







How LTE is configured for deployment



Verizon Cell Tower



How LTE actually works







In the United States, Sprint is the only network operator deploying LTE in the TDD variant. Everyone else is deploying in the FDD variant. The TDD variant becomes more important in Asia, as China Mobile (the largest network operator in the world in terms of subscriber count) is using TDD frequencies for their LTE network. Sprint’s parent company, SoftBank, also uses LTE TDD in its home market of Japan. Fortunately, LTE devices can easily be made to support both variants on a device without too much trouble.

Enough about specs – what about battery life?

Now we lead to the part that most people care about: how it affects battery life. By itself, LTE devices should last roughly as long as their HSPA+ equivalents because of the optimized radios for both downlink and uplink operations. The reason why LTE devices right now eat batteries for breakfast is because the network operators are forcing many of these devices into active dual-mode operation.

For Verizon Wireless, this means that most of their LTE devices connect to both CDMA2000 and LTE simultaneously and stay connected to both. This means that you are eating twice the amount of battery for every minute you are connected than you would if you were connected only to CDMA2000 or LTE. Additionally, when you make calls on Verizon Wireless LTE phones, the CDMA2000 radio sucks down more power because you are talking. Sending and receiving text messages causes pulses of CDMA2000 activity, which cuts your battery life more. Arguably, constantly changing radio states could be worse for battery life than a switch into one mode for a period of time and switching back, so text messages may actually kill the batteries faster.

Then there is handover. Handover is the operation in which a device switches from one network to another or from one tower to another. Handover is the critical component that makes any cellular wireless network possible. Without handover, a user would have to manually select a new tower every time the user leaves the range of a tower. (WiFi is an example of a wireless network technology that doesn’t inherently support handover.) When the user travels outside the range of a WiFi network, the WiFi radio will just drop the connection. For cellular networks, this is even more critical because the range of a tower is not very predictable due to factors outside of anyone’s control (like the weather, etc.). LTE supports handover like all other cellular wireless networks, but it improves on it by doing it much faster when handing over to a supported type of network or cell.

However, Verizon and Sprint are doing handover from LTE to EV-DO and back by plugging in a connection to an enhanced version of the EV-DO data network core called eHRPD. This isn’t a great solution by any means.


The fragile link-up between EV-DO and LTE make handover occur a lot more than it is supposed to, which eats battery life even more. With AT&T and T-Mobile using an HSPA+ network alongside LTE instead of CDMA2000, handover operation is a lot smoother. As far as battery life goes, it should be slightly better than Verizon and Sprint LTE phones because LTE supports fast handover between UMTS and LTE. AT&T LTE phones are normally not forced into active dual-mode operation because HSPA+ lets you use data and talk at the same time. As a consequence, AT&T has no need to force the device into active dual-mode operation. However, battery life will still be pretty bad because LTE signals are still very weak in most AT&T LTE zones, and AT&T LTE devices default to connecting to LTE signals whenever possible.

C Spire Wireless, U.S. Cellular, and other CDMA/LTE operators all have the same problem as Verizon Wireless with LTE battery life because they do the same thing as Verizon Wireless and force active dual-mode operation with most of their devices. As a result, turning off LTE will significantly improve battery life because the phone switches back to single-mode operation. Or in the case of AT&T phones, passive dual-mode operation (for GSM/HSPA+ handover) since they are typically in passive tri-mode operation for GSM/HSPA+/LTE handover. Passive multi-mode operation means that the device isn’t constantly connected to multiple networks, but will establish a connection and hand over the connection if the signal on the current network is too weak or snaps. This is ideal for multi-mode operation, and Sprint switched to doing this last year in order to control costs for new devices that support the tri-band LTE network it brands as “Sprint Spark”. With the launch of Verizon VoLTE last year, Verizon has also increasingly started offering devices with passive multi-mode operation. This means that these new devices now have many of the same energy conservation benefits that have always been present in GSM/UMTS/LTE devices.

