Hybrid and forward error correction transmission techniques for unreliable transport of 3D geometry

The continual improvement in computer performance together with the prevalence of high-speed network connections having high throughput and moderate latencies enables the deployment of multimedia applications, such as collaborative virtual environments, over wide area networks (WANs). These applications can serve as simulated environments in scenarios such as emergency response training to catastrophic disasters, military training, and entertainment. Many of these systems use 3D graphics for display and may be required to distribute geometric models on demand between participants. Progressive meshes provide an attractive mechanism for such distribution. Previous uses of progressive meshes have sent data using reliable protocols (TCP). However, such protocols have disadvantages in on-demand settings, in that they: (1) use flow control, which limits performance in WANs; (2) add additional bandwidth when there is loss; (3) treat all loss as an indication of congestion; and (4) require feature-rich multicast support, which is not always available. In this paper, we modify progressive mesh models to allow reconstruction even in the event of packet loss. We use these modifications in two transmission schemes, a hybrid transmission that uses TCP and UDP to send packets and a forward error correction transmission scheme that uses redundancy to decode the information sent. We assess the performance of these transmission schemes when deployed on network testbeds that simulate wide area and wireless characteristics.Published online: 9 February 2005 Correspondence to : Bobby Bodenheimer     

Route Maintenance in IEEE 802.11 wireless mesh networks

In this paper, we propose a novel Route Maintenance scheme for IEEE 802.11 wireless mesh networks. Despite lack of mobility and energy constraints, reactive routing protocols such as AODV and DSR suffer from frequent route breakages in 802.11 based infrastructure wireless mesh networks. In these networks, if any intermediate node fails to successfully transmit a packet to the next hop node after a certain number of retransmissions, the link layer reports a transmission problem to the network layer. Reactive routing protocols systematically consider this as a link breakage (and therefore a route breakage). Transmission failures can be caused by a number of factors e.g. interference or noise and can be transient in nature. Frequent route breakages result in significant performance degradation. The proposed mechanism considers multiple factors to differentiate between links with transient transmission problems from those links which have permanent transmission problems and takes a coherent decision on link breakage. The proposed mechanism is implemented in AODV for single-radio single-channel mesh network and an extension is incorporated in multi-radio multi-channel scenarios. Simulation results show substantial performance improvement compared to classical AODV and local route repair schemes.     

面向移动计算终端的渐进几何简化方法

在移动计算终端上进行移动三维图形计算是一个重要的课题.针对移动计算终端屏幕小、计算能力低、无线网络带宽受限等特点,研究如何进行移动三维图形的渐进显示具有十分重要的意义.提出了利用Kobbelt四边形细分算法的逆过程迭代地进行简化的方法,通过迭代地把模型分割为奇点和作为简化模型的偶点,实现了对四边形网格几何模型的渐进式简化;提出了渐进显示的模式,通过把每一层的奇点作为可添加的细节信息,可以支持在终端上渐进显示不同细节模型并实现原模型的无损还原.完整的简化方法简单快速,可以高效地实现移动三维图形的渐进简化显示.最后在型号为Mio 336的PDA上的实验结果表明,研究成果在移动计算终端上进行实时交互等方面具有很好的应用前景.     

无线IPTV中RTP—over-TCP传输方案的设计实现以及多TCP传输技术的应用

在无线环境下,TCP的传输效果要好于不带拥塞控制的UDP。为了满足"集中-分布式"无线流媒体系统进行RTP-over-TCP传输的需要,设计实现了一套双TCP通道的传输方案,并考察了TCP阻塞调用和非阻塞调用在单线程多用户调度方式下的性能。另外,还尝试用多TCP传输技术来改进TCP在无线环境中带宽利用率低的问题,仿真实验结果表明,该方案可得到较好的传输效果。     

