There are two principal codes coding a scheme, which is used: one is called block code, the other is called convolutional code. If I consider block code we will consider only linear block codes where the flow-up data from a traffic or from whatever we want to encode is segmented in two K bit blocks and, through some linear transformation, this block of K bit is mapped into N bit block by adding (n-k) paritycheck bits. And this is this "n" bit called block that is sent to the modulator for conversion and for transmission.