rograms, the emergence of other applications, in which both the military and civilian sectors are involved, as playing a role of ever-increasing importance. For example, to minimize mutual interference, the flux density of transmissions from radio transmitters must often be maintained at acceptably low radiation levels. A convenient way to meet these requirements is to spread the power spectrum of the signal before transmission and despread it after reception-the non- hostile equivalent of the military low-probability-of-intercept (LPI) signal design. Another instance in which SS techniques are particularly useful in a non- anti-jam application is in multiple-access communications in which many users share a single communication channel. The assignment of a unique SS sequence to each user allows him or her to transmit simultaneously over the common channel with a minimum of mutual interference, simplifying the network control requirements. Preface to First Edition Extremely accurate positioning can be computed by using signals from several satellites in synchronous and asynchronous orbits. Satellites trans- mitting pseudorandom noise sequences modulated onto the transmitted car- rier signal provide the means for accomplishing the required range and distance determination at any point on the earth. Finally, SS techniques can improve the reliability of transmission in fre- quency-selective fading and multipath environments. Spreading the band- width of the transmitted signal over a wide range of frequencies reduces its vulnerability to interference and often provides some diversity gain at the receiver. At the heart of all these potential applications lies the increasing use of digital forms of modulation for transmitting information, driven by the tremendous advances made over the last decade in microelectronics. This trend no doubt will continue, and thus it should not be surprising that more and more applications for spread-spectrum techniques will continue to sur- face. Indeed, the state-of-the-art is advancing