No abstract

Mobile nodes can encounter many challenges in underwater environments during communication due to turbidity, suspended particles, small bubbles, and turbulence. These factors cause absorption and scattering, ultimately corrupting optical signals. Error-correcting codes can be used to correct certain corrupted bits and thus reduce the errors in a channel. In this work, a Bose-Chaudhuri-Hocquenghem (BCH) (31, 16)-coded underwater wireless optical communication (UWOC) system is proposed to enhance the communication performance between power-efficient sensor nodes. The proposed BCH-coded system needs a reasonable amount of computing capability and is powered by a battery, enabling the node to have an onsite data processing unit and untethered communication. The encoder and decoder algorithms of the BCH code are implemented on the Embedded C software and coded to run on an Atmel ATmega128A microcontroller. The system's performance is evaluated by emulating the effects of scattering and absorption, noise due to surrounding and ambient light, turbidity, air bubbles, and turbulence in a natural underwater environment. Moreover, a 0.5 Mbps BCH-coded link achieves a 93.5% PSR, which is 6% better than that of the uncoded system, at a moderate turbidity level of 64 NTU, in the presence of weak turbulence (induced by a pump at a 2.5 L/min displacement rate) and air bubbles (generated by an aerating jet at an airflow rate of about 1.2 L/min).

A modified Wilkinson Power Divider is proposed in this paper that utilizes defected ground structure (DGS) in parallel with an isolation resistor. The proposed DGS section is incorporated between the output ports, and the isolation resistor is soldered in parallel with the DGS in the ground plane, instead of on the top plane as in a conventional Wilkinson power divider, to achieve improved or preferable isolation. The proposed design is comprised of two pairs of microstrip transmission lines with equal impedances and varied electrical lengths. The parameters of the main circuit and the DGS section are acquired separately. The parameters of the proposed main circuit are derived by applying conjugate matching theory. Dumbbell-shaped DGS is introduced in the ground plane between the output ports, which acts as a parallel resonator, yielding an attenuation pole at the resonant frequency that contributes to improved isolation. By applying the previous well-known circuit theory, the lumped elements of the equivalent circuit of the DGS were achieved. The physical dimensions of the equivalent circuit for the DGS section were obtained by three-dimensional EM simulation. The measured results show improved isolation, return loss and better bandwidth as compared with other similar works. Furthermore, the proposed circuits designed at resonating frequencies of 3 and 2 GHz presented comparatively good return losses, S11 of about −25.54 and −31.24 dB, respectively, and achieved improved isolations, S32 between the output ports, in an order of about −40.83 and −36.05 dB, respectively, which is rather exceptional and desirable.