一种面向移动3D图形的几何简化方法

移动3D图形计算是无线网络和图形学高速发展产生的新研究领域.由于无线网络带宽和移动终端设备显示分辨率的限制,需要将3D图形进行分解压缩,依据不同的分辨率进行内容转码.提出了一种基于改进Loop细分的几何模型简化算法.一个稠密的几何网格通过反复操作3个步骤:顶点分裂、奇点预测和重新三角化,生成由稀疏的基网格和一系列偏移量组成的渐进网格.在奇点预测过程中,将改进Loop细分模板作为预测器.由于Loop细分相关联的顶点数目少,提高了几何模型简化和重建的速度.渐进网格易于在无线网络上渐进传输,并可在移动终端上无损重建3D图形.实验表明,算法简单、效率高,适用于移动环境下3D图形的应用.     

Adaptive online transmission of 3-D TexMesh using scale-space and visual perception analysis

Efficient online visualization of three-dimensional (3-D) mesh, mapped with photo realistic texture, is essential for a variety of applications such as museum exhibits and medical images. In these applications synthetic texture or color per vertex loses authenticity and resolution. An image-based view dependent approach requires too much overhead to generate a 360/spl deg/ display for online applications. We propose using a mesh simplification algorithm based on scale-space analysis of the feature point distribution, combined with an associated visual perception analysis of the surface texture, to address the needs of adaptive online transmission of high quality 3-D objects. The premise of the proposed textured mesh (TexMesh)simplification, taking the human visual system into consideration, is the following: given limited bandwidth, texture quality in low feature density surfaces can be reduced, without significantly affecting human perception. The advantage of allocating higher bandwidth, and thus higher quality, to dense feature density surfaces, is to improve the overall visual fidelity. Statistics on feature point distribution and their associated texture fragments are gathered during preprocessing. Online transmission is based on these statistics,which can be retrieved in constant time. Using an initial estimated bandwidth,a scaled mesh is first transmitted. Starting from a default texture quality,we apply an efficient Harmonic Time Compensation Algorithm based on the current bandwidth and a time limit, to adaptively adjust the texture quality of the next fragment to be transmitted. Properties of the algorithm are proved. Experimental results show the usefulness of our approach.     

A cellular topology-based approach to generating progressive solid models from feature-centric models

Progressive mesh representation and generation have become one of the most important issues in network-based computer graphics. However, current researches are mostly focused on triangular mesh models. On the other hand, solid models are widely used in industry and are applied to advanced applications such as product design and virtual assembly. Moreover, as the demand to share and transmit these solid models over the network is emerging, how to effectively stream the solid models has been considered as one of the major research issues. In this paper, we present a cellular topology-based approach to generating progressive solid models (PSM) from feature-based models. The proposed approach introduces a new scheme for storing and transmitting solid models over the network. The cellular topology (CT) approach makes it possible to effectively generate PSMs and to efficiently transmit the models over the network with compact model size. Thus, an arbitrary solid model SM designed by a set of design features is stored as a much coarser solid model SM⁰ together with a sequence of n detail records that indicate how to incrementally refine SM⁰ exactly back into the original solid model SM=SMⁿ.     

A bandwidth and effective hit optimal cache scheme for wireless data access networks with client injected updates

In this paper, we propose an optimal cache replacement policy for data access applications in wireless networks where data updates are injected from all the clients. The goal of the policy is to increase effective hits in the client caches and in turn, make efficient use of the network bandwidth in wireless environment. To serve the applications with the most updated data, we also propose two enhanced cache access policies making copies of data objects strongly consistent. We analytically prove that a cache system, with a combination of our cache access and replacement policy, guarantees the optimal number of effective cache hits and optimal cost (in terms of network bandwidth) per data object access. Results from both analysis and extensive simulations demonstrate that the proposed policies outperform the popular Least Frequently Used (LFU) scheme in terms of both effective hits and bandwidth consumption. Our flexible system model makes the proposed policies equally applicable to applications for the existing 3G, as well as upcoming LTE, LTE Advanced and WiMAX wireless data access networks.     

