This paper describes the TELIAMADE system, a new indoor positioning system based on time-of-flight (TOF) of ultrasonic signal to estimate the distance between a receiver node and a transmitter node. TELIAMADE system consists of a set of wireless nodes equipped with a radio module for communication and a module for the transmission and reception of ultrasound. The access to the ultrasonic channel is managed by applying a synchronization algorithm based on a time-division multiplexing (TDMA) scheme. The ultrasonic signal is transmitted using a carrier frequency of 40 kHz and the TOF measurement is estimated by applying a quadrature detector to the signal obtained at the A/D converter output. Low sampling frequencies of 17.78 kHz or even 12.31 kHz are possible using quadrature sampling in order to optimize memory requirements and to reduce the computational cost in signal processing. The distance is calculated from the TOF taking into account the speed of sound. An excellent accuracy in the estimation of the TOF is achieved using parabolic interpolation to detect of maximum of the signal envelope at the matched filter output. The signal phase information is also used for enhancing the TOF measurement accuracy. Experimental results show a root mean square error (rmse) less than 2 mm and a standard deviation less than 0.3 mm for pseudorange measurements in the range of distances between 2 and 6 m. The system location accuracy is also evaluated by applying multilateration. A sub-centimeter location accuracy is achieved with an average rmse of 9.6 mm.

In recent decades, collaborative initiatives have become relevant in Latin America, however, the owners of these businesses still face great challenges to mobilize consumers interest. In the research field, many collaborative consumption (CC) researchers have focused on the identification of their predictors; but studies that have explored this phenomenon via motivations perspective are very limited, especially those that focus on the Latin American context. Furthermore, these studies have analyzed on particular consumption activities and consumers with previous experience, restricting the scope of its results. To close this gap, the research has as its purpose the exploration of the motivating factors that best predict the intention to participate in CC activities into one of the three countries with the greatest number of collaborative businesses in the region. The ANOVA and CHAID are applied to a sample of 2080 people. The results reveal that, although enjoyment, sustainability, reputation and economic benefits are significant factors for CC, not all are equally effective in promoting high levels of participation in Latin American context. These findings allow to achieve a better understanding of the collaborative phenomenon, and also they contribute to the development of value proposals and more focused recruitment strategies for potential consumers in the region.

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This paper presents the design and evaluation of an ultrasonic time-of-flight (TOF) measurement system in the context of a smart sensor wireless network. In particular, the ZigBee protocol is used for data transmission and synchronization purposes. Low-cost and low-power restrictions are taken into account in the design. A synchronous measurement scheduling approach is used to minimize the network traffic and, therefore, the power consumption, while avoiding the need of wired connections between the nodes or the use of specific radio link to provide synchronization. A theoretical model that describes the accuracy of the proposed system is derived. This model takes into account both clock drift effects and finite clock resolution of the network nodes. According to the model, the estimation of the TOF is biased due to the clock drifts, and a solution is proposed to compensate this bias. The compensation is based on an accurate estimation that each node performs for its own clock drift. An error analysis of this estimation procedure is also developed, and its effects on the TOF accuracy are presented. A theoretical model of the system that predicts the system performance in terms of TOF accuracies is proposed. An implementation of the TOF measurement system is presented, from which experimental results that validate the theoretical derivations and the effect of the clock drift compensation are obtained. Experimental evaluation of the system also demonstrates that TOF accuracies better than 2 μs are achievable, which will be more than adequate for achieving subcentimetric or even submillimetric precisions in ultrasound-TOF-based distance measurement systems. Even though a particular approach for TOF estimation is considered in this work, most of the derived results are also applicable to other systems involving time synchronous measurements.Index Terms-Local positioning systems (LPSs), ultrasonic pseudorange measurement, wireless sensor networks.

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