Jeffrey B. Schodorf

Array processing techniques for multiuser detection

Techniques often used in the area of adaptive array signal processing are applied to the multiuser detection problem. The results of this effort include a robust detector, suitable for use in the presence of modeling errors, and a reduced-rank detector with improved transient behavior relative to full-rank detectors. Algorithm performance is presented in the form of bit-error-rate (BER) curves and least mean square (LMS)-like learning curves.

Multi-media and World Wide Web resources for teaching DSP

A new digital signal processing (DSP) course designed to build students intuition about signals and systems is presented. The course makes extensive use of multi-media demonstrations to relate real-world signals and discrete-time systems to their mathematical descriptions. In addition to the numerous in-class demonstrations, weekly laboratory exercises have been developed to further strengthen the ties between DSP theory and real-world signals and systems. Many of the in-class demonstrations have been captured on the World Wide Web (WWW), so the students can explore them outside of class. In the near future, the WWW-based demonstrations will be packaged on a CD-ROM as an integral part of a new text.

A constrained adaptive diversity combiner for interference suppression in CDMA systems

A multisensor interference cancellation scheme for CDMA communication systems is presented. The algorithm consists of constrained output power minimization at each sensor followed by optimal combining of the sensor outputs. Knowledge of the desired users code is used to specify the constraint for minimizing the output power at each sensor of the array. If the codes (and timing) of other users (i.e., interferers) are known, they may be incorporated as additional constraints to improve receiver performance. Optimal combining of the individual sensor outputs is achieved by employing the LMS algorithm in tracking mode for the adaptation. The receiver is blind in the sense that only knowledge of the desired users code (not the actual transmitted bit sequence) and associated timing is necessary. Algorithm performance results for Rayleigh fading channels are presented in the form of signal to interference-plus-noise ratios and bit error rate curves.

A blind adaptive interference cancellation scheme for CDMA systems

An interference cancellation scheme for CDMA communication systems is presented. The algorithm is based on constrained optimization where receiver output power is minimized subject to the constraint that a desired code be passed with no distortion. Output power minimization (OPM) schemes have been shown to be equivalent to minimum mean square error (MMSE) approaches. Like MMSE approaches, OPM schemes do not require explicit knowledge of the interference structure. Unlike most MMSE approaches, however, OPM schemes do not require training. The algorithms are blind in the sense that only knowledge of the desired users code (not the actual transmitted bit sequence) and associated timing is necessary. Moreover, the algorithms are linear and, therefore, not susceptible to misconvergence. The particular OPM implementation presented is based on the generalized sidelobe canceller structure which was originally developed for adaptive cancellation of spatial interference in array signal processing applications. Algorithm performance results are presented in the form of signal to interference ratios and bit error rate curves.

Performance evaluation of a hybrid ARQ protocol implementation for EHF SATCOM on the move systems

This paper characterizes the performance of a hybrid automatic repeat request protocol developed for use in EHF SATCOM on the move systems. The protocol consists of Reed-Solomon coding for random error correction and a selective repeat ARQ scheme for blockage mitigation. The implementation is highly configurable and includes support for features such as variable rate FEC coding, arbitrary packet lengths, framing etc. Performance results, including throughput efficiency and latency, as a function of channel conditions and protocol parameters are given.

Error control for Ka-band land mobile satellite communications systems

Error control for Ka-band land mobile satellite communications systems is examined. The dominant propagation effect at Ka-band is signal shadowing caused by obstructions in the propagation path. Depending on the mobile speed, shadow events may last for many seconds and will typically result in attenuations at the receiver too severe to be addressed by raw link margin. The performance of forward error correction coding, automatic repeat request protocols, and various combinations of these two strategies are investigated. Both analytical and simulation results are presented.

Diversity reception for blockage mitigation in EHF land mobile satellite communications systems

Due to severe signal shadowing caused by objects in the propagation path, EHF land mobile satellite communications systems are characterized by intermittent links. One approach to overcoming this so-called signal blockage problem is to employ diversity reception. Two approaches to diversity reception, one temporal and one spatial, are considered in this work. The performance of the schemes are characterized analytically in terms of outage probability reduction and resource efficiency gains. Moreover, the effects of correlation among the diversity channels are also quantified. Analysis results indicate that only a few uncorrelated diversity channels are required to achieve significant improvements. When the diversity channels are correlated, more channels are necessary to achieve similar gains.

DSP first-a first course in ECE

This paper describes a new course that we have developed for computer engineering students. The course, which precedes a traditional course in circuit analysis and a more traditional signals and systems course, combines a traditional textbook and lectures with computer-based demonstrations and hands-on laboratory experience to show how mathematics and computers can be used to understand and solve problems in signal processing applications. An essential part of the course is a computer-based lab where students listen to sounds and see the results of image processing in order to develop intuition for frequency content and filtering. This intuitive connection is central to our approach; it is our attempt to have students relate the physical attributes of certain signals to the mathematical formulas manipulated in system theory. The course materials, including demos, labs, and homework problems and solutions are packaged in a form that can be accessed from the WWW using standard browsers. The same material is also available on a CD-ROM as an integral part of a new text for the course.

EHF SATCOM on-the-move testbed description

This paper describes a software testbed for the development and evaluation of error control techniques for an EHF SATCOM on-the-move system. The testbed consists of a small number of end-user computers connected to one another via a channel simulator (i.e., workstation computer). An overview of the software development effort, including the implementation of error control strategies, the channel simulator, and a few select user applications is presented.

A probabilistic mispointing analysis for land mobile satellite communications systems with directive antennas

A probabilistic analysis of the antenna mispointing phenomenon observed in many land mobile satellite communications systems is presented. Specifically, the PDF of the total mispointing error is derived under the assumption of Gaussian distributed azimuth and elevation mispointing. Both equal and unequal variances with respect to azimuth and elevation mispointing are considered. Moreover, the effect of mispointing on average bit error rate is also determined analytically. The analysis is applicable to a wide range of pointing systems and antenna types.