Addressing the hidden terminal problem in MU-MIMO WLANs with relaxed zero-forcing approach

University of Technology Sydney. Faculty of Engineering and Information Technology.An ever-increasing data rate demand, mainly due to the proliferation of numerous smart devices, enterprises’ mission critical networks, and industry automation, has mounted tremendous pressure on today’s Wireless Local Area Networks (WLANs). Several avenues such as bandwidth, constellation density, the Multiple Input Multiple Output (MIMO) technique, etc., have been explored, e.g., IEEE802.11n/ac standards, to keep up with the demand. Future WLAN standard, e.g., IEEE802.11ax, with potential technologies such as uplink Multi-User (MU)-MIMO, full duplex transmission, etc., is anticipated by 2019. Having said that, there has been a strong emphasis on solving the technical issues with WLANs along with the addition of new frontiers in order to cope with the data rate demanded. One such appending decade-long issue is the inevitable Hidden Terminal (HT) problem in a distributive, decentralised and densely deployed WLANs, which fundamentally arises because of the transmission time overlaps between different transmitters operating at a particular frequency. The consequence is that it causes collisions of signals, which sharply reduces the system throughput. In the context of MU-MIMO based WLANs, several designs for a general network scenario, without the consideration of the HT problem, have been proposed, bringing efficiency by avoiding the collision of signals. However, a dedicated design, which could effectively address the HT problem in MU-MIMO WLANs and also become interoperable (with legacy standards) and feasible with existing hardware, is lacking to the best of our knowledge. In this thesis, we propose a solution for the HT problem which has three fundamental attributes. First, a) at the Physical (PHY) layer, the Zero-forcing (ZF) transmission strategy with fairness and throughput aware precoding is proposed, b) a hybrid scheduling scheme, combining the packet position-based First In First Out (FIFO) and channel quality-based scheme, namely the Best of the Two Choices, is designed, c) at the Medium Access Control (MAC) layer, Degrees-of-Freedom (DoF) based Transmission Opportunity (TXOP) for Access Points (APs) is developed which is backed by an extended Point Coordination Function (PCF), d) an explicit channel acquisition framework is proposed for ZF which has a reduced signaling time overhead of 98.6740 μs compared to IEEE802.11ac. e) performance evaluation methodologies are: i) hardware testbed results of the PHY strategy, which shows a received SNR gain of about 6 dB on average, and about 10 dB in comparison to the HT scenario, ii) simulation results of the MAC design, which shows a constant throughput gain of 4 − 5 times w.r.t. the popular Request to Send/Clear to Send (RTS/CTS) solution. Second, to address the interoperability issue, we purposefully use the standard frame format except for some required logical changes. Notably, the transition mechanism of our design, and for any MAC that uses standard frame formats, is investigated meticulously. The transition condition, transition steps and transition frame formats are detailed. Third, to address a practical constraint of an imperfect Channel State Information (CSI) at APs, a) we incorporate the Finite Rate Feedback (FRF) model in our solution. The effects on system parameters such as quantisation error bounds, throughput loss w.r.t. perfect CSI, etc., are discussed with closed-form analytical expressions, b) instead of an ideal ZF technique, a Relaxed ZF (RZF) framework is considered, in which the interference and power constraints of the optimisation problem are relaxed to the interference upper bound and to the maximum transmit power respectively. Our results lead to a distributive algorithm for calculating the optimal ZF precoding vector which suits the distributive, decentralised and uncoordinated nature of MU-MIMO WLANs

Preparedness and responses to the 2015 earthquake disaster in Nepal : remittances and differential vulnerability by Caste system

