Constant Average Power Single Sideband (CAPSSB) modulation

In a mobile satellite environment, amplitude companded single sideband (ACSSB) schemes for speech transmission can offer a degree of robustness to fading and shadowing that is difficult for alternate approaches to match. One drawback to ACSSB signals is that neither their average nor instantaneous transmit powers are constant. A new single sideband scheme is described which exhibits a nearly constant average transmit power and limits the peak instantaneous transmit power to only a few dB above the average level. In this scheme, a single digital signal processing microprocessor performs all the modulator functions. The architectures of the modulator and demodulator sections are described, and the technique for peak-to-average ratio reduction is discussed. The soft voice activation algorithm is also presented. The system has successfully transmitted speech over the MARECS-B satellite using constant average power single sideband radio in the vehicle and matching equipment in the hub station. These tests showed that the system can transmit voice over a 5 kHz channel with good communications quality when the received carrier to noise power spectral density ratio is 50 dB-Hz or greater.