Fundamental limits and optimal operation in large wireless networks

Wireless adhoc networks consist of users that want to communicate with each other over a shared wireless medium. The users have transmitting and receiving capabilities but there is no additional infrastructure for assisting communication. This is in contrast to existing wireless systems, cellular networks for example, where communication between wireless users heavily relies on an additional infrastructure of base stations connected with a high-capacity wired backbone. The fact that they are infrastructureless makes wireless adhoc networks inexpensive, easy to build and robust but at the same time technically more challenging. The fundamental challenge is how to deal with interference: many simultaneous transmissions have to be accommodated on the same wireless channel when each of these transmissions constitutes interference for the others, degrading the quality of the communication. The traditional approach to wireless adhoc networks is to organize users so that they relay information for each other in a multi-hop fashion. Such multi-hopping strategies face scalability problems at large system size. As shown by Gupta and Kumar in their seminal work in 2000, the maximal communication rate per user under such strategies scales inversely proportional to the square root of the number of users in the network, hence decreases to zero with increasing system size. This limitation is due to interference that precludes having many simultaneous point-to-point transmissions inside the network. In this thesis, we propose a multiscale hierarchical cooperation architecture for distributed MIMO communication in wireless adhoc networks. This novel architecture removes the interference limitation at least as far as scaling is concerned: we show that the per-user communication rate under this strategy does not degrade significantly even if there are more and more users entering into the network. This is in sharp contrast to the performance achieved by the classical multi-hopping schemes. However, the overall picture is much richer than what can be depicted by a single scheme or a single scaling law formula. Nowadays, wireless adhoc networks are considered for a wide range of practical applications and this translates to having a number of system parameters (e.g., area, power, bandwidth) with large operational range. Different applications lie in different parameter ranges and can therefore exhibit different characteristics. A thorough understanding of wireless adhoc networks can only be obtained by exploring the whole parameter space. Existing scaling law formulations are insufficient for this purpose as they concentrate on very small subsets of the system parameters. We propose a new scaling law formulation for wireless adhoc networks that serves as a mathematical tool to characterize their fundamental operating regimes. For the standard wireless channel model where signals are subject to power path-loss attenuation and random phase changes, we identify four qualitatively different operating regimes in wireless adhoc networks with large number of users. In each of these regimes, we characterize the dependence of the capacity on major system parameters. In particular, we clarify the impact of the power and bandwidth limitations on performance. This is done by deriving upper bounds on the information theoretic capacity of wireless adhoc networks in Chapter 3, and constructing communication schemes that achieve these upper bounds in Chapter 4. Our analysis identifies three engineering quantities that together determine the operating regime of a given wireless network: the short-distance signal-to-noise power ratio (SNRs), the long-distance signal-to-noise power ratio (SNRl) and the power path-loss exponent of the environment. The right communication strategy for a given application is dictated by its operating regime. We show that conventional multi-hopping schemes are optimal when the power path-loss exponent of the environment is larger than 3 and SNRs ≪ 0 dB. Such networks are extremely power-limited. On the other hand, the novel architecture proposed in this thesis, based on hierarchical cooperation and distributed MIMO, is the fundamentally right strategy for wireless networks with SNRl ≫ 0 dB. Such networks experience no power limitation. In the intermediate cases, captured by the remaining two operating regimes, neither multi-hopping nor hierarchical-MIMO achieves optimal performance. We construct new schemes for these regimes that achieve capacity. The proposed characterization of wireless adhoc networks in terms of their fundamental operating regimes, is analogous to the familiar understanding of the two operating regimes of the point-to-point additive white Gaussian noise (AWGN) channel. From an engineering point of view, one of the most important contributions of Shannon's celebrated capacity formula is to identify two qualitatively different operating regimes on this channel. Determined by its signal-to-noise power ratio (SNR), an AWGN channel can be either in a bandwidth-limited (SNR ≫ 0 dB) or a power-limited (SNR ≪ 0 dB) regime. Communication system design for this channel has been primarily driven by the operating regime one is in

