Performance of 16-ary DEQAM signalling with a pre-rotated constellation through nonlinear satellite channels

The effects of AM-AM and/or AM-PM conversions of a high-power amplifier (HPA) on the performance of a bandlimited 16-ary differentially encoded quadrature amplitude modulated (16-ary DEQAM) system are investigated in the presence of additive white Gaussian noise. The results obtained by computer simulation show that a combination of moderate output backoff from saturation of the HPA and prerotation of the transmitted signal constellation can considerably improve the system performance. The performance of the proposed system is compared to that of a 16-ary DEQAM system using an RF predistorter. The results show that the degradation due to the AM-AM and AM-PM conversion effects of the HPA tested is much less than that of the sum of the degradations caused by the individual AM-AM and AM-PM conversion effects. Also, the AM-AM signal distortion causes more degradation than does the AM-PM signal distortion, under the same assumed conditions. With pre-rotation and moderate output backoff values of the HPA, the AM-PM distortion in the received signal-space vectors can nearly be eliminated.<>