There is no doubt that 5G promises to change the way we communicate, live and work to a rather large extent. Unlike past mobile technologies, 5G offers capabilities and performance that were once the exclusive domain of wired networks. So it’s no surprise that the deployment of these advanced networks has become more involved than anything that’s come before.
To deliver what 5G can really do, wireless operators have had to work across a much wider range of radio frequency spectrum, from the lower frequencies where the original GSM mobile networks existed, to those used by radar systems and satellites.
HPE
Although wireless carriers are looking to use higher midband and millimeter wave (mmWave) frequencies for the benefits they offer, most 5G deployments have started in the low end of the sub-6 GHz band.
The reason for this was quite simple. These low-band frequencies are where the older GSM, 3G and 4G/LTE technologies have lived for the past two decades. This means that the carriers already had the necessary licenses for this spectrum. They’ve also deployed thousands of cell towers that can be reconfigured to deliver 5G without the need for brand new equipment.
What is low-band 5G?
Low-band frequencies are technically defined as those below 1 GHz. However, in the context of wireless carriers, this covers everything below 2.3 GHz — the frequencies that GSM, 3G and LTE have historically lived on.
In North America, the original GSM services almost exclusively used the 850MHz and 1.9GHz (1900MHz) frequencies. Later, with 3G and LTE, all US carriers expanded to 700MHz and 1.7GHz frequencies, while AT&T also went to the 2.3GHz range, T-Mobile added 600MHz on the bottom, Sprint also set up a 2 ,5GHz. Some carriers in Canada and Mexico also deployed LTE services at 2.6 GHz, but that higher frequency was not licensed for mobile use in the United States at the time.
Jan Jirous/Shutterstock
However, except for Sprint, all major US carriers have generally stuck to four core frequencies: 700MHz, 800MHz, 1.7GHz and 1.9GHz. When T-Mobile merged with Sprint in early 2020, its 2.5GHz 4G/LTE network was shut down so those frequencies could be repurposed for T-Mobile’s Ultra Capacity 5G mid-band service.
When AT&T and T-Mobile started rolling out their 5G networks, they stuck to the frequencies they were already using and licensed for. AT&T deployed its 5G at 850MHz and T-Mobile launched its national network using its 600MHz spectrum. Verizon took a different route and at first avoided the lower frequencies entirely. Instead, it chose the much higher frequency of the mmWave spectrum, giving it a significant speed advantage at the expense of vast coverage.
What does Sub-6 mean?
The term sub-6 has become somewhat confusing, as it was initially used to refer to all frequencies below 6 GHz, as opposed to mmWave, which starts at 24 GHz.
Although the difference between frequencies below 6 GHz and mmWave is quite remarkable, when the industry started using the term below 6, the Federal Communications Commission (FCC) had not yet enabled the intermediate C-band frequencies for 5G use. After operators started deploying 5G in the 2.5 to 4 GHz range, it became clear that not all frequencies below 6 GHz deserved to be grouped together, and some people now use sub-6 only for low-band 5G.
However, this is not universally true. Many will rightly point out that since Sub-6 still means Sub-6GHz, it should apply to all frequencies below 6GHz, including faster frequencies like C-band or even the higher 4-5GHz spectrum that may one day be released, along with the slower 600MHz low-band. Therefore, sub-6 has become an imprecise term and it is better to call the 5G spectrum low-band and mid-band because there are significant differences between the two frequency ranges.
A low-band compromise
Low-band frequencies were the fruit for most operators to start implementing 5G. They already had the necessary spectrum licenses from the FCC and at least some compatible radio equipment and towers in place.
However, more significantly, low-band spectrum has enabled carriers to deploy 5G over a much wider range. Lower frequencies travel further and are not nearly as susceptible to interference from things like buildings and trees.
Unfortunately, the trade-off was that these frequencies did not offer a significant speed advantage over the 4G/LTE networks that were already in place.
In the same way that a multi-band Wi-Fi router offers extended range with slower speeds on the 2.4 GHz band than on the 5 GHz band, cellular signals in the 600 MHz and 850 MHz range can travel long distances, but not very fast.
