Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Subject: search.filters.subject.Intelligent Signal Processing

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Now showing 1 - 10 of 87
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    Scalable Coding of Video Objects
    (1998) Haridasan, Radhakrishan; Baras, John S.; Baras, John S.; ISR; CSHCN
    This paper provides a methodology to encode video objects in a scalable manner with regard to both content and quality. Content scalability and quality scalability have been identified as required features in order to support video coding across different environments. Following the object-based approach to coding video, we extend our previous work on motion-based segmentation by using a time recursive approach to segmenting image sequences and decomposing a video "shot" into its constituent objects. Our formulation of the segmentation problem enables us to design a codec in which the information (shape, texture and motion) pertaining to each video object is encoded independently of the other. The multiresolution wavelet decomposition used in encoding texture information is shown to be helpful in providing spatial scalability. Our codec design is also shown to be temporally scalable. This report was accepted for oral presentation at the IEEE International Symposium on Circuits & Systems, Monterey, Calif., May-June 1998.
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    Image and Video Transmission over Wireless Channels: A Subband Modulation Approach
    (1998) Zheng, H.; Liu, K.J. Ray; ISR
    A new approach of reliable image and video transmission over wireless channels is proposed. The subband modulation which combines source coding and channel modulation schemes achieves high compression efficiency and preferable quality. Further performance gain is obtained by multiresolution modulation and a bits re-mapping scheme that assigns efficient mapping from each source code word to channel modulation points. We show that bits re-mapping schemes perform nearly the same as the optimal mapping design scheme but with much lower complexity. The simulations are carried out on Additive White Gaussian Noise (AWGN) channels and slow Rayleigh fading channels.
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    Subband Coded Image Transmitting over Noisy Channels Using Multicarrier Modulation
    (1998) Zheng, H.; Liu, K.J. Ray; ISR
    In this paper, we present a new loading algorithm for subband coded image transmission on multicarrier modulation systems. The image subbands are transmitted simultaneously, each occupying a number of subchannels. Different modulation rates and powers are assigned to the subchannels transmitting different subbands. Unlike the traditional loading algorithms, which flat the error performance of all the subchannels, the proposed loading algorithm assigns different error performances to the subchannels in order to provide unequal error protection for the subbands data. Numerical examples show that the proposed algorithm yields significant improvement over traditional loading algorithms, especially for spectral-shaped channels.
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    Architecture for Guaranteed Delay Service in High Speed Networks
    (1997) Peris, Vinod; Makowski, Armand; ISR; CSHCN
    The increasing importance of network connections coupled with the lack of abundant link capacity suggests that the day when service guarantees are required by individual connections is not far off. In this dissertation we describe a networking architecture that can efficiently provide end-to-end delay guarantees on a per- connection basis. In order to provide any kind of service guarantee it is imperative for the source traffic to be accurately characterized at the ingress to the network. Furthermore, this characterization should be enforceable through the use of a traffic shaper (or similar device). We go one step further and assume an extensive use of traffic shapers at each of the network elements. Reshaping makes the traffic at each node more predictable and therefore simplifies the task of providing efficient delay guarantees to individual connections. The use of per-connection reshapers to regulate traffic at each hop in the network is referred to as a Rate Controlled Service (RCS) discipline. By exploiting some properties of traffic shapers we demonstrate how the per-hop reshaping does not increase the bound on the end-to-end delay experienced by a connection. In particular, we show that an appropriate choice of traffic shaper parameters enables the RCS discipline to provide better end-to- end delay guarantees than any other service discipline known today. The RCS discipline can provide efficient end-to-end delay guarantees to a connection; however, by definition it is not work-conserving. This fact may increase the average delay that is observed by a connection even if there is no congestion in the network. We outline a mechanism by which an RCS discipline can be modified to be work-conserving without sacrificing the efficient end-to-end delay guarantees that can be provided to individual connections. Using the notion of service curves to bound the service process at each network element, we are able to provide an upper bound on the buffers required to ensure zero loss at the network element. Finally, we examine how the RCS discipline can be used in the context of the Guaranteed Services specification that is currently in the process of being standardized by the Internet Engineering Task Force.
