In this letter, we propose low-complexity linear equalizers for orthogonal time frequency space (OTFS) modulation that exploit the structure of the effective channel matrix in OTFS. The proposed ...approach exploits the block circulant nature of the OTFS channel matrix to achieve significant complexity reduction. For an N × M OTFS system, where N and M are the number of Doppler and delay bins, respectively, the proposed approach gives exact minimum mean square error (MMSE) and zero-forcing (ZF) solutions with just O(MN log MN) complexity, while MMSE and ZF solutions using the traditional matrix inversion approach require O(M 3 N 3 ) complexity. The proposed approach can provide low complexity initial solutions for local search techniques to achieve enhanced bit error performance.
Orthogonal time-frequency space (OTFS) is a two-dimensional (2D) modulation technique designed in the delay-Doppler domain. A key premise behind OTFS is the transformation of a time-varying multipath ...channel into an almost non-fading 2D channel in the delay-Doppler domain such that all symbols in a transmission frame experience the same channel gain. It has been suggested in the recent literature that the OTFS can extract full diversity in the delay-Doppler domain, where full diversity refers to the number of multipath components separable in either the delay or Doppler dimension, but without formal analysis. In this paper, we present a formal analysis of the diversity achieved by the OTFS modulation along with supporting simulations. Specifically, we prove that the asymptotic diversity order of the OTFS (as SNR <inline-formula> <tex-math notation="LaTeX">\rightarrow \infty </tex-math></inline-formula>) is one. However, in the finite SNR regime, the potential for a higher order diversity is witnessed before the diversity one regime takes over. Also, the diversity one regime is found to start at lower BER values for increased frame sizes. We also propose a phase rotation scheme for the OTFS using transcendental numbers and show that the OTFS, with this proposed scheme, extracts full diversity in the delay-Doppler domain.
Peak-to-Average Power Ratio of OTFS Modulation Surabhi, G. D.; Augustine, Rose Mary; Chockalingam, Ananthanarayanan
IEEE communications letters,
06/2019, Volume:
23, Issue:
6
Journal Article
Peer reviewed
In this letter, we analyze the peak-to-average power ratio (PAPR) of orthogonal time frequency space modulation (OTFS) waveform. Towards this, we consider modulation symbols on an <inline-formula> ...<tex-math notation="LaTeX">N\times M </tex-math></inline-formula> delay-Doppler grid, where <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula> are the number of Doppler and delay bins, respectively. We derive an upper bound on the PAPR of the OTFS signal and show that the maximum PAPR grows linearly with <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> (and not with <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula>, the number of subcarriers, as observed in conventional multicarrier schemes such as OFDM). We analytically characterize the complementary cumulative distribution function (CCDF) of the PAPR of OTFS with rectangular pulse for large values of <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>. We present the simulated CCDF of the PAPR of OTFS for different pulse shapes and compare it with those of OFDM and generalized frequency division multiplexing (GFDM). It is shown that OTFS can have better PAPR compared to OFDM and GFDM.
During September-December 2020, we conducted a multicenter retrospective study across India to evaluate epidemiology and outcomes among cases of coronavirus disease (COVID-19)-associated mucormycosis ...(CAM). Among 287 mucormycosis patients, 187 (65.2%) had CAM; CAM prevalence was 0.27% among hospitalized COVID-19 patients. We noted a 2.1-fold rise in mucormycosis during the study period compared with September-December 2019. Uncontrolled diabetes mellitus was the most common underlying disease among CAM and non-CAM patients. COVID-19 was the only underlying disease in 32.6% of CAM patients. COVID-19-related hypoxemia and improper glucocorticoid use independently were associated with CAM. The mucormycosis case-fatality rate at 12 weeks was 45.7% but was similar for CAM and non-CAM patients. Age, rhino-orbital-cerebral involvement, and intensive care unit admission were associated with increased mortality rates; sequential antifungal drug treatment improved mucormycosis survival. The COVID-19 pandemic has led to increases in mucormycosis in India, partly from inappropriate glucocorticoid use.
