Return Channel Spread Spectrum from USATs

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  • For SCPC and TDMA multiple-access
  • Spreader:
    • Reduces transmit signal PSD and thereby interference from USAT remote to adjacent satellites
    • Spectrum replicator (with carrier phase shifts to minimise PAPR)
  • De-spreader:
    • Architecture eliminates need for frequency acquisition
    • Least squares’ fit of estimated phases minimizes variance at low SNRs
    • Coherent combining of sub-carrier signals provides up to 5.5dB gain in SNR
  • Measurements of DVB-RCS2, BPSK-1/2, 512ksps return link with 4x spreader and de-spreader:
    • Es/N0 of each sub-carrier at de-spreader input (dB) Es/N0 of combined signal at de-spreader output (dB) De-spreader gain (dB)
    9.7 13.7 4.0
    5.1 10.3 5.2
    0.0 5.6 5.6
    -5.0 0.6 5.6
    -6.0 -0.5 5.5