Effects of satellite transponder nonlinearities on spread spectrum satellite communication systems

Correlation analysis using the autocorrelation function is applied to assess the effects of satellite-transponder nonlinearities on multiple access SS (spread-spectrum) signals when SS techniques are applied to satellite-communication systems. Both AM/PM-conversion and AM/AM-conversion nonlinearities are employed in the model (parameters k and L). The model can represent various kinds of nonlinearities by choosing the pair of parameters (k, L) and can discuss the effects of AM/AM and AM/PM conversions on SS signals synthetically and individually. The same analysis is then applied to SPC (single-channel-per-carrier) signals for comparison. It is shown that AM/PM conversion degrades the output desire/undesire ratios (DUR) of both SS and SCPC systems as severely as does AM/AM conversion. The difference between the characteristics of underlinear and nonlinear systems is as large for SS signals as for SCPC signals. Direct-sequence SS signals are assumed and the DUR at baseband signal demodulation is adopted as an evaluation criterion.