自适应低轨卫星MAC协议性能分析

针对低轨卫星通信信道碰撞检测能力弱,时延较长和大业务量的特点,提出一种具有接入控制机制的自适应APRMA MAC协议。通过对信道负载和业务优先级判断来确定不同业务的接入概率函数,并且接入概率在每个时隙中通过更新来动态适应系统资源的变化。该MAC协议确保多个终端合理共享有限的无线资源同时,系统能达到高容量。通过仿真对语音业务丢包概率、数据包平均时延和数据业务吞吐量三个衡量协议性能指标与传统协议进行分析对比,证明了APRMA MAC协议显著改善系统性能。     

Multiple sender distributed video streaming

With the explosive growth of video applications over the Internet, many approaches have been proposed to stream video effectively over packet switched, best-effort networks. We propose a receiver-driven protocol for simultaneous video streaming from multiple senders to a single receiver in order to achieve higher throughput, and to increase tolerance to packet loss and delay due to network congestion. Our receiver-driven protocol employs a novel rate allocation algorithm (RAA) and a packet partition algorithm (PPA). The RAA, run at the receiver, determines the sending rate for each sender by taking into account available network bandwidth, channel characteristics, and a prespecified, fixed level of forward error correction, in such a way as to minimize the probability of packet loss. The PPA, run at the senders based on a set of parameters estimated by the receiver, ensures that every packet is sent by one and only one sender, and at the same time, minimizes the startup delay. Using both simulations and Internet experiments, we demonstrate the effectiveness of our protocol in reducing packet loss.     

A real-time flood-routed voice protocol for fibre optic local area networks

A simple real-time flood routing voice (RTFRV) protocol which is suitable for point-to-point arbitrarily connected fibre optic local area networks is described. Simulation on a 3 Mbit/s nine-node mesh network which employs the protocol has shown that it is capable of supporting about 50 simultaneous two-way voice conversations (or 100 users) with packet delay of less than 10 ms and without any loss of information. The overall results suggest that voice transmission on such a network is feasible and that it performs better than voice transmission over Ethernet. Furthermore, the network is also very robust and allows easy network reconfiguration.     

An analytical model for end-to-end communication channel over PLCN based on QBDs

The performance analysis of packet loss in end-to-end communication channel is the basis of adaptive end-to-end protocol design. However, existing analytical models of packet loss cannot provide quantitative information of lossy channel systems. In this paper, an analysis on balance state of end-to-end communication channel over probabilistic lossy communication networks (PLCN) is performed firstly. We then discuss the process of modeling end-to-end communication channel over PLCN using Quasi Birth–Death models (QBDs) in detail. Finally, some characteristics of end-to-end communication channel, such as the stability of channel and the performance of channel packet loss, are analyzed. The experimental results show that the proposed model can analyze quantitatively the stability of end-to-end communication channel and the packet loss probability during time interval [0,t]. The results in the work are helpful for designing adaptive end-to-end communication protocols.     

Dynamic accommodation of the permission probability over the joint voice/data frame reservation multiple access

Some schemes are proposed for dynamic accommodation of the permission probability based on frame reservation multiple access protocol, a variant of PRMA, where the base station broadcasts the acknowledgements for all the slots in a frame which occurs at the end of the frame. One is by adjusting the permission probability with regard to the available slots, once in every frame. Another is to set the permission probability individually, based on the contending number of retrials for each active voice terminal. For the integration of voice and data users, to combine the above mentioned schemes, the speech packet dropping probability and mean data delay techniques are superior to the original PRMA with fixed permission probability, as indicated from the simulation results obtained here.     

An improved UDP protocol for video transmission overInternet-to-wireless networks

Packet video will become a significant portion of emerging and future wireless/Internet traffic. However, network congestion and wireless channel error yields tremendous packet loss and degraded video quality. In this paper, we propose a new complete user datagram protocol (CUDP), which utilizes channel error information obtained from the physical and link layers to assist error recovery at the packet level. We propose several maximal distance separable (MDS) code-based packet level error control coding schemes and derive analytical formulas to estimate the equivalent video frame loss for different versions of user datagram protocol (UDP). We validate the proposed packet coding and CUDP protocol using MPEG-coded video under various Internet packet loss and wireless channel profiles. Theoretic and simulation results show that the video quality can be substantially improved by utilizing the frame error information at UDP and application layer     

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     

SSL协议隐蔽通道的研究与实现

为提升隐蔽通道的网络穿透能力及抗分析性能,提出了一种基于SSL安全协议的新型隐蔽通道。通过SSL握手报文的随机数字段建立隐蔽域,利用SSL握手协商构建消息通道,采用一包一密进行流量变形伪装,通过访问HTTPS服务实现网络隐蔽通道传输。在多种不同HTTPS环境下的实验验证了该方法的可行性,测试结果表明,相比传统存储型隐蔽通道,该隐蔽信道的容量有大幅度提高,单个报文可携带28 Byte信息,且具有更高的抗隐蔽域估计及抗统计画像能力。     

