Energy-efficient design of two-tier femtocell networks

With the exponential increase in mobile internet traffic, future cellular networks face great challenges to satisfy the demand of network capacity. At the same time, high data rate transmission and rapid increasing number of users also seriously burden the power consumption and the cost of cellular networks. Base station (BS) is the main part of power consumption, so reducing energy consumption of the BS can obviously reduce the total energy consumption. This paper investigates the effect on energy efficiency by adopting activity-aware sleeping strategies both in macrocell base station (MBS) and femtocell access point (FAP) in a two-tier femtocell network. By using stochastic geometry, we develop a trade-off between energy saving and coverage extension, regarded as the FAP additional connections by neighboring femtocell user equipment (FUE) or macrocell user equipment (MUE). Specifically, we derive users' coverage probabilities, which is defined as the probability of user connecting to BS, in closed forms with different sleeping strategies and access policies. Moreover, we formulate power consumption minimization and energy efficiency problem and determine the optimal joint MBS-FAP operating regimes. Numerical results show that sleeping scheme and femtocell access mode both have effects on coverage probability and energy efficiency, and the effect of femtocell access mode on coverage probability is greater than sleeping scheme.