  Direction-of-arrival (DOA) estimation refers to the process of retrieving the
direction information of several electromagnetic waves/sources from the outputs
of a number of receiving antennas that form a sensor array. DOA estimation is a
major problem in array signal processing and has wide applications in radar,
sonar, wireless communications, etc. With the development of sparse
representation and compressed sensing, the last decade has witnessed a
tremendous advance in this research topic. The purpose of this article is to
provide an overview of these sparse methods for DOA estimation, with a
particular highlight on the recently developed gridless sparse methods, e.g.,
those based on covariance fitting and the atomic norm. Several future research
directions are also discussed.
