Small cells in UMTS Radio Access Networks: Implications on coverage and energy efficiency

In the last years, several contributions to the subject of reducing the energy consumption in fixed and mobile networks have been proposed. In mobile networks, a promising approach is to shut down base stations in low traffic hours to save energy. In this work, we examine the implications of such base station shutdowns on the UMTS Radio Access Network (RAN) coverage by the example of a German urban city scenario. We first show that the indoor coverage is seriously affected by a macro base station shutdown. Afterwards, we investigate the option of a small cell overlay to sustain network coverage in case of macro base station shutdowns and derive a strategy to operate a heterogeneous UMTS RAN (consisting of small and macro cells) in an energy efficient way. In our example scenario, the dynamic control of a heterogeneous UMTS RAN can lead to energy savings of up to 7.5% compared to a static macro cell operation.