A Low Complexity Optimal LMMSE Channel Estimator for OFDM System

Linear minimum mean square error (LMMSE) is the optimal channel estimator in the mean square error (MSE) perspective, however, it requires matrix inversion with cubic complexity. In this paper, by exploiting the circulant property of the channel frequency autocorrelation matrix RHH, an efficient LMMSE channel estimation method has been proposed for orthogonal frequency division multiplexing (OFDM) based on fast Fourier transformation (FFT) and circular convolution theorem. Finally, the computer simulation is carried out to compare the proposed LMMSE method with the classical LS and LMMSE methods in terms of performance measure and computational complexity. The simulation results show that the proposed LMMSE estimator achieves exactly same performance as conventional LMMSE estimator with much lower computational complexity

Journal of Telecommunications and Information Technology, Improved Signal Detection Techniques for QOSTBC System in Fast Fading Channel, 2020, nr 1

Most existing quasi-orthogonal space time Block coding (QO-STBC) schemes have been developed relying on the assumption that the channel is at or remains static during the length of the code word symbol periods to achieve an optimal antenna diversity gain. However, in time-selective fading channels, this assumption does not hold and causes intertransmit-antenna-interferences (ITAI). Therefore, the simple pairwise maximum likelihood decoding scheme is not sufficient to recover original transmitted signals at the receiver side. To avoid the interferences, we have analyzed several signal detection schemes, namely zero forcing (ZF), two-step zero forcing (TS-ZF), minimum mean square error (MMSE), zero forcing - interference cancelation - decision feedback equalizer (ZF-IC-DFE) and minimum mean square error - interference cancelation { decision feedback equalizer (MMSE-IC-DFE). We have proposed two efficient iterative signal detection schemes, namely zero forcing - iterative interference cancelation - zero forcing { decision feedback equalization (ZF-IIC-ZF-DFE) and minimum mean square error - parallel interference cancelation - zero forcing – decision feedback equalization (MMSE-IIC-ZF-DFE). The simulation results show that these two proposed detection schemes significantly outperform all conventional methods for QOSTBC system over time selective channel

Improved Signal Detection Techniques for QOSTBC System in Fast Fading Channel

Most existing quasi-orthogonal space time block coding (QO-STBC) schemes have been developed relying on the assumption that the channel is flat or remains static during the length of the code word symbol periods to achieve an optimal antenna diversity gain. However, in timeselective fading channels, this assumption does not hold and causes intertransmit-antenna-interferences (ITAI). Therefore, the simple pairwise maximum likelihood decoding scheme is not sufficient to recover original transmitted signals at the receiver side. To avoid the interferences, we have analyzed several signal detection schemes, namely zero forcing (ZF), two-step zero forcing (TS-ZF), minimum mean square error (MMSE), zero forcing – interference cancelation – decision feedback equalizer (ZF-IC-DFE) and minimum mean square error – interference cancelation – decision feedback equalizer (MMSE-IC-DFE). We have proposed two efficient iterative signal detection schemes, namely zero forcing – iterative interference cancelation – zero forcing – decision feedback equalization (ZF-IIC-ZF-DFE) and minimum mean square error – parallel interference cancelation – zero forcing – decision feedback equalization (MMSE-IIC-ZF-DFE). The simulation results show that these two proposed detection schemes significantly outperform all conventional methods for QOSTBC system over time selective channel

Clinico-psycho-social profile of patients brought under consultation-liaison psychiatry care in a large tertiary care referral hospital

Objective: The aim of this study was to access the clinico-psycho-social profile of patients brought under consultation-liaison (CL) psychiatry care in a large tertiary care referral hospital. Materials and Methods: This study included all patients who were referred for CL psychiatry from among the inpatients in the hospital and the emergency department (during off working hours of the hospital) over a period of 1 year. Data were obtained and analyzed in terms of where was the referral placed, by whom, the reason for placing the referral, the primary medical/surgical diagnosis of the patient, the presenting complaints, any past psychiatric history, the psychiatric diagnosis (as per the International Classification of Diseases, Tenth Edition), the investigations advised and their reports, the treatment advised (psychotherapeutic and psychopharmacological), the sociodemographic profile of the patients, and the follow-up details. Results: A total of 157 patients were referred to the CL unit over the study period. Out of these, 125 patients were referred among the inpatients and 32 from the emergency department of the hospital. Majority of the patients were in the age group of 25–50 years and were male. The majority of the referrals were made by general physician; most of the referrals were placed from emergency department. The most common reason for referral was for altered sensorium and behavioral abnormalities. The most common diagnosis was delirium followed by depressive episode and alcohol dependence syndrome. Conclusion: There was higher representation of delirium and alcohol-related cases in our study compared to older studies

