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See detailMulticast multigroup beamforming for per-antenna power constrained large-scale arrays
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2015), 2015-August

Large in the number of transmit elements, multi-antenna arrays with per-element limitations are in the focus of the present work. In this context, physical layer multigroup multicasting under per-antenna ... [more ▼]

Large in the number of transmit elements, multi-antenna arrays with per-element limitations are in the focus of the present work. In this context, physical layer multigroup multicasting under per-antenna power constrains, is investigated herein. To address this complex optimization problem low-complexity alternatives to semi-definite relaxation are proposed. The goal is to optimize the per-antenna power constrained transmitter in a maximum fairness sense, which is formulated as a non-convex quadratically constrained quadratic problem. Therefore, the recently developed tool of feasible point pursuit and successive convex approximation is extended to account for practical per-antenna power constraints. Interestingly, the novel iterative method exhibits not only superior performance in terms of approaching the relaxed upper bound but also a significant complexity reduction, as the dimensions of the optimization variables increase. Consequently, multicast multigroup beamforming for large-scale array transmitters with per-antenna dedicated amplifiers is rendered computationally efficient and accurate. A preliminary performance evaluation in large-scale systems for which the semi-definite relaxation constantly yields non rank-1 solutions is presented. © 2015 IEEE. [less ▲]

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See detailMulticast Multigroup Precoding and User Scheduling for Frame-Based Satellite Communications
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2015), 14(9), 4695-4707

The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to ... [more ▼]

The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to frame multiple users per transmission and the per-antenna transmit power limitations, are addressed. To this end, the so-called frame-based precoding problem is optimally solved using the principles of physical layer multicasting to multiple co-channel groups under per-antenna constraints. In this context, a novel optimization problem that aims at maximizing the system sum rate under individual power constraints is proposed. Added to that, the formulation is further extended to include availability constraints. As a result, the high gains of the sum rate optimal design are traded off to satisfy the stringent availability requirements of satellite systems. Moreover, the throughput maximization with a granular spectral efficiency versus SINR function, is formulated and solved. Finally, a multicast-aware user scheduling policy, based on the channel state information, is developed. Thus, substantial multiuser diversity gains are gleaned. Numerical results over a realistic simulation environment exhibit as much as 30% gains over conventional systems, even for 7 users per frame, without modifying the framing structure of legacy communication standards. [less ▲]

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See detailMulticast Multigroup Precoding and User Scheduling for Frame-Based Satellite Communications
Christopoulos, Dimitrios; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS (2014), 14(9), 4695--4707

The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to ... [more ▼]

The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to frame multiple users per transmission and the per-antenna transmit power limitations, are addressed. To this end, the so-called frame-based precoding problem is optimally solved using the principles of physical layer multicasting to multiple co-channel groups under per-antenna constraints. In this context, a novel optimization problem that aims at maximizing the system sum rate under individual power constraints is proposed. Added to that, the formulation is further extended to include availability constraints. As a result, the high gains of the sum rate optimal design are traded off to satisfy the stringent availability requirements of satellite systems. Moreover, the throughput maximization with a granular spectral efficiency versus SINR function, is formulated and solved. Finally, a multicast-aware user scheduling policy, based on the channel state information, is developed. Thus, substantial multiuser diversity gains are gleaned. Numerical results over a realistic simulation environment exhibit as much as 30% gains over conventional systems, even for 7 users per frame, without modifying the framing structure of legacy communication standards. [less ▲]

Detailed reference viewed: 138 (4 UL)
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See detailMulticast multigroup precoding for frame-based multi-gateway satellite communications
Christopoulos, Dimitrios UL; Pennanen, Harri UL; Chatzinotas, Symeon UL et al

in Advanced Satellite Multimedia Systems Conference and the 14th Signal Processing for Space Communications Workshop (ASMS/SPSC), 2016 8th (2016, October 24)

The present work focuses on the forward link of fixed multibeam broadband satellite systems which employ aggressive frequency reuse patterns in the user-link. For such scenarios, the state-of-the art ... [more ▼]

The present work focuses on the forward link of fixed multibeam broadband satellite systems which employ aggressive frequency reuse patterns in the user-link. For such scenarios, the state-of-the art frame based precoding methods can improve the system performance, exploiting the super framing structure of the latest physical layer evolutions in satellite communications. Nevertheless, the limitations of feeder link need to be considered. Since the increase of the user link capacity leads to a proportional increase in the capacity requirements of the point-to-point feeder link, the deployment of multiple gateways to feed the satellite is examined. The main concept lies in each earth station being dedicated to serve a cluster of beams. In this context, the performance degradation due to inter-cluster interference is quantified. Since inter-cluster interference is expected to primarily affect cluster-edge users, the chosen performance metric is system fairness. Next, coordination between the multiple gateways is proposed as a means to mitigate interference between the different clusters and thus increase the minimum SINR over the coverage. Consequently, the gains in terms of system availability, a crucial metric in satellite communications, are exhibited via numerical system level simulations. The energy efficiency of the proposed system is also presented. [less ▲]