基于马尔可夫链的IEEE802.15.4网络防丢包信道访问机制研究

为了降低802.15.4MAC层数据帧丢包率,在分析丢包率的原因基础上,提出了一种基于Markov链的信道竞争机制模型。通过对网络发送、退避和信道检测状态的稳态概率进行数学推导,研究了信道碰撞和数据帧的丢包率分析式;最后研究了参数数据包到达速率、节点数量、误码率、后退指数、后退等待次数对碰撞概率和丢包率的影响。实验结果表明,与节点无休眠态的802.15.4网络相比,节点丢包率平均降低了23.7%,模型较好地描述了提出的MAC层信道访问机制,合理的网络参数设置能够优化数据帧丢包率,研究结果对无线传感网的应用提供可靠传输优化参考。     

Performance simulation of wireless multimedia systems using NC-PRMA/DA and SNC-PRMA/DA protocols

A noncollision packet reservation multiple access with dynamic allocation (NC-PRMA/DA) scheme is proposed and investigated as a suitable candidate protocol for wireless multimedia communications. Access requests of the existing users in NC-PRMA/DA are conveyed to the base station in a noncollision manner by using a time-frequency signaling scheme. In addition, the scheduling NC-PRMA/DA (SNC-PRMA/DA) scheme, which is NC-PRMA/DA with packet scheduling, is also presented. Mixed voice, variable-rate video, and data traffic is used to demonstrate the efficiency of the proposed schemes for a single-cell environment. Simulation results show that our proposed NC-PRMA/DA and SNC-PRMA/DA protocols outperform the existing PRMA/DA protocol.     

Performance evaluation of tree based data aggregation for real time indoor environment monitoring using wireless sensor network

A fundamental challenge in the implementation of Wireless Sensor Network is to reduce packet loss when channel bandwidth is limited and the energy of sensor is finite. In this paper, a suitable solution is provided for controlling packet loss through tree-based data aggregation and routing. From this perspective, a binary tree-based data aggregation and routing has been proposed which can reduce packet loss and energy dissipation which occurs due to unsuccessful packet delivery. Simulation result using NS-2 shows that binary tree-based data aggregation reduces packet loss up to 63.1% compared to cluster based protocol LEACH, up to 26.5% compared to chain based protocol PEGASIS. Moreover binary tree based data aggregation out performs both LEACH and PEGASIS with respect to the parameters end to end delay, packet delivery ratio and total energy consumption. Our proposed architecture integrates sensor network, mobile device, Access point and Cloud services as a single unit for real time monitoring. An experimental analysis of the proposed approach for indoor environment monitoring is carried out in the university laboratory to evaluate the performance in terms of time and energy consumption.

     

一种基于负载均衡的动态多信道自组网MAC协议

自组网的信道是多跳共享的,使用传统的单信道接入协议会带来隐终端和暴露终端等问题,而目前提出的多信道协议没考虑到负载均衡问题会导致系统性能下降.在本文中提出一种基于负载均衡的动态多信道接入协议,该协议将可用频带分为一个控制信道和多个数据信道,源站与目的站在控制信道上交换控制分组信息来决定在最佳的数据信道上传输数据分组,信道选择是基于信道接收功率最大的原则.仿真结果表明,它比单信道协议有更好的性能.     

基于无线信道的视频通信丢包率控制方法研究

根据3G信道高误码率的特点研究并实现了一种基于实时流控制协议RTCP的视频通信系统的丢包率控制算法,通过接收RTCP协议的RR包中的统计信息,来动态的估算3G信道的误码率和控制数据包发送长度,达到控制数据传输过程中的丢包率的目的.实践证明：该方法具有快速检测3G信道误码率、根据信道的误码率来快速调整数据包发送长度的优点.     

构建Ad Hoc网络跨层协议交互机制

Ad Hoc网络中无线信道的时变特性和网络拓扑的不断变化导致了链路的频繁断续,使得数据包大量丢失.这就要求高层应用协议能够快速访问底层传输协议甚至信道的状态信息,各层协议之间能够根据需要互相交换信息,迅速作出决策,提高分组接收成功率.基于QualNet网络仿真器设计并实现了一种网络协议栈跨层交互的机制.结果表明,利用该机制,能够快速建立跨层协议的交互,使得高层协议及时获取低层协议的有用信息,从而可根据信道的状况动态调节网络协议设置,提高分组发送成功率,优化网络传输的性能.     

