The security-reliability tradeoff (SRT) in free-space optical (FSO) communications is the most critical property to highlight, especially with respect to the development of wireless optical communications. In this paper, opportunistic scheduling selection techniques are used to improve the SRT of multiuser FSO systems under the combined influence of atmospheric turbulence with Fisher-Snedecor F distribution, generalized pointing error, and path losses due to foggy weather. Due to the broadcast nature of wireless optical propagation, the optical transmission from the transmitting users to the legitimate receiver can be easily intercepted by eavesdroppers. Therefore, an optimal user scheduling (OUS) scheme is proposed in this work to protect the legitimate wireless transmission from eavesdroppers, where a user with the highest secrecy capacity is scheduled to transmit his confidential information to the receiver. Closed-form expressions for the outage probability, interception probability, and SRT are derived for the conventional round-robin scheduling (RRS) and the proposed OUS. In addition, an asymptotic analysis for the outage probability, interception probability, and SRT is performed to provide insight into the impact of user scheduling on the system performance. We also propose the use of ''friendly jamming'' techniques, where the user with the lowest secrecy capacity is selected by the authorized receiver to jam the existing interceptor. Finally, another SRT is formulated to determine the impact of a friendly jammer on the secrecy performance of the system. The results show that the proposed OUS outperforms the RRS in terms of intercept probability and SRT performance. The obtained exact and asymptotic results are validated by Monte-Carlo simulations.
Assisting users and restoring human locomotion for patients with lower limb spasticity is a challenging task. Studies focusing on patients with abnormal walking behavior are scarce because there is an important variability from one patient to another. Those patients could benefit the most from rehabilitation and assistive mechatronic devices, there is no generic controlling scheme or any dynamical gain indicator. This contribution introduces a bio-kinematic index which is called Neuro-motor index (NMI), based on electromyographic (EMG) and joint angles measurements. NMI is derived from the nonlinear regression with a combination of two co-contraction indices (CCI), which allows addressing the variability of walking situations. This new index is evaluated on patients with cerebral palsy and a stroke. Then, the estimation error was calculated in comparison with the other co-contraction indices. This estimation shows that this index has the highest signification of joint angles prediction. Thus it can be suitable in adaptive rehabilitation control for spasticity cases.
Cerebral Palsy (CP) is a debilitating neurological disorder that reduces motor function for children with CP. This paper presents the latest trends in the development of the arm exoskeleton for children afflicted by CP. Furthermore, it discusses the prospects for achieving an optimal outcome in rehabilitation and assistance. Nine upper limb exoskeletons, which targeted CP-afflicted children and were developed in recent years, are presented. Three of these exoskeletons are most commonly used in rehabilitation, and the other six are used for assistive purposes. Henceforth, it discusses when CP-afflicted children can make good use of this rehabilitation or assistance. In conclusion, this research should focus on a scalable upper limb exoskeleton that would benefit the majority of children afflicted by CP.
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