Channel Estimation in Multi-user Massive MIMO Systems by Expectation Propagation based Algorithms

Massive multiple input multiple output (MIMO) technology uses large antenna arrays with tens or hundreds of antennas at the base station (BS) to achieve high spectral efficiency, high diversity, and high capacity. These benefits, however, rely on obtaining accurate channel state information (CSI) at the receiver for both uplink and downlink channels. Traditionally, pilot sequences are transmitted and used at the receiver to estimate the CSI. Since the length of the pilot sequences scale with the number of transmit antennas, for massive MIMO systems downlink channel estimation requires long pilot sequences resulting in reduced spectral efficiency and the so-called pilot contamination due to sharing of the pilots in adjacent cells. In this dissertation we first review the problem of channel estimation in massive MIMO systems. Next, we study the problem of semi-blind channel estimation in the uplink in the case of spatially correlated time-varying channels. The proposed method uses the transmitted data symbols as virtual pilots to enhance channel estimation. An expectation propagation (EP) algorithm is developed to iteratively approximate the joint a posterior distribution of the unknown channel matrix and the transmitted data symbols with a distribution from an exponential family. The distribution is then used for direct estimation of the channel matrix and detection of the data symbols. A modified version of Kalman filtering algorithm referred to as KF-M emerges from our EP derivation and it is used to initialize our algorithm. Simulation results demonstrate that channel estimation error and the symbol error rate of the proposed algorithm improve with the increase in the number of BS antennas or the number of data symbols in the transmitted frame. Moreover, the proposed algorithms can mitigate the effects of pilot contamination as well as time-variations of the channel. Next, we study the problem of downlink channel estimation in multi-user massive MIMO systems. Our approach is based on Bayesian compressive sensing in which the clustered sparse structure of the channel in the angular domain is exploited to reduce the pilot overhead. To capture the clustered structure, we employ a conditionally independent identically distributed Bernoulli-Gaussian prior on the sparse vector representing the channel, and a Markov prior on its support vector. An EP algorithm is developed to approximate the intractable joint distribution on the sparse vector and its support with a distribution from an exponential family. This distribution is then used for direct estimation of the channel. The EP algorithm requires the model parameters which are unknown. We estimate these parameters using the expectation maximization (EM) algorithm. Simulation results show that the proposed combination of EM and EP referred to as EM-EP algorithm outperforms several recently-proposed algorithms in the literature

Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar

Bistatic passive radar (BPR) system does not transmit any electromagnetic signal unlike the active radar, but employs an existing Illuminator of opportunity (IO) in the environment, for instance, a broadcast station, to detect and track the targets of interest. Therefore, a BPR system is comprised of two channels. One is the reference channel that collects only the IO signal, and the other is the surveillance channel which is used to capture the targets\u27 reflected signals. When the IO signal reflected from multiple targets is captured in the surveillance channel (SC) then estimating the delays and Doppler shifts of all the observed targets is a challenging problem. For BPR system, the signal processing algorithms developed so far models the IO waveform as a deterministic process and discretizes the delays and Doppler shifts parameters. In this thesis, we deal with the problem of jointly estimating the delays and Doppler shifts of multiple targets in a BPR system (i.e., a two channel system) when the unknown IO signal is modeled as a correlated stochastic process. Unlike the previous work, we take all the delays and Doppler shifts as continuous-valued parameters to avoid straddle loss due to discretization and propose a computationally efficient Expectation-Maximization (EM) based algorithm that breaks up the complex multidimensional maximum likelihood optimization problem into multiple separate optimization problems. The EM algorithm jointly provides the estimates of all the delays and Doppler shifts of the targets along with the estimate of each target\u27s component signal in the SC and the estimate of the unknown IO signal. We also derive the Cramer-Rao lower bound for the considered multitarget estimation problem with stochastic IO signal. Numerical simulations are presented where we compare our proposed EM-based multi-target estimator with the widely used conventional cross correlation estimator under different multitarget environments

Migration to Big Cities from Coastal Villages of Bangladesh: An Empirical Analysis

This paper provides core understanding about phenomenon of migration to big cities from coastal villages of Bangladesh It describes major push-pull factors how migration contributes to reduce or increase vulnerabilities and impacts of migration The paper also depicts lives and livelihoods scenario of five study villages Livelihood sources of coastal communities particularly agriculture and fisheries are climate sensitive This micro level study examines how coastal people perceive climate change on their various activities cross-seeking it with scientific shape and their responses to climate change Findings reveal that many migrants are enforced to move in response to changes in conditions or in their perception of conditions at the places of origi

