Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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The total COVID-19 (SARS-CoV-2) infected cases have reached 139 million worldwide and nearing 3 million deaths on April 16, 2021. The availability of accurate data is crucial as it makes it possible to analyze correctly the infection trends and make better forecasts. The reported recovered cases for many US states are surprisingly low. This could be due to difficulties in keeping track of recoveries and resulted in higher numbers for the reported active cases than the actual numbers on the ground. In this work, based on the typical range of recovery rate for COVID-19, we estimate the active data from the total cases and death cases and bring out a correction for the data for all the US states reported on worldometer. © Society for Disaster Medicine and Public Health, Inc. 2021.

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Disaster Medicine and Public Health Preparedness

Correction in Active Cases Data of COVID-19 for the US States by Analytical study

The reported COVID-19 cases in the United States of America have crossed over 10 million and a large number of infected cases are undetected whose estimation can be done if country-wide antibody testing is performed. In this study, we estimate this undetected fraction of the population by a modeling and simulation approach. We employ an epidemic model SIPHERD in which three categories of infection carriers, symptomatic, purely asymptomatic, and exposed are considered with different transmission rates that are taken dependent on the social distancing conditions, and the detection rate of the infected carriers is taken dependent on the tests done per day. The model is first validated for Germany and South Korea and then applied for prediction of the total number of confirmed, active and dead, and daily new positive cases in the United States. Our study predicts the possible outcomes of the infection if social distancing conditions are relaxed or kept stringent. We estimate that around 30.1 million people are already infected, and in the absence of any vaccine, 66.2 million (range: 64.3–68.0) people, or 20% (range: 19.4–20.5) of the population will be infected by mid-February 21 if social distancing conditions are not made stringent. We find the infection-to-fatality ratio to be 0.65% (range: 0.63–0.67). © 2021 Wiley Periodicals LLC

Journal of Medical Virology

Estimation of undetected symptomatic and asymptomatic cases of COVID-19 infection and prediction of its spread in the USA

Originating from Wuhan, China, in late 2019, and with a gradual spread in the last few months, COVID-19 has become a pandemic crossing 9 million confirmed positive cases and 450 thousand deaths. India is not only an overpopulated country but has a high population density as well, and at present, a high-risk nation where COVID-19 infection can go out of control. In this paper, we employ a compartmental epidemic model SIPHERD for COVID-19 and predict the total number of confirmed, active and death cases, and daily new cases. We analyze the impact of lockdown and the number of tests conducted per day on the prediction and bring out the scenarios in which the infection can be controlled faster. Our findings indicate that increasing the tests per day at a rapid pace (10k per day increase), stringent measures on social-distancing for the coming months and strict lockdown in the month of July all have a significant impact on the disease spread. © 2020 Elsevier Ltd

Chaos, Solitons and Fractals

An epidemic model SIPHERD and its application for prediction of the spread of COVID-19 infection in India

Selective mapping (SLM) is an attractive method to reduce the peak-to-average power ratio (PAPR) without causing any signal distortion in orthogonal frequency division multiplexing (OFDM) systems. The main drawback of this technique is the requirement of sending side information (SI) to the receiver for each data block which results in huge bandwidth and power overheads. Also, it may degrade the bit error rate (BER) performance of the system due to the corruption of SI over the channel. In this paper, we propose a novel technique to reduce PAPR in single input single output and single input multiple output OFDM systems using Hadamard code-based SLM. The proposed method eliminates the need for explicit SI resulting in better bandwidth and power efficiency. The basic idea is to embed the SI of each data block within the data block itself at some specific locations using special multiplying sequences. Furthermore, the proposed scheme yields superior PAPR reduction when compared to that of the conventional SLM for an equivalent system complexity. Simulation studies show that the receiver achieves a better BER performance with the proposed technique as compared to the conventional SLM. © 2017, Springer Science+Business Media New York.

Circuits, Systems, and Signal Processing

An Improved Selective Mapping Technique to Reduce Peak-to-Average Power Ratio in SISO and SIMO OFDM Systems Without Side Information

In non-contiguous orthogonal frequency division multiplexing (NC-OFDM)-based interweave cognitive radio networks, the sidelobe power of secondary users (SUs) must be strictly controlled to avoid the interference between the SUs and the primary users (PUs) of the adjacent bands. Similarly, the inherent issue of high peak-to-average power ratio (PAPR) of the OFDM signal is another drawback of the cognitive radio communication system based on the NC-OFDM technology. A few methods are available in the literature to solve either of these problems individually, while in this paper, we propose a new method for the joint minimisation of sidelobe power and PAPR in NC-OFDM-based cognitive radio networks using Zadoff–Chu (ZC) sequence. In this method, the sidelobe power suppression of SUs is benefited by PUs and the PAPR is reduced for SUs. We modelled a new optimisation problem for minimising the sidelobe power with a constraint on the maximum tolerable PAPR and sidelobe power. The proper selection of ZC sequence, which is crucial for minimising both the issues simultaneously, is achieved by solving the proposed optimisation problem. The proposed technique is shown to provide 7 dB and 20 dB reduction in PAPR and sidelobe power, respectively, without causing any signal distortion along with the improvement in bit error rate (BER) performance. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

International Journal of Electronics

A joint technique for sidelobe suppression and peak-to-average power ratio reduction in non-contiguous OFDM-based cognitive radio networks

