ituting a pow- erful economic incentive to make earth stations inexpensive. Also, the satellite transponders were power-limited rather than bandwidth-limited Equitorial designed an earth station with small antennas that would pick up interfering signals from other geostationary satellites. Direct-sequence spread-spectrum radio signals were used in this design to overcome this interference. One of the commercial spread-spectrum devices most widely used today is a receive-only satellite terminal called GPS. It is based on the U.S. mili- tary global positioning system (GPS) of 24 satellites with non-stationary orbits that transmit broadcast spread-spectrum signals [11]. A GPS receiver can simultaneously receive signals from three satellites and can determine its own position with a high degree of accuracy. Although it was originally intended for military applications, commercial companies have designed a range of GPS products, which are now widely used. In 1980, Hewlett-Packard engineers designed an experimental spread- spectrum radio for indoor applications [12]. Bell Laboratories engineers also tested a similar direct-sequence spread-spectrum radio for indoor applica- tions [13,14]. These experimental systems created in research laboratories were not developed into commercial products. By the late 1980s and early 1990s, the combination of the rapidly growing popularity of mobile radios sparking a demand for more capacity and the availability of the technology needed for low-cost implementation renewed the interest in commercial applications of spread-spectrum mobile radios. During this same period, allowance by the Federal Communications Commission (FCC) of more liberal unlicensed use of spread-spectrum radios prompted the development of a wide variety of commercial spread- spectrum radio applications. We wish to point out that among the many multiple-access techniques under consideration for cellular telephony, we emphasize digital code division multiple access (CDMA) because it is a spread-spectrum tech- nique, 