Project Initiated Citizen Forums at Grassroots in Bangladesh: Lessons Learned

Bangladesh is one of the densely populated countries which recently graduated to lower-middle income country in the world A number of donor-funded nongovernment organizations are working at grassroots for socioeconomic development since long This article aims to diffuse major learning of project-led civic groups at grassroots level It describes about engagement between state guardians and grassroots civil society in Bangladesh A mixed method applying both qualitative and quantitative methodologies was adopted to conduct fieldwork A total of 130 respondents from civil society groups were surveyed for data collection This paper finds that by project interventions citizens of remote coastal areas involved Members of Parliament MPs ministry media and key actors through research interactive policy dialogue and networking They have interest and significant knowledge about lives livelihoods and promoting public policy However organizational sustainability of such civil society groups is fragile in nature due to short duration and stereotype guidance from project This paper concludes that project initiated civil society literally failed to achieve its main advocacy goal that is to promote agreed coastal policy though it improves visionary zeal and capacity among citizens Short duration of project and political unrest are major hindering factors for institutional sustainability of grassroots civil societ

Global Approaches to Medical School Regulation: A Critical Discourse Analysis

Although medical school regulation is ubiquitous, the extent to which it should be based on global principles is unclear. In 2010, the Educational Commission for Foreign Medical Graduates (ECFMG), announced that from 2023, overseas doctors would only be eligible for certification to practise in the United States if they had graduated from a medical school that was accredited by a ‘recognised’ agency. This policy empowered the World Federation for Medical Education (WFME) to create a recognition programme for regulatory agencies around the world, despite a lack of empirical evidence to support medical school regulation. In this study, I employ critical discourse analysis, drawing on the theoretical perspectives of Michel Foucault and Edward Said, to identify discourses that enabled this ‘globalising’ policy decision to take place. The dataset includes a series of documents gathered around three key events: the Edinburgh declaration by WFME in 1988, the first set of global standards for medical schools by WFME in 2003, and the ECFMG ruling about medical school accreditation in 2010. Two discourses, endorsement and modernisation, were dominant throughout this entire period, and framed the move to globalise medical school regulation in terms of altruism and improving medical education worldwide. A discourse of resistance was present in the earlier period of this study but faded away as WFME aligned itself with ECFMG. Two further discourses, protection and control, emerged in the later period of this study, and framed the ECFMG ruling in terms of nationalism and protecting American interests. This study introduces Said’s ‘contrapuntal’ analysis to the field of medical education, synthesising it with Foucauldian principles to propose a new conceptualisation of the relationship between ECFMG and WFME. It goes on to consider the implications of this association for the legitimacy of WFME as an organisation that represents all of the world’s medical schools

Altruism or nationalism? Exploring global discourses of medical school regulation

BACKGROUND: Although medical school regulation is ubiquitous, the extent to which it should be based on global principles is unclear. In 2010, the Educational Commission for Foreign Medical Graduates (ECFMG) announced that from 2023, overseas doctors would only be eligible for certification to practise in the United States if they had graduated from a medical school that was accredited by a 'recognised' agency. This policy empowered the World Federation for Medical Education (WFME) to create a recognition programme for regulatory agencies around the world, despite a lack of empirical evidence to support medical school regulation. METHODS: This study employs critical discourse analysis, drawing on the theoretical perspectives of Michel Foucault and Edward Said, to identify discourses that enabled this 'globalising' policy decision to take place. The dataset includes a series of 250 documents gathered around three key events: the Edinburgh declaration by WFME in 1988, the first set of global standards for medical schools by WFME in 2003 and the ECFMG ruling about medical school accreditation in 2010. FINDINGS: Two discourses, endorsement and modernisation, were dominant throughout this entire period and framed the move to globalise medical school regulation in terms of altruism and improving medical education worldwide. A discourse of resistance was present in the earlier period of this study but faded away as WFME aligned itself with ECFMG after 2010. Two further discourses, protection and control, emerged in the later period of this study and framed the ECFMG ruling in terms of nationalism and protecting American interests. DISCUSSION: This study proposes a new conceptualisation of the relationship between ECFMG and WFME in light of the apparently contradictory policy motivations of altruism and nationalism. It goes on to consider the implications of this association for the legitimacy of WFME as an organisation that represents all of the world's medical schools

Rural-Urban Female Migration in Bangladesh: Need for Information Support and Institutional Responses

