7585289
Proactive Scan: Fast Handoff with Smart Triggers for 802.11 Wireless LAN
It has been a challenging problem to support VoIP-type delay sensitive applications in an 802.11 wireless LAN, because the standard handoff procedure implemented in many current 802.11 products occurs a delay deem unacceptable to VoIP users. To reduce this delay, we have developed a fast handoff scheme called Proactive Scan. It employs two new techniques. The first is to decouple the time-consuming channel scan from the actual handoff, and to eliminate channel scan delay by doing scan early and interleaving it with ongoing traffic in a non-intrusive way. The second technique is a smart trigger that takes into account both uplink and downlink quality and explicitly addresses the link asymmetry which has yet not been touched in previous work. Through implementation and experimentation study, we have shown that Proactive Scan does provide fast handoff and satisfactory performance to VoIP applications. Further, it is a software-only client-only solution that any mobile device can use in any existing 802.11 networks.
8668229
Bounding the power rate function of wireless ad hoc networks
Given a wireless ad hoc network and an end-to-end traffic pattern, the power rate function refers to the minimum total power required to support different throughput under a layered model of wireless networks. A critical notion of the layered model is the realizable graphs, which describe possible hit-rate supplies on the links by the physical and medium access layers. Under the layered model, the problem of finding the power rate function can he transformed into finding the minimum-power realizable graph that can provide a given throughput. We introduce a usage conflict graph to represent the conflicts among different uses of the wireless medium. Testing the realizability of a given graph can be transformed into finding the (vertex) chromatic number, i.e., the minimum number of colors required in a proper vertex-coloring, of the associated usage conflict graph. Based on an upper bound of the chromatic number, we propose a linear program that outputs an upper bound of the power rate function. A lower bound of the chromatic number is the clique number. We propose a systematic way of identifying cliques based on a geometric analysis of the space sharing among active links. This leads to another linear program, which yields a lower bound of the power rate function. We further apply greedy vertex-coloring to fine tune the bounds. Simulations results demonstrate that the obtained bounds are tight in the low power and low rate regime.
1741788
A Compound TCP Approach for High-Speed and Long Distance Networks
Many applications require fast data transfer over high speed and long distance networks. However, standard TCP fails to fully utilize the network capacity due to the limitation in its conservative congestion control (CC) algorithm. Some works have been proposed to improve the connection 鈂s throughput by adopt- ing more aggressive loss-based CC algorithms. These algorithms, although can effectively improve the link utilization, have the weakness of poor RTT fairness. Further, they may severely de- crease the performance of regular TCP flows that traverse the same network path. On the other hand, pure delay-based ap- proaches that improve the throughput in high-speed networks may not work well when the traffic is mixed with both delay- based and greedy loss-based flows. In this paper, we propose a novel Compound TCP (CTCP) approach, which is a synergy of delay-based and loss-based approach. Specifically, we add a scal- able delay-based component into the standard TCP Reno conges- tion avoidance algorithm (a.k.a., the loss-based component). The sending rate of CTCP is controlled by both components. This new delay-based component can rapidly increase sending rate when network path is under utilized, but gracefully retreat in a busy network when bottleneck queue is built. Augmented with this delay-based component, CTCP provides very good bandwidth scalability with improved RTT fairness, and at the same time achieves good TCP-fairness, irrelevant to the windows size. We developed an analytical model of CTCP and implemented it on the Windows operating system. Our analysis and experiment results verify the properties of CTCP.
35872608
On the Performance Analysis of Network-Coded Cooperation in Wireless Networks
Cooperative communication is a powerful technology combating fading in wireless medium. In contrast to conventional cooperation (CC) which allows the relay to simply process and forward what it has heard, network-coded cooperation (NCC) endows network coding capability with the relay, i.e., allows the relay to first encode the data it has received from different sources and then forward the network-coded data to corresponding destinations. In this paper we systematically investigate the performance of NCC in terms of diversity-multiplexing tradeoff as well as exact system outage behavior. Under the assumption (denoted as A) that each destination can reliably overhear the data from other sources, we prove the diversity-multiplexing tradeoff of NCC outperforms that of CC. Moreover, we derive the close form of the system outage probability of NCC as a function of signal-to-noise ratio (SNR). The analytical and numerical results show that by requiring less bandwidth cost, NCC offers a similar or even reduced system outage probability compared with CC, and achieves the same full diversity order as CC at high SNR. Finally we discuss the performance of NCC in case the assumption A is removed. For a wireless network composed of N s-d pairs and a single relay, although there is a certain system outage probability increase for NCC, it still provides the same full diversity order of 2 as CC at high SNR, and has a diversity-multiplexing tradeoff superior to CC.
