Aalborg Universitet Effect of LOS / NLOS Propagation on 5 G Ultra-Dense Networks

The combined presence of Line-of-Sight (LOS) and Non-Lineof-Sight (NLOS) components in the radio propagation environment can severely degrade the Ult ra-Dense Networks (UDNs) performance. Backed by a stochastic geometry model, we show that when the L OS/NLOS propagation components are taken into account, and as the cell density increases, UD Ns suffer from low coverage and the Area Spectral Efficiency (ASE) grows sub-linearly. However , we show that this performance drop can be compensated by increasing the frequency reuse factor or b y steering the network into the partial load regime, which occurs when the base stations outnumber t he users. In the former, it emerges that frequency reuse improves the ASE vs coverage trade-off of ce ll densification with respect to a traditional full frequency reuse, provided there is a degree of freedom o n the density of cells; in addition, this trade-off improves with the frequency reuse factor N . Finally, we investigate the energy efficiency of UDNs for which we show that, as a combined result of LOS/NLOS p ropagation and partial load regime, up to two optimal base station densities exist. As a whole, ou r work provides novel insights on how to overcome the limitations and to take advantage of extreme cell densification in the upcoming 5G wireless networks.