Crosstalk Effects in Quadrature Amplitude Modulation: The Demand for an Optimized Constellation

Crosstalk is a significant issue in multichannel communications that can affect the performance of digital communications. Quadrature Amplitude Modulation (QAM) is a class of modulation methods that uses the orthogonality of signals modulated with carrier frequency and quadrature phase to realize multichannel transmission. This paper focuses on a QAM256 modulation method, where 256 different symbols are constructed on both the in-phase and quadrature phase. The paper conducts a simulation to model the cross-channel interference caused by crosstalk, which affects the performance of demodulation and degrades the bit rate of transmission. The simulation involves a hypothetical channel with a carrier frequency of 5 GHz and a sampling rate of 1 THz. The results show that the crosstalk between adjacent channels for each stream of bits could be affected by order of symbols in the constellation map. The location of 0 and 255 symbols in binary coded constellations are not optimized and could have a significant effect on crosstalk in multichannel data transmission.