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 Rate Efficient Wireless Image Transmission using MIMO-OFDM(2003) Yu, Wei; Safar, Zoltan; Liu, K.J. Ray; Liu, K.J. Ray; ISRIn this paper, we propose a rate efficient JPEG 2000 image transmission system over hybrid wireless networks using MIMO-OFDM. The objective is to minimize the expected end-to-end distortion given the rate constraint, which is achieved by jointly adjusting source coding schemes and channel coding rates. In this system, MIMO-OFDM is used to increase the channel capacity and mitigate the inter-symbol interference, variable rate space frequency codes and Reed Solomon codes are adopted to combat the channel errors, and error resilient source coding schemes are applied to restrict the error propagation. In case network congestion may happen, packet erasure codes are used to alleviate the packet dropping. The advantages of the proposed system lie in three aspects: adaptivity, optimality, and low complexity. Based on the characteristics of the image content, the estimated channel conditions, and the distortion constraint, the proposed low-complexity joint source channel coding and rate control algorithm adjusts the coding and transmission strategies adaptively, which can approximate the optimal solution with a tight bound.Item Anti-Collusion Fingerprinting for Multimedia(2002) Trappe, Wade; Wu, Min; Liu, K.J. Ray; ISRDigital fingerprinting is a technique for identifyingusers who might try to use multimedia content for unintendedpurposes, such as redistribution. These fingerprints are typicallyembedded into the content using watermarking techniques that aredesigned to be robust to a variety of attacks. A cost-effectiveattack against such digital fingerprints is collusion, whereseveral differently marked copies of the same content are combinedto disrupt the underlying fingerprints. In this paper, weinvestigate the problem of designing fingerprints that canwithstand collusion and allow for the identification of colluders.We begin by introducing the collusion problem for additiveembedding. We then study the effect that averaging collusion hasupon orthogonal modulation. We introduce an efficient detectionalgorithm for identifying the fingerprints associated with Kcolluders that requires O(K log(n/K)) correlations for agroup of n users. We next develop a fingerprinting scheme basedupon code modulation that does not require as many basis signalsas orthogonal modulation. We propose a new class of codes, calledanti-collusion codes (ACC), which have the property that thecomposition of any subset of K or fewer codevectors is unique.Using this property, we can therefore identify groups of K orfewer colluders. We present a construction of binary-valued ACCunder the logical AND operation that uses the theory ofcombinatorial designs and is suitable for both the on-off keyingand antipodal form of binary code modulation. In order toaccommodate n users, our code construction requires onlyO(sqrt{n}) orthogonal signals for a given number of colluders.We introduce four different detection strategies that can be usedwith our ACC for identifying a suspect set of colluders. Wedemonstrate the performance of our ACC for fingerprintingmultimedia and identifying colluders through experiments usingGaussian signals and real images.This paper has been submitted to IEEE Transactions on Signal Processing Item Image and Video Transmission over Wireless Channels: A Subband Modulation Approach(1998) Zheng, H.; Liu, K.J. Ray; ISRA 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.Item Subband Coded Image Transmitting over Noisy Channels Using Multicarrier Modulation(1998) Zheng, H.; Liu, K.J. Ray; ISRIn 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.Item Joint Optimal Power Control and Beamforming in Wireless Networks Using Antenna Arrays(1997) Rashid-Farrokhi, F.; Tassiulas, L.; Liu, K.J. Ray; ISR; CSHCNThe interference reduction capability of antenna arrays and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. The MVDR (Minimum Variance Distortionless Responses) beamformer maximizes the Carrier to Interference Ratio (CIR) when it is employed in the receiver of a wireless link. In a system with omnidirectional antennas, power control algorithms are used to maximize CIR as well. In this paper we consider a system with beamforming capabilities in the receiver, and power control. an iterative algorithm is proposed to jointly update the transmission powers and the beamformer weights so that the coverage to the jointly optimal beamforming and transmission power vector. The algorithm is distributed and uses only local interference measurements. In an uplink transmission scenario it is shown how base assignment can be incorporated in addition to beamforming and power control such that a globally optimum solution is obtained. the network capacity increase and the saving