Evaluation of the LTE positioning capabilities in realistic navigation channels

En comunicaciones móviles, los avances de nuevas tecnologías están principalmente impulsados por el incremento en las velocidades de transmisión. Uno de estos avances es el uso de señales multiportadora que permiten una distribución flexible y eficiente de recursos en tiempo y frecuencia. Diversos sistemas utilizan esta característica para combinar funcionalidades de comunicaciones con posicionamiento, debido a la creciente demanda de servicios de datos y localización en dispositivos móviles. Sin embargo, la principal degradación en interiores y escenarios urbanos se produce por el efecto del canal multicamino, que induce un considerable sesgo en la estimación de distancias. Por lo tanto, es necesario contrarrestar el multicamino para alcanzar el máximo rendimiento en posicionamiento. Esta tesis aborda el potencial de las señales multiportadora en comunicaciones móviles para la estimación de distancias en canales severos, caracterizados por denso multicamino. Para ello, se considera el caso práctico del estándar de comunicaciones Long Term Evolution (LTE). Este estándar es de especial interés ya que define una señal multiportadora OFDM dedicada para posicionamiento mediante diferencias en los tiempos de llegada observados (OTDoA), llamada señal de referencia de posicionamiento (PRS). Por lo tanto, la primera parte de la tesis evalúa la precisión de posicionamiento alcanzable utilizando la PRS en LTE con receptores convencionales, como el filtro adaptado o las técnicas basadas en la correlación. La contribución principal de la tesis se encuentra en la segunda parte, con la introducción de la estimación conjunta del tiempo de retardo y la respuesta del canal. Ésta es una solución óptima para señales multiportadora, ya que la estimación de canal se puede implementar fácilmente en el dominio frecuencial. Sin embargo, la mayoría de los algoritmos de estimación conjunta se centran en aplicaciones de comunicaciones, sin considerar la precisión extrema de la estimación de retardo requerida para posicionamiento. Por lo tanto, en esta tesis se propone una innovadora parametrización del canal para caracterizar el multicamino cercano. Este modelo de estimación de canal se basa en el tiempo de retardo y términos equiespaciados junto a un término arbitrario, con una posición variable entre los dos primeros términos equiespaciados. Este nuevo método híbrido se adopta en el estimador de máxima verosimilitud conjunto (JML) del tiempo de retardo para mejorar la estimación de la distancia en presencia de multicamino cercano. La optimalidad del estimador se confirma ya que su varianza alcanza la cota de Cramér-Rao. El rendimiento de este estimador de distancias se compara con los estimadores convencionales en condiciones realistas de navegación. Estas condiciones se caracterizan mediante modelos de canal estándar adoptados en LTE, ruido Gaussiano blanco aditivo (AWGN) y los anchos de banda de LTE. Los resultados en las estimaciones del tiempo de retardo se utilizan para determinar el orden óptimo del modelo de los estimadores, y para evaluar la máxima precisión en la estimación de distancias. Se muestra una mejora importante mediante el estimador JML propuesto en entornos con multicamino cercano. En la última parte de la tesis, el objetivo es validar el rendimiento del estimador de distancias con señales LTE reales. Para ello, se desarrolla un receptor software-defined radio (SDR) para el posicionamiento OTDoA en LTE. Se utiliza un escenario preliminar con cuatro estaciones base sincronizadas para validar el sistema de posicionamiento. A continuación, se obtiene la envolvente del error producido por multicamino (MPEE) en los estimadores JML para los casos de señal emulada y simulada. El trabajo se completa con la validación del rendimiento del nuevo estimador conjunto de distancias, utilizando el receptor SDR en un canal urbano emulado. Los resultados obtenidos muestran la mejora en la precisión de las distancias del nuevo estimador en canales de navegación realistas.The provision of high-data rates leads the advances of new technologies in mobile communications. One of these advances is the use of multicarrier signals that allow a flexible allocation of resources in time and frequency, thus the spectrum can be efficiently shared for different applications. This feature is used by several systems to combine communications and positioning capabilities, due to the increasing demand of data and location services. However, the main impairment in indoor and urban scenarios is the effect of the multipath channel, which induces a considerable bias on the ranging estimation. Thus, countermeasures against multipath are necessary to achieve the ultimate positioning performance. This thesis deals with the ranging capabilities of multicarrier signals in mobile communications over harsh environments, characterized by dense multipath. For this purpose, the practical case of the Long Term Evolution (LTE) mobile communications standard is considered. The LTE standard is of special interest because it defines an OFDM multicarrier signal dedicated to support the observed time difference of arrival (OTDoA) positioning, which is based on ranging estimates with respect to the reference base stations. This pilot signal is called positioning reference signal (PRS), and it is used for time-delay estimation (TDE) in the procedure to locate the mobile device. Thus, the first part of the thesis is aimed to assess the achievable localization capabilities of LTE conventional receivers, e.g. matched filter or correlation-based techniques, using the PRS. Despite the inter-cell interference can be mostly removed by the coordinated transmission of the PRS, multipath notably degrades the positioning accuracy of these conventional estimators. The main contribution of this thesis is provided in the second part, by introducing the joint estimation of time delay and channel response. This is an optimum solution for multicarrier signals, due to the straightforward implementation of the channel estimation in the frequency domain. However, most of the joint estimation algorithms are focused on communication applications, without considering the extreme accuracy of the TDE required for positioning. Thus, a novel channel parameterization is proposed in this thesis to characterize close-in multipath. This channel estimation model is based on the time delay and equi-spaced taps together with an arbitrary-tap with variable position between the first two equi-spaced taps. This new hybrid approach is adopted in the joint maximum likelihood (JML) time-delay estimator to improve the ranging performance in the presence of short-delay multipath. The optimality of this estimator is confirmed because its variance attains the Cram\'er-Rao bound. The ranging performance of this estimator is then compared to conventional estimators in realistic navigation conditions. These conditions are characterized by standard channel models adopted in LTE, additive white Gaussian noise (AWGN) and the LTE signal bandwidths. The resulting time-delay estimations are used to determine the optimum model order of the estimators, and to assess the achievable ranging accuracy. A notable improvement is shown by the JML estimator proposed in close-in multipath scenarios. In the last part of the thesis, the goal is to validate the ranging performance of the proposed estimator using real LTE signals. For this purpose, a software-defined radio (SDR) receiver is developed for OTDoA positioning in LTE. A preliminary scenario with four synchronized base stations is used to validate the positioning engine. Then, the multipath error envelope (MPEE) of the JML estimators is obtained for the emulated and simulated signal cases. The work is completed with the validation of the ranging performance of the new JML time-delay and channel estimator, by using the SDR receiver in an emulated urban channel. The results obtained show the improvement on the ranging accuracy of the new JML estimator over realistic navigation channels

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Correction to: Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

The original version of this article unfortunately contained a mistake

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Evaluation of the LTE positioning capabilities in realistic navigation channels

En comunicaciones móviles, los avances de nuevas tecnologías están principalmente impulsados por el incremento en las velocidades de transmisión. Uno de estos avances es el uso de señales multiportadora que permiten una distribución flexible y eficiente de recursos en tiempo y frecuencia. Diversos sistemas utilizan esta característica para combinar funcionalidades de comunicaciones con posicionamiento, debido a la creciente demanda de servicios de datos y localización en dispositivos móviles. Sin embargo, la principal degradación en interiores y escenarios urbanos se produce por el efecto del canal multicamino, que induce un considerable sesgo en la estimación de distancias. Por lo tanto, es necesario contrarrestar el multicamino para alcanzar el máximo rendimiento en posicionamiento. Esta tesis aborda el potencial de las señales multiportadora en comunicaciones móviles para la estimación de distancias en canales severos, caracterizados por denso multicamino. Para ello, se considera el caso práctico del estándar de comunicaciones Long Term Evolution (LTE). Este estándar es de especial interés ya que define una señal multiportadora OFDM dedicada para posicionamiento mediante diferencias en los tiempos de llegada observados (OTDoA), llamada señal de referencia de posicionamiento (PRS). Por lo tanto, la primera parte de la tesis evalúa la precisión de posicionamiento alcanzable utilizando la PRS en LTE con receptores convencionales, como el filtro adaptado o las técnicas basadas en la correlación. La contribución principal de la tesis se encuentra en la segunda parte, con la introducción de la estimación conjunta del tiempo de retardo y la respuesta del canal. Ésta es una solución óptima para señales multiportadora, ya que la estimación de canal se puede implementar fácilmente en el dominio frecuencial. Sin embargo, la mayoría de los algoritmos de estimación conjunta se centran en aplicaciones de comunicaciones, sin considerar la precisión extrema de la estimación de retardo requerida para posicionamiento. Por lo tanto, en esta tesis se propone una innovadora parametrización del canal para caracterizar el multicamino cercano. Este modelo de estimación de canal se basa en el tiempo de retardo y términos equiespaciados junto a un término arbitrario, con una posición variable entre los dos primeros términos equiespaciados. Este nuevo método híbrido se adopta en el estimador de máxima verosimilitud conjunto (JML) del tiempo de retardo para mejorar la estimación de la distancia en presencia de multicamino cercano. La optimalidad del estimador se confirma ya que su varianza alcanza la cota de Cramér-Rao. El rendimiento de este estimador de distancias se compara con los estimadores convencionales en condiciones realistas de navegación. Estas condiciones se caracterizan mediante modelos de canal estándar adoptados en LTE, ruido Gaussiano blanco aditivo (AWGN) y los anchos de banda de LTE. Los resultados en las estimaciones del tiempo de retardo se utilizan para determinar el orden óptimo del modelo de los estimadores, y para evaluar la máxima precisión en la estimación de distancias. Se muestra una mejora importante mediante el estimador JML propuesto en entornos con multicamino cercano. En la última parte de la tesis, el objetivo es validar el rendimiento del estimador de distancias con señales LTE reales. Para ello, se desarrolla un receptor software-defined radio (SDR) para el posicionamiento OTDoA en LTE. Se utiliza un escenario preliminar con cuatro estaciones base sincronizadas para validar el sistema de posicionamiento. A continuación, se obtiene la envolvente del error producido por multicamino (MPEE) en los estimadores JML para los casos de señal emulada y simulada. El trabajo se completa con la validación del rendimiento del nuevo estimador conjunto de distancias, utilizando el receptor SDR en un