convolution code (CC)

Convolution is a mathematical operation in which another function is created by summing or integrating two functions. In time relation, for example, the function of the input signal can be convolved with that of the pulse response.

Convolutional codes are used in channel coding, especially in heavily interfered transmission systems in radio and mobile communications, satellite communications and space, and satellite-based DVB-S. They operate at high bit rates, which are multiplied by convolution, and with forward error correction( FEC).

In principle, convolutional encoders consist of a multi-stage shift register and multiplexers. Previous and current information characters are stored in the shift register. The level of the shift register determines how many information characters can be temporarily stored in it. In addition, a convolutional encoder has several linear links that provide for encoding. During encoding, the information character to be encoded is shifted into the shift register and linked to the temporarily stored information characters. At the end of the shift register the linked characters are multiplexed and result in the encoded bit stream. The more stages the shift register has, the more combination possibilities the coding has. In this context, one speaks of influence length.

Convolutional codes are not based on an algebraic decoding, but on an estimation of the reception sequence. They are easy to implement and are used in communication technology. Besides the simple convolutional code, there is an improved convolutional code, Convolutional Turbo Coding( CTC). There is also Block Turbo Code( BTC) and Low Density Parity Check( LDPC), which are used in poor reception conditions.