LTE in unlicensed spectrum

LTE in unlicensed spectrum (LTE-U) is a proposal, originally developed by Qualcomm, for the use of the 4G LTE radio communications technology in unlicensed spectrum, such as the 5 GHz band used by dual-band Wi-Fi equipment. It would serve as an alternative to carrier-owned Wi-Fi hotspots.

LTE in Unlicensed spectrum (LTE-U)

LTE-U would allow cellphone carriers to boost coverage in their cellular networks, by using the unlicensed 5 GHz band already populated by Wi-Fi devices. T-Mobile and Verizon Wireless have indicated early interest in deploying such a system as soon as 2016. While cell providers ordinarily rely on the radio spectrum to which they have exclusive licenses, LTE-U would share space with Wi-Fi equipment already inhabiting that band – smartphones, laptops and tablets connecting to home broadband networks, free hotspots provided by businesses, and so on.

LTE-U is intended to let cell networks boost data speeds over short distances, without requiring the user to use a separate Wi-Fi network as they normally would. It differs from Wi-Fi calling; there remains a control channel using LTE, but all data (not just phone calls) flows over the unlicensed 5 GHz band, instead of the carrier's frequencies.

License Assisted Access (LAA)

Ericsson uses the term License Assisted Access (LAA) to describe similar technology. LAA is the 3rd Generation Partnership Project's (3GPP) effort to standardize operation of LTE in the Wi-Fi bands. It uses a contention protocol known as listen-before-talk (LBT), mandated in some European countries, to coexist with other Wi-Fi devices on the same band. The 3GPP's final determination of LBT's requirements is still under standardization.

LTE-U Forum

In 2014, the LTE-U Forum was created by Verizon, in conjunction with Alcatel-Lucent, Ericsson, Qualcomm, and Samsung as members. The forum collaborates and creates technical specifications for base stations and consumer devices passing LTE-U on the unlicensed 5 GHz band, as well as coexistence specs to handle traffic contention with existing Wi-Fi devices.

Controversy

The proposed use of LTE-U by mobile phone network operators is the subject of controversy in the telecommunications industry. Most notably, Google sent the Federal Communications Commission of the United States a 25-page protest, making an argument against LTE-U in highly technical detail. However, by its authors' admission on page 5 of the whitepaper, "Since LTEU equipment is not yet available, LTEU transmissions were emulated with a signal generator." Since Google's study did not use actual LTE-U equipment in the tests, some industry experts have called its conclusions into question, with one commenter calling the study "utterly artificial and speculative" and "embarassing".

The Wi-Fi Alliance and National Cable & Telecommunications Association (NCTA) also voiced opposition to LTE-U approval before more testing can be done, citing concerns that it would severely degrade performance of other Wi-Fi devices.

Subsequently, Qualcomm responded to the allegations made in Google's whitepaper in a detailed filing with the FCC. Qualcomm stated that it conducted tests that were "specifically designed to replicate (to the fullest extent possible) the test scenarios cited in Google’s FCC filing, in particular", and that they "collectively showed that LTE-U coexists very well with Wi-Fi when LTE-U is operating either above or below Wi-Fi’s Energy Detect ('ED') level." Qualcomm explained that the divergence in results was caused by the fact that "the testing the opposing parties conducted for LTE-U/Wi-Fi coexistence below the ED level utilized extremely pessimistic and impractical technical assumptions", whereas Qualcomm's tests were conducted "using a far more realistic setup", including actual LTE-U equipment (versus signal generators in Google's study).

See also

• LTE
• Mobile data offloading
• White spaces (radio)