The development of a real-time waveform generation and capture system for the evaluation of modulation schemes on satellite links

The performance of a satellite communications link is largely defined by the modulation and forward error correction coding scheme used. The ultimate performance is defined by the theoretical Shannon capacity but practical schemes currently fall far short of this limit. To aid the search for improved modulation techniques, a test facility has been developed which will allow potentially advantageous schemes to be evaluated via a satellite link, without the need to develop dedicated modem hardware. The facility has been constructed using a virtual memory computer which handles the generation and capture of analogue waveforms in real time. The generalized design allows the transfer function of a satellite channel with a bandwidth up to 200 kHz to be assessed and so provides for the testing of an arbitrary waveform modulation scheme within this bandwidth limit.