Abstract: A method is disclosed for determining with only sixty-four distance comparisions the distances between a received eight-dimensional vector comprised of four two-dimensional coordinates and each of sixteen non-overlapping subconstellations. In order to limit the comparisons, each subconstellation is represented by a collection of sixteen representational four-coordinate vectors, with each collection having four groups of vectors of the form______________________________________ (a, b, c, d) (a + 2, b + 2, c, d) (a, b, c + 2, d + 2) (a + 2, b + 2, c + 2, d + 2) ______________________________________where each letter represents in a different plane one of a set of points T(0) and its ninety, one hundred and eighty, and two hundred and seventy degree rotations, and +2 represents a one hundred and eighty degree rotation.