A detection technique for high order QAM in the presence of transmitter angular skew

Angular skew arising from imperfect biasing of the transmitter can cause a significant performance degradation in high speed optical QAM systems. A simple approach to detect QAM signal under the effect of angular skew is Gram-Schmidt orthogonalization procedure (GSOP). However, this approach has poor performance when the size of QAM constellation exceeds 256. To solve this problem, a new detection algorithm is proposed. From the results, the proposed technique outperforms the GSOP. It provides the skew tolerance of up to 25-degrees at BER of 10-5 for the expense of 1 dB Eb/No penalty.