Experimental Demonstration of Non-Hermitian Symmetry for DC-SC-FDM in UOWC Systems

This study demonstrates the high spectrum efficiency of DC offset single-carrier frequency division multiplexing (DC-SC-FDM) for underwater optical wireless communications (UOWC). I and Q components were separately transmitted using dual lasers. As a result, the requirement of Hermitian symmetry is alleviated, and the computation time latency is reduced. The Gram–Schmidt orthogonalization procedure was adopted to address the I and Q orthogonality. The system comprises a 1024-point inverse fast Fourier transform (IFFT), a cyclic prefix of 32 samples, and a digital-to-analog converter (DAC) of 400 Msps, and laser diodes possess a wavelength of 553 nm with a power of 150 mW. The study includes real transmissions in a freshwater communication channel and reports experimental results. In addition, the bit error rate has been evaluated. The results show that at the forward error correction (FEC) limit, a communication distance of 10 m can be achieved. A peak-to-average power ratio reduction of 4.96 dB is reached

PERFORMANCE EVALUATION OF A MULTICARRIER MIMO SYSTEM BASED ON DFT-PRECODING AND SUBCARRIER MAPPING

The ever-increasing end user demands are instigating the development of innovative methods targeting not only data rate enhancement but additionally better service quality in each subsequent wireless communication standard. This quest to achieve higher data rates has compelled the next generation communication technologies to use multicarrier systems e.g. orthogonal frequency division multiplexing (OFDM), while also relying on the multiple-input multiple-output (MIMO) technology. This paper is focused on implementing a MIMO-OFDM system and on using various techniques to optimize it in terms of the bit-error rate performance. The test case considered is a system implementation constituting the enabling technologies for 4G and beyond communication systems. The bit-error rate optimizations considered are based on preceding the OFDM modulation step by Discrete Fourier Transform (DFT) while also considering various subcarrier mapping schemes. MATLAB-based simulation of a 2 × 2 MIMO-OFDM system exhibits a maximum of 2 to 5 orders of magnitude reduction in bit-error rate due to DFT-precoding and subcarrier mapping respectively at high signal-to-noise ratio values in various environments. A 2-3dBs reduction in peak-to-average power ratio due to DFT-precoding in different environments is also exhibited in the various simulations

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC

Peak-to-average power ratio reduction for DCO-OFDM underwater optical wireless communication system based on an interleaving technique

In underwater direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) system, high peak-to-average power ratio (PAPR) brings in-band distortion and out-of-band power. It also decreases the signal-to-quantization noise ratio of the analog-to-digital converter and the digital-to-analog converter. A time–frequency-domain interleaved subbanding scheme is proposed to reduce the PAPR of underwater DCO-OFDM system with low computation complexity and bit error rate (BER). The system BER is evaluated by the distances of the underwater optical wireless communication (UOWC), as well as by the signal attenuation of the UOWC channel. A least-square channel estimation method is adopted for adaptive power amplification at the receiver side, to further decrease the system BER

PAPR reduction techniques in generalized inverse discrete fourier transform non-orthogonal frequency division multiplexing system

A promising system of Generalized Inverse Discrete Fourier Transform Non-Orthogonal Frequency Division Multiplexing (GIDFT n-OFDM) system can fulfil the requirement of supporting higher data rate in Fifth Generation (5G) technology. However, this system experience High Peak to Average Power Ratio (PAPR) due to massive number of subcarriers signal is transmitted. In this paper, three types of usual PAPR reduction techniques were applied in GIDFT n-OFDM system which are Clipping, Partial transmit Transform (PTS) and Selective Mapping (SLM). The system performance is compared and evaluated using Complementary Cumulative Distribution Function (CCDF) plot. Simulation results show that SLM technique give significant reduction of PAPR 9 dB of the original performance

Analysis of using OFDM for short-range, multı-user, underwater acoustic communication

Cataloged from PDF version of article.Acoustic waves are being used in several underwater applications, such as SONARs, underwater communication systems. Most of already developed and deployed underwater communication systems use narrow band communication and lacks layered communication approach. In this thesis, we propose a spread spectrum, layered architecture for underwater communication system, such as for SCUBA divers. The communication device shall be designed such that divers can communicate with each other in shallow water, short range in a multi-user fashion and provide not only voice communication but also data transmission as well. The device shall use Orthogonal Frequency Division Multiplexing (OFDM) as a spread spectrum technique. The OFDM technique is selected from other spread spectrum techniques due to it’s inherent ability to combat the channel impairments and flexibility of implementing the communication system using software defined radio (SDR). The spread spectrum system shall operate in 100 kHz to 300 kHz frequency band using wideband acoustic transducers. In this work, we studied a layered architecture for the communication device. We mainly studied the application layer, data link layer and physical layer in order to analyze the achievable data rate and performance. In this work, we tried to find the optimal communication parameters to achieve guaranteed communication performance for possible scenarios. The communication parameters are set in order to achieve best performance for the worst condition. Using the optimal parameters, the system shall occupy 5 users voice and data communication at the same time using the entire frequency band at the same time, however with certain Grade of Service (GOS) the capacity shall be increased. The capacity of the system shall further be increased if the system uses adaptive communication parameters that are adapted to changing channel and user conditions. The system using adaptive communication parameters shall provide at most 16 users’ voice and data communication using the entire frequency band at the same time.Öktem, Kemalettin KeremM.S

Underwater acoustic communications in warm shallow water channels

Ph.DDOCTOR OF PHILOSOPH

Estimação de canal para comunicações subaquáticas utilizando MIMO Massivo

O propósito desta dissertação de mestrado é demonstrar como a inserção das variáveis de ruído impulsivo e estimação de canal, afetam os sistemas de comunicações acústicos subaquáticos, associado à utilização de técnicas de múltiplas antenas (Multiple Input Multiple Output [MIMO]). Também tem como objetivo ilustrar como os sistemas MIMO tendem a comportar-se quando utilizam diferentes recetores, designadamente dois de baixa complexidade, o Equal Gain Combiner (EGC) e o Maximum Gain Combiner (MRC), e um de maior complexidade, o Zero Forcing. Cada um destes recetores foi analisado em diferentes cenários de ambiente, vários de níveis de correlação de canal entre antenas, e perante diferente número de antenas de transmissão e receção. Esta dissertação tende ainda a demostrar como mitigar os efeitos negativos que os sistemas MIMO apresentam relacionado com os altos níveis de correlação causado pelo insuficiente espaçamento entre as antenas, experimentado em comunicações acústicas subaquáticas

Review of Recent Trends

This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe