QAM–OFDM transmission in underwater wireless optical communication system with limited resolution DAC

Underwater wireless optical communication (UWOC) can realize high speed, low delay and flexible information transmission. We experimentally demonstrate a 3-m UWOC system using blue laser diode and avalanche photodiode with quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) transmission. We achieve net bit rates of 6.23 Gb/s at a bit error rate (BER) of 1.55 × 10 −3 , by using 128-QAM OFDM signals. High-order QAM signals require higher bit resolution of digital-to-analog converter (DAC). Therefore, the effect of quantization noise on transmission performance is further investigated. In order to meet the requirement that the BER is lower than 3.8 × 10 −3 , the bit resolution of DAC is required to be at least 5, 6 and 7 bit for 32-QAM, 64-QAM and 128-QAM signals, respectively.