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See detailMulticell LMMSE Filtering Capacity under Correlated Multiple BS Antennas
Chatzinotas, Symeon UL; Imran, Muhammad Ali; Hoshyar, Reza et al

in Multicell LMMSE Filtering Capacity under Correlated Multiple BS Antennas (2010)

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See detailThe Multicell Processing Capacity of the Cellular MIMO Uplink Channel under Correlated Fading
Chatzinotas, Symeon UL; Imran, Muhammad Ali; Hoshyar, Reza

in ICC 2009 (2009)

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See detailMulticenter Alzheimer's and Parkinson's disease immune biomarker verification study
Brosseron, Federic; Schneider, Reinhard UL

in Alzheimer's and Dementia: the Journal of the Alzheimer's Association (2019)

Multiple immunity biomarkers have been suggested as tracers of neuroinflammation in neurodegeneration. This study aimed to verify findings in cerebrospinal fluid (CSF) samples of Alzheimer's disease (AD ... [more ▼]

Multiple immunity biomarkers have been suggested as tracers of neuroinflammation in neurodegeneration. This study aimed to verify findings in cerebrospinal fluid (CSF) samples of Alzheimer's disease (AD) and Parkinson's disease (PD) subjects from the network of the European, Innovative Medicines Initiative–funded project AETIONOMY. [less ▲]

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See detailMulticentric identities in a globalizing world
Valsiner, Jaan UL; Salvatore, Sergio

Book published by Information Age Publishers (2014)

Detailed reference viewed: 39 (0 UL)
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See detailMultichannel Source Separation Using Time-Deconvolutive CNMF
Dias, Thadeu; Alves Martins, Wallace UL; Biscainho, Luiz Wagner

in Journal of Communication and Information Systems (2020), 35(1), 103-112

This paper addresses the separation of audio sources from convolutive mixtures captured by a microphone array. We approach the problem using complex-valued non-negative matrix factorization (CNMF), and ... [more ▼]

This paper addresses the separation of audio sources from convolutive mixtures captured by a microphone array. We approach the problem using complex-valued non-negative matrix factorization (CNMF), and extend previous works by tailoring advanced (single-channel) NMF models, such as the deconvolutive NMF, to the multichannel factorization setup. Further, a sparsity-promoting scheme is proposed so that the underlying estimated parameters better fit the time-frequency properties inherent in some audio sources. The proposed parameter estimation framework is compatible with previous related works, and can be thought of as a step toward a more general method. We evaluate the resulting separation accuracy using a simulated acoustic scenario, and the tests confirm that the proposed algorithm provides superior separation quality when compared to a state-of-the-art benchmark. Finally, an analysis of the effects of the introduced regularization term shows that the solution is in fact steered toward a sparser representation. [less ▲]

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See detailMultiCoSteel – Structural Behaviour of Heavy Composite Columns with Multiple Encased Steel Profiles for High Rise Buildings
Chrzanowski, Maciej UL; Odenbreit, Christoph UL

Speeches/Talks (2016)

The PhD resesarch project“MultiCoSteel” is foussed on the investigation of the beam theory for composite columns with multiple encased steel profiles to find the correct internal stress distributions and ... [more ▼]

The PhD resesarch project“MultiCoSteel” is foussed on the investigation of the beam theory for composite columns with multiple encased steel profiles to find the correct internal stress distributions and stiffnesses. The suitability of the Euler-Bernoulli Theory will be investigated as well as the truss theory and the Vierendeel theory. A complex interaction between steel and concrete materials and lack of knowledge regarding composite behaviour opens opportunities to develop, improve and optimise the system and the design method. Within this research project both aspects will be handled with the objectives; 1) to develop the new, easy-applicable and efficient type of shear connector for an application in composite columns with multiple-encased steel profiles and 2) to prove the design hypothesis of Vierendeel mechanism behaviour. The project is running with close collaboration of industrial partner - ArcelorMittal and it was successfully qualified to the FNR AFR-PPP PhD Grant. [less ▲]

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Peer Reviewed
See detailMulticultural Cities
Carr, Constance UL

in Hutchinson, R. (Ed.) Encyclopedia of Urban Studies (2009)

