8 research outputs found
Exact Outage Probability Analysis of the Mixed RF/FSO System With Variable-Gain Relays
This paper presents a unified analysis of the mixed radio-frequency
(RF)/free-space optics (FSO) relaying system, with multiple variable-gain
amplify-and-forward relays. The partial relay selection (PRS) is employed to
select the active relay for further re-transmission. Due to fast fading
statistics of the first RF hop, it is assumed that the channel state
information of the RF link is outdated, which is used for both the relay gain
adjustment and the PRS procedure. The RF hops are subject to the Rayleigh
fading, while the FSO hop is affected by the atmospheric turbulence and the
pointing errors. The intensity fluctuations of the optical signal caused by
atmospheric turbulence are modeled by the general Malaga (M) distribution,
which takes into account the effect of multiple scattered components. An exact
expression for the outage probability is derived. In addition,
high-signal-to-noise-ratio approximations are provided, which can be used to
efficiently determine the outage probability floor. Numerical results are
validated by Monte Carlo simulations, which are used to examine the effects of
the system and channel parameters on the RF/FSO system performance.Comment: Published in: IEEE Photonics Journa
Outage Probability Analysis of Mixed RF-FSO System Influenced by Fisher-Snedecor Fading and Gamma-Gamma Atmospheric Turbulence
In this paper, we investigate a dual-hop relaying system, composed of radio
frequency (RF) and free-space optical (FSO) link. Decode-and-forward (DF) relay
is employed to integrate the first RF link and the second line-of-sight FSO
links. The RF channel is assumed to be subject to recently proposed
Fisher-Snedecor fading model, which was shown to be convenient for modeling in
realistic wireless communication scenarios. The FSO channel is affected by
Gamma-Gamma distributed atmospheric turbulence. Expression for the outage
probability is derived and utilized to present numerical results. Based on
presented results, the effects of various RF and FSO channels parameters on the
overall system performance are examined and discussed.Comment: Presented at 2018 26th Telecommunications Forum (TELFOR
Mixed RF-VLC Relaying System with Radio-Access Diversity
We present a statistical analysis of a mixed radio-frequency (RF)-visible
light communications (VLC) relaying system, where outdoor millimeter wave based
RF links are utilized to provide backhaul connectivity for indoor VLC
broadcasting. The multiple RF links are assumed to communicate with the VLC
access point through decode-and-forward relay. Novel closed-form outage
probability and average bit error rate expressions are derived and utilized to
obtain numerical results. Monte Carlo simulations validate presented numerical
results, which are further used to examine the effects of system and channel
parameters on system performance.Comment: Presented at 2019 28th Wireless and Optical Communications Conference
(WOCC
Error rate and ergodic capacity of RF-FSO system with partial relay selection in the presence of pointing errors
This paper presents an analysis of a multiple dual-hop relaying system, which is composed of km-class radio frequency (RF)-free-space optical (FSO) links. Partial relay selection based on outdated channel state information (CSI) is employed in order to select active relay for further transmission. Amplify-and-forward relaying protocol is utilized. The RF links are assumed to be subject to Rayleigh fading, and the FSO links are influenced by both GammaâGamma atmospheric turbulence and pointing errors. On the basis of our previously derived expression for cumulative distribution function of the equivalent signal-to-noise ratio of the whole system, we derive novel analytical expressions for the average bit-error rate (BER) and ergodic capacity that are presented in terms of the Meijerâs G-function and extended generalized bivariate Meijerâs G-function, respectively. The numerical results are confirmed by Monte Carlo simulations. Considering the effect of time-correlation between outdated CSI and actual CSI related to the RF channel at the time of transmission, the average BER and the ergodic capacity dependence on various system and channel parameters are observed and discussed. The results illustrate that the temporal correlation between outdated and actual CSI has strong effect on system performance, particularly on BER values, when FSO hop is influenced by favorable conditions
Mixed RF-VLC Relaying Systems for Interference-Sensitive Mobile Applications
Due to their Radio-Frequency (RF) immunity, Visible Light Communications
(VLC) pose as a promising technology for interference sensitive applications
such as medical data networks. In this paper, we investigate mixed RF-VLC
relaying systems especially suited for this type of applications that support
mobility. In this system setup, the end-user, who is assumed to be on a vehicle
that is in dynamic movement, is served by an indoor VLC system, while the
outdoor data traffic is conveyed through multiple backhaul RF links.
Furthermore, it is assumed that a single backhaul RF link is activated by the
mobile relay and due to feedback delay, the RF link activation is based on
outdated channel state information (CSI). The performance of this system is
analyzed in terms of outage probability and bit error rate (BER), and novel
closed form analytical expressions are provided. Furthermore, the analysis is
extended for the case where the average SNR over the RF links and/or LED
optical power is high, and approximate analytical expressions are derived which
determine performance floors. Numerical results are provided which demonstrate
that the utilization of multiple RF backhaul links can significantly improve
overall RF-VLC system performance when outage/BER floors are avoided. This
calls upon joint design of both subsystems. Additionally, the outdated CSI
exploited for active RF selection can significantly degrade the quality of
system performance.Comment: Published in IEEE Transactions on Vehicular Technolog
Impact of Temporary Link Blockage on Ergodic Capacity of FSO System
Freeâspace optical (FSO) systems have attracted much attention from both research and application perspectives owing to their many benefits, such as licenseâfree operation, lowâcost, and high data rates. This paper investigates the ergodic capacity of FSO systems, which is an important metric of system performance. The stochastic temporary laserâbeam blockage, pointing errors, and atmospheric turbulence are simultaneously considered. The results illustrate that the link blockage causes a decreased ergodic capacity. We show that to maximize the ergodic capacity, there is an optimal value of the laserâbeam radius at the waist, which largely depends on pointing errors; however, it is independent of the atmospheric turbulence and the probability of link blockage
Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries
Background
Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks.
Methods
The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned.
Results
A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31).
Conclusion
Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)