A primary ovarian abnormality such as absent menarche (primary amenorrhea) or early depletion of ovarian follicles/arrested folliculogenesis before the age of 40 is described as premature ovarian ...insufficiency (secondary amenorrhea). Itsprevalence is 1% and 0.1 % in women under 40 and 30 respectively. Common Symptoms include palpitations, excessive sweating, flushes, anxiety, depression, and fatigue. There could be a variety of causes, including chromosomal abnormalities, autoimmune diseases, infections, idiopathic diseases, iatrogenic diseases, and so on. Diagnosis is usually done based on the level of hormones like estradiol, Follicle Stimulating Harmone, and LuteinizingHarmone. Considering the complications of premature ovarian failure, it is necessary to educate the female population about this disorder. Hence, the Present review focuses on the etiology, symptoms, complications, diagnosis, and treatment of premature ovarian failure.
In oligodendrocyte processes, methacholine-evoked Ca2+ waves propagate via regions of specialized Ca2+ release kinetics (wave amplification sites) at which the amplitude and rate of rise of local ...Ca2+ signals are markedly higher than in surrounding areas (Simpson, P. B., and Russell, J. T. (1996) J. Biol. Chem. 271, 33493–33501). In the present study we have examined the effects of other phosphoinositide-coupled agonists on Ca2+ in these cells, and the structural specializations underlying regenerative wave amplification sites. Both bradykinin and norepinephrine evoke Ca2+ waves, which initiate at the same loci and propagate through the cell body and multiple processes via identical wave amplification sites. Antibodies against type 2 inositol 1,4,5-trisphosphate receptors (InsP3R2) and calreticulin identify expression of these proteins in oligodendrocyte membranes in Western blots. Immunocytochemistry followed by high resolution fluorescence microscopy revealed that both InsP3R2 and calreticulin are expressed in high intensity patches along processes. Cross-correlation analysis of the profiles of local Ca2+release kinetics during a Ca2+ wave and immunofluorescence for these proteins along cellular processes showed that the domains of high endoplasmic reticulum protein expression correspond closely to wave amplification sites. Staining cells with the mitochondrial dye, MitoTracker®, showed that mitochondria are only found in intimate association with these sites possessing high density endoplasmic reticulum proteins, and they remain in the same locations over relatively long periods of time. It appears, therefore, that multiple specializations are found at domains of elevated Ca2+ release in oligodendrocyte processes, including high levels of calreticulin, InsP3R2 Ca2+ release channels, and mitochondria.
In this paper, we analyze the performance of orthogonal time frequency space (OTFS) modulation with antenna selection at the receiver, where \(n_s\) out of \(n_r\) receive antennas with maximum ...channel Frobenius norms in the delay-Doppler (DD) domain are selected. Single-input multiple-output OTFS (SIMO-OTFS), multiple-input multiple-output OTFS (MIMO-OTFS), and space-time coded OTFS (STC-OTFS) systems with receive antenna selection (RAS) are considered. We consider these systems without and with phase rotation. Our diversity analysis results show that, with no phase rotation, SIMO-OTFS and MIMO-OTFS systems with RAS are rank deficient, and therefore they do not extract the full receive diversity as well as the diversity present in the DD domain. Also, Alamouti coded STC-OTFS system with RAS and no phase rotation extracts the full transmit diversity, but it fails to extract the DD diversity. On the other hand, SIMO-OTFS and STC-OTFS systems with RAS become full-ranked when phase rotation is used, because of which they extract the full spatial as well as the DD diversity present in the system. Also, when phase rotation is used, MIMO-OTFS systems with RAS extract the full DD diversity, but they do not extract the full receive diversity because of rank deficiency. Simulation results are shown to validate the analytically predicted diversity performance.
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