Rel-13 License Assisted Access
R10-based LTE-U cannot be adopted in markets such as Europe or Japan where there are additional unlicensed band regulations, on the channel occupation limit often known as “Listen-Before-Talk” (LBT), minimum bandwidth occupancy, etc. To provide a single global framework that would also work in these markets, 3GPP has started working on Rel-13 LAA (Licensed-Assisted Access). In addition to the LBT regulation, LAA will also meet other regulatory requirements such as transmit Power Spectral Density (PSD) and the channel occupancy bandwidth requirement in Europe. Preserving coexistence with other unlicensed technologies including Wi-Fi is a requirement for Rel-13 LAA.
The LAA design will conform to LBT regulations specified in ETSI EN 301 893 via the Clear Channel Assessment (CCA) procedure. Load-Based Equipment (LBE) design uses enhanced CCA (eCCA) procedures and enables robust LAA operation to coexist with Wi-Fi in the same band as illustrated in the figure below. Note LBT alone is not sufficient to guarantee coexistence and fair sharing with Wi-Fi in all scenarios and additional scheduling techniques are needed.
In addition to LBT via CCA procedure, it is envisioned that Rel-13 LAA would modify existing DL and UL LTE waveforms, add discovery signals to support unlicensed band discovery and access, add beacon signals to reserve the channel for transmission following CCA success and modify HARQ protocol to support asynchronous operation.
3GPP approved LAA as a Rel-13 Study Item (SI) in September 2014. The SI scope covers both Supplemental DL (SDL) and DL/UL CA. The SI is expected to conclude by June 2015 followed by a Work Item. 3GPP Rel-13 completion is expected in the first half of 2016.
Qualcomm plans to showcase Rel-13 LAA SDL aggregation at MWC 2015. The demo uses multiple LAA prototype small cells and UEs based on Qualcomm’s proposal for LAA design, which includes the new waveforms supporting LBT via CCA. While user experience and network capacity are increased by using LAA, co-channel coexistence and fair sharing with Wi-Fi is also showcased.