he same antenna face that transmits the desired signal is transmitting most of the interference as well, SO the rake filter does not discriminate between signal and same-sector interferers. Unlike soft handoff, there is no way to tweak parameters to adjust the multipath loss. The only way to minimize the multipath problem is to avoid multiple radio paths. If we know where our demand is located, then we may be able to select base station lo- cations and sector plans to minimize alternative radio routing. In-building microcells and picocells, for example, could mitigate the multipath problem. 30.4 Power Control and Pilots The CDMA equations assume perfect power control. Even the aggressive combination of open-loop and closed-loop systems used in CDMA systems is not going to do a perfect job of managing the near-far problem. As we said in Sec. 8.5, this is seldom an issue of having enough power. Rather, the issue usually is managing the relative power levels of a user terminal community. Thus, adding a 1.5-dB margin to the power-control process does not add 1.5 dB of safety; rather, it reduces the capacity of the carrier by 1.5 dB, which is 40 percent. This is primarily a problem in the reverse direction. When a user terminal experi- ences a sudden change in its radio signal path, when going into a building, for exam- ple, its signal to the base station is suddenly far worse in comparison with its interfer- ers. The more rapidly radio signal paths change, the greater is the impact on the reverse link. While the forward signal path to the user terminal is also reduced, the interfering signals from the same antenna face are similarly reduced, SO the effect is less pro- nounced. There is still a need to increase forward power to maintain adequate signal quality, but the urgency is not so great. The cdmaOne system has a faster power- control loop for the reverse link than for the forward link for this reason, whereas Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright 