Punctured recursive convolutional encoders and their applications in turbo codes

Puncturing is the predominant strategy to construct high code rate convolutional encoders, and infinite impulse response (IIR) convolutional encoders are an essential building block in turbo codes. In this paper, various properties of convolutional encoders with these characteristics are developed. In particular the closed-form representation of a punctured convolutional encoder and its generator matrix is constructed, necessary and sufficient conditions are given such that the punctured encoders retain the IIR property, and various lower bounds on distance properties, such as effective free distance, are developed. Finally, necessary and sufficient conditions are given on the inverse puncturing problem: representing a known convolutional encoder as a punctured encoder.