08-21-1996 - Laserfiche WebLink

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Figure 8 illustrates two types of cell configurations: the ornni cell configuration, used in rural area. and the sector cell configuration, used in urban areas. A Figure 8 CELL CONFIGURATIONS 2 • 2 Atli* 7© 1 10/ 6 4 opzi A5 12 OMNI CELL CONFIGURATION SECTOR CELL CONFIGURATION The omni cell configuration uses omni or whip antennas, antennas that emit signals in 360 degrees. Whip antennas do not lend themselves to frequency reuse as well as sector antennas. As a result, omni cell configurations are generally used in rural areas since these areas are sparsely populated and consequently do not need extra calling capacity. Urban areas, on the other hand, have denser. populations and require additional calling capacity to accommodate the system's greater number of users. The sector cell configuration provides this extra calling capacity by utilizing sector or panel antennas that divide the omni cell into three segments. The three segments use different frequencies, allowing greater reuse of the channels. Because they have the capacity to handle large volumes of calls, sectored sites are used particularly in areas near high vehicular activity such as freeways and major intersections. Although a cell site's radius depends upon its surrounding topography and its capacity to handle calls, cell sites in rural areas generally have a radius between five and eight miles, and cell sites in urban areas typically have a radius between two and five miles. Types of Cell Sites There are three basic types of cell sites: 1. Coverage sites serve to expand coverage in large areas or in areas with difficult terrains and to enhance coverage for portable systems. These sites allow users to make and maintain calls as they travel between cells. 2. Capacity sites serve to increase a site's capacity to handle calls when surrounding sites have reached their practical channel limits. 16