Why Networks Want to Move to Voice Over LTE
03.27.2012 by Andrew M. Seybold
It appears as though Voice over LTE will become the norm sooner rather than later. Obviously, network operators will have to be careful how they plan to move people.
Long Term Evolution (LTE) is the next-generation wireless technology being deployed by many operators around the world. Even Sprint and Clearwire are ditching their WiMAX offering to change over to LTE. Why? Because it is the most spectrally efficient wireless technology ever developed. It is all-IP-based, which means network switches will be replaced with routers and computers, making them a thing of the past, and it is an evolution. Each new generation of LTE will add more capacity, better edge-of-cell data rates, and thus even more spectral efficiency.
However, LTE was developed from the ground up as a broadband data technology without a voice component. This is one reason it is fast and has lots of capacity for broadband services. The first three generations of cellular wireless technology were developed for voice, and data capabilities were tacked on to meet the growing demand for both voice and data. There is one exception. Qualcomm’s CDMA offers CMDA2000 1X, which is for voice and about 100 Kbps data, and CDMA2000 1xEV-DO, which is designed for data services only. CDMA operators usually deploy some 1X carriers and some EV-DO carriers in each cell site in order to provide both voice and data services.
The only way, then, to offer voice over LTE is to turn it into Voice over IP, or as it is now being called, Voice over LTE (VoLTE). Essentially then, LTE will have voice capability, but it will be analog voice converted to packet data with the packets intermingled and sent along with the broadband data packets. The only caveat here is that VoLTE packets are time critical and MUST be delivered quickly in order to provide voice that sounds like voice. Anyone using VoIP landline phones, usually from cable operators, are already using VoIP and know it works. Those using services such as Vonage and Skype are also using VoIP systems today. VoIP is the future of voice, so naturally companies deploying an LTE network are planning to convert their second and third-generation voice customers to VoLTE at some point.
One comment here before I continue. I have been told on many occasions by people who already have an LTE-capable phone that they don’t think this is a big deal since they are already using LTE and, therefore, voice over LTE. This might be a logical assumption but it is not true. Today’s LTE devices support voice services on the existing 2G and 3G networks NOT over LTE. When you are making a voice call you are using your network operator’s 2G or 3G network—not LTE.
Many engineers have stated that today’s voice over 2G and 3G networks is less expensive for the operator to provide than will be VoLTE. However, there are just as many engineers who don’t agree with that statement. For my part, I believe that it is less expensive to use existing, paid-for 2G and 3G networks for voice since they are in place and operational, and they generally offer better coverage than today’s LTE networks but this is changing rapidly. So why would a company such as Verizon or MetroPCS be acting quickly toward transitioning voice calls up to their LTE network?
The answer is fairly simple. MetroPCS is probably the best example of why and it also appears as though it will be the first in the United States to have VoLTE-capable devices. In its case, MetroPCS has limited spectrum available. Various articles say that in each market the company has about 22 MHz of spectrum. Today that spectrum is divided between CDMA 1X (voice and slow-speed data), EV-DO for broadband data with speeds up to 1 mbps or so, and LTE with much faster data rates and more capacity. Each CDMA 1X carrier requires 1.25 MHz of spectrum as does each EV-DO carrier. Today, the MetroPCS LTE system is based on 5 MHz by 5 MHz or 10 MHz of its total of 22 MHz per market. If it could close down its CDMA 1X and EV-DO networks, it would have the full 22 MHz per market available for its LTE network. This would greatly enhance its LTE data speeds and per-cell-sector capacity. By moving its voice customers to LTE, it can not only refarm its CDMA spectrum using LTE, it can reduce its overall costs by having to support only one technology instead of three. This makes sense not only for MetroPCS but for the other operators as well.
Verizon runs LTE networks on 700 MHz while it runs CDMA 1X and EV-DO on 850 and 1900 MHz. It also owns or is about to purchase some AWS-1 spectrum in the 1700 MHz band. By moving its customers to all-LTE-based devices for both voice and data it could also refarm its 850 MHz, 1900 MHz, and AWS-1 spectrum and convert it to LTE. This would result in less expensive devices (one technology supported, not three), more capacity per area, and less network operation costs.
