ems. Dynamic power control means that the average transmit power of the IS-95 handsets can be less than that in IS-54 and GSM handsets. All three systems also employ convolutional coding with Viterbi decoding. The IS-95 system, however, uses stronger constraint length K = 9 convolutional codes, with rate 1/2 in the cell-to-mobile channel and rate 1/2 in the mobile-to-cell channel. All three digital cellular systems require some level of synchronization among all adjacent cells in a given area. The IS-95 system uses GPS receivers to provide master clocks for each cell. GPS is another widely used com- mercial application of spread-spectrum radios. Overall capacity is the most important feature of the three digital cellu- lar systems. Owing to SO many parameters and other performance issues, it is very difficult to show clearly which system offers the greatest overall capacity. For example, the soft handoff feature of the IS-95 system enhances performance but sacrifices some capacity on the less critical downlink. It is clear, however, that the spread-spectrum CDMA system differs fundamen- tally from the TDMA systems and possesses three key properties that can greatly increase overall system capacity: 100 percent frequency of reuse, flex- ible antenna applications, and voice activation. The issue of capacity will be discussed further in the next sections. 3.4 A NEW PARADIGM FOR DESIGNING RADIO NETWORKS In the military, spread-spectrum radios are primarily used to combat enemy jamming since they tolerate much more interference than conventional radios. Their processing gain, typically defined as the radio of the spread- spectrum signal bandwidth to the conventional signal bandwidth for the same data rate, is a direct measure of how much interference such spread- spectrum radios can tolerate. Since spread-spectrum signals take up a larger bandwidth, they are generally bandwidth-inefficient. That is, if we use the conventional measure of bandwidth efficiency-the number of data bits per signal bandwidth-spread-spectrum 