The steadily growing demand for bandwidth in satellite communications is primarily limited by the available spectra, but also by performance restrictions of the satellite as such. In this context, optical solutions are discussed to an increasing extent. Major reasons are that optical transceivers have lower weight, they are smaller and require less power than traditional radio transmission techniques.
Typically, optical signals are modulated by on-off keying, although this requires a lot of bandwidth with suboptimal use of the energy applied. This approach results also in a less efficient recovery of the transmission parameters in the receiver terminal and an operational point away from the optimum. Bandlimited transmission with appropriate shaping of pulses can help to solve this problem. As a consequence, appropriately designed estimation and synchronization algorithms are of paramount importance, because they allow the efficient demodulation and decoding of optical signals and therefore an operational point close to the channel capacity even under varying link conditions.