DC-free LDPC convolutional codes

Abstract

The use of variable-length error control codes is a natural choice in transmission systems with variable-length data sequences. These systems also employ constrained sequence codes (often called line codes) to ensure that the transmitted symbol sequence is balanced and contains sufficient timing information to facilitate reliable demodulation. We outline how low density parity check convolutional codes (LDPC-CC’s) can be integrated with guided scrambling (GS) constrained sequence codes in a manner that supports variable length sequences and limits the detrimental effects of error extension during GS decoding by placing the LDPC-CC decoder before the GS decoder within the receiver. We present spectra and bit error rate results that demonstrate the advantage of this approach.