Line of Sight
Will LTE-U/LAA Clobber Wi-Fi?

Will LTE-U/LAA Clobber Wi-Fi?

Some carriers are already using carrier-grade Wi-Fi to offload high-speed data. (Image courtesy of Thinkstock).

Have you heard of this latest development in cellular technology? LTE-U is Long-Term Evolution in the Unlicensed spectrum. LAA is Licensed-Assisted Access, another name for a similar technology. LTE-U is the older term while LAA is the new, now more accepted term for the technology. Another term you will hear is LWA or LTE/WiFi Aggregation, a similar technology.  I will use LAA here.

LAA is a method of using the 5 GHz unlicensed Wi-Fi and other spectrums for LTE cellular data.  The big question is whether LAA will interfere with Wi-Fi access points (APs) and hot spots messing up millions of Internet connections. So far, there is an ongoing battle between the cellular carriers and the Wi-Fi interests over the potential deployment of LTE in the unlicensed spectrum.

The fact is that the cellular operators have run out of spectrum, or almost. There are few options for gaining more spectrum needed to expand user capacity and increase data speeds for faster video streaming and other activities. Operators can look forward to a 2016 FCC auction of spectrum, but that means paying billions for a small chunk of new spectrum. Even the main players—AT&T, Sprint, T-Mobile, and Verizon—have trouble spending that kind of money. As a result, they have been eyeing the possibility of using some of the available unlicensed spectrum. This can help the carriers roll out their small-cell LTE Advanced networks.  In the U.S., the unlicensed spectrum in the 5 GHz band is the target—specifically the Unlicensed National Information Infrastructure (U-NII) assignments. Some segments of interest in the U.S. are 5150-5350 MHz and 5470-5850 MHz.  That’s over 500 MHz of bandwidth that can be divided up into 20 MHz LTE channels. Very tempting. There are similar assignments in Europe and Asia. The big problem is that Wi-Fi uses some of this spectrum.

Some carriers are already using carrier-grade Wi-Fi to offload some high-speed data. This mode allows network offload if a nearby Wi-Fi AP is available. You have to wonder if this is just not working well or if the carriers just changing directions.

Most Wi-Fi is in the 2.4 GHz band; 802.11a uses 5 GHz, but it was never popular. Now the latest 802.11ac uses 2.4 and 5 GHz. I am not sure what percentage of Wi-Fi connections use 5 GHz, but it is obviously growing. Can LAA co-exist with Wi-Fi?  Some say yes, others say no.  The real answer is probably, with the right technology.

LAA is just one of a number of spectrum-sharing methods being used now with others in development or in test trials. You need to use cognitive radio technology to make it work. That means frequency-agile modems that can rapidly switch channels if interference is present. The other technology is listen-before-transmit or talk (LBT) or clear-channel assessment (CCA), where you switch to another channel if the current channel is being used. If those approaches can be made to work and power levels are managed, I suspect the LAA can be successful.

The Third-Generation Partnership Project (3GPP), the organization that develops the next cellular standards, is working on LAA right now to be incorporated into the forthcoming LTE Release 13. Companies like Ericsson and Qualcomm already have product in the works. The FCC seems to be staying out of this fight as long as current regulations are met. Some carriers say they will try to implement LAA in 2016 as part of their LTE-A small-cell systems using carrier aggregation. We shall see. If it works, it is just an LTE stop-gap along the path to 5G that is still years away.

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