An Introduction to Linear Recursive Sequences in Spread Spectrum Systems

Spread Spectrum technology is being applied to many areas of modern communications such as Cellular Telephones, Global Positioning Satellite (GPS), and Very Small Aperture Satellite Terminals (VSATS) just to name a few. The core concept behind this technology involves spreading the data to be transmitted over a much broader spectrum than what is conventionally done. The spreading is usually achieved by modulating the data with a pseudo random sequence at a much higher frequency. When you demodulate the composite of the spreading code and data with a locally generated, identical, time aligned spreading code the power from the composite bandwidth is collapsed into the data bandwidth. This process yields an effective gain called processing gain. The measure of processing gain is given as the ratio of the data rate to the spreading code rate. Multiple spread users can coexist in the same bandwidth if each user is assigned a different spreading code. Systems utilizing this technique are called Code Division Multiple Access (CDMA) systems. This article focuses on the properties of Linear Recursive Sequence spreading codes and their uses in Spread Spectrum Systems.