LTE — Mobile panacea?

The ultimate goal of the network operators deploying LTE is to replace everything else they have with it. That means that it needs to become possible to handle voice calls, text messages, network alerts, etc. over the data network. However, no one developed the LTE specification with voice and text messaging in mind. It was designed as a data network only. So how do they solve the problem? By developing a VoIP solution that fits their needs. Two main standards came into existence: VoLGA (Voice over LTE via Generic Access) and VoLTE-IMS (Voice over LTE via IMS). VoLGA was based on GAN (Generic Access Network), which is also known as UMA (Unlicensed Mobile Access). Deutsche Telekom was the only network operator that wanted to use this method, as the design for VoLGA was heavily derived from T-Mobile USA’s implementation of UMA for its WiFi Calling feature. No one else wanting to deploy LTE wanted to use it as a final or interim solution, as it would have meant keeping around the legacy GSM core network for this purpose.

Everyone else supported VoLTE-IMS (now referred to as VoLTE), which allowed them to fully discard their older networks and simplify their network design as they decommissioned legacy networks. However, IMS is much more expensive and difficult to deploy than VoLGA, at least for GSM network operators. But IMS also promised more flexibility. IMS could be used to make real-time video calling with all sorts of additional features possible. And so, Deutsche Telekom dropped VoLGA and joined everyone else in supporting VoLTE.

VoLTE uses an extended variant of SIP (Session Initiation Protocol) to handle voice calls and text messages. For voice calls, VoLTE uses the AMR (Adaptive Multi-Rate) codec, with the wideband version used if supported on the network and the device. The AMR codec has long since been used as the standard codec for GSM and UMTS voice calls. The wideband version supports higher quality speech encoding, which would allow for clearer voice calls. Text messages are supported using SIP MESSAGE requests. Video calling uses H.264 CBP (constrained baseline profile) with AMR-WB audio codec over RTP (Real-time Transport Protocol) with VBR (variable bit rate). With this, video calls over IMS are supposed to be very high quality, no matter what the quality of the data connection. With VBR, the call can adapt to the changing congestion levels of the data network to maintain a quality video call.

In a somewhat ironic twist, T-Mobile USA became the first network in the world to commercially deploy IMS-based voice calling and text messaging by using it for an improved WiFi calling solution. An update to the T-Mobile Samsung Galaxy S II and an update to the T-Mobile HTC Amaze 4G both included the new WiFi Calling solution.

MetroPCS was one of the first carriers in the world to deploy VoLTE, the other being SK Telecom in South Korea. While SK Telecom launched VoLTE nationally, MetroPCS only launched VoLTE in Dallas, TX. Initial implementations of VoLTE clearly showed much lower battery life, but that is largely resolved nowAfter acquiring MetroPCS, T-Mobile reconfigured its two networks for broadly rolling out LTE service and shutting down the CDMA service it inherited from MetroPCS. At the end of the summer of 2014, T-Mobile launched VoLTE and made it available nationwide shortly after the launch. Since it is based on their WiFi calling solution, it is able to support seamless handover from WiFi to LTE and back for voice calls, which no one else has done.

As for Verizon, AT&T, and Sprint deploying VoLTE? Well, Verizon rolled out VoLTE in August 2014 nationallyAT&T launched VoLTE in select parts of the Midwest in May 2014 and has been gradually expanding it since. Sprint has not officially said anything about it yet.

At this point, the major gotcha with VoLTE now is that it requires carrier customized firmware. Setting up a device to use VoLTE requires a lot of configuration, more than what a SIM card can provide. Consequently, only operator branded devices will support VoLTE for now. Some unbranded devices may eventually be preloaded with select operator VoLTE configuration information, but that will remain the exception rather than the rule. Hopefully this particular problem will be addressed soon, because it puts a crimp in any plan to move devices from one operator to another.

