[lukec11]

5G can be many things, but it isn't gigabit wireless speeds, or low latency, or smart microwaves. It can enable those technologies, but what it really is is a telecommunications standard, telling companies how to build out networks.

5G uses the same radio waves that 4G has, in many cases - T-Mobile US, for example, uses 600MHz and 2.5GHZ frequencies for 5G (and 4G). Sprint has been using 2.5GHz for 4G since 2008.

The biggest change that 5G could bring today honestly is capacity - if you've ever tried to use LTE in a busy train station, you can tell the impact that congestion has on that network's subscribers. Thousands of people connected to a few cells leads to significant slowdown. Generally, higher frequencies lead to shorter range and higher throughput, so in specific circumstances like Airports[0] with multiple antennas, 5G can allow for much higher throughput to many devices at once, alleviating congestion.

5G can also more efficiently make use of spectrum, which means 5G networks can reach further than 4G networks built on the same frequency.

There's a lot more to this, and I'd recommend reading into the Wikipedia page[1] on 5G for an in-depth look if you have time - but the basics are, 5G is a standard, not any one set of devices or antennas or expectations.

[0] https://news.tampaairport.com/tpa-welcomes-5g-and-enhanced-4... [1] https://en.wikipedia.org/wiki/5G

[teeray]

The other fun use case related to trains is tons of subscribers on a moving train doing handoffs between towers. Ideally everyone would use the train's wifi, but that rarely happens because the service is shit. Instead you likely have gigantic traffic hitting the MME trying to detach and reattach phones... and then everyone moves out of the new tower's service area... so on and so forth. Hopefully the 5G core's separation of some of MME's responsibilities will help this scenario.

[toomuchtodo]

Could the train not have a 5G base station to aggregate traffic over reliable backhaul?

[teeray]

I think it might be more difficult than it would seem... everything I’ve seen so far in telecom has the assumption that the gNB (the base station) has a fixed location relative to neighboring gNBs. That’s what would facilitate handoffs. You would have to reconfigure parts of the core network as the train moves, so that you could smoothly handle the instance where someone takes a call on the train, disembarks, and the train pulls away. I don’t think the topology is that malleable.

[kodah]

I don't know if this feature got dropped or if it's just not very well covered, but...

There's a feature that allows devices to go into a low power mode. The tower can then "wake up" a device remotely. It's designed for a variety of IOT usecases.

[maffydub]

Going into low-power mode and then being woken up by the tower is standard function (even of 4G) - it's called paging, and pretty much all devices support it.

Unfortunately, although listening for these paging messages requires less power than having a full connection, it's still non-zero.

For really lower-power applications, 5G (and I think some of the later 4G extensions) support Mobile-Initiated Connection Only, which essentially means the device goes into low-power mode but doesn't even listen for paging messages - instead, it wakes up occasionally (maybe even just once a day) and sends and receives messages. The tower knows to not even bother trying to page it.

[rocqua]

Paging goes back to the original GSM (so even before 2G). In fact, the technology of paging predates mobile voice. The technology was used in pagers!

It is a staple of any always-available battery powered device.

[dkdk8283]

Busy train stations should have DAS antennas to support the high density of devices.

[zamadatix]

A multicarrier DAS is $5-$10 per square foot up front and expensive to maintain - these costs typically do not fall on the carrier but deals can be struck depending on volume. 5G looks to minimize the number of locations that need a DAS in the first place so the places that couldn't get a deal don't need one and the ones that could can be covered cheaper by the carrier than the deal would have been for the carrier. Solutions like Wi-Fi Passpoint look to provide a far cheaper alternative (and avoid things like single carrier DAS which is cheaper but only fixes the problem for some) for cases density is sky high (like stadiums) or the location not otherwise coverable.

A DAS can certainly be an answer but it's never been a very attractive one, and that's from when there weren't other options on the horizon.

[rocqua]

> 5G can be many things, but it isn't gigabit wireless speeds, or low latency, or smart microwaves. It can enable those technologies, but what it really is is a telecommunications standard, telling companies how to build out networks.

True enough. In some sense, 5G is just the next version of the protocol that mobile operators run. Its more than just a technical protocol, it comes with organizational practices as well.

However, the current standard was made with much intentionality. It was very much designed to enable gigabit wireless speeds, low latency and smart microwaves.

[reaperducer]

5G can also more efficiently make use of spectrum, which means 5G networks can reach further than 4G networks built on the same frequency.

This part I don't understand. I spend a lot of time on business and pleasure in places where cellular coverage is unavailable or unreliable. I thought that 5G signals don't go as far as 4G, so how can they reach "further" into towns and places that don't have cellular service?

