If you’re one of those consumers who likes to have the latest technology in your technology “toys,” the cellular carriers continue to make that more difficult as they periodically redefine the meaning of the term “5G”. As I noted in one of my earlier blogs, 5G isn’t really a single frequency band or a single technology. In reality, it is principally the “evolution” of cellular communications to the next level of technology. It does include some new frequency spectrum, but it also shares much of that with the 4G networks.
In that earlier post, I noted that the term “5G” covers a rather broad distribution of frequencies from millimeter waves at the many tens of gigahertz all the way down to several hundred megahertz signals “reclaimed” from the old UHF TV band. This is an enormous range of frequencies and the characteristics of the “5G” that employs these frequencies varies dramatically over that range. To say it simply, the 5G implemented using Band 71 in the 617-698 MHz range will be rather different in performance from the 5G implemented in the region of 25 GHz, and it will require different technology to broadcast and receive it.
How Carriers are Quickly Implementing 5G
You may have noticed that in October Verizon made a big advertising splash about somehow increasing the size of its 5G network and when you can expect to be able to access it. You might have thought that Verizon had made a huge investment in new towers and hardware to bring this new capability to you. No, what Verizon had done was to redefine some of its 4G frequency spectrum to be 5G, something that is called Dynamic Spectrum Sharing (DSS).
One of the big drawbacks of millimeter wave 5G is that it does require new towers and hardware and its characteristics result in needing many more towers per square mile of coverage area than does LTE 4G operating at <2 GHz. By using DSS, cellular carriers can provide a “version” of 5G using their existing 4G infrastructure. The benefits of DSS to the carriers are shown in the first figure. DSS implementation is faster and much cheaper for the carriers.
So how do the carriers manage to combine two different technologies on the same towers? They accomplish this magic by “slicing and dicing” both time and frequency space as shown in the second illustration. It’s not essential for us to totally understand how this is done, but the key concept is that the frequencies and “block” of time will be shared by the 4G and 5G signals. The concept is significant because it means that as 5G phones become increasingly available, they find that 5G signals are readily available. This is essentially because they have been “invisibly” integrated with the 4G signals that have been there all along.
Despite Verizon having a big splash about this last month, DSS isn’t something that is limited to Verizon. For the past year T-Mobile has been actively rolling out Band 71 in two phases, a 4G phase and a 5G one. T-Mobile’s acquisition of Sprint gave it a large “chunk” of frequencies in the 2.5 GHz region which is ideal for 5G DSS implementation.
Similarly, AT&T had previously announced an expansion of its 5G coverage to include 28 additional cities using DSS technology, principally focused on the 850 MHz band.
So, all three major carriers are now employing DSS to speed up 5G implementation and reduce their capital costs. Many phones currently being introduced into the market, such as the iPhone 12 and the Pixel 5, are equipped to receive both mm wave 5G and what we’ll call “DSS 5G”.
Setting Real-world Expectations for the Near Future
That should be a big win for the consumer, right? We’ll get 5G sooner than we expected to, right? Well, we will, and we won’t! DSS 5G will be an improvement over 4G, but it will not be the very high-speed technology improvement many of us have been waiting for. Part of the reason for this is simply physics; lower frequency signals can’t carry as much information content as can higher frequency signals. So, the information content of a 600-800 MHz DSS transmission can’t match the information content of a 25 GHz transmission. Furthermore, by sharing the existing lower band structure between 4G and 5G no new bandwidth is being created. Therefore, the information content of the network as a whole doesn’t increase. In fact, there’s a slight capacity decrease because of it, because with DSS, you need to have 4G signaling and 5G signaling in the same band. Therefore, that signaling takes up a little bit of the capacity. So, if one is a bit cynical, they could say that the carriers are actually taking away some bandwidth from users so they can crow about deploying 5G in lots of places! To say it differently, everyone will have a bit less available bandwidth to share because some users will have some form of 5G to use!
The 5G that consumers are going to see, at least for a while, is what we might call “5G Lite.” The following figure dates from January 2020 and shows the download speeds provided by several implementations of 5G technologies. Note that because the figure pre-dates the Verizon press release about its DSS activity, that information isn’t included. Notice that the bars labeled mm wave 5G provide the super-fast speeds that have been touted for 5G. However, the bars representing lower-band 5G (600 MHz and 850 MHz) provide only a modest improvement over currently available 4G speeds. The 5G implementation at 2.5 GHz is nearly as good as the mm wave examples because it utilizes some “new” spectrum which doesn’t have to be shared with 4G.
Making Informed Decisions About Upgrading Hardware
So, what does this all mean to us, the consumers? In my opinion, it means that you shouldn’t throw out your 4G phones and hotspots unless you have another reason to do so. For a number of years, the incremental benefit of switching to 5G-compatible hardware will be modest at best, and that’s assuming that you have 5G DSS service in your part of the country. As more mid-band (<6 GHz) 5G gets built out, overall network speeds will increase, but that’s not going to happen overnight. Millimeter wave 5G will continue to expand in urban areas where population density makes the investment worthwhile. But 4G service will continue to be the backbone of the rural cellular network for quite some time to come, and the routers and modems you purchase today are likely to have many years of service life before they are overtaken by technology advancement.
5G Networks.net, 5G Dynamic Spectrum Sharing (DSS), 7/24/2020
Chaim Gartenberg, Verizon announces its nationwide 5G network, The Verge, 10/13/2020
Linda Hardesty, The 5G of T-Mobile, Verizon and AT&T all rank badly for different reasons, Fierce Wireless, 3/3/2020