Metaheuristic algorithms for frequency assignment problems

Frequency Assignment Problems (FAPs) are among the hardest combinatorial optimization problems of great practical importance in radio communication industries. They arise in practice when an area is to be served by a number of radio transmitters, or a network of radio links is to be established. Each transmitter or link is to be assigned a frequency so that the interference due to unwanted signals from transmitters on receivers has to be acceptable. The frequency assignment is also need to comply with certain regulations and physical characteristics of the transmitters. Moreover the number of frequencies used in the assignment should be minimized. The aim of this paper is to experimentally investigate two rnetaheuristic algorithms namely Simulated Annealing ( SA) and Tabu Search (TS) for solving fixed frequency assignment problems. Here, for the given fixed number of frequencies, we find the assignment to all the transmitters such that the fitness cost function E is minimized. E is formulated so that the number of violated constraints (e(vio)), the sum of the amount by which each constraint is violated (e(sum)), the difference between the largest frequency (f(large)) and the smallest frequency (f(small)) used, the number of distinct frequency used (e(order)) and the largest of the constraint violation, (l(vio)) can be minimized. Both the algorithms are tested on random FAPs with varying number of transmitters and available frequencies. In almost all cases, SA performed better than TS measured in terms of E in getting optimized solutions.