CROSS-LAYER DISTORTION CONTROL FOR DELAY SENSITIVE SOURCES

The existence of layers in the traditional network architecture facilitates the network design by modularizing it and thus enabling isolated design of the different layers. However, due to the inherent coupling and interactions between these layers, their isolated design often leads to suboptimal performance. On the other hand, the recent popularity of realtime multimedia applications has pushed the boundaries of layered designs. Cross-layer network design provides opportunities for significant performance improvement by selectively exploiting the interactions between layers, and therefore has attracted a lot of attention in recent years. Realtime multimedia applications are characterized by their delay-sensitivity and distortion-tolerance. The focus of this thesis is on Source Coding for Delay-Sensitive Distortion-Tolerant data. In particular, we notice that even though using longer descriptions for source symbols results in smaller distortion for each particular symbol, it also increases the delay experienced in the network, which in turn causes information loss for a delay-sensitive source, and therefore, increases the overall distortion of the received message. In this thesis we investigate this trade-off across the layers by considering two different problems. In the first problem, we focus on a single source-destination pair to exploit the interconnection between Source Coding, traditionally a presentation layer component, and Parallel Routing, a network layer issue. We use a Distortion Measure that combines signal reconstruction fidelity with network delay. We minimize this measure by jointly choosing the Encoder Parameters and the Routing Parameters. We look at both single-description and multiple-description codings and perform numerical optimizations that provide insight into design tradeoffs which can be exploited in more complex settings. We then investigate the problem of finding minimum-distortion policies for streaming delay-sensitive distortion-tolerant data. We use a cross-layer design which exploits the coupling between the presentation layer and the transport and link layers. We find an optimum transmission policy for error-free channels, which is independent of the particular form of the distortion function when it is convex and decreasing. For a packet-erasure channel, we find computationally efficient heuristic policies which have near optimal performance

Future Evolution of CSMA Protocols for the IEEE 802.11 Standard

In this paper a candidate protocol to replace the prevalent CSMA/CA medium access control in Wireless Local Area Networks is presented. The proposed protocol can achieve higher throughput than CSMA/CA, while maintaining fairness, and without additional implementation complexity. Under certain circumstances, it is able to reach and maintain collision-free operation, even when the number of contenders is variable and potentially large. It is backward compatible, allowing for new and legacy stations to coexist without degrading one another's performance, a property that can make the adoption process by future versions of the standard smooth and inexpensive.Comment: This paper has been accepted in the Second IEEE ICC Workshop 2013 on Telecommunication Standards: From Research to Standard

Cardiometabolic Risk Factor Changes Observed in Diabetes Prevention Programs in US Settings: A Systematic Review and Meta-analysis

Background: The Diabetes Prevention Program (DPP) study showed that weight loss in high-risk adults lowered diabetes incidence and cardiovascular disease risk. No prior analyses have aggregated weight and cardiometabolic risk factor changes observed in studies implementing DPP interventions in nonresearch settings in the United States. Methods and Findings: In this systematic review and meta-analysis, we pooled data from studies in the United States implementing DPP lifestyle modification programs (focused on modest [5%–7%] weight loss through ≥150 min of moderate physical activity per week and restriction of fat intake) in clinical, community, and online settings. We reported aggregated pre- and post-intervention weight and cardiometabolic risk factor changes (fasting blood glucose [FBG], glycosylated hemoglobin [HbA1c], systolic or diastolic blood pressure [SBP/DBP], total [TC] or HDL-cholesterol). We searched the MEDLINE, EMBASE, Cochrane Library, and Clinicaltrials.gov databases from January 1, 2003, to May 1, 2016. Two reviewers independently evaluated article eligibility and extracted data on study designs, populations enrolled, intervention program characteristics (duration, number of core and maintenance sessions), and outcomes. We used a random effects model to calculate summary estimates for each outcome and associated 95% confidence intervals (CI). To examine sources of heterogeneity, results were stratified according to the presence of maintenance sessions, risk level of participants (prediabetes or other), and intervention delivery personnel (lay or professional). Forty-four studies that enrolled 8,995 participants met eligibility criteria. Participants had an average age of 50.8 years and body mass index (BMI) of 34.8 kg/m2, and 25.2% were male. On average, study follow-up was 9.3 mo (median 12.0) with a range of 1.5 to 36 months; programs offered a mean of 12.6 sessions, with mean participant attendance of 11.0 core sessions. Sixty percent of programs offered some form of post-core maintenance (either email or in person). Mean absolute changes observed were: weight -3.77 kg (95% CI: -4.55; -2.99), HbA1c -0.21% (-0.29; -0.13), FBG -2.40 mg/dL (-3.59; -1.21), SBP -4.29 mmHg (-5.73, -2.84), DBP -2.56 mmHg (-3.40, 1.71), HDL +0.85 mg/dL (-0.10, 1.60), and TC -5.34 mg/dL (-9.72, -0.97). Programs with a maintenance component achieved greater reductions in weight (additional -1.66kg) and FBG (additional -3.14 mg/dl). Findings are subject to incomplete reporting and heterogeneity of studies included, and confounding because most included studies used pre-post study designs. Conclusions: DPP lifestyle modification programs achieved clinically meaningful weight and cardiometabolic health improvements. Together, these data suggest that additional value is gained from these programs, reinforcing that they are likely very cost-effective

Distortion control for delay-sensitive sources

We investigate the problem of finding minimum-distortion policies for streaming delay-sensitive but distortion-tolerant data. We consider cross-layer approaches which exploit the coupling between presentation and transport layers. We make the natural assumption that the distortion function is convex and decreasing. We focus on a single source-destination pair and analytically find the optimum transmission policy when the transmission is done over an error-free channel. This optimum policy turns out to be independent of the exact form of the convex and decreasing distortion function. Then, for a packet-erasure channel, we analytically find the optimum open-loop transmission policy, which is also independent of the form of the convex distortion function. We then find computationally efficient closed-loop heuristic policies and show, through numerical evaluation, that they outperform the open-loop policy and have near optimal performance.This work was supported in part by a subaward from the U.S. Army, prime award W911NF-05-1-0246. Prepared through collaborative participation in the Communications/nand Networks Consortium sponsored by the U.S. Army Research Laboratory under The Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011