To increase wireless system capacity using co-channel signals and multiple receiver antennas, we develop the partitioned Viterbi algorithm (PVA). The PVA estimation complexity increases linearly with each additional co-channel signal rather than exponentially as it does with joint maximum-likelihood sequence estimation (MLSE). The estimation problem involves multiple signals simultaneously transmitted and observed through slow-fading, frequency-selective channels. Although transmission is assumed to be in bursts according to a time-division multiple-access scheme, more than one signal can occupy the same time and frequency slot (these signals are referred to as "co-channel" signals). Separation and estimation of the symbol bursts is accomplished by exploiting channel differences, PVA estimation consists of a set of Viterbi detectors, one per signal, that operate in parallel with cross-coupling to allow approximate interference cancellation by means of tentative decisions. The forward filter of a decision feedback equalizer (DFE) is used to "prefilter" received signals prior to PVA estimation. Prefiltering delays the energy of interfering signals so that tentative decisions become reliable enough to use. Simulation results show PVA performance remains near-optimal with respect to the performance of joint MLSE.

We analyze the performance of coherent optical communication systems which employ polarization shift keying (PolSK) modulation, introducing for the first time the requirements for multilevel, differential PolSK. For M-ary signal constellations with M>2, the three-dimensional (3-D) nature of the signal constellations within Stokes space requires the use of double-differential modulation and detection (M-DDPolSK). Coding constraints on the signals place an additional restriction on such systems. We present detailed analysis and simulations for a 6-DDPolSK modulation scheme in which the signal points are located at the vertices of an octahedron in Stokes space.

A unified approach to interferometry, holography, and the seeing problem is presented. Known interferometric techniques are arranged hierarchically and the concept of the "order" of an interferometer is introduced. When an interferometer is viewing a spatially incoherent object through a randomly fluctuating medium, it is argued that the field of view over which the observed data are isoplanatic depends upon the way in which the data are processed, and the processing methods depend upon the order of the interferometer. By appealing to the principles of Michelson interferometry, intensity interferometry, compound intensity interferometry, off-set holography, and the decomposition of observed radiation into its spatial frequency spectrum, it is found that a convenient characterization can be made of the conditions whereby objects can either be resolved (i.e., the sizes of the objects can be determined) or be imaged faithfully.