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When the returns from two or more targets interfere (i.e., the signals are not resolved in the frequency or time domains) in a monopulse radar system, the direction-of-arrival (DOA) estimate indicated by the monopulse ratio can wander far beyond the angular separation of the targets. Generalized maximum likelihood (GML) detection of the presence of unresolved Rayleigh targets is developed with probability density functions (pdfs) conditioned on the measured amplitude of the target echoes. The Neyman-Pearson detection algorithm uses both the in-phase and quadrature portions of the monopulse ratio and requires no a priori knowledge of the signal-to-noise ratio (SNR) or DOA of either target. Receiver operating characteristic (ROC) curves are given along with simulation results that illustrate the performance and application of the algorithm.

The conditional probability density function (pdf) is developed for each monopulse measurement of a Rayleigh target by conditioning the pdf of the complex monopulse ratio on the measured amplitude of the sum signal. The conditional pdf is used to develop the conditional Cramer-Rao Lower Bound (CRLB) for any unbiased estimator of the direction-of-arrival (DOA). Conditional maximum likelihood (CML) and conditional method of moments (CMM) estimators of the DOA are developed along with estimates of the variances associated with the monopulse ratio and DOA estimate. Using simulation results, the performances of the CML and CMM estimators of the DOA are compared with the performance of standard monopulse ratio and the performances of the variance estimators are also studied.

This paper provides for new approaches to the processing of unresolved measurements as two direction-of-arrival (DOA) measurements for tracking closely spaced targets rather than the conventional single DOA measurement of the centroid. The measurements of the two-closely spaced targets are merged when the target echoes are not resolved in angle, range, or radial velocity (i.e., Doppler processing). The conditional Cramer Rao lower bound (CRLB) is developed for the DOA estimation of two unresolved Rayleigh targets using a standard monopulse radar. Then the modified CRLB is used to give insight into the boresight pointing for monopulse DOA estimation of two unresolved targets. Monopulse processing is considered for DOA estimation of two unresolved Rayleigh targets with known or estimated relative radar cross section (RCS). The performance of the DOA estimator is studied via Monte Carlo simulations and compared with the modified CRLB.

The use of multiple laser transmitters combined with multiple photodetectors is studies for terrestrial, line-of-sight optical communication. The resulting multiple-input multiple-output channel has the potential for combating fading effects of turbulent optical channels. In this paper, the modulation format is repetition Q-ary pulse-position modulation across lasers, with intensity modulation. Ideal photodetectors are assumed, with and without background radiation. Both Rayleigh and log-normal fading models are treated. The focus is upon both symbol and bit-error probabilities for uncoded transmission, and on constrained channel capacity.