FCT: DEE - Documentos de conferências internacionais
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- A Scalable LDPC Coding Scheme for Adaptive HARQ TechniquesPublication . Madeira, João; Viana, Joseanne; Guerreiro, João; Dinis, Rui; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações; UNINOVA-Instituto de Desenvolvimento de Novas TecnologiasIn wireless communication systems, the achievable data rates are always dependent on the characteristics of the wireless channel. Although a system is designed for an expected channel link quality, the channel may deteriorate for certain periods of time due to the changing nature of the propagation environment. A weak channel may lead to transmission errors, which can be corrected by employing Hybrid Automatic Repeat Requests (HARQ). In particular, type II HARQ protocols have become an appealing option since they only involve the transmission of additional parity bits, instead of repeating the original transmission. These additional parity bits can be obtained by puncturing a low rate channel code. However, finding an optimum pattern of puncturing for a specific code is non-trivial. In this work, we propose a retransmission scheme that considers various Low-Density Parity-Check (LDPC) codes of different rates that can be concatenated to perform the encoding and decoding operations, resulting in a lower encoding overhead for successful transmissions, while maintaining efficient decoding. We show that this technique can maintain high throughput and goodput, and a low outage probability, even when the received signal power is suddenly reduced due to the loss of the Line-of-sight (LOS) component.
- Residual Self-Interference Estimation in In-Band Full-Duplex Wireless SystemsPublication . Irio, Luís; Abusabah, Ayman T.; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 TelecomunicaçõesIn this paper, we present a novel method to estimate the distribution of the residual self-interference (SI) power of an in-band Full-duplex (IBFDX) system. Considering the residual SI distribution caused by the uncanceled SI in a post-mixer scheme due to a single propagation tap, we propose a framework capable of estimating the residual SI distribution. The estimator relies on the computation of two estimated parameters, which takes advantage of using the method of moments of the residual SI distribution in a straightforward manner. Additionally, we assess the accuracy of the proposed estimators, considering different sample set lengths adopted in the estimation process. The results testify the quality of the estimation method and its ability to achieve high accuracy, even for a reduced number of samples. This work is of practical importance, particularly when the residual self-interference is mainly due to a line-of-sight component, where the proposed technique can use a small set of samples to predict the residual interference in an accurate way.
- In-Band Full-duplex Residual Self-interference Approximation in Multi-tap Delay Fading ChannelsPublication . Abusabah, Ayman T.; Irio, Luís; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 TelecomunicaçõesResidual self-interference (SI) is primarily a key challenge when designing In-Band Full-duplex (IBFDX) wireless systems. Channel estimation errors are one of the major causes of the residual SI. The SI channel is composed by multiple fading taps which makes the characterization of the residual SI more challenging as multiple copies of the transmitted signal, with variable delays and gains, are eventually aggregated at the receiver. In this paper, we derive an approximation for the distribution of the residual SI power in multi-tap delay fading channels. In particular, we show that under specific conditions the multi-tap fading channel can be represented by a summation of non-identical independent gamma distributions. In a further step, we approximate the summation of the gamma distributions using the Welch-Satterthwaite equation, obtaining a closed form expression for the distribution of the residual SI power. The accuracy of the theoretical approach is evaluated through simulation results. The similarity comparison between simulated data and the proposed model indicates a high accuracy of the adopted approximation when considering low fading uncertainty associated to the taps and low estimation errors. On the other hand, the accuracy of the approximation slightly decreases for higher uncertainty fading scenarios and for higher estimation errors. However, as a final remark, we highlight that the results computed with the model are close to the simulated ones and for most of the applications the model's error can be negligible.
- Optimization-based Determination of TFT Contact Resistances in PythonPublication . Fino, Maria Helena; DEE - Departamento de Engenharia Electrotécnica e de ComputadoresThe paper presents an optimization-based methodology for the determination of thin-film transistors series contact resistancefigmethodology in Python is presented. The validity of results obtained against experimental devices characteristics is demonstrated. The advantage and limitations of the proposed methodology are also discussed.
- Cooperative Platooning and Servicing for Spacecraft Formation Flying using Model Predictive ControlPublication . Pereira, Pedro; Guerreiro, Bruno; Lourenço, Pedro; DEE - Departamento de Engenharia Electrotécnica e de Computadores; CTS - Centro de Tecnologia e Sistemas; UNINOVA-Instituto de Desenvolvimento de Novas TecnologiasThis paper addresses two complementary problems of spacecraft formation flying, namely spacecraft platooning and on-orbit spacecraft servicing, using Model Predictive Control (MPC). With the proposed solutions, these space formation scenarios can be regarded as a cooperative system composed of several spacecraft with a common goal, which may have clear advantages relative to other approaches. For each application scenario, a different optimization problem and MPC design is presented, including relevant constraints to deal with physical limitations, visibility problems, and also to guarantee a collision-free trajectory from other spacecraft or obstacles. The proposed methods are validated with realistic simulation results, showing that all vehicles demonstrate reliable performance following a given trajectory or goal in a formation, while satisfying all the considered constraints.
