Welcome to Spreading Spectrum

Spread spectrum is the backbone of UMTS, but why do we talk about Spreading Spectrum ?

We are actually talking about trading a wider signal bandwidth for better signal to noise ratio, so in my opinion spreading is a more appropriate term to use than spread. Spreading spectrum although associated with the latest telecommunications technologies is nothing new, as early as 1920 experiments were carried out and the military have deployed Spreading Spectrum in frequency hopping communication systems for some time.

I won't go into too much detail on this page but suffice to say spreading spectrum modulation techniques have a wide frequency spectra and the modulated output signals have a greater bandwidth than the signal's bandwidth. A spreading spectrum signal will usually meet the following;

1) Transmitted signal bandwidth will be greater than the information bandwidth.

2) A function other than the information being transmitted would be employed to find the transmitted bandwidth (hence its popularity in early military communications).

Spreading spectrum with regard to commercial communications technology is relatively new. Frequency hopped spreading spectrum was invented by actress the Hedy Lamarr and by the musician George Antheil, the patent was granted in 1942.

The fundamental basis of this technology is the structuring of the signal, which uses direct order, frequency hop or a half-breed of these, which can be used for repeated entrance and/or repeated functions. This technology reduces the possible disturbance to other receivers whilst being secure and increases the immunity to noise and disturbance.

Spreading spectrum is usually used in a successive noise-like signal structure, in order to spread the narrowband information signals over a relatively broad range of frequencies. The receiver resolves the signals one by one to fetch the original information signal.