Ovrrbu-bts. Pdf
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| AirLink 8000
1/30/00 BASE TRANSCEIVER STATION Release 1.00 2 - 14 antennas are relatively common for the 60º beam width. However, the number of sectors is not a fixed number as the system can accommodate different number of sectors as needed. The range of each cell is a function of traffic distribution. The system is designed so that the RBU power can be adjusted to control the nominal cell/sector range from 100m to 30 km. Of course the maximum cell size is dependent on prevailing topography and other environmental conditions and acceptable bit error rate. This system is likely to suffer minimal capacity degradation under a single frequency reuse pattern for the following reasons: -- The directional antennas and fixed application provide the flexibility to setup the RBU and SU antennas so as to minimize interference, something that cannot be achieved with systems using omni SU antennas. An SU is more likely to suffer interference from an adjacent cell rather than an adjacent sector. -- Alternating reverse antenna polarity reduces adjacent sector interference along common boundaries. -- Synchronous CDMA inherently reduces interference effects by rejecting signals outside the time slot (chip boundary). This effect is further enhanced by randomization of the P/N codes. -- The ability to adjust the RBU power to meet the needs of the cell size without sacrificing capacity reduces interference from adjacent cells. -- The system is code limited, not noise or interference limited. Hence there is a buffer for additional interference from adjacent sectors without degrading the capacity. The combined effect of all these factors is that the system can be used in a multi-sectored cellular architecture with just one frequency pair to provide exceptionally high traffic carrying capacity. The following table illustrates different scenarios for load carrying capacity of a single RBU system. The Load Density column indicates the traffic that could be carried with cells sectorized as indicated with one RBU per sector per cell. The actual number of subscribers per RBU is limited to 2,500. Thus in the limit, the system could serve a subscriber density of 460,000 per km2 (which should be more than sufficient for even the most densely populated cities). In the more common urban scenarios with a cell radius of 500m and with a relatively high traffic load of 0.1 Erlangs per subscriber (for a total of 1,000 subscribers per RBU), the system can serve a subscriber density of 9,200 subscribers per km2. All of the numbers stated above are for single frequency re-use. Higher traffic densities can be served with multiple frequency pairs. Thus the system has sufficient margins to serve high subscriber densities even when the traffic carrying capacity is somewhat degraded due to adverse environmental conditions. Scenario Cell Radius Sectors Area/Sector Capacity Load Density Metro 100m 6 (60º) 0.00433 km 2 100 Erlangs 23,000 Erlangs/km 2 Urban 500m 6 (60º) 0.10823 km 2 100 Erlangs 920 Erlangs/km 2 Suburban 1 km 6 (60º) 0.433 km 2 100 Erlangs 230 Erlangs/km 2 Rural 10 km 1 (omni) 314.16 km 2 100 Erlangs 0.32 Erlangs/km 2 |