Multiple access is the ability of many users to communicate with each other while sharing a common transmission medium. Wireless multiple-access communications are facilitated if the transmitted signals are orthogonal or separable in some sense. Signals may be separated in time (1time-division multiple access or TDMA), frequency ( frequency-division multiple access or FDMA), or code ( code-division multiple access or CDMA). CDMA is realized by using spread-spectrum modulation while transmitting signals from multiple users in the same frequency band at the same time. All signals use the entire allocated spectrum, but the spreading sequences or frequency-hoppong patterns differ. Information theory indicates that in an isolated cell, CDMA systems achieve the same spectral efficiency as TDMA or FDMA systems only if optimal multiuser detection is used. However, even with single-user detection, CDMA is advantageous for cellular networks because it eliminates the need for frequency and timeslot coordination among cells and allows carrier-frequency reuse in adjacent cells. Frequency planning is vastly simplified. A major CDMA advantage exists in networks accommodating voice communications. A voice-activity detector activates the transmitter only when the user is talking. Since typically fewer than 40% of the users are talking at any given time, the number of telephone users can be increased while maintaining a specified average interference power. Another major CDMA advantage is the ease with which it can be combined with multibeamed antenna arrays that are either adaptive or have fixed patterns covering cell sectors. There is no practical means of reassigning...