Frequency spectrum is a limited and therefore precious resource, as a finite number of radio frequencies must support a rapidly expanding range of spectrum uses. In this resource-constrained environment, one of the biggest concerns is how LTE, operating primarily in the licensed spectrum, can co-exist with incumbents, such as industrial, scientific and medical users in the unlicensed bands. The key is determining how to do this efficiently and reliably without obtruding on existing users of the unlicensed channels.
