8 research outputs found
On PAPR Reduction in Pilot-Assisted Optical OFDM Communication Systems
Full text linkThis paper presents a novel theoretical characterization of the pilot-assisted (PA) technique proposed for peak-to-average-power-ratio (PAPR) reduction in optical orthogonal frequency division multiplexing (O-OFDM). The two systems considered are direct-current biased O-OFDM (DCO-OFDM) and asymmetrically clipped O-OFDM (ACO-OFDM) in optical wireless communications. The DCO-OFDM and ACO-OFDM time-domain signals approach Gaussian and half-Gaussian distributions, respectively. The PA technique uses P iterations of a pilot sequence to rotate the phase of U data symbols within a PA O-OFDM frame and select the frame with the least PAPR. Thus, we utilize order statistics to characterize the PAPR distributions of the PA DCO-OFDM and ACO-OFDM system. The PA technique results in higher reduction in PAPR for high P but at the expense of increased complexity. In the theoretical framework developed, we are able to determine P that gives reasonable PAPR reduction gain. The theoretical analysis of PAPR reduction effects on the average optical and electrical signal power is studied. Results show that the PA technique is capable of reducing the optical energy per bit to noise power spectral density E b(opt)/N0 ratio required to meet target bit-error-rate in an additive white Gaussian noise channel. Comparisons of the analytical results of PA O-OFDM signal with that of computer simulations show very good agreement.</p
Analysis of PAPR in optical OFDM systems with grouped LEDs
Full text linkThe need for multiple transmit chains poses a major challenge in optical orthogonal frequency division multiplexing (OFDM) system utilising grouped light emitting diodes (LEDs) for the purpose of peak-to-average power ratio (PAPR) reduction. Thus, recent study propose the use of pilot-assisted (PA) electrical PAPR reduction technique to further reduce PAPR and limit the number of transmit chains in the system. This paper presents the application of order statistics to derive the analytical solutions of PAPR distributions in the PA optical OFDM system utilising grouped LEDs. It is shown that the results obtained via analysis are in good agreement with that of computer simulations
Pilot-Aided Frame Synchronization in Optical OFDM Systems
Full text linkEfficient frame synchronization is essential for data recovery in communication systems. In this study, a single pilot sequence is used to achieve both frame synchronization and peak-to-average power ratio (PAPR) reduction. The two systems considered are direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) and asymmetrically clipped O-OFDM (ACO-OFDM). The pilot symbol is allocated to odd indexed subcarriers only. Thus, the synchronization algorithm leverages the mirror symmetric property of the pilot symbol within a frame to detect the start of the pilot signal at the receiver. This scheme has low complexity and gives precise frame synchronization at signal-to-noise ratios as low as 4 dB in an indoor visible light communication (VLC) channel
Deploying a wireless sensor network to track pesticide pollution in Kiu wetland wells: a field study
Full text linkWater pollution from pesticides is a major concern for regulatory agencies worldwide due to expensive detecting mechanisms, delays in the processing of results, and the complexity of the chemical analysis. However, the deployment of monitoring systems utilising the internet of things (IoT) and machine-to-machine communication technologies (M2M) holds promise in overcoming this major global challenge. In this current research, an IoT-based wireless sensor network (WSN) is successfully deployed in rural Kenya at the Kiu watershed, providing in situ pesticide detections and a real-time data visualisation of shallow wells. Kiu is an off-grid community located in an area of intensive agriculture, where residents face a high exposure to pesticides due to farming activities and a reliance on shallow wells for domestic water. The evaluation of path loss models utilising channel characteristics obtained from this study indicate a marked departure from the continuous signal decay with distance. Transmitted packets from deployed sensor nodes indicate minimal mutations of payloads, underscoring systems reliability and data transmission integrity. Additionally, the proposed design significantly reduces the time taken to deliver pesticide measurement results to relevant stakeholders. For the entire monitoring period, pesticide residues were not detected in the selected wells, an outcome validated with lab procedures. These results are attributed to prevailing dry weather conditions which limited the leaching of pesticides to lower layers reaching the water table.</p
Average BER evaluation of the uplink OFDM-based NOMA system under SIC and channel estimation error
