1 Performance of Access Selection Strategies in Cooperative Wireless Networks using Genetic Algorithms V. A. de Sousa Jr., R. A. de O. Neto, F. de S. Chaves, L. S. Cardoso, J. F. Pimentel and F. R. P. Cavalcanti GTEL-UFC: Wireless Telecom Research Group, Federal University of Cear´ a, Fortaleza, Brazil Teleinformatics Engineering Department URL:www.gtel.ufc.br {vicente, neto, fabiano, leosam, julio, rodrigo}@gtel.ufc.br Abstract— Next generation wireless networks are expected to be composed of wireless systems based on different Radio Access Networks (RANs). This expectation is supported by the fact that no single RAN has been able to achieved all communication engineering requirements in the wireless domain and that an optimum trade-off among coverage, capacity, QoS and efficiency seems to be achievable only through a combination of different radio technologies. The use of such RANs as subsystems of a larger wireless network, i.e, a multi-access network, claims for efficient management functions able to coordinate the operation of the subsystems so as to meet the optimum combined network performance. This task is the main objective of Common Radio Resource Management (CRRM), which becomes a fundamental part of the upcoming next generation wireless systems. This paper addresses the issue of access selection in the context of multi-access networks. We intend to provide an analytical formulation to the Generalized Access Selection Problem (GASP) and expose the optimization criteria which define our solution. This solution is obtained using a heuristic strategy based on a Genetic Algorithm (GA) to find a user allocation strategy so that a specific objective function is maximized. We also formulate a Strict version of the Access Selection Problem (SASP), where the users arrive one at a time and the solution is the decision for the RAN they will be assigned to. The benefits of the proposed schemes are demonstrated by means of simulations. Index Terms— Commom Radio Resource Management, Multi-Access Networks, Generalized User Assigment, Genetic Algorithm, Beyond 3G Networks. I. I NTRODUCTION The continuing evolution of mobile communication systems is headed towards a crossroads at which multiple radio access technologies will meet. The upcoming fourth generation of cellular systems is not expected to be comprised of a single advanced radio system, but rather represents the combination of multiple technologies, each with its own peculiarities and applicability. Such a heterogeneous network infra-structure imposes several challenges that must be overcome in order to achieved a successful interworking. The employment of This work is supported by a grant from Ericsson of Brazil - Research Branch under ERBB/UFC.10 Technical Cooperation Contract. V. A. de Sousa Jr. and R. A. de O. Neto are scholarships supported by FUNCAP. efficient radio resource management techniques becomes therefore rather essential, especially when it comes to selecting the most adequate radio access network, being seamless connectivity the ultimate goal. In scenarios where different RANs (Radio Access Networks) can co-exist in the same area and mobile terminals can be connected to different RANs, the Always Best Connected (ABC) concept is highlighted [1]. However, the ABC concept is not easily or completely defined, since some questions about the way it must be implemented are dependent on several particularities. For instance, decisions about the meaning of best, the application scenario and the perspective of whom (user or network operator) may result in different approaches to the ABC concept implementation. Independently of these aspects, the implementation of the ABC concept requires a management of the RAN resources, i.e., it requires a Common Radio Resource Management (CRRM). The main task of CRRM, now an entity, is to assign the new and ongoing connections to the most suitable RAN and, more precisely, to the most suitable cell through a Connection Admission Control (CAC) during call setup and through inter-system handover after the call setup. This must be done in order to share the load of the multi-access system, to distribute the interference and to improve the QoS management. This paper presents studies of Common Radio Resource Management strategies in a multi-access wireless network. Several research projects have been developing a similar investigation on the multi-access subject, such as Anwire [2], Everest [3], Monasidre [4], Ambient Networks [5], Mind [6]. This work manly differs from those produced in such projects in that it is essentially more focused on the CRRM aspects rather than on infra-structure and architectural issues. Everest and Anwire are the most closely related ongoing projects, both approaching the interworking between 3G and WLAN systems, with the latter focusing on the ABC concept. Our studies aim to cope with the access selection problem in a multi-access wireless network. This CRRM problem is treated on two fronts. Firstly, we formulate the access selection problem as a