I had an interesting discussion with Bill Warner earlier this week in which he asked what was the real difference between 3G and 4G. He referred me to a blog post he'd written in early November in which he concluded it was just jargon. Yes, there is a lot of jargon and, as of December 6th, the formal definition is a moving target but there are two potential answers, one focused on technology and one based on ITU definitions.
On the technology side, the biggest difference between 3G and 4G is the way the information is carried on the radio waves. Like the difference between AM and FM (amplitude modulation and frequency modulation) for broadcast radio, mobile phone systems use some newer, very sophisticated digital modulation schemes that happened to be called CDMA and OFDM. The mobile operator's core network has also evolved. Specifically:
- 3G -- uses CDMA modulation and a hybrid core network that treats voice and data differently,
- 4G -- uses OFDM modulation (in some cases with SC-FDMA on the uplink) and an All-IP core network. Note that while OFDM and SC-FDMA sound very different, they use extremely similar computational structures in the silicon chips on which these systems are built.
The ITU answer is more political. Until the ITU began to cave into marketing hype in a December 6th press release, the ITU defined 4G as a downlink capable of 100 Mbps to a moving device (auto & train speeds) and 1 Gbps to a fixed or slowly moving device (pedestrian speeds).
The two candidate systems for 4G (prior to 6 Dec 2010) were LTE-Advanced and WiMAX 802.16m -- both systems that are still in development and likely years away from widespread deployment.
After their press release, things got a lot muddier... Quoting that press release:
IMT-Advanced is considered as “4G”, although it is recognized that this term, while undefined, may also be applied to the forerunners of these technologies, LTE and WiMax, and to other evolved 3G technologies providing a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed. The detailed specifications of the IMT-Advanced technologies will be provided in a new ITU-R Recommendation expected in early 2012.
So suddenly, the stuff the mobile operators are currently touting (today's WiMAX & LTE) is to be considered "4G" even though it falls far short of what was originally envisioned as 4G. Put another way, the ITU has accepted the technology definition. If it's all-IP and it uses OFDM modulation, it's 4G.
[OFDMA/OFDM correction 3-Jan-2011 - Thanks Franz]