Showing papers by "Mehdi Bennis published in 2011"

Coalition formation games for femtocell interference management: A recursive core approach

Abstract: Overlaying low-power, low-cost, femtocells, over existing wireless networks has recently emerged as a means to significantly improve the coverage and performance of next-generation wireless networks. While most existing literature focuses on spectrum sharing and interference management among non-cooperative femtocells, in this paper, we propose a novel cooperative model that enables the femtocells to improve their performance by sharing spectral resources, minimizing the number of collisions, and maximizing the spatial reuse. We model the femtocell spectrum sharing problem as a coalitional game in partition form and we propose a distributed algorithm for coalition formation. Using the proposed algorithm, the femtocells can take autonomous decisions to cooperate and self-organize into a network partition composed of disjoint femtocell coalitions and that constitutes a stable partition which lies in the recursive core of the considered game. Whenever a coalition forms, the femtocells inside this coalition can cooperatively pool the occupied spectral resources. Additionally, the members of any given coalition jointly schedule their transmissions in order to avoid collisions, in a distributed way. Simulation results show that the proposed coalition formation algorithm yields a performance advantage, in terms of the average payoff (rate) per femtocell reaching up to 380% relative to the non-cooperative case.

Distributed Learning Strategies for Interference Mitigation in Femtocell Networks

Abstract: In this paper, the \emph{strategic} coexistence between macro and femtocell tiers is studied using tools from evolutionary game theory and reinforcement learning. In the first case, femto base stations (FBSs) exchange information through a central controller, and adapt their strategies based on their instantaneous payoffs and average payoffs of the femtocell population. A fictitious play formulation is also examined where FBSs maximize their payoffs given the empirical frequency of other femtocells' actions. In the second case, when information exchange among femtocells is no longer possible, each femtocell gradually learns by interacting with its local environment through trials-and-errors, and adapt its strategies. Variant of the evolutionary game approach (referred to as replication by imitation) is also investigated where femtocells probabilistically review their strategies and imitate other femtocells in the network. Finally, the overall performance of the network in terms of spectral efficiency and convergence is shown to be adamantly driven by the type of information available at femtocells.

Decentralized Cross-Tier Interference Mitigation in Cognitive Femtocell Networks

Abstract: In this paper, recent results in game theory and stochastic approximation are brought together to mitigate the problem of femto-to-macrocell cross-tier interference. The main result of this paper is an algorithm which reduces the impact of interference of femtocells over the existing macrocells. Such algorithm relies on the observations of the signal to interference plus noise ratio (SINR) of all active communications in both macro and femtocells when they are fed back to the corresponding base stations. Based on such observations, femto base stations learn the probability distributions over the feasible transmit configurations (frequency band and power levels) such that a minimum time-average SINR can be guaranteed in the macrocells, at the equilibrium. In this paper, we introduce the concept of logit equilibrium (LE) and present its interpretation in terms of the trade-off faced by femtocells when experimenting several actions to discover the network, and taking the action to maximize their instantaneous performance. Finally, numerical results are given to validate our theoretical findings.

Cooperative Interference Alignment in Femtocell Networks

Abstract: Underlay femtocells have recently emerged as a key technology that can significantly improve the coverage and performance of next- generation wireless networks. In this paper, we propose a novel approach for interference management that enables a number of femtocells to cooperate and improve their downlink rate, by sharing spectral resources and suppressing intra-tier interference using interference alignment. We formulate a coalitional game in partition form among the femtocells and propose a distributed algorithm for coalition formation. Using our approach, the femtocell access points can make individual decisions on whether to cooperate or not, while maximizing a utility function that captures the cooperative gains and the costs in terms of transmit power for information exchange. We show that, using the proposed coalition formation algorithm, the femtocells can self-organize into a network partition composed of disjoint femtocell coalitions, which constitutes the recursive core of the game. Simulation results show significant gains in terms of average payoff per femtocell, reaching up to 30% relative to the non-cooperative scheme.

