  We map the ground-state ensemble of antiferromagnetic Ising model of spin-S
on a triangular lattice to an interface model whose entropic fluctuations are
proposed to be described by an effective Gaussian free energy, which enables us
to calculate the critical exponents of various operators in terms of the
stiffness constant of the interface. Monte Carlo simulations for the
ground-state ensemble utilizing this interfacial representation are performed
to study both the dynamical and the static properties of the model. This method
yields more accurate numerical results for the critical exponents. By varying
the spin magnitude in the model, we find that the model exhibits three phases
with a Kosterlitz-Thouless phase transition at 3/2<S_{KT}<2 and a locking phase
transition at 5/2 < S_L \leq 3. The phase diagram at finite temperatures is
also discussed.
