Economic Trade-off of Small Cell Networks: Comparison between the Millimetre Wavebands and UHF/SHF bands

This work aims at evaluating the impact of considering Ultra High Frequency (UHF), Super High Frequency (SHF) and millimetre wavebands (mmWaves), in the optimization of economic trade-off of small cell networks, by considering different path loss models. The two slope urban micro Line-of-Sight (UMiLoS) model for UHF/SHF bands (from the ITU-R 2135 Report) is compared with the modified Friis propagation model for frequencies above 24 GHz. The variation of the carrier-to-noise-plus-interference ratio with the coverage distance is assessed, and its influence in the radio and network optimization process is explored by means of the study of the variation of the equivalent supported throughput at the 2.6, 3.5, 28, 38, 60 and 73 GHz frequency bands. The observed higher supported throughput for the longest cell lengths at the UHF/SHF bands (compared to the millimetre wavebands), is mostly due to the reduction caused by the behaviour of their two-slope propagation model. By assuming null fixed costs (license) for the millimetre wavebands and equal values of the fixed cost at 2.6 and 3.5 GHz, we have analysed the economic trade-off of these pico-cellular networks in regular cellular topologies. We have learned that, on the one hand, at 60 GHz, owing to the oxygen absorption excess, there is an optimum of the revenue in percentage terms for values of the cell length, R, equal to 35 m and a decreasing behaviour after this optimum value, while for the 28, 38 and 73 GHz bands the profit starts to decrease after R ≈ 15 m. On the other hand, in the UHF/SHF bands, the profit is very low for the shortest Rs, and starts to increase at a distance equal to the ratio between the break-point distance and the co-channel reuse factor and achieves maxima for values of R equal to circa 200 and 240 m, at 2.6 and 3.5 GHz, respectively.