  This paper studies the problem of having mobile robots in a multi-robot
system maintain an estimate of the relative position and relative orientation
of near-by robots in the environment. This problem is studied in the context of
large swarms of simple robots which are capable of measuring only the distance
to near-by robots.
  We present two distributed localization algorithms with different trade-offs
between their computational complexity and their coordination requirements. The
first algorithm does not require the robots to coordinate their motion. It
relies on a non-linear least squares based strategy to allow robots to compute
the relative pose of near-by robots. The second algorithm borrows tools from
distributed computing theory to coordinate which robots must remain stationary
and which robots are allowed to move. This coordination allows the robots to
use standard trilateration techniques to compute the relative pose of near-by
robots. Both algorithms are analyzed theoretically and validated through
simulations.
