Browsing by Author "Baras, John S."
Results Per Page
Sort Options
Item Accurate Segmentation and Estimation of Parametric Motion Fields for Object-based Video Coding using Mean Field Theory(1997) Haridasan, Radhakrishan; Baras, John S.; ISR; CSHCNWe 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. Item Adaptive Data Broadcast in Hybrid Networks(1997) Stathatos, K.; Roussopoulos, N.; Baras, John S.; ISR; CSHCNHybrid networks combine multiple communication modes and are fast, emerging as the most viable solution for the ever increasing demand for bandwidth and data services. Taking advantage of this new technology, we are proposing a hybrid scheme which effectively combines broadcast for massive data dissemination and unicast for individual data delivery. The goal is to build highly scalable systems with small response time. In this paper, we describe a technique that continuously adapts the broadcast content to match the hot-spot of the workload. We show that the hot-spot can be accurately obtained by, monitoring the ``broadcast misses'' observed through direct requests.This is a major departure from all other broadcast optimization schemes which are handicapped by their total reliance on complete knowledge of both ``hits'' and ``misses''. We also show that the proposed adaptive scheme performs effectively even under very dynamic and rapidly changing workloads. Extensive simulation results demonstrate both the scalability and versatility of, the technique. Another basic result obtained in this paper is that the overall, system's throughput depends only on the size of the hot-spot and not on the volume of the workload. This has far reaching implications for very large scale and high volume wide area information systems.
Item Adaptive Data Broadcasting Using Air-Cache(1996) Stathatos, K.; Roussopoulos, N.; Baras, John S.; ISR; CSHCNIn the Data AirWaves Project at University of Maryland, we are integrating Direct Broadcast Satellite (DBS) systems with terrestrial networks to provide a hybrid and effective communication substrate lying between data resources and remote/mobile user applications. Smooth integration of these two media balances the need for rapid data dissemination to very large numbers of clients and on-demand interactive data services. This paper describes the air-cache, a method for effective data broadcasting and an algorithm which rapidly adapts the content of the cache based on the ﲭisses which result in explicit (on- demand) data requests. Simulation results show that the hypothesis of adapting based only on the misses performs quite reasonably and has very little deviation from a system that has complete information - both hits and misses.Item Adaptive Identification and Control of Hysteresis in Smart Material Actuators(2003) Tan, Xiaobo; Baras, John S.; ISR; CDCSSHysteresis exhibited by smart materials hinders their wider applicability in actuators and sensors. In this paper methods are studied for recursive identification and adaptive inverse control of smart material actuators, where a Preisach operator with a piecewise uniform density function is used to model the hysteresis. Persistent excitation conditions for parameter convergence are discussed in terms of the input to the Preisach operator. Two classes of recursive identification schemes are explored, one based on the hysteresis output, the other based on the time difference of the output. Asymptotic tracking for the adaptive inverse control method is proved, and the condition for parameter convergence is given in terms of the reference trajectory. Practical implementation issues are also investigated. Simulation and experimental results based on a magnetostrictive actuator are used to illustrate the approach.Item Advanced Orbiting Systems Data Generator/Simulator: A Functional Description of the Software (Version 3)(1994) Baras, John S.; Atallah, George C.; Fuja, Tom E.; Murad, A.; Jang, Kap D.; ISR; CSHCNThe Advanced Orbiting System (AOS) Data Generator/Simulator is a software implementation of the transmitter (data generation) section of the CCSDS Recommendation 701.0-B-2 for Advanced Orbiting Systems: Networks and Data Links. An object-oriented approach to the simulation of a complex, high-performance communication protocol, it makes full use of the concepts of data-encapsulation and inheritance to ease implementation. The backbone of the software is a general-purpose packet description and generation module that may be used as part of any packet- based simulation software. The user-interface to the program is in the form of a command-language, designed to ease the process of generation of large, multiple data-streams. The output of the program may be configured for interpretation by a graphical user interface (for visual inspection of the data), or as a bit-stream suitable for further processing. This paper consists of three sections. The first two sections provide a brief, yet comprehensive description of the above CCSDS Recommendation. The various kinds and qualities of user-services, data units involved, and data-paths defined by the protocol are discussed. The different qualities of service (in terms or data reliability) available to the user (and the error-control schemes used to provide them) are also discussed. The last section describes the structure and user-interfaces of the AOS Data Generator/Simulator.Item Alternative Network Architectures for Supporting Communications from the International Space Station(2002) Nguyen, Alex T.