This paper portrays lives and livelihoods scenario of female associated with ruralurban migration in Bangladesh The techniques deplored are the interview and Focus Group Discussion FGD methods in collecting data Internal migration of female has been increased with complexity This micro level study finds that possible female migrants are enticed in many cases with promises of a better life and dream in cities due to lack of information They are deprived from rights and entitlements whatever engaged in formal or informal employment But evidence pointing that voice of female workers is comparatively loud where protection framework exists This paper urges to take collaborative initiative by stakeholders for developing and disseminating standardized information Information will help female migrants to be informed and decision making In concluding this paper it is recommended that the Government of Bangladesh GoB should develop a comprehensive national policy immediately on rural-urban migration and gradually include informal employment under protection framewor

Polymer Retention during Flow of Polymer Solutions through Porous Media

Polymer solution flow and retention through porous media is of interest to many applications in the oil industry such as drilling, water shut-off and enhanced oil recovery. Operators of mature oil and gas fields are faced with the problem of excessive water production (EWP), which can cause a premature abandonment of some oil and gas wells. It has been found that the injection of high molecular weight polymer solutions through the pay zones of the oil and gas wells would induce a sharp decrease of the water production without affecting the oil and gas production. This effect is called disproportionate permeability reduction (DPR) and the polymer solutions inducing such an effect are called relative permeability modifiers (RPM). Hence, the DPR effect has been utilized in the water shut-off or conformance control of oil and gas wells suffering from EWP. In spite of the extensive research of the DPR effect, there is still a lack of agreement on the mechanisms controlling such an effect and relatively high percentage failures are observed during conformance control field applications. Polymer retention in porous media has been attributed to mechanisms such as bridging-adsorption, adsorption-entanglement, and flow-induced adsorption. These mechanisms have been proposed to account for the increase in flow resistance during or after the flow of polymer solutions through porous media. The DPR effect has been attributed to effects induced by this retained polymer such as steric and lubrication effects, wettability change, segregated oil and water pathways, and swelling and shrinking of the adsorbed polymer layer. The aim of this study is to add knowledge on the effect of polymer solution flow on polymer retention in porous media. In this study, the rheology of high molecular weight polymer solutions was studied using a cone-and-plate setup. Moreover, the characteristics and the effective hydrodynamic thickness of adsorbed polymer layers on glass from these polymer solutions under static conditions were investigated using atomic force microscopy (AFM). Also, quartz crystal microbalance with the dissipation monitoring (QCM-D) was used to investigate the effect of increasing the flow rate of polymer solutions on the adsorbed amount on silica and gold surfaces. Additionally, the mobility reduction and the residual resistance as a result of polymer solution flow through single glass capillaries, 2D and 3D models of porous media were studied. The implementation of the above techniques was used to relate the microscopic effect of the flow of the polymer solutions to the polymer retention in the porous media. The anti-thixotropic behaviour of the polymer solutions, which can be attributed to the shearinduced formation of micron-size transient entanglement networks (TEN), is expected to play a major role in the polymer retention in porous media. These microscopic structures can adsorb on the solid surfaces if the adsorption energy of the polymer/solid system is sufficient. Also, in porous media in which mechanical entrapment is possible, these structures can be entrapped in the small pores and pore throats. Two new mechanisms for polymer retention are proposed in this study: transient-entanglement networks adsorption (TENA) and transient-entanglement networks entrapment (TENE). The TENA is the retention mechanism of the TEN structures in flow systems in which mechanical entrapment is not possible provided that the adsorption energy is sufficient. If mechanical entrapment is possible, then the retention by adsorption and mechanical entrapment are lumped in the TENE mechanism. The results from this study have given a new insight on the flow and retention of polymer solutions through porous media. Hence, it is believed that the improved understanding will improve the design of high molecula

Teachers' Beliefs And Self-Efficacy In Computer Technology Integration For Teaching And Learning : A Comparative Study Between Oman And Malaysia [LB1028.3. H155 2007 f rb].

Kajian ini dijalankan untuk mengkaji faktor-faktor berkaitan integrasi teknologi komputer untuk pengajaran dan pembelajaran. Kajian mengkaji kepercayaan guru dan efikasi kendiri guru dalam mengintegrasi teknologi komputer untuk pengajaran dan pembelajaran sebagai kajian perbandingan antara dua negara, Oman dan Malaysia. This study was designed to investigate factors related to computer technology integration for teaching and learning. The study examined teacher beliefs and self-efficacy with respect to computer technology integration for teaching and learning, as a comparative study across two countries, Oman and Malaysia