This study examined the accessibility of remittances and their effect during a disaster in Thumpakhar VDC. It employed mixed method of data collection to examine the inequalities in a society. The inequality of wealth and savings at household level was found highly shaped by Caste system which privileges high caste and disadvantages low caste in migration opportunities. The result showed that poor and low Caste people are least included in the migration process which revealed many socio-economic barriers they encounter in choosing migration as a livelihood strategy. Further, the role of remittance in disaster preparedness and post-disaster response was empirically tested in the context of various amount of remittance from different destinations. Most interestingly, the selection of these destinations domestically, in the Middle East, and in Western countries was found to be dependent on Caste they belong to. These selections impacted the remittance outcome, and correspondingly the resilience during aftermath of disaster. This study found that low caste people besides being socially rejected in normal times become most vulnerable during the natural disasters due to poor social network and low access to remittance. Therefore, this thesis suggests that low caste people need special programs to help reinvent themselves as a capable workforce to be included in the migration process.M-IE

Effect of CSI quantization on the average rate in MU-MIMO WLANs

In Multi-User Multiple Input Multiple Output (MU-MIMO) Wireless Local Area Networks (WLANs), the optimal-solution such as Dirty Paper Coding (DPC) or the sub-optimal solution Zeroforcing Beamforming (ZFB) with perfect Channel State Information (CSI), is practically limited due to the complexity and the non-availability of perfect CSI at the Access Points (APs)/transmitters. In such a context, ZFB based on channel quantization available at the APs (ZFQ) is the obvious choice for the Multi-User transmission strategy. However, since the quantized CSI is used instead of the perfect CSI at the APs, the quantization error and its impact on the average rate for ZFQ have to be quantified in MU-MIMO WLAN settings. In this paper, we derive a closed-form expression for the upper bound of the channel quantization error and the average rate reduction due to the quantization error with respect to the perfect CSI at the APs. In MU-MIMO WLAN settings, our analytical and numerical studies show that, with an increasing number of antennas at the clients, both the quantization error bound and the average rate reduction increase for ZFQ, in comparison to the ZFB with the perfect CSI.5 page(s

Medium access control protocol to address hidden terminals in MU-MIMO WLANs

We exploit the Degrees of Freedom (DoF) resulting from the deployment of multiple antennas, both at the Access Points (APs) and the clients, to address the Hidden Terminal problem in Multi User (MU) Multiple Input Multiple Output (MIMO) Wireless Local Area Networks (WLANs). This approach permits concurrent transmissions and is able to maintain a constant gain in network throughput in a Hidden Terminal scenario. We treat concurrent transmissions as an integral part of our design, so we adopt and extend the traditional Point Coordination Function (PCF) to manage them. Specifically, contention free period of the traditional PCF is used in uplink and downlink. In addition, based on DoF at APs, our MAC decides the Transmission Opportunity (TXOP) of APs/Transmitters in contrast to many traditional approaches. Besides, our MAC runs a concurrent algorithm at APs which forms an important part for the calculation of precoding vectors (based on the Zeroforcing) in the Physical Layer (PHY). Additionally, a seamless channel sounding process is designed to support the ZF precoding at the PHY which has 98.67μs signaling overhead, lower than IEEE802.11ac. Simulation studies in a typical 6-antenna AP and client scenario show that our MAC provides a remarkable constant network throughput gain of 4-5 times in comparison to traditional RTS/CTS, and a lower signaling overhead than IEEE802.11ac. Besides, our simple fairness algorithm provides a fair share in the throughput among APs, with the Jain Fairness Index greater than 90%.8 page(s

THESIS NO.: 069MSCS655 Visual Cryptography using Image Pixel Transparency SUBMITTED TO THE DEPARTMENT OF ELECTRONICS AND COMPUTER ENGINEERING IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN COMPUTER SYSTEM AND KNOWLEDGE EN

ABSTRACT This thesis makes use of transparency of pixels of the shares, the two or more encrypted images, so as to reveal the secret image. The pixels of shares can be generated randomly or the cover image can be used to generate the first share. The encrypted shares generated using cover image seem to be visually less similar to those generated without using cover image. Also, on the basis of image similarity between shares and original image, further encryption of encrypted shares can be performed. This thesis also compares the outcome when cover image is used and when not used to generate shares. Results show that the latter is more sensitive to the transparency factor (alpha) than the former encouraging the use of properly selected cover image for visual cryptography using pixel transparency

Awareness of eye health and diseases among the population of the hilly region of Nepal

