PERFORMANCE OF THE MPSK AND QAM MODULATION SCHEMES IN THE PRESENCE OF NARROWBAND INTERFERENCE

Modern satellite communication systems involve digital processing of the received uplink signals, which comprise of many signals in an FDMA or CDMA 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 performance of the communication link in the presence of receiver noise and the spurious signals. Various modulation techniques such as MPSK and QAM are considered in some details. Exact results on the probability of bit error and the probability of symbol error are presented for these modulation schemes and are parameterized by the relative power level of the spurious signals.