Alejandro S. Martínez-Sala

Tracking of Returnable Packaging and Transport Units with active RFID in the grocery supply chain

The fresh products supply chain still has room to improve and increase efficiency and even become an intelligent supply chain by means of automating simple but valuable data flows which will be the foundations and first stage for developing new value-added services. The Spanish company ECOMOVISTAND has developed an innovative and ecological packaging and transport unit, called MT, for the grocery supply chain, which can be used in the entire product cycle; that is, the MT serves (1) as packaging at the producer, (2) as transport unit, (3) as storage at warehouses, and (4) as display stand at the supermarket, all in the same mechanical system, being thus a Returnable Packaging and Transport Unit. An MT needs the support of information technologies to achieve its true potential. In this paper we show the work developed in collaboration with ECOMOVISTAND in order to turn the MT into an intelligent product platform by embedding Active RFID tags. Data flows are integrated into an information system, called MEGASTAND, which allows to track MTs over the entire supply chain and provide value-added services to the customers.

Simulation scalability issues in wireless sensor networks

The formidable growth of WSN research has opened challenging issues about their performance evaluation. Despite the steady increase in mathematical analysis and experimental deployments, most of the community has chosen simulation for their study. Although it seems straightforward, this approach becomes quite a delicate matter. Complexity is caused by several issues. First, the large number of nodes heavily impacts simulation performance and scalability. Second, credible results demand an accurate characterization of the sensor radio channel. New aspects inherent in WSN must be included in simulators (e.g., a physical environment and an energy model), leading to different degrees of accuracy vs. performance. Moreover, many necessary models are in the continuous time domain (e.g., heat transmission, battery discharge), and thus complex to integrate into discrete event network simulators. These issues result in exponential growth of overall network state information. Through this survey we review these problems both quantitatively and qualitatively while depicting a common suitable simulation model. We also briefly describe the most significant simulation frameworks available.

An accurate radio channel model for wireless sensor networks simulation

Simulations are currently an essential tool to develop and test wireless sensor networks (WSNs) protocols and to analyze future WSNs applications performance. Researchers often simulate their proposals rather than deploying high-cost test-beds or develop complex mathematical analysis. However, simulation results rely on physical layer assumptions, which are not usually accurate enough to capture the real behavior of a WSN. Such an issue can lead to mistaken or questionable results. Besides, most of the envisioned applications for WSNs consider the nodes to be at the ground level. However, there is a lack of radio propagation characterization and validation by measurements with nodes at ground level for actual sensor hardware. In this paper, we propose to use a low-computational cost, two slope, log-normal path-loss near ground outdoor channel model at 868 MHz in WSN simulations. The model is validated by extensive real hardware measurements obtained in different scenarios. In addition, accurate model parameters are provided. This model is compared with the well-known one slope path-loss model. We demonstrate that the two slope log-normal model provides more accurate WSN simulations at almost the same computational cost as the single slope one. It is also shown that the radio propagation characterization heavily depends on the adjusted model parameters for a target deployment scenario: The model parameters have a considerable impact on the average number of neighbors and on the network connectivity.

Wireless communications deployment in industry: a review of issues, options and technologies

Present basis of knowledge management is the efficient share of information. The challenges that modern industrial processes have to face are multimedia information gathering and system integration, through large investments and adopting new technologies. Driven by a notable commercial interest, wireless networks like GSM or IEEE 802.11 are now the focus of industrial attention, because they provide numerous benefits, such as low cost, fast deployment and the ability to develop new applications. However, wireless nets must satisfy industrial requisites: scalability, flexibility, high availability, immunity to interference, security and many others that are crucial in hazardous and noisy environments. This paper presents a thorough survey of all this requirements, reviews the existing wireless solutions, and explores possible matching between industry and the current existing wireless standards.

Performance evaluation of MAC transmission power control in wireless sensor networks

In this paper we provide a method to analytically compute the energy saving provided by the use of transmission power control (TPC) at the MAC layer in wireless sensor networks (WSN). We consider a classical TPC mechanism: data packets are transmitted with the minimum power required to achieve a given packet error probability, whereas the additional MAC control packets are transmitted with the nominal (maximum) power. This scheme has been chosen because it does not modify the network topology, since control packet transmission range does not change. This property also allows us to analytically compute the expected energy savings. Besides, this type of TPC can be implemented in the current sensor hardware, and it can be directly applied to several MAC protocols already proposed for WSN. The foundation of our analysis is the evaluation of L ratio, defined as the total energy consumed by the network using the original MAC protocol divided by the total energy consumed if the TPC mechanism is employed. In the L computation we emphasize the basic properties of sensor networks. Namely, the savings are calculated for a network that is active for a very long time, and where the number of sensors is supposed to be very large. The nodes position is assumed to be random - a normal bivariate distribution is assumed in the paper - and no node mobility is considered. In the analysis we stress the radio propagation and the distribution of the nodes in the network, which will ultimately determine the performance of the TPC. Under these conditions we compute the mean value of L. Finally, we have applied the method to evaluate the benefits of TPC for TDMA and CSMA with two representative protocols, L-MAC and S-MAC using their implementation reference parameters. The conclusion is that, while S-MAC does not achieve a significant improvement, L-MAC may reach energy savings up to 10-20%.

