| 摘要 |
<p>A microcellular communications network includes a plurality of base station units (106) and corresponding antenna units (102). The base station units are housed in a common location (114). Each includes either conventional transmitters and receivers or all digital transmitter and receiver equipment, and interface circuitry (112) to a mobile telecommunications switching office (110). The microcell traffic output is applied to a frame generator/multiplexer. The output of the frame generator/multiplexer is applied to a digitally modulated laser. The laser output is conveyed by fiber to a remote antenna unit, which demultiplexes the microcell traffic signal and applies it to a digital-to-analog converter. The output of the digital-to-analog converter is applied to a power amplifier, which in turn is connected to a main antenna. RF signals from the mobile units are received at both a main and a diversity antenna. The received signals are filtered, digitized, multiplexed together and transmitted over the optical fiber back to the base station. The strongest signal is selected for use. Deployment of an all digital microcellular communications system occurs in two stages. The method thus allows for the benefit of a digital system to be accomplished in the early stages of the upgrade while without the expense of modifying the digital microcell antenna units in the second stage of the upgrade. Digital filtering of the digitized RF signal is also provided, so that only those channels associated with a cell are extracted for transmission to and from the antenna unit, and a digital passive handoff system provides for an FFT analysis of all traffic in the cell and passive switching in response thereto.</p> |
