Percorrer por autor "Santos, Frederico"
A mostrar 1 - 6 de 6
Resultados por página
Opções de ordenação
- 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.
- Feasibility of Gateway-Less IoT E-Health ApplicationsPublication . Pereira, Carlos; Guimarães, Diana; Mesquita, João; Santos, Frederico; Almeida, Luis; Aguiar, AnaMachine-to-Machine (M2M) communications are a key enabler of Internet of Things (IoT) applications. One domain with growing interest in M2M/IoT is e-health, either for self-monitoring, home monitoring, or hospital systems. However, current sensing devices in this domain rely on short-range communication protocols that require a gateway (GW) for Internet connection. Smartphones have been proposed as GWs in mobile M2M communications due to their enhanced connectivity and sensing capabilities. However, the GW functionality impacts on the smartphone usability, causing undesirable battery depletion and the smartphone itself increases the overall cost of e- health solutions. In this work, we propose converging e-health devices and Wi-Fi towards direct Internet access through the existing Wi-Fi infrastructure and by-passing current GWs. We use recent low-cost ultra low-power Wi-Fi modules and feature them with M2M capabilities supporting their integration in an interoperable e-health framework. We present results on end-to-end latency and power requirements within a concrete e-health use case that show the feasibility of the proposed GW-less solution.
- A Flexible TDMA Overlay Protocol for Vehicles PlatooningPublication . Aslam, Aqsa; Almeida, Luis; Santos, FredericoVehicular Ad-hoc Networks (VANETs) can enable a wide range of vehicle coordination applications such as platooning. A good use of the communication channel is paramount for an adequate quality of service. Currently, IEEE 802.11p is the standard used in VANETs and relies on CSMA/CA, which is prone to collisions that degrade the channel quality. This has led to recent proposals for TDMA-based overlay protocols that synchronize vehicles beacons to prevent or reduce collisions. In this paper, we propose RA-TDMAp that puts together properties of two previous works. On one hand, it allows the nodes in one platoon to remain synchronized even in the presence of interfering traffic, e.g. from other vehicles, by adapting the phase of the TDMA round to escape periodic interference. On the other hand, it reduces channel occupation by having just the leader transmitting with high power, to reach all the platoon at once, while the followers transmit with low power. The order of transmission is such that the leader gathers information from the whole platoon in just one round. We simulated RA-TDMAp in realistic conditions using the PLEXE simulation framework. We show the phase adaptation of the TDMA round and we compare RA-TDMAp to state of the art protocols tailored for platooning, with three networking metrics: channel busy ratio, collisions and safe time ratio, all of which confirm the superiority of RA-TDMAp.
- Impact of Platoon Size on the Performance of TDMA-Based MAC ProtocolsPublication . Aslam, Aqsa; Almeida, Luís; Santos, FredericoVehicular networks are a core component in Intelligent Transportation Systems (ITS) enabling communication among vehicles for collaborative applications. One example of such an application that may bring benefits in reducing travel time, fuel consumption and improving safety is platooning. This application coordinates a group of vehicles that travel together, doing automatic control of inter-distances and speeds [1]. A critical part of this application is the vehicle-to-vehicle (V2V) communication highlighting the importance of improving the channel quality. Existing ITS standards, namely WAVE (USA) and ITS-G5 (Europe), use IEEE 802.11p DSRC (Dedicated Short-Range Communication) [2] that relies on CSMA/CA distributed access arbitration. Despite the Collision Avoidance attribute collisions can still occur and the channel quality can degrade significantly in dense traffic environments.
- Reconfiguring TDMA Communications for Dynamic Formation of Vehicle PlatoonsPublication . Aslam, Aqsa; Santos, Frederico; Almeida, LuísPlatooning is a promising concept used within the Intelligent Transportation System to increase efficiency and safety of road transportation. It is based on periodically sharing the kinematic status of the platoon members to allow reducing inter-vehicle distances in a safe way. This coordination is automatic and depends heavily on the wireless channel. A common technique to improve the channel properties is to use Time-Division Multiple Access (TDMA) that organizes the access to the wireless medium in slots assigned exclusively to each vehicle. However, while platoons are physical and dynamic, the corresponding dynamic reconfiguration of a logical TDMA frame is non-trivial. In this paper we address this Cyber-Physical problem resorting to the RA-TDMAp protocol to track the dynamics of a platoon, specifically joining, merging and leaving. In our solution, we include an adequate admission control block, to verify whether joining or merging can be accepted, and we present the state-machine that handles the reconfiguration process. We validate our TDMA reconfiguration mechanism with simulations using the Plexe/Vein/OMNeT++ framework. We show the effectiveness of the proposed mechanisms which ensures a synchronized start of the platoon control with the TDMA frame reconfiguration.