Mobile-to-mobile MIMO transmit-receive diversity systems: analysis and performance in three-dimensional double-correlated channels

Mobile-to-mobile (M-to-M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M-to-M multiple-input multiple-output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double-correlated Rayleigh-and-Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three-dimensional (3D) M-to-M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal-to-noise ratio per receive antenna in closed-form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.

Analysis and compensation of I/Q imbalance in MIMO transmit-receive diversity systems

In wireless communication systems, all in-phase and quadrature-phase (I/Q) signal processing receivers face the problem of I/Q imbalance. In this paper, we investigate the effect of I/Q imbalance on the performance of multiple-input multiple-output (MIMO) maximal ratio combining (MRC) systems that perform the combining at the radio frequency (RF) level, thereby requiring only one RF chain. In order to perform the MIMO MRC, we propose a channel estimation algorithm that accounts for the I/Q imbalance. Moreover, a compensation algorithm for the I/Q imbalance in MIMO MRC systems is proposed, which first employs the least-squares (LS) rule to estimate the coefficients of the channel gain matrix, beamforming and combining weight vectors, and parameters of I/Q imbalance jointly, and then makes use of the received signal together with its conjugation to detect the transmitted signal. The performance of the MIMO MRC system under study is evaluated in terms of average symbol error probability (SEP), outage probability and ergodic capacity, which are derived considering transmission over Rayleigh fading channels. Numerical results are provided and show that the proposed compensation algorithm can efficiently mitigate the effect of I/Q imbalance.

On the effect of I/Q imbalance on MIMO transmit-receive diversity systems

In practice, all I/Q signal processing receivers face the problem of I/Q imbalance. In this paper, we investigate the effect of I/Q imbalance on the performance of MIMO maximal ratio combining (MRC) systems that perform the combining at the radio frequency (RF) level, thereby requiring only one RF chain. Based on a system modeling that takes the I/Q imbalance into account, we evaluate the performance in terms of average symbol error probability (SEP), outage probability and system capacity, which are derived considering transmission over uncorrelated Rayleigh fading channels. Numerical results are provided to illustrate the effects of system parameters, such as the image- leakage ratio, numbers of transmit and receive antennas, and modulation order of quadrature amplitude modulation (QAM), on the system performance.

Reliability comparison of transmit/receive diversity and error control coding in low-power medium access control protocols

Low-power medium access control (MAC) protocols used for communication of energy constraint wireless embedded devices do not cope well with situations where transmission channels are highly erroneous. Existing MAC protocols discard corrupted messages which lead to costly retransmissions. To improve transmission performance, it is possible to include an error correction scheme and transmit/receive diversity. It is possible to add redundant information to transmitted packets in order to recover data from corrupted packets. It is also possible to make use of transmit/receive diversity via multiple antennas to improve error resiliency of transmissions. Both schemes may be used in conjunction to further improve the performance. In this study, the authors show how an error correction scheme and transmit/receive diversity can be integrated in low-power MAC protocols. Furthermore, the authors investigate the achievable performance gains of both methods. This is important as both methods have associated costs (processing requirements; additional antennas and power) and for a given communication situation it must be decided which methods should be employed. The authors’ results show that, in many practical situations, error control coding outperforms transmission diversity; however, if very high reliability is required, it is useful to employ both schemes together.

Investigations into diversity of A 2x2 MIMO system with the use of an indoor testbed

This paper presents investigations into an indoor 2×2 multiple input multiple output (MIMO) system, whose diversity performance is assessed using a high precision test-bed. In this system, transmitter and receiver are equipped with 180° or 90° 3dB hybrids with their two output ports terminated with co-polar monopole antennas. By feeding a signal to one of the two input ports of the hybrid (while the other input port is matched terminated) different communication channels in a rich-scattering environment can be created. The test-bed allows for the signal strength measurements around the receiver/ transmitter sides for a given feeding configuration of hybrids when the receiver is moved over a circular region in an indoor environment. The signal strengths maps obtained for various modes of this 2×2 MIMO system are foundations for investigating transmit/receive diversity schemes. As the signal strength measurement results are obtained with Bluetooth modules operating in the ISM 2.4 GHz, the results are of importance to many other wireless systems that aim at utilizing MIMO diversity schemes to enhance their performance in this frequency band.

