ief as the system grows. The other sign to look for is the blocking level itself. If the system is reaching satu- ration 1 percent of the time, then we can look at its traffic levels and deduce the CDMA carrier capacity from the traffic engineering principles in Chap. 23. If 10 percent more traffic will raise blocking rates to unacceptable levels with that capacity, then we know it is time to grow the system. 41.2 Adding Power If a base station is running out of power in the forward direction, then a bigger power amplifier may offer capacity relief. Clearly, this is only an option when the reverse di- rection is showing no signs of stress and no signs of impending overload. It does not make sense to spend a lot of money for a shiny new power amplifier only to find the user terminals running out of their transmit power and losing calls anyway. We can only consider adding power in the forward direction if more power is avail- able. We can increase power in two ways, buying a bigger amplifier or using more am- plifiers. When smaller cells are added to a system, we often use smaller power ampli- fiers because their coverage range seems less important. Even for a larger cell, we may have decided to use amplifiers of one average power level, with the expectation that a few base stations might require more power and need a bigger amplifier. The other ap- proach is to divide and conquer, to use separate amplifiers for separate carriers. If a base station's architecture allows it, then we will often put multiple carriers on a sin- gle power amplifier because it saves a lot of money. When that amplifier is no longer powerful enough, we can separate the carriers onto their own amplifiers. Depending on the combining technology available, we may be able to keep the same antenna with multiple-transmit-power amplifiers. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at t