Ng JY, Tan CP, Trinh H, and Ng KY. 2016. A Common Functional Observer Scheme for Three Systems with Unknown Inputs. Journal of the Franklin Institute, vol 353, no 10, pp 2237-2257.
Ng JY, Tan CP, Ng KY, and Trinh H. 2015, New Results in Common Functional State Estimation for Two Linear Systems with Unknown Inputs. International Journal of Control, Automation, and Systems, vol 13, no 6, pp 1538-1543.