Abstract. This paper describes a system, FASoft, for discrete channel frequency assignment. In practice, the assignment of frequencies in a network of compatible equipment is often done manually or by the use of a single computational technique. FASoft incorporates state-of-the-art heuristics, sequential assignment algorithms, and a maximal clique algorithm to aid in the assignment process. Lower bounding procedures are included into the system to assess the performance of the assignment techniques and to provide an assessment of how close a particular assignment is to the optimal. The results show that FASoft produces optimal solutions to several practical examples. IntroductionThe radio spectrum is an important natural resource. Many services, both civil and military, require access to the spectrum in order to function, and the demand for frequencies is increasing year by year. Consequently, efficient management of the spectrum requires that frequencies be assigned, for a particular service, in an optimum or near-optimum manner. In practice, this assignment of frequencies is often done using greedy heuristics, which mimic the way the process may be done manually. These methods produce assignments quickly (even for large problems) but inevitably use more spectrum than is necessary. Exact methods based on graph theory give the optimum solution but are computationally unrealistic for problems involving •>50 transmitters. The purpose of this paper is to show how the so-called metaheuristic techniques (simulated annealing, genetic algorithms, and tabu search) can be used to produce optimum solutions to frequency assignment problems. This paper is concerned with the assignment of discrete channels to the transmitters of a system of compatible equipment. In some applications, such as cellular radio networks, the coverage area is divided into a number of cells, typically hexagonal, with each cell assigned a set of frequencies. We refer to such A software system FASoft will be described which produces a frequency assignment for any problem described by a constraint matrix, not necessarily a cellular system. FASoft can handle constraints with transmitters external to the system under consideration. However, it does not handle issues such as intermodulation products or required bandwidth for different modulation schemes such as digital code division multiple access (CDMA), nor does it address problems such as spread spectrum systems and discrete narrowband systems operating in the same 1921

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Low-lying states in the isotope 130 Xe were populated in a Coulomb-excitation experiment performed at CERN's HIE-ISOLDE facility. The magnitudes and relative signs of seven E 2 matrix elements and one M1 matrix element coupling five low-lying states in 130 Xe were determined using the semiclassical coupled-channel Coulomb-excitation least-squares search code GOSIA. The diagonal E 2 matrix elements of both the 2 + 1 and 4 + 1 states were extracted for the first time. The reduced transition strengths are in line with those obtained from previous measurements. Experimental results were compared with the general Bohr Hamiltonian with the microscopic input from mean-field theory utilizing universal nuclear energy density functional (UNEDF0), shell-model calculations using the GCN50:82 and SN100PN interactions, and simple phenomenological models (Davydov-Filippov and γ-soft). The extracted shape parameters indicate triaxial-prolate deformation in the ground-state band. In general, good agreement between theoretical predictions and experimental values was found, while neither phenomenological model was found to provide an adequate description of 130 Xe.

The frequency assignment problem, known to be NPcomplete, is to find an assignment of radio frequencies to a set of transmitters in a region. The interference level between the frequencies assigned to different communication links has to be acceptable, since otherwise communication will be distorted. Consequently, constraints are defined on pairs of links that limit the choice of frequencies for these pairs. Usually, a fixed number of frequency channels are available with which to make an assignment. The aim is to produce an assignment which minimizes the number of constraint violations. This paper compares the results obtained from using simulated annealing, genetic algorithms and tabu search for determining such an assignment. We report on our computational experiments in terms of the quality of the solutions obtained for realistic, computer-generated problem instances.