# Lattice structure of pseudorandom sequences from shift-register generators

## Abstract

The author develops a theory of the lattice structure of pseudorandom sequences from shift register generators, i.e., Tausworthe sequences and GFSR (generalized feedback shift register) sequences. The author defines an analog of linear congruential sequences in GF{2,x}, the field of all Laurent series over the Galois field of two elements GF(2), and shows that this class of sequences contains as a subclass the Tausworthe sequence. He derives a theorem that links the k-distribution of such sequences and the successive minima of the k-dimensional lattice over GF{2,x} associated with the sequences, thereby leading to the geometric interpretation of the lattice structure in the k-dimensional unit space of these sequences. This result is generalized to define the successive minima for the point set of k-dimensional vectors each consisting of k consecutive terms of GFSR sequences, and it is shown that GFSR sequences have a similar structure to that of Tausworthe sequences. A simulation problem in which shift-register-type pseudorandom sequences yield useless results due to such lattice structures is discussed.