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

A novel motion-model-free UWB short-range positioning method

In recent years, the number of location-based services is increasing and consequently, the researchers’ attentions are captivated in designing accurate real-time positioning systems. Despite having a good performance in outdoor environment, Global Positioning System (GPS) is not capable of estimating an object’s position in an indoor environment precisely. In this paper, we present a novel tracking algorithm for indoor environment with a known floor plan. The object location is estimated by utilizing the information of the multipath components which are created by one physical and some virtual anchors. We will link this information to the floor plan by defining a channel model that has a combination of stochastic and deterministic traits. As we have used only one physical anchor in this paper, we would encounter several challenges such as lack of data association and existence of clutters amid real data. We dealt with these problems through random finite set methodology. Additionally, we will demonstrate that the proposed method is not restricted by the model of motion and is capable to precisely track the trajectory. It will be shown that it provides a better accuracy, particularly in non-linear trajectories, compared with two other relevant models which are adopting linear motion model

Subacute Presentation of Central Cord Syndrome Resulting from Vertebral Osteomyelitis and Discitis: A Case Report

Introduction: Central cord syndrome (CCS) is a clinical syndrome of motor weakness and sensory changes. While CCS is most often associated with traumatic events. There have been few documented cases being caused by abscesses resulting from osteomyelitis.Case Report: A 56-year-old male presented to a regional trauma center complaining of excruciating neck and bilateral upper extremity pain. Computed tomography of the cervical and thoracic regions revealed severe discitis and osteomyelitis of the fourth and fifth cervical (C4-C5) with near-complete destruction of the C4 vertebral body, as well as anterolisthesis of C4 on C5 causing compression of the central canal. Empiric intravenous (IV) antibiotic therapy with ampicillin/sulbactam and vancomycin was initiated, and drainage of the abscess was scheduled. After the patient refused surgery, he was planned to be transferred to a skilled nursing facility to receive a six-week course of IV vancomycin therapy. A month later, patient returned to emergency department with the same complaint due to non-compliance with antibiotic therapy.Discussion: Delayed diagnosis and treatment of osteomyelitis can result in devastating neurological sequelae, and literature supports immediate surgical debridement. Although past evidence has suggested surgical intervention in similar patients with presence of abscesses, this case may suggest that antibiotic treatment may be an alternative approach to the management of CCS due to an infectious etiology. However, the patient had been non-compliant with medication, so it is unknown whether there was definite resolution of the condition.Conclusion: In patients presenting with non-traumatic central cord syndrome, it is vital to identify risk factors for infection in a thoroughly obtained patient history, as well as to maintain a low threshold for diagnostic imaging

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

Effect of lavender on blood brain barrier permeability in rats subjected to ischemia

Background and purpose: Lavender is a medicinal plant with antioxidant activity. Stroke causes long term disability and is associated with oxidative stress. The present study was conducted to evaluate the protective effect of lavender extract against blood brain barrier permeability and its possible mechanisms in an experimental model of stroke. Materials and methods: In this experimental study, 42 male Wistar rats weighing 250 to 300 g were used. The rats were divided into 6 groups (n= 7 per group). Group 1 was ischemic, groups 2 and 3 were ischemic that were given 100 and 200 mg/kg lavender extract, respectively. Group 4 were intact and groups 5 and 6 were intact groups which received lavender extract with dose of 100 and 200 mg/kg. Group 7 was also considered as the sham. Focal cerebral ischemia was induced in rats by the transient occlusion of the middle cerebral artery for 1 hr. Data were analysed with SPSS and comparison of means were compared using One Way Anova. Results: The ethanolic extract of lavender at 200 mg/kg significantly reduced the blood brain barrier permeability in rat stroke model compared with ischemic group. Conclusion: The results indicate that lavender extract has neuroprotective activity against cerebral ischemia and alleviated neurological function in rats

The Effect Of Cyperus Rotundus Ethanolic Extract On Motor Coordination In A Rat Model Of Alzheimer

Background and Objective: Alzheimer's disease (AD) is a degenerative disorder that leads to progressive cognitive decline. The memory dysfunction of AD has been associated with a cortical cholinergic deficiency and loss of cholinergic neurons of the nucleus basalis of Meynert (NBM). This study investigated the effect of ethanolic extract of Cyperus rotundu tubers (CRT) on motor activity in NBM-lesioned rat model of AD and intact rats. Materials and Methods: In this experimental study 49 Wistar rats were divided into 7 groups. For this purpose, Wistar rats received bilateral electric lesions of the NBM. The control and sham groups received distilled water while NBM-lesioned group received CRT extract for 20 days with doses of 100 and 200 mg/kg. Intact rats received CRT extract for 20 days without any surgery. The motor activity was assessed with Rotarod apparatus. Data were analyzed using one- way Anova and LSD test. Results: Use of ethanolic extract of CRT for 20 days improved motor activity in NBM-lesioned rats that received extract with a dose of 100 mg/kg. Ethanolic extract of CRT in the intact rats for 20 days significantly reduced motor activity when compared with the control group. Conclusion: The results of this study suggest that ethanolic extract of CRT is useful in NBM-induced lesion rats via inducing some changes in acetylcholine levels in the brain