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Smart Glasses Not Ready to Wear

Talks give skeptical takes on AR, 5G
1/23/2018 00:01 AM EST
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Biased analysis
IanD   1/23/2018 5:23:43 AM
A perfect example of how to skew numbers to prove an argument -- lets's compare 4G and 5G range/cost by choosing the lowest possible frequency for 4G (700MHz) and the highest possible frequency for 5G (28GHz), so that the cell size for 5G is almost 100x smaller, then conclude that 5G will be more expensive because it needs 100x more basestations. What a surprise...

For the ultra-high-rate ultra-small cells (0.2km2) 5G will use 26GHz and up (40GHz, 70GHz). For high-rate normal-density cells (2km2) it will use 3.4GHz-3.8GHz. For lower-rate low-density cells (20km2) it will use 700MHz. The last two cases are similar to 4G, except more advanced signal processing will be used to give higher data rates and more users per cell. In these cases cost per bit should be lower than 4G, not higher.

The >26GHz bands are targeted at completely different applications than the lower bands, precisely because the data rate is much higher and the cell size is much smaller, so doing a cost ber bit comparison with the lower bands is utterly pointless and misleading -- I doubt that anybody thinks an entire city would have coverage at these frequencies (at least, not for a very long time) because of the huge number of basestations required, but for sure large buildings (offices, shopping malls) will have it.

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Re: Biased analysis
tb100   1/23/2018 12:25:24 PM
5G doesn't necessarily mean mmwave high frequency bands. TMobile says that they are going to implement 5G across the US on their recently purchased 600MHz band. 

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Re: Biased analysis
Bert22306   1/23/2018 4:34:27 PM
Well, unless we are just indulging in mindless hype, the various goals assigned to 5G, to differentiate it from 4G, definitely require higher frequencies than 4G, if just to achieve the cell capacity. That's why you almost always see discussion in the multiple GHz range. I've seen goals stated as 10X and even much more, for a single 5G cell compared with 4G. With 4G, the ideal aggregate cell capacity, assuming everyone is close to the base station, is about 1 Gb/s. To improve significantly over that, you need a combination of wider channels and MIMO. The entire 600 MHz band is not enough for this, and in fact, only 84 MHz from the 600 MHz band are even available.

Plus, users per cell are also supposed to increase, compared to 4G. It seems like every new article one reads raises the bar on these criteria, for 5G. Anyway, if you're going to require channel widths on the order of 100 to 160 to 320 MHz and more, you are pretty much mandating channels up in the multi-GHz range. With the higher frequencies involved, plus what is required to offer at least a 10X increase in link capacity for each user, you will certainly need denser cells than used in 4G, and you will certainly need a much more elaborate backhaul network.

From the start, my thinking has been that claiming the 600 MHz band will be used for "5G" is a now familiar marketing ploy, without a lot of technical foundation. The first applications of 5G appear to be for fixed wireless broadband, "wireless FTTH" deployments. These too will consist of high density cells, high frequencies, short range. The backhaul networks for these, whether from Verizon, AT&T, or Google Fiber 2.0, are going to be the same backhaul networks needed for FTTH. Numbers don't lie. You cannot offer individual homes 100 Mb/s and more, in real neighborhoods, with anything that resembles 4G today. In this new 5G so-called "wireless FTTH" service, one base station would be able to serve maybe 10-12 homes? That's the ballpark. You need a dense mesh of base stations, just for this reason. You also need very high frequency channels.

Sure, you can use the 600 MHz band to offer broadband to a couple of farmhouses out in the boonies. Spectrum reuse is not a factor, and cell capacity can be relatively very small. No need to pretend that's 5G service. There's nothing 5G about that scenario. Just use IEEE 802.22 and you're done.

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