Design and Analysis of Distributed Averaging with Quantized Communication

Consider a network whose nodes have some initial values, and it is desired to design an algorithm that builds on neighbor to neighbor interactions with the ultimate goal of convergence to the average of all initial node values or to some value close to that average. Such an algorithm is called generically "distributed averaging," and our goal in this paper is to study the performance of a subclass of deterministic distributed averaging algorithms where the information exchange between neighboring nodes (agents) is subject to uniform quantization. With such quantization, convergence to the precise average cannot be achieved in general, but the convergence would be to some value close to it, called quantized consensus. Using Lyapunov stability analysis, we characterize the convergence properties of the resulting nonlinear quantized system. We show that in finite time and depending on initial conditions, the algorithm will either cause all agents to reach a quantized consensus where the consensus value is the largest quantized value not greater than the average of their initial values, or will lead all variables to cycle in a small neighborhood around the average. In the latter case, we identify tight bounds for the size of the neighborhood and we further show that the error can be made arbitrarily small by adjusting the algorithm's parameters in a distributed manner

Power-Optimal Feedback-Based Random Spectrum Access for an Energy Harvesting Cognitive User

In this paper, we study and analyze cognitive radio networks in which secondary users (SUs) are equipped with Energy Harvesting (EH) capability. We design a random spectrum sensing and access protocol for the SU that exploits the primary link's feedback and requires less average sensing time. Unlike previous works proposed earlier in literature, we do not assume perfect feedback. Instead, we take into account the more practical possibilities of overhearing unreliable feedback signals and accommodate spectrum sensing errors. Moreover, we assume an interference-based channel model where the receivers are equipped with multi-packet reception (MPR) capability. Furthermore, we perform power allocation at the SU with the objective of maximizing the secondary throughput under constraints that maintain certain quality-of-service (QoS) measures for the primary user (PU)

On Spectrum Sharing Between Energy Harvesting Cognitive Radio Users and Primary Users

This paper investigates the maximum secondary throughput for a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable power supply. The SU maintains a finite energy queue and harvests energy from natural resources and primary radio frequency (RF) transmissions. We propose a power allocation policy at the PU and analyze its effect on the throughput of both the PU and SU. Furthermore, we study the impact of the bursty arrivals at the PU on the energy harvested by the SU from RF transmissions. Moreover, we investigate the impact of the rate of energy harvesting from natural resources on the SU throughput. We assume fading channels and compute exact closed-form expressions for the energy harvested by the SU under fading. Results reveal that the proposed power allocation policy along with the implemented RF energy harvesting at the SU enhance the throughput of both primary and secondary links

Optimal Spectrum Access for a Rechargeable Cognitive Radio User Based on Energy Buffer State

This paper investigates the maximum throughput for a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable power supply. The SU maintains a finite energy queue and harvests energy from natural resources, e.g., solar, wind and acoustic noise. We propose a probabilistic access strategy by the SU based on the number of packets at its energy queue. We investigate the effect of the energy arrival rate, the amount of energy per energy packet, and the capacity of the energy queue on the SU throughput under fading channels. Results reveal that the proposed access strategy can enhance the performance of the SU.Comment: arXiv admin note: text overlap with arXiv:1407.726

Cooperative Access in Cognitive Radio Networks: Stable Throughput and Delay Tradeoffs

In this paper, we study and analyze fundamental throughput-delay tradeoffs in cooperative multiple access for cognitive radio systems. We focus on the class of randomized cooperative policies, whereby the secondary user (SU) serves either the queue of its own data or the queue of the primary user (PU) relayed data with certain service probabilities. The proposed policy opens room for trading the PU delay for enhanced SU delay. Towards this objective, stability conditions for the queues involved in the system are derived. Furthermore, a moment generating function approach is employed to derive closed-form expressions for the average delay encountered by the packets of both users. Results reveal that cooperation expands the stable throughput region of the system and significantly reduces the delay at both users. Moreover, we quantify the gain obtained in terms of the SU delay under the proposed policy, over conventional relaying that gives strict priority to the relay queue.Comment: accepted for publication in IEEE 12th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 201

Role of N-terminal pro B-type natriuretic peptide in acute exacerbation of chronic obstructive pulmonary disease

