Browsing by Author "Marques, Paulo"
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- An efficient long distance echo cancellerPublication . Ferreira, Artur; Marques, PauloThis paper describes an implementation of a long distance echo canceller, operating on full-duplex with hands-free and in real-time with a single Digital Signal Processor (DSP). The proposed solution is based on short length adaptive filters centered on the positions of the most significant echoes, which are tracked by time delay estimators, for which we use a new approach. To deal with double talking situations a speech detector is employed. The floating-point DSP TMS320C6713 from Texas Instruments is used with software written in C++, with compiler optimizations for fast execution. The resulting algorithm enables long distance echo cancellation with low computational requirements, suited for embbeded systems. It reaches greater echo return loss enhancement and shows faster convergence speed when compared to the conventional approach. The experimental results approach the CCITT G.165 recommendation levels.
- An SEM investigation of the pozzolanic activity of a waste catalyst oil refineryPublication . Costa, Carla; Marques, Paulo; Carvalho, P. A.The most active phase of the fluid catalytic cracking (FCC) catalyst, used in oil refinery, is zeolite-Y which is an aluminosilicate with a high internal and external surface area responsible for its high reactivity. Waste FCC catalyst is potentially able to be reused in cement-based materials - as an additive - undergoing a pozzolanic reaction with calcium hydroxide (Ca(OH)2) formed during cement hydration [1-3]. This reaction produces additional strength-providing reaction products i.e., calcium silicate hydrate (C-S-H) and hydrous calcium aluminates (C-A-H) which exact chemical formula and structure are still unknown. Partial replacement of cement by waste FCC catalyst has two key advantages: (1) lowering of cement production with the associated pollution reduction as this industry represents one of the largest sources of man-made CO2 emissions, and (2) improving the mechanical properties and durability of cement-based materials. Despite these advantages, there is a lack of fundamental knowledge on pozzolanic reaction mechanisms as well as spatial distribution of porosity and solid phases interactions at the microstructural level and consequently their relationship with macroscopical engineering properties of catalyst/cement blends. Within this scope, backscattered electron (BSE) images acquired in a scanning electron microscope (SEM) equipped with Energy-Dispersive Spectroscopy (EDS) and by X-ray diffraction were used to investigate chemical composition of hydration products and to analyse spatial information of the microstructure of waste FCC catalyst blended cement mortars. For this purpose mortars with different levels of cement substitution by waste catalyst as well as with different hydration ages, were prepared. The waste FCC catalyst used is produced by the Portuguese refinery company Petrogal S.A.
- Design of pulsed waveforms for space debris detection with ATLASPublication . Pandeirada, João; Bergano, Miguel; Marques, Paulo; Barbosa, Domingos; Freitas, José; Coelho, Bruno; Ribeiro, ValerioATLAS is the first Portuguese radar system that aims to detect space debris. The article introduces the system and provides a brief description of its capabilities. The sys tem is capable of synthesizing arbitrary amplitude modu lated pulse shapes with a resolution of 10 ns. Given that degree of freedom we decided to test an amplitude mod ulated chirp signal developed by us and a nested barker code. These waveforms are explained as well as their ad vantages and drawbacks for space debris detection. An experimental setup was developed to test the system re ceiver and waveforms are processed by digital matched filtering. The experiments test the system using different waveform shapes and noise levels. Experimental results are in agreement with simulation and show that the chirp signal is more resilient to Doppler shifts, has higher range resolution and lower peak-to-sidelobe ratio in compari son with the nested barker code. Future work in order to increase detection capabilities is discussed at the end.
- Developing a data fusion concept for radar and optical ground based SST stationPublication . Coelho, Bruno; Barbosa, Domingos; Berganoa, Miguel; Pandeirada, João; Marques, Paulo; Correia, Alexandre C. M.; Freitas, José Matias deAs part of the Portuguese Space Surveillance and Tracking (SST) program, a tracking radar and a double Wide Field of View Telescope system (4.3° x 2.3°) are being installed at the Pampilhosa da Serra Space Observatory (PASO) in the centre of continental Portugal, complementing an already installed deployable optical sensor for MEO and GEO surveillance. The tracking radar will track space debris in Low Earth Orbit (LEO) up to 1000 km and at the same time the telescope will also have LEO tracking capabilities. This article intends to discuss possible ways to take advantage of having these two sensors at the same location. Using both types of sensors takes advantage of the radar measurements which give precise radial velocity and distance to the objects, while the telescope gives better sky coordinates measurements. With the installation of radar and optical sensors, PASO can extend observation time of space debris and correlate information from optical and radar provenances in real time. During twilight periods both sensors can be used simultaneously to rapidly compute new TLEs for LEO objects, eliminating the time delays involved in data exchange between sites in a large SST network. This concept will not replace the need for a SST network with sensors in multiple locations around the globe, but will provide a more complete set of measurements from a given object passage, and therefore increase the added value for initial orbit determination, or monitoring of reentry campaigns of a given location. PASO will contribute to the development of new solutions to better characterize the objects improving the overall SST capabilities and constitute a perfect site for the development and testing of new radar and optical data fusion algorithms and techniques for space debris monitoring.
