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Spread Spectrum Essay

1002 words - 5 pages


In today’s wireless communications the technology has come a long way since its beginnings back in the early nineteen hundreds and has become so advance that most countries have their own regulator. In the UK the regulator for wireless standards is called Ofcom which has been established since 2003. In the US the regulator is Federal Communications Commission and has been established since 1934. These regulators govern what frequency band companies can purchase to provide a wireless mobile service to customers.
The term spread spectrum is used in data communications and is a technique in which the transmitted signal is distributed over a wide frequency band, much wider than ...view middle of the document...

This creates a wideband signal which makes it appear to have noise and gives it an advantage of being hard to detect and intercept. It is accomplished by placing a much higher frequency signal into the baseband signal. The correlation between the modulated baseband and the original signal is called the processing gain. The higher the processing gains, the lower the power density needed to transmit the information.
When modulating the baseband signal a pseudo-random noise (PN) code is used. A PN code is made up of a random binary sequence which is known as a chip for mixing the data with the code. In order to recover the received signal, the code with which the signal was originally produced with in the transmitter is reproduced in the receiver and mixed with the modulated signal. If the incoming signal and the locally generated PN code match then the original signal can be recovered.
Another method used for signal modulating is frequency hopping (FH) which is similar to using a PN code. FH works by instead of spreading a signal over a greater bandwidth than the baseband signal and mixing it with a code, the signal bandwidth is unchanged and is hopped over a number of channels, each having the same bandwidth as the transmitted signal.

Motivation for Spread Spectrum

The spread spectrum technology can be traced back to 1903 when a Serbian-American inventor named Nikola Tesla first filed for U.S patent which describes a system that would allow radio communications without the messages or signals being intercepted. Although the paper never mentioned the word “frequency hopping” it was however entitled “Method of Signalling”.
The technology didn`t go unnoticed by the military and in 1915 the Germans were making use of the frequency hopping to stop the British intercepting there conversations. The military found out that the technology provided a low probability of intercept and anti-jam features which made it difficult for an enemy to snoop on secret conversations....

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