DC-Free Error-Correcting Codes Based on
Mao‐Ching Chiu · 2001
A new construction of direct current (dc)-free error- correcting codes based on convolutional codes is proposed. The new code is constructed by selecting a proper subcode from a con- volutional code composed of two different component codes. The encoder employs a Viterbi algorithm as the codeword selector so that the selected code sequences satisfy the dc constraint. A lower bound on the free distance of such codes is proposed, and a proce- dure for obtaining this bound is presented. A sufficient condition for these codes to have a bounded running digital sum (RDS) is proposed. Under the assumption of a simplified codeword selec- tion algorithm, we present an upper bound on the maximum ab- solute value of RDS and derive the sum variance for a given code. A new construction of standard dc-free codes, i.e., dc-free codes without error-correcting capability, is also proposed. These codes have the nice property that the decoder can be implemented by simple symbol-by-symbol hard decisions. Finally, under the new construction, we propose several codes that are suitable for the sys- tems that require small sum variance and good error-correction capability.