  A new particle acceleration process in a developing Alfv\'{e}n turbulence in
the course of successive parametric instabilities of a relativistic pair plasma
is investigated by utilyzing one-dimensional electromagnetic full particle
code. Coherent wave-particle interactions result in efficient particle
acceleration leading to a power-law like energy distribution function. In the
simulation high energy particles having large relativistic masses are
preferentially accelerated as the turbulence spectrum evolves in time. Main
acceleration mechanism is simultaneous relativistic resonance between a
particle and two different waves. An analytical expression of maximum
attainable energy in such wave-particle interactions is derived.
