SSMA signal transmission over QPSK modulated signal

The superposition of a spread-spectrum multiple-access (SSMA) signal transmission over a quadrature phase-shift-keyed (QPSK) modulated channel is proposed to achieve higher transmission efficiency per transponder and to reduce the lower transmitter power of a small earth station. Experimental results show that under the condition of D/U=20 dB, the required error probability, P _e=1×10^-4, of the QPSK channel is achieved with only 1-dB degradation by using a coding rate of 7/8 forward error correction (FEC), and the required P_e of 1×10 ^-4 for the SSMA channel is achieved with 7-dB degradation by using a coding rate of =1/2 FEC. The link budget shows that the proposed schemes makes it possible to use a low-power SSPA to realize small earth stations