This is according to research published this month in Computer by a trio of researchers at Peking University that describes a sensing method based not on the conventional received signal strength (RSS) model—which provides information about an environment based on how that environment attenuates a signal—but on an alternative known as channel-state information (CSI), which provides a much richer picture of electromagnetic waves as they bounce around an indoor space.
RSS positioning has been around for about 15 years and was developed into a project called RADAR by researchers at Microsoft. Its operation is pretty crude. Take an indoor space, and then map it out according to WiFi signal strength at different locations. Stick all of this data into a table, and when it comes time to locate an actual device in that space, it's just a matter of matching the observed signal strength to the corresponding location in the table. It's cheap, at least.