Transmit diversity vs. spatial multiplexing in modern MIMO systems

A contemporary perspective on the tradeoff between transmit antenna diversity andspatial multiplexing is provided. It is argued that, in the context of most modern wirelesssystems and for the operating points of interest, transmission techniques that utilizeall available spatial degrees of freedom for multiplexing outperform techniques that explicitlysacrifice spatial multiplexing for diversity. In the context of such systems, therefore,there essentially is no decision to be made between transmit antenna diversity and spatialmultiplexing in MIMO communication. Reaching this conclusion, however, requires thatthe channel and some key system features be adequately modeled and that suitable performancemetrics be adopted; failure to do so may bring about starkly different conclusions. Asa specific example, this contrast is illustrated using the 3GPP Long-Term Evolution systemdesign.

On high-rate full-diversity 2x2 space-time codes with low-complexity optimum detection

The 2×2 MIMO profiles included in Mobile WiMAX specifications are Alamouti’s space-time code (STC) fortransmit diversity and spatial multiplexing (SM). The former hasfull diversity and the latter has full rate, but neither of them hasboth of these desired features. An alternative 2×2 STC, which is both full rate and full diversity, is the Golden code. It is the best known 2×2 STC, but it has a high decoding complexity. Recently, the attention was turned to the decoder complexity, this issue wasincluded in the STC design criteria, and different STCs wereproposed. In this paper, we first present a full-rate full-diversity2×2 STC design leading to substantially lower complexity ofthe optimum detector compared to the Golden code with only a slight performance loss. We provide the general optimized form of this STC and show that this scheme achieves the diversitymultiplexing frontier for square QAM signal constellations. Then, we present a variant of the proposed STC, which provides a further decrease in the detection complexity with a rate reduction of 25% and show that this provides an interesting trade-off between the Alamouti scheme and SM.

Peak and persistent excess of genetic diversity following an abrupt migration increase.

Genetic diversity is essential for population survival and adaptation to changing environments. Demographic processes (e.g., bottleneck and expansion) and spatial structure (e.g., migration, number, and size of populations) are known to shape the patterns of the genetic diversity of populations. However, the impact of temporal changes in migration on genetic diversity has seldom been considered, although such events might be the norm. Indeed, during the millions of years of a species' lifetime, repeated isolation and reconnection of populations occur. Geological and climatic events alternately isolate and reconnect habitats. We analytically document the dynamics of genetic diversity after an abrupt change in migration given the mutation rate and the number and sizes of the populations. We demonstrate that during transient dynamics, genetic diversity can reach unexpectedly high values that can be maintained over thousands of generations. We discuss the consequences of such processes for the evolution of species based on standing genetic variation and how they can affect the reconstruction of a population's demographic and evolutionary history from genetic data. Our results also provide guidelines for the use of genetic data for the conservation of natural populations.

Health care-associated native valve endocarditis: importance of non-nosocomial acquisition.

BACKGROUND: The clinical profile and outcome of nosocomial and non-nosocomial health care-associated native valve endocarditis are not well defined. OBJECTIVE: To compare the characteristics and outcomes of community-associated and nosocomial and non-nosocomial health care-associated native valve endocarditis. DESIGN: Prospective cohort study. SETTING: 61 hospitals in 28 countries. PATIENTS: Patients with definite native valve endocarditis and no history of injection drug use who were enrolled in the ICE-PCS (International Collaboration on Endocarditis Prospective Cohort Study) from June 2000 to August 2005. MEASUREMENTS: Clinical and echocardiographic findings, microbiology, complications, and mortality. RESULTS: Health care-associated native valve endocarditis was present in 557 (34%) of 1622 patients (303 with nosocomial infection [54%] and 254 with non-nosocomial infection [46%]). Staphylococcus aureus was the most common cause of health care-associated infection (nosocomial, 47%; non-nosocomial, 42%; P = 0.30); a high proportion of patients had methicillin-resistant S. aureus (nosocomial, 57%; non-nosocomial, 41%; P = 0.014). Fewer patients with health care-associated native valve endocarditis had cardiac surgery (41% vs. 51% of community-associated cases; P < 0.001), but more of the former patients died (25% vs. 13%; P < 0.001). Multivariable analysis confirmed greater mortality associated with health care-associated native valve endocarditis (incidence risk ratio, 1.28 [95% CI, 1.02 to 1.59]). LIMITATIONS: Patients were treated at hospitals with cardiac surgery programs. The results may not be generalizable to patients receiving care in other types of facilities or to those with prosthetic valves or past injection drug use. CONCLUSION: More than one third of cases of native valve endocarditis in non-injection drug users involve contact with health care, and non-nosocomial infection is common, especially in the United States. Clinicians should recognize that outpatients with extensive out-of-hospital health care contacts who develop endocarditis have clinical characteristics and outcomes similar to those of patients with nosocomial infection. PRIMARY FUNDING SOURCE: None.

