E. Casilari

Modeling of Current Consumption in 802.15.4/ZigBee Sensor Motes

Battery consumption is a key aspect in the performance of wireless sensor networks. One of the most promising technologies for this type of networks is 802.15.4/ZigBee. This paper presents an empirical characterization of battery consumption in commercial 802.15.4/ZigBee motes. This characterization is based on the measurement of the current that is drained from the power source under different 802.15.4 communication operations. The measurements permit the definition of an analytical model to predict the maximum, minimum and mean expected battery lifetime of a sensor networking application as a function of the sensor duty cycle and the size of the sensed data.

A wireless monitoring system for pulse-oximetry sensors

This paper presents a wireless medical monitoring system. The system permits to receive and process in a single concentrator node (e.g. a laptop or a simple handheld device) the pulse-oximetry signals from one ore several monitored patients without using any wired infrastructure. The system, which is based on a piconet of Bluetooth sensors, can retransmit the medical signals by WLAN and GPRS. The paper describes the practical application scenarios in which this type of systems could be of great utility.

A Comparative Study of VoIP Standards with Asterisk

Since the apparition of Voice over IP (VoIP), many standards (mainly signaling protocols and codecs) have arisen with the aim of enabling voice calls through data networks. This paper describes a comparative study to evaluate the performance of a representative set of these standards when transmitting voice streams in a packet network. Asterisk PBX software is employed to define a testbed that allows to monitor diverse performance parameters in actual VoIP connections after the call establishment phase. Performed tests include the use of SIP and IAX (with and without trunking) signaling protocols as well as four different codecs. The obtained Results (expressed in terms of processor utilization, memory usage and network bandwidth consumption) show the clear benefits of employing IAX with trunking.

Modeling of HTTP traffic

In this letter, the authors show that the behavior of Web users strongly affects the dynamics of TCP connections in the Internet. Analyzing actual and systematically generated HTTP traces, it is proved that the time between the downloads of two pages is critical to determine the re-utilization of connections. On the other hand, the use of the 1.1 version of the HTTP standard does not significantly affect the traffic generated by HTTP 1.0 browsers. In this sense, the heavy-tailed nature of the size of HTTP connections can be considered an invariant property.

Analysis of Android Device-Based Solutions for Fall Detection

Falls are a major cause of health and psychological problems as well as hospitalization costs among older adults. Thus, the investigation on automatic Fall Detection Systems (FDSs) has received special attention from the research community during the last decade. In this area, the widespread popularity, decreasing price, computing capabilities, built-in sensors and multiplicity of wireless interfaces of Android-based devices (especially smartphones) have fostered the adoption of this technology to deploy wearable and inexpensive architectures for fall detection. This paper presents a critical and thorough analysis of those existing fall detection systems that are based on Android devices. The review systematically classifies and compares the proposals of the literature taking into account different criteria such as the system architecture, the employed sensors, the detection algorithm or the response in case of a fall alarms. The study emphasizes the analysis of the evaluation methods that are employed to assess the effectiveness of the detection process. The review reveals the complete lack of a reference framework to validate and compare the proposals. In addition, the study also shows that most research works do not evaluate the actual applicability of the Android devices (with limited battery and computing resources) to fall detection solutions.

An analytical model to estimate path duration in MANETs

Mobile Ad Hoc Networks (MANETs) are strongly impacted by the mobility of the ad hoc nodes. Mobility models help engineers to abstract the changes of position in network users. Different mobility models have already been proposed to characterize the behaviors of mobile devices that are greatly correlated to the conditions of the possible scenarios where networks can be deployed. In the context of mobile ad hoc networks, the Random WayPoint model has received significant attention and it has become one of the most employed mobility patterns. However, a formal description of the time during which a generic N-hop path is valid has not been proposed yet for this model. In this paper, the authors provide an analytical model for link duration as well as an analytical study of path duration in multi-hop wireless networks. The predicted results are compared with measured data and good agreement is reported.

Automatic Fall Detection System Based on the Combined Use of a Smartphone and a Smartwatch.

