.1 and determine optimal power levels. The live system has to try power levels, make measurements, and send corrections. This is a two-way street because the user termi- nal has to make its own measurements and send its own power instructions. In AMPS, the base station measures the received power of the mobile telephone, computes the ra- dio path gain, and instructs its own radio and the mobile telephone what power levels to use. This kind of inference is not good enough for CDMA. In CDMA, we determine the need for power-level adjustment by looking at the sig- nal quality, as measured by the error rate. How do we measure signal quality in CDMA? The forward error-correction systems provide bit error rate (BER) estimates. The error correction figures out which bits are wrong and corrects them. It also can tell the power-control system how often it had to do this. If this number is higher than an optimal level, then the power-control system tells the transmitter to turn up the power. And conversely, when this is lower than the optimal level, it tells the transmitter to turn down the power. The radio link is therefore in a constant state of small corrections in its quest to maintain optimal power. It may seem odd that we reduce power in order to increase the number of errors an ideal level. However, in CDMA, a low error rate is an indicator that this signal is using more than its allotted percentage of the entire signal power. This call is clear, but at a cost of greater interference for all the other calls on the cell. Reducing the power on this one call will bring all the calls on the one cell closer to equal in received power. Sometimes the raw bit stream has too many errors to resolve, but this happens when the signal is really lousy. When it does happen, there is no dispute that a power-up mes- sage is called for. Another approach is to measure the E/No directly rather than using the BER. For each bit, we take the total amplitude of all its chips-just add them all up. Then we do the PN-code arithmetic and recomp