Pseudo Noise

Pseudo Noise is an important feature of modulating data that is transmitted wirelessly. Also known as Pseudo Random code, it is a sequence of numbers that look random, but can be recreated relatively easily.

The pseudo noise is generated using an algorithm based on inputted numbers and this 'noise' is multiplied with the data that needs to be transmitted to produce a 'spreaded' version of the signal. The spreading of the signal usually transforms the signal into one that is below the natural noise level. This makes the signal hard to trace and intercept or scramble.

Spread Signal below noise level

The pseudo noise is unique to each user, so that users can transmit and receive data simultaneously without the user receiving the wrong data or the data of one user transforming with another because the have the same spreading code (pseudo noise code).

There are a few pseudo noise techniques that are used for CDMA, such as; Gold Codes, Walsh- Hadamard Code, M-Sequence Code, Barker Code and Kasami Code.

We will be focussing mainly on Walsh- Hadamard Code and M-Sequence Code.