基于多链路聚合的弱客户端数据传输模型

针对当前制约无线网络应用发展的无线低带宽和有线宽带速度的不对称现状,提出一种面向弱客户端的多链路聚合传输模型。采用通用的TCP/IP编程接口,可以有效地提高低带宽客户端数据传输的速率和稳定性,并具有良好的可靠性、可用性和负载均衡,从而尽可能地利用所有链路的带宽以达到最佳的传输速度。     

Perceptually Optimized 3-D Transmission Over Wireless Networks

Many protocols optimized to transmissions over wireless networks have been proposed. However, one issue that has not been looked into is considering human perception in deciding a transmission strategy for three-dimensional (3D) objects. Several factors, such as the number of vertices and the resolution of texture, can affect the display quality of 3D objects. When the resources of a graphics system are not sufficient to render the ideal image, degradation is inevitable. It is therefore important to study how individual factors affect the overall quality, and how the degradation can be controlled given limited bandwidth resources and possibility of data loss. In this paper, the essential factors determining the display quality are reviewed. We provide an overview of our research on designing a 3D perceptual quality metric integrating two important ones, resolution of texture and resolution of mesh, that control the transmission bandwidth requirements. A review of robust mesh transmission considering packet loss is presented, followed by a discussion of the difference of existing literature with our problem and approach. We then suggest alternative strategies for packet transmission of both 3D texture and mesh. These strategies are then compared with respect to preserving 3D perceptual quality under packet loss     

Models and algorithms for efficient multiresolution topology estimation of measured 3-D range data

In this paper, we propose a new efficient topology estimation algorithm to construct a multiresolution polygonal mesh from measured three-dimensional (3-D) range data. The topology estimation problem is defined under the constraints of cognition, compactness, and regularity, and the algorithm is designed to be applied to either a cloud of points or a dense mesh. The proposed algorithm initially segments the range data into a finite number of Voronoi patches using the K-means clustering algorithm. Each patch is then approximated by an appropriate polygonal and eventually a triangular mesh model. In order to improve the equiangularity of the mesh, we employ a dynamic mesh model, in which the mesh finds its equilibrium state adaptively, according to the equiangularity constraint. Experimental results demonstrate that satisfactory equiangular triangular mesh models can be constructed rapidly at various resolutions, while yielding tolerable modeling error.     

混合无线网络容量及延迟性能的研究

混合无线网络是在Ad hoc网络中添加基站的新型网络模型，其容量是评估网络性能的重要参数。本文研究了混合无线网络的容量问题。首先建立了谊网络的网络模型，在考虑延迟时间的基础上提出一种新的路由策略，一定程度地保证了数据传输的实时性。在此基础上运用图论中数学计算的方法推导了混合无线网络容量数学期望的分析表达式，这是本文的重要结论，对于未来混合无线网络的设计与分析都具有指导意义。     

MeshVision: an adaptive wireless mesh network video surveillance system

The major surveillance camera manufacturers have begun incorporating wireless networking functionality into their products to enable wireless access. However, the video feeds from such cameras can only be accessed within the transmission range of the cameras. These cameras must be connected to backbone infrastructure in order to access them from more than one hop away. This network infrastructure is both time-consuming and expensive to install, making it impractical in many rapid deployment situations (e.g., to provide temporary surveillance at a crime scene). To overcome this problem, we propose the MeshVision system that incorporates wireless mesh network functionality directly into the cameras. Video streams can be pulled from any camera within a network of MeshVision cameras, irrespective of how many hops away that camera is. To manage the trade-off between video stream quality and the number of video streams that could be concurrently accessed over the network, MeshVision uses a bandwidth adaptation mechanism. This mechanism monitors the wireless network looking for drops in link quality or signs of congestion and adjusts the quality of existing video streams in order to reduce that congestion. A significant benefit of the approach is that it is of low cost, requiring only a software upgrade of the cameras.     

