Lecture Notes 11: Direct-Sequence Spread-Spectrum Modulation

In this lecture we consider direct-sequence spread-spectrum systems. Unlike frequency-hopping, a direct-sequence signal occupies the entire bandwidth continuously. The signal is obtained by starting with a narrowband signal and directly modulating a high bandwidth signal. As with frequency hopping direct-sequence has advantages when the channel contains a jamming like signal. The jamming could be intentional and hostile, self jamming (multipath), and multiuser jamming. In the remained of this chapter we examine the capabilities of direct-sequence is these three environments. Below we show the transmitter and receiver for a direct-sequence system. The data sequence b t consists of a sequence of data bits of duration T . The data sequence is multiplied with a binary spreading sequence a t which has N components called chips per data bit.