Digital coding technique which avoids loss of synchronization

A method for encoding a digital input signal into a digital output signal, said method comprising the steps of

• receiving said digital input signal, said digital input signal having m signal levels;
• and
• transforming said digital input signal into said digital output signal such that said digital output signal is not identical to said digital input signal, said digital output signal having n levels, where n>m, said transforming means, providing a transformation which is always a function of all priorly received said digital input signal levels, performed in a number system having a modulus of n.

Decoding apparatus which transforms a digital input signal into a digital output signal, said apparatus comprising

• means for receiving said digital input signal, said digital input signal having n signal levels;
• and
• means responsive to said digital input signal for transforming this signal into said digital output signal such that said digital output signal is not identical to said digital input signal, said digital output signal having m signal levels, where n>m, said transforming means providing a transformation, which is always a function of successive values of said digital input signal, performed in a number system having a modulus of n.

A method of decoding a digital input signal into a digital output signal, said method comprising the steps of

• receiving said digital input signal, said coded output signal having n signal levels and;
• means responsive to said digital input signal for transforming this signal into said digital output signal such that said digital output signal is not identical to said digital input signal, said digital output signal having m signal levels, where n>m, said transforming step providing a transformation, which is always a function of successive values of said digital input signal, performed in a number system having a modulus of n.

Encoding apparatus which transforms a digital input signal into a coded digital output signal, said apparatus comprising

• means for receiving said digital input signal, said digital input signal having m signal levels and said digital input signal having a value equal to any one of said m signal levels at each of a plurality of times, and
• means responsive to said digital input signal for transforming the signal into said coded digital output signal having n signal levels, where n is greater than m, and wherein said digital input signal is not identical to said digital output signal, said transforming means providing a transformation which is invariant with the values of said digital input signal at two consecutive times in said plurality of times, said transformation being a function of all priorly received digital input signal levels, performed in a number system having a modulus of n.