Channel alternation and rotation for tri-sectored directional antenna cellular systems

Due to discrete reuse cluster sizes, disjoined and uniformed channel assignment, conventional tri-sectored cellular systems have not taken full advantage of antenna directivities. In this paper, we present a novel Channel Alternation and Rotation (CAR) scheme to coordinate channel assignment with antenna directivities. In CAR, cell layout is based on two-tier cell-reuse structure and each cell is allocated one extra channel set for channel alternations and rotations. The extra channel set gives network designer the flexibility to assign channels according to nearest front lobe interference avoidant strategy to enhance co-channel interference ratio (CII). CAR allows deployment of smaller, non-integer reuse cluster sizes based on CII requirements, thus increases frequency reuse efficiency. CAR reuse plans can increase channel capacity up to 31.25% while still maintain comparable CII margins. CAR is simple and can be employed in any existing directional antenna system, Therefore, it truly does not impose any additional cost.