The 4G Cell Phone & Mobile Device FAQ

NOTE: This article focuses on cell networks in the U.S. Also, MHz = megahertz.

What is 4G LTE?

Ever since the first cell phone was released in 1983 [1], cell phones have been getting more and more sophisticated. A cell phone couldn't be a cell phone, however, if there was no cell network to connect to. In that regard, cell networks have gone through four major waves of change, and these waves of change are referred to as generations. 4G refers to the latest generation, and LTE (Long Term Evolution) [2] is the technology being used for 4G by all the four major carriers (AT&T [3], Sprint [4], T-Mobile [5], and Verizon [6]). 1G is so old that it predates the current cell phone carriers and is no longer used.

Is LTE the only 4G technology? Is there a 3G version of LTE?

No and no. HSPA+ (High Speed Packet Access) [7] and WiMAX are the two other 4G technologies. HSPA+ is used by AT&T [7] and T-Mobile [5] and is based on the earlier 3G technology HSPA (notice the lack of a +). Since HSPA+ is an extension of older technology, it is intended as a bridge to full LTE coverage. WiMAX is used by Sprint, but Sprint has announced that it will switch to LTE [4] and will stop including WiMAX technology in its phones [8]. Finally, LTE is a 4G-only technology.

How are the LTE networks from the four major carriers progressing?

AT&T expects its LTE network to cover 300 million people by year-end 2014 [3], Sprint expects its LTE network to reach 250 million people by 2013 [4], T-Mobile expects its LTE network to cover 200 million by the end of 2013 [9], and Verizon's LTE network currently covers over 90% of the U.S. population [6].

What are the benefits of getting an LTE-equipped device?

There are five potential benefits of getting an LTE-equipped device. These are faster and expanded data coverage, Voice over LTE (VoLTE) (this itself has three possible benefits), and simultaneous phone calling and web surfing without using Wi-Fi. Although the first benefit is fairly self-explanatory, the remaining benefits require further explanation.

First, let's look at some of the background for VoLTE. Initially, the LTE networks built by the carriers were being used only for data. However, on Aug. 7, 2012, MetroPCS became the first U.S. carrier to launch VoLTE, which basically means that its LTE network is now useable for voice as well as data [10]. SK Telecom and LG Uplus will be the first carriers to use VoLTE in South Korea, while other carriers are expected to launch VoLTE at later dates [11].

The three potential benefits you can get with VoLTE are less dropped calls, Rich Communication Suite (RCS), and HD Voice [11] [12]. The basic gist of RCS is that it will, as the name applies, enhance communication. For example, according to PCMag Mobile Lead Analyst Sascha Segan, one of the things that RCS will do is to "merge picture and video messaging with phone calls and show who's online right in your phone book" [13]. HD Voice, meanwhile, improves voice quality - however, it is only an optional feature [11].

There is also the issue of simultaneous phone calling and web surfing without using Wi-Fi. If you are a Verizon customer, buying an LTE-equipped phone may allow you to talk on the phone and browse the Internet at the same time without using Wi-Fi. You do not need to get an LTE-equipped phone to do this for AT&T or T-Mobile. For Sprint, this may be achieved by getting a WiMAX or LTE phone, although getting an LTE phone is the better choice since LTE is the network technology Sprint will be focusing on for the future.

In regards to this last benefit, you may be wondering what's so bad about using Wi-Fi instead of the cell network to browse the Internet. Well, it really isn't that bad (and in fact can save you money), but some may consider it an inconvenience. If an owner of a mobile device is using Wi-Fi to browse the Internet on the mobile device, the owner is probably in one of the following scenarios:

The owner has connected his or her mobile device to his or her Wi-Fi network at home. The problem with this is that if the owner is not at home then the Wi-Fi, and thus the Internet, would go away.
The owner has connected his or her mobile device to a public Wi-Fi network. There are two problems here: the first is that there are still plenty of places without public Wi-Fi, and the second is that connecting to a Wi-Fi network other than your own can present potential security issues.
The owner has connected his or her mobile device to a wireless hotspot. A hotspot is a small device that converts a cellular network signal to a Wi-Fi signal. The only real problem with this strategy is that there is an extra device you have to carry around, albeit a small one.

Are there any differences between the LTE from the different carriers?

Yes. The main difference between the LTE from different carriers is that the different carriers will be using different frequencies for LTE. The main frequencies that will be used for LTE in the U.S. are the 700 MHz, Advanced Wireless Services (AWS) [14], and Personal Communications Service (PCS) [15] frequencies.

