An effective way to confine the signal in its own coverage cell and reduce its interference in the other co-channel cells is to tilt a directional antenna beam pattern downward at certain angle. A typical antenna vertical beam pattern is shown in figure. When the beam pattern is tiled downward, the field strength received by a distant mobile unit diminishes. The average signal to interference ration in an interfered cell region interfered by a serving cell antenna site is improved by tilting the antenna gain pattern downward some predetermined amount. It must be understood that the signal-to-interference ratio in any way serving cell will increase if antenna beam pattern are tiled downward from other cell sites. This means that the degree of tilting of the antenna beam pattern at each cell site has to be especially chosen to reduce further co-channel interference in the system other than using directional antenna alone.
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