道具有丢包的网络化反馈系统最优渐近跟踪问题, 本文所提方法的有效性和可行性.     

Capacity analysis of dual-hop wireless communication systems over α–μ fading channels

In this paper, we consider a dual hop wireless communication system with a non-regenerative relay and study its performance over the α–μ fading channel. Specifically, we derive closed-form expressions for the moment generating function (MGF), the cumulative distribution function (CDF), and the probability density function (PDF) of the harmonic mean of the end-to-end signal-to-noise ratio (SNR) assuming the α–μ fading model. We also derive closed-form expressions for the end-to-end capacity and outage capacity of the system herein. The obtained expressions can be reduced to study the performance of dual hop communication systems over other fading channel models by using the proper values for the α and μ parameters, such as Rayleigh, Nakagami-m, and Weibull fading models. Numerical results are provided for the obtained expressions and conclusion remarks are drawn.     

Competitive On-Line Switching Policies

Abstract. Consider the following problem. A switch connecting n input channels to a single output channel must deliver all incoming messages through this channel. Messages are composed of packets , and in each time slot the switch can deliver a single packet from one of the input queues to the output channel. In order to prevent packet loss, a buffer is maintained for each input channel. The goal of a switching policy is to minimize the maximum buffer size. The setting is on-line; decisions must be made based on the current state without knowledge of future events. This general scenario models multiplexing tasks in various systems such as communication networks, cable modem systems, and traffic control. Traditionally, researchers analyzed the performance of a given policy assuming some distribution on the arrival rates of messages at the input queues, or assuming that the service rate is at least the aggregate of all the input rates. We use competitive analysis, avoiding any prior assumptions on the input. We show O(log n )-competitive switching policies for the problem and demonstrate matching lower bounds.     

TCP Performance and Behaviors with Local Retransmissions

TCP has been the dominant transport protocol over the global Internet, and its performance over a hybrid wireless/wireline network has attracted much attention in recent years. This paper investigates the end-to-end TCP performance, in terms of normalized throughput, effective goodput, and packet delay, over wireless lossy links with local retransmissions. The results reveal that local retransmissions can increase the normalized TCP throughput in different wireless bandwidth, delay, and error settings, at the cost of a decrease in effective goodput and an increased packet delay. The performance observation is explained by the explored TCP endpoint behaviors, including the spurious timeout and duplicated acknowledgment. Analysis shows that spurious timeouts with local retransmissions are rare due to the conservative TCP timeout algorithm. However, spurious duplicated acknowledgments have negative impact and a further improvement with the D-SACK proposal is evaluated.     

End-to-End Security Across Wired-Wireless Networks for Mobile Users

ABSTRACT

Recent advances in mobile computing and wireless communication technologies are enabling high mobility and flexibility of anytime, anywhere service access for mobile users. As a result, network connections of such users often span over heterogeneous networking environments consisting of wired and wireless networking technologies. Both network heterogeneity and user mobility make the securing of data transmission over heterogeneous networks challenging and complex. In this paper, we focus on the challenge of providing secure end-to-end network transmissions to wireless mobile users. To minimize service interruption during ongoing secure sessions of mobile users, we present the design and implementation of an approach based on the well-known Internet Protocol Security (IPSec) standard. We conducted a performance evaluation of our implementation using a Voice over IP (VoIP) application over an actual network testbed. Our empirical performance results demonstrate a packet loss improvement of 17% to 34% (for various VoIP packet sizes) and a handoff delay improvement of almost 24% validating the high efficiency of our proposed approach.