US Patent 7567501 Embedded keying

Method of communicating digital data in which frames (8) are transmitted cyclically whereby a first number of symbols is transmitted according to a first keying mode (II) using a first constellation, and a second number of symbols is transmitted according to a second keying mode (L) using a second constellation. The first and second keying modes (H, L) are used at predetermined positions in the frame, whereby both the symbols according to the first and second keying mode carry information under at least an operative traffic phase.