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    Architecture, Design, Simulation and Performance Evaluation for Implementing ALAX -- The ATM LAN Access Switch Integrating the IEEE 1355 Serial Bus
    (1997) Charleston, Giles C.; Makowski, A.; ISR; CSHCN
    IEEE 1355 is a serial bus standard for Heterogeneous Inter Connect (HIC) developed for "enabling high-performance, scalable, modular and parallel systems to be built with low system integration cost." However to date, few systems have been built around this standard specification. In this thesis, we propose ALAX -- an internetworking switching device based on IEEE 1355. The aim of the thesis is two-fold. First, we discuss and summarize research works leading to the architecture, design and simulation development for ALAX; we synthesize and analyze relevant data collected from the simulation experiments of the 4- port model of ALAX (i.e., 4-by-4 with four input and output queues) -- these activities were conducted during the 2-year length of the project. Secondly, we expand the original 4-by-4 size of the ALAX simulation model into 8-, 12- and 16-port models and present and interpret the outcomes. Thus, overall we establish a performance assessment of the ALAX switch, and also identify several critical design measurements to support the ALAX prototype implementation. We review progresses made in Local Area Networks (LANs) where traditional software-enabled bridges or routers are being replaced in many instances by hardware-enabled switches to enhance network performance. Within that context, ATM (Asynchronous Transfer Mode) technology emerges as an alternative for the next generation of high-speed LANs. Hence, ALAX incarnates our effective approach to build an ATM-LAN interface using a suitable switching platform. ALAX currently provides the capability to conveniently interconnect legacy Ethernet and ATM- based networks. Its distributed architecture features a multi- processor environment of T9000 transputers with parallel processing capability, a 32-by-32 way non-blocking crossbar fabric (C104 chipset) partitioned into Transport (i.e., Data) and Control planes, and many other modules interlaced with IEEE 1355- based connectors. It also employs existing and emerging protocols such as LANE (LAN Emulation), IEEE 802.3 and SNMP (Simple Network Management Protocol). We provide the component breakdown of the ALAX simulation model based on Optimized Network Engineering Tools (OPNET). The critical parameters for the study are acceptable processor speeds and queuing sizes of shared memory buffer at each switch port. The performance metric used is the end-to-end packet delay. Finally, we end the thesis with conclusive recommendations pertaining to performance and design measurement, and a brief summary of areas for further research study.
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    Accurate Segmentation and Estimation of Parametric Motion Fields for Object-based Video Coding using Mean Field Theory
    (1997) Haridasan, Radhakrishan; Baras, John S.; ISR; CSHCN
    We formulate the problem of decomposing a scene into its constituent objects as one of partitioning the current frame into objects comprising it. The motion parameter is modeled as a nonrandom but unknown quantity and the problem is posed as one of Maximum Likelihood (ML) estimation. The MRF potentials which characterize the underlying segmentation field are defined in a way that the spatio-temporal segmentation is constrained by the static image segmentation of the current frame. To compute the motion parameter vector and the segmentation simultaneously we use the Expectation Maximization (EM) algorithm. The E-step of the EM algorithm, which computes the conditional expectation of the segmentation field, now reflects interdependencies more accurately because of neighborhood interactions. We take recourse to Mean Field theory to compute the expected value of the conditional MRF. Robust M-estimation methods are used in the M- step. To allow for motions of large magnitudes image frames are represented at various scales and the EM procedure is embedded in a hierarchical coarse-to-fine framework. Our formulation results in a highly parallel algorithm that computes robust and accurate segmentations as well as motion vectors for use in low bit rate video coding.

    This report has been submitted as a paper to the SPIE conference on Visual Communications and Image Processing - VCIP98 to be held in San Jose, California on Jan 24- 30, 1998.