Recently, AT&T warned users on its network that if they have only 2G phones (GSM/EDGE) they need to start replacing them with generation three and four devices as it is planning to move away from its 2G network (first), migrating its customer base to 3G and 4G networks. AT&T is supporting GSM/EDGE, HSPA and HSPA+, and now LTE. Moving away from GSM will open up some 850 and 1900 MHz spectrum that can then be used for HSPA+ and/or LTE (my bet is LTE).
The vision of all network operators, over time, is to replace all of their networks with a single LTE network (but on different portions of the spectrum). This makes sense for both the network operators and their customers. Hopefully, as more spectrum becomes available in the United States and around the world, the regulators of the spectrum will understand that LTE is designed to work in as little as 1.4 MHz (times 2), up to 20 MHz (times 2) in several steps. Add to that the fact that guard bands need to be built into the spectrum allocations and this means that a 10X10 MHz system (which is what Verizon is using) would really require an 11X11 MHz portion of spectrum (the amount that Verizon bought at auction), but that the spectrum AT&T bought in the A and B Blocks (5X5 MHz) is not ideal. In the future this should probably be 6X6 MHz portions.
However, as part of its evolution, at some point LTE will support aggregation of spectrum across different portions of the spectrum. When this happens, operators will be able to combine dissimilar portions of the spectrum for more bandwidth or keep their network in smaller segments. All this means is that LTE is being designed and evolved as a smart technology and since the back-end is all-IP, these types of spectrum consolidations will be easier and will result in more efficient use of the spectrum held by each operator.
It appears as though Voice over LTE will become the norm sooner rather than later. Obviously, network operators will have to be careful how they plan to move people. The norm for phone replacement is something like eighteen months, but as the network operators found out when turning off their analog cellular systems, some people buy a phone and hang onto it for years. Most of these people are not into texting, Internet access, or movies or videos. They simply want to have a phone to make calls and for times of emergencies. I hear complaints all of the time from my older friends about not being able to find a simple, easy-to-use voice phone in the stores. Perhaps the network operators need to look at this market segment as they move toward shutting down their 2G and 3G networks.
All of today’s phones and smartphones will have to be replaced and this will take time, for some network operators more than others, and there will be a cost associated with this transition as well. For networks with 5-10 million customers, this task will be easier but still expensive when compared to their size, but for the AT&Ts and Verizons of the world with more than 80 million customers each, this will be a longer-term and more expensive transition. Granted, new phones are coming into the market at a fast pace and some are upgrading their phones more often than eighteen months, but many are not, and corporations with thousands of customers are not likely to move to replace all of their devices at once.
There is an issue I have with this move. I fully understand the whys of it, and they are compelling for sure. But for more than thirty years of my career, I have seen a number of systems try to share voice and data on the same network and in many cases the results have not been what was desired. Voice MUST ALWAYS have priority if the calls are to get through. The more voice users there are on a common network and within the same cell sector, the less bandwidth is available for data services. I have to wonder if any network operator would put in two LTE carriers, one for voice and one for broadband data services. For example, if I had enough spectrum I could build out a 1.4 or 3 MHz LTE network for voice services and another 10 MHz network for broadband data services. I am guessing that no one will try that until later on in the LTE evolution when we have experience with mixing voice and data, priority levels, Quality of Service, and other LTE features.
The move to Voice over LTE is inevitable. The timetable for completion of the transition is anyone’s guess. Those who desperately need more capacity on their limited amounts of spectrum will move to VoLTE the fastest but everyone will be making the move because it makes sense. What does not make sense to me is that we will finally have a worldwide wireless standard in LTE, but we won’t have world LTE phones. As of today, LTE is being built out on 41 different portions of the spectrum around the world. Over time, as the 2G and 3G systems are replaced with LTE systems we will come closer to the ultimate goal of one technology and one device. However, until that time, in many cases when we roam it will be by making use of 2G and 3G networks and not LTE networks. I don’t plan to be in the early adopter pool when it comes to Voice over LTE but I know that I will be gently pushed and then shoved into it over time by the network operators.
Andrew M. Seybold