17722556
Network-Adaptive Cache Management Schemes for Mixed Media
For efficently caching mixed-media, this paper discusses several network-adaptive cache management schemes. Considering the characteristics of different types of media, we first proposed a multi-level page-size management scheme. Then, a media-characteristic-weighted replacement policy is presented to improve the hit ratio of mixed media including continuous and noncontinuous media. Lastly, a network-condition- and media-quality-adaptive resource management mechanism is described to dynamically re-allocate cache resource for different types of media according to their request patterns. Simulation results demonstrate effectiveness of our propsoed approaches.
206750751
Error robust scalable audio streaming over wireless IP networks
Streaming high-fidelity audio over wireless Internet protocol (IP) networks is a challenging task because the networks present not only packet losses, but also residual bit errors. These losses and errors have severe adverse effect on the compressed audio bitstream. To solve this problem, this paper introduces error resilience in conjunction with error protection for scalable audio streaming over wireless networks. Specifically, error resilience is achieved by performing bitstream data partitioning and reversible variable length coding in the audio coder. Error protection is provided by layered product channel code to simultaneously handle packet losses and residual bit errors. Both the row and column codes of the product code provide unequal error protection for different layers of the audio bitstream by considering the characteristics of the scalable audio. Rate-distortion optimization is performed to determine the best source-channel coding tradeoff that minimizes the average expected end-to-end distortion. Simulation results demonstrate the effectiveness of our proposed approach.
14103418
Front Tracking: A Parallelized Approach for Internal Boundaries and Interfaces
Internal boundaries and interfaces are an important part of many fluid and solid modeling problems. Front Tracking contains a general interface framework, closely related to the non-manifold geometry used in CAD solid modeling packages, to support numerical simulation of such fluid problems. It can thus be considered to be a systematic application of the ideas of computational geometry to computational fluid dynamics. It is based on the principle that finite differences behave best when applied to differentiable functions, and that weak derivatives of nondifferentiable functions can be replaced by regularized expressions such as jump conditions. Front Tracking offers superior resolution for fluid problems with important discontinuities and interfaces, and in some cases, it has provided the unique method to obtain correct answers. Here we present Computer Science issues which have contributed to the success of Front Tracking: software design and organization — modularity, data structures and data hiding.
10598810
An orthogonal genetic algorithm for multimedia multicast routing
Many multimedia communication applications require a source to send multimedia information to multiple destinations through a communication network. To support these applications, it is necessary to determine a multicast tree of minimal cost to connect the source node to the destination nodes subject to delay constraints on multimedia communication. This problem is known as multimedia multicast routing and has been proved to be NP-complete. The paper proposes an orthogonal genetic algorithm for multimedia multicast routing. Its salient feature is to incorporate an experimental design method called orthogonal design into the crossover operation. As a result, it can search the solution space in a statistically sound manner and it is well suited for parallel implementation and execution. We execute the orthogonal genetic algorithm to solve two sets of benchmark test problems. The results indicate that for practical problem sizes, the orthogonal genetic algorithm can find near optimal solutions within moderate numbers of generations.
5129992
Content-Based Image Retrieval Using Multiple-Instance Learning
We explore the application of machine learning techniques to the problem of content-based image retrieval (CBIR). Unlike most existing CBIR systems in which only global information is used or in which a user must explicitly indicate what part of the image is of interest, we apply the multiple-instance (MI) learning model to use a small number of training images to learn what images from the database are of interest to the user.
27590229
Spectral histogram representations for visual modeling
We present spectral histogram representations for visual modeling. Based on a generative process, the representation is derived by partitioning the frequency domain into small disjoint regions and assuming independence among the regions. This gives rise to a set of filters and a representation consisting of marginal distributions of those filter responses. A distinct advantage of our representation is that it can be effectively used for different classification and recognition tasks, which is demonstrated by experiments and comparisons in texture classification, face recognition, and appearance-based 3D object recognition. The marked improvement over existing methods justifies our principle that effective priori knowledge should be derived from physical generative processes.
3992721
Error minimization in approximate range aggregates
Histogram techniques have been used in many commercial database management systems to estimate a query result size. Recently, it has been shown that they are very effective to support approximation of query processing especially aggregates. In this paper, we investigate the problem of minimizing average errors of approximate aggregates using histogram techniques. Firstly, we present a novel linear-spline histogram model that is more accurate than the existing models. Secondly, we propose a novel histogram construction technique for minimizing such average errors, which is shown to generate a near optimal histogram. Our experiment results demonstrate that the new histogram construction techniques lead to a great accuracy improvement on the existing techniques.