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    Designing Broadcast Schedules for Information Dissemination through Broadcasting
    (1997) Su, Chi-Jiun; Tassiulas, Leandros; Tassiulas, Leandros; ISR; CSHCN
    Broadcast data delivery is encountered in many applications where there is a need to disseminate information to a large user community in a wireless asymmetric communication environment. In this paper, we consider the problem of scheduling the data broadcast such that the access latency experienced by the users is low. In a push-based system, where the users cannot place requests directly to the server and the broadcast schedule should be determined based solely on the access probabilities, we formulate a deterministic dynamic optimization problem, the solution of which provides the optimal broadcast schedule. Properties of the optimal solution are obtained and then we propose a suboptimal dynamic policy which achieves mean access latency close to the lower bound. The policy has low complexity, it is adaptive to changing access statistics, and is easily generalizable to multiple broadcast channels. In a pull-based system where the users may place requests about information items directly to the server, the scheduling can be based on the number of pending requests for each item. Suboptimal policies with good performance are obtained in this case as well. Finally, it is demonstrated by a numerical study that as the request generation rate increases, the achievable performance of the pull- and push- based systems becomes almost identical.
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    Service Integration in Next Generation VSAT Networks
    (1997) Hadjitheodosiou, Michael H.; ISR; CSHCN
    Very Small Aperture Terminal (VSAT) satellite networks have so far been successful in the provision of specific communication services to geographically dispersed users. However, user demands are becoming more complex, and VSAT networks are expected to provide a much wider range of services (voice, data and multimedia). We investigate how this service integration could be achieved and show that performance improvements are possible if efficient multi-access protocols and speech compression with voice activity detection techniques are used. We also discuss the future role VSATs could play in the provision of access to the Integrated Broadband Communications Network to remote users. We discuss the possibility of using VSATs for ATM service provision. The need for careful consideration of the advantages and limitations of using VSAT networks for this type of service is discussed. Finally, we highlight a method for dynamic bandwidth allocation in a broadband satellite network.
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    A Five-Phase Reservation Protocol (FPRP) for Mobile Ad Hoc Networks
    (1997) Zhu, Chenxi; Corson, M. Scott; ISR; CSHCN
    A new single channel, TDMA-based broadcast scheduling protocol, termed the Five-Phase Reservation Protocol (FPRP), is presented for mobile ad hoc networks. The protocol jointly and simultaneously performs the tasks of channel access and node broadcast scheduling. The protocol allows nodes to make reservations within TDMA broadcast schedules. It employs a contention-based mechanism with which nodes compete with each other to acquire the TDMA slots. The FPRP is free of the ``hidden terminal" problem, and is designed such that reservations can be made quickly and efficiently with minimal probability of conflict. It is fully distributed and parallel (a reservation is made through a localized conversation between nodes in a 2-hop neighborhood), and is thus arbitrarily scalable. A ``multihop ALOHA" policy is developed to support the FPRP. This policy uses a multihop, pseudo-Baysian algorithm to calculate contention probabilities and enable faster convergence of the reservation procedure. The performance of the protocol is studied via simulation, and the node coloring process is seen to be as effective as an existing centralized approach. Some future work and applications are also discussed.
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    Heavy Traffic Limits Associated with M|GI|Input Processes
    (1997) Tsoukatos, K.P.; Makowski, Armand M.; ISR; CSHCN
    We study the heavy traffic regime of a discrete-time queue driven by correlated inputs, namely the M|GI|input processes of Cox. We distinguish between M|GI|processes with short- and long- range dependence, identifying for each case the appropriate heavy traffic scaling that results in non-degenerate limits. As expected, the limits we obtain for short-range dependent input involve the standard Brownian motion. Of particular interest are the conclusions for the long-range dependent case: The normalized queue length can be expressed as a function not of a fractional Brownian motion, but of an a-stable, 1/a self-similar independent increments levy process. The resulting buffer asymptotics in heavy traffic display a hyperbolic decay, of power 1 - a. Thus M|GI|processes already demonstrate that, within long-range dependence, fractional Brownian motion does not necessarily assume the ubliquitous role that standard Brownian motion plays in the short-range dependence setup.