Capacity Growth of Heterogeneous Cellular Networks

Heterogeneous cellular networks are composed of a mixture of macro and small (pico) cells embedded in the macro network. We assume uniform traffic for simplicity, and study the scaling of area spectral efficiencies (ASE) as pico densities are increased. It is found that median ASE grows linearly with the number of picos, with a slope as low as one, i.e. only one pico cell per macro sector is necessary to double median ASE. The pico must be placed intelligently rather than randomly, and need only transmit at -20dB power EIRP relative to the macro. The effectiveness of the pico at such low power is due in part to the improvement in area coverage of an omni vs. a 3 sectored antenna. As pico density increases 5-percentile SINR decreases, causing poor scaling of edge rates. However, cell association bias was found to be an effective means of restoring the otherwise poor scaling of 5th-percentile rates.