Ovrrbu-bts. Pdf
tải về 0.71 Mb. Chế độ xem pdf
|
- Điều hướng trang này:
- 1.6.6 System Capacity
| AirLink 8000
1/30/00 BASE TRANSCEIVER STATION Release 1.00 2 - 13 It is not always desirable to have an extended range. In a dense urban or even a suburban setting, one needs to deploy the system in a cellular architecture as depicted below. To reduce interference between sectors and between cells in such a deployment, one needs to limit the range of an RBU - overall as well as selectively in specific directions. Such range control may be accomplished using directional master antenna at the RBU as well by controlling overall RBU power. This system has been designed with a dynamic range control of 100m to 30 km. Hence in a dense urban setting with need for pico-cell deployment, the RBU range can be pulled back to as low as 100m. In an overlay network with scattered users or in a semi-rural setting the range may be extended to 30 km and beyond. Of course the actual range that can be realized depends on site specific conditions. 1.6.6 System Capacity As mentioned before, the system is rated to provide at least 100 simultaneously active 32kbps channels using 3.5 MHz bandwidth in each direction. Traffic engineering based on the nature, distribution, holding time and other parameters would determine the number and type of subscribers that can be put on a single RBU. Traditional cellular deployment involving sectors, cells, and multiple frequency pairs is the most pragmatic approach to increase capacity in presence of limited spectrum availability. A typical 6 sector cell layout is depicted below with reverse circular polarity. There are three main parameters to consider when designing the cellular layout — range of each cell, number of sectors in each cell, and the frequency reuse pattern (in adjacent sectors and cells). If a number of frequency pairs are available, it is best to use different frequencies in adjacent sectors to minimize co- channel interference. However, unlike the analog and TDMA systems, the system does function with minimal capacity loss even with one frequency pair. In any situation, additional frequency pairs will increase the overall traffic carrying capacity of the system. The number of sectors is a function of traffic to be carried, actual distribution of traffic, and the antenna availability and cost. To reduce adjacent sector interference reverse circular polarization is recommended with adjacent sector antennas having alternating Right Hand (RHcp) and Left Hand (LHcp) circular polarity. This alternating circular polarity provides an additional 6 dB separation, thereby decreasing adjacent sector interference. For uniformly distributed traffic, a 6 sector approach is recommended as LHcp RHcp LHcp RHcp RHcp LHcp Six sector hexagonal cell layout with reverse circular polarity in adjacent sectors |