We propose a new and efficient image-based representation for networked virtual environments, cal... more We propose a new and efficient image-based representation for networked virtual environments, called the sprite tree. A sprite tree organizes multiple reference images efficiently and compactly for accelerating the rendering of complex virtual scenes. Using our basic construction and rendering methods, the results show that a sprite tree can efficiently organize the pixels from hundreds of distinctive reference images and accelerate the rendering of a complex scene. Furthermore, we propose the sprite view similarity to (i) largely reduce the lighting artifacts in the rendered images, and (ii) significantly reduce the redundancy and the tree size with little loss of the visual quality. Keywords 3D image warping • Image-based rendering • Remote rendering • Networked virtual environments 1 Introduction Networked virtual environments (NVEs) have several popular applications such as multiplayer online games (e.g. World
Acm Transactions on Multimedia Computing Communications and Applications, May 1, 2013
We propose an access pattern-driven distributed caching middleware named APRICOD, which can be bu... more We propose an access pattern-driven distributed caching middleware named APRICOD, which can be built on top of any existing content discovery system. APRICOD caters for fast and scalable content discovery in peer-to-peer media streaming systems, especially when user interactions that leads to non-continuous media access (such as random seek in video and teleportation in virtual environment) are present. APRICOD caches query results based correlations among media objects accessed by users, reducing the content discovery time. Our evaluation using a VoD access trace shows that close to 70% of non-continuous access queries can be resolved with a single hop using APRICOD.
Packet loss is a serious problem that severely affects the quality of multimedia streaming over e... more Packet loss is a serious problem that severely affects the quality of multimedia streaming over error-prone networks. To reduce the variability of packet loss and delay, packets can be transmitted over different network paths (path diversity), after being coded by error-concealment source coding methods like Multiple Description Coding (MDC) or Layered Coding (LC). Researches in this area lead to a common belief that MDC is better than LC when the network conditions (packet loss rate, bandwidth) are grave [1, 2]. However, in this paper, we show that the decision of which packets to send over which paths can greatly affect the performance of LC and MDC, therefore the quality of the streams received. Particularly, using our analytical framework and polynomial algorithms for finding optimal packet allocations, we show that LC outperforms MDC under various critical network conditions.
European Journal of Operational Research, Nov 1, 2009
Just-in-time (JIT) trucking service, i.e., arriving at customers within specified time windows, h... more Just-in-time (JIT) trucking service, i.e., arriving at customers within specified time windows, has become the norm for freight carriers in all stages of supply chains. In this paper, a JIT pickup/delivery problem is formulated as a stochastic dynamic traveling salesman problem with time windows (SDTSPTW). At a customer location, the vehicle either picks up goods for or delivers goods from the depot, but does not provide moving service to transfer goods from one location to another. Such routing problems are NP-hard in deterministic settings, and in our context, complicated further by the stochastic, dynamic nature of the problem. This paper develops an efficient heuristic for the SDTSPTW with hard time windows. The heuristic is shown to be useful both in controlled numerical experiments and in applying to a real-life trucking problem.
This paper presents a unified set of abstractions and operations for hardware devices, software p... more This paper presents a unified set of abstractions and operations for hardware devices, software processes, and media data in a distributed audio and video environment. These abstractions, which are provided through a middleware layer called Indiva, use a file system metaphor to access resources and high-level commands to simplify the development of Internet webcast and distributed collaboration control applications. The design and implementation of Indiva are described and examples are presented to illustrate the usefulness of the abstractions.
Page 1. The Design and Im plem entation of a Distributed Data Capture and Processing Fram ework f... more Page 1. The Design and Im plem entation of a Distributed Data Capture and Processing Fram ework for rround Penetrating Radar Allen Bruce Wallis A dissertation submitted to the Department of Electrical Engineering, University ...
Developing applications to control audio/video equipment and the interface between conventional a... more Developing applications to control audio/video equipment and the interface between conventional audio/video signals and Internet streaming media is difficult. Consequently, widespread deployment and use of streaming media in day-today activities has been slow to develop. This paper describes a middleware system and application program interface designed to solve this problem. The system, called INDIVA, provides a hierarchical name space for accessing and controlling audio/video equipment, software services for processing media streams, and conference resources. The design and implementation of the system is described and examples are presented that illustrate how it can be used to implement direct manipulation interfaces for Internet streaming media. This middleware can also be used to implement control and automation systems for Internet webcasting and distributed collaboration systems.
