Opportunistic Radar in IEEE 802.11ad Networks

In this paper, we study the feasibility of an opportunistic radar, which exploits the probing signals transmitted during the sector level sweep of the IEEE 802.11ad beamforming training protocol. Several solutions are presented to detect the presence of prospective obstacles and estimate their position, radial velocity, and backscattered signal amplitude, which differ in the amount of prior information as to the transmitted signal and the channel fluctuation. Also, we derive the Cramér-Rao bound as a benchmark for the proposed estimators: The derivation of these bounds is per se relevant, as it generalizes classical results to the case where the echo is not entirely contained in the observation window. Numerical examples are provided to assess performance of the proposed solutions. The results indicate that the close-to-one detection probability is achievable up to 90 m with a probability of false alarm of 1e-4 and Swerling-I target fluctuation; in this region, the target delay is estimated with an accuracy smaller than the symbol interval (corresponding to a range resolution smaller than 10 cm) with probability close to one, while the velocity estimate is generally quite poor as a consequence of the very short duration of the probing signal.