In this paper we propose a simple, yet flexible and efficient, channel estimator for the uplink i... more In this paper we propose a simple, yet flexible and efficient, channel estimator for the uplink in broadband orthogonal frequency division multiplexing (OFDM) systems. The processing is performed in the time-domain, by extracting the Channel’s Impulse Response (CIR) for each user from a joint training signal. In this OFDM system, the pilot sequence we advocate, where all users share the same pilot sub-carriers, consists of one OFDM-symbol endowed with time-shifted properties per user, which isolates each user’s CIR and is robust against multi-user interference. The feasibility of our approach is substantiated by system simulation results obtained using BRAN-A broadband mobile wireless channel model.
This paper addresses the important problem of detecting and tracking vehicles in outdoor dynamic ... more This paper addresses the important problem of detecting and tracking vehicles in outdoor dynamic scenes as part of a real-time traffic surveillance system. The proposed solution is based on a dual-stage approach, using a pixel-level stage to extract foreground object from background scenes and a block-level stage to detect and track vehicles. The pixel-level stage combines a multi-background modelling with a dynamic thresholding, using a low-scale quasi-connected-components as a first stage for image object grouping/cleaning. The blocklevel performs a 8x8 block-region analysis defining a block energy function that is used to label the blocks belonging to different vehicles and track them over a stack of images. This approach has proven to be very helpful for occlusion reasoning. The proposed solution has the ability to overcame some of the most difficult problem that arise in outdoor scenes such as illumination variations, shadow-casts and waving movement resulting from trees and camera vibration. The performance and robustness of the proposed algorithm is shown using real highway traffic monitoring situations.
In this paper it is described a solution to detect wrong way drivers on highways. The proposed so... more In this paper it is described a solution to detect wrong way drivers on highways. The proposed solution is based on three main stages: Learning, Detection and Validation. In the first stage, the orientation pattern of vehicles motion flow is learned and modelled by a mixture of gaussians. The second stage (Detection and Temporal Validation) makes use of the learned orientation model to detect objects moving on lane's opposite direction. The third and final stage uses an Appearance based approach to ensure the detection of a vehicle before triggering an alarm. This methodology has proven to be quite robust in terms of different weather conditions, illumination and image quality. Some experiments carried out with several movies from traffic surveillance cameras on highways show the robustness of the proposed solution.
A expressão da tensão estipulada difere, conforme o cabo é de campo radial (secção 1.2.4) ou não.... more A expressão da tensão estipulada difere, conforme o cabo é de campo radial (secção 1.2.4) ou não. Num cabo de campo radial, Uo é diferente de U, sendo a razão entre ambos geralmente igual a .
In this paper we propose a simple, yet flexible and efficient, channel estimator for the uplink i... more In this paper we propose a simple, yet flexible and efficient, channel estimator for the uplink in broadband orthogonal frequency division multiplexing (OFDM) systems. The processing is performed in the time-domain, by extracting the Channel’s Impulse Response (CIR) for each user from a joint training signal. In this OFDM system, the pilot sequence we advocate, where all users share the same pilot sub-carriers, consists of one OFDM-symbol endowed with time-shifted properties per user, which isolates each user’s CIR and is robust against multi-user interference. The feasibility of our approach is substantiated by system simulation results obtained using BRAN-A broadband mobile wireless channel model.
This paper addresses the important problem of detecting and tracking vehicles in outdoor dynamic ... more This paper addresses the important problem of detecting and tracking vehicles in outdoor dynamic scenes as part of a real-time traffic surveillance system. The proposed solution is based on a dual-stage approach, using a pixel-level stage to extract foreground object from background scenes and a block-level stage to detect and track vehicles. The pixel-level stage combines a multi-background modelling with a dynamic thresholding, using a low-scale quasi-connected-components as a first stage for image object grouping/cleaning. The blocklevel performs a 8x8 block-region analysis defining a block energy function that is used to label the blocks belonging to different vehicles and track them over a stack of images. This approach has proven to be very helpful for occlusion reasoning. The proposed solution has the ability to overcame some of the most difficult problem that arise in outdoor scenes such as illumination variations, shadow-casts and waving movement resulting from trees and camera vibration. The performance and robustness of the proposed algorithm is shown using real highway traffic monitoring situations.
In this paper it is described a solution to detect wrong way drivers on highways. The proposed so... more In this paper it is described a solution to detect wrong way drivers on highways. The proposed solution is based on three main stages: Learning, Detection and Validation. In the first stage, the orientation pattern of vehicles motion flow is learned and modelled by a mixture of gaussians. The second stage (Detection and Temporal Validation) makes use of the learned orientation model to detect objects moving on lane's opposite direction. The third and final stage uses an Appearance based approach to ensure the detection of a vehicle before triggering an alarm. This methodology has proven to be quite robust in terms of different weather conditions, illumination and image quality. Some experiments carried out with several movies from traffic surveillance cameras on highways show the robustness of the proposed solution.
A expressão da tensão estipulada difere, conforme o cabo é de campo radial (secção 1.2.4) ou não.... more A expressão da tensão estipulada difere, conforme o cabo é de campo radial (secção 1.2.4) ou não. Num cabo de campo radial, Uo é diferente de U, sendo a razão entre ambos geralmente igual a .
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Papers by Miguel Ribeiro