Interference management in self-organized femtocell networks: The BeFEMTO approach

Abstract: Recently, femtocell technology has gained significant interest in the wireless communication community, as a potential solution for satisfying the rapid increase in demand for wireless access, improving the poor indoor coverage, and offloading the macrocell network. Operational deployment of uncoordinated femtocells sets out new technological challenges, among which are cross-tier interference between the macro and femtocells, and co-tier interference among femtocells, in the same spectrum band. The Broadband Evolved Femto networks (BeFEMTO) project addresses these technical challenges aiming at developing advanced femtocell technologies based on LTE-A, enabling a cost-efficient provisioning of ubiquitous broadband services. The BeFEMTO project also focuses on novel concepts such as self-organizing femtocell networks, in which the goal is to develop and evaluate solutions to limit the interference impact to end-users'. In this paper, we first give an overview of the BeFEMTO project followed by preliminary results based on recent development of distributed algorithms in context aware learning mechanisms. Next, the performance assessment of self-organizing radio resource management algorithms and interference mitigating techniques for macro-femtocell coexistence is given.

Interference Management in Femtocell Networks Using Distributed Opportunistic Cooperation

Abstract: Femtocells are envisioned to be deployed in indoor environments in order to improve both radio coverage and spectrum efficiency. This paper focuses on the self-organization of indoor femtocells, which includes mechanisms of cooperation. In this context, we propose a solution to automatically form cooperating groups among severely interfered femtocells in order to avoid interference. A hybrid access policy is proposed and compared to the closed and open policies. Results show that, as stated in the Braess Paradox, pervasive cooperation may be detrimental, when available resources are highly contended. Conversely, in particular cases, a marginal selfish behavior of femtocells can be preferable.

Securing the backhaul for mobile and multi-homed femtocells

Abstract: The evolution of femtocells in residential networks expects to accelerate dramatically in next few years. The Femto Access Points (FAPs) connect subscribers to the operator through the residential broadband access or the public Internet. The connectivity between the FAP and the core network has a high risk of being compromised. In this paper, we have discussed, how Host Identity Protocol (HIP) can be adapted in femtocell technology. This research work presents several enhancements to the femtocell technology such as strong authentication, service registration, identity verification and node multi-homing. In addition, Encapsulating Security Payload (ESP) is used to provide confidentiality, data origin authentication, connectionless integrity, anti-replay service and limited traffic flow confidentiality. Moreover, enhanced mobility support by means of locator/identity separation and node multi-homing is discussed in the scope of 3GPP femtocells.

Coordination Mechanisms for Stand-Alone Femtocells in Self-Organizing Deployments

Abstract: We investigate coordination mechanisms for controlling the co-channel interference generated by stand-alone femtocells in two-tier coexistence scenarios. Stochastic geometry is used to model network deployment scenarios, while the cumulants concept is utilized to characterize the probability distribution of the aggregate interference at a tagged user. The rationale for using coordination mechanisms is to opportunistically reuse resources without compromising ongoing transmissions on overlay macrocells, while still guaranteeing Quality of Service in both tiers. Results have shown that the analytical framework matches fairly well with numerical results obtained with Monte Carlo simulations. Yet coordination mechanisms improve performance of overlay macrocell network by substantially diminishing co-channel interference.

Spectrum Leasing as an Incentive towards Uplink Macrocell and Femtocell Cooperation

Abstract: The concept of femtocell access points underlaying existing communication infrastructure has recently emerged as a key technology that can significantly improve the coverage and performance of next-generation wireless networks. In this paper, we propose a framework for macrocell-femtocell cooperation under a closed access policy, in which a femtocell user may act as a relay for macrocell users. In return, each cooperative macrocell user grants the femtocell user a fraction of its superframe. We formulate a coalitional game with macrocell and femtocell users being the players, which can take individual and distributed decisions on whether to cooperate or not, while maximizing a utility function that captures the cooperative gains, in terms of throughput and delay.We show that the network can selforganize into a partition composed of disjoint coalitions which constitutes the recursive core of the game representing a key solution concept for coalition formation games in partition form. Simulation results show that the proposed coalition formation algorithm yields significant gains in terms of average rate per macrocell user, reaching up to 239%, relative to the non-cooperative case. Moreover, the proposed approach shows an improvement in terms of femtocell users' rate of up to 21% when compared to the traditional closed access policy.