TABLE OF CONTENTS In this chapter we consider the spread-spectrum transmission schemes that demand channel bandwidth much greater than is required by the Nyquist sampling theorem. You will recall from Chapter 2 that the minimum bandpass bandwidth required for data transmission through an ideal channel is equal to the data symbol rate. You will also recall that wideband reception allows a large amount of input noise power to the detector and thus degrades the quality of the detected data. Therefore, the receivers for spread-spectrum schemes have to convert the received wideband signals back to their original narrowband waveforms before detection. This process generates a certain amount of processing gain that can be used to combat radio jamming and interference. We will describe and discuss in detail the properties and methods of generation of the functions used in creating wide spectrum signals. Finally, we consider the multiple access properties of the spread-spectrum systems and outline the analytical model for evaluating the system performance.
There was intensive use of communications warfare during World War II. This technique outlined the ability to intercept and interfere with hostile communications. Consequently, this procedure stimulated a great deal of interest which led to the development of secure communications systems and work in this field was carried out on two fronts. Firstly, development in communication theory initiated encryption schemes (Shannon, 1949) to provide certain information protection. Secondly, work was initiated to harness the development of a new technology. This technology is called the Spread-Spectrum techniques (Scholtz, 1982),...
