There’s been a lot of buzz about 5G over the last year—much of it, sadly, none too coherent. Today, we’re going to take a detailed, realistic look at how we can expect 5G to improve cellular broadband, with a focus on the impact we might be able to expect on gaming. Surprise: the news is actually not bad!

What is 5G?

Before we can talk about what to expect from 5G, we need to talk about what 5G actually is—and isn’t. 5G, short for “fifth generation,” is the next cellular communications protocol. 5G is not, specifically, any given frequency or band. There are two major bands 5G can operate on—millimeter wave, and sub-6GHz. Exactly which frequencies within those bands your devices will use varies from carrier to carrier, and country to country.

The sub-6GHz band isn’t new territory; the frequencies in use there are the same ones carriers already use for 4G / LTE service. Sub-6Ghz can further be divided into low-band—under 1GHz—and mid-band, at 2.5GHz-3.5GHz. Low-band offers greater range from the tower, but at lower speeds; the mid-band offers greater speed, but lower range. It’s worth noting that “lower range” isn’t necessarily a curse—the greater the range from the tower, the more users you have sharing the same finite amount of airtime, and the lower the speeds and less predictable the latency you’ll see.

While we do expect 5G to be significantly better than 4G on sub-6GHz bands, millimeter wave—around 24GHz-39GHz in the USA—is what most of the breathless 5G coverage you’ve seen in the past specifically refers to.

The amount of sheer bandwidth available to millimeter wave—or just “mmWave” for short—is pretty crazy. The spec allows 800MHz individual channel widths, at which we can expect edge data rates (the lower boundary of rates you’d see from a reliable connection) of 400Mbps.

But throughput isn’t usually the killer metric for gaming—latency is. We’re going to cast a more skeptical eye at this later, but mmWave is eventually expected to provide OTA (over the air) latency of under one millisecond.

A closer look at sub-6GHz 5G

At this point, you might be wondering why anyone would bother with sub-6GHz bands at all, when they don’t and can’t offer similar bandwidth, throughput, and latency to mmWave. While mmWave can certainly outrun low- or mid-band connections, it’s got some pretty severe drawbacks. In short, the higher the frequency of a given band, the less capable it is of penetrating obstacles.

At less than 1GHz, the sub-6GHz low-band flavor is hardly impacted by most obstacles at all—you typically need something on the order of a mountainside in between your device and the tower to make significant impact on the connection quality. But you also have very little bandwidth to work with, sharply limiting maximum speeds. Today, you might see 100Mbps or even 200Mbps from a 5G low-band connection—but those numbers will almost certainly drop sharply once 5G adoption picks up.

Mid-band—2.5GHz to 3.5GHz—is a good compromise for urban areas. It doesn’t penetrate walls and similar obstacles as well as the low-band does, but that’s as much blessing as curse—lower penetration makes it easier for a large number of towers in a device-dense few square miles to operate without interfering as much with one another. Mid-band 5G is slightly higher frequency than modern 4G, whose higher band typically runs either just below or just above 2.4GHz Wi-Fi.

Mid-band channels are wider than low-band channels, with proportionately higher speeds—ranging from 125Mbps on the low end, to 500Mbps or higher under more ideal circumstances.

A realistic look at mmWave

This brings us back to millimeter wave—the Shangri-La of 800MHz channel widths, sub-millisecond latency, and free puppies for everyone. At least, that’s what much of the marketing around 5G has sounded like.

The problem is, mmWave frequencies are absolutely terrible at penetrating obstacles. We spoke at length to Qualcomm engineers, who confirmed what we already knew about 30GHz-40GHz RF—it’s not going to penetrate buildings directly. With that said, mmWave is a lot more useful than you might think based on that one fact alone.

Although mmWave frequencies won’t penetrate exterior walls directly, they bounce from hard surfaces well—and the resulting radio frequency multi-path propagation is absolutely usable. In September 2019, a PC Magazine reporter demonstrated getting better than 400Mbps on the wrong side of an elevator shaft from a 5G panel, and more than 1Gbps on the other side of an interior wall.

The usability of RF multipath propagation—”echoes” bounced from hard surfaces such as concrete buildings and sidewalks—makes mmWave a pretty reasonable proposition for outdoor users. The range is still quite low compared to mid-band frequencies, but this is (again) as much blessing as it is curse. Lower range means you need more towers, but it also means comparatively fewer users per tower, less interference from fewer other users within “earshot”, and thus more airtime effectively available per user.

The expected widespread availability of mmWave for outside users will make a big impact on the quality of mid-band available to inside users. (Remember, there’s only so much airtime to go around.) If you can split your load up among non-overlapping spectra by serving outside users with mmWave and inside users with mid-band sub-6GHz, the amount of airtime available for each goes up sharply.

https://arstechnica.com/?p=1699835