14717474
A Novel Approach to Contention Control in IEEE 802.11e-Operated WLANs
In this paper, we devise, in compliance with the IEEE 802.11e protocol, a novel MAC-centric approach, called MAC contention control (MCC), to maximizing the bandwidth utilization and achieving proportional bandwidth allocation. We first show that approaches based on estimating the number of competing nodes and then setting the contention window size may not converge (and in some cases diverge) because of network dynamics. Then, by studying the optimality condition derived in our prior work, we identify two parameters (referred to as control references) that remain approximately constant when the network operates at the optimal operational point, regardless of the number of competing nodes in each AC. We instrument MCC to measure these control references, compare measurement results to their optimal control reference levels, and adjust the packet dequeuing rate from the interface queues in an additive-increase-multiplicative-decrease (AIMD) fashion and with respect to prespecified bandwidth allocation ratio associated with its AC. In some sense, MCC controls the rate of passing packets from the interface queues to to the MAC access function, and thus practically controls the effective number of competing nodes. We have conducted an extensive simulation study, and demonstrated the superiority of MCC to 802.11e in terms of both the achievable network throughput and the capability of achieving proportional bandwidth allocation. This, coupled with the fact that MCC does not require change in firmware and can be practically deployed, makes MCC a viable approach to contention control in IEEE 802.11e-operated WLANs.
14850039
Provisioning Quality Controlled Medium Access in UltraWideBand-Operated WPANs
Quality of service (QoS) provisioning is one of the most important criteria in newly emerging UWB-operated WPANs, as they are expected to support a wide variety of applica- tions from time-constrained, multimedia streaming to throughput- hungry, content transfer applications. As such, the Enhanced Distributed Coordinated Access (EDCA) mechanism has been adopted by MultiBand OFDM Alliance in its UWB MAC proposal. In this paper, we conduct a rigorous, comprehensive, theoretical analysis and show that with the currently recommended parame- ter setting, EDCA cannot provide adequate QoS. In particular, without responding to the system dynamics (e.g., taking into account of the number of active class-i stations), EDCA cannot allocate bandwidth in a deterministic proportional manner and the system bandwidth is under-utilized. After identifying the deficiency of EDCA, we propose, in compliance with the EDCA-incorporated UWB MAC protocol proposed in (15) (20), a framework, along with a set of theoretically grounded methods for controlling medium access with determin- istic QoS for UWB networks. We show that in this framework, 1) real-time traffic is guaranteed of deterministic bandwidth via a contention-based reservation access method; 2) best-effort traffic is provided with deterministic proportional QoS; and moreover, 3) the bandwidth utilization is maximized. We have also validated and evaluated the QoS provisioning capability and practicality of the proposed MAC framework both via simulation and empirically by leveraging the MADWifi (Multiband Atheros Driver for WiFi) Linux driver for Wireless LAN devices with the Atheros chipset.
5668129
A reactive channel model for expediting wireless network simulation
A major problem with leveraging event-driven, packet-level simulation environments, such as ns2[6], J-Sim[1], OpNet[2]), and QualNet[3]), in conducting wireless network simulation is the vast number of events generated, a majority of which are related to signal transmission in the PHY/MAC layers.In this extended abstract, we investigate the operations of signal transmission in the various stages: signal propagation, signal interference, and interaction with the PHY/MAC layers, and identify where events can be reduced without impairing the accuracy. We propose to leverage the MAC/PHY state information, and devise (from the perspective of network simulation) a reactive channel model (RCM) in which nodes explicitly register their interests in receiving certain events according to the MAC/PHY states they are in and the corresponding operations that should be performed. The simulation study indicates that RCM renders an order of magnitude of speed-up without compromising the accuracy of simulation results. An advantage of RCM with respect to the implementation is that there is no need to re-design the channel model for each specific MAC layer, and the modification made in the MAC/PHY layers is quite modest (e.g., a few API changes). This, coupled with the performance gain, suggests that RCM is an attractive, light-weight mechanism for expediting wireless network simulation.
8404805
Fractal Dimensions for Percolation and Phase Transition Models: Theory and New Monte Carlo Calculation Method
3771585
Icon-based visualization of large high-dimensional datasets
High dimensional data visualization is critical to data analysts since it gives a direct view of original data. We present a method to visualize large amount of high dimensional data. We divide dimensions of data into several groups. Then, we use one icon to represent each group, and associate visual properties of each icon with dimensions in each group. A high dimensional data record will be represented by multiple different types of icons located in the same position. Furthermore, we use summary icons to display local details of viewer's interests and the whole data set at meantime. We show its effectiveness and efficiency through a case study on a real large data set.
20310851
A mobile agent-based active network architecture for intelligent network control
The innovation and evolution of network technologies and services to enhance network functionality have traditionally encountered the problems of backward-compatibility and standardization. To resolve the related issues, active networks have been introduced to enable specific customization of network functionality without the lengthy standard-mediated committee processes. In this paper, we exploit the capability of mobile agent technology to construct an active network architecture. We argue that the mobile agent can be a building block for specific network customizations, and introduction of new network functionality. Both integrated and discrete operational models of network customizations can be supported in our prototype implementation. For the service development and deployment, an abstract service structure and a service loading mechanism are presented. Furthermore, we provide an agent management/control mechanism and devise a service management/control mechanism, which is either not available or incomplete in the other related work. The proposed architecture allows new service introduction, and as a result, achieves improved network functionality.
1952111
Manifold Based Analysis of Facial Expression
We propose a novel approach for modeling, tracking and recognizing facial expressions. Our method works on a low dimensional expression manifold, which is obtained by Isomap embedding. In this space, facial contour features are first clustered, using a mixture model. Then, expression dynamics are learned for tracking and classification. We use ICondensation to track facial features in the embedded space, while recognizing facial expressions in a cooperative manner, within a common probabilistic framework. The image observation likelihood is derived from a variation of the Active Shape Model (ASM) algorithm. For each cluster in the low-dimensional space, a specific ASM model is learned, thus avoiding incorrect matching due to non-linear image variations. Preliminary experimental results show that our probabilistic facial expression model on manifold significantly improves facial deformation tracking and expression recognition.
863906
Per-Flow Queueing by Dynamic Queue Sharing
Per-flow queuing is believed to be able to guarantee advanced Quality of Service (QoS) for each flow. With the dramatic increase of link speed and number of traffic flows, per-flow queuing faces a great challenge since millions of queues need to be maintained for implementation in a traditional sense. In this paper, by setting only a small number of physical queues, we propose a Dynamic Queue Sharing (DQS) mechanism to achieve an equal performance to the pure per-flow queuing with a lower cost. The proposed mechanism is based on an interesting fact that the number of simultaneous active flows in the router buffer is far less than that of in-progress flows. In DQS, a physical queue is dynamically created on-demand when a new flow comes and then dynamically released when the flow temporarily pauses. Hashing and binary sorting tree (or linked list) are combined to manage the mapping between flows and queues, so as to isolate flows in different queues. Theoretical analysis and traces experiments are conducted to evaluate DQS. The results demonstrate that when the parameters are well set, the operation delay is less than two time cycles in average with an extra memory of 16k bits.