Browsing by Author "Santos, Pedro M."
Now showing 1 - 10 of 16
Results Per Page
Sort Options
- 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.
- Demonstrating RA-TDMAs+ for robust communication in WiFi mesh networksPublication . Almeida, Diogo; Gutiérrez Gaitán, Miguel; D'Orey, Pedro; Santos, Pedro M.; Pinto, Luís; Almeida, LuisThis work will demonstrate a new flavor of the RA-TDMA set of protocols, namely RA-TDMAs+, which uses IEEE-802.11 (WiFi) COTS hardware in ad-hoc mode to set up a dynamic mesh network of mobile nodes with highbandwidth. The protocol uses topology tracking to configure the TDMA frame and robust relative synchronization to define the TDMA slots without resorting to a global clock and in the presence of interfering traffic. The demo will set up a small-scale testbed using COTS hardware, thus evidencing the feasibility of the approach, and it will show 1clive plots 1d of the temporal (synchronization) and topological views of the network.
- Development of a Hardware in the Loop Ad- Hoc Testbed for Cooperative Vehicles PlatooningPublication . Vasconcelos Filho, Ênio; Mendes, Bruno; Santos, Pedro M.; Tovar, EduardoCooperative Cyber-Physical Devices (Co-CPS) are reaching into the most diverse areas and pose new integration challenges. This is particularly true between cooperative autonomous machines, where safety and reliability must often be guaranteed without human presence. Among these scenarios, Cooperative Vehicular Platooning (Co-VP) applications present an exciting promise: improving road occupation, reducing accidents, and providing fuel savings. However, due to their high complexity and safety-critical characteristics, these applications must be validated to ensure their reliability before being applied in real scenarios, particularly regarding their underlying communication transactions. This paper presents an architecture for validating a Co-VP system via Hardware In the Loop (HIL) integration of IEEE 802.11 communications, and co-simulation support of a 3D simulator. We propose a use case with one scenario of communication profile according to the ETSI IT-G5 model and information exchange frequencies between the vehicles. Through these scenarios that mimic realistic conditions of Co-VP applications, we observe the impacts of such variations on the number of messages, network delays, and lateral and longitudinal platoon errors.
- EDF Scheduling and Minimal-Overlap Shortest-Path Routing for Real-Time TSCH NetworksPublication . Gutiérrez Gaitán, Miguel; Almeida, Luis; Santos, Pedro M.; Meumeu Yomsi, PatrickWith the scope of Industry 4.0 and the Industrial Internet of Things (IIoT), wireless technologies have gained momentum in the industrial realm. Wireless standards such as WirelessHART, ISA100.11a, IEEE 802.15.4e and 6TiSCH are among the most popular, given their suitability to support real-time data traffic in wireless sensor and actuator networks (WSAN). Theoretical and empirical studies have covered prioritized packet scheduling in extenso, but only little has been done concerning methods that enhance and/or guarantee real-time performance based on routing decisions. In this work, we propose a greedy heuristic to reduce overlap in shortest-path routing for WSANs with packet transmissions scheduled under the earliest-deadline-first (EDF) policy. We evaluated our approach under varying network configurations and observed remarkable dominance in terms of the number of overlaps, transmission conflicts, and schedulability, regardless of the network workload and connectivity. We further observe that well-known graph network parameters, e.g., vertex degree, density, betweenness centrality, etc., have a special influence on the path overlaps, and thus provide useful insights to improve the real-time performance of the network.
- Edge-aided V2X collision avoidance with platoons: Towards a hybrid evaluation toolsetPublication . Pereira, João; Kurunathan, Harrison; Filho, Ênio; Santos, Pedro M.Infrastructure-brokered collision avoidance is an Intelligent Transportation Systems (ITS) application built on top of Vehicle-to-Everything (V2X) links. An edge-hosted ITS service receives information from road-side sensors (or CAM messages in V2X-enabled vehicles) and detects impending collisions where vehicles cannot sense or contact each other directly. If so happens, it issues a warning message through network-to-vehicle links. Another relevant ITS application is platooning, through which vehicles following each other closely can benefit of improved fuel economy, and that can be further enhanced through communication. In case of emergency braking in platoons, the response times of network and edge-hosted services must be minimal to ensure no collision amongst the platoon or any other road user. In this paper we present the implementation of a simulation framework tailored (but not limited) to evaluate the presented use-case. This complex and multi-layered use-case can be handled by a dedicated ITS service that leverages the sensing, radio and computing resources available at infrastructure and vehicles, and requires a realistic evaluation framework prior to deployment. Such framework is mostly based on simulation, albeit, to the extent possible, actual devices or services should be used; the present work is a step towards that hybrid setup.
