Method of processing ambient radio frequency data for activity recognition

A building system comprising:

• a wireless radio device including a transmitting component configured to transmit a radio frequency (RF), and a receiving component configured to receive the RF to accomplish a primary task;
• and
• an activity recognition system configured to perform an activity recognition task, the activity recognition system including a sniffer configured to sample and measure ambient RF signals over time, control circuitry including one or more processors and one or more storage mediums, RF background data stored in at least one of the one or more storage mediums and indicative of no activity, a computer instruction stored in at least one of the one or more storage mediums and executed by at least one of the one or more processors, wherein the computer instruction is configured to process the measured ambient RF signals, subtract background from ambient RF data indicative of the ambient RF signals, convert the process ambient RF signals to a plurality of successive images, and apply an image-based algorithm to compare the plurality of successive images to the RF background data, and thereby determine activity recognition, wherein the noise content of the ambient RF data is reduced by removing a mean value of multiple Channel State information (CSI) subcarriers at the same time index to subtract common mode noise.