Performance of OOK and Low-Order PPM Modulations in Optical Communications When Using APD-Based Receivers

This correspondence compares OOK and low-order PPM signaling formats in terms of bit error probabilities versus required signal counts per bit. The results show that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values are from 200 to 400. When using QPPM,
k_{eff} = 0.006
, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 10
^-6
bit error probability.