Adaptive playout scheduling and loss concealment for voice communication over IP networks

The quality of service limitation of today's Internet is a major challenge for real-time voice communications. Excessive delay, packet loss, and high delay jitter all impair the communication quality. A new receiver-based playout scheduling scheme is proposed to improve the tradeoff between buffering delay and late loss for real-time voice communication over IP networks. In this scheme the network delay is estimated from past statistics and the playout time of the voice packets is adaptively adjusted. In contrast to previous work, the adjustment is not only performed between talkspurts, but also within talkspurts in a highly dynamic way. Proper reconstruction of continuous playout speech is achieved by scaling individual voice packets using a time-scale modification technique based on the Waveform Similarity Overlap-Add (WSOLA) algorithm. Results of subjective listening tests show that this operation does not impair audio quality, since the adaptation process requires infrequent scaling of the voice packets and low playout jitter is perceptually tolerable. The same time-scale modification technique is also used to conceal packet loss at very low delay, i.e., one packet time. Simulation results based on Internet measurements show that the tradeoff between buffering delay and late loss can be improved significantly. The overall audio quality is investigated based on subjective listening tests, showing typical gains of 1 on a 5-point scale of the Mean Opinion Score.     

无线网状网络的多路径路由与调度算法

提出了一种保障服务质量的多路径路由算法,数据分组可通过多条不同的路径进行传输,以提升网络总吞吐量性能.进一步提出了一种多路径调度策略.通过使用调度策略,基于当前可用带宽信息和路径所引入的时延信息,数据分组在传输前可被分成多段并通过不同的路径发送,根据路径时延调整优化调度策略,从而使得数据可通过在不同的路径上进行更高效地传输.仿真实验进一步验证了本文提出的路由机制和调度策略在不同网络负载下的优越性.     

Adaptive end-to-end QoS for multimedia over heterogeneous wireless networks

There has been a surge of interest for multimedia applications over wireless networks in recent years. A colossal number of ways have been proposed to decrease delay, delay jitter and loss in wireless networks and good user-perceived quality in video over internet. This paper studies the multimedia over heterogeneous wireless networks, requirements and problems, and proposes a new scheme to overcome the obstacles. The proposed scheme, takes into account the effects of Application-Level Wireless Multilevel ECN marking (AWMECN), thus helps us overcome the congestion/loss mistake problems. For handoff, handover and lossy link problems, it is considered that a freezing mechanism is in use in application layer and assumed that the upper layers can be aware of disconnection periods to make the rate adaptation decisions. Also a new scheme has been added to receiver to gracefully degrade the quality when no other action is available to combat the long delays without data which is caused by handoffs and wireless temporary disconnections. The transport layer mechanism is chosen to be UDP for avoiding TCP regarding problems. We believe that obtaining a good quality of video depends on good performance of all layers and tried to use the best mechanism in each layer.     

无线多跳网络视频流的联合源编码优化算法

由于网络媒体的共享性和不可靠性,对无线多跳网络中视频流的支持面临更大的技术挑战.研究了视频流优化问题并提出了一种联合源网络编码机制.该机制将视频流的源分段,并分为不同的世代,以达到视频流质量的最大化.算法首先分析世代规模对网络性能如源速率、编码效率和解码延时的影响,然后为了使源速率较大,在源端产生较多数据分组,并设计一种联合网络编码机制确定各个中间节点发送到网络中分组的最佳数量,使视频流的质量达到最高.仿真实验结果表明,在世代规模合适的情况下,使用所提联合源编码机制可以增强无线多跳网络视频流的性能.     

适宜普适无线网的地震实时数据压缩重传算法

分析使用普适无线网构建地震实时数据远程传输共享应用平台的不足,现有的 STEIM1 和 STEIM2 压缩算法无法满足波动增大和频率增高的原始数据压缩.针对现有压缩算法的不足,提出了新的三向数据分布区间压缩和重传算法,减少普适无线网的链路负载和增加应用层控制,降低延时抖动,大幅提升平台运行率,使其达到了实用化效果.     

