Performance comparison of indoor VLC system employing SAC-OCDMA technique

Performance comparison of indoor visible light communication (VLC) system with spectral amplitude coding-optical code division multiple access (SAC-OCDMA) techniques using Khazani-Syed (KS) code is examined. Bit error rate (BER) of three different codes was investigated in terms of background optical noise interference in the system. The result shows that KS code offers a slightly better performance under the influence of ambient light noise interference with a lower code length, a few number of filters and lower BER

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Performance analysis of different sac-ocdma codes for indoor visible light communication system

Indoor visible light communications (VLC) are promising technology where light-emitting-diode (LEDs) are used to transmit data in the form of visible light (white-light) in free space. This technology gains several attractions due to its free licenses, and abundant unregulated bandwidth in the optical spectrum region. It is evident that indoor VLC systems are susceptible to ambient light noise that causes interference which tends to degrade communication channel. Recently, Hadamard matrix code was applied to the indoor VLC system in order to achieve a low error probability in LED-based system. However, with the results obtained, there is a need for improvement by analyzing other SAC-OCDMA code. Therefore, this research focuses on the performance analysis of different spectral amplitude coding optical code division multiple access (SAC-OCDMA) codes for an indoor visible light communication system. This is to provide a better quality of service (QoS) with a lower bit error rate (BER), high signal to noise ratio (SNR) for a long transmission distance for indoor use, under the influence of both direct sunlight with a filter and indirect sunlight without a filter. In order to achieve this, a proper choice of the system components such as a transmitter, modulation format, coding, filtering, and the receiver were made. This can be evaluated through computer simulations, by analyzing the bit error rate (BER), signal to noise ratio (SNR), received the optical power signal and the eye diagram performance. The results obtained from the simulation shows that among the three codes that were subjected to the influence of background light noise interference. KS code offers a significant improvement of 21.05% difference in term of propagation distance, by achieving a long transmission distance under the influence of indirect sunlight without a filter and direct sunlight with a filter at a bit rate of 622 Mbps, with also 11.76 % improvement in transmission distance with 1Gbps bit rate. It is evident from the result that KS code can perform better under the influence of indirect sunlight without a filter, which is the major source of ambient light noise interference in an indoor environment. Therefore, this research proposed a model that can be used as a solution for the next generation of indoor VLC system, employing SAC-OCDMA optical access network