Performance Analysis of CSMA/CA Protocol for High-speed Wireless LANs

In this paper, we present an exact analysis to numerically evaluate the performance of the multiple random access method with non-persistent carrier sense multiple access with collision-avoidance (CSMA/CA) protocol for high-speed and realizing fully-distributed wireless LANs. The collision-avoidance portion of CSMA/CA in this model is performed with a random pulse transmission procedure, in which a user with a packet ready to transmit initially sends some pulse signals with random intervals within a collision-avoidance period before transmitting the packet to verify a clear channel. The system model consists of a finite number of users to efficiently share a common channel. The time axis is slotted, and a time frame has a large number of slots and includes two parts: the collision-avoidance period and the packet-transmission period. A discrete-time Markov process is used to model the system operation. The number of slots in a frame can be arbitrary, dependent on the chosen lengths of the collision-avoidance period and packet-transmission period. The influence of possible length of the collision-avoidance period and packet-transmission period, and pulse transmission probabilities on the network performance are discussed, based on the results of the utilization of channel and average packet delay for the different packet generation rate.     

改进的无线Mesh网路由判据算法及其路由协议

为了改善802.11s无线Mesh网传输过程中因重传次数过大而造成的丢包问题,根据实际无线传输中的网络重传次数特性,提出一种基于最大重传次数的空中传播时间改进路由判据算法.同时为了缓解因单根节点造成的网络拥塞,提高实际场景中边缘节点的传输性能,并保证网络中所有节点使用无线信道资源的公平性,基于树的寻径机制从拓扑结构的角度,提出一种改进的多根节点的混合无线Mesh网路由协议(M-HWMP).理论及仿真结果表明,改进的路由判据算法及路由协议优化了无线Mesh网传输不同数据流时的吞吐量、时延特性,并在一定程度上避免了网络拥塞.     

实现基于RTCP协议的参考图象法的探讨

目前视频图象在 IP分组网中的传输正被日益广泛地应用 (如 :视频电话、视频会议 ) .但是 ,由于 IP分组网固有的特点 ,致使 IP分组包丢失的现象不可避免 ,并极大地影响了视频传输的服务质量 .由于参考图象选择法RPS(Reference Picture Selection)是一种较好的视频图象差错复原的方法 ,因此 ,为了改善因分组包丢失而对视频传输带来的质量下降问题 ,利用 RTCP协议提供反馈信息和利用参考图象选择法进行视频图象复原 ,实现了一种在 IP分组网中进行视频传输的差错控制机制 .实践证明 ,通过这种方法不仅可减小因分组包丢失而对视频图象信息带来的损害 ,而且可提高视频图象的传输质量 ,此方法适用于基于分组网的视频传输系统 .     

Stabilization of linear discrete‐time networked control systems via protocol and controller co‐design

This paper investigates the stabilization problem for networked control systems (NCSs) with communication constraint and packet loss. The communication constraint considered is that only one network node is allowed to access a shared communication channel during one time‐slot, and a feedback control is performed with only partially available measurements and control inputs. By taking random packet loss into consideration, a stochastic switched system model is presented to describe the NCS. A sufficient condition is derived for the NCS to be mean‐square exponentially stable, and it is shown that the system performance specified by the exponential decay rate critically depends on the network accessing rates (NARs) of the network nodes and the packet loss probability. The state feedback controller and scheduling protocol, which allocates the NARs, are co‐designed such that the NCS achieves a minimal decay rate. Finally, an illustrative example is given to show the effectiveness of the proposed design approach. Copyright © 2014 John Wiley & Sons, Ltd.     

无线多跳网络结合功率控制的物理载波侦听分析模型

载波侦听阈值的选取对无线多跳网络MAC层的协议性能有着重要影响.已有研究中忽略了确认报文、累积干扰在不同的载波侦听阈值下对系统性能的影响,并在分析中夸大了隐藏节点所导致的信道冲突.针对上述问题,提出了一种结合功率控制的物理载波侦听分析模型.该模型以网络整体性能为优化目标,对全网的累积干扰与空间复用度进行分析,给出节点的平均信道容量.此外,对信道状态建立马尔可夫链模型,提出了4类载波侦听范围内发生的信道冲突以及两类全网累积干扰所引发的信道冲突.分析上述各类冲突对信道利用率的影响,并结合节点的平均信道容量给出优化的载波侦听阈值以及传输功率.与已有研究相比,模型中明确分析确认报文、累积干扰以及隐藏节点对信道冲突的影响.分析结果表明,如果不考虑上诉因素将无法获得最优的载波侦听范围,并且会导致网络性能的下降.     

面向数据包丢失补偿的网络化广义预测控制

针对网络化控制系统中存在的数据包丢失,考虑了基于状态空间模型的网络化广义预测控制问题;在假设反馈通道和控制通道的数据包丢失过程确定可知的情况下,提出了一种采用预测器和预测控制器分别补偿反馈通道和控制通道的数据包丢失对系统性能影响的方法,通过把广义预测控制问题转化为滚动线性二次型最优跟踪问题,基于动态规划给出了网络化广义预测控制器的设计方法,并基于Ricoati差分方程非负定解的单调性,给出了末端加权矩阵保证系统稳定性的充分条件,最后通过仿真验证了所提出方法的有效性.