An improved channel coding algorithm for low-frequency spectral suppression

Abstract

An improved low-frequency spectral suppression (LOFS) code is introduced and analyzed as a method to suppress low-frequency energy in a digital baseband signal with significantly lower redundancy than required methods. Alternatively, the LOFS code will suppress more energy near DC with a given redundancy when compared to current coding methods, allowing insertion of a pilot tone which leads to a simple unambiguous carrier recovery subsystem that can track system-induced noise. The LOFS code reduces redundancy by adding control bits in word format for multilevel signals, that is, control bits for multiple frames are inserted in one symbol duration. Use of this LOFS code could reduce the redundancy of currently used digital transmission systems from 4% to 1%. Analysis of computer simulations shows that a premodulation high-pass filter, while significantly degrading the uncoded PAM signal, causes little degradation of the coded data and keeps data to pilot interference to a minimum. Experimental hardware results are included to verify simulation results. >