GSM POWER CONTROL
The fact that the distance from the mobile to the BTS can vary over such a wide range means that the power transmitted by both the mobile and the BTS can also vary greatly. Under the GSM rules, it is compulsory to use accurate power control on the uplink (i.e. mobile transmitting), but optional on the downlink. This is because the mobile generally needs to be as small and light as possible for commercial reasons (hence the battery needs to be small), but also to reduce interference on the uplink, which is normally seen as the more vulnerable side of the air interface link. On the downlink side, however, we have a BTS with unlimited mains power, and the BCCH carrier must be transmitted at full cell power at all times anyway, so many networks do not use downlink power control.
The BTS and the mobile both measure the level of signal they receive, and these measurements are compared with the maximum and minimum limits set by the network operator. Bearing in mind that the BTS is constantly transmitting at full power, if the BTS received signal level from the MS is too high or too low, then the MS is ordered to adjust its output accordingly.
0 Comments