Browsing by Author "Robles, Ramiro"
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- 5G network as key-enabler for vehicular platooningPublication . Duarte, Paulo; Soyturk, Mujdat; Robles, Ramiro; Araújo, Marco; Yaman, Berkay; Goes, Adriano; Mendes, Bruno; Javanmardi, Gowhar; Gutiérrez Gaitán, MiguelThe future of goods transportation will rely on increased efficiency, lower risks, and diminished delays through the use of vehicle platoons that benefit from vehicular connectivity using V2X (Vehicle to Everything) applications. This article describes a system that offers the aforementioned vehicular connectivity to platoons, based on AI-enhanced 5G for resource allocation in wireless platoon intra-communications under three scenarios (latency emergency braking, platoon wireless resource management in tunnels, V2X communications interference in a traffic congestion). Demos are described for each of the scenarios, targeting different layers, starting by the PHY (physical) layer where propagation models are implemented, then a simulation-based MAC (medium access control) layer that allows the allocation of resources to the connected User Equipments (UE) and finally a management and orchestration layer capable of monitoring and managing the radio network, offering features such as network slicing management using O-RAN (Open Radio Access Network) standards.
- Active Flow Control for Aerospace Operations by means of a Dense Wireless Sensor and Actuator NetworkPublication . Robles, Ramiro; Loureiro, João; Tovar, Eduardo; Viana, Júlio; Cintra, João; Rocha, AndréThis paper presents the design of an active flow control (AFC) system for commercial aircraft based on a dense wired/wireless sensor and actuator network. The goal is to track gradients of pressure across the surface of the fuselage of commercial aircraft. This collected information will be used to activate a set of actuators that will attempt to reduce the skin drag effect produced by the separation between laminar and turbulent flows. This will be translated into increased lift-off forces, higher speeds, longer ranges and reduced fuel consumption. The paper describes the architecture of the system in the context of the European research project DEWI (dependable embedded wireless infrastructure) using the concept of the DEWI Bubble. A simulator architecture is also proposed to model each process of the AFC system and the DEWI Bubble. To the best of our knowledge this is the first approach towards the use of wireless sensor technologies in the field of active flow control.
- Active Flow Control using Dense Wireless Sensor and Actuator NetworksPublication . Robles, Ramiro; Viana, Júlio; Loureiro, João; Cintra, João; Rocha, André; Tovar, EduardoThis paper describes the design of an active flow control (AFC) system for aeronautics applications based on dense wireless sensor and actuator networks (WSANs). The objective of this AFC system is to track gradients of pressure (or wall shear stress) across the surface of the fuselage of commercial aircraft. This collected information is used to activate a set of actuators that will attempt to reduce the skin drag effect produced by the separation between laminar and turbulent flows. This is expected to be translated into increased lift-off forces, higher vehicle speeds, longer ranges and reduced fuel consumption. The paper describes the architecture of the system in the context of the European research project DEWI (dependable embedded wireless infrastructure) using the concept of the DEWI Bubble and its three-tier architecture especially designed to ensure dependability and interoperability in industrial WSANs. A system-level simulator is also proposed to model each process of the AFC system and the aeronautics DEWI Bubble infrastructure, highlighting the interactions between the network simulation and the results of the computational fluid dynamics (CFD) simulation. The key element in the proposed solution is a polygonal patch of wired sensors and actuators. This patch is provided with a wireless link to a central coordinator or access point conveniently located in the aircraft to maximize coverage to a network of distributed patches. A trade-off between scalability, size of the patches, fluid speed/viscosity, sampling sensor and actuator rates in space and time, and the capacity/delay characteristic of the wireless inter-patch and the wireline intra-patch communication technologies is also here discussed. The hybrid wireless/wired sensor and actuator network achieves great flexibility, scalability, manageability, troubleshooting, and modularity as compared to a solution exclusively based on wireline or wireless components. The final details of the prototype and results in a wind tunnel test-bed are here described, demonstrating the validity of the concept and the use of wireless technologies for aeronautical applications (flexible architecture and innovative services). Future issues regarding security, safety and trustiness of the AFC system are also briefly introduced in the context of the spin-off European project SCOTT (secure connected trusted things).
