Asymptotics of Transmit Antenna Selection: Impact of Multiple Receive Antennas

Consider a fading Gaussian MIMO channel with $N_\mathrm{t}$ transmit and $N_\mathrm{r}$ receive antennas. The transmitter selects $L_\mathrm{t}$ antennas corresponding to the strongest channels. For this setup, we study the distribution of the input-output mutual information when $N_\mathrm{t}$ grows large. We show that, for any $N_\mathrm{r}$ and $L_\mathrm{t}$, the distribution of the input-output mutual information is accurately approximated by a Gaussian distribution whose mean grows large and whose variance converges to zero. Our analysis depicts that, in the large limit, the gap between the expectation of the mutual information and its corresponding upper bound, derived by applying Jensen's inequality, converges to a constant which only depends on $N_\mathrm{r}$ and $L_\mathrm{t}$. The result extends the scope of channel hardening to the general case of antenna selection with multiple receive and selected transmit antennas. Although the analyses are given for the large-system limit, our numerical investigations indicate the robustness of the approximated distribution even when the number of antennas is not large.Comment: 6 pages, 4 figures, ICC 201

On Robustness of Massive MIMO Systems Against Passive Eavesdropping under Antenna Selection

In massive MIMO wiretap settings, the base station can significantly suppress eavesdroppers by narrow beamforming toward legitimate terminals. Numerical investigations show that by this approach, secrecy is obtained at no significant cost. We call this property of massive MIMO systems `secrecy for free' and show that it not only holds when all the transmit antennas at the base station are employed, but also when only a single antenna is set active. Using linear precoding, the information leakage to the eavesdroppers can be sufficiently diminished, when the total number of available transmit antennas at the base station grows large, even when only a fixed number of them are selected. This result indicates that passive eavesdropping has no significant impact on massive MIMO systems, regardless of the number of active transmit antennas.Comment: 7 pages, 2 figures; To be presented in IEEE Global Communications Conference (Globecom) 2018 in Abu Dhabi, UA

Optimal Number of Transmit Antennas for Secrecy Enhancement in Massive MIMOME Channels

This paper studies the impact of transmit antenna selection on the secrecy performance of massive MIMO wiretap channels. We consider a scenario in which a multi-antenna transmitter selects a subset of transmit antennas with the strongest channel gains. Confidential messages are then transmitted to a multi-antenna legitimate receiver while the channel is being overheard by a multi-antenna eavesdropper. For this setup, we approximate the distribution of the instantaneous secrecy rate in the large-system limit. The approximation enables us to investigate the optimal number of selected antennas which maximizes the asymptotic secrecy throughput of the system. We show that increasing the number of selected antennas enhances the secrecy performance of the system up to some optimal value, and that further growth in the number of selected antennas has a destructive effect. Using the large-system approximation, we obtain the optimal number of selected antennas analytically for various scenarios. Our numerical investigations show an accurate match between simulations and the analytic results even for not so large dimensions.Comment: 6 pages, 4 figures, IEEE GLOBECOM 201

Body image and meta-worry as mediators of body dysmorphic disorder

Objectives: Meta-worry and attitudes towards the body have been largely overlooked as potential risk factors for body dysmorphic disorder (BDD) despite theorizing that a negative body image may play a critical role in the development of this disorder. Participants: The purpose of this study was to evaluate the fit of a theoretical model specifying body image and meta-worry as mediators between cognitive, metacognitive beliefs and body dysmorphic disorder(BDD) in a nonclinical sample of 635 participants (304 male and 331 female). Results: The data supported the model, and meta-worry and body image significantly mediated the relationship between cognitive, metacognitive beliefs and BDD. These findings provide essential preliminary evidence that body image may represent a necessary but not sufficient risk factor for BDD and that treatment for BDD should consider targeting body-related pathology in addition to meta-worry. Conclusion: The model may prompt future research into body dysmorphic disorder

Ictal verbal help-seeking: Occurrence and the underlying etiology.

PURPOSE: Ictal verbal help-seeking has never been systematically studied before. In this study, we evaluated a series of patients with ictal verbal help-seeking to characterize its frequency and underlying etiology. METHODS: We retrospectively reviewed all the long-term video-EEG reports from Jefferson Comprehensive Epilepsy Center over a 12-year period (2004-2015) for the occurrence of the term help in the text body. All the extracted reports were reviewed and patients with at least one episode of documented ictal verbal help-seeking in epilepsy monitoring unit (EMU) were studied. For each patient, the data were reviewed from the electronic medical records, EMU report, and neuroimaging records. RESULTS: During the study period, 5133 patients were investigated in our EMU. Twelve patients (0.23%) had at least one episode of documented ictal verbal help-seeking. Nine patients (six women and three men) had epilepsy and three patients (two women and one man) had psychogenic nonepileptic seizures (PNES). Seven out of nine patients with epilepsy had temporal lobe epilepsy; six patients had right temporal lobe epilepsy. CONCLUSION: Ictal verbal help-seeking is a rare finding among patients evaluated in epilepsy monitoring units. Ictal verbal help-seeking may suggest that seizures arise in or propagate to the right temporal lobe

Comparison of health-related quality of life after percutaneous coronary intervention and coronary artery bypass surgery

BACKGROUND: Health-related quality of life (HRQOL) evaluation is an important measure of the impact of the disease. As more people with coronary heart disease (CHD) live longer, doctors and researchers want to know how they manage in day to day life. It looked like adults with CHD had a decrease QOL. The aim of this study was to comparison of HRQOL of patients who underwent percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG) and to assess its main determinants in the whole sample of coronary artery disease (CAD) patients. METHODS: The study was carried out to estimate HRQOL of 109 patients who underwent invasive coronary revascularization PCI (n = 75) and CABG (n = 34). We applied HRQOL after 6 months and 2 years in both groups and scores were compared. The HRQOL data were obtained using MacNew Heart Disease questionnaire with dimensions emotional, physical and social that estimated. Data entry and analysis were performed by SPSS 16.0. RESULTS: A total MacNew scale in CABG and PCI group in 6 months after treatment were 45.32 ± 13.75 and 53.52 ± 15.63, respectively (P = 0.0100). After 2 years HRQOL mean changed to 51.176 ± 14.80 and 49.55 ± 16.22, respectively, in CABG and PCI group (P = 0.4280). Our results in within-group analysis showed total MacNew scale and its subscales were changed significantly after 2 years in CABG and PCI group�s scores were detected. We found in the whole sample of CAD patients those who had a higher level of income and education and were not either overweight or obese experienced better HRQOL. CONCLUSION: Our results showed that patients who underwent PCI experienced significantly higher HRQOL in 6 months after revascularization but over 24 months follow-up no difference was observed between the two groups. © 2016, Isfahan University of Medical Sciences(IUMS). All rights reserved