Quadrature-quadrature phase shift keying with constant envelope

A modulation method for modulating simultaneously four streams of data pulses, the modulation method comprising the steps of:

• coding each of the four streams of data pulses into a respectively associated stream of data words, each such data word being formed of a predetermined number of the data pulses from the associated one of the data pulse streams, and a parity check bit, said parity check bit having a value responsive to a mathematical operation performed using said predetermined number of the data pulses;
• combining a pulse-shaping signal with respective ones of first and second carrier signal components, each of said first and second carrier signal components having the same frequency as the other and a quadrature phase relationship with respect to the other, to produce first and second composite modulation signals, each having first and second frequency components;
• combining subtractively said first and second frequency components associated with each of said first and second composite modulation signals, to produce first and third modulation signals;
• combining additively said second and first frequency components associated with each of said first and second composite modulation signals, to produce second and fourth modulation signals;
• and
• combining said first, second, third, and fourth modulation signals with respective ones of said four streams of said data words, to produce respectively corresponding first, second, third, and fourth modulated streams of pulses having predetermined pulse shapes and quadrature pulse phase relationships with respect to one another, combining said first, second, third, and fourth modulated streams of pulses, whereby a transmission signal formed of the combination of said first, second, third, and fourth modulated streams of pulses has a constant envelope.