An inherent issue of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technique is its high peak-to-average power ratio (PAPR) over distinct antennas. Selective mapping (SLM) is one of the most prevalent methods to reduce the PAPR without inducing any signal deformation in OFDM or MIMO-OFDM systems. The main drawback of the SLM technique is the need for sending side information (SI) with each OFDM data symbol for retrieving the transmitted data. In this paper, we present a low complexity SLM technique using Hadamard sequence to substantially reduce the PAPR in MIMO-OFDM systems without the need for transmitting SI thus resulting in improved data rate/ bandwidth efficiency. Simulation studies show that the proposed method achieves a significant reduction in PAPR and improves the bit error rate (BER) performance of the communication system as compared to some prevailing methods. © 2017

Physical Communication

A bandwidth efficient selective mapping technique for the PAPR reduction in spatial multiplexing MIMO-OFDM wireless communication system

This paper presents a novel generic method for the carrier frequency offset (CFO) estimation and reduction of peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing based wireless communication systems. Estimation of CFO using null subcarriers embedded in one or more pilot symbol is one of the best known CFO estimation techniques that achieve an estimation range of inverse of the sampling interval with low implementation complexity. We propose to exploit a few null subcarriers in the pilot symbol for PAPR reduction by switching with some data subcarriers in the data block of which the PAPR is intended to be minimized. We define a new cost function for the PAPR reduction at the transmitter and CFO estimation at the receiver and the computational complexity of its evaluation is made significantly low by applying Cuckoo search optimization algorithm. Also, the proposed method requires less side information to be send to the receiver as compared to many of the prevailing PAPR reduction methods. Computer simulation studies reveal that the proposed combined technique offers significant performance advantage for both PAPR reduction and CFO estimation concurrently. © 2015, Springer Science+Business Media New York.

Telecommunication Systems

A combined technique for carrier frequency offset estimation and peak-to-average power ratio reduction in OFDM systems using null subcarriers and Cuckoo search algorithm

Cognitive radio systems based on non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is a promising technique that can provide efficient bandwidth utilization for high data rate wireless communication systems under frequency selective fading environments. Nevertheless, the sidelobe power of the secondary users (SU) in NC-OFDM modulated signals create out-of-band power (OBP) which induce interference to the primary users (PU) in the cognitive radio system. Moreover, OFDM has an inherent problem of high peak to average power ratio (PAPR). In this paper, we present a joint method for the PAPR reduction and sidelobe suppression based on partial transmit sequence (PTS) method. The objective is modelled as an optimization problem to minimize PAPR with a constraint on the maximum tolerable sidelobe power. The key idea is to generate some phase factors that meet the constraints of the proposed joint optimization problem. We examine the performance of the proposed joint method by computer simulation studies and the results show that it can significantly reduce PAPR and sidelobe power simultaneously. © 2015 IEEE.

2015 IEEE International Conference on Signal Processing, Informatics, Communication and Energy Systems, SPICES 2015

Joint PAPR and sidelobe reduction in non-contiguous OFDM based cognitive radio systems

Orthogonal frequency division multiplexing (OFDM) is a spectral efficient multi-carrier modulation technique which offers many advantages in wireless as well as wired communication systems. Major issues of OFDM implementation are its high peak to average power ratio (PAPR) and extreme sensitivity to carrier frequency offset (CFO). In this paper, we propose a new scheme named optimum null swapping for combined PAPR reduction and CFO estimation in OFDM systems by using one training symbol (pilot) with some null subcarriers embedded in it. We exploit certain number of nulls in the pilot symbol for swapping with some data subcarriers of the data block in such a way as to reduce PAPR. By the proper allocation of null subcarriers based on some specific sequences at the transmitter, CFO is estimated at the receiver using the same pilot OFDM symbol. The computational complexity of the new objective function for the proposed joint optimum null swapping scheme is made significantly low by using the Tabu search algorithm. Moreover, the proposed method demands less side information to be send to the receiver for the reverse swapping of nulls in order to retrieve original data symbols. Simulation results show that the proposed joint scheme offers substantial reduction in PAPR apart from CFO estimation without any additional bandwidth overhead. © 2015, Springer Science+Business Media New York.

Wireless Personal Communications

A Novel Joint Method for Frequency Offset Estimation and Peak-to-Average Power Ratio Reduction in OFDM Systems Using Null Subcarriers

Despite its many advantages for high data rate transmission over frequency selective channels, one of the challenging issues faced by orthogonal frequency division multiplexing (OFDM) system is its high peak to average power ratio (PAPR). Selective mapping (SLM) is an efficient technique to reduce PAPR in OFDM without causing signal distortion. However SLM has high system complexity since it requires large number of inverse fast Fourier transform (IFFT) operations. And also it demands the transmission of side information for each data block which results in huge bandwidth overhead. In this paper, we propose an improved SLM technique with either Gold or Hadamard code which ensures low system complexity to achieve the same PAPR reduction performance as that of conventional SLM. Also the proposed SLM method promises superior PAPR reduction compared to that of conventional SLM for identical system complexities. Moreover, the proposed SLM approach needs less side information to be send to the receiver resulting in improved bandwidth efficiency. Simulation studies show that considerable reduction in PAPR than conventional SLM method is achieved for identical number of multiplying phase sequences. The effect of non-linear distortion caused by high PAPR is also studied and the proposed method is shown to ensure linear operation over a large dynamic range of high power amplifier (HPA) in an OFDM transmitter. © 2014 IEEE.