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​What is 4G?

This is a question that I have discussed with perhaps hundreds (literally) of people throughout the mobile wireless industry over the last 5 years or so. ABI Research considers today's WiMAX (802.16e) and LTE technologies to be 4G. Some people in the industry agree with us on this, and others disagree. Now that the ITU has officially accepted 802.16m and LTE-Advanced as IMT-Advanced technologies, this issue has come up again. What makes it more confusing is that where the ITU mostly referred to IMT-2000 and IMT-Advanced in the past, they are including "3G" and "4G" with these groupings, respectively. WiMAX and LTE, in ABI Research's opinion, are still 4G technologies. Here is why:

Designation of technology generations (1G through 4G) are used to describe different types of air interfaces. They are grouped like this:

  • 1G - analog, frequency division
  • 2G - shift to digital, frequency + time division [TDMA]
  • 3G - frequency + code division [CDMA]
  • 4G - orthogonal frequency division [OFDMA] (and offshoots of OFDMA)
It has been argued that some of the criteria to meet IMT-2000 or IMT-Advanced are arbitrary, such as the data rate - why 100 Mbps and not 107 Mbps or 39 Mbps? It's just a number - a number that is necessary to set a threshhold to meet a goal, but it does not change what the technology fundamentally is.

Within 2G, technologies in a family are compatible. The latest iterations of EDGE can fall back to older iterations of EDGE, back to GPRS, and even back to GSM. Within 3G, it is the same. The most complex version of HSPA+ can fall back to a very simple and slower version of HSPA+, back to HSPA, back to HSDPA, and even back to WCDMA. EV-DO Rev B can fall back to Rev A and back to Rev 0. (It can even fall back to CDMA 2000 1x, because it is based on CDMA.)
All 2G air interfaces are based off of a form of TDMA. All 3G air interfaces are based on a form of CDMA. WiMAX and LTE are not based on CDMA, but rather OFDMA.

Of course, WiMAX and LTE do not meet IMT-Advanced specifications. WiMAX 2 (802.16m) and LTE-Advanced, however, do meet IMT-Advanced specifications. 802.16m can fall back to 802.16e, and LTE-Advanced can fall back to LTE. So if the IMT-Advanced-compliant versions are 4G, then today's WiMAX and LTE technologies surely must be 4G technologies as well, because they are forward and backwards compatible. A 4G technology cannot fall back to a 3G technology - that is impossible.

As a background, it was the WiMAX Forum who lobbied hard to get WiMAX (802.16e) accepted as an IMT-2000 technology. It is not because the WiMAX Forum thought it was also a 3G technology. It has to do with a different reason - spectrum. The WiMAX Forum wanted the possibility and potential of WiMAX to have access to IMT-2000-designated spectrum. The 3GPP pushed for LTE to be accepted as an IMT-2000 technology as well.

Some people will say that dual-carrier HSPA+ with 64 QAM with MIMO can go faster than today's initial WiMAX technologies. Yes, they can. But it is not just about speed, but about the combination of speed, latency, capacity, and cost/MB. There is where WiMAX and LTE are different. More importantly, it is more about the fundamental radio technology being used.

Some people describe 1G through 4G as marketing terms. They are certainly used as marketing terms because they are easier to grasp than "IMT-2000" or "IEEE 802.16e." But they are more than just marketing terms, because engineers and product managers use "3G" and "4G" as well, since they are shorter to say and align very well with the fundamental technologies behind them.

WiMAX and LTE are based on OFDMA and are something completely different from the 3G technologies on the market. They have room for improvement in their current form, but as their IMT-Advanced versions develop and come to market, today's 4G technologies will not be left stranded because they will be compatible with the coming IMT-Advanced-compliant 4G technologies.

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