Everyone seems to agree that mobile 5G networks using millimeter wave spectrum will require denser backhaul networks, as the millimeter waves will not reach as far as lower-frequency spectrum.
How much new fiber will be required depends on how much smaller the cell sites are, existing assets to be leveraged and what has to be done to deploy smaller 4G cells, as 4G will continue to be the fallback for 5G users for some years, outside of the urban cores where 5G using millimeter wave will be deployed earliest.
At least in urban areas, Verizon expects its millimeter-wave mobile 5G network will need to support small cells spaced every 1.000 feet or so, though in less-dense areas 2,000-foot spacing might work.
So fiber to every other light pole is one way to think about small cell placements using millimeter wave frequencies in urban areas.
Earlier thinking had been that millimeter wave small cells would have a transmission radius of about 50 meters (165 feet) to 200 meters (656 feet, a tenth of a mile). That works out to a small cell diameter of about 1300 feet, or about a quarter of a mile).
That is why Verizon executives now talk about small cell radios for 5G in urban areas spaced 1,000 feet apart. So backhaul would be to radios located about a quarter mile apart.
Keep in mind that street lights are spaced at distances from 100 feet (30.5 meters) to 400 feet (122 meters) on local roads. So small cells might be located on every other light pole in some cases, or perhaps only on every 10th pole in other cases. It just depends on pole spacing.
The other important issue is that 4G will be upgraded with small cell coverage as well, to increase 4G capacity, even as new radios are introduced. From a mobile phone user perspective, experience might not be noticeable if 5G rolls over to 4G, so long as the 4G network itself continues to be upgraded.
That is why we so often talk about 5G being built upon 4G. From a user experience perspective, advanced 4G and early 5G might provide such similar experience that the actual network does not matter very much, if at all.
Also, it remains to be seen how new 3.5-GHz and C-band assets might be deployed. Some argue that the same infrastructure used for 4G small cells also works for 5G using 3.5-GHz spectrum.