canal urbano emulado. Los resultados obtenidos muestran la mejora en la precisión de las distancias del nuevo estimador en canales de navegación realistas.The provision of high-data rates leads the advances of new technologies in mobile communications. One of these advances is the use of multicarrier signals that allow a flexible allocation of resources in time and frequency, thus the spectrum can be efficiently shared for different applications. This feature is used by several systems to combine communications and positioning capabilities, due to the increasing demand of data and location services. However, the main impairment in indoor and urban scenarios is the effect of the multipath channel, which induces a considerable bias on the ranging estimation. Thus, countermeasures against multipath are necessary to achieve the ultimate positioning performance. This thesis deals with the ranging capabilities of multicarrier signals in mobile communications over harsh environments, characterized by dense multipath. For this purpose, the practical case of the Long Term Evolution (LTE) mobile communications standard is considered. The LTE standard is of special interest because it defines an OFDM multicarrier signal dedicated to support the observed time difference of arrival (OTDoA) positioning, which is based on ranging estimates with respect to the reference base stations. This pilot signal is called positioning reference signal (PRS), and it is used for time-delay estimation (TDE) in the procedure to locate the mobile device. Thus, the first part of the thesis is aimed to assess the achievable localization capabilities of LTE conventional receivers, e.g. matched filter or correlation-based techniques, using the PRS. Despite the inter-cell interference can be mostly removed by the coordinated transmission of the PRS, multipath notably degrades the positioning accuracy of these conventional estimators. The main contribution of this thesis is provided in the second part, by introducing the joint estimation of time delay and channel response. This is an optimum solution for multicarrier signals, due to the straightforward implementation of the channel estimation in the frequency domain. However, most of the joint estimation algorithms are focused on communication applications, without considering the extreme accuracy of the TDE required for positioning. Thus, a novel channel parameterization is proposed in this thesis to characterize close-in multipath. This channel estimation model is based on the time delay and equi-spaced taps together with an arbitrary-tap with variable position between the first two equi-spaced taps. This new hybrid approach is adopted in the joint maximum likelihood (JML) time-delay estimator to improve the ranging performance in the presence of short-delay multipath. The optimality of this estimator is confirmed because its variance attains the Cram\'er-Rao bound. The ranging performance of this estimator is then compared to conventional estimators in realistic navigation conditions. These conditions are characterized by standard channel models adopted in LTE, additive white Gaussian noise (AWGN) and the LTE signal bandwidths. The resulting time-delay estimations are used to determine the optimum model order of the estimators, and to assess the achievable ranging accuracy. A notable improvement is shown by the JML estimator proposed in close-in multipath scenarios. In the last part of the thesis, the goal is to validate the ranging performance of the proposed estimator using real LTE signals. For this purpose, a software-defined radio (SDR) receiver is developed for OTDoA positioning in LTE. A preliminary scenario with four synchronized base stations is used to validate the positioning engine. Then, the multipath error envelope (MPEE) of the JML estimators is obtained for the emulated and simulated signal cases. The work is completed with the validation of the ranging performance of the new JML time-delay and channel estimator, by using the SDR receiver in an emulated urban channel. The results obtained show the improvement on the ranging accuracy of the new JML estimator over realistic navigation channels