On-board processing for Ka-band applications

The work reported arose from a study carried out for the European Space Agency to examine the impact of 20/30 GHz operation on the on-board processing requirements for a satellite system intended to serve private user networks of small fixed terminals interconnected with 2 Mb/s ISDN-like links. Fading in Ka band leads to the requirement of expensive HPAs in the user terminals. It is therefore an advantage to use FEC on the uplink. Continuous mode transmission simplifies on-board decoding (and interleaving), and allows higher coding gains. A simple access scheme is FDMA with variable data-rate channels, therefore a nonuniform demultiplexer is required on-board. There are two methods that belong to the same general class. The fast convolution method is inherently more efficient than the analysis-synthesis method since clock synchronism can be exploited and the output sampling rate can be decimated down to the symbol rate. The frequency resolution is inherently larger and the placement of carrier frequencies are more flexible. CDMA is attractive as its complexity is similar to TDMA, since demultiplexing in the code domain requires only additions