The messy future of 4G

We’ve only scratched the surface of what LTE is all about, but this article includes pretty much everything that LTE subscribers would care about. Some of the other aspects of LTE include SON (self-organizing network) capabilities, which allows it to flexibly allocate capacity to parts of the cellular network as it is needed by redistributing connections to an optimal configuration at any given time. Handover to WiFi is another cool feature, too. However, most of the features like the former are pretty much only seen from a network operator’s side of things, and things like the latter may never actually be implemented.

LTE is a significant leap in optimized cellular wireless technology though. If you wish to get the highly-technical details of LTE and its ever-evolving specifications, check out the 3GPP’s specification series for LTE. Specifications for eHRPD and associated CDMA2000 specifications are available on the 3GPP2’s website. The VoLGA specifications are available on the VoLGA Forum’s website. The 3GPP hosts the IMS specifications, with the GSM Association hosting IMS Profile for Voice and SMS specifications on their website. We’ve covered the major highlights in this article, as there is way too much to cover. As the specifications detail, there were many improvements at every level of a cellular network that result in a high-performance, optimized network.

Whether LTE becomes the success story of the mobile industry remains to be seen. Network operators around the world are only now deploying it, and already it is turning into a mess. The 3GPP has already approved nearly 45 frequency bands for LTE. Over 30 of them are for LTE FDD and the rest are for LTE TDD. Roaming is going to be very difficult on LTE. For North America alone, there are ten FDD bands and one TDD band for LTE. For Europe and Africa, there are four bands for FDD LTE and two bands for TDD LTE. For Asia and Oceania, there are the same four FDD bands for Europe, three more frequency bands for FDD, and two more TDD bands. The rest of the bands have yet to be used, but they are going to be used. Someone is going to have to figure out how to fit more bands on an LTE device without sacrificing portability. Fortunately, a number of bands are supersets/subsets of other bands, so some are easier to support than others.


And then there’s the 4G mess. Contrary to popular belief, LTE at the current stage was not always considered 4G. The International Telecommunications Union (or ITU) determines what can be considered 4G. Originally, the ITU declared that the collection of requirements known as IMT-Advanced determined what would be considered 4G. LTE did not make the cut (though a future version of it called LTE-Advanced did). Neither did WiMAX or HSPA+. However, the American and Canadian network operators’ collective influence made the ITU revise their specification on what 4G is to include any wireless technology significantly evolved from 3G technologies. Most technophiles are of the opinion that the IMT-Advanced specification determines what can be considered 4G, while most business people prefer the newer definition for 4G. For the purposes of this article, the revised standard is considered 4G. While this is out of the scope of this article (and also not really important either), I’m laying it out now to prevent any arguments. This means that LTE, HSPA+, and WiMAX are all considered 4G technologies, though WiMAX is still officially on the list of 3G technologies too.

Since LTE-Advanced Release 10 has been codified and equipment is available, a number of operators around the world have started using LTE-Advanced features. AT&T has deployed carrier aggregation in many of the same areas it has launched VoLTE, and Sprint intends to launch carrier aggregation in areas where the company has rolled out its tri-band “Spark” network. T-Mobile USA has been deploying and testing it since it started its rollout of LTE service so that it can maximize the benefits of LTE-Advanced equipment in as many areas as possible. While T-Mobile isn’t broadly using carrier aggregation yet, it certainly has the option to do so, in the future.

I don’t know what the future holds for LTE, but it will certainly be very interesting. This is the most exciting time in the mobile industry since the switchover from analog to digital back in the early 1990s. LTE represents a paradigm shift from hybrid voice and data networks to data-only networks. Going forward, wireless network technology is likely to become more widely used because it will become easier to obtain than wireline services (cable, DSL, etc.). It is doubtful that it would fully replace wireline data services though. Hopefully, the issues we face with LTE now will go away over time.

As LTE continues to improve, we’ll continue to see a steady migration of usage from older networks to LTE, especially operators using CDMA networks as a legacy technology. While we may not have ubiquitous connectivity for a long time due to the sheer number of bands and configurations, new technology geared to improve the situation is always coming.