in mobile power achieved by beamforming are evaluated through numerical study.Item Fast Blind Adaptive Algorithms for Equalization and Diversity Reception in Wireless Communications Using Antenna Arrays(1996) Li, Ye; Liu, K.J. Ray; ISRTo combat the multipath and time-variant fading of wireless communication channels, antenna arrays are usually used to improve the quality and increase the capacity of communication service. This paper investigates the fast blind adaptive algorithms for the equalization and diversity combining in wireless communication systems using antenna arrays. Two second- order statistics based algorithms, SOSA and MSOS, for equalization and diversity combining are proposed and their convergence in noiseless and noisy channels is analyzed. Since the proposed algorithms use only second-order statistics or correlation of the channel outputs, they converge faster than the higher-order statistics based algorithms, which is also confirmed by computer simulations examples.Item Fractal Modeling and Segmentation for the Enhancement of Microcalcifications in Digital Mammograms(1996) Li, Huai; Liu, K.J. Ray; Lo, Shih-Chung B.; ISRThe objective of this research is to model the mammographic parenchymal, ductal patterns and enhance the microcalcifications using deterministic fractal approach. According to the theory of deterministic fractal geometry, images can be modeled by deterministic fractal objects which are attractors of sets of two dimensional affine transformations. The Iterated Functions Systems and the Collage Theorem are the mathematical foundations of fractal image modeling. In this paper, a methodology based on fractal image modeling is developed to analyze and extract various mammographic textures. We show that general mammographic parenchymal and ductal patterns can be well modeled by a set of parameters of affine transformations. Therefore, microcalcifications can be enhanced by taking the difference between the original image and the modeled image. Our results are compared with those of the partial wavelet reconstruction and morphological operation approaches. The results demonstrate that the fractal modeling method is an effective way to enhance microcalcifications, and thereby facilitate the radiologists' diagnosis. It may also be able to improve detection and classification of microcalcifications in a computer system.Item A Structured Low Rank Matrix Pencil for Spectral Estimation and System Identification(1996) Razavilar, J.; Li, Ye; Liu, K.J. Ray; ISRIn this paper we propose a new parameter estimation algorithm for damped sinusoidal signals. Parameter estimation for damped sinusoidal signals with additive white noise is a problem of significant interests in many signal processing applications, such as analysis of NMR data and system identification. The proposed algorithm estimates the signal parameters using a matrix pencil constructed from the measured data. To reduce the noise effect, rank deficient Hankel approximation of prediction matrix is used. We show that the performance of the estimation can be significantly improved by structured low rank approximation of the prediction matrix. Computer simulations also show that the noise threshold of our new matrix pencil algorithm is significantly low than those of the existing algorithms.Item Simultaneous Diversity Combining and Decoding for Fast Time- Varying Mobile Radio Channels(1996) Wang, H.; Liu, K.J. Ray; ISRIn slowly time-varying mobile radio channels, adaptive diversity combining can reduce multipath fading of desired signal and suppress interfering signals. However, for fast time-varying fading channels, there exist no effective techniques to achieve the same results. The continued use of decision directed adaptive array algorithms will cause error propagation. This paper presents a novel adaptive diversity combining technique with QRD- RLS based parallel weights tracking and a proposed M-D decoder. With moderate increase in complexity, this system significantly reduces error propagation in the decision directed array systems while maintaining the same tracking speed. Its effectiveness and much better performance then that of the conventional technique has been confirmed by computer simulation.Item Blind Adaptive Equalization of SIMO Channels Based on Second- Order Statistics(1996) Li, Ye; Liu, K.J. Ray; ISRThis article investigates blind adaptive equalization for single- input/multiple-output (SIMO) channels. A second-order statistics based algorithm (SOSA) and a modified second-order statistics based algorithm (MSOSA) for equalization of SIMO channels are presented. Computer simulation demonstrates that the new algorithms converge faster than fractionally spaced constant- modulus algorithm (FS-CMA). The proposed algorithms can be applied in wireless communication systems with antenna arrays to combat the multipath fading.