The IST METRA Project

This article summarizes the main achievementsof the Multi-Element Transmit andReceive Antennas (METRA) Project, an ISTresearch and technological development project carried out between January 2000 and June 2001 by Universitat Politècnica de Catalunya, the Center for Personkommunikation of Aalborg University, Nokia Networks, Nokia Mobile Phones, and Vodafone Group Research and Development.The main objective of METRA was the performanceevaluation of multi-antenna terminals incombination with adaptive antennas at the basestation in UMTS communication systems. 1 AMIMO channel sounder was developed that providedrealistic multi-antenna channel measurements.Using these measured data, stochasticchannel models were developed and properly validated.These models were also evaluated inorder to estimate their corresponding channelcapacity. Different MIMO configurations andprocessing schemes were developed for both theFDD and TDD modes of UTRA, and their linkperformance was assessed. Performance evaluationwas completed by system simulations thatillustrated the benefits of MIMO configurationsto the network operator. Implementation cost vs.performance improvement was also covered bythe project, including the base station and terminalmanufacturer and network operator viewpoints.Finally, significant standards contributionswere generated by the project and presented to the pertinent 3GPP working groups.

Investigations into MIMO systems from an electromagnetic perspective

The paper presents investigations into multiple input multiple output wireless communication systems, which are carried out from an electromagnetic perspective. The first part of the paper focuses on signal propagation models, which can be used for determining the MIMO system capacity or its performance when various space-time coding schemes are applied. Two types of models are considered. In the first model, array antennas are treated in an exact electromagnetic manner but interactions with scattering objects are incorporated using an approximate single bounce scattering approach. The other model is a simple but exact electromagnetic (EM) model, which takes into account EM interactions between antennas and scatterers. In this model, parallel wire dipoles represent antennas as well as scatterers. The second part of the paper reports on investigations into two types of MIMO testbeds. The first one is a simple transmit/receive diversity tested while the other one is a full MIMO testbed. The paper briefly describes the results obtained during the undertaken investigations

Communication across cultures? An intercultural approach to customer service in the hotel industry: a study with globally branded hotels in the United Kingdom

In a professional and business-social context such as that of global hotel brands in the United Kingdom, intercultural communication, contacts and relationships are found at the heart of daily operations and of customer service. A large part of the clientele base of hotels in the United Kingdom is formed by individuals who belong to different cultural groups that travel in the country either for leisure or business. At the same time, the global workforce which is recruited in the hotel industry in the United Kingdom is a reality here to stay. Global travelling and labor work mobility are phenomena which have been generated by changes which occur on a socio-economic, cultural and political level due to the phenomenon of globalization. The hotel industry is therefore well acquainted with the essence of different cultures either to be accommodated within hotel premises, as in the case of external customers, or of diversity management where different cultures are recruited in the hotel industry, as in the case of internal customers. This thesis derives from research conducted on eight different global hotel brands in the United Kingdom in particular, with reference to three, four and five star categories. The research aimed to answer the question of how hotels are organized in order to address issues of intercultural communication during customer service and if intercultural barriers arise during the intercultural interaction of hotel staff and global customers. So as to understand how global hotel brands operate the research carried out focused in three main areas relating to each hotel: organizational culture, customer service–customer care and intercultural issues. The study utilized qualitative interviews with hotel management staff and non-management staff from different cultural backgrounds, public space observations between customers and staff during check-in and checkout in the reception area and during dining at the café-bar and restaurant. Thematic analysis was also applied to the official web page of each hotel and to job advertisements to enhance the findings from the interviews and the observations. For the process of analysis of the data interpretive (hermeneutic) phenomenology of Martin Heidegger has been applied. Generally, it was found that hotel staff quite often feel perplexed by how to deal with and how to overcome, for instance, language barriers and religious issues and how to interpret non verbal behaviors or matters on food culture relating to the intercultural aspect of customer service. In addition, it was interesting to find that attention to excellent customer service on the part of hotel staff is a top organizational value and customer care is a priority. Despite that, the participating hotel brands appear to have not yet, realized how intercultural barriers can affect the daily operation of the hotel, the job performance and the psychology of hotel staff. Employees indicated that they were keen to receive diversity training, provided by their organizations, so as to learn about different cultural needs and expand their intercultural skills. The notion of diversity training in global hotel brands is based on the sense that one of the multiple aims of diversity management as a practice and policy in the workplace of hotels is the better understanding of intercultural differences. Therefore global hotel brands can consider diversity training as a practice which will benefit their hotel staff and clientele base at the same time. This can have a distinctive organizational advantage for organizational affairs in the hotel industry, with potential to influence the effectiveness and performance of hotels.

