What would be the coverage of 5G Small Cells? I understand that this would highly depend upon terrain and the vendor material, however, I am looking for a thumb rule guideline to used at the master planning level to establish how many small cell antennas shall be allocated along a proposed road (flat terrain). I am planning to allocate them in street lighting poles (at around 8-10m height)
Which 5G band are you expecting to use ? - the local choice of frequency is key. Also the data rate. If you only want narrow band data transmission you can allow it to fall back onto the more strongly coded modes, and this will give you a higher range. The mm-wave spectrum offers super wide bandwidths, (30 GHz and upto 50GHz are mooted) but will be more useful for a network on the user, a range of a few metres, and can probably be ignored for a road.
In the UK for example, the frequencies for the first 5G roll-outs will be 3.5GHz or so, which is inherantly a much shorter range than the original mobile networks on 900MHz and 1800MHz, so you may expect the cells to be half the radius of the existing ones, however to a degree this can be recovered by cunning use of lower data rates at longer ranges.
Even so most conops I have seen assume that the existing 2g,3g and 4g networks will provide the wide area coverage (4g on 800MHz is very promising as a solution to more rural coverage), and 5g is more of a fill-in service. Use of MIMO and beam formed antennas may help in your case of a road if it is straight and reasonably flat. Would you only have 5g? That would be something of a limitation.
You may find it useful to read the COST231 reports on propagation, here as a quite technical, (but still overly-simple) introduction to the issue of modelling radio propagation and netwoerk planning for cellular phones. Especially chapter 4 (about 100 pages) considers the types of approach to modelling in terms of cell size. I appreciate that the mathematics 'fit' to reality has only been verified for the original bands, less than 2GHz , but I am not aware of anything that comprehensive of an introduction that is newer.