- Adding Quality in the User Requirements Specification A first approachPublication . Guerra-García, César; Caballero, Ismael; Cardenas-Juarez, Marco; Robles, RamiroUsers need trusting in data managed by software applications that are part of Information Systems (IS), which supposes that organizations should assuring adequate levels of quality in data that are managed in their IS. Therefore, the fact that an IS can manage data with an adequate level of quality should be a basic requirement for all organizations. In order to reach this basic requirement some aspects and elements related with data quality (DQ) should be taken in account from the earliest stages of development of software applications, i.e. “data quality by design”. Since DQ is considered a multidimensional and largely context-dependent concept, managing all specific requirements is a complex task. The main goal of this paper is to introduce a specific methodology, which is aimed to identifying and eliciting DQ requirements coming from different viewpoints of users. These specific requirements will be used as normal requirements (both functional and non-functional) during the development of IS awareness of data quality.
- Joint Beamforming, Terminal Scheduling, and Adaptive Modulation with Imperfect CSIT in Rayleigh Fading Correlated Channels with Co-channel InterferencePublication . Robles, Ramiro—This paper presents a resource allocation algorithm for multi-user wireless networks affected by co-channel interference. The analysis considers a network with one base station (BS) that uses a multiple antenna transmitter (beamformer) to schedule (in a time-division manner) transmissions towards a set of J one-antenna terminals in the presence of K persistent interferers. The transmitter is assumed to employ MaximumRatio Combining (MRC) beamforming with spatially-correlated branches and channel envelopes modelled as Rayleigh-distributed processes. The BS has access to an imperfect (outdated) copy of the instantaneous Channel State Information (CSI) of each terminal. Based on this CSI at the transmitter side (CSIT), the BS proceeds to select (at each time interval or time-slot) the terminal with the highest channel strength for purposes of transmission. This imperfect CSIT is also used to calculate the coefficients of the beamformer that will be used to transmit information towards the scheduled terminal, as well as for selecting the most appropriate modulation format (threshold-based decision). In addition, the transmission towards each scheduled terminal is assumed to experience persistent co-channel interference that will degrade the quality of the information reception process. The main merits of this work are the following: 1) joint analysis of MRC-based beamforming, terminal scheduling based on maximum channel strength, and modulation assignment, and 2) joint modelling of the effects of spatial correlation, co-channel interference and imperfect CSIT. Results suggest that scheduling helps in rejecting co-channel interference and the degrading effects of imperfect CSIT. Spatial correlation could some times lead to better performance than the uncorrelated case, particularly in the low SNR (Signal-to-Noise Ratio) regime. Conversely, uncorrelated branches always outperform the correlated case in the high SNR regime. The use of higher numbers of antennas also improve performance of the system. However, spatial correlation tends to accumulate over the antenna array thus leading to a more noticeable performance degradation and more allocation errors due to the outdated CSIT assumption.
- Joint spectrum and antenna selection diversity for V2V links with ground reflectionsPublication . Robles, Ramiro; Gutiérrez Gaitán, Miguel; Javanmardi, Gowhar; Kurunathan, HarrisonThis paper addresses the study of a fading-rejection algorithm based on joint spectrum and antenna selection in a vehicle-to-vehicle (V2V) multiple antenna system. The central objective of this selective scheme is to provide resilience against the destructive effects of the superposition of line-of-sight (LOS) and ground-reflected signals. The paper also provides an extension to channels that combine such deterministic superposition of multiple paths and reflections with an uncorrelated double scattering component, which shows how the algorithm is also beneficial under more general channel modelling assumptions. A multiple-ray performance model is used to describe the deterministic signal interactions between multiple antennas across contiguous vehicles. The antenna selection component is shown to reject deterministic fading, particularly at short values of the inter-vehicular distance. By contrast, when the spectrum bands are correctly chosen, the spectrum selection component can exhibit gains for a wider range of inter-vehicular distances than its antenna selection counterpart. This indicates that both components of the proposed solution are, in some cases, complementary, and therefore, they should be considered together in V2V multiple antenna design. Derivation of the statistics of the selective scheme considering an additional double scattering stochastic channel component is here proposed. Simulation results from all expressions show important gains for a given range of inter-vehicular distances.
- Network Diversity Multiple Access in Rayleigh Fading Correlated Channels with Imperfect Channel and Collision Multiplicity EstimationPublication . Robles, Ramiro; Tovar, Eduardo; McLernon, Desmond C.; Ghogho, MounirNetwork diversity multiple access or NDMA is the family of algorithms with the highest potential throughput in the literature of signal-processing-assisted random access. NDMA uses the concept of \emph{protocol-induced retransmissions} to create an adaptive source of physical (PHY) layer diversity. This adaptive diversity is used to resolve packet collisions (via signal separation) without the explicit need (or as a complement) of a multiple antenna receiver. This paper proposes a further improvement on the modelling of NDMA by considering the effects of imperfect channel and collision multiplicity estimation. In addition, this work considers channel correlation between consecutive retransmissions (i.e., temporal correlation). Conventionally, the analysis of NDMA assumes that any error in the collision multiplicity estimation translates into the loss of all contending packets. This is an optimistic assumption because even when the multiplicity has been correctly estimated, errors can still occur. On the other hand, it is also pessimistic because correct reception can also occur when the multiplicity has been incorrectly estimated. This paper presents a more detailed study of the performance of NDMA considering these more specific detection/reception cases.
