Direction of arrival estimation based on a mixed signal transmission model employing a linear tripole array

Direction of arrival (DOA) estimation is an important topic in array signal processing. Currently, most research activities are focused on the single signal transmission (SST) type of signals, i.e. only one physical signal is used to carry the information from a transmitter to a receiver with a given polarisation setting. However, to make full use of the degrees of freedom in spatial domain, signals based on the dual signal transmission (DST) model are more and more widely used, i.e., two signals with different polarisations carrying different information are employed for communication between the transmitter and the receiver. But there is rarely any work on DOA estimation of DST signals. Motivated by such a problem, the paper proposes two methods for DOA estimation of signals based on a mixed signal transmission (MST) model, i.e., a mixture of SST and DST signals. The first method provides a two-step solution and estimate the DOA of the SST signals first and then the DST signals second. The second method estimates the DOA of all signals in one step. Moreover, CRB (Cramér-Rao Bound) for the estimation model is derived to evaluate the performance the proposed methods.