700 MHz LTE will be used by AT&T [16] and Verizon [17]. However, the two carriers will be using different parts of the 700 MHz frequency spectrum. A breakdown of who's using what parts is shown below [18 page 7] [19 page 10] [20] [21] [22] (PSBB = Public Safety Broadband [19 page 3]):

Band	Blocks	Frequency in MHz	Owner
12	Lower A Lower B Lower C	698-704 up, 728-734 down 704-710 up, 734-740 down 710-716 up, 740-746 down	Assorted Mainly AT&T Mainly AT&T
13	Upper C	777-787 up, 746-756 down	Verizon
14	Upper D PSBB	788-793 up, 758-763 down 793-798 up, 763-768 down	Public safety groups Public safety groups
17	Lower B Lower C	704-710 up, 734-740 down 710-716 up, 740-746 down	Mainly AT&T Mainly AT&T

Next up are the AWS frequencies. AWS LTE will be used by AT&T [16], T-Mobile [5], and Verizon [22]. AWS uses 1710-1755 MHz for uplink, 2110-2155 MHz for downlink [23], and is sometimes referred to as 1700/2100 MHz for simplicity purposes [16].

Finally, there are the PCS frequencies. PCS LTE will be used by Sprint [4]. PCS uses 1850-1910 MHz for uplink, 1930-1990 MHz for downlink, and is sometimes referred to as 1900 MHz for simplicity purposes [24 page 32].

If someone were to make a single LTE device compatible with all the 700 MHz, AWS, and PCS frequencies, could that device then work on any cell network?

Theoretically yes. The problem, however, with such a device is that to fit in all those different LTE frequencies, you might have to take out older non-LTE technologies. This is similar in principle to how Sprint is removing WiMAX in its phones to "fit" LTE, with the idea being that you can only pack so much technology into one device. An LTE-only device might not be practical until the end of 2014 when all the major LTE networks reach near-nationwide status. Even then, the major carriers would probably also have to sign LTE roaming agreements, although there would be no reason to sign LTE roaming agreements if full-frequency LTE devices did not exist, so it's a bit of a chicken-and-egg problem. A roaming agreement is when two or more carriers using compatible technology allow their phones to get a signal on each other's networks.

Are there ANY carriers that have interoperable 4G LTE devices?

Yes - AT&T and T-Mobile, but this wasn't always the case. When T-Mobile first constructed its HSPA and HSPA+ networks, it used the AWS frequencies. By contrast, AT&T has used the PCS frequencies for HSPA and HSPA+. When T-Mobile announced that it would begin constructing an AWS LTE network in 2013, it also announced that it would be switching its HSPA and HSPA+ networks from AWS to PCS, thus putting T-Mobile's technologies perfectly in line with AT&T's technologies [5].

I am looking at a device that says it is compatible with 2100 MHz HSPA and/or 2100 MHz LTE. Does this mean that the device is compatible with AWS HSPA and/or AWS LTE?

No. If a device lists 2100 MHz without listing 1700 MHz it is referring to a totally different set of frequencies. The 2100 MHz frequencies use 1920-1980 MHz for uplink and 2110-2170 MHz for downlink [25] and are used internationally [26] [27].

Sources

1. Motorola DynaTAC 8000x. RETRO BRICK.

10. MetroPCS Launches World's First Commercially Available Voice Over LTE Service and VoLTE-Capable 4G LTE Smartphone. Aug. 7, 2012. MetroPCS Communications, Inc.

12. Rich Communication Suite (RCS) Initiative. Feb. 7, 2008. Ericsson.

14. Advanced Wireless Services (AWS) Spectrum. Mar. 29, 2005. Federal Communications Commission.

15. Broadband Personal Communications Service (PCS). FCC Encyclopedia. Federal Communications Commission.

19. Chris Helzer and Doug Hyslop. 700 MHz Band Analysis. May 6, 2010. Wireless Strategy, LLC.

23. The AWS RF challenge. Radio Frequency Systems (RFS).

24. Mark Hoffman. An Overview of Wireless Standards & Technology: Past, Present and Future. ACETEC.

26. Kent German. Finding a global phone. World phone guide. Updated Nov. 7, 2012 10:35 AM PST. CNET. ©CBS Interactive Inc.

27. Marguerite Reardon. Will 4G LTE devices ever roam internationally?. Mar. 12, 2012 1:51 PM PDT. CNET. ©CBS Interactive Inc.