EXPLICIT DISTRIBUTION OF SELECTED TWO-DIMENSIONAL AND THREE-DIMENSIONAL STATISTICS OF THE (0,1)-SEQUENCE

Abstract

The joint distributions of the given number of 2-chains and the given number of 3-chains of a fixed form of a random bit sequence are considered, which allow performing a statistical analysis of local sections of this sequence. All configurations consisting of two consecutive zeros or ones of a bit sequence of a given length act as 2-chains. In turn, 3-chains are all configurations consisting of three consecutive either ones (provided that the 2-chains are zero) or zeros (provided that the 2-chains are one), as well as 3-chains all configurations are considered that consist either of three consecutive digits: one, zero and one (provided that the 2- chains are zero), or of three consecutive digits: zero, one and zero (provided that the 2- chains are one). The paper establishes explicit expressions for two-dimensional and three-dimensional joint distributions of events, reflecting the number of some combinations of the indicated chains in a finite random bit sequence. One of the basic assumptions is that zeros and ones in a bit sequence are independent, equally distributed random variables. The proofs of the formulas for the distributions of these events are based on counting the number of corresponding favorable events, provided that the bit sequence contains a fixed number of zeros and ones. As examples of using explicit expressions of joint distributions, tables are given in which the values of the probabilities of the events listed above for a random bit sequence of length 40 (tables 1–3) and length 24 (table 4) are given for some fixed values of the number of 2-chains and the number 3-chains under the assumption that zeros and ones appear independently and uniformly. For clarity, tables 1‑3 are illustrated with bubble charts. The established formulas may be of interest for the problems of testing local sections formed at the output of pseudo-random number generators, for some problems of protecting information from unauthorized access, as well as in other areas where it becomes necessary to analyze bit sequences.