Purpose: To collect information regarding awareness and knowledge of eye health and diseases among the population of the hilly region of Nepal. Methods: In a population-based survey, 1834 participants were enrolled in to the study. Field procedures included the development of a survey questionnaire, field orientation, pretesting, and household data collection. Association between knowledge of eye diseases was derived using the Chi-square test and odds ratios with a 95% confidence interval. A P value of ≤0.05 was considered significant. Results: Most participants were 31–40 years old (33.4%), female (51.1%), of upper caste (43.4%), Hindus (83.3%), received secondary level of education (34.4%), and involved in agriculture (48.6%). Awareness of cataract, night blindness, glaucoma, strabismus, and systemic diseases was 74.6%, 53.4%, 17.4%, 70.8%, and 46.5%, respectively. Knowledge regarding these diseases among those aware was 39.1%, 72.2%, 50.9%, and 92.3%, respectively. Awareness of cataract was significantly higher (88.4%) among higher caste groups (P < 0.001; OR, 4.29; 95% CI, 3.34–5.54), followed by business as an occupation (88.2%; P = 0.001; OR, 2.65; 95% CI, 1.44–4.9). Awareness of night blindness was significantly higher among students (72.6%; P < 0.001; OR, 2.46; 95% CI, 1.65–3.67). Conclusion: There was a general lack of awareness and knowledge of common eye diseases. Improved awareness and knowledge are required for the prevention, early treatment, and access to eye care

Oxidant–antioxidant status and assessment of cardiovascular morbidity in Pan Masala containing Tobacco users: a cross-sectional study

Abstract Objective Pan Masala containing Tobacco (PMT) use contributes significantly to the overall world tobacco burden especially in south Asian country like Nepal. Oxidative stress caused by it may leads to cardiovascular disease, peripheral vascular disease, hypertension, etc. Therefore, this work proposes to study the antioxidant and oxidative stress along with cardiovascular morbidity in PMT users. Results Hundred PMT users and 80 non-user controls with age and sex matched were enrolled. There was a significant difference in blood pressure, albumin, uric acid, vitamin C, vitamin E, malondialdehyde (MDA), total cholesterol, triglycerides, low density lipoprotein cholesterol between the two groups (p < 0.001). We observed statistically significant (p < 0.001) decrease in antioxidant and increase oxidative stress in PMT users. Duration and quantity of PMT user were significantly associated with the MDA level

Urology during COVID-19 pandemic crisis: A systematic review

Background Coronavirus disease 2019 (COVID-19) has evolved as a pandemic of unimaginable magnitude. The health care system is facing a tremendous challenge to provide ethical and quality care. The transformation of the patient-based care to population-based care during the COVID-19 pandemic has raised ethical dilemma among urologists. Our objective is to explore the consensus in modified standard urology care, that can be adopted and applied during COVID-19 and similar pandemic. Methods We adopted an exploratory study design using secondary data. The data were extracted from a web-based medical library using keywords “COVID-19,” “severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),” and “urology.” We identify and extrapolate (screening, eligibility, and inclusion) the data using PRISMA protocol, and summarize pandemic standard urology care under four main themes: (1) general urology care, (2) choice of surgical modality, (3) triage, and (4) urology training. Result We identified 63 academic papers related to our research question. The majority are expert opinions and perspectives on urology care. The common consensus is triage-based urology care and surgeries. Life or organ threatening conditions need immediate attention. Universal protective measures (personal protective equipment, safe operative environment) and protocol-based patient care are necessary to prevent and control SARS-CoV-2 infection. Conservation of the resources and its rational distribution provide an ethical basis for population-based health care during a pandemic. Informed decision making serves best to patients, families, and society during the public health crisis. Conclusion COVID-19 pandemic tends to transform standard urology practice into crisis standard population-based care. The consensus in crisis is drawn from evolving pieces of medical evidence and public health ethics. The provision of urology care during a pandemic is based on the availability of resources; severity of the disease, consequences of deferment of service, and dynamics of the pandemic