Application of narrow-beam antennas and fractional loading factor in cellular communication systems

It is well known that cellular system capacity can be increased by reducing the cell cluster size N. Reducing the cluster size, however, increases cochannel interference. In recent years, several techniques have been proposed for controlling the cochannel interference and simultaneously reducing the cluster size. In this paper, we combine two proposed capacity improvement methods and explore the effectiveness of reducing cochannel interference using narrow-beam antennas ("smart antennas") with the fractional loading factor. As shown in this paper, it is possible to increase capacity by many times by decreasing the cluster size (i.e. increasing frequency reuse), although the proper combination of antenna specifications and fractional loading is surprisingly nonintuitive. The first cochannel mitigation technique uses base-station antennas with narrow beams in the direction of the desired mobile stations and significant side lobe attenuation in the direction of undesired users. The second technique exploits the fact that interference is related to the loading factor p _ch, which defines the probability that a given channel is in use within a cell. We show that large capacity gains with respect to a reference cellular system (N = 7, three sectors per cell) can be obtained by combining these two techniques. This paper provides insight for system-level deployment of high-capacity cellular systems and can be extended to fixed wireless systems as well.