Generalized low-density codes with BCH constituents for full-diversity near-outage performance

A new graph-based construction of generalized low density codes (GLD-Tanner) with binary BCH constituents is described. The proposed family of GLD codes is optimal on block erasure channels and quasi-optimal on block fading channels. Optimality is considered in the outage probability sense. Aclassical GLD code for ergodic channels (e.g., the AWGN channel,the i.i.d. Rayleigh fading channel, and the i.i.d. binary erasure channel) is built by connecting bitnodes and subcode nodes via a unique random edge permutation. In the proposed construction of full-diversity GLD codes (referred to as root GLD), bitnodes are divided into 4 classes, subcodes are divided into 2 classes, and finally both sides of the Tanner graph are linked via 4 random edge permutations. The study focuses on non-ergodic channels with two states and can be easily extended to channels with 3 states or more.

Full diversity product codes for block erasure and block fading channels

We show how to build full-diversity product codes under both iterative encoding and decoding over non-ergodic channels, in presence of block erasure and block fading. The concept of a rootcheck or a root subcode is introduced by generalizing the same principle recently invented for low-density parity-check codes. We also describe some channel related graphical properties of the new family of product codes, a familyreferred to as root product codes.

A comparison of full-rate full-diversity 2x2 space-time codes for WiMAX systems

Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband wireless access include three MIMOprofiles employing 2×2 space-time codes (STCs), and two of these MIMO schemes are mandatory on the downlink of Mobile WiMAX systems. One of these has full rate, and the other has full diversity, but neither of them has both of the desired features. The third profile, namely, Matrix C, which is not mandatory, is both a full rate and a full diversity code, but it has a high decoder complexity. Recently, the attention was turned to the decodercomplexity issue and including this in the design criteria, several full-rate STCs were proposed as alternatives to Matrix C. In this paper, we review these different alternatives and compare them to Matrix C in terms of performances and the correspondingreceiver complexities.

De-hyping transmit diversity in modern MIMO cellular systems

A contemporary perspective on the tradeoff between transmit antenna diversity and spatial multi-plexing is provided. It is argued that, in the context of modern cellular systems and for the operating points of interest, transmission techniques that utilize all available spatial degrees of freedom for multiplexingoutperform techniques that explicitly sacrifice spatialmultiplexing for diversity. Reaching this conclusion, however, requires that the channel and some key system features be adequately modeled; failure to do so may bring about starkly different conclusions. As a specific example, this contrast is illustrated using the 3GPP Long-Term Evolution system design.

Education as a mirror of Spanish society: challenges and policies towards multiple diversity

The ways in which the dominant cultural majority frames the educationalsystem determine perceptions of its own identity and understandings ofthe ‘other.’ In this article I take a political approach, by examining themanagement of cultural diversity within Spanish education policies, treating“education as the mirror of society”. This article analyzes Spanish challengesand policies approaches towards the management of immigrationrelated diversity in education. The main finding is that there is not one approach,but several, due to both the decentralized character of the educationsystem and the multiplicity of diversity that is at stake (i.e. language,religion, culture etc.)

