Abstract: Quadrature amplitude modulation with two carrier signals orthogonal relative to one another is often used for the transmission of digital television and/or radio signals from a head end to subscribers in coaxial cable networks. This modulation method, however, is poorly suited for the return channel from the subscribers to the central because, due to the multitude of subscribers, the subscriber signals are often transmitted in burst mode. Thus, there is not adequate time for the phase-exact recovery of the carrier signals at the reception side. A single sideband amplitude modulation of the digital transmission signals is therefore undertaken for the carrier-frequency transmission of digital signals in burst mode.

Abstract: In a passive optical telecommunication system having a central station communicating via respective optical waveguides with a number of decentralized stations, an electrical carrier signal is DPSK-modulated in the upstream transmission, after which the electrical signal modulated in this way effects the intensity modulation of the emitted light; in the downstream signal transmission, the emitted light is intensity-modulated by a preferably scrambled NRZ baseband signal. The carrier signal is derived by frequency multiplication from the regenerated reception clock signal of the decentralized station.