The current state of mobile networks is that we use 2.5G and 3G networks—mid-second-gen and newer third-gen data protocols. On the Verizon and Sprint side, known as CDMA, 2.5G is referred to as 1XRTT, or just 1X. On the AT&T and T-Mobile side, GSM, the 2.5G flavor is EDGE. Verizon and Sprint’s 3G is EVDO, while AT&T and T-Mobile have HSDPA (you might not know that one, since they usually just say “3G”).
Second gen wireless was basically just the leap to a digital network, and third gen is a closer attempt at true mobile broadband—kind of. Right now, with their 3G networks, they can all get you typical speeds of around 1 Megabit per second downstream, give or take (though the specs are rated for peak speeds of 3Mbps down on EVDO Rev. A, and 3.6 on HSDPA). 3G has a bit of breathing room left in it—EVDO Rev. B is capable of downstream speeds of 14.7Mbps , while the current HSDPA spec will go up to 14.4Mbps downstream with the right equipment, and depending on how far down the HSPA spec sheet you wanna go, maybe even faster.
But the fourth generation is already on its way. Technically, no wireless technology is officially 4G. But that’s what everybody’s calling WiMax and Long-Term Evolution, because they both promise crazyfast mobile internet speeds that leave the current 3G in the dirt. In the US, the main WiMax player is Clearwire, which Sprint owns 51 percent of after they combined their operations into one company and actually gave WiMax a chance to live. LTE is championed by AT&T (which makes sense because it was developed initially by companies who mainly build GSM networks like AT&T and T-Mobile’s). Verizon also selected LTE, which blew everyone away at first because Verizon isn’t in the GSM camp, but it makes sense because Verizon’s parent company, Vodafone, is gung-ho for LTE in Europe, where everyone’s on GSM.
WiMax and LTE, use the same fundamental technology, they both use orthogonal frequency-division multiplexing access and they’re both IP (internet protocol) based. More simply, you can kind of think of the difference between WiMax and LTE as a software, not a hardware thing (kind of like Macs and PCs using the same Intel chip). Alcatel-Lucent, who makes the 4G wireless hardware, is actually building hardware that is on a common platform. In fact, some point in the future it’s possible to harmonize”LTE and WiMax.
Here’s what the fundamental difference is: Time division duplexing versus frequency division duplexing. AT&T TDD is like CB radios or walkie-talkies—when one person is talking, the other person can’t talk. The same channel is used for downstream and upstream, so the transmission is divided up over very tiny increments of time. Clearwire’s says they currently use a 2/3 downstream and 1/3 upstream split, so 2/3 of the time, you’re swallowing data, and 1/3 of the time. With LTE, it’s more like a modem or phone conversation. It separates the available bandwidth into two parts—one operating downstream full time, and one operating upstream—so you both can talk back and forth at the same time.
The special think about WiMax and LTE is, how fast can they really get. The amswer is, The channel width. LTE and WiMax use really fat wireless channels, so they can move a lot of data at once. For example, peak speed for LTE in 10MHz is about 140Mbps and peak speed in 20MHz is about 300Mbps. The thing about them being OFDM is that it makes them more flexible than 3G, since they can use a wide range of spectrum—LTE can use anything from the 1.4MHz channel up through 20MHz—whereas current 3G always uses 5MHz.
WiMax is no slouch either, technically capable of up to 72Mbps.
Another thing about those superfat channels is that they don’t reach as far out from the tower, and your response drops (obviously) as you get farther away. They’re going to need to build more cell sites. That’s why building out 4G is very pricey. If you thought 3G rollout was slow, 4G might be slower.
Here’s what the real-soon-future looks like: Verizon isn’t dicking around, and is doing commercial rollouts of LTE in 2010, while AT&T is following up with their commercial trials in 2011. (AT&T says Verizon “is in a big rush to move to LTE because their 3G technology gives them no room” to increase bandwidth and that red is a stupid color, nyah nyah nyah.) Clearwire has rolled out WiMax to a few cities already, and plans to have 120 million covered by the end of 2010. Verizon says they’re getting about 60Mbps in testing, but expect it to be more like cable modem speeds when it launches—like Clearwire has now. For the reasons we mentioned above, and also because there won’t be devices that can handle that kind of ridiculous speed—as you probably guessed, battery life being a major reason.
Will one standard eventually beat the other into submission, slinking away into the night, arm and arm with Betamax and HD DVD? Well, LTE does have a lot of momentum—the two biggest carriers in the US are rolling with it, and as part of the GSM family, you can bet all of the GSM carriers all over the world will be on board. In fact, there’s no real technological reason to pick one over the other and just like now where multiple technologies exist for economic reasons, it’ll be the same thing with WiMax and LTE.
