Onboard regenerative repeater

Use of on-board regenerative repeaters as part of a satellite transponder system is shown to enhance performance as measured by the energy-per-bit-to-noise ratios required for both up- and down-links. In particular, link budget design involving coherent QPSK with differential encoding or differential QPSK on the up-link and coherent QPSK on the down-link is discussed. Depending on backoff conditions, coherent QPSK may provide energy-per-bit-to-noise ratio reductions of 4.6 to 6.8 dB on the down-link. Although differential QPSK on the up-link reduces this improvement somewhat, it may provide a simple on-board demodulator option.