We collected mobility traces of 84,208 avatars spanning 22 regions over two months in Second Life... more We collected mobility traces of 84,208 avatars spanning 22 regions over two months in Second Life, a popular networked virtual environment. We analyzed the traces to characterize the dynamics of the avatars mobility and behavior, both temporally and spatially. We discuss the implications of the our findings to the design of peer-to-peer networked virtual environments, interest management, mobility modeling of avatars, server load balancing and zone partitioning, client-side caching, and prefetching.
... of Computer Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Sin... more ... of Computer Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Singapore 119260 RN De Silva e-mail: [email protected] WT Ooi e-mail ... Each region has a teleportation point called the landing point, where all arriving avatars will appear at. ...
This paper presents a unified set of abstractions and operations for hardware devices, software p... more This paper presents a unified set of abstractions and operations for hardware devices, software processes, and media data in a distributed audio and video environment. These abstractions, which are provided through a middleware layer called Indiva, use a file system metaphor to access resources and high-level commands to simplify the development of Internet webcast and distributed collaboration control applications. The design and implementation of Indiva are described and examples are presented to illustrate the usefulness of the abstractions.
ACM Transactions on Multimedia Computing, Communications, and Applications, 2015
Zoomable video streaming refers to a new class of interactive video applications, where users can... more Zoomable video streaming refers to a new class of interactive video applications, where users can zoom into a video stream to view a selected region of interest in higher resolutions and pan around to move the region of interest. The zoom and pan effects are typically achieved by breaking the source video into a grid of independently decodable tiles. Streaming the tiles to a set of heterogeneous users using broadcast is challenging, as users have different link rates and different regions of interest at different resolution levels. In this paper, we consider the following problem: given the subset of tiles that each user requested, the link rate of each user, and the available time slots, at which resolution should each tile be sent, to maximize the overall video quality received by all users. We design an efficient algorithm to solve the problem above, and evaluate the solution on a testbed using 10 mobile devices. Our method is able to achieve up to 12dB improvements over other heuristic methods.
2013 IEEE International Conference on Multimedia and Expo (ICME), 2013
ABSTRACT Secret image sharing is a method for distributing a secret image amongst n data stores, ... more ABSTRACT Secret image sharing is a method for distributing a secret image amongst n data stores, each storing a shadow image of the secret, such that the original secret image can be recovered only if any k out of the n shares is available. Existing secret image sharing schemes, however, do not support scaling and cropping operations on the shadow image, which are useful for zooming on large images. In this paper, we propose an image sharing scheme that allows the user to retrieve a scaled or cropped version of the secret image by operating directly on the shadow images, therefore reducing the amount of data sent from the data stores to the user. Results and analyses show that our scheme is highly secure, requires low computational cost, and supports a large number of scale factors with arbitrary crop.
ABSTRACT The mismatch between increasingly large video resolution and constrained screen size of ... more ABSTRACT The mismatch between increasingly large video resolution and constrained screen size of mobile devices has led to the proposal of zoomable video systems based on tiled video. In the current system, a tiled video frame is constructed from multiple tiles in a single resolution stream. In this paper, we explore the perceptual effect of mixed-resolution tiles in tiled video, in which tiles within a video frame could come from streams with different resolutions, with the aim to tradeoff bandwidth and perceptual video quality. To understand how users perceive the video quality of mixed-resolution tiled video, we conducted a psychophysical study with 50 participants on tiled videos where the tile resolutions are randomly chosen from two resolution levels with equal probability. The experiment results show that in many cases, we can mix tiles from HD (1920×1080p) stream and tiles from 1600×900p stream without being noticed by the viewers. Even when participants notice quality degradation in videos combined with tiles from HD stream and tiles from 960×540p stream, the majority of participants still accept the degradation when viewing videos with low and medium motion; and greater than 40% of participants accept the quality degradation when viewing video with dense motion.
Proceedings of the 8th ACM workshop on Performance monitoring and measurement of heterogeneous wireless and wired networks - PM2HW2N '13, 2013
ABSTRACT Prior work reveals that unfairness in CSMA networks is mainly caused by three asymmetrie... more ABSTRACT Prior work reveals that unfairness in CSMA networks is mainly caused by three asymmetries: (i) information asymmetry; (ii) channel asymmetry; and (iii) rate asymmetry. In this paper, we develop a simple yet accurate analytical model that jointly characterizes all three asymmetric conditions. Our model allows us to estimate the throughput of two contending flows, given the contention window (CW) values. The model can be applied to remedy unfair issues in these topologies, by enabling CW tuning mechanisms to quantify the resulting throughput. The model is flexible enough to support three different fairness objectives. Further, we illustrate how to apply our CW tuning mechanism to an extensive set of asymmetric topologies. Using simulations and testbed measurements, we show that our CW tuning mechanism is effective in mitigating unfairness in the presence of the three fundamental asymmetric conditions.
We propose a new and efficient image-based representation for networked virtual environments, cal... more We propose a new and efficient image-based representation for networked virtual environments, called the sprite tree. A sprite tree organizes multiple reference images efficiently and compactly for accelerating the rendering of complex virtual scenes. Using our basic construction and rendering methods, the results show that a sprite tree can efficiently organize the pixels from hundreds of distinctive reference images and accelerate the rendering of a complex scene. Furthermore, we propose the sprite view similarity to (i) largely reduce the lighting artifacts in the rendered images, and (ii) significantly reduce the redundancy and the tree size with little loss of the visual quality. Keywords 3D image warping • Image-based rendering • Remote rendering • Networked virtual environments 1 Introduction Networked virtual environments (NVEs) have several popular applications such as multiplayer online games (e.g. World
Acm Transactions on Multimedia Computing Communications and Applications, May 1, 2013
We propose an access pattern-driven distributed caching middleware named APRICOD, which can be bu... more We propose an access pattern-driven distributed caching middleware named APRICOD, which can be built on top of any existing content discovery system. APRICOD caters for fast and scalable content discovery in peer-to-peer media streaming systems, especially when user interactions that leads to non-continuous media access (such as random seek in video and teleportation in virtual environment) are present. APRICOD caches query results based correlations among media objects accessed by users, reducing the content discovery time. Our evaluation using a VoD access trace shows that close to 70% of non-continuous access queries can be resolved with a single hop using APRICOD.
Packet loss is a serious problem that severely affects the quality of multimedia streaming over e... more Packet loss is a serious problem that severely affects the quality of multimedia streaming over error-prone networks. To reduce the variability of packet loss and delay, packets can be transmitted over different network paths (path diversity), after being coded by error-concealment source coding methods like Multiple Description Coding (MDC) or Layered Coding (LC). Researches in this area lead to a common belief that MDC is better than LC when the network conditions (packet loss rate, bandwidth) are grave [1, 2]. However, in this paper, we show that the decision of which packets to send over which paths can greatly affect the performance of LC and MDC, therefore the quality of the streams received. Particularly, using our analytical framework and polynomial algorithms for finding optimal packet allocations, we show that LC outperforms MDC under various critical network conditions.
European Journal of Operational Research, Nov 1, 2009
Just-in-time (JIT) trucking service, i.e., arriving at customers within specified time windows, h... more Just-in-time (JIT) trucking service, i.e., arriving at customers within specified time windows, has become the norm for freight carriers in all stages of supply chains. In this paper, a JIT pickup/delivery problem is formulated as a stochastic dynamic traveling salesman problem with time windows (SDTSPTW). At a customer location, the vehicle either picks up goods for or delivers goods from the depot, but does not provide moving service to transfer goods from one location to another. Such routing problems are NP-hard in deterministic settings, and in our context, complicated further by the stochastic, dynamic nature of the problem. This paper develops an efficient heuristic for the SDTSPTW with hard time windows. The heuristic is shown to be useful both in controlled numerical experiments and in applying to a real-life trucking problem.
This paper presents a unified set of abstractions and operations for hardware devices, software p... more This paper presents a unified set of abstractions and operations for hardware devices, software processes, and media data in a distributed audio and video environment. These abstractions, which are provided through a middleware layer called Indiva, use a file system metaphor to access resources and high-level commands to simplify the development of Internet webcast and distributed collaboration control applications. The design and implementation of Indiva are described and examples are presented to illustrate the usefulness of the abstractions.
Page 1. The Design and Im plem entation of a Distributed Data Capture and Processing Fram ework f... more Page 1. The Design and Im plem entation of a Distributed Data Capture and Processing Fram ework for rround Penetrating Radar Allen Bruce Wallis A dissertation submitted to the Department of Electrical Engineering, University ...
Developing applications to control audio/video equipment and the interface between conventional a... more Developing applications to control audio/video equipment and the interface between conventional audio/video signals and Internet streaming media is difficult. Consequently, widespread deployment and use of streaming media in day-today activities has been slow to develop. This paper describes a middleware system and application program interface designed to solve this problem. The system, called INDIVA, provides a hierarchical name space for accessing and controlling audio/video equipment, software services for processing media streams, and conference resources. The design and implementation of the system is described and examples are presented that illustrate how it can be used to implement direct manipulation interfaces for Internet streaming media. This middleware can also be used to implement control and automation systems for Internet webcasting and distributed collaboration systems.
We collected mobility traces of 84,208 avatars spanning 22 regions over two months in Second Life... more We collected mobility traces of 84,208 avatars spanning 22 regions over two months in Second Life, a popular networked virtual environment. We analyzed the traces to characterize the dynamics of the avatars mobility and behavior, both temporally and spatially. We discuss the implications of the our findings to the design of peer-to-peer networked virtual environments, interest management, mobility modeling of avatars, server load balancing and zone partitioning, client-side caching, and prefetching.