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Peer Reviewed
See detailMulticultural Diplomacy
Murdock, Elke UL

Scientific Conference (2017, May 24)

In this interactive workshop I firstly explore the concept of multiculturalism in its many facets. Participants’ own understanding, interpretations and views of the term multiculturalism will be gathered ... [more ▼]

In this interactive workshop I firstly explore the concept of multiculturalism in its many facets. Participants’ own understanding, interpretations and views of the term multiculturalism will be gathered. These personal experiences and views will then be contrasted with scholarly explorations of the term, starting with the origins in the human rights movements. Theoretical analyses of the idea(l) of multiculturalism will then be presented, including misleading and current conceptualizations. The second part of the workshop focuses on the applied side or (multi)-cultural competences necessary to navigate today’s multicultural world. What are the key competences lying at the heart of multicultural diplomacy, ensuring sustainable development? Guided by developmental psychological theory, the diversity model applied by the German Academy for International Cooperation and the Council of Europe deliberations on cultural competences we will interactively develop and discuss a catalogue of competences conducive to living as equals in culturally diverse societies. [less ▲]

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See detailThe Multicultural Ideology Scale (MIS): Factor structure and measurement invariance
Stogianni, Maria UL; Murdock, Elke UL

Scientific Conference (2018, July 02)

The concept of multiculturalism has been widely used in cross-cultural research to describe positive attitudes towards a culturally plural society and practices that support cultural diversity. To date ... [more ▼]

The concept of multiculturalism has been widely used in cross-cultural research to describe positive attitudes towards a culturally plural society and practices that support cultural diversity. To date, attitudes towards multiculturalism among majority and minority group members have been assessed with the same instruments. However, there is little psychometric evidence that these measures operate appropriately in various cultural contexts. The purpose of the present study was to investigate the factor structure of the Multicultural Ideology Scale (MIS; Berry & Kalin, 1995) and test its measurement invariance across different language versions and ethnic groups. The entire sample consisted of 1572 adolescents and adults in Luxembourg, including native majority members (N = 693) and immigrants from diverse ethnic backgrounds (N = 879). Participants were given the option to complete the questionnaire in one of the following languages: English, German or French. The unidimensional model of multicultural ideology did not show an acceptable fit of the data across all language versions of the MIS. Exploratory and confirmatory factorial analyses revealed a two-factor structure, which was partially invariant across two different language versions (English and German). The two factors reflected positive and negative attitudes towards cultural diversity respectively. Subsequent multigroup confirmatory factor analyses supported configural and metric invariance across majority and minority group members. Scalar invariance was not established, indicating that respondents across these two groups conceptualize multiculturalism in different ways. Implications of these findings are discussed together with methodological issues concerning the assessment of measurement invariance. [less ▲]

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See detailMulticultural societies - and the disappearance of culture?
Murdock, Elke UL; Stogianni, Maria UL

Scientific Conference (2019, September 01)

Vertovec (2007) describes countries with a heterogeneous population in terms of origin and migration status as super-diverse. Within these plurally composed societies the boundaries between minority and ... [more ▼]

Vertovec (2007) describes countries with a heterogeneous population in terms of origin and migration status as super-diverse. Within these plurally composed societies the boundaries between minority and majority become blurred and norms, values and symbols may be negotiated dependent on context. For people growing up in such a multicultural context it is the norm to be with people of different cultural backgrounds and language skills. Reinders (2006) has introduced the term co-culturation, as distinct from enculturation and acculturation, to describe the process of engagement with cultural diversity by both, natives and those with migration background. In a sample of adolescents growing up in multicultural Luxembourg, we highlight the interplay between migration status, friendship patterns, family relations, well-being and identity. Students (N = 85) attending a Luxembourgish secondary school participated in this questionnaire study (Mage = 16.45, SD = 1.09, 46 male, 39 female). The majority (n = 68) of the students were born in Luxembourg, 17 are natives (born to two Luxembourgish parents), 43 are second generation, 17 first generation and 6 are of mixed parentage. We assessed language competence and use, friendship patterns and family relationships. Measures also included the Brief Multidimensional Students’ Life Satisfaction Scales (BMSLSS) which assesses satisfaction with life in different domains and the Multigroup Ethnic Identity Measure (MEIM) scale. The results indicate that friendship patterns are formed on the basis of the characteristics of the individual rather than based on the country of origin. Few statistically significant differences could be found in terms of country of origin/ migration status and various outcome measures. The results can be interpreted in the co-culturation framework. For this cohort of adolescents, culture contact is the norm and salience of cultural background appears to weaken as a result. However, the Luxembourgish language plays an important unifying role. [less ▲]

