Exact analysis of weighted centroid localization

Source localization of primary users (PUs) is a geolocation spectrum awareness feature that can be very useful in enhancing the functionality of cognitive radios (CRs). When the cooperating CRs have limited information about the PU, weighted centroid localization (WCL) based on received signal strength (RSS) measurements represents an attractive low-complexity solution. In this paper, we propose a new analytical framework to calculate the exact performance of WCL in the presence of shadowing, based on results of the ratio of two quadratic forms in normal variables. In particular, we derive an exact expression for the root mean square error (RMSE) of the two-dimensional location estimate. Numerical results confirm that the derived framework is able to predict the performance of WCL capturing all the essential aspects of propagation as well as CR network spatial topology

Blind localization of radio emitters in wireless communications

The proliferation of wireless services is expected to increase the demand for radio spectrum in the foreseeable future. Given the limitations of the radio spectrum, it is evident that the current fixed frequency assignment policy fails to accommodate this increasing demand. Thus, the need for innovative technologies that can scale to accommodate future demands both in terms of spectrum efficiency and high reliable communication. Cognitive radio (CR) is one of the emerging technologies that offers a more flexible use of frequency bands allowing unlicensed users to exploit and use portions of the spectrum that are temporarily unused without causing any potential harmful interference to the incumbents. The most important functionality of a CR system is to observe the radio environment through various spectrum awareness techniques e.g., spectrum sensing or detection of spectral users in the spatio-temporal domain. In this research, we mainly focus on one of the key cognitive radio enabling techniques called localization, which provides crucial geo-location of the unknown radio transmitter in the surrounding environment. Knowledge of the user’s location can be very useful in enhancing the functionality of CRs and allows for better spectrum resource allocations in the spatial domain. For instance, the location-awareness feature can be harnessed to accomplish CR tasks such as spectrum sensing, dynamic channel allocation and interference management to enable cognitive radio operation and hence to maximize the spectral utilization. Additionally, geo-location can significantly expand the capabilities of many wireless communication applications ranging from physical layer security, geo-routing, energy efficiency, and a large set of emerging wireless sensor network and social networking applications. We devote the first part of this research to explore a broad range of existing cooperative localization techniques and through Monte-Carlo simulations analyze the performance of such techniques. We also propose two novel techniques that offer better localization performance with respect to the existing ones. The second and third parts of this research put forth a new analytical framework to characterize the performance of a particular low-complexity localization technique called weighted centroid localization (WCL), based on the statistical distribution of the ratio of two quadratic forms in normal variables. Specifically, we evaluate the performance of WCL in terms of the root mean square error (RMSE) and cumulative distribution function (CDF). The fourth part of this research focuses on studying the bias of the WCL and also provides solutions for bias correction. Throughout this research, we provide a case study analysis to evaluate the performance of the proposed approaches under changing channel and environment conditions. For the new theoretical framework, we compare analytical and Monte-Carlo simulation results of the performance metric of interest. A key contribution in our analysis is that we present not only the accurate performance in terms of the RMSE and CDF, but a new analytical framework that takes into consideration the finite nature of the network, overcoming the limitations of asymptotic results based on the central limit theorem. Remarkably, the numerical results unfold that the new analytical framework is able to predict the performance of WCL capturing all the essential aspects of propagation as well as the cognitive radio network spatial topology. Finally, we present conclusions gained from this research and possible future directions

Cooperative blind localization of primary user in a cognitive radio environment

Blind localization has emerged as an important topic addressing the challenges faced by any cognitive radio (CR) network. The estimation of the primary user (PU) position in a CR network is made difficult because generally cooperation between the PU and the secondary user (SU) does not exist. This presents a challenge since PU parameters such as transmit power, path loss exponent, noise variance and the location of the PU are not known. Hence, the need for a robust, accurate and rangefree localization technique that does not require any knowledge of such parameters. In this paper, we investigate the localization performance when combining the database technique and the centroid localization techniques.We adopt a two-stage localization strategy. In the first stage, a mean-square error (MSE) method is used to find a close match between the actual received power and the database power and subsequently the PU estimates. Centroid localization (CL) and weighted centroid localization (WCL) techniques are then adopted in the second-stage as fusion strategies to give an estimate of the PU. We also analyse the rootmean squared error (RMSE) of the CL and WCL techniques. We further compare our results with the direct centroid localization techniques without involving the database

