| Following the communications develop rapidly and the telephone popular rate daily enhancement, when people set the telephone in the densely populated city or the mountainous area, will face the questions which are hard to be solved in lays down last section of subscriber's lines, the copper and the twisted pair wire at 4 - 5 kilometers length appears high loop circuit resistance, the communication quality can not be ensured, it costs too much time and labour force and it is expensives to layout lines in mountainous , the islands as well as citizens.In order to solve this so-called "the last mile, achieved the set rapidly, the price inexpensive , the WLL(Wireless Local Loop) appear such as a important part of AccessNetwork(AN) technology.AN is the implement system that between local switch and subscriber terminal, it may partial or completely replace traditional the user local network, it contains multiplexing, cross connection transfer fuction.t, which transmission medium has multiplicity, and nimbly supports each access type and bussiness. AN divides wire and wireless.Wireless access refers partly or completely adopt wireless method between switch point and subscriber terminal. The typical wireless access system is mainly controller, operation maintenance center, base depot, the fixed subscriber unit and the mobile termination and so on.The working frequency of 450MHz wireless access technology is 460.5-462.0MHz, central station launches 460.5-462.0 MHz terminal launch frequency band. It uses FDD wireless access system, which uses the FDMA technology, big area system network, covers area is big. The system may conveniently connects with the switchboard, provides the voice, facsimile, data transmission and so on. The control channel to dynamic allocation channels, the airborne command uses MSK modulation digital common channel in the system, which connect quickly. 450MHz wireless access technology is most widespread, mature wireless access solution at present. |
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