基于多重降质复合信道的UWOC系统误码率性能研究

Bit Error Rate Performance Study of UWOC System Based on Multiple Degenerate Composite Channels

针对海水信道吸收、散射、气泡和湍流效应等对水下无线光通信系统性能的影响,建立融合多重降质效应的水下无线光复合信道模型。基于Mie散射理论计算水下微气泡群的体散射函数、散射系数和散射相函数。湍流信道模型采用混合指数广义伽玛分布进行建模。随后,将复合信道对信号的衰减以及湍流噪声等效传递至光信号,推导出了复合信道在通断键控调制方式下误码率的封闭表达式。此外,研究了湍流强度、气泡数量、链路距离和海水水质等参数对误码率性能的影响。研究结果显示,随着链路距离的延伸,误码率线性增长,表现出退化趋势;港口海水因其较高浊度和丰富的悬浮颗粒,难以保证系统通信的可靠性。此外,气泡的存在和链路距离的扩展同样会显著加剧误码率的恶化。

Underwater Wireless Optical Communication(UWOC)capitalizes on the blue-green segment of the light spectrum which is subject to minimal attenuation in marine environments,thereby rendering it optimal for the conveyance of information.The advantages of UWOC are manifold,it boasts of swift data transmission,negligible latency,and fortified confidentiality.However,UWOC grapples with significant barriers which encompass the limitation of transmission range and the deleterious effects attributable to the intrinsic properties of seawater,as well as marine turbulence-factors like absorption,scattering,bubbles and turbulence that collectively compromise communicative efficiency.To systematically confront these impediments and to gauge the comprehensive influence of the aforementioned factors on UWOC system efficacy,this inquiry has formulated an integrative underwater wireless optical channel model.This archetype not only encapsulates solitary influences but also their concomitant interactions and aggregate impact on signal transmission.By harnessing the Mie scattering theorem,the research meticulously delineates the volume scattering function,the scattering coefficient,and the phase function of microbubble assemblages in seawater—pivotal determinants essential for the assessment of scattering phenomena on the propagation of optical signals.Addressing turbulence,an elaborate channel model featuring a mixed exponential generalized Gamma distribution is employed,defining the statistical behavior of turbulence to faithfully represent the stochastic and unpredictable nature of the channel.This study extends its analysis to include the repercussion of signal attenuation and acoustic noise as a consequence of turbulence,effectively projecting these perturbations onto the optical signals disseminated through the composite channel.Importantly,it elucidates a closed-form expression for the Bit Error Ratio(BER)within the composite channel,employing On-Off Keying(OOK)modulation,thus establishing a theoretical groundwork for the analysis of UWOC system performance.The research delves into the impact of critical determinants such as turbulence strength,bubble density,transmission range,and marine water quality on the BER metrics of UWOC systems.It is discerned that heightened turbulence intensity incrementally necessitates a greater minimum Signal to Noise Ratio(SNR)at the receiver end to maintain a predetermined average BER.Consistent with this SNR,an augmentation in turbulence intensity conspicuously degrades system throughput,inducing a systematic deterioration in BER performance.Within a transparent seawater milieu at a transmission span of 20 m,with a bubble concentration of 3×10^(6) per cubic volume,the system′s mean BER is recorded at 4.57×10^(-4).As the bubble density escalates to 9×10^(6) and subsequently to 9×10^(7) per cubic volume,the average BER correspondingly declines to 5.76×10^(-4) and 1.19×10^(-2).In scenarios of turbulence characterized by a scintillation index of 1.9328,the system is adept at sustaining low BER transmissions.Ensuring dependable communication quality with an average BER falling below 10-3 across an array of aquatic environments-be it crystalline seawater,littoral waters,or murky harbor waters-the utmost permissible transmission distances with bubble presence(at a density of 1×107 per cubic volume)are confined to 22.5 m,10.4 m,and 2.3 m respectively.Absent bubble interference,these distances are extendable to 28.0 m,13.5 m,and 2.7 m.Given the pronounced absorption and scattering induced by elevated turbidity and suspended particulates,securing long-range communication in silt-laden harbor waters presents a significant hurdle.Additionally,the study substantiates that elevating the link distance precipitates an almost linear augmentation in BER,indicative of a noteworthy degeneration in signal integrity.The outcomes not only underscore the exigency of crafting and fine-tuning UWOC systems attuned to the vicissitudes of the oceanic realm but also accentuate the latent efficacy of modulation methodologies and channel coding strategies as instrumental in amplifying system competence.