  Recent works have considered two qualitatively different approaches to
overcome line-of-sight limitations of 3D sensors used for perception:
cooperative perception and infrastructure-augmented perception. In this paper,
motivated by increasing deployments of infrastructure LiDARs, we explore a
third approach, cooperative infrastructure perception. This approach generates
perception outputs by fusing outputs of multiple infrastructure sensors, but,
to be useful, must do so quickly and accurately. We describe the design,
implementation and evaluation of Cooperative Infrastructure Perception (CIP),
which uses a combination of novel algorithms and systems optimizations. It
produces perception outputs within 100 ms using modest computing resources and
with accuracy comparable to the state-of-the-art. CIP, when used to augment
vehicle perception, can improve safety. When used in conjunction with offloaded
planning, CIP can increase traffic throughput at intersections.
