Two-dimensional synchronization patterns for minimum ambiguity

A number of closely related combinatorial problems corresponding to specific assumptions about the type of time-frequency sequence which may be appropriate in a particular application, are formulated in terms of square or rectangular arrays of dots with appropriate constraints on the two-dimensional correlation function. The current state of knowledge concerning each of these problems is summarized. It is hoped that more general constructions may be found, leading to larger families of solutions, as well as better computational algorithms for finding individual solutions which may lie outside of the general families.