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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Item Reliable Multicasting via Satellite: Delay Considerations(2000) Stephen M. Payne; Baras, John S.; Baras, John S.; ISR; CSHCNMany different reliable multicast protocols have been proposed and analyzed in the current literature. Since satellites are naturallya braodcast medium, multicast communications have the potential togreatly benefit from their wide-scale deployment. The performance ofreliable multicast protocols needs to be studied and become betterunderstood over networks including satellite links. Most of the analysisperformed on these protocols has dealt with bandwidth usage, bufferrequirements, and processing delay. Very few studies address thetransmission delay incurred from using reliable multicast protocols. Hybriderror control protocols have been studied in terms of bandwidth and delay.The effects of different estimation schemes coupled with autoparityusage are investigated and results are compared. Simple adaptive mechanismsused with a local recovery scheme are found to offer the best overallresults in terms of reducing recovery latency and satellite bandwidth usage.Item Window Distribution of Multiple TCPs with Random Loss Queues(1999) Misra, Archan; Baras, John S.; Ott, Teunis; Baras, John S.; ISR; CSHCNIn this paper, we consider the case of multiple ideal and persistent TCP flows (flows that are assumed to be performing idealized congestion avoidance) interacting with queue management algorithms that perform random drop-based buffer management. Our objective is to determine the stationary congestion window distribution of each of the TCP flows whenthe router port implements algorithms like RED (Random Early Detection)or ERD (Early Random Drop).We first present an analyticaltechnique to obtain the 'mean' queue occupancy and the 'mean' of the individual TCP windows. Armed with this estimate of the means, wethen derive the window distribution of each individual TCPconnection. Extensive simulation experiments indicate that, under a wide variety of operating conditions, our analytical method is quite accurate in predicting the 'mean' as well asthe distributions. The derivation of the individual distributions is based upon a numerical analysis presented which considers the case of a single TCP flow subject to variable state-dependent packet loss.
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 Delay Monitoring in ATM Networks(1999) Arora, Anubhav; Baras, John S.; Mykoniatis, George; Baras, John S.; ISR; CSHCNATM networks provide end-to-end QoS guarantees to connectionsfor their lifetime, in the form of bounds on delays, errors andlosses. Performance management involves measurement of theseparameters accurately and taking control measures if required, toimprove performance. This is very important for real time connectionsin which losses are irrecoverable and delays cause interruptions inservice. In this paper, we concentrate on delay monitoringmechanisms. After presenting the OAM standard for ATM and a fewsolutions in the literature, problems still remaining are formulatedand directions being pursued to obtain solutions are indicated.This paper was published in the Proceedings of the 3rd Annual Conferenceon Advanced Telecommunications and Information Distribution ResearchProgram (ATIRP), pp. 259-263, February 1-5, 1999, University of Maryland,University College, MD.
Item A Video Transmission System Based on Human Visual Model for Satellite Channel(1999) Gu, Junfeng; Jiang, Yimin; Baras, John S.; ISR; CSHCNThis paper presents a practical architecture for joint source-channel coding of human visual model-based video transmission over satellite channel. Perceptual distortion model just-noticeable-distortion (JND) is applied to improve the subjective quality of compressed videos. 3-D wavelet decomposition can remove spatial and temporal redundancy and provide scalability of video quality.In order to conceal errors occurring under bad channel conditions, a novel slicing method and a joint source channel coding scenario that combines RCPC with CRC and utilizes the distortion information to allocate convolutional coding rates are proposed. A new performance index based on JND is proposed and used to evaluate the overall performance at different signal-to-noise ratios (SNR). Our system uses OQPSK modulation scheme.
This paper has been submitted to Globecomm99, Rio de Janeiro, Brazil, December 5-9, 1999.
Item Internet Service via Broadband Satellite Networks(1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCNThe demand for Internet bandwidth has grown rapidly in the past few years. A new generation of broadband satellite constellations promises to provide high speed Internet connectivity to areas not served by optical fiber, cable or other high speed terrestrial connections. However, using satellitelinks to supply high bandwidth has been difficult due to problems with inefficient performance of the Internet's TCP/IP protocol suite over satellite. We describe an architecture for improving the performance of TCP/IP protocols over heterogeneous network environments, especially networks containing satellite links. The end-to-end connection is split into segments, and the protocol on the satellite segment is optimized for the satellite link characteristics. TCP congestion control mechanisms are maintained on each segment, with some coupling between the segments to produce the effect of end-to-end TCP flow control. We have implemented this design and present results showing that using such gateways can improve throughput for individual connections by a large factor over paths containing a satellite link.The research and scientific content in this material has been published in the Proceedings of the SPIE, vol. 3528, February 1999, 169-180. Item An End-to-End Measurement-Based Scheduling Architecture for ATM Networks(1999) Arora, Anubhav; Baras, John S.; Mykoniatis, George; ISR; CSHCNATM networks provide end-to-end QoS guarantees to connections for theirlifetime in the form of bounds on delay, error and/or loss. Theguarantees are important for real-time connections in which losses areirrecoverable and delays cause interruptions in service. Performancemanagement involves measurement of QoS parameters and applying controlmeasures, if required, to improve performance or resource utilization. Inthis paper, we propose a new hierarchical scheduling algorithm based ondynamic priorities which are adaptive to end-to-end QoS measurements madeon QoS sensitive (real-time) connections. This architecture can providebounds on average delay and delay variation with varying backgroundnetwork traffic.This paper has been submitted to INFOCOM 2000, Tel Aviv Israel, March 26-30, 2000.
Item A Practical Transmission System Based on the Human Visual Model for Satellite Channels(1999) Gu, Junfeng; Jiang, Yimin; Baras, John S.; Baras, John S.; ISR; CSHCNThis paper presents a practical architecture for joint source-channel coding of human visual model-based video transmission over a satellite channel. Perceptual distortion model just-noticeable-distortion (JND) is applied to improve the subjective quality of compressed videos. 3-D wavelet decomposition can remove spatial and temporal redundancy and provide the scalability of video quality.In order to conceal errors occurring under bad channel conditions, a novel slicing method and a joint source channel coding scenario that combines RCPC with CRC and utilizes the distortion information to allocate convolutional coding rates are proposed. A new performance index based on JND is proposed and used to evaluate the overall performance at different signal-to-noise ratios (SNR). Our system uses OQPSK modulation scheme.
The research and scientific content in this material has been submitted to Globecom'99. 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, Canada