Abstract
Underwater wireless optical communication is facing absorption, scattering problems, which, in principle, can be greatly resolved by underwater photon-counting communication (UPCC) technology that exhibits high-sensitivity communication characteristics in long-range underwater wireless optical communication. Recent studies on UPCC are mainly focused on a single intensity modulation such as on–off keying (OOK) and pulse position modulation (PPM) technologies, and the comprehensive analysis of communication performance combing OOK modulation and digital pulse modulations remains a lack. To this, by using a UPCC system based on a single-photon avalanche diode, we reveal the communication performances of OOK, PPM, differential pulse interval modulation (DPIM), differential pulse position modulation (DPPM), and dual-header pulse interval modulation, and find that (1) the PPM has the longest transmission distance at the same bit error ratio when M > 2, but the lowest communication rate under identical modulation bandwidth and average transmit power; and (2) the DPPM and DPIM perform the optimum communication performance at the fixed communication rate when M = 8. We thus conclude that the DPPM and DPIM have advantages of low modulation bandwidth and long time slot time compared with PPM, indicating the significance of reducing the difficulty of signal synchronization and the complexity of the underwater photon-counting system accordingly.
Highlights
Lasers, since their invention, have been widely used in the fields of sensing [1], communication [2], and measurement [3] because of their special characteristics such as high directionality, high brightness, monochromaticity, and good coherence
The same analysis is done under a fixed communication rate
The article compares the variation of bit error ratio (BER) with a transmission distance of communication system for on–off keying (OOK), pulse position modulation (PPM), differential pulse interval modulation (DPIM), differential pulse position modulation (DPPM), and dual-header pulse interval modulation (DH-PIM) under the same modulation bandwidth
Summary
Since their invention, have been widely used in the fields of sensing [1], communication [2], and measurement [3] because of their special characteristics such as high directionality, high brightness, monochromaticity, and good coherence. Achieving long-range, high-speed underwater wireless optical transmission still faces challenges due to the existence of severe water attenuation and the bandwidth limitations of blue–green wavelength devices [9] This makes high-speed signal modulation and demodulation techniques and high-sensitivity reception techniques an important research topic in the field of UWOC. High-energy utilization modulation technologies represented by pulse position modulation (PPM) and high-sensitivity reception technology represented by photon-counting have become hot topics to improve power efficiency and achieve long-distance transmission. Compared with OOK modulation, PPM has higher power utilization efficiency but lower bandwidth utilization [22], which is often used in photon-counting communication systems to improve sensitivity. Where η is the photon detection efficiency of SPAD, the average photon arrival rate λs, and λb is related to the received optical power PR of signal and background Pb; the relational expression is given as: λs ηPR hν (8). For PPM, DPIM, DMMP, and DH-PIM symbol, the symbol error ratio (SER) for a continuous output L-order digital pulse modulation signal is [38]: PSER 1
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