On the capacity of picocellular networks

The orders of magnitude increase in projected demand for wireless cellular data require drastic increases in spatial reuse, with picocells with diameters of the order of 100-200 m supplementing existing macrocells whose diameters are of the order of kilometers. In this paper, we observe that the nature of interference changes fundamentally as we shrink cell size, with near line of sight interference from neighboring picocells seeing significantly smaller path loss exponents than interference in macrocellular environments. Using a propagation model proposed by Franceschetti, which compactly models increased interference in small cells, we show that the network capacity does not scale linearly with the reduction in cell size with standard frequency reuse strategies. Rather, more sophisticated resource sharing strategies based on beamforming and base station cooperation are required to realize the potential of small cells in providing high spectral efficiencies and quasi-deterministic guarantees on availability. Numerical results justifying these conclusions include Chernoff bounds on outage probability for random base station deployment (according to a spatial Poisson process), and simulations for deployment in a regular grid.