w, or the signal is weak, or the receiver cannot resolve the errors even with forward error correction (FEC) in place. If the radio conditions change too rapidly, then the power-control loops can get caught by surprise and leave some errors in the bit stream. Data errors may be a symptom of parameters set with too much optimism. If a data service is supposed to have a BER of 10-5, then we should add some margin to this BER for CDMA channel environmental factors, particularly changes in the channel en- vironment. The inner and outer power-control loops set Eb/No based on BER and set power to achieve Eb/No. If the power-control setting for BER is too high, even if it is lower than the true target BER, then the CDMA channel will exceed the true target BER from time to time. We need some headroom, some extra BER margin, to ensure adequate error rates in a changing CDMA radio environment. A wireless service provider in 3G CDMA is a data service provider. And that data ser- vice comes with subscriber expectations of performance. We may have to spend some more money, and therefore charge some more money, to meet those expectations. How- ever, this probably makes more sense than selling inferior service that falls short of sub- scriber expectations. If we fall short of subscriber expectations, no matter how low the price, people will talk about our system, and what they say is not likely to be very nice. 40.7 Reasons for Change and Growth There are several reasons to modify and expand a wireless telephone system. We can fix quality and capacity problems, anticipate growth in demand, provide new services, anticipate change in service mix of demand, or upgrade equipment. These activities are distinct from repairing equipment that breaks, but repair and improvement can be co- ordinated to work well together. The easiest reason to change a wireless telephone system is to fix something that is wrong with it. In these discussions we are not writing about repairing equipment that Downloaded from Digital Engineering Library @ Mc