  The spatiotemporal information plays crucial roles in a multi-agent system
(MAS). However, for a highly dynamic and dense MAS in unknown environments,
estimating its spatiotemporal states is a difficult problem. In this paper, we
present BLAS: a wireless broadcast relative localization and clock
synchronization system to address these challenges. Our BLAS system exploits a
broadcast architecture, under which a MAS is categorized into parent agents
that broadcast wireless packets and child agents that are passive receivers, to
reduce the number of required packets among agents for relative localization
and clock synchronization. We first propose an asynchronous broadcasting and
passively receiving (ABPR) protocol. The protocol schedules the broadcast of
parent agents using a distributed time division multiple access (D-TDMA) scheme
and delivers inter-agent information used for joint relative localization and
clock synchronization. We then present distributed state estimation approaches
in parent and child agents that utilize the broadcast inter-agent information
for joint estimation of spatiotemporal states. The simulations and real-world
experiments based on ultra-wideband (UWB) illustrate that our proposed BLAS
cannot only enable accurate, high-frequency and real-time estimation of
relative position and clock parameters but also support theoretically an
unlimited number of agents.
