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Comment by PaulHoule | Hacker News Reader

3G and prior "cellular" systems were inefficient because they can't reuse the same frequency in adjacent cells. See the diagram here

https://www.geeksforgeeks.org/frequency-reuse/

Here you have 7 different frequencies used in different groups of cells.

In 4G all frequencies can be used in all the cells. If you are between two or three cells you are probably receiving a signal from (and being received by) multiple cells and they are sharing the RF baseband to make it possible. That plus a big bag of tricks let 4G achieve radically better spectral efficiency through "spatial diversity"

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4G also reuses the frequencies in the exact same way, the primary difference between 3G and 4G is that 3G used CDMA and did not have the higher modulation desities, (capped at QPSK) while 4G LTE went up to 64QAM, so more bits per symbol.

4G did not use spatial separation, that requires beamforming, that is most certainly not deployed in 4G, 4G LTE uses MIMO. Spatial separation is deployed in 5G but only at the mm-wave bands due to the 1/2 wavelength separation required between antenna elements, hence, impractical with longer wavelengths.

3G (UMTS) was reuse 1, not reuse 7 !

This is not the only mistake from this website you mention : e.g. in the page "difference-between-gsm-and-cdma" I read "GSM Data speed rate: 42Mbps in HSPA" (but HSPA is 3G and an evolution of UMTS and is using WCDMA, compared to GSM which is 2G and is using TDMA). I guess when they mention "CDMA" or "3G" (which is are generic terms that also apply to UMTS) they mean "CDMA from 3GPP2", which is not used in Europe. I didn't read everything but from the little I have seen I don't find this website very reliable...

> Here you have 7 different frequencies used in different groups of cells.

You should only need 4 different frequencies: https://en.wikipedia.org/wiki/Four_color_theorem

For hexagons you can get by with 3, https://en.wikipedia.org/wiki/Hexagonal_tiling#Uniform_color...

You'd think so but practically the signal bleeds across to second-adjacent cells and a real channel plan needs more than that.

Look at how the 3 WiFi channels in 2.4GHz land is nowhere near sufficient for good spatial diversity and it is even a struggle with the 5GHz channels that aren't gated to avoid interference with radar.

Indeed. In fact, the link I responded to shows a pattern matching the 7 color 3-uniform distribution I linked to

That only works if you have exact edges and that each BTW uses only one base channel (iirc, they mix and match as much as possible)

Yes, each cell interferes with the next, that is call co-channel interference. That is a major factor that limits the capacity of a cellular network. There are a number of approaches used to manage that, carriers spend a lot of money and employ many engineers designing around that.

SON (Self Optimizing Network) is the latest tech that is being deployed on 4G and 5G to help combat that.

BTW, this is one of the reasons you can get much higher tputs with mm-wave because the beams do not propagate very far which makes keeping co-chan down, that's the good news, the bad news is it doesn't propagate well, which means you need way more nodes.

It's not a hard stop between cells. You don't have radio signals and then suddenly nothing because of reflections, absorbtions and the very nature of log scale of signal distance drop off..

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