- On the Throughput Region of Wireless Random Access Protocols with Multi-Packet Reception using Multi-Objective OptimizationPublication . Robles, RamiroThis paper presents a new approach for the analysis and characterization of the throughput region of wireless random access protocols enabled with multi-packet reception (MPR) capabilities. The derivation of a closed-form expression for the envelope of the throughput region under the assumption of an arbitrary number of terminals is an open issue in the literature. To partially fill this gap, a new method based on multi-objective optimization tools is herein presented. This innovative perspective allows us to identify the envelope of the throughput region as the Pareto frontier solution that results from maximizing simultaneously all individual terminal throughput functions. To simplify this problem, a modified MPR model is proposed that mimics the conditions of collision model protocols, but it also inserts new physical (PHY) layer features that allow concurrent transmission or MPR. The N-reception model is herein introduced, where collisions of up to N signals are assumed to be always correctly resolved from a population of J terminals, where N can be related to the number of antennas or degrees of freedom of the PHY-layer used at the receiver to resolve a collision. It is shown that by using this model and under the assumption of N=J−1 , the Pareto frontier expression can be obtained as a simple extension of the ALOHA solution. Unfortunately, for cases with N
- Orthogonal Space-Time Block Coding for Double Scattering V2V Links with LOS and Ground ReflectionsPublication . Gaitán, Miguel Gutiérrez; Javanmardi, Gowhar; Robles, RamiroThis work presents the performance analysis of space-time block codes (STBCs) for vehicle-to-vehicle (V2V) fast-fading channels in scenarios with modified line-of-sight (LOS). The objective is to investigate how the V2V MIMO (multiple-input multiple-output) system performance is influenced by two important impairments: deterministic ground reflections and an increased Doppler frequency (time-variant channels). STBCs of various coding rates (using an approximation model) are evaluated by assuming antenna elements distributed over the surface of two contiguous vehicles. A multi-ray model is used to study the multiple constructive/destructive interference patterns of the transmitted/received signals by all pairs of Tx–Rx antenna links considering ground reflections. A double scattering model is used to include the effects of stochastic channel components that depend on the Doppler frequency. The results show that STBCs are capable of counteracting fades produced by destructive self-interference components across a range of inter-vehicle distances and for a range of Doppler frequency values. Notably, the effectiveness of STBCs in deep fades is shown to outperform schemes with exclusive receive diversity, despite the interference created by the loss of orthogonality in time-varying channels with a moderate increase of Doppler frequency (mainly due to higher vehicle speeds, higher frequency or shorter time slots). Higher-order STBCs with rate losses are also evaluated using an approximation model, showing interesting gains even for low coding rate performance, particularly when accompanied by a multiple antenna receiver. Overall, these results can shed light on how to exploit transmit diversity in time-varying vehicular channels with modified LOS.
- Performance Analysis of MRC Receivers with Adaptive Modulation and Coding in Rayleigh Fading Correlated Channels with Imperfect CSITPublication . Robles, Ramiro; Lavendelis, Egons; Tovar, EduardoThis paper addresses the performance analysis of an adaptive wireless link with one antenna transmitter and a multiple antenna maximum-ratio combining (MRC) receiver. Two main assumptions are used in this paper: (1) Rayleigh fading correlated channels (i.e., MRC branch correlation) and (2) imperfect (outdated) channel state information at the transmitter (CSIT) side. he main contribution of this work lies in the derivation of analytic expressions (in terms of a series expansion) of the statistics of correct packet reception conditional on the decisions made by the transmitter based on outdated CSIT. he novelty of this derivation is the joint modelling of spatially correlated branches, imperfect CSIT, and adaptive modulation based on threshold-trigger decision. Contrary to common belief, the results presented here suggest that spatial correlation not always afects the performance of the MRC receiver: at low signal-to-noise ratio (SNR), correlation can improve performance rather than degrading it. In contrast, at high SNR, correlation is found to always degrade performance. At high SNR, correlation tends to worse the degrading efects of imperfect CSIT, particularly when the number of antennas increases. Imperfect CSIT causes errors in the assignment of MCSs, thus reducing throughput performance. hese errors become more evident in the high SNR regime, particularly when the values of branch correlation and the number of antennas increase.