Write a note on power control
6. Write a note on power control.
Power Control: The power level can be controlled only by the mobile transmitting switching office (MTSO), not by the mobile units, and there can be only limited power control by the cell sites as a result of system limitations.
The reasons are as follows. The mobile transmitted power level assignment must be controlled by the MTSO or the cell site, not the mobile unit or, alternatively, the mobile unit can lower the power level but cannot arbitrarily increase it. This is because the MTSO is capable of monitoring the performance of the whole system and can increase or decrease the transmitted power level of those mobile units to render optimum performance. The MTSO will not optimize performance for any particular mobile unit unless a special arrangement is made.
Function of the MTSO: The MTSO controls the transmitted power levels at both the cell sites and the mobile units. The advantages of having the MSTO control the power levels are described here.
1. Control of the mobile transmitted power level. When the mobile unit is approaching the cell site, the mobile unit power level should be reduced for the following reasons.
a) Reducing the chance of generating inter-modulation products from a saturated receiving amplifier.
b) Lowering the power level is equivalent to reducing the chance of interfering with other cochannel cell sites.
c) Reducing the near-end-far-end interference ratio.
Reducing the power level if possible is always the best strategy.
2. Control of the cell-site transmitted power level. When the signal received from the mobile unit at the cell site is very strong, the MTSO should reduce the transmitted power level of that particular radio at the cell site and, at the same time, lower the transmitted power level at the mobile unit. The advantages are as follows.
a) For a particular radio channel, the cell size decreases significantly, the cochannel reuse distance increases, and the cochannel interference reduces further. In other words, cell size and cochannel interference are inversely proportional to cochannel reuse distance.
b) The adjacent channel interference in the system is also reduced. However, in most cellular systems, it is not possible to reduce only one or a few channel power levels at the cell site because of the design limitation of the combiner. The channel isolation in the combiner is 18 dB. If the transmitted power level of one channel is lower, the channels having high transmitted power levels will interfere with this low-power channel. The manufacturer should design an unequal power combiner for the system operator so that the power level of each channel can be controlled at the cell site.
3. The power transmitted from a small cell is always reduced, and so is that from a mobile unit. The MTSO can facilitate adjustment of the transmitted power of the mobile units as soon as they enter the cell boundary.