State of Iowa Affirmative Action/Diversity Plan and Report, FY2008

Each department will submit by July 31st an Affirmative Action/Diversity Plan to DAS, who will receive it on behalf of the Diversity Council. This document is to report on your activities and accomplishments for FY 2008, and report on your intended activities for FY 2009. For the purposes of this document, the term protected classes refers specifically to females, minorities, and persons with disabilities. Protected classes may be subject to numerical goal setting in employment. The term diversity includes the protected classes, but also includes broader differences, such as age, sexual orientation, and religion. These differences are not subject to numerical goal setting in employment, but may be protected by non-discrimination statutes and policies. Please refer to Executive Order Four and the State’s EEO/AA Policy for more details.

Analysis and compensation of power amplifier nonlinearity in MIMO transmit diversity systems

The nonlinearity of high-power amplifiers (HPAs) has a crucial effect on the performance of multiple-input-multiple-output (MIMO) systems. In this paper, we investigate the performance of MIMO orthogonal space-time block coding (OSTBC) systems in the presence of nonlinear HPAs. Specifically, we propose a constellation-based compensation method for HPA nonlinearity in the case with knowledge of the HPA parameters at the transmitter and receiver, where the constellation and decision regions of the distorted transmitted signal are derived in advance. Furthermore, in the scenario without knowledge of the HPA parameters, a sequential Monte Carlo (SMC)-based compensation method for the HPA nonlinearity is proposed, which first estimates the channel-gain matrix by means of the SMC method and then uses the SMC-based algorithm to detect the desired signal. The performance of the MIMO-OSTBC system under study is evaluated in terms of average symbol error probability (SEP), total degradation (TD) and system capacity, in uncorrelated Nakagami-m fading channels. Numerical and simulation results are provided and show the effects on performance of several system parameters, such as the parameters of the HPA model, output back-off (OBO) of nonlinear HPA, numbers of transmit and receive antennas, modulation order of quadrature amplitude modulation (QAM), and number of SMC samples. In particular, it is shown that the constellation-based compensation method can efficiently mitigate the effect of HPA nonlinearity with low complexity and that the SMC-based detection scheme is efficient to compensate for HPA nonlinearity in the case without knowledge of the HPA parameters.

On the effect of power amplifier nonlinearity on MIMO transmit diversity systems

Nonlinearity of high-power amplifier (HPA) plays a crucial role in the performance of multiple-input multiple-output (MIMO) systems. In this paper, we investigate the performance of MIMO orthogonal space-time block coding (STBC) systems in the presence of nonlinear HPA. Specifically, we assess the impact of HPA nonlinearity on the average symbol error probability (SEP), total degradation (TD), and system capacity of orthogonal STBC in uncorrelated Nakagami-m fading channels. Numerical results are provided and show the effects of several system parameters, such as the output back-off (OBO) of nonlinear HPA, numbers of transmit and receive antennas, and modulation order of quadrature amplitude modulation (QAM), on performance.

Consequences of Simulated Loss of Open Cerrado Areas to Bird Functional Diversity

Over the past 35 years, more than two thirds of the Cerrado`s original expanse has been taken by agriculture. Even if some attempts have been made to conserve closed cerrado physiognomies, open cerrado physiognomies, richer in species and more fragile, have been systematically ignored. These open physiognomies are used by almost half of the Cerrado bird species, many of which being endemics. Using data from 11 surveys carried out in Cerrado landscapes, we asked what would happen to bird functional diversity if open cerrado species became extinct. Open cerrado birds would be able to keep on average 59% of the functional diversity. If they became extinct, on average 27% of the functional diversity would be lost. In this case, the remaining functional diversity would be lower than what would be expected by chance in five sites. Although many functions were shared by both open cerrado and forest species, there was some degree of complementarity between them, highlighted by the decrease in functional diversity when the former became extinct. Destruction of open cerrado physiognomies would lead to a habitat simplification, decrease in bird functional diversity, and, ultimately, to a considerable impact on community functioning. Thus, open cerrado physiognomies must receive much more conservation attention than they are currently receiving, because they maintain a high bird functional diversity that would otherwise be considerably diminished Were open cerrado species to become extinct.