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See detailMulticultural society - multiple ways to negotiate identity
Murdock, Elke UL

Scientific Conference (2019, April 30)

The 21st century has been called the “age of migration” (Castles & Miller, 2009). International migration is a growing phenomenon, both in terms of scope and complexity and affects virtually all countries ... [more ▼]

The 21st century has been called the “age of migration” (Castles & Miller, 2009). International migration is a growing phenomenon, both in terms of scope and complexity and affects virtually all countries in the world (United Nations, 2009). The global migration system has changed over recent decades with regard to origins and destinations for migration. In the 20th century, Europe was a major area for emigration, but has now become a target for immigration, with most European countries, including Iceland, hosting significant minority immigrant populations. In Luxembourg, nearly half of the population is foreign – the foreign population percentage currently stands at 48%. Within this context majority and minority become fluid with the migration process itself being fluid, ranging from daily migration (transnational commuters), to medium-term stays, return visits and permanent immigration including uptake of citizenship. Within such a plurally composed society, culture contact is a permanent feature in daily life. Nationality becomes a salient feature as culture contact tends to prompt reflection, resulting in questioning and (re-)negotiation of national identity. This affects both the native and the diverse immigrant population – with diversity going beyond the level of country of origin as many individuals have very complex biographies. Using multicultural, multilingual Luxembourg as a case study example, I will present examples for the construal process of national identity for different groups, illustrating how (national) identity is negotiated at individual level. As can be expected, the identity construal process becomes more complex within a multicultural context. [less ▲]

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See detailMulticulturalism and Acculturation in the Multicultural Context of Luxembourg
Murdock, Elke UL; Ferring, Dieter UL

Scientific Conference (2013, June 02)

Even within a globalizing world, Luxembourg takes an exceptional position with a foreign population of 43%, which rises to 66% in the capital. Luxembourg can thus be called a “natural laboratory” ... [more ▼]

Even within a globalizing world, Luxembourg takes an exceptional position with a foreign population of 43%, which rises to 66% in the capital. Luxembourg can thus be called a “natural laboratory” regarding the macro-level conditions for multiculturalism. In a series of quantitative studies we have investigated how this plural composition of society is experienced at the individual or micro level. In a first study, we examined factors contributing to the endorsement of multiculturalism by various Luxembourg resident groups, i.e. native Luxembourgers, residents with migration background, sojourners and daily commuters (total n= 621). Within these groups we differentiated between mono-cultural and bi- or multicultural individuals. We determined the respective in-group, assessed the strength of in-group identification, between-group contacts and the perception of the cultural distance between groups. At trait level we tested the relationship between Schwartz Values structures and the endorsement of multiculturalism. Initial results point to a strong association between the value dimension self-transcendence and multiculturalism. Other work in progress focuses on a more in-depth analysis of the (national) identity processes of adolescents who are raised in families of mixed nationalities (bicultural “by birth”). In this study, we address the question if biculturalism is experienced as doubling of resources or as a strain and which individual or context factors will contribute to either outcome. [less ▲]

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See detailMulticulturalism and Acculturation in the Multicultural Context of Luxembourg
Murdock, Elke UL; Ferring, Dieter UL

Scientific Conference (2013, July 10)

Even within a globalizing world, Luxembourg takes an exceptional position with a foreign population of 43%, which rises to 66% in the capital, where cultural diversity is used in external branding ... [more ▼]

Even within a globalizing world, Luxembourg takes an exceptional position with a foreign population of 43%, which rises to 66% in the capital, where cultural diversity is used in external branding (Multiplicity). The present series of studies form part of a work in progress aimed at enhancing the understanding of multiculturalism and the management of cultural diversity. Starting point is a society that can be described as multicultural in a demographic sense, offering ample opportunity for second culture exposure. How is this opportunity for culture-contact experienced by its various resident groups? In a series of quantitative studies we examined the endorsement of multiculturalism, which is the acceptance of the plural composition of societies, by various Luxembourg resident groups, who differ by length of stay in Luxembourg: native Luxembourgers, those who have lived there for a few generations and sojourners. Within these groups we differentiated between mono-cultural and bi- or multicultural individuals. Broadly defined, multicultural individuals have internalized more than one culture. We determined the respective in-group, assessed the strength of in-group identification, between group contacts and the perception of the cultural distance between groups. At trait level we tested the relationship between Schwartz Values structures and the endorsement of multiculturalism. Findings are discussed with respect to acculturation processes in multicultural societies. [less ▲]

Detailed reference viewed: 106 (10 UL)