- Capacity and Energy Efficiency Trade-off in Multi-Packet Reception Wireless SystemsPublication . Abusabah, Ayman T.; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de ComputadoresThe radio access in Internet-of-Things (IoT) networks requires minimizing the energy consumption while achieving the capacity requirements especially for high density deployment. The Multi-Packet Reception (MPR) systems can potentially increase the capacity of devices due to the capability of decoding multiple transmitted packets at the receiver. However, the aggregate interference in such scenarios can lead to unfair distribution of the resources and eventually waste of energy. Therefore, this work provides an analytical characterization of the trade-off between capacity and energy consumption while regulating the channel access of multiple transmitters to a single-MPR receiver. The theoretical modeling considers different densities of spatially distributed nodes and their channel propagation conditions, in addition to different capture sensitivity thresholds at the receiver. The model is validated through simulation and it is shown to be an effective tool to identify the optimal channel access probability that maximizes the capacity per energy consumption.
- Improving Attack Trees Analysis using Petri Net modeling of Cyber-AttacksPublication . Pasandideh, Shabnam; Gomes, Luis; Maló, Pedro; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CTS - Centro de Tecnologia e Sistemas; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-C1 Sistemas Digitais e PercepcionaisCyber security is one general concern to all network-based organizations. In recent years, by significant increasing cyber-attacks in critical infrastructures (CIs) the need of smart prediction, awareness and protection systems is not deniable. The first step for security assessment is on recognizing and analyzing attacks. In this paper, one of the graphical security assessments named Attack Tree (AT) is used to illustrate one kind of cyber-attacks scenario in Industry 4.0 and the system's behavior is analyzed by Petri Nets.
- Welcome to YEF-ECE 2021Publication . Camarinha-Matos, Luís; Martins, João; DEE - Departamento de Engenharia Electrotécnica e de Computadores; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CTS - Centro de Tecnologia e Sistemas; DEE2010-C2 Robótica e Manufactura Integrada por Computador; DEE2010-B1 Energia
- Abnormal Signaling SIP Dialogs Detection based on Deep LearningPublication . Pereira, Diogo; Oliveira, Rodolfo; Kim, Hyong S.; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 TelecomunicaçõesThe detection of abnormal sequences of SIP messages in real-time is crucial to avoid SIP signaling-based attacks. In this paper, we propose a deep learning approach to detect signaling patterns of multimedia sessions established with the Session Initiation Protocol (SIP). The approach is based on a recurrent neural network (RNN). We study the performance of different Long Short-term Memory (LSTM) RNN architectures, which are trained using a SIP signaling dataset of trustworthy SIP dialogs captured by a SIP server. The trained RNNs are then used to detect the SIP dialogs in real-time. After characterizing the dataset adopted for the training, validation, and testing, we present the experimental results obtained for the different RNN architectures, showing that the classification probability of trustworthy SIP dialogs exceeds 93% in the test stage. Finally, we present two methodologies to detect abnormal SIP dialogs, i.e., not contained in the trustworthy training dataset. After a detailed analysis of the skewness and kurtosis computed with the numerical RNN outputs, we show that they can be used as classification features. The first method is based on a K-means unsupervised classifier, while the second one is based on a semi-supervised threshold-based classifier. Experimental results show that the threshold-based classifier achieves 99.45% of detection probability, showing the effective utility of the proposed methodology to detect abnormal SIP sequences in a short period of time.
- Vehicle Trajectory Prediction based on LSTM Recurrent Neural NetworksPublication . Ip, Andre; Irio, Luis; Oliveira, Rodolfo; DEE2010-A1 Telecomunicações; DEE - Departamento de Engenharia Electrotécnica e de ComputadoresThis work presents an effective tool to predict the future trajectories of vehicles when its current and previous locations are known. We propose a Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) prediction scheme due to its adequacy to learn from sequential data. To fully learn the vehicles' mobility patterns, during the training process we use a dataset that contains real traces of 442 taxis running in the city of Porto, Portugal, during a full year. From experimental results, we observe that the prediction process is improved when more information about prior vehicle mobility is available. Moreover, the computation time is evaluated for a distinct number of prior locations considered in the prediction process. The results exhibit a prediction performance higher than 89%, showing the effectiveness of the proposed LSTM network.