Trellis codes with passband spectral nulls

Abstract

In a data transmission system using a predetermined trellis code, the output signal points are selected from a predetermined alphabet representing (k+n)-bit input words by using the values of n bits of each input word, and bits from previous input words, to identify a particular one of 2.sup.m subsets of the signaling alphabet m>n. The other k bits of the input word identify an ensemble of four signal points of the identified subset. This ensemble is characterized by having a first signal point whose odd components and even components each sum to a value no less than zero, a second signal point whose odd components sum to a value no less than zero and even components a value no greater than zero, a third signal point whose odd components sum to a value no greater than zero and even components a value no less than zero, and a fourth signal point whose odd components and even components each sum to a value no greater than zero. Two running sums of odd and even cmponents of the signal points previously generated are separately maintained. At any point in time, the system always manages to select and output a signal point in the identified ensemble so as to drive the individual running sums of the respective odd components and even components toward zero simultaneously. This scheme provides a passband signal having a spectral null at a carrier frequency.