Data Transmission Error Probabilities in the Presence of Low-Frequency Removal and Noise

It is frequently desirable, or unavoidable, that the low-frequency components of a data signal be eliminated. This may occur through the use of capacitor or transformer coupling in the terminal equipment or in the baseband transmission facilities. Another instance results from the necessity of removing low-frequency baseband components before modulation in order to provide a spectral guard band in the vicinity of the carrier frequency. Since dc is usually completely attenuated, no linear operation can correct for low-frequency removal. One commonly used approach uses nonlinear feedback to restore the low-frequency components.1 Another solution to this problem involves dc-free signal formats. 2,3 We evaluate the penalty resulting from the removal of low-frequency components from a standard format data signal (Nyquist I shaping) and a partial response signaling format (multilevel extension of duobinary with precoding.) 4 Clearly, in both of these cases, the degradation is most severe when the transmitted data sequence contains long strings of identical digits. In fact, when the system bandwidth is less than the signaling rate, which is usual in data 255