Both T-Mobile ("America's Largest 4G Network") and Verizon Wireless ("The Fastest, Most Advanced 4G Network in America") have been running TV commercials for their now-available 4G services, leading to all kinds of confusion in the marketplace as to just exactly what 4G is anyway.
3G (officially, IMT-2000) has had the advantage of a formal definition from the International Telecommunications Union (ITU), that being 144 Kbps when moving at highway speeds, 384 Kbps when moving not so fast, and 2 Mbps when not moving at all or indoors. The ITU also publishes a list of qualifying technologies. As it turns out, the ITU has also now formally defined 4G, technically known as IMT-Advanced, with performance ranging from 100 Mbps when moving to 1 Gbps when not. I have been repeatedly on record as taking a position against defining any class of wireless technology by throughput due to the always-present differences between peak and actual speeds, said actual speeds always being much lower due to the vagaries of radio propagation (the most important of which is various forms of fading extant as a function of the geometry and range between transmitter and receiver), protocol overhead, and traffic congestion, among other artifacts. Users are regardless left feeling somewhere between uneasy and cheated by such specsmanship. I prefer a definition of 4G as follows: wireless, mobile, broadband, all-IP, with support for time-bounded traffic (via CoS prioritization). All-IP is the critical element here, and required to match the evolution of services on wire. But note again that there is no mention of throughput in my definition - throughput will always vary with the above-noted factors, as well as carrier policies that could define CoS by how much a given subscriber is willing to pay - more money, and one gets to the head of the queue more often subject, of course, to reasonable fair-access rules. Implying any kind of throughput without a corresponding SLA has no meaning at all, and carriers don't want to provide SLAs again for obvious reasons. Regardless, advances in radio technology continue to result in the potential for higher throughput, but I think such will most often be realized as higher overall capacity rather than a given user necessarily getting more bits per second.
But as we now have a formal definition of 4G from an authority that seems empowered to provide such definitions, it's important to point out that there are no 4G technologies meeting this definition today. The ITU has certified LTE-Advanced and a formalized specification of the yet-to-be-ratified IEEE 802.16m standard known as WirelessMAN-Advanced as qualifying as 4G. But what about Clearwire's (resold by Sprint) Clear WiMAX, formerly (informally) 3.5G? And how about T-Mobile's HSPA+, formerly (informally) 3.75G? And how about Verizon's (and soon AT&T's) LTE, formerly (and, again, informally) 3.9G? All of these are marketed as 4G today, and, of course, all have different footprints and performance than can differ geographically, temporally, and, as above, just because. And, perhaps surprisingly, WiMAX is recognized as a 3G technology, and not 4G, by, you guessed it, the ITU.
OK, it's not unusual for marketing definitions to vary significantly from their formal technical counterparts. As long as customers understand, just as has the case with every G, that a class-based definition in no way implies interoperability, all should be right with the world, and the inevitable shakeout and a variety of technological evolutions will occur regardless. I'm again on record as saying that LTE will dominate in the 4G (marketing definition) space, eventually capturing 80% of the market, but still leaving plenty of opportunity, on a global basis, for HSPA+ and WiMAX. How well the proponents of the latter two capitalize on this opportunity remains to be seen; the two-year lead famously claimed by the WiMAX crowd has now most certainly evaporated. 2011 is going to be a big year for LTE, but I'm not expecting critical mass (enough coverage and service for reliable businesses access) until 2014 or so. And real, official 4G? It's not even on the radar screen. My guess is perhaps 2020 or so.
And then there's the issue of what I have been calling the 98-Mbps gap between 3G and the formal definition of 4G. I'm not sure the ITU is doing itself any favors here by creating definitions like this, although they do vaguely refer to "Enhanced IMT-2000" from time to time. Regardless, if they want to be the authority here, they need to eliminate inconsistencies and obvious issues like what to call systems that operate between two and 100 Mbps. We can, of course, ignore definitions here for the most part, using the "if it looks like a duck and quacks like a duck it's a duck" rule. But marketplace confusion is never a good thing, especially when customers are being asked to commit to pricey, long-term strategies.