Distributed Adaptive Algorithms for Optimal Opportunistic Medium Access

We examine threshold-based transmission strategies for distributed opportunistic medium access in a scenario with fairly general probabilistic interference conditions. Specifically, collisions between concurrent transmissions are governed by arbitrary probabilities, allowing for a form of channel capture and covering binary interference constraints as an important special case. We address the problem of setting the threshold values so as to optimize the aggregate throughput utility of the various users, and particularly focus on a weighted logarithmic throughput utility function (Proportional Fairness). We provide an adaptive algorithm for finding the optimal threshold values in a distributed fashion, and rigorously establish the convergence of the proposed algorithm under mild statistical assumptions. Moreover, we discuss how the algorithm may be adapted to achieve packet-level stability with only limited exchange of queue length information among the various users. We also conduct extensive numerical experiments to corroborate the theoretical convergence results.14 page(s

Changes in Self-Efficacy and Social Support after an Intervention to Increase Physical Activity Among Adults with Type 2 Diabetes in Oman:A 12-month follow-up of the MOVEdiabetes trial

Objectives: This study aimed to describe changes in self-efficacy (SE) and social support (SS) 12 months after the MOVEdiabetes trial, an intervention designed to increase physical activity (PA) among adults with type 2 diabetes mellitus in Oman. Methods: The original MOVEdiabetes trial was conducted between April 2016 and June 2017 in Muscat, Oman. The intervention group (IG) received personalised PA consultations, pedometers and monthly messages using a web-based application, while the comparison group received usual care. Self-reported SE and SS from family and friends were assessed using validated psychosocial scales. Results: Of the 232 original participants in the trial, a total of 174 completed the 12 months follow-up study period (response rate: 75%). However, based on intention-to-treat analysis with several imputation procedures for missing data at 3 and/or 12 months, there was a significant increase in SE scores in the IG (+10.3, 95% confidence interval [CI]: 7.1–13.5; P <0.001); however, the correlation with PA levels was weak (+4.2, 95% CI: 2.7–5.7; P <0.001). Higher SE scores were noted in those without comorbidities (+12.2, 95% CI: 6.8–17.6; P <0.001) and with high income levels (+9.7, 95% CI: 5.2–14.2; P <0.001). Additionally, SS scores increased significantly among those in the IG who received support from friends (+2.3, 95% CI: 1.1–3.7; P <0.001), but not family (+1.2, 95% CI: −0.4–2.8; P = 0.110). The reliability of the scales was acceptable for SE and SS from family, but poor for SS from friends (Cronbach’s alpha coefficients = 0.82, 0.82 and 0.40, respectively). Conclusion: The PA intervention was associated with positive changes in SE and SS from friends. However, further tools for assessing psychosocial influences on PA are needed in Arab countries.   KEYWORDS Physical Activity; Type 2 Diabetes Mellitus; Self-Management; Health Behaviors; Social Support, Self-Efficacy; Primary Healthcare; Oman

Joint Polling and Contention Based Feedback Algorithm to Exploit Multiuser Diversity

Abstract — One of the most promising approaches to boost the communication efficiency in wireless systems is the use of multiuser diversity (MUDiv), where the fading of channels is exploited. The mechanism of scheduling the user with the best channel condition is called opportunistic scheduling (OS). In this paper we propose a joint polling and contention based feedback (JPCF) algorithm that exploits MUDiv while reducing the feedback load. The guard time, which is between bursts, is divided into minislots that alternate between polling-based feedback minislot (p-minislot) and contention-based feedback minislot (c-minislot). During the minislot, users feedback their channel qualities if above a predetermined threshold. We analyze the scheduling algorithm under slow Rayleigh fading assumption and derive the closed-form expressions of the feedback load as well as the system capacity. We also consider the delay resulting from the time needed to schedule a user and derive the system throughput. The scheduling algorithm is compared with other scheduling algorithms. Index Terms — Multiuser diversity, adaptive modulation, feedback load, spectral efficiency and probability of access

Compliance of amblyopic patients with occlusion therapy: A pilot study

Background: Increasing evidence shows that good compliance with occlusion therapy is paramount for successful amblyopia therapy. Purpose: To study the degree of compliance and explore factors affecting compliance in patients undergoing occlusion therapy for amblyopia in our practice. Design: Nonrandomized clinical intervention study. Materials and Methods: A total of 31 families with a child (aged 2-12 years), undergoing unilateral amblyopia treatment at the pediatric ophthalmology clinic of Sultan Qaboos University Hospital, Oman, were recruited for this one month study. Parents were interviewed and completed a closed-ended questionnaire. Clinical data including, visual acuity, refraction, diagnosis and treatment, for each patient was collected from the hospital chart and was entered in a data collection sheet. Compliance with occlusion therapy was assessed by self-report accounts of parents and was graded into good, partial, or poor. Association between various factors and degree of compliance was studied using logistic regression modeling. Results: Only 14 (45%) patients showed good compliance to occlusion therapy. 17 (55%) patients were noncompliant. Improvement in visual acuity strongly correlated with compliance to patching (P = 0.008). Other variables that were studied included, age at onset of therapy; gender; degree of amblyopia; type of amblyopia; use of glasses; and compliance with glasses. These did not emerge as significant predictors of compliance. All but one family with poor compliance stated that the main challenge in following the recommendation to patch for requisite hours was in getting their child to cooperate. Only in one instance, the family cited nonavailability of patches as the main hindrance to compliance. 10/31 (32%) families expressed a desire for more information and 18/31 (58%) parents did not understand that amblyopia meant decreased vision. Conclusion: Poor compliance is a barrier to successful amblyopia therapy in our practice. Improvement in visual acuity is associated with better compliance with patching. Parents find it difficult to comprehend and retain verbal explanations of various components regarding occlusion therapy for amblyopia. Future study with a larger sample of patients is recommended to investigate the factors affecting compliance with amblyopia therapy and determine predictors for poor compliance