  Multi-point vehicular positioning is one essential operation for autonomous
vehicles. However, the state-of-the-art positioning technologies, relying on
reflected signals from a target (i.e., RADAR and LIDAR), cannot work without
line-of-sight. Besides, it takes significant time for environment scanning and
object recognition with potential detection inaccuracy, especially in complex
urban situations. Some recent fatal accidents involving autonomous vehicles
further expose such limitations. In this paper, we aim at overcoming these
limitations by proposing a novel relative positioning approach, called
Cooperative Multi-point Positioning (COMPOP). The COMPOP establishes
cooperation between a target vehicle (TV) and a sensing vehicle (SV) if a LoS
path exists, where a TV explicitly lets an SV to know the TV's existence by
transmitting positioning waveforms. This cooperation makes it possible to
remove the time-consuming scanning and target recognizing processes,
facilitating real-time positioning. One prerequisite for the cooperation is a
clock synchronization between a pair of TV and SV. To this end, we use a
phase-differential-of-arrival based approach to remove the TV-SV clock
difference from the received signal. With clock difference correction, the TV's
position can be obtained via peak detection over a 3D power spectrum
constructed by a Fourier transform (FT) based algorithm. The COMPOP also
incorporates nearby vehicles, without knowing their locations, into the above
cooperation for the case without a LoS path. The effectiveness of the COMPOP is
verified by several simulations concerning practical channel parameters.