无线多媒体传感器网络QoS路由算法研究

由于廉价的CMOS摄像头、麦克风的出现,以及对含有丰富信息的图像,视频和音频信息需求导致了无线多媒体传感器网络-(WMSN)的出现.WMSN具有资源有限、可变的信道容量、数据高度冗余等特点,使得WMSN的QoS路由具有极大的挑战性.提出了一种基于Mesh结构的WMSN,并在该结构体系下,提出了一种基于蚁群算法的QoS路由算法.实验研究表明,蚁群算法具有不依赖全局信息的优点,具有应用于WMSN的前景.实验同时表明,决定蚁群算法收敛速度以及会影响传感器网络性能的一些关键参数较难确定,需要进一步研究.     

基于贪婪-改进果蝇算法的无线传感器网络路由协议

针对无线传感器网络(WSNs)中簇首选择和传输问题,基于贪婪和改进果蝇算法提出一种新型网络路由协议CRP-FOAGA.该协议结合节点位置和剩余能量建立适值函数,通过改进果蝇算法实现适值函数的最优求解,利用贪婪算法实现簇头节点的多跳传输.仿真结果表明:该算法合理规划了簇头节点分布,降低了网络能耗,提升了网络的寿命,具有更好的性能.     

自适应半径调整的无线传感器网络覆盖算法

针对随机分布的无线传感器网络中节点分布不均匀造成的覆盖冗余,以及同时存在的覆盖空洞,提出了一种自适应半径调整无线传感器网络覆盖算法,通过阈值判断监测区域内传感器节点密度,根据监测区域内传感器节点疏密程度,利用节点半径步长系数对监测区域内节点半径进行自适应调整,建立无线传感器节点发射功率与节点发射半径的模型,计算无线传感器发射功率,通过实验和仿真,表明上述方法能够保证网络覆盖率的基础上减少无线传感器网络总功耗,提高网络寿命.     

A QoS-based dynamic pricing approach for services provisioning in heterogeneous wireless access networks

In this paper we propose a simple QoS-based dynamic pricing approach for services provisioning in a heterogeneous wireless access network environment which attempts to increase user’s satisfaction level by firstly, maximizing the provided QoS level, and secondly, by applying dynamic pricing strategies according to the QoS. These strategies will allow service providers to maximize their profits. Simulation results demonstrate that the proposed dynamic pricing approach benefits both users and wireless service providers (WSPs). Results also suggest that users have better overall satisfaction due to a better QoS level and fairer prices. The analysis shows that our proposed pricing approach contributes to an increase in WSPs profits compared to the application of the flat-rate pricing model in a competitive market-model.     

A utility-based algorithm for joint uplink/downlink scheduling in wireless cellular networks

The major driver for deploying next generation wireless cellular systems is their ability to efficiently deliver resource-demanding services, many of which require symmetric communication between an uplink mobile user and a downlink mobile user that belong to the same network. In this work, we propose a utility-based joint uplink/downlink scheduling algorithm suitable for wireless services involving pairwise communication among mobile users. While most existing literature focuses on downlink-only or uplink-only scheduling algorithms, the proposed algorithm aims at ensuring a utility function that jointly captures the quality of service in terms of delay and channel quality on both links. By jointly considering the time varying channel conditions in both the uplink and the downlink directions, the proposed algorithm avoids wasting of resources and achieves notable performance gains in terms of increased number of active connections, lower packet drop rate, and increased network throughput. These gains are achieved with a tradeoff cost in terms of complexity and signaling overhead. For overhead reduction in practical scenarios, we propose an implementation over clusters within the network.     

实时无线传感器网络的跨层优化设计

首先概述了当前传感器网络的特点和发展现状,然后提出一种实时无线传感器网络的跨层设计方案,并详细阐述了该体系结构中各层的主要功能,最后总结了该优化设计。     

大规模无线传感器网络定位算法研究

在同一仿真平台上比较了3种分布式定位算法,Ad Hoc positioning,Robust positioning和N-Hopmultilateration,并介绍了每种算法的基本原理和实现方法,抽象出一种适用于大规模无线传感器网络的通用三阶段分布式定位结构体系。仿真结果显示了3种算法在不同场景下的定位误差情况,比较了3种算法的优劣,同时,也对不同的网络环境参数对网络定位性能的影响做出了分析。     

