Abstract
Underwater wireless optical communication (UWOC) is able to provide large bandwidth, low latency, and high security. However, there still exist bandwidth limitations in UWOC systems, with a lack of effective compensation methods. In this paper, we systematically study the bandwidth limitation due to the transceiver and underwater channel through experiments and simulations, respectively. Experimental results show that by using the 7-tap maximum likelihood sequence estimation (MLSE) detection, the maximum bitrate of the simple rectangular shape on–off-keying (OOK) signaling is increased from 2.4 Gb/s to 4 Gb/s over 1 GHz transceiver bandwidth, compared to the conventional symbol-by-symbol detection. For the bandwidth limitation caused by the underwater channel, we simulate the temporal dispersion in the UWOC by adopting a Monte Carlo method with a Fournier–Forand phase function. With MLSE adopted at the receiver, the maximum available bitrate is improved from 0.4 to 0.8 Gb/s in 12 m of harbor water at the threshold of hard-decision forward-error-correction (HD-FEC, 3.8 × 10−3). Moreover, when the bitrate for 0.4 Gb/s 12 m and 0.8 Gb/s 10 m OOK transmission remains unchanged, the power budget can be reduced from 33.8 dBm to 30 dBm and from 27.8 dBm to 23.6 dBm, respectively. The results of both experiments and simulations indicate that MLSE has great potential for improving the performance of bandwidth-limited communication systems.
Highlights
The mature and available technology is based on acoustic communication
Volume Scattering Phase Function The core of the Monte Carlo simulation of seawater scattering is the interaction between a single photon and scattering particles, with the photon scattering depending on the volume scattering phase function of the scattering medium
The maximum likelihood sequence estimation (MLSE) algorithm can mitigate the ISI introduced by channel temporal dispersion according to a sequence of bits [28,29]
Summary
High-bandwidth underwater wireless communication has gained increasing interest recently and is considered to be applicable in many marine engineering fields, such as underwater high-definition video transmission and deep-sea observation. Many previous underwater optical transmission experiments have proposed several solutions to increase the channel bandwidth from Megahertz to Gigahertz (GHz). In [4–11], several experiments have demonstrated from hundreds Mbps to more than ten Gbps for meters’ UWOC transmission with on-off-keying (OOK) or high order modulation. X. Liu et al have experimentally demonstrated a 2.70 Gbps data rate over a 34.5 m underwater transmission distance by Photonics 2022, 9, 182 transmission with on-off-keying (OOK) or high order modulation. The device of the receiver itself produces background radiation noise and dark are reflected in the underwater channel impulse response. CInhatnhniselpMarotd,ewl e model the underwater channel characteristics of the UWOC system by adIonptthinisgptahret,MwoenmtooCdaerllothme eutnhdoedr[w17a–te2r1]chtoagnentehlecrhwairtahctaeFriosutircnsioerf–tFhoerUanWdO(FCF)sypshtaesme fbuynacdtiopnt[in21g].the Monto Carlo method [17–21] together with a Fournier–Forand (FF) phase functWioen u[2s1e].the Monte Carlo method to simulate the process of photon propagation in waterWteo uosbetatihnethMeocnhtaenCnaerllroesmpeotnhsoedfutoncstiimonulaht(et )thme penroticoensesdofabpohvoet.oTnhperoMpoangtaetiCoanrlion mwaettherodtoisopbtraoipnotsheed cahsaanknienldreosfpnounmseerfiucnalctciaolncuhla(tt)iomn emnettiohnoeddgaubidoevde.byThperoMbaobnitleityCtahreloomryet,hcoodmmis opnrloypsooslevdinagsmaakniyndcoomf pnuutmateiornicaallpcraolcbulelmatisounsimngetrhaonddogmuidoerdpsbeyudporo-rbaanbdiolimty nthuemorbye,rcso.mItmisoonflgyrseoaltvsiniggnmifiacnayncceomfopr uUtWatiOonCaltoprsotubdleymtsheusminugltriapnadthomtraonrspmsiesusdioon-roafnldigohmt annudmtbeemrsp.oIrtalischofargarcetaetrissitgicnsifiocfatnhcee ufonrdeUrWwaOteCr tcohasntundeyl itnhesemawulattiepra.thThtreaMnsomnitsesiConarloof mligehtht oadndis twemidpeolyraul scehdarianctthereisrteicsesaorfchthoef uscnadteterrwinagtecrhcahraanctneerilsitnicsseoafwaasteera.wTatheer Mmoednitae [C2a2r–l2o6]m. Epahcohtopnhiostoinnitiisaliinzietidalwizietdh wwietihghwte(iwgh=t (1w), l=o1ca),tiloonca(t0io, n0,(00),,0a,n0d),parnodpapgroaptiaognattiimone t(itm=e0()t. =A0ft)e. rAsfetevrersaelvienrtaelrianctteiroancs-, ttihoenps,htohteonphisotdoenteicsteddetbeycttehdebpyhtohteoeplehcottroicealelcdteritceacltodre(tPecDto) ro(rPaDbs)oorrbaebdscoormbepdlectoemlypbleytethlye bsuystpheensduesdpepnadrteidclpesa.rFtiicgleusr.eF2igsuhroew2ssthhoewssimthuelastiimonulflaotiwoncfhloarwt fcohraertacfohrpehaochtopnhmotootniomn ointtihoenMinotnhtee MCaornlotemCeatrhloodm[e1t8h].od [18]
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