Introduction to SFDMA multiple access networks and their possible implementation in terrestrial DVB return channels

This article presents a new so-called SFDMA (synchronous frequency division multiple access) multiple access system. The system is obtained from a FDMA system by the addition of a frequency locking for the carriers and of a time synchronisation for the modulations, both on a common reference, generally broadcast by a base station. These frequency locking and time synchronisation allow the base station, on the receiving side, to reconstitute an OFDM multiplex, possibly after multicarrier filtering, and to process it in the usual way for those kind of signals. A description of the SFDMA system is given, which presents the signal modulation and demodulation procedures, the system requirements and performance and potential medium access techniques. The advantages of the system are then listed. Finally, an example of the SFDMA network is given, that has been endorsed by the INTERACT ACTS project as a technical solution for terrestrial DVB return channel systems to provide interactive DVB programs