Beamforming Optimization for Full-Duplex Wireless-powered MIMO Systems

We propose techniques for optimizing transmit beamforming in a full-duplex multiple-input-multiple-output (MIMO) wireless-powered communication system, which consists of two phases. In the first phase, the wireless-powered mobile station (MS) harvests energy using signals from the base station (BS), whereas in the second phase, both MS and BS communicate to each other in a full-duplex mode. When complete instantaneous channel state information (CSI) is available, the BS beamformer and the time-splitting (TS) parameter of energy harvesting are jointly optimized in order to obtain the BS-MS rate region. The joint optimization problem is non-convex, however, a computationally efficient optimum technique, based upon semidefinite relaxation and line-search, is proposed to solve the problem. A sub-optimum zero-forcing approach is also proposed, in which a closed-form solution of TS parameter is obtained. When only second-order statistics of transmit CSI is available, we propose to maximize the ergodic information rate at the MS, while maintaining the outage probability at the BS below a certain threshold. An upper bound for the outage probability is also derived and an approximate convex optimization framework is proposed for efficiently solving the underlying non-convex problem. Simulations demonstrate the advantages of the proposed methods over the sub-optimum and half-duplex ones.Comment: 14 pages, accepte

Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials, 201

Investigating the Effects of Aerobic Exercise with Blood Flow Restriction on Vastus Lateralis Muscle Oxygenation

Blood flow restriction training (BFRT) is a novel adaptation to traditional forms of aerobic or resistance exercise. By restricting blood flow to the active skeletal muscles, previous research has demonstrated that it can induce similar benefits to musculoskeletal health as non-blood flow restricted (BFR) exercise, despite exercising at lower intensities and for a shorter duration of time. The mechanisms through which BFRT stimulates physiological adaptations remains uncertain however, one proposed stimulus is localized skeletal muscle hypoxia. This thesis aimed to investigate this stimulus by assessing muscle oxygenation during low-intensity aerobic exercise with BFR. Vastus lateralis oxygenation was assessed using continuous-wave near-infrared spectroscopy in 15 participants (n=15) during 20 minutes of BFR and non-BFR exercise sessions. Significant differences in muscle tissue oxygenation was observed (P<0.001) indicating that BFR during low-intensity walking exercise reduced muscle oxygenation more so than non-BFR exercise. Furthermore, significant differences in total hemoglobin (THb) and deoxygenated hemoglobin (HHb) were observed (P<0.05 and P<0.001, respectively), such that THb and HHb were significantly greater during BFR-exercise versus non-BFR exercise. Oxygenated hemoglobin (O2Hb) on the other hand, was not significantly different between exercise sessions. These findings suggest that BFR during low-intensity aerobic exercise may induce a localized hypoxic response in the skeletal muscle tissues distal to the cuffs. The reduction in muscle oxygenation in the presence of increased tissue blood volume may suggest that BFRT influences oxygenation by moderating blood flow through the active skeletal muscle tissues during exercise

Increase in Low-Frequency Oscillations in fNIRS as Cerebral Response to Auditory Stimulation with Familiar Music

Recognition of typical patterns of brain response to external stimuli using near-infrared spectroscopy (fNIRS) may become a gateway to detecting covert consciousness in clinically unresponsive patients. This is the first fNIRS study on the cortical hemodynamic response to favorite music using a frequency domain approach. The aim of this study was to identify a possible marker of cognitive response in healthy subjects by investigating variations in the oscillatory signal of fNIRS in the spectral regions of low-frequency (LFO) and very-low-frequency oscillations (VLFO). The experiment consisted of two periods of exposure to preferred music, preceded and followed by a resting phase. Spectral power in the LFO region increased in all the subjects after the first exposure to music and decreased again in the subsequent resting phase. After the second music exposure, the increase in LFO spectral power was less distinct. Changes in LFO spectral power were more after first music exposure and the repetition-related habituation effect strongly suggest a cerebral origin of the fNIRS signal. Recognition of typical patterns of brain response to specific environmental stimulation is a required step for the concrete validation of a fNIRS-based diagnostic tool

Hospital Home-Bound Education: Are Teachers Prepared to Implement Transition Plans Post-Hospitalization for Student Success?

Homebound instruction presents many challenges for teachers. Teachers are frequently not prepared to provide such services. Teachers are frustrated in recognizing that homebound services do not provide sufficient depth and intensity of instruction that some students may need. The purpose of this study was to bring awareness of what happens during the transition of a hospital homebound student post-hospitalization and their academic success. A qualitative case study allowed me to gather and analyze students’ needs that addressed their medical conditions. These important aspects included not only the hospital homebound teachers, students, and staffs’ behaviors/views on the overall program, but also the perceptions of those who interacted with the students, the context of the program, outside constituents, comparisons to other homebound programs, and other qualitative variables. The data-based case study was guided by looking at the needs of hospital home bound students, the needs of hospital homebound teachers, and what supports could be provided to hospital homebound teachers. All of the students that I interviewed for this study have experienced some form of significant social and emotional stress that has impaired their performance at school, as well as their physical and mental health. Current school supports do not appear to be meeting the diverse school-based needs of students with chronic illness. Hospital homebound instruction often is provided to students after regular school hours, only qualified staff members who are able to take on the extra duties of homebound instruction after their regular working day should be considered. The results revealed that this diverse group of students required multiple supports in order to be effective in their respective positions. More specifically, it was evident that teachers still feel unprepared to educate hospital homebound students and that they lack specific resources for them to be successful