A DFT-based Low Complexity LMMSE Channel Estimation Technique for OFDM Systems

The linear minimum mean square error (LMMSE) channel estimation technique is often employed in orthogonal frequency division multiplexing (OFDM) systems because of its optimal performance in the mean square error (MSE) performance. However, the LMMSE method requires cubic complexity of order O(N 3 p ), where Np is the number of pilot subcarriers. To reduce the computational complexity, a discrete Fourier transform (DFT) based LMMSE method is proposed in this paper for OFDM systems in the frequency selective channel. To validate the proposed method, the closed form mean square error (MSE) expression is also derived. Finally, a computer simulation is carried out to compare the performance of the proposed LMMSE method with the classical LS and LMMSE methods in terms of bit error rate (BER) and computational complexity. Results of the simulation show that the proposed LMMSE method achieves exactly the same performance as the conventional LMMSE method, with much lower computational complexity

An Ordered QR Decomposition based Signal Detection Technique for Uplink Massive MIMO System

Signal detection turns out to be a critical challenge in massive MIMO (m-MIMO) system due to the deployment of large number of antennas at the base station. Although, the minimum mean square error (MMSE) is one of the popular signal detection method, but, it requires matrix inversion with cubic complexity. In order to reduce computational complexity, several suboptimal signal detection methods were proposed such as Gauss-Seidel, successive over relaxation, Jacobi, Richardson methods. Although, these methods provide low complexity but their performance are limited to MMSE method. In this paper, we have proposed two signal detection techniques namely QR decompositions (QRD) and ordered QRD (OQRD). Finally, the performances of proposed signal detection methods are compared with various conventional methods in terms of symbol error rate (SER) and computational complexity. The simulation results validate that the proposed methods outperform the MMSE method with substantially lower computational complexity

A DFT-based Low Complexity LMMSE Channel Estimation Technique for OFDM Systems, Journal of Telecommunications and Information Technology, 2022, nr 1

The linear minimum mean square error (LMMSE) channel estimation technique is often employed in orthogonal frequency division multiplexing (OFDM) systems because of its optimal performance in the mean square error (MSE) performance. However, the LMMSE method requires cubic complexity of order O(N 3 p ), where Np is the number of pilot subcarriers. To reduce the computational complexity, a discrete Fourier transform (DFT) based LMMSE method is proposed in this paper for OFDM systems in the frequency selective channel. To validate the proposed method, the closed form mean square error (MSE) expression is also derived. Finally, a computer simulation is carried out to compare the performance of the proposed LMMSE method with the classical LS and LMMSE methods in terms of bit error rate (BER) and computational complexity. Results of the simulation show that the proposed LMMSE method achieves exactly the same performance as the conventional LMMSE method, with much lower computational complexity

Prevalence and patterns of tobacco use and nicotine dependence among males industrial workers

Background: Tobacco use is an important preventable health risk factor in India. Aim: This study was carried out to estimate the prevalence of current tobacco use, factors and extent of dependence associated with its use among male workers of an industrial organization. Materials and Methods: A total of 759 participants randomly selected from the population of employees were administered questionnaire in Hindi containing demographic profile, patterns of smoking, and use of smokeless tobacco and alcohol. Results: Forty-one percent of the surveyed males (n = 750) used tobacco either by smoking or smokeless method or both (9.7% used both, 23.4% smoked, and 27.3% used smokeless tobacco). The maximum percentage was among the 26–30 years' age group, and the married persons (45.4%, OR = 2.17, P < 0.05). Tobacco use was associated with lower educational qualifications, history of tobacco use in family members, and drinking alcohol. Seventy-two percent of the nicotine users reported being influenced by their peers in initiating the habit, 59.4% of the users reported being advised to stop tobacco use by a health professional, and 52.9% had attempted quitting the habit more than once. Twenty percent of our sample were dependent on nicotine and the highest prevalence was seen in those using both smoking and the smokeless tobacco. Conclusions: The Prevalence of Tobacco Use and Nicotine Dependence among male industrial employees is significant and necessitates Tobacco awareness and cessation programs regarding Tobacco use

Munchausen syndrome: Playing sick or sick player

Munchausen syndrome is rare factitious disorder which entails frequent hospitalization, pathological lying and intentional production of symptoms for sick role. Management requires collateral history taking, sound clinical approach, exclusion of organicity and addressing psychological issues. A case which presented with unusual symptoms of similar dimension is discussed here. The case brings out finer nuances in evaluation and management of this entity