An orthogonal chaotic vector shift keying digital communication scheme is presented. The main characteristics of the scheme are increased data transmission rates with greatly improved robustness and an increase in security of communications links because of the structure of the scheme and the nature of the message bearer. Compared with some existing schemes, for example, quadrature chaos shift keying (QCSK) reported in the literature, the noise rejection is improved by an increase in the `inter-symbolic separation`. Furthermore, a new method of characterising non-linear processing elements in complex communication schemes has been presented. Based on this, a simple modelling and evaluation method to determine the bit error rates of these schemes is derived. Various simulated results are presented to demonstrate these achievements.