The explicit solution of the filtering problem with exponential criteria for a general Gaussian signal is obtained through an approach which is based on a conditional Cameron-Martin type formula. This key formula is derived for conditional expectations of exponentials of some quadratic functionals of a general continuous Gaussian process. The formula involves conditional expectations and conditional covariances in some auxiliary optimal filtering problem which is used in the proof. Closed form equations of Ito-Volterra and Riccati-Volterra type for these ingredients are provided. Particular cases for which the results can be further elaborated are investigated. Author for correspondence. Fax: +33 2 43 83 35 79. 1
Marina L. Kleptsyna, Alain Le Breton, Michel Viot