Mobile working Toolkit

Story: Mobile broadband working group replaced

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LTE (Long Term Evolution) 4G is being defined and is agreed on the use of OFDMA for the downlink and SC-OFDM for the uplink. This is a major shift for the leading cellular efforts from CDMA to an OFDM base of technologies.

The IEEE usually defines standards based on evolution of technologies to serve specific needs. It doesn't usually set out to define two competing camps that use very similar sets of technologies. When 802.20 was first proposed it was defined for 'high speed wireless broadband. At the time, 802.16 was oriented to be the wireless metro area network - wireless Ethernet that extended across a wide swatch of frequencies and was not focusing on mobility. So, 802.20 was set up to develop OFDM solutions for 'high speed' applications while 802.16 (WiMAX) was mandated for applications up to 120 kph. The fact that the 802.16 effort was so focused on fixed-nomadic applications stemmed from the make up of the companies involved: specialist WBB companies with few inputs from incumbent cellular suppliers. That vacuum left the slot open for 802.20 to be proposed for mobile applications... albeit on the contention that it was for high speed, not a duplicate of WiMAX.

But several companies (Flarion included) communicated in the group that they could extend 802.20 to apply to nomadic, portable, and low speed mobile applications as well. In other words, they set out early on to ignore the mandate of being focused on 'high speed'. OFDM can be 'optimized' to be used for fixed or for mobile applications using the same framework system. 802.16 needed to shift to use of OFDMA in order to provide that flexibility. And all of the advanced systems are embarking on increased use of MIMO-AAS (MAS), adaptive modulation and other technologies needed to enhance bandwidth and performance.

LTE looks very likely to use SC-OFDM (single carrier OFDM) on the uplink because this provides a way to spread energy to reduce PAPR - peak to average power ratio. That is because the user's handset or other device has less power than a base station. WiMAX uses SOFDMA (scalable OFDMA) on both the up and down links and seeks reduction of power by using advanced power regulation, adaptive modulation and a more granular network topology than is typical of cellular systems.

These systems are enormously complex and use several sub-sets of technology that vary somewhat and can be optimized to trade off for bandwidth, power, and distance. But the fact is that they are all trending toward a similar basket of core technologies. The expression of these systems will have more to do with how they are used (the systems 'architecture') and the applications that ride on top of them than the core technologies themselves. Those nuts and bolts are things to write about but end users don't know or care as long as they deliver cool services.

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