Existing PHY-layer authentication

PHY-layer authentication exploits the physical layer information.

Received signal strength indicators
Received signal strength
Channel state information
Hardware fingerprints

All the PHY method mentioned above are based on the assumptions:

The test needs the known radio propagation and spoofing model
A large number of training data to get the test threshold

Moreover, the complexity and variability of channels in practical wireless environments, the PHY-layer authentication can't tell the difference between multiple users at the same time.