Detection performance of security system using radio waves based on space-time signal processing

We proposed the indoor event detection system with signal subspace spanned by eigenvector for office or home security. The system monitors a whole room or home with only a pair of transmitter and receiver. The receiver uses an antenna array. We monitor events based on not received signal strength that is susceptible to noise but signal subspace spanned by eigenvector that is inherent to its environment. When an event (e.g. a person intrudes into a house) occurs, the propagation environment changes, and thus the signal subspace changes. Monitoring this change, we detect an event. The change of eigenvector tells us whether a person is in motion or remains motionless. We reported the principle of our security system and some fundamental detection performance of the system using dipole antennas arranged linearly or circularly as the receiver, although they are not necessarily arranged regularly. In this paper, we report various experimental detection results of the proposed security system using patch antennas set up on a box at the receiver such as intrusion, baggage stolen and the effect of outside of the room. Moreover, we evaluate the detection performance of the eigenvalue-based security system. We show that the eigenvalue-based security system can detect some events that the eigenvector-based security system cannot. Then we show that depending on application demands, using both the eigenvector and the eigenvalue for the security system is a promising technique.