Matrix Method for Multiple Wireless Orthogonal Frequency-Coded SAW Sensor Tags Identification

Reflected signals from multiple wireless surface acoustic wave (SAW) sensors are generally asynchronous, which causes difficulty in simultaneous identification of multiple SAW sensor tags. This paper proposes a matrix method for multiple SAW sensor tags identification based on orthogonal frequency code (OFC). The characteristics of ideal overlapped signals from multiple OFC SAW tags are analyzed. According to the analysis, the amplitudes and the phases of the overlapped signals with the same center frequency from the identical reflector positions of different tags can be measured. A matrix equation for the relationship between the measurable values and the amplitudes delay of signals from each tag is presented. Tag identification is accomplished by solving this matrix equation. According to the characteristics of this matrix equation, the maximum number of simultaneous identifiable tags is roughly equal to the square of the number of selectable matching frequencies of reflectors. A set of simultaneous identifiable tags are selected. All tags randomly chosen from this tag set can be identified correctly by the simulation test. This result verifies that the matrix method for multiple OFC SAW sensor tags identification is feasible in theory.