1,722,602 research outputs found
Ji-Su Kim
No full text학위논문(박사)--아주대학교 일반대학원 :전자공학과,2014. 8DoctoralThe current wireless networks with orthogonal frequency division multiple access (OFDMA) system gives us high speed wireless communication. With high speed, variety mobile services that have different traffic characteristics and requirements have been produced. However, the interference sensitivity of OFDMA system degrades performances of cell-edge users. In addition, the diversity of mobile services causes a channel quality asymmetry between a downlink and an uplink in OFDMA system. Unfortunately, conventional mobility management schemes have not taken account the channel quality asymmetry and the diversity of service traffic. Therefore, this dissertation presents advanced mobility schemes considering the channel quality asymmetry and the diversity of service traffic for improving service continuity and user-perceived performance.
The first proposed mobility scheme is a handover scheme considering downlink-uplink channel quality asymmetry. The proposed handover scheme determines an appropriate handover timing and handover direction according to an estimated uplink channel quality and a measured downlink channel quality. For exploiting an uplink channel quality in handover, an efficient uplink channel estimation method is also proposed. The proposed method estimates an uplink signal strength using the measured downlink signal strength and predicts an uplink interference on the basis of the interference-level information that is from neighbor base stations. To improve user-perceived performances, the proposed handover scheme adjusts weights of handover criteria according to service traffic pattern. Simulation results show that the proposed uplink estimation method can accurately compute the uplink channel quality of neighbor cells where the estimation error rate is less than 0.7%. The simulation results also show that the proposed handover scheme reduces handover-call-dropping probability by up to 69% compared to LTE-Advanced system and the proposed scheme outperforms previous studies in terms of throughput and mean opinion score (MOS). In addition, the end-to-end delay of the proposed scheme is better than that of LTE-Advanced system by 26%.
The second proposed mobility scheme is the user-centric mobility scheme that exploits multipath communication to support seamless mobility. For that, the service continuity management (SCM) protocol is newly designed. SCM has four functional blocks which are located between the application layer and the transport layer. SCM monitors quality of experience (QoE) and makes multiple sessions for one service using multiple radio adaptors in order to maintain QoE requirements. To improve the efficiency of the proposed multipath communication scheme, a high efficiency transport method is proposed. The proposed scheme sends identical packets over multiple paths to improve reliability; likewise, different packets are sent to improve throughput, simultaneously. The simulation results show that the user-centric mobility scheme enable a mobile device to reduce service interruptions during handover in heterogeneous networks. Numerical results indicate that the proposed transport scheme achieves the maximum transport control protocol (TCP) throughput when the proportion of same and different packets is adjusted according to link conditions
Essays on International Migration using Big Data Analytics
Get PDFHow can social big data help to understand issues related to international migration?
Official data such as census, survey and administrative data have been traditionally
the main data source to study migration. However, these data have some limitations.
They are inconsistent across different nations because countries employ
different definitions of international migration and characterisations of migrants.
Moreover, collecting traditional data is costly and time consuming, thus tracking
instantaneous
ows of migrants becomes diffcult. This becomes even harder when
tracking emigrants because of the lack of motivation from citizens to declare their
departure. In recent years, however, we are provided with other alternative data
sources for migration. The availability of social big data such as Facebook, and
Twitter data allows us to study social behaviours both at large scale and at a granular
level, and to peek into real-world phenomena. Although known to suffer from
other types of issues, such as selection bias, these data could bring complementary
value to standard statistics.
In this work, we employ social big data to study international migration. We
try to answer the question through an analysis of various phases of migration, using
both traditional data and novel data sources. The first phase includes the journey,
and we study migration stocks on Twitter, providing benefits and drawbacks of
using such data to study international migration. Here, a generic methodology is
developed to identify migrants within the Twitter population. This describes a
migrant as a person who has the current residence different from the nationality.
The residence is defined as the location where a user spends most of his/her time in
a certain year. The nationality is inferred from linguistic and social connections to
a migrant's country of origin. This methodology is validated first with an internal
gold standard dataset and second with Italian register data and Eurostat, and shows
strong performance scores and correlation coefficients.
The second phase concerns the integration of migrants in the destination country
and attachments to their home country. We explore Twitter data to build a
novel methodology to quantify and understand migrants' different integration types.
Here, We describe four different integration types which are assimilation, integration, marginalisation and separation using two dimensions: the preservation of links
to the home country and culture, i.e. home attachment index, and creation of new links and adoption of cultural traits from the new residence country, i.e. destination
attachment index. The two dimensions are validated by performing a null model
analysis. It shows significant differences between the actual indices and the null
model indices, confirming that the two indices are not produced at random.
Lastly, We examine the effect of the presence of migrants on political choices of
the natives, using a German case study. Specifically, We are interested in understanding
whether exposure to reception centres for asylum-seekers in Berlin affected
the votes obtained by the radical right AfD in the 2019 European elections, at the
electoral district level. We analyse this relationship at a very small scale based on
geo-localization techniques and high-resolution spatial data. We study this in a wide
range of contextual conditions, including variables such as districts' socio-economic
deprivation, the share of established non-European residents, and the geographical
location of the districts. Overall the findings show that exposure to reception centres
in Berlin is negatively correlated with the AfD vote share. However, the results show
remarkable differences between East and West Berlin and between districts characterised
by different levels of socio-economic deprivation. Exposure and AfD vote
shares are more strongly correlated in Western districts and in better-of districts.
This work is thus aimed at providing a practical contribution to international
migration studies by offering novel methods and analyses for identifying, quantifying
and understanding dynamics of migration to better shape the policies of international
migration
Ji su fei qing ge cang bei. v.1
No full text楊守敬用雙鈎法摹出自秦至唐古碑33種彙刊[成]此書."香港中文大學圖書館中國古籍庫"提供電子版.Yang Shoujing yong shuang gou fa mo chu zi Qin zhi Tang gu bei 33 zhong hui kan [cheng] ci shu.Cover title."Xianggang Zhong wen da xue tu shu guan Zhongguo gu ji ku" ti gong dian zi ban
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
