This blog is by Antti Toskala, head of Radio Standardization at Nokia Networks.
LTE is already the most versatile mobile radio access technology (RAT) ever created. It is available on more licensed frequency bands than any other RAT, using both Time Division and Frequency Division Duplexing, and with carrier aggregation delivering speeds that would have seemed far-fetched just a decade ago. LTE is even being readied for machine-to-machine communications in the form of LTE-M, with 3GPP Release 12 defining (and Release 13 continuing the work) simplifications to the LTE modem to reduce complexity and cost.
Now, a new flavor of LTE is being looked at by 3GPP. Dubbed LTE-U, this would run over unlicensed spectrum, especially the 5 GHz frequency band. Complementing licensed band LTE operation, LTE-U would make much-needed capacity available to operators, particularly in hotspots and corporate environments. The official term in 3GPP is License Assisted Access (LAA) for LTE, to highlight the aspect of working together with licensed band operation.
Already, the idea is causing heated debate across the industry – see this LinkedIn discussion, for example.
So, what’s the problem? Well, unlicensed spectrum has long been the preserve of Wi-Fi. Wi-Fi is well established, low cost and embedded in billions of devices. On the other hand, LTE is spectrally more efficient to deliver a larger capacity bang, offers dynamic off-loading, delivers greater coverage for the same power, and is easy to integrate into an operator’s existing radio networks. Such advantages are leading some people in the industry to think that LTE-U could kill off Wi-Fi in the long run.
While understandable, that fear is unfounded: LTE-U and Wi-Fi can co-exist nicely – they will be friends, not foes.
A prime aim of the standardization work is to ensure that LTE-U and Wi-Fi will coexist on the same unlicensed bands. When running LTE and Wi-Fi on the same 20 MHz carrier, both networks should use Listen-Before-Talk to check that the available channel is free before transmission occurs. This doesn’t mean it’s always possible to transmit immediately if the intended channel is occupied, but it allows the two technologies to co-exist smoothly. Furthermore, the interference of an LTE network on a Wi-Fi network is no different to the interference caused by another Wi-Fi network.
LTE-U is intended for public indoor cells, outdoor hot spots or corporate environments where LTE licensed networks provide coverage, but where additional capacity would be beneficial. The 3GPP work will not define LTE-U as a stand-alone system: LTE-U will only be used in conjunction with a Primary Cell, which ensures the connection is maintained and always located on the licensed band carrier. LTE-U will not cover residential use.
LTE-U is clearly an attractive solution to tap the unused potential of the 5 GHz spectrum, and 3GPP Release 13 is expected to include support for LTE operation on the unlicensed band. It should be ready by mid-2016, then 3GPP will define the necessary bands and band combinations to be used with the 5 GHz band.
So LTE is about to add yet another trick to its repertoire and, if implemented correctly, is ready-made to help operators implement substantial added capacity where it’s most needed – in the busiest hotspots.
I don’t think there’s any question that LTE-U and Wi-Fi will become BFF – Best Friends Forever.
Read our Whitepaper “LTE for unlicensed spectrum” here.
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