Constrained cluster based blind localization of primary user for cognitive radio networks

Blind localization of primary user (PU) is a geo-location spectrum awareness feature that can be very useful in enhancing the functionality of cognitive radios (CRs) in terms of minimizing the interference to the PU. However, the estimation of the PU position within the region is made difficult because cooperation between the PU and the secondary user (SU) does not exist and therefore the PU signal parameters remain unknown to the SU. The centroid-based localization techniques have significantly been adopted as suitable candidates that do not require knowledge of such parameters. In this paper we investigate the localization performance of such techniques by imposing constraints to the selection of the SU nodes, termed as SU cluster, to estimate the PU location. In particular, we impose a minimum distance constraint between any two SU nodes and group the qualifying nodes into a cluster. Only the SU nodes from the constrained cluster can take part in localizing the PU. We simulate the proposed method for a shadow fading wireless environment and compare the results with the centroid and the weighted centroid based blind localization methods. Our results show that the mean squared error in the estimation of the position of the PU is significantly improved for the proposed method compared to the two standard centroid localization techniques especially when the true PU location is away from the center of the region

Blind Localization of Primary Users with Sectorial Antennas

It is essential to estimate the position of primary users (PUs) for the further development of cognitive radio (CR) networks. Great efforts have been done to seek for localization algorithms with high performance but low computation. In a CR network, PUs do not cooperate with secondary users (SUs), which makes localization challenging. Due to this feature, received signal strength (RSS)- based localization techniques, such as weighted centroid localization (WCL) can be one of the best candidates. However, most of the existing works in this area did not consider the directionality of the antennas. In this paper, we propose a blind localization algorithm using the signal strength received by different sectors of the SU antenna. Then a scoring strategy is applied to all the sectors to estimate the PU location. Two scoring strategies are proposed. Numerical results show that the proposed sectorial antenna technique is robust to PU locations and channel conditions. Compared with WCL, it offers a great improvement in the performance

Statistical Distribution of Position Error in Weighted Centroid Localization

A low complexity weighted centroid localization (WCL) is an attractive solution that enables cognitive radios (CRs) to have a geolocation awareness of the radio environment. In this paper, we propose a new analytical framework to calculate the exact performance of WCL, based on received signal strength (RSS) measurements, in the presence of independent and identically distributed (i.i.d) as well as correlated shadowing. Based on results on the ratio of two quadratic forms in normal variables, we derive an exact expression for the cumulative distribution function (CDF) of the two-dimensional location estimate. Numerical results confirm that the derived framework is able to predict the performance of WCL capturing all the essential aspects of propagation as well as CR network spatial topology, including finite-sized network

Accurate Analysis of Weighted Centroid Localization

Source localization of primary users (PUs) is a spectrum awareness feature that can be very useful in enhancing the functionality of cognitive radios (CRs). When the cooperating CRs have limited information about the PU, weighted centroid localization (WCL) based on received signal strength (RSS) measurements represents an attractive low-complexity solution. This paper proposes a new analytical framework to accurately calculate the performance of WCL based on the statistical distribution of the ratio of two quadratic forms in normal variables. In particular, we derive an analytical expression for the root mean square error (RMSE) and an exact expression for the cumulative distribution function (CDF) of the two-dimensional location estimate. The proposed framework accounts for the presence of independent and identically distributed (i.i.d.) shadowing as well as correlated shadowing with distance-dependent intensity. The methodology is general enough to include the analysis of the one-dimensional error, which leads also to the evaluation of the bias of the position estimate. Numerical results confirm that the analytical framework is able to predict the performance of WCL capturing all the essential aspects of propagation as well as CR network spatial topology

