Satellite-switched Frequency Division Multiple Access (SS-FDMA)

Satellite-switched frequency division multiple access (SS-FDMA) is a multiple-access architecture in which multiple narrowband FDMA uplink carriers are dynamically routed onboard the satellite to different downlink beams or frequency channels through a switching function. Rather than each uplink carrier being permanently translated to a fixed downlink frequency and beam, the satellite performs in-orbit switching to interconnect uplink and downlink resources according to traffic demand.

In an SS-FDMA system, individual users transmit continuous single-carrier FDMA signals, while the satellite employs an RF, IF, or digital switching matrix to assign each uplink carrier to the appropriate downlink beam or destination. Switching may be controlled by network signaling or satellite command, enabling flexible beam-to-beam connectivity and more efficient utilization of satellite capacity than conventional fixed-assignment FDMA.

SS-FDMA differs from traditional bent-pipe FDMA systems, which have static frequency and beam mappings, and from fully regenerative systems, which demodulate and decode user signals onboard. Historically, SS-FDMA was widely used in early multibeam GEO satellites to support inter-regional telephony and trunking networks, and the concept remains relevant in modern systems employing digital onboard processing and software-controlled switching.