I recently read the rather interesting announcement from NTT DoCoMo where they demonstrated LTE running over the unlicensed 5GHz band. They report a 60% increase in spectral efficiency over IEEE 802.11n Wi-Fi. The article also noticed that LTE-U is now referred to as Licensed-Assisted Access using LTE or LAA-LTE. This caused me to pause, and think about several things.
The comparison between LAA-LTE and Wi-Fi is not (and should not be) about spectral efficiency. Rather it is about several other factors:
And if you really want to talk about speeds and feeds, it's interesting that the test was done against 802.11n, when 802.11ac is now widely available, providing speeds that exceed LTE-Advanced speeds of 1 Gbps (IEEE 802.11 ac Wave 1 provides maximum speed of 1.3 Gbps and Wave 2 provides maximum speed of 3.5 Gbps). It's also important to note that LAA-LTE has not been defined yet and so it's very likely that the LAA-LTE implementation tested here does not have the politeness mechanisms required in certain regulatory domains like Europe. These mechanisms allow fair usage of the unlicensed spectrum by allowing other users an opportunity to transmit and share the spectrum. These mechanisms already integrated into Wi-Fi will add additional overhead to LAA-LTE that will reduce its spectral efficiency, a factor that needs to be taken into account in any comparison.
Reality Check
Hype is interesting, butlet's take stock of where the industry is today. The main goal for LTE in unlicensed spectrum is to leverage the relatively large amount of unlicensed spectrum in order to provide a better mobile service. Given the transmit power restrictions imposed on unlicensed bands, it is expected to be primarily deployed in small cells. No standards exist for LTE in unlicensed spectrum. However, the mobile industry is discussing certain technical proposals. These describe an LTE carrier in unlicensed spectrum combined with a LTE carrier in a licensed spectrum using either carrier aggregation (CA) or supplemental downlink (SDL) where all control channels are on the licensed spectrum LTE carrier. Specifically, the industry proposals do not describe a "stand-alone" LTE in unlicensed spectrum system where there is no licensed LTE carrier. Operators will not be able to leverage someone else's unlicensed LTE hotspot, they will need to deploy their own (unlike with Wi-Fi). It cannot be overstated that LTE in unlicensed spectrum is meant as supplementary technology to LTE (which is by definition operable only in licensed spectrum).
I'll just conclude by noting that Cisco is supportive of the LAA-LTE initiative and is participating in 3GPP standards work on this topic. However, I don't think that LAA-LTE replaces carrier grade Wi-Fi because of the factors I mentioned earlier. As a result, it is vitally important for the industry that the LAA-LTE standard ensures fair usage of unlicensed spectrum with all other technologies using the same spectrum like Wi-Fi.
We contributed to the 3GPP workshop in June, and will work closely with the industry and in the standards to ensure that LAA-LTE co-exists with Wi-Fi in order to ensure that the global investment operators and Enterprises have made in Wi-Fi, in the billions of dollars, is enhanced by LAA-LTE, and not disrupted. It goes without saying that the mobile networks of the future will use all aspects of licensed and unlicensed bands and technology to deliver the best mobile experience possible in any given environment.
Tweet us @CiscoSPMobility if you have any questions about LTE.