Bit-precision requirements on the A/D converter in a QAM receiver

An analog-to-digital (A/D) converter at a quadrature-amplitude modulation (QAM) receiver introduces quantization noise which is assumed to be independent of the random Gaussian noise introduced in the transmission path. Hence, the effective carrier-to-noise ratio threshold is smaller than what is calculated by assuming random-noise performance. A method for calculating the quantization noise power with a given bit-precision for an A/D converter is described. This involves the calculations of the peak-to-average ratio of the QAM scheme of interest. This analysis can then be used to determine the bit-precision requirements of the A/D converter, which has a direct correlation to the cost of a QAM receiver. For 64-QAM operation with the given parameters, a 9 bit A/D converter is shown to offer the best trade-off between performance and cost