Energy efficiency gains in interference-limited heterogeneous cellular mobile radio networks with random micro site deployment

Energy efficiency considerations recently gained attention due to ecological aspects, that is to say lowering CO2 emissions and reducing energy consumption. Furthermore, it is important to assess energy efficiency improvements from an operator's point of view, since energy costs are increasing and providing ubiquitous high speed mobile access may scale up the operators' operational expenditure. One of two promising approaches to enhance a network's operation regarding energy efficiency is to utilize smaller micro cells within one large macro cell. Another approach is to regard macro base stations as coverage providers for areas in between micro cells, while reducing their maximum transmit powers to a minimum. In this paper we investigate on the energy efficiency of a heterogeneous OFDM-based mobile network in the downlink taking into account the co-channel interference based on varying traffic demand per area. Furthermore, we carry out an assessment of potential energy savings of the two approaches mentioned above. For a sufficiently large traffic demand, increasing deployment densitiy through additional micro sites may maximize a network's energy efficiency. In that case the network operates at a load of less than 50 %. Moreover, a further gain of energy efficiency of about 20 % can be achieved due to macro site transmit power reduction while still providing coverage.