Compact Reformed Input and State Filter and its Application to Decryption Circuit Design

Recently, an alternate approach of simultaneous input and state estimation (ASISE) was proposed for linear time-invariant continuous-time stochastic systems. This new method employs a system reformation technique to transform the original system into one that can reflect all online estimable unknown inputs in the measurement equation. Consequently, a reformed input and state filter (RISF) is derived as the center filter of the ASISE, which potentially reduces the computational complexity of the estimation. This study further proposes a practical design for a compact RISF (CRISF). The potential application of the proposed CRISF to design a secure communication system is also addressed.