A Survey on Cell Selection Schemes for Femtocell Networks

Abstract

With ever increasing number of mobile devices, operators have to search for new alternative to handle user demands. Deployment of additional base stations is always an option to improve coverage of capacity. However, it comes with the cost of incresed operational and capital expenditure. Interestingly, it has been seen that nearly 80% of mobile data demands are originating from indoor home and office users. To handle these indoor demands, deployment of small, low power femtocell access points have been suggested. However, in current deployment scenario, most femtocell are underutilised. To improve user association and resource utilization in femtocell, various cell selection schemes have been suggested. In this paper, we analyse various cell selction schemes available in the literature. Additionally, we look at energy efficiency aspect of these cell selection schemes. Keywords—Femtocell, cell selection schemes, energy efficiency, performance evaluation I. Introduct ion With availability of smart phones and tablets, users now expect 24X7 connectivity to the Internet. As these Internet devices are getting cheaper and cheaper, the demands for wireless data is increasing. Study shows that cellular data demands are expected to increase 18 fold by the end of year 2020 [1]. To handle these demands, cellular operators are deploying additional base stations, using better modulation and coding techniques. However, they are still unable to satisfy this increasing data demands. Interestingly, nearly 80% of mobile data demands are originating from indoors [2]. Also, these indoor users experience the worst signal quality due to high wall penetration loss. To overcome this indoor data demand problem, cellular operators are deploying small, low cost, low power femtocell base stations. Femtocell are miniature cellular base stations deployed inside users homes and offices to provide improved coverage and bitrate.Femtocell have proved to improve network capacity and coverage by eliminating wall loss and spatial reuse of available spectrum [3]. Inherent low transmission capabilities of femtocell when combined with high path loss limit the users association in femtocell. To reap the gains of femtocell deployment, more users should be offloaded to femtocells. Regarding this, various cell selection schemes have been suggested in the literature. Most basic techniques based on Reference Signal Received Power (RSRP) based association where users get associated with base stationshaving highest received signal power [4]. However, such techniques may not be optimal in terms of users' Quality of Service (QoS). Considering users' perspective, expected bitrate based association is suggested in [5][6]. These techniques try to associated users to base stations based on the expected bitrate they might receive. Expected bitrate based association performs better then RSRP based techniques because it incorporates schedulingopportunities at base stations. To best of our knowledge, a comprehensive analysis of energy efficiency aspect of cell selection schemes is not done in the literature. In this paper, we analyse various cell selection techniques available for femtocell networks. We explain each of them in details with corresponding advantage and limitations. Additionally, we also look at energy efficiency aspect of these cell selection techniques which was ignored in all previous works. Rest of the papers is organises as follows. In section II, we get an overview of femtocell architecture. Section III discusses various cell selection schemes for femtocell based cellular network, along with their advantages and limitations. Section IV discusses performance of various cell selection schemes in terms of network capacity and energy efficiency. Finally, we conclude our work in section V with direction for future research. I