  This paper proposes a method for designing BS clusters and cluster patterns
for pair-wise BS coordination. The key idea is that each BS cluster is formed
by using the 2nd-order Voronoi region, and the BS clusters are assigned to a
specific cluster pattern by using edge-coloring for a graph drawn by Delaunay
triangulation. The main advantage of the proposed method is that the BS
selection conflict problem is prevented, while selected users are guaranteed to
communicate with their two closest BSs in any irregular BS topology. With the
proposed coordination method, analytical expressions for the rate distribution
and the ergodic spectral efficiency are derived as a function of relevant
system parameters in a fixed irregular network model. In a random network model
with a homogeneous Poisson point process, a lower bound on the ergodic spectral
efficiency is characterized. Through system level simulations, the performance
of the proposed method is compared with that of conventional coordination
methods: dynamic clustering and static clustering. Our major finding is that,
when users are dense enough in a network, the proposed method provides the same
level of coordination benefit with dynamic clustering to edge users.