Directional antenna channel modeling in urban area using ray tracing

Directional antenna are regarded as one of the key technologies to achieve higher signal quality and data rate. Evidence has shown that the directional antenna channel features can be very different from the omnidirectional ones. Therefore, it is essential to characterize the directional antenna channel model (DACM), since an accurate, easy-to-implement DACM plays a vital role in the wireless network design, optimization and utilization. In this paper, we cluster the incident rays based on the azimuth direction of arrival at the receiver and extract the features concerning the number of clusters, the distribution of the cluster center and the cluster power ratio. The proposed DACM is derived by the ray tracing method and is feasible for a typical urban scenario within a range of a few hundred meters. Moreover, our proposed model is verified by both ray tracing and numerical simulations. In this paper, we present the model derivation methodology, recommend the model parameters and offer an implementation guideline

EXPECTED ROLES OF NURSES AND MIDWIVES IN BOTSWANA

AimThe roles and tasks of nurses and midwives have developed significantly over the years, calling for adjustment to the current local consumer needs and expectations. This qualitative study was conducted to explore the perceived tasks and roles of nurses and midwives.Significance of the studyThe results of this study will provide guidance for development of a culturally relevant Sub Saharan nursing and midwifery practice model, and curriculum development.MethodsThe larger descriptive cross sectional qualitative regional study involved 9 Sub-Saharan African countries. We present the Botswana component of this study. Respondents were patients, community leaders, and nurse-leaders, selected through purposive sampling from different settings. The University Of Botswana Office Of Research and Development, and the Ministry of Health Research and Development Committee gave permission for the study. Participants gave written informed consent, completed a 16-item demographic questionnaire, and engaged in focus group discussions about the perceived tasks and roles of nurses and midwives. Qualitative data were textually analysed to generate themes and subthemes, supported by verbatim excerpts.ResultsRespondents stated that nurses and midwives in Botswana operate at different levels of the health care system, with dependent, interdependent and independent roles. Nurses and midwives were expected to be receptive, patient, respectful, compassionate, and knowledgeable about their work. The perceived roles included caring, collaboration, advocacy, leadership, supervision, mentoring, management and other expanded roles.Discussion/Conclusion/recommendationsParticipants highlighted the expanded roles that nurses and midwives performed beyond their scopes of practice and education, hence the need for regulation, training and incentives. Â

An innovative educational approach to professional development of medical laboratory scientists in Botswana

Mabel KM Magowe,1 Jenny H Ledikwe,2,3 Ishmael Kasvosve,1 Robert Martin,2 Kabo Thankane,3 Bazghina-werq Semo2,31Faculty of Health Sciences, University of Botswana, Gaborone, Botswana; 2Department of Global Health, University of Washington, Seattle, Washington, USA; 3Botswana International Training and Education Center for Health, Gaborone, BotswanaPurpose: To address the shortage of laboratory scientists in Botswana, an innovative, one-year academic bridging program was initiated at the University of Botswana, to advance diploma-holding laboratory technicians towards becoming laboratory scientists holding Bachelor’s degrees. An evaluation was conducted, which described the outcomes of the program and the lessons learned from this novel approach to meeting human resource needs.Methods: This was a cross-sectional, mixed-methods evaluation. Qualitative interviews were conducted with graduates of the Bachelor of Science (BSc) Medical Laboratory Sciences (MLS) bridging program, along with the graduates’ current supervisors, and key informants who were involved in program development or implementation. The quantitative data collected included a written questionnaire, completed by program graduates, with a retrospective pre-test/post-test survey of graduates’ confidence, in terms of key laboratory competencies.Results: The BSc MLS bridging program produced thirty-three laboratory scientists over 3 years. There was a significant increase in confidence among graduates, for specified competencies, after the program (P<0.05). Graduates reported acquiring new skills and, often, accepting new responsibilities at their former workplace, particularly in relationship to leadership and management. Five graduates enrolled in advanced degree programs. Most graduates assumed increased responsibility. However, only two graduates were promoted after completing the training program. The lessons learned include: the importance of stakeholder involvement, the need for data to identify local needs, financial sustainability, catering for the needs of adult learners, and ensuring a technically challenging work environment, conducive to the application of skills learned during training.Conclusion: A strong public health and clinical laboratory system is essential for the rapid detection and control of emerging health threats, and for patient care. However, there is a need to adequately prepare laboratory human resources, to ensure efficient and effective laboratory services. Advancement of laboratory technicians towards becoming laboratory scientists, through a bridging program, can provide the necessary skills within a short time.Keywords: human resources for health, medical laboratory science education, bridging progra