  An important natural phenomenon surfaces that satisfactory synchronization of
self-driven particles can be achieved via sharply reduced communication cost,
especially for high density particle groups with low external noise.
Statistical numerical evidence illustrates that a highly efficient manner is to
distribute the communication messages as evenly as possible along the whole
dynamic process, since it minimizes the communication redundancy. More
surprisingly, it is discovered that there exist some abnormal regions where
moderately decreasing the communication cost can even improve the
synchronization performance. A phase diagram on the noise-density parameter
space is given, where the dynamical behaviors can be divided into three
qualitatively different phases: normal phase where better synchronization
corresponds to higher communication cost, abnormal phase where moderately
decreasing communication cost could even improve the synchronization, and the
disordered phase where no coherence among individuals is observed.
