19-09-2017, 03:41 PM
In telecommunications and radio communications, spread spectrum techniques are methods by which a signal (eg, an electrical, electromagnetic or acoustic signal) generated with a particular bandwidth is deliberately propagated in the frequency domain, giving result a signal with a wider bandwidth. These techniques are used for a variety of reasons, including establishing secure communications, increasing resistance to natural interference, noise and jamming, to prevent detection, and to limit the power flux-density (e.g. by satellite).
A conventional wireless signal has a frequency, usually specified in megahertz (MHz) or gigahertz (gigahertz), which does not change over time (except for small and rapid fluctuations that occur as a result of modulation). When you hear a signal at 103.1 MHz on an FM stereo receiver, for example, the signal remains at 103.1 MHz. It does not go up to 105.1 MHz or up to 99.1 MHz. The radio frequency dial digits remain the same at all times. The frequency of a conventional wireless signal is kept as constant as the state of the art allows, so the bandwidth can be kept within certain limits, and therefore the signal can be easily located by someone who wants to retrieve the information .
There are at least two problems with conventional wireless communications that may occur under certain circumstances. First, a signal whose frequency is constant is subject to catastrophic interference. This occurs when another signal is transmitted at, or very close to, the desired signal frequency. Catastrophic interference may be accidental (as in amateur radio communications) or may be deliberate (as in times of war). Second, a constant frequency signal is easy to intercept and therefore not suitable for applications where information must be kept confidential between the source (transmitting party) and the destination (receiving party).
A conventional wireless signal has a frequency, usually specified in megahertz (MHz) or gigahertz (gigahertz), which does not change over time (except for small and rapid fluctuations that occur as a result of modulation). When you hear a signal at 103.1 MHz on an FM stereo receiver, for example, the signal remains at 103.1 MHz. It does not go up to 105.1 MHz or up to 99.1 MHz. The radio frequency dial digits remain the same at all times. The frequency of a conventional wireless signal is kept as constant as the state of the art allows, so the bandwidth can be kept within certain limits, and therefore the signal can be easily located by someone who wants to retrieve the information .
There are at least two problems with conventional wireless communications that may occur under certain circumstances. First, a signal whose frequency is constant is subject to catastrophic interference. This occurs when another signal is transmitted at, or very close to, the desired signal frequency. Catastrophic interference may be accidental (as in amateur radio communications) or may be deliberate (as in times of war). Second, a constant frequency signal is easy to intercept and therefore not suitable for applications where information must be kept confidential between the source (transmitting party) and the destination (receiving party).