Method for generating modem transmission signals with quadrature amplitude modulation

In a method for generating modem transmission signals with quadrature amplitude modulation (QAM) wherein sample values of elementary bandpass signals are stored in digitally coded form, and including weighting the elementary bandpass signals with coefficients depending on the information to be transmitted and forming the modem transmission signals by superposition of the thus weighted elementary bandpass signals, the improvement, in the case of n-PSK modulation where n=8, 12, 16 . . . , comprising the steps of:

• selecting the phase positions of the elementary bandpass signals so that the two dimensional four quadrant phase diagram is symmetrical to the axis .phi.=0 with one of the elementary bandpass signals lying on the axis .phi.=0;
• storing 1/4n+1 elementary bandpass signals, which cannot be derived from any other bandpass signal of said phase diagram neither due to symmetry with the axes .phi.=0 or .phi.=90.degree., respectively, nor by symmetry to the origin of said phase diagram, in a digital memory;
• and obtaining the remaining elementary bandpass signals by one of the following:
• (a) reading one of the stored signals out of the digital memory in a forward direction and weighting same with a -1 coefficient,
• (b) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a +1 coefficient, and
• (c) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a -1 coefficient.

In a method for generating modem transmission signals with quadrature amplitude modulation (QAM) wherein samples of elementary bandpass signals, which may be of longer duration than the duration of a symbol to be transmitted, are stored in digitally coded form, with the inherent phase and amplitude of the stored elementary bandpass signals depending on the potential coded information symbols to be transmitted, and forming the modem transmission signals by superposition of elementary bandpass signals selected according to the information to be transmitted, the improvement, in the case of n-PSK modulation wherein n=4, 8, 12, 16 . . . , comprising the steps of:

• rotating the elementary bandpass signals plottable as points on a two dimensional four quadrant signal space diagram such that these signals are symmetrically arranged with respect to the axis .phi.=0 of this signal space diagram, and no elementary bandpass signal coincides with the axis .phi.=0;
• storing 1/4n elementary bandpass signals, which cannot be derived from any other elementary bandpass signal of the signal space neither due to symmetry with the axis .phi.=0, or the axis .phi.=90.degree., respectively, nor by symmetry to the origin of the signal space, in a digital memory;
• and obtaining the remaining elementary bandpass signals by one of the following:
• (a) reading one of the stored signals out of the digital memory in forward direction and weighting same with a -1 coefficient,
• (b) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a +1 coefficient, and
• (c) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a -1 coefficient.

In a method for generating modem transmission signals with quadrature amplitude modulation (QAM) wherein samples of elementary bandpass signals, which may be of longer duration than the duration of a symbol to be transmitted, are stored in digitally coded form, with the inherent phase and amplitude of the stored elementary bandpass signals depending on the potential coded information symbols to be transmitted, and forming the modem transmission signals by superposition of elementary bandpass signals selected according to the information to be transmitted, the improvement, in the case of n-PSK modulation where n=8, 12, 16 . . . , comprising the steps of:

• rotating the elementary bandpass signals plottable as points on a two dimensional four quadrant signal space diagram such that these signals are symmetrically arranged with respect to the axis .phi.=0 of this signal space diagram with one of the elementary bandpass signals lying on the axis .phi.=0;
• storing 1/4n+1 elementary bandpass signals which cannot be derived from any other elementary bandpass signal of the signal space neither due to symmetry with the axes .phi.=0 or .phi.=90.degree., respectively, nor by symmetry to the origin of the signal space diagram, in a digital memory;
• obtaining the remaining elementary bandpass signals by one of the following:
• (a) reading one of the stored signals out of the digital memory in a forward direction and weighting same with a -1 coefficient,
• (b) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a +1 coefficient, and
• (c) reading one of the stored signals out of the digital memory in a backward direction and weighting same with a -1 coefficient.