室外Wi-Fi网状网在农村的发展和应用

基于Wi-Fi的室外无线网状网因具有高带宽、低价格、可扩展、易维护等优势.近年来在热点覆盖、无线城市等领域的应用迅速发展,其低成本优势也使室外无线网状网成为农村无线宽带覆盖的最有竞争力技术之一.中国科学院计算技术研究所在北京怀柔区渤海镇北沟成功地建设了一个覆盖130多个用户的无线网状网.本文讲述在建设中遇到的问题与积累的经验,以及关于建设宽带Wi-Fi乡村的技术和商业问题的探讨.由于用户需求的刚性,作者认为在农村发展宽带无线网络比无线城市更有优势.     

Improving Delay and Jitter Performance in Wireless Mesh Networks for Mobile IPTV Services

Wireless mesh networking has recently emerged as a promising technology for the next-generation wireless networks. In wireless mesh networks (WMNs), it is practically attractive to support the low-cost quality-of-service (QoS) guaranteed mobile TV service. To meet this need, our study addresses how to improve the delay and jitter performance of mobile IPTV services over IEEE 802.11 based WMN. Particularly, we first discuss the adaptation of IEEE 802.11 MAC layer to construct a WMN with emphasis on mobile IPTV service; we then develop an enhanced version of Guaranteed-Rate (GR) packet scheduling algorithm, namely virtual reserved rate GR (VRR-GR), to further reduce the delay and suppress the jitter in multiservice network environment. Simulation results show that our proposed approach can satisfyingly prioritize mobile IPTV services in WMN, while providing non-IPTV services with what they need as well.      

OFDM光网络中软件定义的信号传输性能优化

针对正交频分复用(OFDM)光网络,提出两项OFDM传输性能优化技术,分别可以抑制OFDM信号的旁瓣分量和降低峰均功率比(PAPR)。通过在每个OFDM符号前插入一段软件定义的旁瓣抑制码(SSC),OFDM信号旁瓣可以得到显著抑制,从而有效降低密集波分复用-正交频分复用(DWDM-OFDM)系统中的相邻载波干扰。此外,利用软件定义的方式更改保护频带(FGB),以降低OFDM信号的PAPR,改善信号传输性能。通过实验对两项OFDM传输性能优化技术进行了验证。     

Multi-hop Delay Performance in Wireless Mesh Networks

Wireless Mesh Network (WMN) technology is an attractive solution to meet the demand of broadband network access anywhere and anytime. In order to effectively support delay-sensitive applications such as video streaming and interactive gaming in a WMN, it is crucial to develop feasible methodologies and techniques for accurately analyzing, predicting and guaranteeing end-to-end delay performance over multi-hop wireless communication paths. In this paper, we extend the link-layer effective capacity model and derive a lower bound of delay-bound violation probability, or complementary cumulative distribution function, over multi-hop wireless connections. A fluid traffic model with cross traffic and a Rayleigh fading channel with additive Gaussian noise and Doppler spectrum are considered in our study. The average multi-hop delay and jitter performance bounds are also obtained. Analytical results are verified by extensive computer simulations under different traffic load and wireless channel conditions. We find that multi-hop delay performance is much more sensitive to traffic load and maximum Doppler rate than traffic correlation.     

Availability-Aware Provisioning Strategies for Differentiated Protection Services in Wavelength-Convertible WDM Mesh Networks

In an optical WDM mesh network, different protection schemes (such as dedicated or shared protection) can be used to improve the service availability against network failures. However, in order to satisfy a connections service-availability requirement in a cost-effective and resource-efficient manner, we need a systematic mechanism to select a proper protection scheme for each connection request while provisioning the connection. In this paper, we propose to use connection availability as a metric to provide differentiated protection services in a wavelength-convertible WDM mesh network. We develop a mathematical model to analyze the availabilities of connections with different protection modes (i.e., unprotected, dedicated protected, or shared protected). In the shared-protection case, we investigate how a connection's availability is affected by backup resource sharing. The sharing might cause backup resource contention between several connections when multiple simultaneous (or overlapping) failures occur in the network. Using a continuous-time Markov model, we derive the conditional probability for a connection to acquire backup resources in the presence of backup resource contention. Through this model, we show how the availability of a shared-protected connection can be quantitatively computed. Based on the analytical model, we develop provisioning strategies for a given set of connection demands in which an appropriate, possibly different, level of protection is provided to each connection according to its predefined availability requirement, e.g., 0.999, 0.997. We propose integer linear programming (ILP) and heuristic approaches to provision the connections cost effectively while satisfying the connections' availability requirements. The effectiveness of our provisioning approaches is demonstrated through numerical examples. The proposed provisioning strategies inherently facilitate the service differentiation in optical WDM mesh networks.     

