Browsing by Author "Almeida, Luis"
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- AdaptC: programming adaptation policies for WSN applicationsPublication . Gaur, Shashank; Almeida, Luis; Tovar, EduardoEvolution in both hardware and software technologies has enabled Wireless Sensor Networks(WSNs) to target a multiplicity of domains. Programming for such advanced WSNs remains a challenging process for users, especially as the WSN may need to make changes as per outcomes from different scenarios during execution. Usually, various adaptation policies are written while programming such applications to enable changes. However it is difficult for the programmer to anticipate changes for new scenarios. It also becomes difficult to reuse these adaptation policies. In this paper, we propose AdaptC, an abstraction for such adaptation policies that facilitates re-usability and expansion across various WSNs. We also present concepts for the design and implementation of AdaptC. We evaluate the abstraction for multiple use cases and compare it against existing work.
- An Intersection Management Protocol for Mixed Autonomous and Legacy VehiclesPublication . Reddy, Radha; Almeida, Luis; Tovar, EduardoAn important element in urban traffic management is the Intersection Management (IM) that deals with traffic lights signaling (either real or virtual). Intersections are vulnerable to traffic congestion and accidents. Therefore, this paper investigates a synchronous intersection management protocol for mixed autonomous and humandriven vehicles in the context of decentralized traffic management.
- Assessing the ESP8266 WiFi module for the Internet of ThingsPublication . Mesquita, João; Guimarães, Diana; Pereira, Carlos; Santos, Frederico; Almeida, LuisThe Internet of Things (IoT) is experiencing rapid growth and being adopted across multiple domains. For example, in industry it supports the connectivity needed to integrate smart machines, components and products in the ongoing Industry 4.0 trend. However, there is a myriad of communication technologies that complicate the needed integration, requiring gateways to connect to the Internet. Conversely, using IEEE 802.11 (WiFi) devices can connect to existing WiFi infrastructures directly and access the Internet with shorter communication delays and lower system cost. However, WiFi is energy consuming, impacting autonomy of the end devices. In this work we characterize a recent WiFi-enabled device, namely the ESP8266 module, that is low cost and branded as ultra-low-power, but whose performance for IoT applications is still undocumented. We explore the built-in sleep modes and we measure the impact of infrastructure parameters beacon interval and DTIM period on energy consumption, as well as packet delivery ratio and received signal strength as a function of distance and module antenna orientation to assert area coverage. The ESP8266 module showed suitability for battery powered IoT applications that allow 2–4 days recharge cycles on a 1000mAh battery with seconds-scale transmission intervals.
- Assessing the ESP8266 WiFi module for the Internet of ThingsPublication . Mesquita, João; Guimarães, Diana; Pereira, Carlos; Santos, Frederico; Almeida, LuisThe Internet of Things (IoT) is experiencing rapid growth and being adopted across multiple domains. For example, in industry it supports the connectivity needed to integrate smart machines, components and products in the ongoing Industry 4.0 trend. However, there is a myriad of communication technologies that complicate the needed integration, requiring gateways to connect to the Internet. Conversely, using IEEE 802.11 (WiFi) devices can connect to existing WiFi infrastructures directly and access the Internet with shorter communication delays and lower system cost. However, WiFi is energy consuming, impacting autonomy of the end devices. In this work we characterize a recent WiFi-enabled device, namely the ESP8266 module, that is low cost and branded as ultra-low-power, but whose performance for IoT applications is still undocumented. We explore the built-in sleep modes and we measure the impact of infrastructure parameters beacon interval and DTIM period on energy consumption, as well as packet delivery ratio and received signal strength as a function of distance and module antenna orientation to assert area coverage. The ESP8266 module showed suitability for battery powered IoT applications that allow 2-4 days recharge cycles on a 1000mAh battery with seconds-scale transmission intervals.
- Automatic Allocation of Tasks in T-Res for WSNPublication . Gaur, Shashank; Almeida, Luis; Tovar, EduardoThis paper presents a demo of an extension developed to support an existing programming abstraction for IoT: mT-Res. mT-Res is an extension of the T-Res programming abstraction, which allows users to write applications using a web framework without low level knowledge of resources. The paper describes an automated mechanism for allocate resources to such applications and adapt to changes in those resources.
- Characterization and Modeling of the Bicycle-Antenna System for the 2.4GHz ISM BandPublication . Pinto, Luis; M. Santos, Pedro; Almeida, Luis; Aguiar, AnaVehicular communication is rapidly becoming a standard reality, and precise models are necessary for accurate performance estimates. Alongside cars and trucks, smaller vehicles such as scooters and bicycles are also set to participate in V2X networking, but have received considerably less attention. In this work, we present an extensive characterization of the gain pattern of a bicycle and antenna system for the IEEE 802.11g standard. We measure the radiation patterns of the antenna of a commodity 2.4 GHz WiFi module mounted on six distinct positions on the body of six archetypal bicycles in an anechoic chamber. The RSSI sample set per angle and antenna position is characterized statistically and input into an empirical model of the gain pattern of the bicycle-antenna system. We define a bicycle-to-X propagation model that pairs the proposed bicycle-antenna gain and a log-distance shadowing path loss model, and conduct outdoor measurement campaign for evaluation. We observe that the gain model measured in chamber matches the measured RSSI at small distances, whereas at larger distances it provides less accuracy.
