Abstract:This article studies the strictly regular (k,r)-SAT problem by restricting the k-SAT problem instances, where each variables occurs precisely r=2s times and each of the positive and negative literals occurs precisely s times. By constructing a special independent random experiment, the study derives an upper bound on the satisfiability threshold of the strictly regular random (k,r)-SAT problem via the first moment method. Based on the fact that the satisfiability threshold of the strictly regular and the regular random (k,r)-SAT problems are approximately equal, a new upper bound on the threshold of the regular random (k,r)-SAT problem is obtained. This new upper bound is not only below the current best known upper bounds on the satisfiability threshold of the regular random (k,r)-SAT problem, but also below the satisfiability threshold of the uniform random k-SAT problem. Thus, it is theoretically explained that in general the regular random (k,r)-SAT instances are harder to satisfy at their phase transition points than the uniform random k-SAT problem at the corresponding phase transition points with same scales. Finally, numerical results verify the validity of our new upper bound.