High performance power control and opportunistic fair scheduling in TH-PPM UWB ad-hoc multimedia networks

Ultra wideband (UWB) systems are currently an important wireless infrastructure for high performance short-range communications and mobile applications. Indeed, forming ad-hoc networks among various UWB enabled devices is considered as an important mobile data exchange operating environment. In our study, we explore the problem of jointly optimizing the power level and data rate used in the devices in such a UWB based ad-hoc network. We propose a practical optimization algorithm based on judicious power control for real-time applications and opportunistic scheduling for non-real-time applications. Simulation results indicate that our proposed techniques are effective under various practical scenarios.

高精度低功耗无线传感器网络时间同步算法

通过对无线传感器网络参考广播同步（RBS）算法的研究,针对RBS多跳算法网络开销大和不能实现全网同步的问题,在基于环形网络拓扑的参考广播环形同步（RBRS）算法基础上,提出一种改进的RBRS （IRBRS）算法.该算法引入可变周期同步法：根据贝叶斯最大后验估计原理,估算出最大相位偏差来决定同步周期,从而减少节点同步次数,并且采用最小二乘线性回归法,周期性拟合时钟偏移.运用Matlab环境进行仿真,仿真结果表明：IRBRS算法同步精度显著提高,并且能量消耗显著减少,更有利于延长无线传感器网络的寿命.     

拥塞敏感的无线传感器网络路由算法

如何延长无线传感器网络的生命周期是一个重要的挑战.提出了一种新的拥塞敏感的路由算法,该算法充分考虑了路由选择过程中的数据负载与邻节点的缓存、信道竞争等状态的关系,每个节点以此计算一个能反映本地拥塞状态的权值,节点选择权值最高的下游节点作为下一跳来平衡下游节点的能耗和数据负载,同时降低下游节点的拥塞可能性.模拟实验表明:...     

Proactive cooperative scheduling and buffer management for multimedia networks

Is it possible, and to what extent feasible, for link schedulers and buffer managers in multimedia networks with propagation delays to relieve effectively congestion by means of feedback signaling? We show that a proactive cooperative control algorithm for distributed resource scheduling and buffer management obviates the problem of propagation delays. The algorithm is based on traffic predictions of correlated input traffic streams into network nodes. Nodes projecting to be under stress signal their neighboring upstream nodes for the latter to readjust their flow rates, whileguaranteeing quality of service as negotiated at call setup. Detailed implementations of the adaptive, feedback control mechanisms of distributed asynchronous algorithms that project future overload conditions are presented. The design allows the underlying single-node link scheduling and buffer management algorithm to be run in either a cooperative or a noncooperative mode of operation.     

一种可自维护的无线传感器网络拓扑控制算法

在温室、救灾等环境监测过程中,无线传感器网络会因频繁发生自然故障和遭受恶意攻击而引起网络可生存性问题,针对这一问题提出了一种可自维护的具有抗毁性的拓扑控制算法。仿真结果表明,该算法能够简单有效地构建并维护容错拓扑结构,在节点失效时保证网络拓扑容错抗毁,使得无线传感器网络具有可生存的能力。     

基于大坝监测的无线传感器网络结构的设计

针对大坝安全监测的特点,充分利用多跳和分簇的优势,在对几种典型无线传感器网络进行比较的基础上,提出了一种应用于大坝监测的无线传感器网络结构。功耗、可靠性等性能分析论证了其可行性。     

基于RSSI的WSN吞吐量自适应优化策略

基于MicaZ型节点参数分别建立了ARQ技术和FEC技术的吞吐量模型,分析并仿真了各参数对吞吐量的影响,得出ARQ技术的最优数据帧长和FEC技术的最优BCH码,进而提出了一种基于RSSI测距技术的吞吐量自适应优化策略,以适应无线传感器网络(WSN)中动态变化的网络拓扑。该策略依据RSSI测距技术测量节点间的通信距离,自适应地为数据包选择最优的差错控制策略来提高WSN的吞吐量。仿真结果表明,在吞吐量和动态范围方面,该策略整体上优于单纯的ARQ或者FEC方案。