Level Division Multiplexing of Service Channels in Multilevel Digital Transmissions

Level Division Multiplexing (LDM) is a technique suitable for the addition of supplementary information within multilevel digital transmissions using either amplitude modulation or frequency modulation. Its principle of operation is based on the addition of a supplementary modulation area outside that normally provided for, which does not produce any worsening of the transmission quality of the main information signal. The supplementary information can be added without identifying the frame of the main information signal, but simply by arranging the supplementary information in a frame of its own, which is completely independent of the frame of the main information signal. An example of application (the addition of 4 service channels within the DSA2 system) shows that the LDM technique is particularly suitable for the addition of service channels in PAM/FM digital microwave radio links.