AbstractObjectivesAcute exacerbation of chronic obstructive pulmonary disease (AECOPD) is a major public health problem. Recognition of comorbid heart dysfunction in such patients is often difficult. The aim of this work is to evaluate the role of N-terminal pro B-type natriuretic peptide (Nt-pro BNP) in AECOPD with respiratory failure.Patients and methodsThis study was conducted on 20 patients with AECOPD and respiratory failure. All patients were subjected to history taking, clinical examination, routine laboratory investigations, arterial blood gases analysis, echocardiography and estimation of plasma level of NT-pro BNP.ResultsPatients were classified into 3 groups: Group I: those without heart dysfunction (40%), Group II: those with diastolic heart failure (40%), and Group III: those with systolic heart failure (20%). NT-pro BNP mean±SD in group I was 673.38±416.02, in group II 1962±847.88, and in group III 6776.75±1433.59pg/ml. There was a statistically significant difference between the three groups (p=0.001). NT-pro BNP showed a statistically significant inverse correlation with pH (p=0.005), ejection fraction (p=0.007) and a direct one with both left ventricular systolic (p=0.008) and diastolic (p=0.016) dimensions and E/A (p=0.016). The NT-pro BNP significantly decreased after recovery from AECOPD (p=0.030). The receiver operating characteristic curve demonstrated a ruling out of LV dysfunction in AECOPD of a sensitivity of 100% and a specificity of 60%; and a ruling in of a sensitivity of 48% and a specificity of 67%.ConclusionPlasma BNP is usually elevated in AECOPD and is related to right or left ventricular systolic or diastolic dysfunction

Optimal Strategies for Dynamic Weight Selection in Consensus Protocols in the Presence of an Adversary

Abstract-In this paper, we consider optimal design strategies in consensus protocols for networks vulnerable to adversarial attacks. First we study dynamic (multi-stage) weight selection optimal control for consensus protocols. For the general (multi-stage) case, the solution exists but can rarely be expressed in closed-form. In view of this, we apply optimization techniques to obtain a locally (and possibly globally) optimizing feasible control path. For the one-stage case, however, we obtain a closed-form solution for the optimal control and provide sufficient conditions for the existence of a control that makes the system reach consensus in only one iteration. We then consider a game theoretical model for the problem of a network with an adversary corrupting the control signal with noise. We derive the optimal strategies for both players (the adversary and the network designer) of the resulting game using a saddle point equilibrium (SPE) solution in mixed strategies

Viral Hepatitis A to E in South Mediterranean Countries

Viral hepatitis represents an important health problem in the South Mediterranean countries, Egypt, Libya, Tunisia, Algeria and Morocco. Emerging natural history and epidemiological information reveal differences in the overall epidemiology, risk factors and modes of transmission of viral hepatitis A, B, C, D, E infections in the South Mediterranean region. The differences in the in incidence and prevalence of viral hepatitis across North African countries is attributed to variations in health care and sanitation standards, risk factors and immunization strategies. The active continuous population movement through travel, tourism and migration from and to the South Mediterranean countries contribute to the spread of infections due to hepatitis viruses across borders leading to outbreaks and emergence of new patterns of infection or introduction of uncommon genotypes in other countries, particularly in Europe

Evaluation of pediatric bradycardia: A single center experience

Background: Heart rate is an integral part of the clinical assessment of the children with acute illness and is commonly used in pediatric early warning scores. Objective: The aim of this study was to assess our current practice for evaluation and management of bradycardia in children. Patients and methods: The study was conducted in Pediatric Arrhythmia Clinic, Neonatal Intensive Care Unit and Pediatric Intensive Care Unit from March 2020 to August 2021. 61 Neonates and children aged from 1 day to 18 years presenting with bradycardia were included in this study. Predeath bradycardia was excluded. Full medical history, physical examination, basic investigations, 12 leads ECG and echocardiography were performed to all patients. Thyroid function tests, 24 hours Holter monitoring, and stress ECG were done if indicated. Results: 61 patients were included in the study. Heart rate ranged from 44 to 94 beat/minute with mean 69.44 beat/minute, the most common form of presentation was abnormal echocardiography. Hypocalcemia was present in 85.2% of patients. 70.5% of patients had sinus bradycardia, 13% had complete heart block (CHB),10% of patients had long QTc Syndrome with sinus bradycardia, 3.3% had 1st and 2nd degree heart block, 1.6% had ECG changes of ALCAPA with sinus bradycardia and 1.6% had ventricular ectopic. Conclusion: It could be concluded that bradycardia in children needs accurate assessment to rule out the need of acute intervention and to decrease the risk of life-threatening conditions