Spread Spectrum

Spread Spectrum- The first major application of spread spectrum techniques (SST) arose during the mid-sixties, when NASA employed the method to precisely measure the range to deep space probes. In the following years, the US military became enamored of SST do to its ability to withstand jamming (i.e. intentional interference), and it ability to resist eavesdropping.

   Spread spectrum is a form of wireless communications on which the frequency of the transmitted signal is deliberately varied. These results in a much greater bandwidth than the signal would have if its frequency were not varied. A conventional wireless signal specified in megahertz or gigahertz, which does not change with time. Most spread spectrum signal use a digital scheme called frequency hopping. The transmitter frequency change abruptly, many times each second. Between “hops”, the transmitter frequency is stable. The length of time that the transmitter remains on a given frequency between hops is known as the dwell time. A few spread spectrum circuits employ continuous frequency variation, which is an analog scheme.