- Development of the first portuguese radar tracking sensor for space debrisPublication . Pandeirada, João; Bergano, Miguel; Neves, João; Marques, Paulo; Barbosa, Domingos; Coelho, Bruno; Ribeiro, ValerioCurrently, space debris represents a threat for satellites and space-based operations, both in-orbit and during the launching process. The yearly increase in space debris represents a serious concern to major space agencies leading to the development of dedicated space programs to deal with this issue. Ground-based radars can detect Earth orbiting debris down to a few square centimeters and therefore constitute a major building block of a space debris monitoring system. New radar sensors are required in Europe to enhance capabilities and availability of its small radar network capable of tracking and surveying space objects and to respond to the debris increase expected from the New Space economy activities. This article presents ATLAS, a new tracking radar system for debris detection located in Portugal. It starts by an extensive technical description of all the system components followed by a study that estimates its future performance. A section dedicated to waveform design is also presented, since the system allows the usage of several types of pulse modulation schemes such as LFM and phase coded modulations while enabling the development and testing of more advanced ones. By presenting an architecture that is highly modular with fully digital signal processing, ATLAS establishes a platform for fast and easy development, research, and innovation. The system follows the use of Commercial-Off-The-Shelf technologies and Open Systems which is unique among current radar systems.
- Directional Moving Target Indication for Civil Traffic Monitoring Using Single Channel SARPublication . Marques, PauloThis paper presents a novel moving target indicator which is selective with respect to a direction of interest. Preliminary results indicate that the obtained selectivity may have high interest in civil traffic monitoring using single channel SAR data.
- Evaluation of a low-cost COTS bio radar for vital signs monitoringPublication . Silva, Fábio; Almeida, Rita; Pinho, Pedro; Marques, Paulo; Lopes, Sérgio IvanWith the beginning of the COVID-19 pandemic, there was a need for the Health Care Workers (HCW) to pay more attention to the vital signs of their patients. One way for this to happen, while respecting the social distance, is using contactless technologies, e.g. the bio radar. This way, the HCW will be able to monitor the respiration and heart rates of the patient, without getting close to him. For this to be possible, the best radar configurations were studied, as well as other important aspects that should be taken into consideration while monitoring a patient, for the results obtained to be reliable.
- Improved detection for passive radar by illumination matching on reference channelPublication . Marques, PauloA novel technique for enhancing the detection of targets of interest is presented for application on the context of passive radar. The methodology is inspired on the well known Matched Illumination technique used in active systems and applies to scenarios where the targets can be modeled as having a few predominant scatterers. Since passive systems have no control over the signals which are transmitted by the illuminators of opportunity, the paper proposes to match the signal received on the reference channel. Results show that the correlation function will be enhanced for the targets of interest, relatively to the remaining targets and the clutter on the target region.
- Long distance real-time echo cancellationPublication . J. Ferreira, Artur; Marques, Paulo; Carvalho, HélderThis paper describes an implementation of a long distance echo canceller, operating on full-duplex with handsfree and in real-time with a single Digital Signal Processor (DSP). The proposed solution is based on short length adaptive filters centered on the positions of the most significant echoes, tracked by time delay estimators. To deal with double talking situations a speech detector is employed. The floating-point DSP TMS320C6713 from Texas Instruments is used with software written on the C++ programming language using some compiler optimizations to reduce execution time. The resulting algorithm enables long distance echo cancellation with low computational requirements. It reaches greater echo return, loss enhancement and shows faster convergence speed than the conventional solu tion. Our experimental results also approach the CCITT G.165 recommendation for echo cancellers.
- Low-carbon cement with waste oil-cracking catalyst incorporationPublication . Costa, Carla; Marques, PauloThe present paper shows preliminary results of an ongoing project which one of the goals is to investigate the viability of using waste FCC catalyst (wFCC), originated from Portuguese oil refinery, to produce low carbon blended cements. For this purpose, four blended cements were produced by substituting cement CEM I 42.5R up to 20% (w/w) by waste FCC catalyst. Initial and final setting times, consistency of standard paste, soundness and compressive strengths after 2, 7 and 28 days were measured. It was observed that the wFCC blended cements developed similar strength, at 28 days, compared to the reference cement, CEM I 42.5R. Moreover, cements with waste FCC catalyst incorporation up to 15% w/w meet European Standard EN 197-1 specifications for CEM II/A type cement, in the 42.5R strength class.