PHASE NOISE ANALYSIS IN THE PRESENCE OF SPURIOUS SIGNALS

Modern satellite communication systems involve digital processing of the received uplink signals, which are composed of many signals in an FDMA mode. In such systems, the multichannel signal after downconversion to the baseband or an appropriate IF frequency, is input to a nonlinear device such as an analog-to-digital converter (ADC). The output of the ADC is then input to the DSP unit which may perform various functions such as channelization, switching, etc., all in the digital domain. Such systems may introduce spurious signals, which may arise from many possible sources, including the ADC, the frequency synthesizer and other subsystems in the DSP processor. This paper presents a mathematical analysis of the phase noise at the output of phase demodulator in the presence of receiver noise and the spurious signal. Such analysis is extremely important in evaluating the performance of various modulation techniques such as MPSK, QAM, and PSK/PM. The latter modulation technique is one of the techniques used for satellite telemetry links. Using the results on the distribution of the phase noise, the results on the performance of various modulation techniques are then presented in the paper.