Evaluation of WiFi beacon transmissions for wireless based passive radar

Wireless transmissions are a potentially powerful and widely available source of transmissions for passive radar detection. In this work we have carried out a detailed study on the use of IEEE 802.11 (WiFi) transmissions in a passive radar system. The WiFi transmission sequence has been found to be complex and dependent on the user environment but is dominated by direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM) signals. An ambiguity function analysis of the DSSS based WiFi beacon signal has been carried out followed by field measurements using a wireless based passive radar system. Range and Doppler characterization of this system is reported and compared with the theoretical predictions. Detection of moving human targets has been achieved for the first time using 802.11 transmissions. This work shows that this technique has considerable promise for a low cost and widely deployable detection and tracking system.