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCNIn order to support the communications needs of the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. We address three communications options and evaluate an architecture for the direct to ground option, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We focus on a particular user requirements, and examine the system communications links, and coverage availability. These parameters, along with high-level cost estimates, are compared to using commercial relay satellites, and an enhanced TDRSS. The direct to ground option is viable for store-and-forward applications and cost comparable to commercial constellations, but TDRSS is the choice for real-time or continuous data applications.Item Analysis and Design of Robust Key Schemes for Multicast Communications(1999) R. Poovendran; Baras, John S.; Baras, John S.; ISR; CSHCNRecent literature presents several rooted tree based member deletion/revocation schemes trying to simultaneously minimize the key storage whileproviding efficient member deletion/revocation. Many of these approaches have different solutions and provide different values for the number of keys to be stored and distributed.In this paper, we show that these problems can be systematically studied using basic concepts from information theory. In particular, we show that the entropy of member revocation event plays a major role in defining the key allocation requirements. We then relate the entropy of member revocation event to bounds on the key length.
We also show that the optimal Huffman coding strategy used in leads to security weaknesses. A method for generating key management schemes to withstand varying degrees of member collusion is also presented.
ATIRP 4th Annual Conference
Item An Analysis of Delay-Constrained Opportunistic Scheduling for Cellular Wireless Systems(2004) Srinivasan, Roshni; Baras, John S.; Baras, John S.; ISR; CSHCNBase station schedulers in 3G and evolving 4G cellular systems use knowledge of the time-varying channel conditions of mobile users to exploit the multiuser diversity inherent in wireless networks. Although such opportunistic schedulers significantly improve the system throughput by scheduling users when their channel conditions are most favorable, they could degrade the user experience as a result of unfair resource allocation and increased variability in the scheduled rate and delay. The growing need to provide service differentiation between delay-sensitive multimedia traffic and non real-time data traffic over packet switched air-interfaces underscores the need for these schedulers to incorporate delay constraints.
In this work, we focus primarily on the trade-off between the realization of multiuser diversity gain and the provision of delay guarantees. Our main contribution is an analytical characterization of the distributions of the delay and rate offered by an opportunistic scheduler. The scheduling metric used in the algorithm combines the rate requested by the user and scheduling delay in a general form. Our analysis of a wireless system with a finite number of users in discrete time is strongly supported by system simulations of a time-slotted cellular downlink shared by multiple mobile users with independent, fading channels. We also compute closed form expressions for the scheduler statistics using a continuous approximation. The results in this paper can be used to evaluate system performance and provision resources to support Quality of Service (QoS) guarantees in broadband wireless networks.Item An Architecture for Internet Service via Broadband Satellite Networks(1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCNHigh bandwidth satellites hold out the promise of a rapidly deployablecommunications infrastructure with a natural support for mobility. However,the Transmission Control Protocol (TCP), widely used in the Internet, performspoorly over satellite links, and this presents an obstacle to thedeployment of such systems. We present an architecture that overcomesthese problems and provides an approach to building complex heterogeneousnetworks from simple units. We also present some results from our initialimplementation, which uses TCP connection splitting to improve TCPperformance over satellite links.Item Asymmetric Internet Access over Satellite-Terrestrial Networks(1996) Arora, Vivek; Suphasindhu, N.; Baras, John