Power Control in CDMA Systems

As discussed in class, power control is used in CDMA systems to limit the detrimental effects of multiple-access interference. It aims to ensure that signals transmitted by the mobiles arrive at the base station at the same power level. This problem addresses some of the network management aspects associated with power control.

1. Approximately how long does the received power level at the base station in a cellular communication network remain constant? On which parameters does your answer depend? What is a typical value for the time the received power remains constant?
2. What does your answer imply regarding the frequency with which power control commands have to be issued from the base station to a mobile?
3. Assume that the received power level can vary as much as 80 dB and that the received power level has to be controlled within 1 dB. How many bits are required at the minimum in a power control message?
4. Assume that power control commands are issued every 3 ms and that a power control message contains 10 bits. What is the required bit rate for power control message between the base station and a mobile? What is the total bit rate for power control messages if a base stations communicates with 100 mobile stations?
5. Explain why power control in the reverse directions, from the base station to the mobile, is much less of a concern.