8041199
Scheduling in buffered WDM packet switching networks with arbitrary wavelength conversion capability
Optical networking is a promising candidate for high-speed communication networks because of its huge bandwidth. In this paper we study optimal scheduling in buffered WDM packet switching networks with arbitrary wavelength conversion ability. We focus on limited range wavelength conversion while considering full range wavelength conversion as a special case of it. We formalize the problem of maximizing network throughput and minimizing total delay in such a network as finding an optimal matching in a weighted bipartite graph. We then give a simple and fast algorithm called the scan and swap algorithm that solves the problem in O(kB/sup 2/) time, where k is the number of wavelengths per fiber and B is the buffer length, as compared to other existing algorithms that need at least O(k/sup 2/B/sup 2/ + k/sup 2/BN) time where N is the number of input fibers.
15452852
Battery-aware router scheduling in wireless mesh networks
Wireless mesh networks emerge as a flexible, low-cost and multipurpose networking platform with wired infrastructure connected to the Internet. A critical issue in mesh networks is to maintain network activities for a long lifetime with high energy efficiency. As more and more outdoor applications require long-lasting, high energy efficient and continuously-working mesh networks with battery-powered mesh routers, it is important to optimize the performance of mesh networks from a battery-aware point of view. Study in battery technology reveals that discharging of a battery is nonlinear. Batteries tend to discharge more power than needed, and reimburse the over-discharged power later if they have sufficiently long recovery time. Intuitively, to optimize network performance, a mesh router should recover its battery periodically to prolong the lifetime. In this paper, we introduce a mathematical model on battery discharging duration and lifetime for wireless mesh networks. We also present a battery lifetime optimization scheduling algorithm (BLOS) to maximize the lifetime of battery-powered mesh routers. Based on the BLOS algorithm, we further consider the problem of using battery powered routers to monitor or cover a few hot spots in the network. We refer to this problem as the spot covering under BLOS policy problem (SCBP). We prove that the SCBP problem is NP-hard and give an approximation algorithm called the spanning tree scheduling (STS) to dynamically schedule mesh routers. The key idea of the STS algorithm is to construct a spanning tree according to the BLOS policy in the mesh network. The time complexity of the STS algorithm is O(r) for a network with r mesh routers. Our simulation results show that the STS algorithm can greatly improve the lifetime, data throughput and power consumption efficiency of a wireless mesh network
5688571
Enhancing Downlink Performance in Wireless Networks by Simultaneous Multiple Packet Transmission
In this paper, we consider using simultaneous Multiple Packet Transmission (MPT) to improve the downlink performance of wireless networks. With MPT, the sender can send two compatible packets simultaneously to two distinct receivers and can double the throughput in the ideal case. We formalize the problem of finding a schedule to send out buffered packets in minimum time as finding a maximum matching problem in a graph. Since maximum matching algorithms are relatively complex and may not meet the timing requirements of real-time applications, we give a fast approximation algorithm that is capable of finding a matching at least 3/4 of the size of a maximum matching in O(|E|) time, where |E| is the number of edges in the graph. We also give analytical bounds for maximum allowable arrival rate, which measures the speedup of the downlink after enhanced with MPT, and our results show that the maximum arrival rate increases significantly even with a very small compatibility probability. We also use an approximate analytical model and simulations to study the average packet delay, and our results show that packet delay can be greatly reduced even with a very small compatibility probability.
15502339
Optimal parallel scheduling algorithm for WDM optical interconnects with recirculating buffering
We study scheduling algorithms in WDM optical interconnects with recirculating buffering. The interconnect we consider has wavelength conversion capabilities. We focus on limited range wavelength conversion while considering full range wavelength conversion as a special case. We formalize the problem of maximizing throughput and minimizing packet delay in such an interconnect as a matching problem in a bipartite graph and give an optimal parallel algorithm that runs in O(Bk/sup 2/), as compared to O((N+B)/sup 3/k/sup 3/) time if directly applying other existing matching algorithms, where N is the number of input/output fibers, B is the number of fiber delay lines and k is the number of wavelengths per fiber.
18081212
A novel analytical model for electronic and optical switches with shared buffer
Switches with shared buffer have lower packet loss probabilities than other types of switches when the sizes of the buffers are the same. In the past, the performance analysis for electronic shared buffer switches has been carried out extensively. However, due to the strong dependencies of the output queues in the buffer, it is very difficult to find a good analytical model. Existing models are either accurate but have exponential complexities or not very accurate. In this paper, we propose a novel analytical model called the aggregation model for switches with shared buffer. This model can be used for analyzing both electronic and optical switches, and has perfect accuracies under all tested conditions and has polynomial time complexity. It is based on the idea of induction: first find the behavior of 2 queues, then aggregate them into one block; then find the behavior of 3 queues while regarding 2 of the queues as one block, then aggregate the 3 queues into one block; then aggregate 4 queues and so on. When a sufficient number of queues have been aggregated, the behavior of the entire switch is found. We believe that the new model represents the best analytical model for shared buffer switches so far.