(FWIW, there are a number of places in my regular [pre-pandemic] travels where the 3G signal is better and even faster than 4G signals.)

[lukec11]

There's a common misconception that 5G specifically means you need to use millimeter wave (very high-band) networks. 5G can be on the same frequency as 4G, and it is more efficient than 4G - so with greater efficiency, it's easier to get usable output from that signal than with 4G. The signals will go "as far" regardless of 3G/4G/5G assuming they're broadcasted at the same frequency and power level, but the device being able to use it is a different story.

The reason 2G and 3G can sometimes reach further than LTE is for a similar reason - because it's easier to "hang onto" a 2/3G signal. The reason it's easier though is different - not because 3G is more efficient, but because it's less complex. This reddit thread[0] explains it better than I can, so I'll paste a comment from it here:

>>> The modulation scheme (how the digital "data" is packed into the "analog" wave to transmit it over the air) is simpler for [2G], which requires a lower wave quality to decode. It's the same reason you are more likely to get an [2G] signal farther away than LTE

Note that the reason 3G might be "faster" is probably due more to the congestion issue I talked about before - when the LTE network is oversubscribed, meaning too many people are connected to it and are slowing it down, sometimes dropping back to 3G (which very few people are connected to in 2021) can lead to you fighting less over your data.

[0] https://www.reddit.com/r/tmobile/comments/lwwkrl/when_was_th...

[fomine3]

But how much is 5G faster than LTE in same frequency usage? Higher QAM would improve throughput but only on great place near the station.

[Foivos]

Better beamforming means that at the same distance from the BS you have better signal quality, so you can use higher QAM.

[enkrs]

True, millimeter wave bands, introduced in 5G, don't go as far as 4G. But those bands are in the 5G standard additionally to the lower bands similar to 4G, and are beneficial in places like busy airports, train stations and urban areas. 5G does not mandate to only use the millimeter wave bands (or, for the mater of act, to use them at all).

So in rural areas 5G signals would still use frequencies similar to 4G,so the more efficient use of spectrum will improve coverage and speed.

Regarding the observation that sometimes 3G signals are better than 4G - that might as well be because 4G has problems with congestion when many clients are connected to the same base station. One of areas which also 5G is also improving.

[toast0]

5G is several parts. The high frequency, hugh bandwidth stuff doesn't go far.

The same as existing mobile frequency stuff has about the same penetration as existing service, but because its more efficient, it allows towers to increase power to expand their coverage area. Generally towers will modulate their output power to reduce coverage when congested, hoping devices will attach to other towers; works well when there's enough towers with overlapping coverage, but not as well when towers are sparse.

It doesn't have to be purely power either, antenna angle makes a big difference, and phased antennas mean you can change effective angle without mechanically changing the angle.

[zaptrem]

5G is just instructions on how devices should talk over radio waves. The waves the devices decide to talk over very dramatically. On the short-range end, they can talk on 30-60ghz bands; these bands have lots of room to talk, but they’re hard to hear, especially through walls or long distances. On the other end, they can talk on frequencies as low as <600mhz. These are great at penetrating barriers (they’re probably what you use in the middle of nowhere) but there’s less room (free spectrum real estate available) to talk.

[kalleboo]

> FWIW, there are a number of places in my regular [pre-pandemic] travels where the 3G signal is better and even faster than 4G signals

This will rely heavily on the network design decisions made. Where I live, the digital TV switchover happened after LTE buildout was well on it's way, so all those juicy 700 MHz bands went to LTE. I literally can't remember the last time I saw my phone on 3G here, even out in the countryside with marginal coverage/dropouts. It's been at least 4 years.

[pottertheotter]

The thing that is confusing is two things are wrapped up together as "5G": (a) the actual 5G standards, and (b) the spectrum that is used. To add to the confusion, (b) is composed of frequency and bandwidth, and those are often different both between and within countries.

For instance, one of the biggest benefits of 5G is that channels (bandwidth) can be much wider, and several can be stacked together, which means more data can be transferred. But even though that can be done, there may not be enough spectrum at a specific frequency to be able to take advantage of that.

Then the high-band (millimeter wave) can have even more channels than the low- and mid-band 5G. But high-band doesn't travel far and it doesn't penetrate walls well.

If you want a good primer on it that is accessible, I recommend the regularly updated "What Is 5G?" article from Sascha Segan at PCMag.[1] I think he's the best journalist writing about 5G.

[1] https://www.pcmag.com/news/what-is-5g