  Free space optical communication has been applied in many scenarios because
of its security, low cost and high rates. In such scenarios, a tracking system
is necessary to ensure an acceptable signal power. Free space optical links
were considered unable to support optical mobile communication when nodes are
randomly moving at a high speed because existing tracking schemes fail to track
the nodes accurately and rapidly. In this paper, we propose a novel tracking
system exploiting multiple beacon laser sources. At the receiver, each beacon
laser's power is measured to estimate the orientation of the target. Unlike
existing schemes which drive servo motors multiple times based on consecutive
measurements and feedback, our scheme can directly estimate the next optimal
targeting shift for the servo motors based on a single measurement, allowing
the tracking system to converge much faster. Closed-form outage probability
expression is derived for the optical mobile communication system with ideal
tracking, where pointing error and moving statistics are considered. To
maintain sufficient average power and reduce the outage probability, the
recommended size of a source spot is expressed in closed form as a function of
the target's statistics of random moving, providing insights to the system
design.