Factors Influencing the School Experience of Children with Epilepsy

Objectives:To examine the effects of some characteristics of the epileptic child on school experience, a cross-sectional descriptive study was conducted.Methods:The data were collected from 110 children with epilepsy between the ages of 10–18 and followed-up by an education and research hospital’s neurology clinic in Istanbul. The “Form of the Factors Affecting the School Experience of Children” and the “Parent Form” containing the socio-demographic characteristics of children with epilepsy and their parents were used in the collection of the data.Results:In our study, we found out that 12.7% of the children were dropout; 56.4% were moderately successful and 14.5% were not good at their lessons; 47.2% were absent from school for 15 days or more, and 4.5% repeated a grade level. It was revealed that children with epilepsy have problems with school, friends, and teachers.Conclusion:Duration of disease and seizure frequency was found to be factors affecting the school experience of the child. The child, family, and teachers were recommended training suitable for the school experience of children with epilepsy

Factors that are hindering and facilitating sleep quality of children with intellectual disabilities and their mothers: A qualitative study

Background Sleep is an important physiological need for children with intellectual disabilities and their mothers. The present study aims to obtain detailed information on the factors that are hindering and facilitating the sleep quality of children with intellectual disabilities and their mothers. Twenty-one mothers of children with intellectual disabilities aged 2-18 years were interviewed to identify their perceptions of the factors that hindered or facilitated the quality of their sleep and that of their children. The interviews were transcribed, coded and analysed thematically using the MAXQDA qualitative data analysis program. Findings The interview data generated three main themes relating to factors that are hindering and facilitating sleep quality in children with intellectual disabilities and their mothers: physiological, psychological and environmental factors. Mothers reported that sleep problems negatively affect themselves and their children with intellectual disabilities. Parent education and counselling on topics of environmental regulation, methods of coping with stress and establishing and maintaining routines are recommended to enhance sleep quality

Network Simplification: the Gaussian N-Relay Diamond Network

We consider the Gaussian $N$-relay diamond network, where a source wants to communicate to a destination through a layer of $N$-relay nodes. We investigate the following question: What fraction of the capacity can we maintain by using only $k$ out of the $N$ relays? We show that in every Gaussian $N$-relay diamond network, there exists a subset of $k$ relays which alone provide approximately a fraction $\frac{k}{k+1}$ of the total capacity. The result holds independent of the number of available relay nodes $N$, the channel configurations and the operating SNR. The approximation is within $3\log N+3k$ bits/s/Hz to the capacity

What Influences Herbal Medicine Use? - Prevalence and Related Factors

Aims: The use and cost of complementary/alternative medicine (CAM) has been gaining in importance worldwide. Herbal medicine is one of the most commonly used methods. To understand the effectiveness, reliability, and quality of CAM and provide standardization in its analysis, its prevalence and the factors influencing its use must be identified. This study was conducted to identify the prevalence of CAM use and the effective factors in our population

Factors affecting knowledge levels of oncology nurses about skin cancer and sun protection

Objective This is a descriptive, cross-sectional and observational study that determines the factors affecting the knowledge levels of oncology nurses for skin cancer and sun protection. Materials & Methods This study was performed on the members of the Turkish Oncology Nursing Association and oncology nurses working in hospitals in Turkey between November 2019 and March 2020. Data were collected by using the Nurse Information Form and Skin Cancer and Sun Knowledge (SCSK) scale. For data analysis, average and percentage calculations and multiple linear regression analyses were used. The significance level was set atp We found those female nurses who were above 40 years of age and having darker skin tone due to excessive sun exposure, with a family history of skin cancer, and educated on skin cancer, performed better on the SCSK scale. We found a statistically significant difference between the mean scores of skin cancer and sun exposure. Using multiple regression analysis, a model was created based on the relationship between variables. In this model, the personality traits of oncology nurses are responsible for higher (91.1%) knowledge levels on skin cancer and sun exposure. Conclusion In conclusion, it is important to consider factors that will influence an individual's behaviour while developing skin cancer and sun protection programmes