aintain a low co-channel interference level. Similar guard times are needed for narrowband signals to separate assigned time slots in TDMA systems. Up to 20 percent of the total capacity needed for guard bands (FDMA) or guard times (TDMA) is eliminated in the spread-spectrum CDMA systems, which are designed to perform with some level of interference. In Part 5, Chapter 2, we make a distinction between SSMA and CDMA. With SSMA, we assume that transmitters are not synchronized in time and that interference from other users is modeled as Gaussian noise. Massey and Mittelholzer [21] have characterized the case in which users are not time-synchronized as "asynchronous code division multiple access" (A- CDMA). Here, one can use the SSMA assumption of Gaussian noise interference or take into account all the random time shifts of the inter- ference signals. Massey and Mittelholzer characterize the case when trans- Commercial Applications mitters are all time-synchronized as "synchronous code division multiple access" (S-CDMA). For S-CDMA systems, specific spread-spectrum spreading codes can enhance performance to a greater degree than in A- CDMA systems. Although the IS-95 system uses an overall network time reference, the inbound signal (from mobile units to cell site) is treated as an A-CDMA system, and interference can be modeled as Gaussian noise. For large cell sizes with some multipath delays larger than a chip-time interval, mobile unit signals cannot be easily synchronized. In this direction, signals in a cell are not orthogonal. The outbound signal (from cell site to mobile units) is S-CDMA, since all signals originate from one location and can be time-syn- chronized. In military spread-spectrum radio applications, interference derives from enemy jammers not under any control by the communication system. For a large network of cells in a commercial application, on the other hand, inter- ference can be tightly controlled among all radios, since all are part of the name system. This tight control of mutual interfe