Optimal phase threshold for D-band vector millimeter-wave system with frequency sextupled

Optical radio-frequency vector signal generated by optical carrier suppression in one single-electrode modulator can realize frequency sextupled that has the advantage of low cost and simple architecture. However, in the transmitter side, pre-coding of phase or amplitude is necessary in order to match the phase or amplitude of the recovered quadrature amplitude modulation (QAM) signal. After square-law detection at photodiode, the detected QAM signals usually have one non-uniform phase distribution because the characteristics of the optical and electrical devices are not perfect. In order to reduce the bit error rate, we propose to use optimal threshold of error decision for nonuniform phase distribution. Using this scheme, The receiver sensitivity, at the hard-decision forward-error-correction threshold, 3.8 x 10(-3), is improved by 3 dB for 4 Gbaud (8 Gbit/s) quadrature-phase-shift-keying millimeter wave signal at 144 GHz.