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What is a Spread Spectrum?

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  • Written By: Solomon Branch
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 07 September 2016
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The term spread spectrum refers to a method of transmitting a signal in which the signal is spread by purposely varying the frequency at which it is being sent. There are several advantages to this, including a wider bandwidth and the avoidance of objects or other frequencies that might interfere with the original signal. Using a spread spectrum can also make the signal more secure and stop it from being intercepted.

Spread spectrum uses, often called spread spectrum technique, are primarily concerned with security and interference. Typically, when a signal is generated it needs to stay in the same frequency range, such as a radio station. Tuning into a radio station means setting the radio to the same signal frequency; if the frequency is changed, the station is also changed. It is fine for the signal to stay in the same range in a situation like a radio station, but in some instances the signal needs to either be blocked from being intercepted or changed to avoid interference.

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The spread spectrum technique accomplishes this goal by alternating the signal during its transmission period. Two common ways it alters the signal during transmission are frequency hopping and the direct sequence spread spectrum technique. Frequency hopping uses a digital signal that “hops” between the original signal and a different frequency. In between the hops, referred to as the dwell time, the frequency is the same. The switching sequence is a complicated formula that the device transmitting the signal and the one receiving both calculate and use to transform the signal to and from its original state.

Direct sequence spectrum technique, which is more reliable but less efficient that frequency hopping, works by breaking up bits of data and spreading them across a frequency range. The original signal is divided by another signal, known as a chip, which moves at a higher rate of speed. This chip transmits code responsible for dividing up the signal and placing the information in a different frequency range. The same chip codes are used by the receiving device to rebuild the signal back to its original form.

The use of spread spectrum has increased over the years due to deregulation, and it is used in a wide array of telecommunications and communication fields. It was first used in the military in the 1950s for secure communications, and usage spread in the early 1980s for use in many satellite communications across the world. More recently, it has been utilized in wireless technologies, including cell phones and wireless networking.

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