In radio networks, refarming is the process of transitioning a specific radio frequency band from one technology or use, to another.
In mobile networks, it is common to upgrade from older technologies to newer ones (3G to 4G, etc.) Typically, there is an extended transition period where two or more generations of technology are deployed (and active) at one time. This ensures that older customer devices continue to work even if they don't support the newer technology. However, different technologies generally cannot operate simultaneously at the same exact frequencies, in the same geographic area.
Carriers may deploy new technologies using new radio frequency bands (newly purchased and/or newly made available by the government) or using bands they already own and use with older technologies. In the latter case, it is called refarming.
Even when a new technology is initially deployed using a new band, the carrier will eventually want to phase out the older technologies in existing bands, replacing them with the newer technology (refarming) as well. This is because older technologies are generally less efficient, so moving all radio bands and all customers to newer technologies lets the carrier make the best use of its radio license assets, and offer better mobile service to more customers.
Radio frequency bands for phones are typically sub-divided into blocks. Each block is owned (licensed) by a specific company (carrier) in a given geographic area. These blocks are further sub-divided into channels. This allows a carrier to transition the blocks they own from one technology to another in phases, by assigning a certain portion of channels to the new technology, while leaving other channels on the old technology, and changing that mix over time. This is a gradual refarming.
Refarming can also be done more abruptly, if the carrier has sufficient capacity where the older technology is still deployed in other bands, or if the company is prepared to switch off the older technology altogether.