LTE in Unlicensed Spectrum

Mobile broadband traffic loads are increasing rapidly which is leading to the need for additional radio spectrum to satisfy the demand. LTE networks are mostly deployed in spectrum from 700 MHz to 2.6 GHz. While LTE mobile broadband in licensed spectrum is highly efficient due to its exclusive occupancy of the spectrum, the amount of available licensed spectrum can be limited and expensive.

The amount of unlicensed spectrum (especially in the 5 GHz band) assigned or currently planned to be assigned is comparable to, or even more than, the amount of licensed spectrum available. Many operators have already deployed Wi-Fi access points to offload some cellular traffic to the unlicensed spectrum bands.

LTE is currently the most advanced mobile technology and many operators are upgrading their networks to LTE and planning a roadmap toward LTE-A. LTE operating in licensed spectrum will be the main deployment, but to further expand LTE capacity to meet future traffic demands, proposals are underway to adapt the LTE air interface to operate in the unlicensed spectrum.

Extending LTE-A to unlicensed spectrum is the latest in a series of innovations to address the challenge in the growth of mobile data. Bringing LTE-A to unlicensed spectrum is a basic concept but with many benefits. It involves taking advantage of the large number of small cells that are being deployed and employing CA (Carrier Aggregation) of unlicensed spectrum with the licensed spectrum. The existing core network is unaffected and in essence, the whole system works as a unified LTE network to take advantage of the capacity of both licensed and unlicensed spectrum bands efficiently.

Since bringing LTE-A to unlicensed spectrum is an alternative to carrier Wi-Fi, the effect on existing Wi-Fi networks is an important consideration. LTE in unlicensed spectrum must be designed to coexist harmoniously with Wi-Fi and in many cases it may be a better neighbour than Wi-Fi itself. The 3GPP is studying the coexistence of both technologies, while conforming to all the regulatory requirements of the different spectrum bands.