Abstract:

In practical underwater wireless optical communication (UWOC) system,turbulence and receiver noise are two important factors that limit the system performance.In this paper,with shot and thermal noise,the average bit error rate (ABER) performance of orthogonal frequency division multiplexing (OFDM) assisted UWOC system based on the avalanche photodiodes (APD) over the weak oceanic turbulence condition has been investigated.To effectively characterize the impacts of absorption,scattering and misalignment as well as underwater optical turbulence,a composite fading model has been adopted in this work where beam spread function (BSF) is utilized.After that,the analytical expressions of ABER in shot-noise-limited and thermal-noise-limited conditions are derived,respectively.Under shot-noise-limited condition,in this paper we analyze the ABER performance affected by various parameters,specifically,receiver noise temperature,average optical signal intensity and APD gain.Similarly,under thermal-noise-limited condition with partial coherent beams (PCB) being adopted,the specific impact of underwater optical turbulence on the reliability of the considered UWOC system is also illustrated.Numerical results reveal that,for the internal factors of the photodetector,the receiver temperature and average optical signal intensity will affect the ABER performance of the system.Furthermore,choosing an appropriate APD gain can obtain a better ABER performance of the UWOC system.Moreover,PCB and the underwater turbulence will affect the ABER performance.

Key words: underwater wireless optical communication, partially coherent beams, avalanche photodiodes, beam spread function