考虑APD的部分相干光OFDM-UWOC系统性能

Performance of APD-based OFDM-UWOC system with partially coherent beams

对于实际的水下无线光通信系统,系统误码性能主要受到海洋湍流和接收机噪声的制约。考虑散粒噪声和热噪声的影响,对弱海洋湍流环境下基于雪崩光电二极管的部分相干光辅助OFDM-UWOC系统的误码性能进行了分析。研究中利用波束扩展函数建立了吸收、散射、未对准和海洋湍流共同影响下的聚合信道衰落模型,进而分别导出不同噪声限制下的系统平均误码率理论表达式。受散粒噪声限制时,研究了接收机噪声温度、平均接收光强及雪崩光电二极管雪崩增益值的大小对系统可靠性的影响;受热噪声限制时,给出了部分相干光特征参数和海洋湍流特性参数对该系统可靠性的影响。结果表明,对于雪崩光电二极管而言,接收机温度和平均接收光强大小都会在一定程度上影响系统误码性能。因此,通过选择合适的雪崩光电二极管雪崩增益值,能够在一定程度上提升该OFDM-UWOC系统的误码性能。此外,部分相干光和海洋湍流的变化会对系统的误码性能产生影响。

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.