Channel sampling. The users first place ▇▇▇▇▇ and ▇▇▇ and the distance between their NIC cards is < 5cm. A user then starts the TDS program on ▇▇▇▇▇ and makes ▇▇▇▇▇ an initiator. ▇▇▇▇▇ sends a message to other devices and ask them (including ▇▇▇▇▇) to start listening to a same public WiFi source. Current WiFi standard uses orthogonal frequency-division multiplexing (OFDM) and there are 56 orthogonal subcarrier signals to carry data on parallel data streams. Hence at a same time, the CSI measurement of a WiFi source includes up to 56 sample values from different sub-carriers. Figure 5 shows samples of amplitude values from three sub-carriers of a same WiFi source. Note that ▇▇▇▇▇ and ▇▇▇ have highly correlated sample values, but ▇▇▇’s measurement is very different to theirs.
Appears in 2 contracts
Sources: Authentication and Key Agreement, Authentication and Key Agreement