Due to their widespread popularity, decreasing costs, built-in sensors, computing power and communication capabilities, Android-based personal devices are being seen as an appealing technology for the deployment of wearable fall detection systems. In contrast with previous solutions in the existing literature, which are based on the performance of a single element (a smartphone), this paper proposes and evaluates a fall detection system that benefits from the detection performed by two popular personal devices: a smartphone and a smartwatch (both provided with an embedded accelerometer and a gyroscope). In the proposed architecture, a specific application in each component permanently tracks and analyses the patient’s movements. Diverse fall detection algorithms (commonly employed in the literature) were implemented in the developed Android apps to discriminate falls from the conventional activities of daily living of the patient. As a novelty, a fall is only assumed to have occurred if it is simultaneously and independently detected by the two Android devices (which can interact via Bluetooth communication). The system was systematically evaluated in an experimental testbed with actual test subjects simulating a set of falls and conventional movements associated with activities of daily living. The tests were repeated by varying the detection algorithm as well as the pre-defined mobility patterns executed by the subjects (i.e., the typology of the falls and non-fall movements). The proposed system was compared with the cases where only one device (the smartphone or the smartwatch) is considered to recognize and discriminate the falls. The obtained results show that the joint use of the two detection devices clearly increases the system’s capability to avoid false alarms or ‘false positives’ (those conventional movements misidentified as falls) while maintaining the effectiveness of the detection decisions (that is to say, without increasing the ratio of ‘false negatives’ or actual falls that remain undetected).

On the Capability of Smartphones to Perform as Communication Gateways in Medical Wireless Personal Area Networks

This paper evaluates and characterizes the technical performance of medical wireless personal area networks (WPANs) that are based on smartphones. For this purpose, a prototype of a health telemonitoring system is presented. The prototype incorporates a commercial Android smartphone, which acts as a relay point, or “gateway”, between a set of wireless medical sensors and a data server. Additionally, the paper investigates if the conventional capabilities of current commercial smartphones can be affected by their use as gateways or “Holters” in health monitoring applications. Specifically, the profiling has focused on the CPU and power consumption of the mobile devices. These metrics have been measured under several test conditions modifying the smartphone model, the type of sensors connected to the WPAN, the employed Bluetooth profile (SPP (serial port profile) or HDP (health device profile)), the use of other peripherals, such as a GPS receiver, the impact of the use of the Wi-Fi interface or the employed method to encode and forward the data that are collected from the sensors.

Type-2 fuzzy decision support system to optimise MANET integration into infrastructure-based wireless systems

Mobile ad hoc networks are able to extend the coverage area of Internet access points by establishing multihop communication paths. Due to diverse factors such as the mobility of the nodes, the propagation conditions or the traffic status, the communication paths present a lifetime. In fact, the quality of the Internet connection mainly depends on the durability of the employed communication routes. In order to improve the network performance, the nodes should select the best route in terms of its remaining lifetime. Since the factors impacting the route lifetime are unpredictable, the route remaining lifetime cannot be analytically derived. Under these circumstances, a fuzzy-logic system outstands as a potential solution to estimate the stability of the routes. This paper analyses the potentiality of this kind of solution. In particular, the paper presents a fuzzy logic system which should be installed in the mobile nodes to distributedly identify the stable routes. In particular, the system is supported by an interval-based type-2 fuzzy logic. Being a type-2 fuzzy logic system, it is able to cope with inexact estimations. This ability is necessary to avoid the use of additional messages which will occupy the scarce wireless medium. On the other hand, an interval-based fuzzy system provides the simplicity demanded by the energy-constrained mobile devices. As a novelty, the two outputs of the interval-based fuzzy system are employed. The use of each output depends on the traffic state of the mobile node. By means of extensive simulations, we demonstrate the goodness of the proposed system.

An adaptive gateway discovery for mobile ad hoc networks

One of the main aspects that affect the performance of hybrid ad hoc networks is the discovery and selection of Internet gateways. Similar to conventional ad hoc route discovery, this procedure could be accomplished employing three different strategies: proactive, reactive and hybrid. In the proactive gateway discovery, the gateway periodically generates Modified Router Advertisement (MRA) messages. The election of the time between two consecutive MRAs (T) may greatly impact on the network performance (a low T could lead to unnecessary control packets meanwhile a high T could induce nodes keep invalid routes to external hosts). The optimum value of T depends on the network conditions as the load, the node density or the node mobility. In order to dynamically adjust the T interval, in this work we present a new adaptive scheme which is supported by a control system based on a genetic algorithm. The simulation results show that the proposed algorithm is able to decrease the network congestion and achieve lower end-to-end delay.