基于网络利用率最大化来提高无线Mesh网络中TCP协议的传输性能

In Wireless Mesh Networks (WMNs), the performance of conventional TCP significantly deteriorates due to the unreliable wireless channel. To enhance TCP performance in WMNs, TCP/LT is proposed in this paper. It introduces fountain codes into packet reorganization in the protocol stack of mesh gateways and mesh clients. Furthermore, it is compatible with conventional TCP. Regarded as a Performance Enhancement Proxies (PEP), a mesh gateway buffers TCP packets into several blocks. It simultaneously processes them by using fountain encoders and then sends them to mesh clients. Apart from the improvement of the throughput of a unitary TCP flow, the entire network utility maximization can also be ensured by adjusting the scale of coding blocks for each TCP flow adaptively. Simulations show that TCP/LT presents high throughput gains over single TCP in lossy links of WMNs while preserving the fairness for multiple TCPs. As losses increase, the transmission delay of TCP/LT experiences a slow linear growth in contrast to the exponential growth of TCP.     

LTE-Advanced中继系统中的VoIP业务系统性能研究

对基于中继传输的LTE-Advanced下行系统中的数据包传输机制进行了分析,并提出基于最大时延优先调度准则(MLWDF,modified largest weighted delay first)的分布式中继系统Voice over Internet Protocol(VoIP)业务调度方案.基于LTE-Advanc...     

VoIP over Wi-Fi Networks: Performance Analysis and Acceleration Algorithms

The expected VoIP call capacity in a one hop IEEE 802.11b network with G.711 voice codec is about 85 simultaneous calls, but the actual observed capacity is only 5 calls even at the highest data rate and under zero loss conditions. In this paper we analyze the reasons behind this inferior performance of VoIP traffic. We also present algorithms at the medium access control layer to improve the observed call capacity. Using ns-2 based simulations, we evaluate the algorithms and show that performance improvements of more than 300% can be achieved. Finally, using a testbed implementation of one of the proposed algorithms, we show its feasibilty in real world VoIP implementations. An earlier version of this paper was published in the IEEE Conference on Broadband Communications, Networks, and Systems (BroadNets) 2007 [1]. This work was supported in part by the National Science Foundation under grants CNS-0519733 and CNS-0721296, and the Georgia Tech Broadband Institute. Yeonsik Jeong was also supported under the Korea Research Foundation Grant KRF-2005-214-D00362 funded by the Korean Government (MOEHRD). This work was performed when Y. Jeong was a research scientist in the GNAN research group at Georgia Institute of Technology.     

发展中的VoIP服务

IP电话（VoIP）技术和应用发展非常迅速,尤其近一两年来,随着技术进步和话音质量的提高,它以低廉的资费,强烈冲击着传统的电话业务,引起人们的普遍关注,人们是注的焦点,在于IP电话能否提供和传统PSTN同样质量的话音业务,能否替代传统话音业务．在此基础上怎样发挥其各种优势。VoIP技术还在演进,如需要解决服务质量保障、安全问题等,业务领域也不再仅限于固定传统话音服务,分析目前VoIP业务的现状,并对未来VoIP业务功能作出预测。     

Performance Evaluation of CANCAR Algorithm in Realistic Wireless Mesh Networks

Wireless Personal Communications - A new technique for designing compact, notched filter is presented in this paper. The proposed approach is based on the design and optimization of micro strip...     

Enhancing the Performance of Video Streaming in Wireless Mesh Networks

Multihop wireless mesh networks (WMNs) provide ubiquitous wireless access in a large area with less dependence on wired networks. However, some emerging applications with high bandwidth requirement and delay and loss constraints, such as video streaming, suffer poor performance in WMNs, since high compression rates and/or high packet loss rates deteriorate the video quality. In this paper, we propose a novel mechanism composed of (1) a network route selection scheme which provides paths for multiple video streams with the least interference, called Minimum Interference Route Selection (MIROSE) and (2) an optimization algorithm that determines the compression rates depending on the network condition, called Network State Dependent Video Compression Rate (NSDVCR) algorithm. Simulation results of the proposed mechanisms show the significant improvement of the video quality measured with a popular metric, Peak-Signal-to-Noise Ratio (PSNR), compared with standard routing and default compression rates.     

Performance of Hierarchical Aggregation in Differentiated Services Networks

We address the use of hierarchical aggregation in DiffServ networks. We propose two analytical models to study the tradeoffs between signaling load and resource utilization. In the case of the signaling load, we introduce a novel performance metric that captures, simultaneously, the state information stored and the rate of signaling messages processed at routers. In the first analytical model, based on multidimensional birth–death processes, the offered load is detailed at the flow level, which allows accurate assessment of the signaling load. The second analytical model accommodates time-varying offered loads, which allows studying the tradeoffs between the time-scale of the aggregate demand and the time-scale of signaling. Our results, which also include analysis using measured traces, show that hierarchical aggregation can introduce very high signaling gains with a small penalty in terms of resource utilization, allowing significant savings in terms of network cost.     