S.; Dillon, Douglas; ISR; CSHCNDirecPCtm's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only satellite links for downstream data delivery and public telephone networks at the modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. Our principle object is to lower cost and efficiently provide high bandwidth access to Internet services such as file transfer, the World Wide Web, and the MBONE. In the initial protocol implementation, we achieved four times higher throughput than that of Today's high-speed modems (28.8 Kbps) alone2. This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques, TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths. Furthermore, we are investigating how to extend IP multicast services to such hybrid networks. The broadcast nature of Satellite communication makes it an efficient way for high- bandwidth multicast transmission.- A revised version of this technical report has been published in
Proceedings of the AIAA: 16th International Communications Satellite Systems Conference and Exhibit, Part 1, pp. 476-482, Washington, D.C., February 25-29, 1996.Item ATM in Hybrid Networks(1996) Baras, John S.; ISR; CSHCNA discussion of the extensions or modifications required to integrate ATM into hybrid networks, i.e. seamlessly interconnected terrestrial and space, wireline and wireless networks will be presented. In this context, the discussion will include: interoperability problems and issues, asymmetric channels, and various data rates. Several issues with proposed standards will also be addressed.A revised version of this technical report has been published in Proceedings of Design SuperCon 1996, Vol. Day One, pp. 1-1 thru 1-13, Santa Clara, CA, January 30-February 1, 1996. Item Automated Network Fault Management(1997) Baras, John S.; Ball, Michael O.; Gupta, Sonjai K.; Viswanathan, P.; Shah, P.; ISR; CSHCNFuture military communication networks will have a mixture of backbone terrestrial, satellite and wireless terrestrial networks. The speeds of these networks vary and they are very heterogeneous. As networks become faster, it is not enough to do reactive fault management. Our approach combines proactive and reactive fault management . Proactive fault management is implemented by dynamic and adaptive routing. Reactive fault management is implemented by a combination of a neural network and an expert system. The system has been developed for the X.25 protocol. Several fault scenarios were modeled and included in the study: reduced switch capacity, increased packet generation rate of a certain application, disabled switch in the X.25 cloud, disabled links. We also modeled occurrence of alarms including severity of the problem, location of the event and a threshold. To detect and identify faults we use both numerical data associated with the performance objects (attributes) in the MIB as well as SNMP traps (alarms). Simulation experiments have been performed in order to understand the convergence of the algorithms, the training of the neural networks involved and the G2/NeurOn-Line software environment and MIB design.Item An Automated, Distributed, Intelligent Fault Management System for Communication Networks(1999) Li, Hongjun; Baras, John S.; Mykoniatis, George; ISR; CSHCNIn this paper we present a Distributed Intelligent Fault Management (DIFM) system for communication networks. The overall architecture of the proposed system is based on a distributed, cooperative, multi-agent paradigm, with probabilistic networks as the framework for knowledge representation and evidence inferencing. We adopt the management by delegation paradigm for network monitoring and integrate both hard and soft faults.Item Bayesian Hypothesis Testing for Boolean Random Sets with Radial Convex Primary Grains Using Morphological Skeleton Transforms(1991) Sidiropoulos, N.; Baras, John S.; Berenstein, Carlos A.; ISRWe consider the problem of binary hypothesis testing for planar Boolean random sets with radial convex primary grains. We show that this problem is equivalent to the problem of binary hypothesis testing for Poisson points on a subset of R cube . The log-likelihood ratio for Poisson points can therefore be applied to observation points on this subset of R cube. Several interesting results pertaining to the asymptotic performance of the log-likelihood ratio for Poisson points are known. A major difficulty with this approach is that the test is based on observation points on a subset of R cube, and is not directly given in terms of the observation of a realization of a Boolean random set. An efficient means of mapping realizations of planar Boolean random sets to corresponding realizations of Poisson point processes on this subset of R cube is needed in order to implement the test. We show that this can be achieved via a class of morphological transformations known as morphological skeleton transforms. These transforms are flexible