Error rate considerations for 256-QAM systems in presence of adjacent channel interference

Performance degradation of 256-QAM systems in the presence of adjacent channel interference and thermal noise is studied. The authors consider two adjacent interferers of the same modulation format as the useful signal, placed symmetrically around it. The results are presented as equivalent carrier-to-noise (C/N) degradation for different channel spacings and carrier-to-interference (C/I) ratios. To allow easy comparison with 64-QAM systems, the authors present the degradation of these systems for the same values as those of the 256-QAM schemes. It is found that for C/I=0 dB and for a 256-QAM system using raised-cosine filters with alpha =0.5