This strategy allowed T-Mobile to be the first operator to launch a national 5G network in all 50 states. These 600MHz signals could travel long distances, allowing T-Mobile to cover significantly more territory with fewer towers. However, as an OpenSignal report from early 2020 showed, speeds weren’t dramatically better than T-Mobile’s 4G/LTE network.
OpenSignal
Meanwhile, operators in other countries such as South Korea have opted to use midband spectrum for their 5G deployments, boasting more impressive numbers, while Verizon topped the charts thanks to its use of mmWave. However, it’s also important to note that Verizon’s 500Mbps speeds were only available to 0.4% of its customers. Sprint also posted better numbers thanks to its 2.5GHz midband spectrum.
Verizon was late to the party, but it also ended up deploying a low-band national 5G network in late 2020 to bring 5G to the other 99% of its customers. For its low-band 5G, Verizon has chosen the 850MHz, 1.9GHz and 1.7-2.1GHz bands.
Sharing the ether
The problem wasn’t just the lower frequencies used by AT&T and T-Mobile. Since 5G technology is more advanced than 4G/LTE, it should work faster even at 600MHz and 850MHz.
However, when AT&T and T-Mobile deployed 5G on those frequencies, they couldn’t simply shut down the 4G/LTE services that were already running there. They had to find a way for 5G to coexist peacefully with these older wireless technologies.
So they turned to a technology known as Dynamic Spectrum Sharing (DSS), a 5G feature specifically designed to allow it to work alongside 4G/LTE on the same frequencies. In simple terms, DSS allows 5G data to be inserted into any unused gaps in 4G/LTE transmissions.
The use of DSS enabled a much faster rollout of 5G deployments by exploiting unused 4G/LTE capacity, but it also had one major drawback. DSS is a feature of 5G, so 5G signals knew how to share the airwaves with 4G/LTE signals, but LTE never learned how to share.
Therefore, DSS 5G is forced to give way to 4G/LTE signals, which always have priority. On a busy or congested 4G/LTE network, 5G performance suffers.
On Verizon, DSS results were so poor that PCMag’s Sascha Segan told Verizon iPhone users to turn off 5G, calling DSS a “desperately slow system” after tests revealed the carrier’s DSS 5G was almost never faster than 4G, and in fact is slower in larger cities like New York and Chicago.
Reserve spectrum
Unfortunately, the problem is that operators want to push the perception of 5G offerings. They want people to see the “5G” icon light up on their smartphones, even if it doesn’t deliver performance that’s better than 4G/LTE. Consider the trick AT&T pulled a few years ago with its “5G Evolution” network, giving its customers a “5G E” icon for its slightly improved 4G/LTE network.
AT&T nonsense aside, seeing “5G” on your phone usually means you’re connected to an actual 5G network. However, that doesn’t mean you’ll see impressive 5G speeds. If you use low-band 5G frequencies, you’ll get low-band 5G speeds that usually won’t be much better than using 4G/LTE.
Adam Doud / Digital trends
Nevertheless, even as operators deploy faster networks using mid-band and C-band spectrum, there will always be room for low-band 5G. With a wide range offered by the 600MHz-850MHz spectrum, these are the frequencies that operators will continue to rely on to cover less populated areas. It’s simply not worth putting up dozens of new towers to cover a relatively small number of customers.
Carriers used a similar strategy even in the days of GSM. In Canada, 1.9 GHz was used exclusively in larger urban centers, while 850 MHz was used for rural coverage. Frequency licensing issues have prevented this approach from such widespread use in the United States. However, operators still tended to use higher frequencies in cities and lower frequencies in the countryside wherever possible.
Now that carriers have relatively large chunks of midband spectrum to play with, 5G deployments are falling even more dramatically. Most 5G users will be covered by mid-band spectrum, with faster mmWave and higher capacity deployed in densely populated areas where network congestion is a problem, such as stadiums and airports. Low-band 5G will effectively become backup spectrum to ensure you still have 5G when nothing better is available.
The good news is that low-band 5G speeds should improve as more people switch to 5G smartphones and leave 4G/LTE technology behind, avoiding congestion issues as 5G DSS no longer has to give up as much space to older mobile technologies. Eventually, 4G/LTE will be phased out entirely, although we’ll probably be moving to 6G by then.
Editor’s recommendations
Categories: GAMING
Source: newstars.edu.vn