LTE at 50 Mbps? Don’t hold your breath

Even though Verizon CTO Dick Lynch tried to stay away from the download-speed numbers game when we spoke to him recently about the company’s plans for Long Term Evolution, you can’t hide from the mainstream tech media’s need for simple figures for long. So it’s not a surprise to see a whole bunch of people taking the “LTE trial speeds of 50-60 Mbps” from Lynch’s presentation at the Mobile World Congress this week and running with that as a projected speed for Verizon’s eventual 4G wireless offering.

Our take? Don’t hold your breath waiting for those kind of speeds.

With the limited amount of spectrum Verizon has available at 700 MHz, a safer guess would be seeing them offering someting in the range of 10-15 Mbps download speeds — not revolutionary, but certainly a magnitude of order better than Verizon’s current pokey 3G offering.

So far, Lynch and Verizon won’t pin down any specifics of their planned deployments. But when they do, the key one to look for is the channel size — specifically, how wide of a channel Verizon will use to pump out that wireless LTE data. There’s a lot of wireless-physics details involved, but a simple rule of thumb is that for best results you want to deploy three equal-sized channels for maximum coverage and minimal interference. Since Verizon only has 20 Mhz of spectrum “depth” in its 700 MHz frequency holdings, the best it can probably hope for is 5 MHz channels — which is a far smaller pipe than the 20 MHz channels used for those 50-60 Mbps tests.

At the very least, Verizon’s aggressiveness on the LTE publicity front seems to have stirred the pot at AT&T, which announced the first tentative dates for its slower-paced LTE rollout. Motorola, which offers some good LTE info on its websites, didn’t get any of the Verizon infrastructure pie, with those deals going instead to Alcatel-Lucent and Ericsson.

The key line from the Verizon press release to remember should be this one:

These field trials have demonstrated download rates of 50 to 60 Mbps peak speeds, though actual average download results will not be determined until the commercial launch of the new Verizon Wireless LTE network.

That will be a number worth waiting to hear.

About Paul Kapustka

Paul Kapustka is a longtime journalist who has spent more than two decades covering the information technology business, Paul most recently has been focusing on mobility and how it has changed the computing and collaborative landscape. His newest project outside Mobile Enterprise 360 is a research and analysis operation called WiFi Journal. He is also editor in chief of Mobile Sports Report, which covers the intersection of mobile technology and sports business. Paul is also the founder of Sidecut Reports, a research firm that covered the emergence of 4G technology in the cellular marketplace.

Comments

  1. Arnon Kohavi says:

    Paul, I think Femtocells may allow higher data rates, as the channels can be re-used more efficiently. It will be interesting to see if that will be the case: obviously, my cable service will need to support 50mbps in the backhaul…

  2. @Arnon femtos may be a point solution but they don’t address the market need for fast mobile wireless, which users would likely want to see as a *replacement* for their current landline broadband.

    I could see power users wanting a femto but at what cost… if Verizon’s current femto is any evidence that means a few hundred for the femto, a couple hundred for an LTE device… and how much for LTE services? With data caps?

    Clearly… we need more details.

  3. 60 mbps shared among all users of the tower. heh

  4. Arnon Kohavi says:

    I think we need to separate between “nomadic” and “mobile”. Even in an iPhone, one “consumes” high data rate usually when one is stationary (difficult to walk/run staring at screen). So I, at least see a distinction between true mobile usage, that likely needs lower data rates, and nomadic usage, where WiFi & Femto Cells can do the trick.
    People/offices will not replace their DSL/Cable/Fiber with 4G because it will always be slower/more expensive and less reliable than a wireline+wifi solution. And the wireless carriers don’t have capacity for that.

  5. @Arnon I think you have some good points about nomadic/mobile use but not sure I agree with the second part; Towerstream is already doing pretty well using WiMax to replace or undercut T-1 lines; not only is it usually cheaper it’s faster to install and more scalable/flexible if you need to move offices.

    It also looks like Clearwire may offer more products along the lines of their prototype WiMax/Wi-Fi router — a portable answer to the distinction in your first point. The tradeoff may be whether the mobility is more attractive than the reliability/speed of a wired connection.

  6. Brett Glass says:

    There’s this little, minor law of Information Theory called Shannon’s Law which governs how fast you can transmit data reliably over a given amount of spectrum. And it makes it rather doubtful that you could get 50 Mbps out of LTE. On the other hand, private (not municipal) wireless ISPs like myseif are doing 50 Mbps right now. And we can continue to do it so long as municipal networks don’t eat up the available spectrum and interfere.

  7. In any case, these speeds are the raw bit rate of the channel, not the net, loaded performance of a user application.

    Our tests of 3G cellular suggest that no more than a third of the channel rate is really delivered to a give user on average. I see no reason to believe we will see better numbers from LTE.

    Or WiMax for that matter.

    Also, the bit rate is closely coupled to the cell size as well as the channel size.

  8. So if we look at a best case of “172.8 Mbit/s for 2×2 antennas for every 20 MHz of spectrum” (from an Agilent whitepaper) and then divide that into 3 channels,per the author, and then divide by 3 per Ken Biba’s comment, we’re looking at 19Mb down in the best case of a 5km cell, quickly falling to 10mb if the cells are further apart. That sound about right?

    @Ken Biba: how many users/cell does your divide by 3 rule hold? just 3 as it might imply?

  9. @Chris the math is not that simple. As Ken states there are questions about network load and app performance. As Brett notes the real-world performance of other wireless technologies makes the LTE claims suspect.

    My main point is — Verizon and AT&T really don’t have enough spectrum *depth* right now to run anything bigger than 5 MHz channels. And if you look at the Motorola chart in this post:

    http://www.sidecutreports.com/2009/03/24/motorola-mobile-lte-demos-coming-at-ctia/

    You see 5 MHz channels at best will deliver about 7.85 Mbps on the download. At best. So — PLEASE don’t hold your breath for 50 Mbps over LTE. It isn’t going to happen soon enough to save you if you try.