- A Clockless Synchronisation Framework for Cooperating Mobile RobotsPublication . Oliveira, Luis; Almeida, Luis; Mossé, DanielCooperating mobile robots are real-time systems that often require mutual synchronisation, either to carry out cooperative sensing and actuation, or to improve the quality of wireless communications. Concerning this last aspect, a common technique to improve the communication channel is to eliminate access collisions by allocating predefined disjoint time slots to robots, in a circular list, which is known as Time Division Multiple Access (TDMA). This technique typically requires a global clock to identify each slot. However, this method is not robust with respect to asynchronous transmissions generated by external or joining nodes. Consequently, this work proposes a global TDMA protocol that allows for real-time and guaranteed delivery of messages within deadlines, given its predictable schedule, and that: i) applies to dynamic mesh networks of cooperating mobile robots; ii) synchronises slots in a relative fashion using locally perceived delays of message exchanges that are globalised throughout the network, thus not relying on a global clock; and iii) tolerates external traffic and asynchronous joining robots using underneath standard ad-hoc wireless RF technologies that provide CSMA-type arbitration. We describe our protocol and prove that under common operating conditions all robots eventually reach synchronisation. We also propose a heuristic for the few cases that were not covered by the previous proof, which always led to consensus under extensive simulation testing. To the best of our knowledge, this is the first guaranteed clockless synchronisation approach for ad-hoc networks of mobile robots that works over commodity wireless protocols.
- Comparing Admission Control Architectures for Real-Time EthernetPublication . Alvarez, Ines; Moutinho, Luis; Pedreiras, Paulo; Bujosa, Daniel; Proenza, Julian; Almeida, LuisIndustry 4.0 and Autonomous Driving are emerging resource-intensive distributed application domains that deal with open and evolving environments. These systems are subject to stringent resource, timing, and other non-functional constraints, as well as frequent reconfiguration. Thus, real-time behavior must not preclude operational flexibility. This combination is motivating ongoing efforts within the Time Sensitive Networking (TSN) standardization committee to define admission control mechanisms for Ethernet. Existing mechanisms in TSN, like those of AVB, its predecessor, follow a distributed architecture that favors scalability. Conversely, the new mechanisms envisaged for TSN (IEEE 802.1Qcc) follow a (partially) centralized architecture, favoring short reconfiguration latency. This paper shows the first quantitative comparison between distributed and centralized admission control architectures concerning reconfiguration latency. Here, we compare AVB against a dynamic real-time reconfigurable Ethernet technology with centralized management, namely HaRTES. Our experiments show a significantly lower latency using the centralized architecture. We also observe the dependence of the distributed architecture in the end nodes' performance and the benefit of having a protected channel for the admission control transactions.
- Comparing the Ecological Footprint of Intersection Management Protocols for Human/Autonomous ScenariosPublication . Reddy, Radha; Almeida, Luis; Santos, Pedro M.; Tovar, EduardoThe design of Intelligent Intersection Management (IIM) schemes for fully Autonomous Vehicles (AVs) and mixed with Human-driven Vehicles (HVs) has focused mainly on throughput maximization and users’ safety. However, new IIM strategies should consider environmental factors and human health conditions in their design, given their impact on fuel wastage and emission of dangerous air pollutants. In this paper, we compare the ecological footprint of two IMM protocols that follow opposite paradigms in handling AVs and HVs with an internal combustion engine. We consider Round-Robin (RR) that favors the crossing of multiple consecutive cars from one road at a time and the recently proposed Synchronous Intersection Management Protocol (SIMP) that favors the crossing of multiple cars simultaneously, one from each road. Through experiments in the SUMO simulator, we observe that SIMP promotes more fluid traffic flows, causing traffic throughput to be up to 3.7 times faster and consume less fuel than the RR schemes, with similar results for vehicular emissions (PMx, NOx, CO, CO 2 , and HC).
- Complex Intersections with a Dedicated Road Lane per Crossing DirectionPublication . Reddy, Radha; Almeida, Luis; Santos, Pedro M.; Tovar, EduardoComplex intersections are often busier with a separate road lane per crossing direction, i.e., left, straight, and right. These intersections eliminate the diverging and merging conflicts; thus, vehicles only fall under crossing conflicts within intersections. However, the traditional way of serving vehicles from one road at a time increases traffic congestion and hinders performance. To address this issue, we extended the synchronous framework for complex intersections with a separate road lane per crossing direction, which was initially presented for single-lane and two-lane intersections in which roads are shared among vehicles with different crossing directions. We compare the performance of our synchronous framework against the traditional Round-Robin (RR) intersection management approach.