A wireless sensor networks MAC protocol for real-time applications

Wireless sensor networks (WSN) are designed for data gathering and processing, with particular requirements: low hardware complexity, low energy consumption, special traffic pattern support, scalability, and in some cases, real-time operation. In this paper we present the virtual TDMA for sensors (VTS) MAC protocol, which intends to support the previous features, focusing particularly on real-time operation. VTS adaptively creates a TDMA arrangement with a number of timeslots equal to the actual number of nodes in range. Thus, VTS achieves an optimal throughput performance compared to TDMA protocols with fixed size of frame. The frame is set up and maintained by a distributed procedure, which allows sensors to asynchronously join and leave the frame. In addition, duty cycle is increased or decreased in order to keep latency constant below a given deadline. Therefore, a major advantage of VTS is that it guarantees a bounded latency, which allows soft real-time applications.

Design, Implementation and Evaluation of an Indoor Navigation System for Visually Impaired People.

Indoor navigation is a challenging task for visually impaired people. Although there are guidance systems available for such purposes, they have some drawbacks that hamper their direct application in real-life situations. These systems are either too complex, inaccurate, or require very special conditions (i.e., rare in everyday life) to operate. In this regard, Ultra-Wideband (UWB) technology has been shown to be effective for indoor positioning, providing a high level of accuracy and low installation complexity. This paper presents SUGAR, an indoor navigation system for visually impaired people which uses UWB for positioning, a spatial database of the environment for pathfinding through the application of the A* algorithm, and a guidance module. The interaction with the user takes place using acoustic signals and voice commands played through headphones. The suitability of the system for indoor navigation has been verified by means of a functional and usable prototype through a field test with a blind person. In addition, other tests have been conducted in order to show the accuracy of different relevant parts of the system.

Integration of Directional Antennas in an RSS Fingerprinting-Based Indoor Localization System.

In this paper, the integration of directional antennas in a room-level received signal strength (RSS) fingerprinting-based indoor localization system (ILS) is studied. The sensor reader (SR), which is in charge of capturing the RSS to infer the tag position, can be attached to an omnidirectional or directional antenna. Unlike commonly-employed omnidirectional antennas, directional antennas can receive a stronger signal from the direction in which they are pointed, resulting in a different RSS distributions in space and, hence, more distinguishable fingerprints. A simulation tool and a system management software have been also developed to control the system and assist the initial antenna deployment, reducing time-consuming costs. A prototype was mounted in a real scenario, with a number of SRs with omnidirectional and directional antennas properly positioned. Different antenna configurations have been studied, evidencing a promising capability of directional antennas to enhance the performance of RSS fingerprinting-based ILS, reducing the number of required SRs and also increasing the localization success.

An IEEE 802.11 protocol test-bed in industrial environments using personal computing devices

IEEE 802.11 is being currently considered to develop telecommunications infrastructures in industrial environments. However, in such environments there may exist a high level of electromagnetic fields (EMF) contamination, due to the machinery in use. Wireless LANs are sensitive to this type of hazard, and therefore the performance of the protocols may be affected inside the industrial facilities. In this paper we conduct a study of the wireless link performance in these industrial scenarios, using personal computing devices. Such equipments will be likely used by employees rather than conventional computers. Since the results do not characterize the environment itself, but the set of environment and hardware, a proper measurement test-bed must include direct measurements with these devices. Besides, due to limitations in these equipments, a specific protocol to measure pairs of packet error probability and latency is also developed. Results reveal a significant linear dependency between both magnitudes, and a large correlation coefficient in the measurements under high EMF activity at mid-large ranges (distances greater than 5 meters)

Garment Counting in a Textile Warehouse by Means of a Laser Imaging System

Textile logistic warehouses are highly automated mechanized places where control points are needed to count and validate the number of garments in each batch. This paper proposes and describes a low cost and small size automated system designed to count the number of garments by processing an image of the corresponding hanger hooks generated using an array of phototransistors sensors and a linear laser beam. The generated image is processed using computer vision techniques to infer the number of garment units. The system has been tested on two logistic warehouses with a mean error in the estimated number of hangers of 0.13%.