What is LTE-LAA?
LTE-LAA (Licensed Assisted Access) is an LTE-Advanced Pro feature defined in 3GPP Release 13 that enables mobile operators to aggregate licensed LTE carriers with carriers operating in the 5 GHz unlicensed spectrum band. LAA uses Listen-Before-Talk (LBT) channel access to coexist fairly with Wi-Fi and other unlicensed band users. The licensed carrier serves as the primary cell (PCell) providing reliable connectivity, while the unlicensed carrier acts as a secondary cell (SCell) providing additional capacity.
How Does LTE-LAA Work?
LAA implements a contention-based channel access mechanism called LBT (similar to Wi-Fi’s CSMA/CA) to ensure fair sharing of the 5 GHz band. Before transmitting on the unlicensed channel, the eNB performs a Clear Channel Assessment (CCA) — listening for energy on the channel. If the channel is free, the eNB transmits for a maximum Channel Occupancy Time (COT). LAA initially supported downlink-only operation (Release 13); enhanced LAA (eLAA, Release 14) added uplink transmission on unlicensed carriers. The licensed anchor carrier ensures control plane reliability and is always available, while the unlicensed carrier provides opportunistic additional throughput. LAA supports 20 MHz carrier bandwidth in the 5150–5925 MHz range.
Use Cases
Urban capacity enhancement in high-density areas, enterprise and venue small cell deployments, supplemental downlink/uplink using unlicensed 5 GHz spectrum, Wi-Fi offload alternative using LTE technology, and operator spectrum augmentation without new licensed spectrum acquisition.
3GPP / Standards Reference
3GPP TS 36.211/213 (Release 13+ — LAA physical layer), 3GPP TR 36.889 (Study on LAA), ETSI EN 301 893 (5 GHz harmonised standard)
Related Terms
Carrier Aggregation | LTE-Advanced Pro | LTE | FDD | TDD
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