  Currently, most of existing research in direction of arrival (DOA) estimation
is focused on single signal transmission (SST) based signal. However, to make
full use of the degree of freedom provided by the system in the polarisation
domain, the dual signal transmission (DST) model has been adopted more and more
widely in wireless communications. In this work, a DOA estimation method for a
mixture of SST and DST signals (referred to as the mixed signal transmission
(MST) model) is proposed. To our best knowledge, this is the first time to
study the DOA estimation problem for such an MST model. There are two steps in
the proposed method, which deals with the two kinds of signals separately. The
performance of the proposed method is compared with the Cram\'{e}r-Rao Bound
(CRB) based on computer simulations.
