Game Theory and Femtocell Communications: Making Network Deployment Feasible

Femtocell base stations (FBSs), also known as Home eNodeBs (HeNBs), are short-range low-power and low-cost base stations with third party backhaul (e.g., DSL or cable mo-dem). They are usually deployed and controlled by end-users who desire better indoor signal transmission and reception. With the help of such FBSs, the network operator is able to extend the high quality coverage inside peoples' homes without the need of additional expensive cellular towers. At the same time, FBSs offload traffic from the overlay macrocell network and subsequently improve the overall network capacity. Nevertheless, despite FBSs promise, many concerns still remain, especially cross-tier interference. Two particular aspects of FBSs give rise to serious interference issues: (a) the co-channel spectrum sharing between femtocells and macrocells as well as among femtocells, (b) the " random " location of user-installed FBSs (they can be deployed anywhere inside the macrocell area with no-prior warning). First, unlike Wi-Fi access points, FBSs serve users in licensed spectrum, to guarantee Quality-of-Service (QoS). Moreover, instead of allocating dedicated licensed channels to FBSs, sharing the spectrum is preferable from an operator's perspective (higher spectral efficiency). Secondly, FBSs are installed by end-users in a " plug-and-play " manner, which translates into " randomness " in their locations. For these two reasons, interference in two-tier networks is quite different than in conventional cellular networks, which endangers their successful coexistence. A typical scenario is the " Dead Zone " or " Loud Neighbor " problem, where mobile users transmit and receive signals at positions near FBSs but far from the macrocell BSs, causing significant macro-to-femto interference in the uplink. In the downlink, these users likewise suffer from low signal to interference ratios (SIRs) because of the strong interference from the FBSs. These affects are akin to the well known near-far problem, but exacerbated by the decentralization and lack of coordinated power control inherent in two-tier networks. In addition, because of the non-existent coordination between FBSs and macrocell BSs, centralized cooperation to mitigate cross-tier interference is deemed infeasible, hence two-tier networks need to adopt decentralized strategies for interference management. Game Theory (GT) is a mathematical tool that analyzes interactions among decision 1.1. INTRODUCTION 3 makers. GT is seen as a natural paradigm to study and analyze wireless networks where players compete for the same resources. The importance of studying the coexistence between macro-and femtocells from a game theoretical perspective is multi-fold: First, by model-ing the dynamic spectrum …