14844081
Constructing battery-aware virtual backbones in sensor networks
A critical issue in wireless sensor networks is to construct energy efficient virtual backbones for routing, broadcasting and data propagating. The minimum connected dominating set (MCDS) has been proposed as a backbone to reduce power dissipation and prolong network lifetime. However, we find that an MCDS cannot guarantee maximum network lifetime as it does not consider the battery discharging behavior. Recent study in battery technology reveals that the discharging of a battery is not linear. Batteries tend to discharge more power than needed, and reimburse the over-discharged power later if they have sufficiently long recovery time. In order to optimize network performance and construct an energy efficient virtual backbone in sensor networks, battery-awareness should be considered. In this paper we first study the mathematical battery discharging model and provide a simplified battery model suitable for implementation in sensor networks. We then introduce the concept of battery-aware connected dominating set (BACDS) and show that in general the BACDS can achieve longer lifetime than the MCDS. Then we show that finding a minimum BACDS (MBACDS) is NP-hard and give a distributed approximation algorithm to construct the BACDS. The resulting BACDS constructed by our algorithm is at most (8+/spl Delta/)opt size where /spl Delta/ is the maximum node degree and opt is the size of an optimal BACDS. The time and message complexities of the algorithm are O(n) and O(n(/spl radic/n+logn+/spl Delta/)), respectively, where n is the number of nodes in the network. The simulation results show that the BACDS constructed by our algorithm can save a significant amount of energy and achieve up to 30% longer network lifetime than the MCDS. To the best of our knowledge, this is the first work considering battery-awareness in the construction of connected dominating sets.
2311753
Fundamental trade-offs in aggregate packet scheduling
In this paper, we investigate the fundamental trade-offs in aggregate packet scheduling for support of guaranteed delay service. In our study, we consider two classes of aggregate packet scheduling algorithms: the static earliest time first (SETF) and dynamic earliest time first (DETF). Through these two classes of aggregate packet scheduling (and together with the simple FIFO packet scheduling algorithm), we show that, with additional timestamp information encoded in the packet header for scheduling purposes, we can significantly increase the maximum allowable network utilization level, while, at the same time, reducing the worst-case edge-to-edge delay bound. Furthermore, we demonstrate how the number of the bits used to encode the timestamp information affects the trade-off between the maximum allowable network utilization level and the worst-case edge-to-edge delay bound. In addition, the more complex DETF algorithms have far superior performance than the simpler SETF algorithms. These results illustrate the fundamental trade-offs in aggregate packet scheduling algorithms and shed light on their provisioning power in support of guaranteed delay service.
6686875
Comparison between geometry-based and Gabor-wavelets-based facial expression recognition using multi-layer perceptron
The authors investigate the use of two types of features extracted from face images for recognizing facial expressions. The first type is the geometric positions of a set of fiducial points on a face. The second type is a set of multi-scale and multi-orientation Gabor wavelet coefficients extracted from the face image at the fiducial points. They can be used either independently or jointly. The architecture developed is based on a two-layer perceptron. The recognition performance with different types of features has been compared, which shows that Gabor wavelet coefficients are much more powerful than geometric positions. Furthermore, since the first layer of the perceptron actually performs a nonlinear reduction of the dimensionality of the feature space, they have also studied the desired number of hidden units, i.e., the appropriate dimension to represent a facial expression in order to achieve a good recognition rate. It turns out that five to seven hidden units are probably enough to represent the space of feature expressions.
16878671
Full-sharing: efficient bandwidth scheduling for video streaming over broadband cable networks (BCNs)
Broadband Cable Networks (BCNs) bring high-speed Internet access to home and make emerging multimedia streaming applications feasible. However, bandwidth contention is still a challenging problem in providing efficient IP-based Video-On-Demand (VOD) service on BCNs, due to the lack of effective approaches to exploit the unique characteristics of BCNs. To address the bandwidth contention issue, we propose an efficient video scheduling technique, called full-sharing scheduling in this paper. This technique fully exploits the unique characteristics of BCNs to reduce the bandwidth consumption of video sessions sharing a cable channel of fixed capacity, thereby maximizing the number of simultaneous video sessions on the single channel. Furthermore, we analyze the expected bandwidth and the session blocking probability of a video under the full-sharing scheduling. Based on this analysis, we design an efficient video assignment mechanism for maximizing the profit of a VOD system in scheduling videos on BCNs. Through both analysis and simulation, we show that our approach minimizes the bandwidth consumption of video sessions compared with the previous approaches and has significant advantages on BCNs. The proposed approach is also directly applicable on other broadcast/multicast networks in which clients have sufficient buffer and downstream bandwidth, e.g., satellite broadband networks.
28168487
Channel condition ARQ rate control for real-time wireless video under buffer constraints
Many emerging applications involve real-time packet video transmission over noisy wireless networks. To ensure reliable video transmission, an automatic repeat request (ARQ) scheme is used for repairing packet loss over a channel by retransmitting corrupted packets. However, an ARQ resolves the problem of packet loss at the expense of varying an effective channel rate as well as introducing extra latency. These properties increase the difficulty of rate control for real-time wireless video when the buffer overflow and underflow are taken into account. Therefore, we propose a novel ARQ-based rate control scheme, called "channel condition ARQ rate control" by using embedded coding to design an efficient retransmission policy for wireless video. This scheme achieves both maximal channel utilization and smooth video quality perceived at an end-host, which has a low implementation complexity under buffer constraints. We have conducted extensive simulations to verify the efficiency and robustness of the proposed scheme.
3682795
Multibody grouping via orthogonal subspace decomposition
Multibody structure from motion could be solved by the factorization approach. However, the noise measurements would make the segmentation difficult when analyzing the shape interaction matrix. This paper presents an orthogonal subspace decomposition and grouping technique to approach such a problem. We decompose the object shape spaces into signal subspaces and noise subspaces. We show that the signal subspaces of the object shape spaces are orthogonal to each other. Instead of using the shape interaction matrix contaminated by noise, we introduce the shape signal subspace distance matrix for shape space grouping. Outliers could be easily identified by this approach. The robustness of the proposed approach lies in the fact that the shape space decomposition alleviates the influence of noise, and has been verified with extensive experiments.