Dynamics of diversity within the Mossos d’Esquadra

This chapter offers a case-study of diversity and diversity policies withinthe Mossos d’Esquadra, the police force of the Catalan autonomous communityin Spain. The case is described in a comprehensive way (includingpolicies in all relevant policy areas: recruitment, retention, and promotion)and at the same time analyzed with a new analytical framework (includingthe definition of diversity, the motivation for diversity within the organisation,and the facilitation of diversity within the organisation with policies).The goal of the chapter is twofold. First, offer a deeper understanding ofthe dynamics of diversity within this police force. Second, demonstrate theacademic potential of this new analytical framework.

Strain diversity of mycobacteria isolated from pulmonary tuberculosis patients at Debre Birhan Hospital, Ethiopia.

BACKGROUND: Ethiopia ranks seventh in the list of 22 high tuberculosis (TB) burden countries, with an incidence rate of 379 cases per 100 000 population for TB all forms. However, information on the genomic diversity of Mycobacterium tuberculosis in Ethiopia is limited. OBJECTIVE: To investigate the molecular characteristics of M. tuberculosis strains implicated in pulmonary TB in the study area. METHODS AND RESULTS: A cross-sectional study was conducted using socio-demographic, clinical and culture data combined with molecular typing analysis. The proportion of TB and M. tuberculosis isolates was not associated with risk factors (P > 0.05). Of 99 sputum samples, 80.8% were culture-positive. Speciation of isolates showed that 88.8% were M. tuberculosis. Further characterisation led to the identification of 27 different spoligotype patterns of M. tuberculosis; the most dominant shared types were SIT149, SIT53 and SIT54. Of the 27 strains, three strains were new and were reported to the SITVIT database. More than two thirds of the strains belonged to the Euro-American lineage. CONCLUSION: This study shows the presence of several clusters and new strains of M. tuberculosis circulating in pulmonary TB patients in the study area, suggesting recent transmission. Nationwide studies are recommended to map the population structure of M. tuberculosis and set control measures.

Toleration and the fair terms of engagement with diversity

The aim of this paper is to examine the various controversies over the genuineproblems of toleration in a plurally diverse polity as both historically andconceptually, toleration is one of the foundational characteristics that defines thevery essence of a plurally diverse polity and the basic virtue associated with a liberalconception of citizenship. In section 1, I present the main philosophical andconceptual issues related to the toleration-based approach to diversity in liberalpolitical theory. In section 2 I identify the conditions and the circumstances oftoleration. I articulate in Section 3 the most pressing objections against toleration. Ipresent in section 4 two competing approaches to the toleration-based approach todiversity is faced with. In the concluding section, I outline a modified conception oftoleration that mediates between different requirements associated with the twoprincipled commitments of the liberal version of the rights-based conception ofcitizenship.

Teaching ethnic diversity in journalism school

It has been found that the symbolic elites have a prominent role in the discursive reproduction of racism in society, because they control the public discourse through which many ethnic prejudices are spread and shared. This special position of the mass media requires that the professional education of journalists, also featuring such topics as ethnic studies, diversity and racism, is optimally adapted to the multicultural societies in Europe, North America and Australia. This paper reports about an extensive research project examining ethnic education of journalists in these white-dominated countries, by examining the websites of many journalism and communication departments. Consistent with the general finding that white symbolic elites primarily deny or ignore (their) racism in society, none of the academic programs, anywhere in the world, mentions special classes on racism in the mass media. Finally, a practical proposal is made for a course on ethnic reporting in multicultural societies.

Introducing diversity in public organisations : diminishing theoretical ambiguity and controversy by empirical research

Many theoretical dissertations have an unclear definition of diversity and when interpreting strategies of organizational diversity policies, theories often contradict each other. It is argued that this ambiguity and controversy can be diminished by basing theory on diversity and diversity policy more on qualitative structured descriptive empirical comparisons.This argument is elaborated in two steps. First, diversity is shown to be a social construction: dynamic and plural in nature, dependent on the social-historical context. Second, the common theoretical dichotomy between diversity policy as equal opportunities or as diversity management in shown to be possibly misleading; empirical studies indicate more practical differentiation in types of diversity policy, manifested in public and private organizations. As qualitative comparisons are rare, especially in the European context and especially among public organizations, this article calls for more contributions of this kind and provides an analytical framework to assist scholars in the field of diversity studies.