Reconfigurable FDMA satellite on-board processing

Most commercial satellite systems today are based on multiple beam FDMA formats, in which uplink users are assigned frequency subbands filtered off by present front end bandpass filters, and circuit switched to form the downlink FDMA beams. It would be advantageous to have a reconfigurable version of this front end processor that would permit changes in the subband bandwidths upon command, producing a processor that can adapt to various applications. Filter band reconfiguration is best performed with digitized front ends and digital filter banks, which can be reconfigured by adjusting specific filter parameters. The primary concern is the effective filtering, applied to the uplink subbands reconfiguration, which may cause differences in subband signal power, collected noise, crosstalk and aliasing.. This effect is examined and the dependence on the choice of digital filtering is shown. Two basic reconfigurable processors appear to be favored. In one case the subbands are produced by sequentially dividing down the available satellite bandwidth, and reconfiguration obtained by, tapping off at the desired stage. In the second architecture, the band is divided to its narrowest subband and reconfiguration is achieved by, properly combining outputs for larger subbands. Some hardware issues are discussed.