Full text linkThe non-orthogonal multiple access (NOMA) scheme has been recognized as a promising candidate for future generation wireless communication networks that require a high data rate and spectral efficiency. In order to achieve a superior spectral efficiency, the orthogonal frequency division multiplexing (OFDM) technique with the robust channel estimation algorithm can be combined with the NOMA scheme. However, due to the inherent problem of inter-carrier interference in the OFDM-based systems, channel estimation using training symbols are not usually perfect. Furthermore, the successive interference cancellation (SIC) process commonly carried out in NOMA systems to address the interference among users is also imperfect under practical scenarios. Thus, a theoretical framework of the OFDM-based NOMA system to analyze the effect of both the imperfect SIC and channel estimation errors is presented in this paper. In particular, the effect of both the channel estimation errors and imperfect SIC, introduced at the receiver, on the bit error rate (BER) performance metric is analyzed under Rayleigh fading channel conditions. Our analytical results are compared to the corresponding simulation results for different design parameters. It is shown that the analytical and simulation results are in good agreement. Moreover, while revealing the importance of CSI and SIC, the results equally show that the assumption of perfect CSI and SIC is not practical, hence the need for accurate schemes for improved BER performance
Towards autonomous optical camera communications : Light source localisation using deep learning
Full text linkThis research significantly improves the link reliability and robustness of optical camera communications (OCC) by leveraging deep learning for light source modulation filtering, reflection filtering, and precise light source localisation. By using image sensors as receivers in OCC, data transmission is not only enabled, but other applications are also facilitated, such as detecting objects and humans, making OCC highly attractive in healthcare, intelligent transport systems, and indoor positioning. However, the position of the desired signal in the received image frame must be tracked in dynamic scenarios (i.e., nonstationary applications), in order to maintain the communication link. Moreover, as sixth-generation (6G) wireless networks envision highly autonomous systems that rely on seamless integration of communication and sensing, deep learning is key to enabling robust and adaptive light source localisation and sensing in OCC, which enables vision-based autonomy in dynamic environments. It should be noted that a deep learning-based approach provides more accuracy even when there are multiple noise sources in the environment, reflections, and complex backgrounds, and under mobility conditions, in which traditional light source detection/tracking methods are not effective. Hence this study investigates the use of a deep learning-based approach by analysing the detection accuracy under different configurations and unseen images. The results obtained demonstrate consistently high detection performance with average precision (at an intersection-over-union threshold of 0.70 of 0.84 to 0.97. These results pave the way for autonomous receivers that will be able to select signals intelligently and decode them
Mythologizing the transition : a comparative study of Bahram Beyzaee and Wolfe Soyinka
Full text linkBahram Beyzaee, the Iranian playwright, screenwriter and filmmaker, and Wole Soyinka, the Nigerian poet, playwright, and novelist have produced artistic works that transcend the limitations of time and locality to become powerful comments on human life and socio-political and cultural institutions. This research study examines the major themes and dramatic techniques of these two writers to demonstrate how, in two very different cultural settings, traditional modes and themes appear in modem art forms to renegotiate cultural identity. I argue that both writers place themselves in a post postcolonial position which rather than being concerned about 'writing back against the centre' reflects on the cultural shortcomings that leaves their people at the mercy of vicious internal and external forces. I also demonstrate how they demythologize the traditional superstitious beliefs that haunt the present, foreground the inauthenticity of the modern hybrid obsessions that distort everyday life in their countries and mythologize and glorify the positive aspects of history and contemporary life to redefine cultural identity in terms of the best their cultures can offer. The first two chapters give an account of the history of Iranian and Nigerian performance forms in the context of socio-political, cultural, literary and artistic movements and traditions. The third chapter proceeds to present a short discussion of the theatrical vision and themes of Beyzaee and Soyinka and embarks on a general comparison of the two writers. Chapter four is focused on Beyzaee and Soyinka's depiction of the intellectuals as sacrificial heroes whose death may initiate social purgation and cultural regeneration and liberation. Chapter five is less mythical and more sociopolitical. It is a reflection on the writers' portrayal of women in their works and their success or failure in transcending literary and cultural stereotypes in a world where the means of production and socio-economic facts and the cultural developments associated with them demand a rapid movement away from patriarchal values. Chapter six is devoted to the study of another major issue in the process of cultural transition, namely, redefining the position of ethnic minorities in the myth of nationhood. This last chapter is followed by a brief conclusion, discussing the results and the future possibilities of drama in the context of rapid transition
