Genetic algorithm for the assignment of cells to switches in personal communication networks

C. Hedible, S. Pierre
2000 Canadian Conference on Electrical and Computer Engineering. Conference Proceedings. Navigating to a New Era (Cat. No.00TH8492)  
Introduction ersonal Communication Network (PCN) is a wireless communication network which integrates various services such as voice, video, electronic mail, accessible from a single mobile terminal. These various services are offered in an area called coverage zone which is divided into cells. In each cell is installed a base station which manages all the communications within the cell. In the cover zone, cells are connected to special units called switches which are located in mobile
more » ... centers (MSC). When a user in communication goes from a cell to another, the base station of the new cell has the responsibility to relay this communication by allotting a new radio channel to the user. Supporting the transfer of the communication from a base station to another is called handoff. This mechanism, which primarily involves the switches, occurs when the level of signal received by the user reaches a certain threshold. We distinguish two types of handoffs. In the case of Figure 1 for example, when a user moves from cell B to cell A, it refers to soft handoff because these two cells are connected to the same switch. The MSC which supervises the two cells remains the same and the induced cost is low. On the other hand, when the user moves from cell B to cell C, there is a complex handoff. The induced cost is high because both switches 1 and 2 remain active during the procedure of handoff and the database containing information on subscribers must be updated. The total operating cost of a cellular network includes two components: the cost of the links between the cells (base station) and the switches to which they are joined, and the cost generated by the handoffs between cells. It appears therefore intuitively more discriminating to join cells B and C to the same switch if the frequency of the handoffs between them is high. The problem of assigning cells to switches essentially consists of finding the configuration that minimizes the total operating cost of the network. The resolution of this problem by an exhaustive search method would entail a combinatorial explosion, and therefore an exponential growth of execution times. This problem belongs to the class of NP-complete problems, well-known especially in operational research. It relates to the problems of warehouse location [1] and graph partitioning [5]. This paper formulates the problem, proposes an algorithm for its solution, then summarizes and analyzes the computational results. Formulation Of The Problem The problem of assigning cells to switches in a cellular mobile network, as described by Merchant and Sengupta [6], can be formulated as follows: Given n cells and m switches, a matrix of the wiring costs between cells and switches, a matrix of handoff costs between cells, minimize the total cost of the network, by choosing the assigning configuration, under constraints of switches' capacity. Locations of cells and switches are known. c ik denotes the cost of wiring cell i to switch k, λ i the call rate generated in cell i, and M k the
doi:10.1109/ccece.2000.849631 fatcat:pyq6apjmnfeotb2oqkcqd2ffym