... of Computer Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Sin... more ... of Computer Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore, Singapore 119260 RN De Silva e-mail: [email protected] WT Ooi e-mail ... Each region has a teleportation point called the landing point, where all arriving avatars will appear at. ...
This paper presents a unified set of abstractions and operations for hardware devices, software p... more This paper presents a unified set of abstractions and operations for hardware devices, software processes, and media data in a distributed audio and video environment. These abstractions, which are provided through a middleware layer called Indiva, use a file system metaphor to access resources and high-level commands to simplify the development of Internet webcast and distributed collaboration control applications. The design and implementation of Indiva are described and examples are presented to illustrate the usefulness of the abstractions.
ACM Transactions on Multimedia Computing, Communications, and Applications, 2015
Zoomable video streaming refers to a new class of interactive video applications, where users can... more Zoomable video streaming refers to a new class of interactive video applications, where users can zoom into a video stream to view a selected region of interest in higher resolutions and pan around to move the region of interest. The zoom and pan effects are typically achieved by breaking the source video into a grid of independently decodable tiles. Streaming the tiles to a set of heterogeneous users using broadcast is challenging, as users have different link rates and different regions of interest at different resolution levels. In this paper, we consider the following problem: given the subset of tiles that each user requested, the link rate of each user, and the available time slots, at which resolution should each tile be sent, to maximize the overall video quality received by all users. We design an efficient algorithm to solve the problem above, and evaluate the solution on a testbed using 10 mobile devices. Our method is able to achieve up to 12dB improvements over other heuristic methods.
2013 IEEE International Conference on Multimedia and Expo (ICME), 2013
ABSTRACT Secret image sharing is a method for distributing a secret image amongst n data stores, ... more ABSTRACT Secret image sharing is a method for distributing a secret image amongst n data stores, each storing a shadow image of the secret, such that the original secret image can be recovered only if any k out of the n shares is available. Existing secret image sharing schemes, however, do not support scaling and cropping operations on the shadow image, which are useful for zooming on large images. In this paper, we propose an image sharing scheme that allows the user to retrieve a scaled or cropped version of the secret image by operating directly on the shadow images, therefore reducing the amount of data sent from the data stores to the user. Results and analyses show that our scheme is highly secure, requires low computational cost, and supports a large number of scale factors with arbitrary crop.
ABSTRACT The mismatch between increasingly large video resolution and constrained screen size of ... more ABSTRACT The mismatch between increasingly large video resolution and constrained screen size of mobile devices has led to the proposal of zoomable video systems based on tiled video. In the current system, a tiled video frame is constructed from multiple tiles in a single resolution stream. In this paper, we explore the perceptual effect of mixed-resolution tiles in tiled video, in which tiles within a video frame could come from streams with different resolutions, with the aim to tradeoff bandwidth and perceptual video quality. To understand how users perceive the video quality of mixed-resolution tiled video, we conducted a psychophysical study with 50 participants on tiled videos where the tile resolutions are randomly chosen from two resolution levels with equal probability. The experiment results show that in many cases, we can mix tiles from HD (1920×1080p) stream and tiles from 1600×900p stream without being noticed by the viewers. Even when participants notice quality degradation in videos combined with tiles from HD stream and tiles from 960×540p stream, the majority of participants still accept the degradation when viewing videos with low and medium motion; and greater than 40% of participants accept the quality degradation when viewing video with dense motion.
Proceedings of the 8th ACM workshop on Performance monitoring and measurement of heterogeneous wireless and wired networks - PM2HW2N '13, 2013
ABSTRACT Prior work reveals that unfairness in CSMA networks is mainly caused by three asymmetrie... more ABSTRACT Prior work reveals that unfairness in CSMA networks is mainly caused by three asymmetries: (i) information asymmetry; (ii) channel asymmetry; and (iii) rate asymmetry. In this paper, we develop a simple yet accurate analytical model that jointly characterizes all three asymmetric conditions. Our model allows us to estimate the throughput of two contending flows, given the contention window (CW) values. The model can be applied to remedy unfair issues in these topologies, by enabling CW tuning mechanisms to quantify the resulting throughput. The model is flexible enough to support three different fairness objectives. Further, we illustrate how to apply our CW tuning mechanism to an extensive set of asymmetric topologies. Using simulations and testbed measurements, we show that our CW tuning mechanism is effective in mitigating unfairness in the presence of the three fundamental asymmetric conditions.
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Papers by Wei Tsang Ooi