Aggregate Interference Modeling in Cognitive Radio Networks with Power and Contention Control

In this paper, we present an interference model for cognitive radio (CR) networks employing power control, contention control or hybrid power/contention control schemes. For the first case, a power control scheme is proposed to govern the transmission power of a CR node. For the second one, a contention control scheme at the media access control (MAC) layer, based on carrier sense multiple access with collision avoidance (CSMA/CA), is proposed to coordinate the operation of CR nodes with transmission requests. The probability density functions of the interference received at a primary receiver from a CR network are first derived numerically for these two cases. For the hybrid case, where power and contention controls are jointly adopted by a CR node to govern its transmission, the interference is analyzed and compared with that of the first two schemes by simulations. Then, the interference distributions under the first two control schemes are fitted by log-normal distributions with greatly reduced complexity. Moreover, the effect of a hidden primary receiver on the interference experienced at the receiver is investigated. It is demonstrated that both power and contention controls are effective approaches to alleviate the interference caused by CR networks. Some in-depth analysis of the impact of key parameters on the interference of CR networks is given via numerical studies as well.Comment: 24 pages, 8 figures, submitted to IEEE Trans. Communications in July 201

Review of interference avoidance schemes in femtocell networks

Femtocell is a solution to increase the system capacity and coverage to meet the high demand of the next generation of services on broadband wireless access. However, the deployment of a new femtocell layer may have an undesired impact on the performance of the macrocell layer. The allocation of spectrum resources and the avoidance of electromagnetic interference are some of the more urgent challenges that operators face before femtocells become widely deployed. In this paper different interference avoidance schemes are described and compared. Special attention is paid to the use of uplink and downlink power control and self-configuration and self-optimization techniques for the avoidance of interference. From the review, we conclude that frequency planning is suitable for interference avoidance schemes for unplanned location of femtocells deployment

Low-complexity medium access control protocols for QoS support in third-generation radio access networks

One approach to maximizing the efficiency of medium access control (MAC) on the uplink in a future wideband code-division multiple-access (WCDMA)-based third-generation radio access network, and hence maximize spectral efficiency, is to employ a low-complexity distributed scheduling control approach. The maximization of spectral efficiency in third-generation radio access networks is complicated by the need to provide bandwidth-on-demand to diverse services characterized by diverse quality of service (QoS) requirements in an interference limited environment. However, the ability to exploit the full potential of resource allocation algorithms in third-generation radio access networks has been limited by the absence of a metric that captures the two-dimensional radio resource requirement, in terms of power and bandwidth, in the third-generation radio access network environment, where different users may have different signal-to-interference ratio requirements. This paper presents a novel resource metric as a solution to this fundamental problem. Also, a novel deadline-driven backoff procedure has been presented as the backoff scheme of the proposed distributed scheduling MAC protocols to enable the efficient support of services with QoS imposed delay constraints without the need for centralized scheduling. The main conclusion is that low-complexity distributed scheduling control strategies using overload avoidance/overload detection can be designed using the proposed resource metric to give near optimal performance and thus maintain a high spectral efficiency in third-generation radio access networks and that importantly overload detection is superior to overload avoidance

The flying hot wire and related instrumentation

A flying hot-wire technique is proposed for studies of separated turbulent flow in wind tunnels. The technique avoids the problem of signal rectification in regions of high turbulence level by moving the probe rapidly through the flow on the end of a rotating arm. New problems which arise include control of effects of torque variation on rotor speed, avoidance of interference from the wake of the moving arms, and synchronization of data acquisition with rotation. Solutions for these problems are described. The self-calibrating feature of the technique is illustrated by a sample X-array calibration

Post-COVID Patients With New-Onset Chronic Pain 2 Years After Infection: Cross-Sectional Study

Background: Although pain is common in non-hospitalized post-COVID-19 syndrome, only a few studies have provided information on the pain experience of these patients. Aim: To identify the clinical and psychosocial profile associated with pain in non-hospitalized patients with post-COVID-19 syndrome. Method: In this study there were three groups: healthy control group, successfully recovered group, and post-COVID syndrome group. Pain-related clinical profile and pain-related psychosocial variables were collected. Pain-related clinical profile included: pain intensity and interference (Brief Pain Inventory), central sensitization (Central Sensitization Scale), insomnia severity (Insomnia Severity Index), and pain treatment. Pain-related psychosocial variables were: fear of movement and (re)injury (Tampa Scale for Kinesiophobia), catastrophizing (Pain Catastrophizing Scale), depression, anxiety and stress (Depression, Anxiety and Stress Scale), and fear-avoidance beliefs (Fear Avoidance Beliefs Questionnaire). Results: In all, 170 participants were included in the study (healthy control group n = 58, successfully recovered group n = 57, and post-COVID syndrome group n = 55). Post-COVID syndrome group obtained significantly worse punctuation in pain-related clinical profile and psychosocial variables than the other two groups (p < .05). Conclusions: In conclusion, patients with post-COVID-19 syndrome have experienced high pain intensity and interference, central sensitization, increased insomnia severity, fear of movement, catastrophizing, fear-avoidance beliefs, depression, anxiety, and stres

Anxiety and attention to threat: cognitive mechanisms and treatment with attention bias modification

Anxiety disorders are common and difficult to treat. Some cognitive models of anxiety propose that attention bias to threat causes and maintains anxiety. This view led to the development of a computer-delivered treatment: attention bias modification (ABM) which predominantly trains attention avoidance of threat. However, meta-analyses indicate disappointing effectiveness of ABM-threat-avoidance training in reducing anxiety. This article considers how ABM may be improved, based on a review of key ideas from models of anxiety, attention and cognitive control. These are combined into an integrative framework of cognitive functions which support automatic threat evaluation/detection and goal-directed thought and action, which reciprocally influence each other. It considers roles of bottom-up and top-down processes involved in threat-evaluation, orienting and inhibitory control in different manifestations of attention bias (initial orienting, attention maintenance, threat avoidance, threat-distractor interference) and different ABM methods (e.g., ABM-threat-avoidance, ABM-positive-search). The framework has implications for computer-delivered treatments for anxiety. ABM methods which encourage active goal-focused attention-search for positive/nonthreat information and flexible cognitive control across multiple processes (particularly inhibitory control, which supports a positive goal-engagement mode over processing of minor threat cues) may prove more effective in reducing anxiety than ABM-threat-avoidance training which targets a specific bias in spatial orienting to threat

Hiatus Avoidance and Metrification in the Rigveda

Using new corpus resources for Rigvedic poetics, we address various aspects of the poets\u27 treatment of vowel hiatus and pre-vocalic shortening (correption), including their strategies for avoidance of these phenomena in certain contexts. Using observed vs. expected tests, we demonstrate, for one, that hiatus avoidance is correlated with degree of metrical-prosodic juncture. For example, hiatus is actively avoided both at the caesura in trimeter verse and between padãs, but its avoidance is weaker in the latter case. In conducting these tests, we control for a confound (interference) from pre-vocalic shortening, which requires us to address the problem of whether it was optional or obligatory within the hemistich. It turns out that /V̄1#V22 patterns as metrically heavier than /Ṽ1#V2/ in the aggregated, though not as heave as /V̄C#V/. We then discuss different means by which the poets avoid setting up underlying hiatus junctures, including lexical avoidance (i.e., word selection), morphological avoidance (i.e., allomorph selection), and syntactic avoidance (i.e., word reordering). This last technique, whose existence we support with two different rests, is particularly striking, in that syntax (word order) is shown to be sensitive to phonotactics (marked junctures)