More diversity, less tolerance? The effect of type of cultural diversity on the erosion of tolerance in Swiss municipalities

Immigration and the ways in which host societies receive newcomers pose challenges for modern civil societies. This article contributes to the ongoing discussion about how ethnic diversity influences tolerance towards immigrants. Compared to previous studies, we analyse tolerance as a sequential concept in order to uncover the effects of contextual diversity on attitudes towards immigrants and the granting of certain rights to this group. Moreover, we distinguish different shares of ethnic groups based on their ethnic and cultural origins both on the independent and dependent variable. The analysis relies on a subnational survey of sixty municipalities in Switzerland, revealing that only certain ethnic groups are seen as an economic and cultural threat.

Diversity of neuronal connexins in the mammalian retina

Many neurons in the mammalian retina are electrically coupled by intercellular channels or gap junctions, which are assembled from a family of proteins called connexins. Numerous studies indicate that gap junctions differ in properties such as conductance and tracer permeability. For example, A-type horizontal cell gap junctions are permeable to Lucifer Yellow, but B-type horizontal cell gap junctions are not. This suggests the two cell types express different connexins. My hypothesis is that multiple neuronal connexins are expressed in the mammalian retina in a cell type specific manner. Immunohistochemical techniques and confocal microscopy were used to localize certain connexins within well-defined neuronal circuits. The results of this study can be summarized as follows: AII amacrine cells, which receive direct input from rod bipolar cells, are well-coupled to neighboring AIIs. In addition, AII amacrine cells also form gap junctions with ON cone bipolar cells. This is a complex heterocellular network. In both rabbit and primate retina, connexin36 occurs at dendritic crossings in the AII matrix as well as between AIIs and ON cone bipolar cells. Coupling in the AII network is thought to reduce noise in the rod pathway while AII/bipolar gap junctions are required for the transmission of rod signals to ON ganglion cells. In the outer plexiform layer, connexin36 forms gap junctions between cones and between rods and cones via cone telodendria. Cone to cone coupling is thought to reduce noise and is partly color selective. Rod to cone coupling forms an alternative rod pathway thought to operate at intermediate light intensity. A-type horizontal cells in the rabbit retina are strongly coupled via massive low resistance gap junctions composed from Cx50. Coupling dramatically extends the receptive field of horizontal cells and the modulation of coupling is thought to change the strength of the feedback signal from horizontal cells to cones. Finally, there are other coupled networks, such as B-type horizontal cells and S1/S2 amacrine cells, which do not use either connexin36 or Cx50. These results confirm the hypothesis that multiple neuronal connexins are expressed in the mammalian retina and these connexins are localized to particular retinal circuits. ^

Characterization Of Microsatellite Markers Developed From Prosopis Rubriflora And Prosopis Ruscifolia (leguminosae - Mimosoideae), Legume Species That Are Used As Models For Genetic Diversity Studies In Chaquenian Areas Under Anthropization In South America.

Prosopis rubriflora and Prosopis ruscifolia are important species in the Chaquenian regions of Brazil. Because of the restriction and frequency of their physiognomy, they are excellent models for conservation genetics studies. The use of microsatellite markers (Simple Sequence Repeats, SSRs) has become increasingly important in recent years and has proven to be a powerful tool for both ecological and molecular studies. In this study, we present the development and characterization of 10 new markers for P. rubriflora and 13 new markers for P. ruscifolia. The genotyping was performed using 40 P. rubriflora samples and 48 P. ruscifolia samples from the Chaquenian remnants in Brazil. The polymorphism information content (PIC) of the P. rubriflora markers ranged from 0.073 to 0.791, and no null alleles or deviation from Hardy-Weinberg equilibrium (HW) were detected. The PIC values for the P. ruscifolia markers ranged from 0.289 to 0.883, but a departure from HW and null alleles were detected for certain loci; however, this departure may have resulted from anthropic activities, such as the presence of livestock, which is very common in the remnant areas. In this study, we describe novel SSR polymorphic markers that may be helpful in future genetic studies of P. rubriflora and P. ruscifolia.