Multiresolution and fast decompression for optimal web-based rendering

Limited bandwidth is a strong constraint when efficient transmission of 3D data to Web clients and mobile applications is needed. In this paper we present a novel multi-resolution WebGL based rendering algorithm which combines progressive loading, view-dependent resolution and mesh compression, providing high frame rates and a decoding speed of million of triangles per second in JavaScript. The method is parallelizable and scalable to very large models.The algorithm is based on the local multi-resolution approaches provided by the community, but ad-hoc solutions had to be studied and implemented to provide adequate performances. In particular, a compression mechanism that reached very high compression rate without impact on rendering performance was implemented. Moreover, the data partition strategy was modified in order to be able to load different types of data (i.e. point clouds) and better adapt to the potentials and limitations of web-based rendering.     

R-D optimized progressive compression of 3D meshes using prioritized gate selection and curvature prediction

A rate-distortion (R-D) optimized progressive coding algorithm for three-dimensional (3D) meshes is proposed in this work. We propose the prioritized gate selection and the curvature prediction to improve the connectivity and geometry compression performance, respectively. Furthermore, based on the bit plane coding, we develop a progressive transmission method, which improves the qualities of intermediate meshes as well as that of the fully reconstructed mesh, and extend it to the view-dependent transmission method. Experiments on various 3D mesh models show that the proposed algorithm provides significantly better compression performance than the conventional algorithms, while supporting progressive reconstruction efficiently.     

Performance evaluation for on-demand routing protocols based on OPNET modules in wireless mesh networks

In wireless networks, users expect to get access to the network securely and seamlessly to share the data flow of access points anytime and anywhere. However, either point-to-point or point-to-multipoint methods in traditional wireless networks make the network bandwidth decrease rapidly, which cannot meet the requirements of users. Recently, a new wireless broadband access network, wireless mesh networks (WMNs), has emerged. As one of the key technologies in WMNs, wireless routing protocols plays an important role in performance optimization of WMNs. Therefore, in this paper, we address the on-demand routing protocols by focusing on dynamic source routing (DSR) protocol and ad hoc on-demand distance vector (AODV) routing protocol in WMNs. Then, we use the OPNET modules to establish the simulation models of DSR and AODV protocols in WMNs. Simulation and results show that, DSR protocol that is based on the dynamic source routing is not suitable for wireless transmission, while AODV routing protocol that is based on the purpose-driven routing is suitable for wireless transmission with rapid change of network topology.     

一种视觉相关的三维图形几何压缩传输算法

通过对要传输的三维图形进行分层处理,并在接收端建立BSP二叉树,提取与视觉相关的层和可见三角形信息,使传输数据迅速减少,但又不影响接收端对敏感数据的处理和显示。     

A new joint strategy of radio channel allocation and power control for wireless mesh networks

For wireless mesh networks, it is critical to allocate the limited number of radio channels efficiently while mitigating the co-channel inference to improve network performance. For this reason, after extensively reviewing the related work, we present a new joint radio channel allocation (RCA) and power control (PC) strategy for wireless mesh networks. First, we formulate the RCA problem as a multiple objective optimization problem, with the constraints of transmission power and traffic data rates, while effective channel utilization (ECU) is chosen as the target metric for optimization. Second, we incorporate the channel status into the model of MAC protocols, including as signal-to-noise ratio (SNR) and transmission power. Consequently, the PC is incorporated into the ECU for channel allocation. Third, we propose to directly maximize the ECU to find both optimal radio channel and transmission power. The resulting strategy is a fully distributed RCA/PC algorithm without relying on a coordination mechanism among mesh routers. Our extensive simulation results have demonstrated that the proposed algorithm significantly outperforms the existing RCA strategies and the standard MAC protocols in performance such as throughput, packet dropping, delay and delay jitter.     

A multi-layer experimental study of multimedia and QoS communication in wireless mesh networks

A significant issue in Mesh networks is to support multimedia transmissions while providing Quality of Service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for a wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We design and implement a campus test-bed for supporting multimedia traffic in mobile wireless mesh networks, and investigate in detail some possible improvements on a number of layers to enable multimedia transmission over wireless networks with QoS support. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoder’s output bit rate based on the available network bandwidth to improve the quality of the received video. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.