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.

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.

An R/sub 0/ analysis for a noncoherent DPSK channel that includes a 1-bit A/D converter in the receiver front-end is presented. The analysis results are used to obtain probability of error bounds that characterize the channel when a rate R=1/2, constraint length L=7 convolutional code is used. The advantage of the R/sub 0/ approach is that quantization thresholds for the soft-decision decoder can be optimized analytically, without relying on lengthy simulations. However, once the thresholds are optimally chosen, simulations are used to verify the validity of the bounds.

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.

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 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 user's 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 user's 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.

An adaptive space-time processing system for dynamic spatial channels in a CDMA mobile communications network is presented. The proposed system consists of an adaptive sensor array that estimates the desired directions and waveforms, followed by adaptive linear equalizers that refine the waveform estimates by compensating for the mobile radio uplink channel. Capacity gains are achieved through code reuse, which is made possible by performing the spatial processing after the codes have been decorrelated with one another. Simulation results for a two sensor array in a variety of interference scenarios are presented in the form of bit error rate curves.