ANALOG-TO-DIGITAL CONVERTERS LOAD FACTOR ANALYSIS FOR WIDEBAND COMMUNICATION SATELLITE SYSTEMS

In modern satellites systems the uplink RF wideband signal after downconversion to IF is input to the analogto-digital converter, the output of which is digitally processed for the purpose of channelization and switching of signals. In such systems, a major implementation limitation is the A/D converter, which needs to operate at a rate at least two times the received wideband signal bandwidth. In the case of a wideband signal comprised of many multiplexed signals, the spectral distribution of quantization noise is also of significant interest. Another very important consideration in the ADC performance analysis is the signal clipping effect occurring whenever the instantaneous input signal amplitude exceeds the maximum linear range of the quantizer. Since clipping cannot be avoided in most practical situations, the signal power to the quantization plus clipping noise power ratio is of utmost interest. Such a ratio is in general a function of the quantizer load factor that in turn is the ratio of the input signal average power and the maximum peak power at the quantizer output. The paper presents simulation results on the quantizer load factor analysis when the input signal is comprised of a specified number of digitally modulated carriers. As simulation examples, 8-PSK and 16-QAM modulation schemes are considered with and without band limiting filtering.