Traditional block transform image coding systems generate artifacts near block boundaries which degrade low bit rate coded images. To reduce these artifacts, a class of unitary transformations, called lapped orthogonal transforms (LOT), is investigated. The basis function on which the signal is projected are overlapped for adjacent blocks. An example of an LOT optimized in terms of energy compaction is numerically derived, using an augmented Lagrangian optimization algorithm. Using this LOT, intraframe coding experiments for 256*240 pixel images were performed at bit rates between 0.1 and 0.35 bits/pixel. The LOT improved the coded image subjective quality over other transforms. The LOT was also used in interframe full-motion video coding experiments for head and shoulder sequences at 28 and 56 kb/s. Significant improvement resulted at low data rates and if no motion compensation were used. However, the improvement was no longer significant at 56 kb/s with full motion compensation.>

A sonar imaging technique which uses specially coded waveforms to project different sound signals in different directions was previously proposed. In this context, the problem of creating a set of frequency-hopped code words that have mutually small correlation properties has arisen. The authors report on their progress in designing these frequency-hopped signals for multibeam sonar imaging. The special case is considered in which medium spreading effects destroy the phase coherence of the imaging system. A design strategy is discussed which has allowed the design of a set of frequency-hopped code words that exhibit good performance bounds with respect to incoherent processing. The design strategy is a systematic constructions technique which can be used with any size Galois field GF(p) to generate p-1 codes of length p. Various theorems are presented and examples of the performance of the technique are illustrated for time-bandwidth products of interest in terms of sonar.>

This paper describes the design of frequency-hopped signals for a multi-beam imaging system. A frequency hopping pattern is a frequency-coded uniform pulse train. The signal is divided into M time intervals, with each interval assigned a different frequency chosen from a set of N frequencies. A set of N patterns composed of N-1 frequencies can be generated using first-order Reed-Solomon codewords. These patterns exhibit very good correlation properties. In a frequency-hopped multi-beam imaging system, each beam is associated with a pattern and transmits a coded waveform. All N beams can be transmitted simultaneously resulting in a high scan-rate, high resolution imaging device. Furthermore, in the presence of noise and medium spreading effects, a frequency-hopped imaging device performs better than conventional systems by showing better noise rejection and less sensitivity to spreading effects.