Orthogonal Frequency Division Multiplexing (OFDM), a group of sub-tones mostly interferes with the same group of sub-tones in a neighbor cell even if the systems are not time-synchronized. Thus in OFDM or Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, interference can now be predicted and avoided with fine granularity on the basis of frequency [1]. In contrast to a reuse 1 system in which all cells use all frequency resources without any restrictions, inter-cell interference coordination (ICIC) makes use of the frequency dimension.

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Overlapping coverage of multiple radio access technologies provides new multiple degrees of freedom for tuning the fairnessthroughput tradeoff in heterogeneous communication systems through proper resource allocation. This paper treats the problem of resource allocation in terms of optimum air interface and cell selection in cellular multi-air interface scenarios. We find a close to optimum allocation for a given set of voice users with minimum QoS requirements and a set of best-effort users which guarantees service for the voice users and maximizes the sum utility of the best-effort users. Our model applies to arbitrary heterogeneous scenarios where the air interfaces belong to the class of interference limited systems like UMTS or to a class with orthogonal resource assignment such as TDMA-based GSM or WLAN. We present a convex formulation of the problem and by using structural properties thereof deduce two algorithms for static and dynamic scenarios, respectively. Both procedures rely on simple information exchange protocols and can be operated in a completely decentralized way. The performance of the dynamic algorithm is then evaluated for a heterogeneous UMTS/GSM scenario showing high-performance gains in comparison to standard load-balancing solutions.

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In this paper we cover the problem of resource allocation in terms of optimum air-interface and cell selection in cellular, heterogeneous multi-air-interface scenarios. For a given set of voice users with minimum quality of service requirements and a set of best effort users we find the optimum allocation that guarantees service for the voice users and maximizes the sum utility of the best effort users. Our model applies for arbitrary heterogeneous scenarios where the air-interfaces belong to the class of interference limited systems like UMTS or to a class with orthogonal resource assignment such as TDMA based GSM or WLAN. We achieve convexity of the problem by a transformation into the domain of mean square errors. Using a dual problem formulation we derive straight forward assignment rules and develop a decentralized algorithm, which solves the optimization problem. Simulation results for a heterogeneous UMTS/GSM scenario show high performance gains of the proposed a lgorithm compared to a Load Balancing strategy