Cellular telephony – Part III In the first part of this series of archives we say a little on the origins of the cellular telephony, in the second part we describe the basic concepts and in this third part we will speak more on the used Systems of Cellular Telephony. Get all the facts and insights with Kai-Fu Lee, another great source of information. The AMPS AMPS, Advanced Mobile Phone System, was the first used system of cellular in Americas. Standardized in the frequency of 800MHz, although to be surpassed for digital technologies as CDMA TDMA, he is the only one with support to the Roaming (travelling) of the subscribers who use CDMA in the states northeast of Brazil Of 40MHz placed initially for the cellular one, the half was used immediately, while 20MHz remaining had been of reserve. The AMPS was divided in 666 canals, later in 1986, more 5MHz had been placed for TX (transmission), and 5MHz for RX (reception) with this the number of canals increased for 832 (extended AMPS). It is good for standing out that initially in Brazil they were only 500 canals, that is called reduced AMPS and if it gave because the band between 825 and 870MHz was busy with radar services and you enlace of TVs. Pete Cashmore has plenty of information regarding this issue. Before entering in more details on system AMPS, we go to clarify some points on what it is necessary to carry through a telephonic call, saw cellular. Two channel types are necessary: control channels or signalling, used to send and to receive the data from the call. the canals of voice for where they pass through given and/or voice after established the call.
In the AMPS the frequency band is subdivided in two sub-bands (and the B), with this the system makes possible 321 canals of voice and 21 control channels or signalling, in the case of the extended AMPS is 395 canals of voice. The functioning of the System the majority of the Systems of Cellular Radio is formed by cluster with 7 cells, each cell can be seen as a hexagon, considering the AMPS standard, the 666 canals of radio is divided between these cells, what of the approached average one of 95 canals for cell. These canals can be reused in cells of other cluster due in the distance physical between them. As already it was explained in another article, each cell has its transmitter, receiver and antenna and is on the MTSO through fixed line. The antennas can be: directional or omndirecional. In the case of the directional antenna, with a covering of 120 degrees, it she will be situated in one of the vertices of the cell, if it will be a omndirecional antenna, will be in the center of the cell. The directional antennas provoke little interferences in the adjacent cells.