T-Mobile, working with Ericsson, will trial Licensed Assisted Access (LAA) in 2015. LAA, which is also known as LTE-Unlicensed, uses spectrum in the unlicensed 5GHz band aggregated with licensed spectrum to increase network capacity in the downlink. This trial should help answer questions about the effectiveness of LTE in unlicensed spectrum and encourage greater support for the technology to be used in LTE-A networks.
Supporters of LTE LAA hope the positives outweigh the concerns
LAA for LTE has quickly gained momentum over the last 12 months. T-Mobile and Ericsson aren't alone in their interest in the technology. NTT DoCoMo and Huawei demonstrated it in mid-2014. Other vendors like Alcatel-Lucent, Nokia, Qualcomm, and ZTE have also been involved in the study of the technology. This bodes well when it comes to developing a possible mobile ecosystem needed for LAA to flourish.
The benefits of LAA are fairly obvious. First, 5GHz can provide mobile operators with access to hundreds of MHz of extra spectrum at no cost. Aggregating this spectrum with licensed spectrum can significantly increase the speed of the downlink connection. Ericsson estimates that using only 4% of the existing 5GHz band could increase LTE downlink speeds by 150Mbps.
We have already seen mobile operators adopt carrier aggregation as their first step towards deploying LTE-A. LAA is really just another form of carrier aggregation, as LAA has to be used in conjunction with licensed spectrum. Licensed spectrum would handle the call control functions, with 5GHz being used as a capacity boost. As the licensed and unlicensed spectrum will need to be coordinated, and 5GHz has limited range, most likely LAA will only be used with small cells such as Ericsson's RBS 6402 pico cell. Having the control plane functions confined to licensed spectrum limits LTE LAA to only existing licensed spectrum owners.
Like any new technology, there are concerns. Qualcomm's support for LAA doesn't guarantee device vendors will support it. To get device vendors onboard, operator interest will need to extend beyond T-Mobile. Broader operator support will no doubt hinge on T-Mobile's trial. Can T-Mobile and Ericsson show that LAA actually doesn't interfere with Wi-Fi, which currently uses the 5GHz band as well? If LAA interferes with Wi-Fi you can be sure government regulators will come down hard on LAA and halt its progress. The 3GPP recognizes this concern and is working to ensure there is no interference between LAA and Wi-Fi, but LAA isn't fully standardized and won't be until 2016.
The Coming of LTE Advanced Networks, TE0006-000933 (September 2014)
Daryl Schoolar, Principal Analyst, Intelligent Networks