Multiple amplitude and phase shift keyed signal modulation method

Claim 1

In a multi-phase modulation method in which digital words each having a word length of k data bits control the generation of a modulated carrier in a manner such that each digital word value is associated with a particular amplitude and phase of the modulated carrier, and in which the modulated carrier is formed of a combination of three oscillating signals having identical frequencies, shifted in phase by 120° relative to one another, and each having a selected amplitude, the digital words being associated with the oscillating signals in such a manner that a first group of digital words is represented only by modulated carrier phases which possess equal angular spacings in the 360° phase plane and at least one further digital word is represented by a zero amplitude carrier formed by combining the three oscillating signals each having the identical selected amplitude or by suppressing all three oscillating signals, the improvement wherein: each digital word has a length of at least 3 bits; there is a plurality of further digital words each represented by a zero amplitude carrier, at least three bits of each further digital word differing from the corresponding at least three bits of each other further digital word; and said method comprises modulating the carrier in response to successive bits of each digital word for producing, during the period of each digital word, a first modulated carrier segment representing the digital word and two further modulated carrier segments representing redundant digital words derived from the digital word represented by the first modulated carrier segment and having values which permit error-free determination, during subsequent demodulation, of the digital word represented by the first modulated carrier segment.