Superposed transmission of high speed QPSK signals and SSMA-QPSK signals in non-linear channels

Spread-spectrum multiaccess quadrature phase-shift keying (SSMA-QPSK) signal transmission superposed over high-speed QPSK modulated signals is proposed and analyzed experimentally. Experimental results show that when the SSMA-QPSK signal power to QPSK signal power ratio equals -30 dB, the scheme can transmit 20 SSMA-QPSK channels and a high-speed QPSK channel over the same transponder simultaneously and realize 1.530 b/s/Hz of frequency utilization efficiency (superposed transmission of 60-Mb/s QPSK signals and 20 32-kb/s SSMA-QPSK signals over a 36-MHz transponder).<
>