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Cellular Moves Into Unlicensed Bands

February 20, 2018

Author: Bob Wheeler

After years of development and regulatory battles, LTE is finally moving into unlicensed spectrum—specifically the 5GHz band. The first deployment, by T-Mobile, uses the LTE-Unlicensed (LTE-U) specification, which predates the 3GPP’s Licensed Assisted Access (LAA) standardized in Release 13. Both versions supplement one licensed LTE anchor carrier with a 5GHz downlink. In 2017, Release 14 specified enhanced LAA (eLAA), which adds 5GHz uplinks but still requires a licensed anchor.

Several mobile-network operators (MNOs) are focusing on LAA for 2018 deployments, with most bypassing the LTE-U precursor. Another industry ad hoc specification, MulteFire, allows operation solely in unlicensed spectrum, forgoing the licensed anchor. It enables private networks operated by an enterprise or by a so-called neutral host: an operator that lacks licensed spectrum.

Separately, regulators are opening up new spectrum around 3.5GHz, but in most regions, these bands will be licensed for 5G use. In the U.S., however, the FCC in 2015 established the Citizen Broadband Radio Service (CBRS) to permit sharing of 3.5GHz spectrum. Operators could employ the CBRS band in LTE carrier aggregation or in standalone fashion using TD-LTE.

Because most MNOs lack adequate licensed spectrum to deliver gigabit LTE, LAA provides a path to these speeds. Owing to the combination of power limits and poor propagation, however, 5GHz LAA requires the installation of small cells. CBRS is interesting because it offers higher power and less contention, which should improve range and quality of service. MNOs may skip LTE LAA, however, and instead use the 3.5GHz band for 5G. Similarly, 5G will probably overtake eLAA and will soon consume much of MNOs’ capital budgets.

Subscribers can view the full article in the Microprocessor Report.

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