March 4, 2016 | by Wayne Smith

Unlicensed Spectrum LTE (LTE-U)

The specifications for LTE were published in the 3rd Generation Partnership Project’s (3GPP) Release 8. LTE-A specifications were published in Release 10. Now there is a high likelihood that LTE-U specifications will be published in Release 13 due out late in 2015. The 3GPP stated it is motivated to ensure this technology is frequency agnostic, can be deployed indoors and outdoors and can co-exist with WiFi and other networks.

LTE in unlicensed spectrum (LTE-U) is a proposal to use LTE-A radio communications technology in the unlicensed spectrum such as the 5 GHz band currently occupied by dual-band WiFi technologies. LTE-U is also referred to as Licensed-Assisted Access (LAA) LTE. Currently a number of access technologies such as 802.11 (WiFi), 802.15.1 (Bluetooth) and 802.15.4 (ZigBee) are used in bands known as Unlicensed or Licensed-Exempt bands. LTE-U would serve as an alternative to carrier deployed WiFi. Several radio equipment manufacturers like Qualcomm, Alcatel-Lucent and Ericsson are pushing for the new standard. T-Mobile and Verizon have both expressed interest in this technology, and see it as a possible future small cell solution.

LTE-U technology uses the same air-interface and evolved packet core technology as LTE-A. Some LTE-A air-interface specifications will need modification in countries that require Listen-Before-Talk (LTB), but the USA is not one of these nations. Manufacturers claim that LTE-U is minimally disruptive to WiFi in the same band although LTE-A doesn’t have a politeness protocol like WiFI. WiFI is designed to back off if it senses interference from other users. This is a serious concern since the 3GPP has stated that it must be able to co-exist with other network technologies. If friendly co-existence between networks is enabled, LTE-U could be deployed in licensed and unlicensed bands almost seamlessly in the USA. LTE-A’s ability to aggregate carriers between the licensed and unlicensed frequency bands enables higher data rates, better efficiency and more robust mobility than WiFi. It basically provides a common technology across different cell sizes.

The proposed technology establishes new protocols that coordinate between primary and secondary cell interactions. Primary cells are licensed LTE-A cells and secondary cells are the unlicensed LTE-U space. The primary cell maintains the control functions between the two cells. The primary and secondary cells will share loads based on relative traffic volumes and capacities.

If LTE-U can be implemented in existing LTE networks seamlessly, it offers broadband providers a low cost avenue to implement small cell in-building and outdoor small cell networks. This is another solution to the never ending capacity growth problems networks are experiencing. It also opens the door to new marketing opportunities that are currently dominated by WiFi technologies. The question is, will this technology be deployed in the near future in the USA? T-Mobile already announced that it is deploying a Nokia LTE-U indoor product with expectations of outdoor deployment in late 2016.