  Extremely large-scale antenna arrays (ELAA) play a critical role in enabling
the functionalities of next generation wireless communication systems. However,
as the number of antennas increases, ELAA systems face significant bottlenecks,
such as excessive interconnection costs and high computational complexity.
Efficient distributed signal processing (SP) algorithms show great promise in
overcoming these challenges. In this paper, we provide a comprehensive overview
of distributed SP algorithms for ELAA systems, tailored to address these
bottlenecks. We start by presenting three representative forms of ELAA systems:
single-base station ELAA systems, coordinated distributed antenna systems, and
ELAA systems integrated with emerging technologies. For each form, we review
the associated distributed SP algorithms in the literature. Additionally, we
outline several important future research directions that are essential for
improving the performance and practicality of ELAA systems.