shape-size analysis tools based on elementary morphological and set-theoretic operations. This is the principal contribution of this paper.Item Biologically-Inspired Acoustic Wear Analysis(2001) Varma, S.; Baras, John S.; Shamma, S. A.; ISR; CAARWe report on a novel method of acoustic wear analysis using spectral classification based on a model of mammalian audition. This approach uses biologically-inspired pre-processing filters that give a multi- resolution representation of the sound timbre. A Tree Structured Vector Quantizer (TSVQ) is used to create a classification tree based on the wear labels. We have obtained encouraging results for tools of different diameters, cutting different materials. Trees trained on one kind of data seem to generalize well to new data sets.The research and scientific content in this material have been accepted for the Nonlinear Signal and Image Processing (NSIP) 2001 Conference at Baltimore, MD, 2001 Item Broadcast Scheduling for Push Broadcast Systems with Arbitrary Cost Functions(2007) Raissi-Dehkordi, Majid; Baras, John S.; ISRIn this report the problem of broadcast scheduling in Push broadcast systems is studied. We introduce an optimization approach that leads to well justified policies for Push broadcast systems with generalized cost functions. In particular, we apply our results to a Push broadcast system with different deadlines associated to the files while allowing the files to have unequal demand rates and lengths. We will show that our proposed policy covers some of the previously investigated Push systems as special cases and is applicable to a wide range of cost functions assigned to the files. We also calculate the optimal average cost for our experimental settings and show, through extensive simulation studies, that our results closely match that value for each experiment.Item Caching and Multicasting in DBS Systems(1999) Liu, Mingyan D.; Karir, Manish; Baras, John S.; Baras, John S.; ISR; CSHCNThe use of Caching and Multicasting has been studied extensively inthe context of terrestrial networks. However, the use of thesetechnologies in a Direct Broadcast Satellite(DBS) system remains unclear.In this paper we discuss possible choices of caching and multicasting schemes, motivated by current applications in the terrestrial Internet,that could be considered for a DBS system. We examine their advantages and disadvantages as well as the tradeoffs involved in combinations of different approaches. We also propose some uses of these technologies and describe an architecture that enhances the performance and efficiency of a DBS system. This paper is published in the Proceedings of International Workshop on Group Communication, International Conference on Parallel Processing, September 1999.Item A Carrier Frequency Estimation Method of MPSK Signals and Its Systolic VLSI Implementation(1999) Jiang, Yimin; Ting, Wen-Chun; Verahrami, Farhad B.; Richmond, Robert L.; Baras, John S.; Baras, John S.; ISR; CSHCNIn this paper we present an autocorrelation-based method for estimating the carrier frequency offset of an MPSK signal with random data modulation. Although autocorrelation-based techniques imply heavy usage of hardware resources, this technique is scalable and lends itself well to systolic VLSI implementations. The performance of the open-loop estimator presented is close to the Cramer-Rao lower bound (CRLB) for the frequency estimation from a block of random PSK symbols at low signal-to-noise (SNR) ratios. The estimator can be used in frequency acquisition of burst and continuous modems operating under low SNR and large frequency offset conditions.
This paper has been submitted to 33rd Annual Conference on InformationSciences and Systems, March 17-19, 1999, John Hopkins University,Baltimore, Md.Item Carrier Frequency Estimation of MPSK Modulated Signals(1999) Jiang, Yimin; Richmond, Robert L.; Baras, John S.; Baras, John S.; ISR; CSHCNIn this paper we concentrate on MPSK carrier frequency estmation based on random data modulation. We present a fast, open-loop frequency estimation and tracking techinque, which combines a feedforward estimator stuctureand a recursive least square (RLS) predictor. It is suitable for the frequency estimation and large frequency acquisition and tracking required of burst mode satellite modems operating under the condition of low SNR and large burst-to-burst frequency offset. The performance of the estimator is analyzed in detail and simulation results are shown. Finally, the non-linear impact of data modulation removal methods is discussed. The estimator we derived is easily implemented with digital hardware.
This paper has been submitted to the 1999 International Conferenceon Communications, June 6-10, 1999, Vancouver, CanadaItem A case for in-kernel data streaming over the file subsystem(1998-10-15) Gupta, Sandeep; Baras, John S.; Kelley, Stephen; Roussopoulos, Nick(Also cross-referenced as UMIACS-TR-96-36)