This paper presents an enhanced version of a novel radio interferometric positioning technique for node localization in wireless sensor networks that provides both high accuracy and long range simultaneously. The ranging method utilizes two transmitters emitting radio signals at almost the same frequencies. The relative location is estimated by measuring the relative phase offset of the generated interference signal at two receivers. Here, we analyze how the selection of carrier frequencies affects the precision and maximum range. Furthermore, we describe how the interplay of RF multipath and ground reflections degrades the ranging accuracy. To address these problems, we introduce a technique that continuously refines the range estimates as it converges to the localization solution. Finally, we present the results of a field experiment where our prototype achieved 4~cm average localization accuracy for a quasi-random deployment of 16 COTS motes covering the area of two football fields. The maximum range measured was 170~m, four times the observed communication range. Consequently, node deployment density is no longer constrained by the localization technique, but rather by the communication range.

The Sieve of Eratosthenes is an efficient algorithm for computing the successive primes. Rendered informally, it is as follows: 1. Write down the successive “plurals”: 2, 3, 4, … 2. Repeat: (a) Take the first number that is not circled or crossed out. (b) Circle it. (c) Cross out its proper multiples. 3. What is left (i.e. the circled numbers) are the successive prime numbers.

Abstract “Catamorphisms” are functions on an initial data type (an inductively defined domain) whose inductive definitional pattern mimics that of the type. These functions have powerful calculation properties by which inductive reasoning can be replaced by equational reasoning. This paper introduces a generalisation of catamorphisms, dubbed “paramorphisms”. Paramorphisms correspond to a larger class of inductive definition patterns; in fact, we show that any function defined on an initial type can be expressed as a paramorphism. In spite of this generality, it turns out that paramorphisms have calculation properties very similar to those of catamorphisms. In particular, we prove a Unique Extension Property and a Promotion Theorem for paramorphisms.

The programming language B has been designed for personal computing. In B, variables need not be declared, nor formal parameters specified. Nevertheless, B is strongly typed. All type requirements can be checked statically. To signal type violations on the spot during editing, the computations can be organized so that local the source text require a modest amount of recomputation.

It is proved that in the general case of arbitrary context-free schemes a program is (partially) correct with respect to given initial and final assertions if and only if a suitable finite system of intermediate assertions can be found. Assertions are allowed from the extended state space $\mathcal {V} \times \mathcal {V}$. This result contrasts with the results of [2], where it is proved that if assertions are taken from the original state space $\mathcal {V}$, then in the general case an infinite system of intermediate assertions is needed. The extension of the state space allows a unification in the relational framework of [2], of the (essence of the) results of [2], and of [4], [5] and [6], and provides a semantic counterpart of the use of auxiliary variables.