- Empirical Evaluation of Short-Range WiFi Vessel-to-Shore Overwater CommunicationsPublication . d'Orey, Pedro; Gutiérrez Gaitán, Miguel; Santos, Pedro M.; Ribeiro, Manuel; Sousa, J. Borges de; Almeida, LuísUnmanned vehicles used in ocean science, defense operations and commercial activities collect large amounts of data that is further processed onshore. For real-time information exchange, the wireless link between the unmanned vehicle and onshore devices must be reliable. In this work, we empirically evaluate a WiFi link between an autonomous underwater vehicle on the surface and an onshore device under real-world conditions. This work allowed i) collecting a large-scale realistic dataset and ii) identifying major factors impairing communication in such scenarios. The TX-RX antenna alignment, the operation mode (manual vs automatic) and varying reflecting surface induced by AUV mobility lead to sudden changes (e.g. nulls) in the received signal strength that can be larger than 20 dB. This study provides useful insights to the design of robust vessel-to-shore short-range communications.
- Empirical Performance Models of MAC Protocols for Cooperative Platooning ApplicationsPublication . Aslam, Aqsa; Santos, Pedro M.; Santos, Frederico Miguel; Almeida, LuisVehicular ad-hoc networks (VANET) enable vehicles to exchange information on traffic conditions, dynamic status and localization, to enhance road safety and transportation efficiency. A typical VANET application is platooning, which can take advantage of exchanging information on speed, heading and position to allow shorter inter-vehicle distances without compromising safety. However, the platooning performance depends drastically on the quality of the communication channel, which in turn is highly influenced by the medium access control protocol (MAC). Currently, VANETs use the IEEE 802.11p MAC, which follows a carrier sense multiple access with collision avoidance (CSMA/CA) policy that is prone to collisions and degrades significantly with network load. This has led to recent proposals for a time-division multiple access (TDMA)-based MAC that synchronize vehicles’ beacons to prevent or reduce collisions. In this paper, we take CSMA/CA and two TDMA-based overlay protocols, i.e., deployed over CSMA/CA, namely PLEXE-slotted and RA-TDMAp, and carry out extensive simulations with varying platoon sizes, number of occupied lanes and transmit power to deduce empirical models that provide estimates of average number of collisions per second and average busy time ratio. In particular, we show that these estimates can be obtained from observing the number of radio-frequency (RF) neighbours, i.e., number of distinct sources of the packets received by each vehicle per time unit. These estimates can enhance the online adaptation of distributed applications, particularly platooning control, to varying conditions of the communication channel.
- Experimental Evaluation of Urban Points-of-Interest as Predictors of I2V 802.11 Data TransfersPublication . Santos, Pedro M.; M. Sousa, Luís; Aguiar, AnaSmart Cities will leverage the Internet-of-Things (IoT) paradigm to enable cyber-physical loops over urban processes. Vehicular backhauls contribute to IoT platforms by allowing sensor/actuator nodes near roads to explore opportunistic connections to passing vehicles when other communication backhauls are unavailable. A placement process of nodes that includes vehicular networks as a connectivity backhaul requires estimates of infrastructure-to-vehicle (I2V) wireless service at potential deployment sites. However, carrying out I2V measurement campaigns at all potential locations can be very expensive; so, predictive models are necessary. To this end, qualitative characteristics of a potential site, such as infrastructural points-of-interest (POI) relating to traffic (i.e., traffic lights, crosswalks) and fleet activities (i.e., bus stops, garbage bins) can inform about the vehicles' mobility patterns and quality of the I2V service. In this paper, we show the contribution of POI (and site-specific information) to I2V transfers, leveraging a real-world dataset of geo-referenced I2V WiFi link measurements in urban settings. We present the distributions of throughput with respect to distance per POI class and site, and apply exponential regression to obtain practical throughput/distance models. We then use these models to compare I2V transfer estimation methodologies with different levels of POI-specific data and data resolution. We observe that I2V transfer estimate accuracy can improve from an average over-estimation of 18.3% with respect to measured values, if site or POI-specific information metrics are not used, to 9.3% in case such information is used.
- A Glimpse at Bicycle-to-Bicycle Link Performance in the 2.4GHz ISM BandPublication . Santos, Pedro M.; Pinto, Luis; Aguiar, Ana; Almeida, LuisBicycle-to-bicycle (Bi2Bi) communication can be implemented by well-established technologies in the 2.4GHz ISM band: IEEE 802.11, Bluetooth or IEEE 802.15.4. These technologies have distinct performance due to different physical and data link layers. In this paper, we characterize the mentioned 2.4 GHz-operating technologies over opportunistic links established between bicycles using commodity hardware. We find that, in Bi2Bi links, Blue-tooth, IEEE 802.11 at 24 Mbit/s, and IEEE 802.11 with automatic rate adaptation can communicate only in the immediate surroundings (under 15m of range), to maxima of 1.5 Mbit/s, 17 Mbit/s and 25 Mbit/s, respectively. IEEE 802.15.4 and IEEE 802.11 at 1 Mbit/s sustain connectivity up to 30 and 40 meters and peak transfer rates of 50 kbit/s and 800 kbit/s respectively. In addition, we observed that, in all measurement scenarios, link performance depended strongly on whether bicycles were approaching or moving away, rather than on whether one was at the front or back of the other.