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In three-dimensional space an embedded network is called gradient-constrained if the absolute gradient of any differentiable point on the edges in the network is no more than a given value m. A gradient-constrained minimum Steiner tree T is a minimum gradient-constrained network interconnecting a given set of points. In this paper we investigate some of the fundamental properties of these minimum networks. We first introduce a new metric, the gradient metric, which incorporates a new definition of distance for edges with gradient greater than m. We then discuss the variational argument in the gradient metric, and use it to prove that the degree of Steiner points in T is either three or four. If the edges in T are labelled to indicate whether the gradients between their endpoints are greater than, less than, or equal to m, then we show that, up to symmetry, there are only five possible labellings for degree 3 Steiner points in T. Moreover, we prove that all four edges incident with a degree 4 Steiner point in T must have gradient m if m is less than 0.38. Finally, we use the variational argument to locate the Steiner points in T in terms of the positions of the neighbouring vertices. [ABSTRACT FROM AUTHOR]

Recently Rubinstein et al. gave a new proof of the NP-completeness of the discretized Steiner problem, that is, the problem of finding a shortest network connecting a given set of points in the plane where all vertices are integer points and a discretized metric is used. Their approach was to consider the complexity of the PALIMEST problem, the Steiner problem for sets of points lying on two parallel lines. In this paper, we give a new proof of this theorem, using simpler, more constructive arguments. We then extend the result to a more general class of networks known as APE-Steiner trees in which certain angles between edges or slopes of edges are specified beforehand. [ABSTRACT FROM AUTHOR]

A full Steiner tree T for a given set of points P is defined to be linear if all Steiner points lie on one path called the trunk of T. A (nonfull) Steiner tree is linear if it is a degeneracy of a full linear Steiner tree. Suppose P is a simple polygonal line. Roughly speaking, T is similar to P if its trunk turns to the left or right when P does. P is a left-turn (or right-turn) polygonal spiral if it always turns to the left (or right) at its vertices. P is an infinite spiral if n tends to infinity. In this paper we first prove some results on nonminimal paths and the decomposition of Steiner minimal trees, and then, based on these results, we study the case in which an infinite spiral P has a Steiner minimal tree that is linear and similar to P itself. [ABSTRACT FROM AUTHOR]

In multistage parallel interference cancellation, the tentative decisions for different users at each stage are mutually correlated, and they are also correlated with Gaussian noise. By taking the correlations into consideration and employing Price's theorem, an analytical model is proposed to refine the variance evaluation of the final decision variable. It is shown that the refined variance is very close to that obtained by simulation and can improve the accuracy in bit error rate evaluation [ABSTRACT FROM PUBLISHER]