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Coded GFDM with decision feedback equaliser for enhanced performance in underwater wireless optical communication

Hema R., Ananthi A., Diana D. C.

Opto-Electronics Review

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2024

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Vol. 32, No. 1

art. no. e148697

EN

Underwater wireless optical communication is the best alternative for many applications especially for high bandwidth data communication between underwater objects and vehicles. The implementation of coding scheme along with advanced modulation technique and equalisation methods is identified as a key research scope for enhancing the performance of the system. In this paper, the coded generalised frequency division multiplexing (GFDM) technology is employed to provide high-data rates and less out-of-band emission. The Bose-Chaudhuri-Hocquenghem (BCH) and Reed-Solomon (RS) coding schemes along with equalisation techniques namely normalised least mean square (NLMS)-based decision feedback equalisers (DFE), minimum mean square error (MMSE) and zero forcing (ZF) are utilized to reduce inter symbol interference (ISI). The bit error rate (BER) performance is evaluated in the presence of pointing error (PE) and turbulence using Monte Carlo channel modelling simulations. The results showed that RS coding with NLMS-DFE outperforms other techniques and achieves a BER of roughly 10⁻⁵ with a signal-to-noise ratio levels below 20 dB. The simulation results demonstrate that RS code with 15 total symbols per code word and 3 data symbols, i.e., RS (15, 3) and BCH code with 31 total symbols in a code word and 6 data symbols, i.e., BCH (31, 6) provided the best error performance among other coding schemes employed. It is inferred that RS (15, 3) coded 2 × 2 multiple input multiple output systems with NLMS-DFE achieved a BER value of 1.1925 × 10⁻⁵ at 11 dB which is 16 dB less than uncoded system. Thus, the coded GFDM improves overall BER performance and has the potential to provide higher reliability for internet of underwater things (IoUT) applications.

2

Variable antennas positions solution to reduce pointing errors due to wind speed and temperature coupled effects during free space optical link using matrix Rician pointing error model

Teuma Mbezi Michel, Eke Samuel, Som Idelette Hermine Judith, Mouangue Ruben Martin

Optica Applicata

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2023

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Vol. 53, nr 3

393--406

EN

Pointing errors (PE) during free space optical (FSO) transmission can be caused by laser beam wander due to thermal and wind dynamic instability. The aim of this work is to study the coupled effects of temperature and wind speed on PE using matrix Rician pointing error (MRPE) model; then show how variable antennas height can reduce PE due to wind speed and temperature coupled effects. To achieve this purposes, average PE expression was established using MRPE model. Then considering a Gaussian beam wave and Monin–Obukhov similarity functions for the structure parameters of temperature, explicit relationship was established between average PE, temperature and wind speed. It comes out of this study that under dynamic turbulence, one can appropriately modify temperature to reduce PE due to dynamic instability and reciprocally. Depending on turbulence large cells or frozen turbulence eddies distribution, PE can be reduced by appropriately modified antennas height or the distance between transmitter and receiver. That is why this work suggests to install variable or dynamic antennas (rather than fixed ones) which could intelligently modify its positions according to laser beam wander created by atmospheric turbulence.

3

Impact of Finite-Sized Aperture on the Performance of Differential Multihop DF-FSO Network

Agarwal Deepti, Yadav Poonam

International Journal of Electronics and Telecommunications

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2022

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Vol. 68. No. 4

807--813

EN

This paper investigates the differential binary modulation for decode-and-forward (DF) based relay-assisted free space optical (FSO) network under the effect of strong atmospheric turbulence together with misalignment error (ME). The atmospheric fading links experience K-distributed turbulence. First we derive novel closed form expression for average bit error rate (BER) and outage probability (OP) in terms of Meijer’s G function. Further, the OP of differential DF-FSO system with multiple relays is derived. We also analyze the asymptotic performance for the sake of getting the order of diversity and the coding gain. The power allotment term is utilized to examine the effect of different power allotment techniques on BER and OP. The simulation results have been used to validate the derived analytical results.

4

Optical path pointing error and coaxiality analysis of APT system of space laser communication terminal

Furui Zhang, Ping Ruan, Junfeng Han

Optica Applicata

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2021

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Vol. 51, nr 2

203--222

EN

Precision beam pointing is the key indicator for APT (acquisition, pointing and tracking) system in space laser communication. The laser travels inside the optical system and the pointing vector will be affected by an assembly error of the axis and reflectors. In this paper, the model of the optical path pointing error and coaxiality error induced by the assembly error are established; the error distribution is given and a quantitative analysis is performed. The results show that the magnitude of pointing error is affected by the axis assembling error greatly but its distribution is susceptible to the reflector assembly error. Finally, the correction of coaxiality is performed and tested. The experimental results show that the coaxiality error can be greatly improved and the mean value of the coaxiality error of a beacon path and a signal path are 14 and 9.6 μrad, respectively, which meets the requirements. This work can provide guidance for design and assembly of the APT and contribute to the improvement of its pointing performance.

5

FSO system performance analysis based on novel Gamma–Chi-square irradiance PDF model

Todorović Jelena, Spalević Petar, Panić Stefan, Milosavljević Bojana, Gligorijević Milan

Optica Applicata

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2021

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Vol. 51, nr 3

335--348

EN

In order to provide a novel analytically traceable free space optics (FSO) channel model for describing turbulence based irradiance fluctuations, following basic scintillation theory principles, we have derived closed-form expression for probability density function (PDF) of a new statistical Gamma–Chi-square model. Further, capitalizing on provided model, error performances of FSO system over on-off keying (OOK) transmission scheme both in the presence of atmospheric turbulence and misalignment fading (pointing error) is investigated. For both cases, the average bit error rate (ABER) at the receiving side of the system is determined in an analytically closed form. The results are graphically presented in order to analyze the impact of different levels of turbulence, as well as other relevant parameters, on the quality of the received signal in the OOK modulated FSO system.

6

Synthesis and Optimization of Neural Network Parameters for Control of Non-linear Objects

Aleksander M., Pohrebennyk V., Strembitskyy M.

Przegląd Elektrotechniczny

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2014

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R. 90, nr 5

207--210

EN

The possibility of using artificial neural network (ANN) for the construction of precise control of dynamic objects with variable parameters is considered. Approach to the synthesis of topology and learning algorithm based on recurrent Elman’s ANN with auxiliary feedback is suggested. The results of modeling of ANN operation in the system of control guided by large-sized antennas are given.

PL

Opisano możliwość wykorzystania sztucznej sieci neuronowej (SSN) do precyzyjnego sterowania dynamicznych obiektów o zmiennych parametrach. Przedstawiono syntezę topologii i uczenia algorytmu opartego na SSN Elmana z dodatkowych informacji. Zaprezentowano wyniki modelowania SSN do zarządzania systemem pozycjonowania dużych anten.