International Journal of Applied Information Systems (IJAIS) – ISSN : 2249-0868 Foundation of Computer Science FCS, New York, USA Volume 2– No.2, May 2012 – www.ijais.org 40 Cognitive Interference Management for Autonomic Femtocell Networks KaoutharSethom, InnoV’Com Lab SUPCOM, Tunisia Fadoua Mhiri InnoV’Com Lab Time Université, Tunisia RidhaBouallegue InnoV’ComLab SUPCOM,University of Carthage, Tunisia Guy Pujolle PHARE/LIP6, University of Paris France ABSTRACT The femtocell concept is an emerging technology for deploying the next generation of the wireless networks, aiming at indoor coverage enhancement, increasing capacity, and offloading the overlay macrocell traffic. Nevertheless, one of the most critical issues in femtocells deployment is the potential interference, thus mitigating the overall system capacity. Inspired by the cognitive radio technology which enables a station to cognize and adapt to the communication environment to reach the optimum network performance, this paper presents a joint power control and scheduling algorithm for interference management in femtocell networks. Simulations were conducted under Matlab. Theyshow the efficiency of our proposal and its ability to improve the overall throughputas well asreducing the energy consumption. General Terms Wireless Networks Keywords Femtocells, Interference, Cognitive approach, Energy efficiency, QoS. 1. INTRODUCTION Femtocells are single mode, power efficient, backward compatible, low cost and easy to install devices. They can increase the capacity of macrocell as they use the same spectrum as that of macrocell [1][2]. As the radius of Femtocell is much smaller as compared to that of macrocell, that is why it can provide high data rates in any environment such as home or office. Moreover, femtocells can also be a cost effective solution for enterprises because of their self-organizing networks characteristics. Nevertheless, installing femtocells inside enterprise environments, where more than one femtocell may be necessary, and where many guest users may enter the femtocell coverage, leads to major technical challenges.One of the most critical issues in femtocellsdeployment is the potential interference between nearby femtocells. The available gains from intercell interference awareness in cellular networks have been identified in several papers, see for example, [3-5] and the references therein. To alleviate interference, one typical solution is to divide the entire available spectrum into several frequency bands. Thus, each femtocell uses different frequency band. This deployment is referred to the “dedicated channel” deployment. However, the performance of this solution is limited by the assigned bandwidth, which makes it infeasible to be applied to the dense femto-networks deployment where each femtocell can only utilize a very limited bandwidth. As a result, a practical solution turns to be the co-channel deployment where femtocells share all available spectrum of the network. To mitigate interference in the co-channel deployment, dynamically power adapting schemes in femto-networks had been considered effective to alleviate interference when the system adapt wideband code division multiple access (WCDMA) [6]–[7]. However, considering that orthogonal frequency division multiple access (OFDMA) had been endorsed by 3GPP LTE-A and WiMAX, new interference mitigation manners are needed. Considering that the major cause of interference in OFDMA is that femtocells installed in an ad-hoc manner for large deployment occupy the same radio resources (subcarriers and OFDM symbols), a centralized radio resources allocation scheme had been proposed in [8] to prevent the femto-network from the co-use of radio resources. However, since an enormous number of femto-networks can be expected to overlay a large network, the computational complexity and large among of scheduling related information exchanges are challenges. As a result, a radio resource management scheme for each femtocell shall be able to “autonomously” utilize the radio resources not occupied by others so as to mitigate interference while providing QoS guarantees. Inspired by the cognitive radio technology which enables a station to cognize and adapt to the communication environment to reach the optimum network performance [9]–[10], this paper presents a joint power control and scheduling algorithm. We propose „TRIPLET Algorithm‟ to surmount 3 concepts in a distributed architecture: „interference mitigation‟, „energy efficiency‟ and „user‟s QoS‟. Thus, we formulate a multi- objective optimization problem with mixed integer variables for the joint power control, base station assignment, and channel assignment scheme. 2. SYSTEM MODEL 2.1 Network Model The aim of coverage optimization in residential femtocell deployments is to ensure that leakage of coverage by a single femtocell into public spaces will be minimized while at the same time maximizing indoor coverage [6]. For femtocell deployments in enterprise environments however, a group of femtocells are deployed to work together to jointly provide continuous coverage in a large building or campus to satisfy the QoS requirements, which also increases the technical challenges of interference management, power efficiency and overall system capacity. The requirements for efficient resource partitioning scheme in this case differ significantly from residential femtocell deployments. The power and resource allocation management in femtocell environment is complex and surcharge the network with