Performance Analysis of Uplink Scheduling Algorithms for VoIP Services in the IEEEE 802.16e OFDMA System

While the voice over Internet protocol (VoIP) services is expected to be widely supported in wireless mobile networks, the performance of VoIP services has not previously been evaluated in the IEEE 802.16e orthogonal frequency division multiple access (OFDMA) system taking the adaptive modulation and coding scheme into consideration. To support real-time uplink service flows, three different types of scheduling have been designed in the IEEE 802.16e standard: the unsolicited grant service (UGS), the real-time polling service (rtPS), and the extended rtPS (ertPS). In this paper, we compare the three real-time scheduling algorithms in terms of the performance of VoIP services by using the analytical and simulation models that we developed.

Performance Analysis of Network Coding Based Two-Way Relay Wireless Networks Deploying IEEE 802.11

In this paper, we investigate the performance analysis of the IEEE 802.11 DCF protocol at the data link layer. We analyze the impact of network coding in saturated and non-saturated traffic conditions. The cross-layer analytical framework is presented in analyzing the performance of the encode-and-forward (EF) relaying wireless networks. This situation is employed at the physical layer under the conditions of non-saturated traffic and finite-length queue at the data link layer. First, a model of a two-hop EF relaying wireless channel is proposed as an equivalent extend multi-dimensional Markovian state transition model in queuing analysis. Then, the performance in terms of queuing delay, throughput and packet loss rate are derived. We provide closed-form expressions for the delay and throughput of two-hop unbalanced bidirectional traffic cases both with and without network coding. We consider the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queuing systems for the buffer behavior at the relay node. To overcome the hidden node problem in multi hop wireless networks, we develop a useful mathematical model. Both models have been evaluated through simulations and simulation results show good agreement with the analytical results.     

Optimization of Mobile IPv6-Based Handovers to Support VoIP Services in Wireless Heterogeneous Networks

The support of voice over Internet Protocol (VoIP) services in next-generation wireless systems requires the coupling of mobility with quality of service. The mobile node can experience disruptions or even intermittent disconnections of an ongoing real-time session due to handovers. The duration of such interruptions is called disruption time or handover delay and can heavily affect user satisfaction. Therefore, this delay needs to be minimized to provide good-quality VoIP services. In this paper, the focus is on the network layer mobility, specifically on mobile Internet Protocols (MIPs), since they are natural candidates for providing mobility at layer 3. Using analytical models, the authors evaluate MIPv4, MIPv6, fast MIPv6 (FMIPv6), and hierarchical MIPv6 (HMIPv6) and compare their performances in terms of handover delay for VoIP services. To optimize the handover delay, the authors propose to use the adaptive retransmission timer described in this paper. The results obtained using the adaptive timer technique show that for a 3% frame error rate and a 128-kb/s channel, the handoff delay is about 0.075 s (predictive) and 0.051 s (reactive) for FMIPv6. It is around 0.047 s [intra-mobile anchor point (MAP)] and 1.47 s (inter-MAP) for HMIPv6, around 1 s for MIPv6, and 0.26 s for MIPv4     

第三代移动网络中的VoIP技术

简要论述了在第三代移动网络中应用VoIP所需解决的一些关犍技术。讨论VoIP在GPRS和UMTS中的应用，最后就VoIP的QOS问题进行了研究和分析。     

港湾网络IP分组话音解决方案

近几年，随着数据业务的迅猛发展以及IP技术的不断成熟和完善，网络的IP化已经成为业界公认的发展方向，同时也催生了业务的IP化。     

基于联盟的6G无人机通信网络优化概述

随着6G网络和无人机(UAV)技术的迅猛发展,无人机通信网络将成为6G空天地一体化网络融合的关键组成部分,在战场侦查、野外救援和物联网信息传输等民用和军用领域发挥重要作用。针对无人机群大规模、高动态和自组织等特性,以6G网络任务驱动为出发点,该文提出基于联盟的6G无人机通信网络优化框架。围绕联盟形成、联盟任务实施和联盟资源管理对无人机联盟工作原理展开论述。结合博弈论、机器学习和在线决策,给出了无人机通信网络资源优化方法和仿真示例。最后,对6G无人机通信网络的应用前景和亟需解决的问题进行了开放性讨论。     

针对移动M2M业务的优化技术研究

传感器网络和移动通信网络相结合已经成为必然的趋势。但现有的3G、LTE移动通信系统的设计目标是人与人（H2H）通信,没有针对机器间（M2M）通信特点进行优化,难以适应M2M业务复杂的应用环境和海量的用户容量。文章针对移动M2M业务的优化技术进行了探讨。     

Fast Approximate Dimensioning and Performance Analysis of Mesh Optical Networks

This paper presents a collection of approximation formulas that allow a network planner to quickly estimate the size of a mesh optical network with limited inputs. In particular, it provides a set of equations that relate number of sites, average fiber connectivity, demand load and capacity for various mesh protection architectures. These results can be used to easily and quickly estimate the amount of traffic that can be carried over a given network, or, conversely, given the traffic to be supported, to assess the characteristics of the topology required (in terms of number of nodes, connectivity). Finally, this analysis can be used to estimate the restoration performance that can be expected without resorting to extensive simulation studies.