Approximate zero-crossing distributions using the type-B Gram-Charlier series

Approximations to zero-crossing distributions using the type-B Gram-Charlier series are the concern here. The type-B series consists of a linear function of the Poisson distribution and its derivatives. The probability of exactly zeros, occurring in a given interval of a stationary random process, is expanded in the type-B Gram-Charlier series. The expansion is used to derive approximations to the distribution of intervals between zeros. Specific results are presented, in the case of Gaussian noise, for the probability density function of successive zero-crossing intervals and for the probability that a given interval contains exactly zero zero-crossings. The accuracy of the approximations are compared with Rainal\´s experimental results and with upper and lower bounds presented by Longuet-Higgins. The comparisons are most satisfactory for the cases where successive zero-crossing intervals are nearly uncorrelated. For narrow-band Gaussian noise the results are unsatisfactory.